Nanochemistry is the evolution of the subject of research in chemistry. Objects and concepts of nanochemistry

Nanochemistry is a branch of chemistry that studies the properties, structure and characteristics of chemical transformations of nanoparticles. A distinctive feature of nanochemistry is the presence of a size effect - a qualitative change in physicochemical properties and reactivity with a change in the number of atoms or molecules in a particle. Usually, this effect is observed for particles smaller than 10 nm, although this value has a conditional value.

Directions of research in nanochemistry

Development of methods for assembling large molecules from atoms using nanomanipulators; study of intramolecular rearrangements of atoms under mechanical, electrical and magnetic influences.

Synthesis of nanostructures in supercritical fluid flows; development of methods for directed assembly of nanocrystals.

Development of the theory of physical and chemical evolution of ultrafine substances and nanostructures; creation of ways to prevent chemical degradation of nanostructures.

Obtaining new catalysts for the chemical and petrochemical industries; study of the mechanism of catalytic reactions on nanocrystals.

Study of the mechanisms of nanocrystallization in porous media in acoustic fields; synthesis of nanostructures in biological tissues.

Study of the phenomenon of self-organization in groups of nanocrystals; search for new ways to prolong the stabilization of nanostructures by chemical modifiers.

The purpose of the research is to develop a functional range of machines that provide:

New catalysts for the chemical industry and laboratory practice.

Methodology for preventing chemical degradation of technical nanostructures; methods for predicting chemical degradation.

Getting new drugs.

A method for treating oncological diseases by carrying out intratumoral nanocrystallization and applying an acoustic field.

New chemical sensors; methods for increasing the sensitivity of sensors.

Nanotechnologies in energy and chemical industry

Nanotechnology (Greek nanos - "dwarf" + "techno" - art, + "logos" - teaching, concept) is an interdisciplinary field of fundamental and applied science and technology, dealing with innovative methods (in the areas of theoretical justification, experimental methods of research, analysis and synthesis, as well as in the field of new industries) obtaining new materials with desired properties. Nanotechnology uses the latest technologies for manipulating single atoms or molecules (movement, permutations, new combinations). A variety of methods (mechanical, chemical, electrochemical, electrical, biochemical, electron beam, laser) are used to artificially organize a given atomic and molecular structure of nanoobjects.

Nanotechnologies in energy

Nanotechnologies in the field of energy and mechanical engineering

In this area, the development of NT goes in two directions:

1- creation of structural materials,

2- surface nanoengineering

Creation of construction materials,

To create fundamentally new structural materials with the inclusion of ultradispersed (or nanodispersed) elements, we went along the following path. The first is the addition of ultrafine elements as dopants. For structural materials in mechanical engineering and energy, fullerenes are exotic, very expensive. The second direction is the creation of ultrafine systems (UDS) of non-metallic inclusions in steels and alloys, carried out by thermoplastic, thermal or plastic deformation. It turned out that it is possible to control the performance properties of structural materials not only by introducing alloying components, which, according to metallurgists, are practically exhausted, but also by means of deformation of any nature. With such an impact, crushing of non-metallic inclusions occurs. Traditional annealing and tempering are nothing but nanotechnologies in metallurgy.

As a result of such influences, it is possible to obtain steels (nitrogen steels in Prometheus), in which high strength is combined with ductility, that is, precisely those properties that are lacking in the energy sector, in mechanical engineering, to obtain materials with desired characteristics. And nanotechnology makes it possible to successfully obtain such materials.

Members:

Igor Vladimirovich Melikhov- Corresponding Member of the Russian Academy of Sciences, Professor of the Faculty of Chemistry, Moscow State University. Lomonosov

Viktor Evgenievich Bozhevolnov- Candidate of Chemical Sciences, Researcher, Faculty of Chemistry, Moscow State University. Lomonosov

Topic overview

Nanosystems are usually understood as a set of bodies surrounded by a gas or liquid medium, the size of which remains within the range of 0.1–100 nm. The word itself is derived from the Greek. nanos- "dwarf". Such bodies can be polyatomic clusters and molecules, nanodroplets and nanocrystals. These are intermediate forms between atoms and macroscopic bodies, which determines the importance of studying nanosystems.

A feature of nanobodies, i.e. ultra-small bodies, is that their size is commensurate with the radius of action of the forces of interatomic interaction, that is, with the distance to which the atoms of the body must be removed so that their interaction does not affect its properties to a noticeable extent. Due to this feature, nanobodies interact with each other and with the environment differently than macrobodies. The specificity of the interaction is so great that a special direction of scientific research has been formed for the study of nanosystems, which can be called the physicochemistry of nanosystems or, for short, nanochemistry.

It is essential that the mass of nanoparticles is small enough for each particle to participate in thermal motion as a whole. The latter circumstance unites all their varieties and is of fundamental importance, since it provides the possibility of self-assembly of nanoparticles into the corresponding nanostructures by searching by trial and error and ultimately finding thermodynamic optimums.

The boundaries of the nanointerval in chemistry are conditional. The properties of a body are sensitive to its size to varying degrees. Some of the properties lose their specificity at a size of more than 10 nm, others - more than 100 nm. Therefore, in order to exclude fewer properties from consideration, the upper limit of the nanointerval should be taken equal to 100 nm. Thus, the boundaries of nanosubstances themselves are expanding and a larger field is being opened up for research and further generalizations.

Naturally, nanostructures exist in nature, and examples of the formation of nanosubstances in protein bodies are primarily interesting here. The most important biological reactions occurring in a living cell take place in protein nanostructures. An example is the pigment-protein complex of the reaction center of photosynthesis, in which six molecules of chlorophyll nature are built into the protein matrix with a repeating accuracy of tenths of an angstrom. These pigments perform the process of converting solar energy into separated charge energy with a quantum efficiency of 100% due to extremely fast electron transfer between the pigments. Such efficiency is not known even in physics. The electron transfer time between pigments is determined experimentally, giving a value of less than 20 femtoseconds. The motion of the nuclear subsystem with the corresponding frequencies is also experimentally determined, which creates the necessary nuclear configuration for the electron transfer and for the stabilization of the separated charges. Combining these data with X-ray diffraction analysis makes it possible to establish the molecular mechanisms and pathways of electron transfer between pigments in such a nanostructure.

Another example of nanostructures that have arisen naturally in nature belongs to the field of mineralogy. Thus, the study of samples of lunar soil, which for about 4.5 billion years was subjected to proton bombardment by the solar wind, showed a number of usually irreversible processes that took place in it. There, the reduction of oxides, of which all rocks usually consist, took place to depths inversely proportional to the metal-oxygen bond energy. The easier this bond was broken, the deeper the regolith underwent restoration processes, sometimes down to the zero valence state. Iron was reduced at the maximum depth, chromium at a shallower depth, silicon, manganese, magnesium, etc., even closer to the surface - all 12 main rock-forming elements. But there was another significant event: on the surface, the process of amorphization of crystals took place, that is, they simply collapsed, and, as studies performed at the Institute of Ore Deposits showed, they collapsed to a nano state.

Biological nanostructures can be isolated, purified, crystallized and studied using the entire arsenal of physical and chemical methods, including NMR, EPR, optical, ultraviolet, infrared spectroscopy with the highest time resolution - about 15 femtoseconds. Experimental studies of these nanostructures are accompanied by quantum physical calculations of molecular dynamics and interaction of electrons. And at the same time, everything that becomes known about biological nanostructures and their structure can be used in the synthesis of chemical models necessary for nanotechnology.

At the same time, in order to avoid excessive generalizations, it must be remembered that there is a fundamental difference between the condensation of biological nanoparticles into biological superstructures and the formation of atomic or ordinary molecular nanoaggregates. The shape, chemical structure and surface topography of biological nanoblocks (proteins, nucleic acids), as a rule, very strictly determine the size and shape of biological superstructures resulting from self-assembly, especially if it occurs, so to speak, in vivo. In the inorganic world, these determining factors are much less pronounced. Significant fluctuations and very wide size distributions can occur here.

The physicochemistry of nanosystems developed at one time as part of physics and chemistry. Now it is a relatively young field of science, which is developing very rapidly. The rate of increase in the number of publications in the scientific literature can serve as a quantitative characteristic of its progress. Since it is often impossible to decide to what extent a publication refers specifically to the nanointerval and concerns general chemistry or, already specifically, nanochemistry, it is difficult to determine their exact number, but estimates can be made. As can be said from preliminary data, the physical chemistry of nanosystems developed without any significant leaps, and the total number of publications reached 2.5–3 million by the end of the last century, with the main world publications naturally dating back to the 1990s. In the first half of the century, the most significant contribution to nanochemistry was made by specialists who studied colloids and aerosols, and in the second half by polymers, proteins, natural compounds, fullerenes, and tubulenes.

As far as nanophysics is concerned, there are, in turn, two different areas in it. One is related to the creation of powders from nanoparticles or polycrystals with nanometer-sized crystallites. Another area is associated with the word "mesoscopic" - a cross between "micro" and "macro". In this case, we are talking about the properties of individual particles of nanometer size. They are sometimes called artificial atoms because, like atoms, they have a discrete radiation spectrum.

We can say that there was a real boom in physics when they learned how to make such particles from metals, conductors, semiconductors, superconductors, and most importantly, they learned how to include such a particle in an electrical circuit, that is, to pass current only through it. This phenomenon, like the phenomenon of the Coulomb blockade, was theoretically predicted at the Kharkov Institute of Physics and Technology for Low Temperatures, and then this phenomenon was experimentally discovered at Moscow State University. M. V. Lomonosov. It was shown that even if one electron enters a metal nanoparticle, then due to the low capacitance, the corresponding Coulomb energy will significantly exceed the temperature. As a result, there is a "blockade" of the electric current.

Now, on the basis of the so-called Coulomb "blockade", a single-electron transistor has already been created. This is the ultimate miniaturization as it runs on one (!) electron. This transistor has been operating for several years and has been successfully used as a measuring device in physics. A gigantic progress in sensitivity is associated with it. The use of nanoparticles from superconductors makes it possible to make so-called qubits (quantum bits of information), which will become the main element of quantum computers.

Thus, it is obvious that nanotechnologies are now unusually widely distributed in various areas of natural science knowledge. Here, several main areas can be distinguished, however, this selection will be rather arbitrary, since these areas often intersect with each other and, most importantly, rely on similar techniques. The main areas of research include:

Synthesis of fullerenes and fullerene-like structures. Study of high-temperature superconductivity of metals.

Cluster atomic mobility (first of all, the melting and freezing points of clusters are studied, which are lower than those of solids, specific solid-liquid states of clusters are studied, etc.).

Nanocluster reactions (mainly cluster sputtering and peculiarities of cluster photochemical reactions are studied).

The study of quantum dots (semiconductor clusters, their optical properties, light-emitting diodes with adjustable wavelength of radiation are studied).

Study of magnetic properties, measurement of changes in the magnetic moment per atom during the transition from the collective magnetism of a solid body to the shell structure of a cluster.

At present, the physicochemistry of nanosystems has approached a new stage of development, which can be called the stage of visualization of atoms and nanoparticles with observation of their interaction. in situ. Methods of autoionic, electron, atomic force and tunneling microscopy were developed, which made it possible to observe the behavior of an individual atom and the state of an individual nanobody. The sensitivity of spectral methods has now been brought to a level at which it is possible to measure the fluorescence and luminescence of an individual molecule, and to judge the structure of molecules consisting of 50 atoms or more from infrared spectra. Observations of individual atoms and nanobodies have become available to a wide range of researchers. Although it is now believed that obtaining a reliable image of a single atom or molecule is a great scientific achievement, it has ceased to be unique. For example, in 2000, a report in the journal Nature (work by T. Fishlock et al.) that it was possible to observe individual bromine atoms on the surface of a copper single crystal and, using special nanomanipulators, to move one of the atoms, almost without shifting the rest, perceived as a scientific sensation. Publications in 2002 on the visualization and movement of DNA molecules by nanomanipulators are considered as an important, but ordinary event. Apparently, nanochemistry is faced with the possibility of "assembling" nanobodies from atoms using nanomanipulators and revealing how the properties of nanobodies change immediately at the moment of detachment of an atom or its attachment with visualization of the intermediate stages of the process.

Now the physical chemistry of nanosystems has all the features of an independent branch of science: its own range of research objects, theory, experiment (search methodology) and the scope of the results.

A rather practical area can be called a special branch of the physicochemistry of nanosystems - the creation of organized nanometer films, mainly the so-called monolayer (!) Langmuir-Blodgett films. Such films are obtained to create systems with controlled tunneling, and for this purpose molecular complexes are used as the basis for single-electron films. Work is underway to create Langmuir-Blodgett nanolayers containing nucleic acids, which is of particular interest for creating a test system for DNA immobilization. That is, speaking summarily and cautiously, nanochemistry in its organic field is the first step, the basis for modeling and programming protein bodies.

Objects of nanochemistry research- ultrafine substances obtained by vapor condensation and precipitation from solutions; aerosols and colloidal solutions, natural substances consisting of polyatomic molecules; products of polymerization, fine grinding of solids or intense liquid spray; block solids, in which the boundaries of the blocks are so pronounced that the blocks themselves can be considered as quasi-particles; clays and sea suspensions; bottom sediments, etc.

Theory of nanosystems develops methods for calculating the behavior of nanobodies based on "first principles". The consideration is based on the evolution equation for the function φ (Х i , t) of the distribution of nanobodies (nanoparticles) according to the parameters Х i , their state, which includes such indicators as the rate of evolution of the nanosystem, the set of rates of directional change and coefficients of fluctuations of the state parameters Х i at the moment t. In this case, the set of state parameters X i includes spatial coordinates and velocities, mass, characteristics of the composition, shape, and structure of each nanoparticle using conservation codes.

The rates of directed change in the state parameters and the fluctuation coefficients are presented as a function of the state parameters ξ i of the medium around the nanoparticles. As applied to the spatial coordinates and velocities of nanoparticles, these functions are represented as laws of motion in classical mechanics. As applied to the mass and shape characteristics, these functions are expressed in terms of the frequencies of addition and detachment of atoms from nanoparticles. Frequencies are usually calculated on the assumption that atoms move in accordance with the laws of classical mechanics at a certain potential of interatomic interactions. When the composition and structure of nanoparticles are calculated, it is assumed that the atomic nuclei of a nanoparticle move according to the laws of classical mechanics (with quantum mechanical corrections) in an electron-nuclear medium described by the Schrödinger equation. This assumption opens up the possibility of revealing the connection between the potential of interatomic interactions and the electron-nuclear characteristics of atoms and the subsequent transition to the calculation of the rate of evolution from "first principles". So far, such a calculation is far away, but the theory of nanosystems is developing rapidly.

Experiment revealed hundreds of regularities in the behavior of nanosystems. We single out two of them, the most common in our opinion.

1. Most natural and technogenic nanosystems are far from equilibrium, and their state is constantly changing as they move towards equilibrium.

Nanosystems are formed along two routes: condensation and dispersion. In the first case, the initial bodies evaporate or dissolve, after which the resulting vapors are condensed, and an ultrafine substance is precipitated from the solution. In the second case, mechanical energy is supplied to the initial bodies in an amount sufficient for their decay into nanoparticles. The implementation of both routes requires an intense influx of energy into the initial system, so that immediately after the appearance of nanoparticles, the system is far from equilibrium. As soon as the influx of energy stops, the system evolves towards equilibrium.

The simplest example of the evolution of a system can be the condensation route of transformation of a single crystal consisting of identical atoms and located in a closed volume of its saturated vapor. If such a single crystal is heated to melting and subsequent evaporation of the melt, and then the resulting vapor is rapidly cooled to the initial temperature of the system, then as the system cools, nanoparticles are generated and coarsened. They are combined into aggregates that are ordered. The boundaries between nanoparticles in aggregates disappear, and they turn into microcrystals. When microcrystals are kept in steam for a long time, the smallest and defective ones evaporate, while the larger and more perfect ones continue to grow. And so on until the original single crystal is recreated in the system. During the entire time interval from the moment when a noticeable amount of nanoparticles has already accumulated in the vapor until the moment when most of the nanoparticles reach a size of 100 nm, the system is in the nanostate. Then - it inevitably goes into equilibrium, the appearance of nanoparticles stops and, moreover, the particles that have arisen can also go into the stage of decay, if artificial conditions for their conservation are not created.

With the dispersive route of transformations of a single crystal under conditions of a sufficient stationary influx of mechanical energy, the size of the fragments into which the single crystal breaks up decreases until the processes leading to the destruction of fragments are compensated by their aggregation and intergrowth.

If the influx of mechanical energy is so great that, with such compensation, most of the fragments have a nanometer size, then the system remains in a stationary nanostate until the energy influx decreases. When the inflow stops, the fragments will begin to coalesce and become larger. This weight continues until the original single crystal is recreated in the system. The condensation and spergation routes of system evolution turn out to be more complex if chemical reactions occur in the system.

2. The second regularity of the existence and emergence of nanosystems revealed in the course of a series of experiments can be formulated briefly, although this is a very important discovery: nanosystems are variable. This means that nanobodies simultaneously located in the system have different properties, and the "scatter" of properties is large and largely determines the behavior of the system.

Nanoparticles have different size, shape and speed of spatial movement, which manifests itself, for example, in Brownian motion. The chemical composition of nanoparticles is also variable due to the sorption of different amounts of medium molecules. The main cause of variability is thermal motion, but thermal fluctuations are synchronized due to the cooperative interaction of atoms. The degree of synchronization increases with the directed supply of substances and energy to the system. If the system is nonequilibrium, then each property of nanoparticles changes like the motion of a body in a fluid flow: it is carried away by the flow during random walks around the trajectory of directed motion. In this case, the rate of directed change of each property is characterized by the value G i , and the intensity of wandering - by the value D i . As applied to the spatial displacement of nanoparticles, the G i value corresponds to the medium drift rate, and the D i value corresponds to the Brownian diffusion coefficient. As applied to the mass of nanoparticles, the G i value is close to the average rate of their enlargement, and the D i value characterizes the fluctuations in the frequencies of attachment of medium molecules to nanoparticles. Data on the values ​​of G i and D i is not much, but the available information indicates that the values ​​of D i are very large.

The frequency of attachment of atoms (molecules) of the medium to a nanoparticle with an ordered structure depends nonmonotonically on the number of its constituent atoms. It sharply decreases when the number of atoms in a particle becomes equal to one of the "magic numbers", the set of which is determined by the structure of the particle. For clusters with icosahedral arrangement of atoms, "magic numbers" correspond to the number of atoms in successive coordination spheres around the central atom. In faceted nanocrystals, the probability of attachment of an atom is significantly reduced if the number of atoms that have joined earlier is sufficient to form a monolayer on its faces, and during periods of cluster growth, the probability of attachment of new atoms to the nanocrystal is high, and in periods between the formation of layers, it is small, therefore, "magic the numbers n i correspond to the number of atoms in the nanocrystal at the instants t i of the nucleation of two-dimensional clusters. In peptide molecules formed on the DNA matrix. the frequency of addition of new amino acids becomes zero after the number of atoms and molecules of the peptide ceases to meet the requirements of DNA.

These regularities make the study of nanosystems an extremely science-intensive task. The variability of nanosystems makes it necessary to measure the parameters of the state of a set of nanoparticles, and their evolutionary nature makes it necessary to monitor the change in the properties of this set over time. In this case, it is necessary to determine the multidimensional function φ (X i , t) in a wide range of medium properties. It is not surprising that almost all nanosystems have been studied in fragments, and the fragments do not add up to a complete picture of their behavior. Nevertheless, thousands of applied problems have been solved within the framework of nanochemistry.

Applied physical chemistry of nanosystems includes:

Development of theoretical foundations for the use of nanosystems in engineering and nanotechnology, methods for predicting the evolution of specific nanosystems in the conditions of their use, as well as the search for optimal methods of operation;

Creation of theoretical models of the behavior of nanosystems in the synthesis of nanomaterials and the search for optimal conditions for their production;

The study of biological nanosystems and the creation of methods for using nanosystems for medicinal purposes;

Development of theoretical models for the formation and migration of nanoparticles in the environment and methods for cleaning natural waters or air from nanoparticles.

Of the listed areas of applied nanochemistry, the second one is currently the most developed, which seems natural, since in this area purely scientific interests and purely theoretical problems fall into the area of ​​purely practical and even economic interests. Although it is too early to say that everything that could be done at this stage in the development of science has been done in this area. As an example, one can cite such an area as metallurgy, where work is now being actively carried out on the synthesis of new nanomaterials and the development of new nanotechnologies. The effectiveness of the creation and use of nanomaterials is obvious. Thus, the strength of a metal with a nanostructure is 1.5–2 times, and in some cases even 3 times, greater than the strength of an ordinary metal. Its hardness is 50–70 times greater, and its corrosion resistance is 10–12 times greater. It is known that the structure of a metal strongly affects its properties: the finer the grain size, the larger the interaction surface between the phase components of the structure, which is the basis for improving its properties. The average metal grain size today is 5–7 microns; in practice, they usually do not reach nanosize yet. To obtain metals with nanostructures, special technological methods are needed, which are currently being actively developed, but which are still too complex to be applied in wide production. These technologies go in two main directions. The first is the creation of so-called nanopowders, from which the desired nanomaterial is then made. Another method of grinding the original structure can be called deformation: due to repeated deep deformation of the metal, the proper level of structure and, accordingly, properties is achieved.

These technologies are now being widely developed in the United States and Japan, and partly in China and Korea, so it is in these countries that science has probably reached the most optimal solution to some issues and problems. So far, only the first step in this direction has been taken in our country: the Scientific Council of the Russian Academy of Sciences on nanomaterials has been established. But little has been done so far, and we note with regret that so far Russia is not among the top two dozen countries actively developing nanotechnologies.

When mentioning the phrase "nanostructures", first of all, we mean new types of metal and crystals, the creation of which opens the way for new "nanoelectronics" based on one of the most amazing properties of nanocrystals - their defect-freeness. However, nanochemistry is now also related to another area of ​​science, approaching rather to biology. In practice, this direction is used in the development of completely new medical technologies.

As an example of developments in the third direction, one can state the idea of ​​creating anti-cancer nanosystems directly in tumor tissue. Laboratory experiments have shown that if reagents are introduced into the polymer body, the interaction of which results in the formation of goethite or hydroxyapatite nanoparticles. then the introduction of reagents can be organized in such a way that the nanoparticles that have arisen in the volume of the body have almost no effect on the structure of the polymer. But if, after the formation of nanoparticles, an acoustic field is applied to the body, then it will heat up to 43 °C in a time during which the body without nanoparticles will hardly change temperature. This suggested that if we find substances whose nanoparticles can be formed in cancer cells with a much higher probability than in healthy tissue, then cancer cells can be selectively heated and “killed”. And such substances have been found. Interesting results were obtained on the effect of one of them (terophthal) on the development of a cancerous tumor in mice. It became obvious that terophthal nanoparticles by themselves do not affect the development of the tumor, and the acoustic field only weakly slows down its growth. But if the field is applied after the formation of terophthal nanoparticles. and only for 10 minutes, the tumor volume decreases by 80% within a week. These facts emphasize the promise of studying the evolution of nanosystems in biological media.

Nanoworld - lives according to the same laws, no matter what area of ​​its existence we take. Therefore, nanosystems in chemistry turn out to be close to biological nanostructures. The main biological and molecular complexes and enzymes have sizes on the order of 5–50 nm, which is also characteristic of chemical nanosystems. However, in contrast to chemistry and geology, biology knows highly organized structures of nanocomplexes that determine the passage of many hundreds of biological processes in a living cell with high efficiency. Biological nanostructures contain protein carriers (RNA molecules are still present in the ribosomes) with a characteristic secondary, tertiary, quaternary structure. These structures, depending on their functions, are encrusted with various cofactors included in the active centers. The position of all atoms in these nanosystems is so reproducible that for their three-dimensional crystals, X-ray diffraction analysis demonstrates the position of each atom (and there may be 10 thousand or more) with an accuracy of tenths of an angstrom.

New research methods, which made it possible to visualize both the nanoparticles themselves and their interaction with each other, have made the physicochemistry of nanosystems a fashionable science. But its attractiveness is not associated with random circumstances, but is predetermined by the logic of the development of science. This logic inevitably leads to the fact that the research of nanosystems becomes extremely science-intensive and expensive. Many countries have launched special national programs, providing them with appropriate funding.

Today, the physical chemistry of nanosystems is a harmoniously developing area of ​​science in which theory and experiment are combined with the systematic flow of scientific information into applied areas. As a matter of fact, at present, the development of nanotechnologies and the development of methods for creating and studying nanosubstances can be called one of the most important areas of science in the 21st century. As the famous physicist Feynman said 30 years ago, penetration into the nanoworld is an endless path of a person, on which he is practically not limited by materials, but follows only his own mind. Indeed, at present, discoveries in nanosubstance and its properties are taking place in various fields - chemistry, physics, biology. So, for example, it was experimentally established that when water is purified by electric discharges, it acquires bactericidal properties. Their nature was not clear, since the chemical composition of the water did not change. But then it was found that as a result of the erosion of the electrodes, nanoparticles remain in the water, which largely affect its properties.

But the most important discovery of the nanoworld is undoubtedly for such a field as microelectronics. Currently, in particular, work is underway to create nanostructures using ion beams. With a sufficient amount of energy and providing the metal with free protons, structures with a size of the order of ten nanometers can be obtained. On such scales, the dielectric passes into the metal, and crystallization occurs very quickly. Then multilayer nanostructures are created, which will form the basis of electronic circuits of the future. And if now magnetic disks carry hundreds of gigabytes of information, then with the use of new technologies they will measure the information contained on them in hundreds of terabytes.

In Russia, many outstanding scientists, including a significant number of members of the Department of Chemistry and Materials Sciences of the Russian Academy of Sciences, are involved in nanochemistry problems. However, most of them do not have systematic access to instruments, without which modern diagnostics of nanosystems is impossible. Thanks to the efforts of academicians O. M. Nefedov and V. A. Kabanov, a significant contribution to the physical chemistry of nanosystems was made during the implementation of the Federal Target Scientific and Technical Program “Research and Development in Priority Areas of Civil Science and Technology Development” in 1999–2001. It is important to implement academic programs led by Academicians M. V. Alfimov and N. P. Lyakishev, as well as a number of other specialized projects.

Bibliography

Ivanovsky A. L., Shveikin G. P. Quantum chemistry in materials science. Yekaterinburg, 1997

Melikhov IV Elementary acts of crystallization in media with high supersaturation//Izvestiya RAN. Ser. chem. 1994. No. 10

Melikhov IV Some directions of development of the ideas of technological science//Theoretical. basics of chem. technologies. 1998. V.32. No. 4

Melikhov IV Patterns of crystallization with the formation of nanodispersed solid phases//Inorganic materials. 2000. V.36. Number 3

Melikhov IV Trends in the development of nanochemistry//Ros. chem. magazine. T.46. No. 5

Nanotechnology in the next decade / Ed. M. K. Roko. M., 2002

Nikolaev A. L., Raevsky P. M. Sonodynamic therapy of malignant tumors//Ros. chem. magazine. 1998. V.42. No. 5

Petrov Yu. I. Clusters and small particles. M., 1986

Uvarov N. F. Boldyrev V. V. Dimensional effects in the chemistry of heterogeneous systems//Advances in Chemistry. 2001. V. 70. No. 4

Clusters of Atoms and Molecules//Springer Series on Chem. Physics. 1994.V.52

Handbook of Nanostructured Meterials and nanotechnology/Ed. by H.S. Nalwa. N.Y., 1994. V. 1–5

Magnetite Biomaterization and Magnetoreception in Organisms: A new Biomagnetism/Ed. by J. L. Kirschvink, D. S. Jones, J. B. Macfadden. N.Y., 1985

Course Curriculum

V.V. EREMIN,
A.A. DROZDOV

LECTURE #1
What is hidden behind the prefix "nano"?

Nanoscience and nanochemistry

In recent years, in newspaper headlines and in magazine articles, we have increasingly come across words that begin with the prefix "nano". On radio and television, we are almost daily informed about the prospects for the development of nanotechnology and the first results obtained. What does the word "nano" mean? It comes from the Latin word nanus- "dwarf" and literally indicates a small particle size. In the prefix "nano" scientists put a more precise meaning, namely one billionth part. For example, one nanometer is one billionth of a meter, or 0.000,000,001 m (10–9 m).

Why did nanoscale attract the attention of scientists? Let's do a thought experiment. Imagine a cube of gold with an edge of 1 m. It weighs 19.3 tons and contains a huge number of atoms. Let's divide this cube into eight equal parts. Each of them is a cube with an edge half the size of the original one. The total surface has doubled. However, the properties of the metal itself do not change in this case (Fig. 1). We will continue this process further. As soon as the length of the edge of the cube approaches the size of large molecules, the properties of the substance will become completely different. We have reached the nano level, i.e. obtained cubic gold nanoparticles. They have a huge overall surface area, which leads to many unusual properties and makes them look nothing like ordinary gold. For example, gold nanoparticles can be evenly distributed in water, forming a colloidal solution - a sol. Depending on the particle size, the gold sol may have an orange, purple, red, or even green color (Fig. 2).

The history of the preparation of gold sols by reduction from its chemical compounds is rooted in the distant past. It is possible that they were the “elixir of life” mentioned by the ancients and obtained from gold. The famous physician Paracelsus, who lived in the 16th century, mentions the preparation of "soluble gold" and its use in medicine. Scientific research on colloidal gold began only in the 19th century. Interestingly, some of the solutions prepared at that time are still preserved. In 1857, the English physicist M. Faraday proved that the bright color of the solution is due to small particles of gold in suspension. Currently, colloidal gold is obtained from chloroauric acid by reduction with sodium borohydride in toluene with a surfactant added to it, which increases the stability of the sol (see lecture No. 7, task 1).

Note that such an approach to obtaining nanoparticles from individual atoms, i.e. from bottom to top in size, often called ascending (eng. - bottom up). It is characteristic of chemical methods for the synthesis of nanoparticles. In the thought experiment we described on dividing a gold bar, we took the opposite approach - top-down ( top-down), which is based on the fragmentation of particles, as a rule, by physical methods (Fig. 3).

We can meet with gold nanoparticles not only in a chemical laboratory, but also in a museum. The introduction of a small amount of gold compounds into molten glass leads to their decomposition with the formation of nanoparticles. It is they who give the glass that bright red color, for which it is called the "golden ruby".

With materials containing nano-objects, mankind got acquainted many centuries ago. In Syria (in its capital Damascus and other cities) in the Middle Ages they learned how to make strong, sharp and sonorous blades and sabers. The secret of making Damascus steel for many years was passed on by masters to each other in deep secrecy. Weapons steel, not inferior in properties to Damascus, was also prepared in other countries - in India, Japan. Qualitative and quantitative analysis of such steels did not allow scientists to explain the unique properties of these materials. As in ordinary steel, they contain, along with iron, carbon in an amount of about 1.5% by weight. In the composition of Damascus steel, metal impurities were also found, for example, manganese, which accompanies iron in some ores, and cementite, iron carbide Fe 3 C, formed during the interaction of iron with coal in the process of its recovery from ore. However, having prepared steel of exactly the same quantitative composition as Damascus, scientists could not achieve the properties that are inherent in the original.

When analyzing a material, it is necessary first of all to pay attention to its structure! Having dissolved a piece of Damascus steel in hydrochloric acid, German scientists discovered that the carbon contained in it forms not ordinary flat graphite flakes, but carbon nanotubes. This is the name of the particles obtained by twisting one or more layers of graphite into a cylinder. There are cavities inside the nanotubes, which in Damascus steel were filled with cementite. The thinnest threads of this substance bind individual nanotubes to each other, giving the material extraordinary strength, viscosity and elasticity. Now they have learned how to produce carbon nanotubes in large quantities, but how the medieval “technologists” managed to get them is still a mystery. Scientists suggest that the formation of nanotubes from coal, which fell into steel from a burning tree, was facilitated by some impurities and a special temperature regime with repeated heating and cooling of the product. This was precisely the secret that was lost over the years, which artisans owned.

As we can see, the properties of a nanosubstance and a nanomaterial differ significantly from the properties of objects with the same qualitative and quantitative composition, but not containing nanoparticles.

In the Middle Ages, the creation of substances that we today call nanomaterials was approached empirically, i.e. through many years of experience, many of which ended in failure. Artisans did not think about the meaning of the actions they performed, did not even have an elementary idea about the structure of these substances and materials. At present, the creation of nanomaterials has become the object of scientific activity. The scientific language has already established the term "nanoscience" (Eng. nanoscience), which denotes the area of ​​study of nanometer-sized particles. Since from the point of view of the phonetics of the Russian language this name is not very successful, you can use another, also generally accepted - "nanoscale science" (eng. - nanoscale science).

Nanoscience is developing at the intersection of chemistry, physics, materials science and computer technology. It has many applications. The use of nanomaterials in electronics is expected to increase the capacity of storage devices by a factor of a thousand, and hence reduce their size. It has been proven that the introduction of gold nanoparticles into the body in combination with X-ray irradiation inhibits the growth of cancer cells. Interestingly, gold nanoparticles themselves do not have a healing effect. Their role is reduced to the absorption of X-rays and directing it to the tumor.

Doctors are also waiting for the completion of clinical trials of biosensors for diagnosing oncological diseases. Nanoparticles are already being used to deliver drugs to body tissues and increase the efficiency of absorption of sparingly soluble drugs. The application of silver nanoparticles to packaging films can extend the shelf life of products. Nanoparticles are used in new types of solar cells and fuel cells - devices that convert the energy of fuel combustion into electrical energy. In the future, their use will make it possible to abandon the combustion of hydrocarbon fuels at thermal power plants and in internal combustion engines of vehicles - and in fact they make the greatest contribution to the deterioration of the environmental situation on our planet. So nanoparticles serve the task of creating environmentally friendly materials and ways of energy production.

The tasks of nanoscience are reduced to the study of mechanical, electrical, magnetic, optical and chemical properties of nanoobjects - substances and materials. Nanochemistry as one of the components of nanoscience, it is engaged in the development of synthesis methods and the study of the chemical properties of nanoobjects. It is closely related to materials science, since nanoobjects are part of many materials. Medical applications of nanochemistry are very important, including the synthesis of substances related to natural proteins, or nanocapsules that serve to carry drugs.

Achievements in nanoscience serve as the basis for the development nanotechnology– technological processes of production and application of nano-objects. Nanotechnologies have little in common with those examples of chemical industries that are considered in the school chemistry course. This is not surprising - after all, nanotechnologists have to manipulate objects with a size of 1–100 nm, i.e. having the size of individual large molecules.

There is a strict definition of nanotechnology*: this is a set of methods and techniques used in the study, design, production and use of structures, devices and systems, including targeted control and modification of the shape, size, integration and interaction of their constituent nanoscale elements (1–100 nm) to obtain objects with new chemical physical and biological properties. The key in this definition is the last part, which emphasizes that the main task of nanotechnology is to obtain objects with new properties.

Dimensional effect

Nanoparticles are usually called objects consisting of atoms, ions or molecules and having a size of less than 100 nm. Metal particles are an example. We have already talked about gold nanoparticles. And in black and white photography, when light hits the film, silver bromide decomposes. It leads to the appearance of particles of metallic silver, consisting of several tens or hundreds of atoms. Since ancient times, it has been known that water in contact with silver can kill pathogenic bacteria. The healing power of such water is explained by the content of the smallest particles of silver in it, these are nanoparticles! Due to their small size, these particles differ in properties both from individual atoms and from a bulk material consisting of many billions of billions of atoms, such as a silver ingot.

It is known that many physical properties of a substance, such as its color, thermal and electrical conductivity, and melting point, depend on the particle size. For example, the melting temperature of gold nanoparticles 5 nm in size is 250° lower than that of ordinary gold (Fig. 4). As the size of the gold nanoparticles increases, the melting temperature increases and reaches a value of 1337 K, which is typical for a conventional material (which is also called the bulk phase or macrophase).

Glass acquires color if it contains particles whose dimensions are comparable to the wavelength of visible light, i.e. are nanosized. This explains the bright color of medieval stained-glass windows, which contain various sizes of metal nanoparticles or their oxides. And the electrical conductivity of a material is determined by the mean free path - the distance that an electron travels between two collisions with atoms. It is also measured in nanometers. If the size of a metal nanoparticle turns out to be less than this distance, then one should expect the appearance of special electrical properties in the material, which are not characteristic of an ordinary metal.

Thus, nanoobjects are characterized not only by their small size, but also by the special properties that they exhibit, acting as an integral part of the material. For example, the color of “golden ruby” glass or a colloidal solution of gold is caused not by one gold nanoparticle, but by their ensemble, i.e. a large number of particles located at a certain distance from each other.

Individual nanoparticles containing no more than 1000 atoms are called nanoclusters. The properties of such particles differ significantly from the properties of a crystal, which contains a huge number of atoms. This is due to the special role of the surface. Indeed, reactions involving solids do not occur in the volume, but on the surface. An example is the interaction of zinc with hydrochloric acid. If you look closely, you can see that hydrogen bubbles form on the surface of zinc, and the atoms located in the depth do not participate in the reaction. Atoms lying on the surface have more energy, because. they have fewer neighbors in the crystal lattice. A gradual decrease in particle size leads to an increase in the total surface area, an increase in the fraction of atoms on the surface (Fig. 5), and an increase in the role of surface energy. It is especially high in nanoclusters, where most of the atoms are on the surface. Therefore, it is not surprising that, for example, nanogold is many times more chemically active than ordinary gold. For example, gold nanoparticles containing 55 atoms (diameter 1.4 nm) deposited on the surface of TiO 2 serve as good catalysts for the selective oxidation of styrene with atmospheric oxygen to benzaldehyde ( Nature, 2008):

C 6 H 5 -CH \u003d CH 2 + O 2 -> C 6 H 5 -CH \u003d O + H 2 O,

while particles with a diameter of more than 2 nm, and even more so ordinary gold, do not show catalytic activity at all.

Aluminum is stable in air, and aluminum nanoparticles are instantly oxidized by atmospheric oxygen, turning into oxide Al 2 O 3 . Studies have shown that aluminum nanoparticles with a diameter of 80 nm in air are overgrown with an oxide layer with a thickness of 3 to 5 nm. Another example: it is well known that ordinary silver is insoluble in dilute acids (except nitric). However, very small silver nanoparticles (no more than 5 atoms) will dissolve with the release of hydrogen even in weak acids such as acetic acid, for this it is enough to create the acidity of the solution pH = 5 (see lecture No. 8, task 4).

The dependence of the physical and chemical properties of nanoparticles on their size is called size effect. This is one of the most important effects in nanochemistry. He has already found a theoretical explanation from the standpoint of classical science, namely, chemical thermodynamics. Thus, the dependence of the melting point on the size is explained by the fact that the atoms inside the nanoparticles experience additional surface pressure, which changes their Gibbs energy (see lecture No. 8, task 5). Analyzing the dependence of the Gibbs energy on pressure and temperature, one can easily derive an equation relating the melting temperature and the radius of nanoparticles – it is called the Gibbs–Thomson equation:

where T pl ( r) is the melting temperature of a nanoobject with a radius of nanoparticles r, T pl () - melting point of ordinary metal (bulk phase), solid-l - surface tension between the liquid and solid phases, H pl is the specific heat of fusion, tv is the density of the solid.

Using this equation, it is possible to estimate from what size the properties of the nanophase begin to differ from the properties of a conventional material. As a criterion, we take the difference in the melting point of 1% (for gold, this is about 14 ° C). In the "Brief Chemical Reference" (authors - V.A. Rabinovich, Z.Ya. Khavin) we find for gold: H pl \u003d 12.55 kJ / mol \u003d 63.71 J / g, tv \u003d 19.3 g / cm 3. In the scientific literature for surface tension, the value of solid-l \u003d 0.55 N / m \u003d 5.5–10 -5 J / cm 2 is given. Let's solve the inequality with these data:

This estimate, although rather rough, correlates well with the value of 100 nm, which is usually used when talking about the limiting sizes of nanoparticles. Of course, here we did not take into account the dependence of the heat of fusion on temperature and surface tension on particle size, and the latter effect can be quite significant, as evidenced by the results of scientific research.

Many other examples of the size effect with calculations and qualitative explanations will be given in lectures #7 and #8.

Classification of nanoobjects

There are many different ways to classify nanoobjects. According to the simplest of them, all nanoobjects are divided into two large classes - solid (“external”) and porous (“internal”) (scheme).

Scheme

Classification of nanoobjects
(from a lecture by Prof. B.V. Romanovsky)

Solid objects are classified by dimension: 1) three-dimensional (3D) structures, they are called nanoclusters ( cluster- accumulation, bunch); 2) flat two-dimensional (2D) objects - nanofilms; 3) linear one-dimensional (1D) structures - nanowires, or nanowires (nanowires); 4) zero-dimensional (0D) objects - nanodots, or quantum dots. Porous structures include nanotubes (see lecture 4) and nanoporous materials, such as amorphous silicates (see lecture No. 8, task 2).

Of course, this classification, like any other, is not exhaustive. It does not cover a rather important class of nanoparticles - molecular aggregates obtained by methods of supramolecular chemistry. We will look at it in the next lecture.

Some of the most actively studied structures are nanoclusters- consist of metal atoms or relatively simple molecules. Since the properties of clusters depend very strongly on their size (size effect), their own classification has been developed for them - according to size (table).

Table

Classification of metal nanoclusters by size
(from a lecture by Prof. B.V. Romanovsky)

It turned out that the shape of nanoclusters significantly depends on their size, especially for a small number of atoms. The results of experimental studies, combined with theoretical calculations, showed that gold nanoclusters containing 13 and 14 atoms have a planar structure, in the case of 16 atoms they have a three-dimensional structure, and in the case of 20 they form a face-centered cubic cell resembling the structure of ordinary gold. It would seem that with a further increase in the number of atoms, this structure should be preserved. However, it is not. A particle consisting of 24 gold atoms in the gas phase has an unusual elongated shape (Fig. 6). Using chemical methods, it is possible to attach other molecules to clusters from the surface, which are able to organize them into more complex structures. It was found that gold nanoparticles combined with fragments of polystyrene molecules [–CH 2 –CH(C 6 H 5)–] n or polyethylene oxide (–CH 2 CH 2 O–) n, when they enter water, they are combined by their polystyrene fragments into cylindrical aggregates resembling colloidal particles - micelles, and some of them reach a length of 1000 nm. Scientists suggest that such objects can be used as anti-cancer drugs and catalysts.

Natural polymers such as gelatin or agar-agar are also used as substances that transfer gold nanoparticles into solution. By treating them with chloroauric acid or its salt, and then with a reducing agent, nanopowders are obtained that are soluble in water with the formation of bright red solutions containing colloidal gold particles. (For more details on the structure and properties of metal nanoclusters, see lecture No. 7, tasks 1 and 4.)

Interestingly, nanoclusters are present even in ordinary water. They are agglomerates of individual water molecules connected to each other by hydrogen bonds. It has been calculated that in saturated water vapor at room temperature and atmospheric pressure, there are 10,000 dimers (H 2 O) 2 , 10 cyclic trimers (H 2 O) 3 and one tetramer (H 2 O) 4 per 10 million single water molecules. In liquid water, particles of a much larger molecular weight, formed from several tens and even hundreds of water molecules, have also been found. Some of them exist in several isomeric modifications that differ in the form and order of connection of individual molecules. Especially many clusters are found in water at low temperatures, near the melting point. Such water is characterized by special properties - it has a higher density compared to ice and is better absorbed by plants. This is another example of the fact that the properties of a substance are determined not only by its qualitative or quantitative composition, i.e. chemical formula, but also its structure, including at the nanolevel.

Among other nanoobjects, nanotubes have been most thoroughly studied. This is the name given to lingering cylindrical structures with dimensions of several nanometers. Carbon nanotubes were first discovered in 1951 by Soviet physicists L.V. Radushkevich and V.M. Lukyanovich, but their publication, which appeared a year later in a domestic scientific journal, went unnoticed. Interest in them arose again after the work of foreign researchers in the 1990s. Carbon nanotubes are a hundred times stronger than steel, and many of them are good conductors of heat and electricity. We have already mentioned them when talking about Damascus blades. You will learn more about carbon nanotubes in lecture No. 4.

Recently, scientists have managed to synthesize nanotubes of boron nitride, as well as some metals, such as gold (Fig. 7, see p. fourteen). In terms of strength, they are significantly inferior to carbon ones, but, due to their much larger diameter, they are able to include even relatively large molecules. To obtain gold nanotubes, heating is not required - all operations are carried out at room temperature. A colloidal solution of gold with a particle size of 14 nm is passed through a column filled with porous alumina. In this case, gold clusters get stuck in the pores present in the aluminum oxide structure, uniting with each other into nanotubes. To free the formed nanotubes from aluminum oxide, the powder is treated with acid - aluminum oxide dissolves, and gold nanotubes settle at the bottom of the vessel, resembling algae in a micrograph.

An example of one-dimensional nanoobjects are nanothreads, or nanowires- this is the name of extended nanostructures with a cross section of less than 10 nm. With this order of magnitude, the object begins to exhibit special, quantum properties. Let us compare a copper nanowire 10 cm long and 3.6 nm in diameter with the same wire, but 0.5 mm in diameter. The size of an ordinary wire is many times greater than the distances between atoms, so the electrons move freely in all directions. In a nanowire, electrons are able to move freely only in one direction - along the wire, but not across, because its diameter is only a few times the distance between atoms. Physicists say that in a nanowire, electrons are localized in transverse directions, and delocalized in longitudinal directions.

Known nanowires of metals (nickel, gold, copper) and semiconductors (silicon), dielectrics (silicon oxide). With the slow interaction of silicon vapor with oxygen under special conditions, it is possible to obtain silicon oxide nanowires, on which, like twigs, globular silica formations resembling cherries hang. The size of such a "berry" is only 20 microns (µm). Molecular nanowires stand somewhat apart, an example of which is the DNA molecule - the keeper of hereditary information. A small number of inorganic molecular nanowires are molybdenum sulfides or selenides. A fragment of the structure of one of these compounds is shown in fig. 8. Thanks to the presence d-electrons in molybdenum atoms and the overlap of partially filled d-orbitals this substance conducts electric current.

Research on nanowires is currently being carried out at the laboratory level. However, it is already clear that they will be in demand when creating computers of new generations. Semiconductor nanowires, like conventional semiconductors, can be doped** according to R- or n-type. Already now on the basis of nanowires created p–n- transitions with an unusually small size. Thus, the foundations for the development of nanoelectronics are gradually being created.

The high strength of nanofibers makes it possible to reinforce various materials, including polymers, in order to increase their rigidity. And the replacement of the traditional carbon anode in lithium-ion batteries with a steel anode coated with silicon nanowires made it possible to increase the capacity of this current source by an order of magnitude.

An example of two-dimensional nanoobjects are nanofilms. Due to their very small thickness (only one or two molecules), they transmit light and are invisible to the eye. Polymer nanocoatings made of polystyrene and other polymers reliably protect many items used in everyday life - computer screens, cell phone windows, glasses lenses.

Single nanocrystals of semiconductors (for example, zinc sulfide ZnS or cadmium selenide CdSe) up to 10–50 nm in size are called quantum dots. They are considered zero-dimensional nano-objects. Such nanoobjects contain from one hundred to one hundred thousand atoms. When a quantum semiconductor is irradiated, an “electron-hole” pair (exciton) appears, the movement of which in a quantum dot is limited in all directions. Due to this, the exciton energy levels are discrete. Passing from the excited state to the ground state, the quantum dot emits light, and the wavelength depends on the size of the dot. This ability is being used to develop next-generation lasers and displays. Quantum dots can also be used as biological labels (markers), connecting them to certain proteins. Cadmium is rather toxic, therefore, in the production of quantum dots based on cadmium selenide, they are coated with a protective shell of zinc sulfide. And to obtain water-soluble quantum dots, which is necessary for biological applications, zinc is combined with small organic ligands.

The world of nanostructures already created by scientists is very rich and diverse. In it you can find analogues of almost all macro-objects of our ordinary world. It has its own flora and fauna, its own lunar landscapes and labyrinths, chaos and order. A large collection of various images of nanostructures is available at www.nanometer.ru. Does all of this find practical application? Of course no. Nanoscience is still very young - it is only about 20 years old! And like any young organism, it develops very quickly and is only just beginning to benefit. So far, only a small part of the achievements of nanoscience has been brought to the level of nanotechnologies, but the percentage of implementation is constantly growing, and in a few decades our descendants will be perplexed - how could we exist without nanotechnologies!

Questions

1. What is called nanoscience? Nanotechnology?

2. Comment on the phrase "every substance has a nanolevel."

3. Describe the place of nanochemistry in nanoscience.

4. Using the information given in the text of the lecture, estimate the number of gold atoms in 1 m 3 and in 1 nm 3.

Answer. 5,9 10 28 ; 59.

5. One of the founders of nanoscience, the American physicist R. Feynman, speaking about the theoretical possibility of mechanical manipulation of individual atoms, back in 1959 said the phrase that became famous: “There is a lot of space down there” ("There's plenty of room at the bottom"). How do you understand the scientist's statement?

6. What is the difference between physical and chemical methods of obtaining nanoparticles?

7. Explain the meaning of the terms: "nanoparticle", "cluster", "nanotube", "nanowire", "nanofilm", "nanopowder", "quantum dot".

8. Explain the meaning of the term "size effect". What properties does it show?

9. Copper nanopowder, unlike copper wire, quickly dissolves in hydroiodic acid. How to explain it?

10. Why does the color of colloidal solutions of gold containing nanoparticles differ from the color of an ordinary metal?

11. A spherical gold nanoparticle has a radius of 1.5 nm, the radius of a gold atom is 0.15 nm. Estimate how many gold atoms are contained in a nanoparticle.

Answer. 1000.

12. What type of clusters does the Au 55 particle belong to?

13. What other products, besides benzaldehyde, can be formed during the oxidation of styrene with atmospheric oxygen?

14. What are the similarities and differences between water obtained by melting ice and water formed by the condensation of steam?

15. Give examples of nano-objects of dimension 3; 2; one; 0.

Literature

Nanotechnologies. ABC for everyone. Ed. acad. Yu.D. Tretyakov. Moscow: Fizmatlit, 2008; Sergeev G.B. Nanochemistry. M.: Book House University, 2006; Ratner M., Ratner D. Nanotechnology. A simple explanation of another brilliant idea. Moscow: Williams, 2007; Rybalkina M. Nanotechnology for everyone. M., 2005; Menshutina N.V.. Introduction to nanotechnology. Kaluga: Publishing house of scientific literature Bochkareva N.F., 2006; Lalayants I.E. Nanochemistry. Chemistry (Publishing House "First of September"), 2002, No. 46, p. one; Rakov E.G. Chemistry and nanotechnology: two points of view. Chemistry (Publishing House "First of September"), 2004, No. 36, p. 29.

Internet resources

www.nanometer.ru – information site dedicated to nanotechnologies;

www.nauka.name - popular science portal;

www.nanojournal.ru - Russian electronic Nanojournal.

* Officially adopted by the Russian state corporation Rosnanotech.

** Doping is the introduction of small amounts of impurities that changes the electronic structure of the material. - Note. ed.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

Federal State Educational Institution of Higher Education

"Magnitogorsk State Technical University named after I.I. G.I. Nosov"

Department of Physical Chemistry and Chemical Technology

in the discipline "History of chemistry and chemical technology"

on the topic "Nanochemistry"

Performer: Perevalova Ksenia Olegovna, 2nd year student, group zTXB-15.1

Head: Ponurko Irina Vitalievna, associate professor, candidate of technical sciences, associate professor

Magnitogorsk, 2017

Introduction

2. Basic concepts of nanoscience

Conclusion

List of sources used

Introduction

In the history of human development, there are several important historical stages associated with the development of new materials and technologies.

Today, science has come close to the possibility of direct action on individual atoms and molecules, which has created a fundamentally new trend in development, which has received the general name of nanotechnology. The creation and study of structures and objects with controlled parameters and specified properties at the nanolevel is one of the most important technological problems of our time. This is due to the unique properties of materials in the nanostructural state, close to fundamental limitations, the possibility of creating "intelligent" materials with predetermined programmable properties, the development of new technologies for processing materials and modifying their surface, with a general trend towards miniaturization of products, the creation of fundamentally new objects. , devices and even new industries.

Nanotechnologies represent a wide range of scientific, technological and industrial areas combined into a single technological culture based on operations with matter at the level of individual atoms and molecules. This is not just about new technologies, but about processes that will change all segments of industry and areas of human activity, including the information environment, healthcare, the economy, and the social sphere.

The introduction of nanotechnologies requires the creation of new approaches to engineering education, adaptation to new ideas.

In this study, the main aspects of nanotechnology are considered.

1. The history of the formation of nanoscience

The prehistory of modern nanotechnologies is connected with the centuries-old research efforts of scientists from many countries of the world and has its own long historical trail. Let's consider the most significant stages.

1661 Irish physicist and chemist R. Boyle, one of the founders of the Royal Society of London, in his work "Skeptic Chemist" pointed out the potential importance of the smallest particles - clusters ("corpuscles").

Criticizing Aristotle's view of matter, consisting of four fundamental principles (earth, fire, water and air), the author suggested that all material objects consist of ultra-small corpuscles, which are quite stable and in different combinations form various substances and objects.

Subsequently, the ideas of Democritus and Boyle were accepted by the scientific community.

1857 The English physicist M. Faraday, the founder of the theory of the electromagnetic field, for the first time obtained stable colloidal solutions of gold (liquid systems with the smallest particles of the dispersed phase, moving freely and independently of each other in the process of Brownian motion). Subsequently, colloidal solutions began to be widely used for the formation of nanosystems.

1861 The English chemist T. Graham introduced the division of substances according to the degree of dispersion of the structure into colloidal (amorphous) and crystalloid (crystalline).

An example of the first use of nanotechnology can be considered the invention in 1883 by the American inventor D. Eastman, the founder of the well-known company Kodak, of roll film, which is an emulsion of silver halide deposited on a transparent elastic base (for example, from cellulose acetate), which decomposes under the action of light to form nanoparticles pure silver, which are the image pixels.

1900 German physicist M. Planck introduced the concept of quantum of action (Planck's constant) - the starting point for quantum theory, the provisions of which are essential in describing the behavior of nanosystems.

1905 The first scientist who used measurements in nanometers is considered to be the famous physicist A. Einstein, who theoretically proved that the size of a sugar molecule is one nanometer (10 -9 m).

1924 French physicist Louis de Broglie put forward the idea of ​​the wave properties of matter, thereby laying the foundation for quantum mechanics, which studies the motion of microparticles. The laws of quantum mechanics are especially relevant when creating nanoscale structures.

1931 German physicists M. Knoll and E. Ruska created an electron transmission microscope, which became the prototype of a new generation of devices that made it possible to look into the world of nanoobjects.

1939 Siemens produces the first industrial electron microscope with ? 10 nm.

1959 American physicist, Nobel laureate R. Feynman, in a famous lecture at the California Institute of Technology, known as "There's Plenty of Room at the Bottom", expressed the idea of ​​controlling the structure of matter at the atomic level: “By learning to regulate and control structures at the atomic level, we will obtain materials with completely unexpected properties and discover completely unusual effects.

The development of manipulation techniques at the atomic level will solve many problems.” This lecture became, in a certain sense, a launching pad for nanoresearch. Many of the visionary ideas expressed by R. Feynman, which seemed fantastic (about engraving lines a few atoms wide with an electron beam, about manipulating individual atoms to create new small structures, about creating electrical circuits on a nanometer scale, about using nanostructures in biological systems), today already implemented.

1966 American physicist R. Young, who worked at the National Bureau of Standards, invented a piezo motor, which is used today in scanning probe microscopes for precise positioning of a nanotool.

1968 Employees of the scientific division of the American company Bell A. Cho and D. Arthur developed the theoretical foundations of surface nanomachining.

1971 Bell and IBM companies obtained the first semiconductor films of single-atom thickness - quantum wells, which marked the beginning of the era of "practical" nanotechnology.

R. Young put forward the idea of ​​the Topografiner device, which served as a prototype of the probe microscope.

1974 The term "nanotechnology" was first proposed by the Japanese physicist N. Taniguchi in his report "On the Basic Concept of Nanotechnology" at an international conference long before the start of large-scale work in this area. The term was used to describe the ultra-fine processing of materials with nanometer precision. The term "nanotechnology" was proposed to refer to mechanisms smaller than one micrometer in size.

1981 German physicists G. Binning and G. Rohrer, employees of IBM (International Business Machines Corporation), created a scanning tunneling microscope (Nobel Prize in 1986) - the first device that allows not only to obtain a three-dimensional image of a structure from an electrically conductive material with resolution of the order of the size of individual atoms, but also to influence the substance at the atomic level, i.e. manipulate atoms, and, consequently, directly collect any substance from them.

1985 A team of scientists consisting of G. Kroto (England), R. Curl, R. Smalley (USA) discovered a new allotropic form of carbon in nature - fullerene and studied its properties (Nobel Prize 1996). The possibility of the existence of spherical highly symmetrical carbon molecules was predicted in 1970 by Japanese scientists E. Osawa and Z. Yoshilda.

In 1973, Russian scientists D. A. Bochvar and E. G. Galpern proved the stability of such molecules by theoretical quantum chemical calculations.

1986 A scanning atomic force microscope was created (authors - G. Binning, K. Kuatt, K. Gerber, employees of IBM, Nobel Prize in 1992), which made it possible, in contrast to the scanning tunneling microscope, to study the atomic structure of not only conductive, but also any materials, including organic molecules, biological objects, etc.

Nanotechnology has become known to the general public. The basic system concept, which comprehended previous achievements, was voiced in the book of the American futurologist, employee of the laboratory of artificial intelligence of the Massachusetts Institute of Technology E. Drexler "Engines of Creation: The Coming Era of Nanotechnology". The author predicted the active development and practical application of nanotechnologies. This forecast, calculated for many decades, is justified step by step with a significant lead in time.

1987 The first single-electron transistor was created by American physicists T. Futon and G. Dolan (Bell Labs).

French physicist J.M. Len introduced the concepts of "self-organization" and "self-assembly", which have become key in the design of nano-objects.

1988-1989 Two independent groups of scientists led by A. Fehr and P. Grunberg discovered the phenomenon of giant magnetic resistance (GMR) - a quantum mechanical effect observed in thin films of alternating ferromagnetic and non-magnetic layers, which manifests itself in a significant decrease in electrical resistance in the presence of an external magnetic field. The use of this effect makes it possible to record data on hard disks with atomic information density (Nobel Prize 2007).

1989 The first practical achievement of nanotechnology was demonstrated: using a scanning tunneling microscope manufactured by IBM, American researchers D. Eigler,

E. Schweitzer laid out three letters of the company logo ("IBM") from 35 xenon atoms by moving them sequentially on the surface of a nickel single crystal.

1990 A team of scientists led by W. Kretschmer (Germany) and

D. Huffman (USA) created an effective technology for the synthesis of fullerenes, which contributed to the intensive study of their properties and the identification of promising areas of their application.

1991 Japanese physicist S. Iijima discovered a new form of carbon

native clusters - carbon nanotubes, which exhibit a whole range of unique properties and are the basis for revolutionary changes in materials science and electronics.

In Japan, a state program has begun to develop the technique of manipulating atoms and molecules - the Atomic Technology project.

1993 The first nanotechnological laboratory is organized in the USA.

1994 First demonstration of a laser based on self-organized quantum dots (D. Bimberg, Germany).

1998 Dutch physicist S. Dekker created the first nanotransistor based on nanotubes.

Japan launched the Astroboy program to develop nanoelectronics capable of operating in space.

1999 American scientists M. Reid and D. Tour developed unified principles for the manipulation of both a single molecule and their chain.

The element base of microelectronics has overcome the barrier of 100 nm.

2000 The US launched a massive nanotechnology research program called the National Nanotechnology Initiative (NNI).

The German physicist R. Magerle proposed the technology of nanotomography - creating a three-dimensional picture of the internal structure of a substance with a resolution of 100 nm. The project was funded by Volkswagen.

2002 Employees of the Hewlett Research Center

Packard (USA) F. Cukes and S. Williams patented a technology for creating chips based on intersecting nanowires with complex logic implemented at the molecular level.

S. Dekker combined a carbon nanotube with DNA, obtaining a single nanomechanism.

2004 The University of Manchester (Great Britain) created graphene - a material with a graphite structure one atom thick, a promising substitute for silicon in integrated circuits (for the creation of graphene, scientists A. Game and K. Novoselov were awarded the Nobel Prize in 2010).

2005 Altar Nanotechnologies (USA) announced the creation of a nanoaccumulator.

2006 Researchers at US Northwestern University develop the first "printing press" for nanostructures, a facility that allows more than 50,000 nanostructures to be simultaneously produced in the nanoscale range with atomic precision and the same molecular pattern on the surface, which is the foundation for future mass production of nanosystems.

For the first time in the world, American scientists from IBM managed to create a fully functional integrated circuit based on a carbon nanotube.

D. Tour from Rice University (USA) created the first moving nanosystem - a molecular machine ~ 4 nm in size.

A group of scientists from the University of Portsmouth (UK) has developed the first DNA-based electronic bionanotechnological switch, which is a promising basis for communication between the "world" of living organisms and the "world" of computers.

Scientists from the California Institute of Technology (USA) have developed the first portable biosensor-blood analyzer (lab-on-chip portable laboratory).

2007 Intel (USA) began to produce processors containing the smallest structural element ~ 45 nm in size.

Employees of the Institute of Technology (Georgia, USA) have developed a scanning lithography technology with a resolution of 12 nm.

The above and other studies, discoveries, inventions gave a powerful impetus to the application of nanotechnological methods in industry. The rapid development of applied nanotechnology began.

The first commercial nanomaterials appeared - nanopowders, nanocoatings, bulk nanomaterials, nanochemical and nanobiological preparations; the first electronic devices, sensors for various purposes based on nanotechnology were created; Numerous methods for obtaining nanomaterials have been developed.

Many countries of the world are actively involved in research on nanotechnology issues at the level of governments and heads of state, assessing the prospects for the future. Leading universities and institutes of the world (USA, Germany, Japan, Russia, England, France, Italy, Switzerland, China, Israel, etc.) have established laboratories and departments of nanostructures headed by well-known scientists.

Nanotechnologies are already being used in the most significant areas of human activity - radio electronics, the information sphere, energy, transport, biotechnology, medicine, and the defense industry.

Today, more than 50 countries of the world are involved in nanoresearch.

For the unique results of research in this area, 8 Nobel Prizes were awarded.

2. Basic concepts of nanoscience

Nanoscience emerged as an independent discipline only in the last 7-10 years. The study of nanostructures is a common direction for many classical scientific disciplines. Nanochemistry occupies one of the leading places among them, as it opens up practically unlimited possibilities for the development, production and research of new nanomaterials with desired properties, often superior in quality to natural materials.

Nanochemistry is a science that studies the properties of various nanostructures, as well as the development of new ways to obtain, study and modify them.

The priority task of nanochemistry is to establish a relationship between the size of a nanoparticle and its properties.

The objects of nanochemistry research are bodies with such a mass that their equivalent size remains within the nanointerval (0.1 - 100 nm).

Nanoscale objects occupy an intermediate position between bulk materials on the one hand, and atoms and molecules on the other. The presence of such objects in materials gives them new chemical and physical properties. Nanoobjects are an intermediate and connecting link between the world in which the laws of quantum mechanics operate and the world in which the laws of classical physics operate.

Figure 1. Characteristic sizes of objects of the surrounding world

Nanochemistry investigates the production and properties of various nanosystems. Nanosystems are a set of bodies surrounded by a gas or liquid medium. Such bodies can be polyatomic clusters and molecules, nanodroplets and nanocrystals. These are intermediate forms between atoms and macroscopic bodies. The size of the systems remains within 0.1 - 100 nm.

Table 1. Classification of objects of nanochemistry by phase state

nanoscience nanoparticle nanochemistry classification

The range of objects studied by nanochemistry is constantly expanding. Chemists have always sought to understand what the features of nanometer-sized bodies are. This led to the rapid development of colloidal and macromolecular chemistry.

In the 80-90s of the XX century, thanks to the methods of electron, atomic force and tunneling microscopy, it was possible to observe the behavior of metal nanocrystals and inorganic salts, protein molecules, fullerenes and nanotubes, and in recent years such observations have become massive.

Table 2. Objects of nanochemical studies

Thus, the following main characteristics of nanochemistry can be distinguished:

1. The geometric dimensions of objects lie on the nanometer scale;

2. Manifestation of new properties by objects and their sets;

3. Possibility of control and precise manipulation of objects;

4. Objects and devices assembled on the basis of objects receive new consumer properties.

3. Features of the structure and behavior of some nanoparticles

Nanoparticles made of atoms of inert gases are the simplest nanoobjects. Atoms of inert gases with completely filled electron shells weakly interact with each other through van der Waals forces. When describing such particles, the model of hard balls is used.

Metal nanoparticles. In metallic clusters of several atoms, both covalent and metallic types of bonds can be realized. Metal nanoparticles are highly reactive and are often used as catalysts. Metal nanoparticles usually take the correct shape - octahedron, icosahedron, tetradecahedron.

Fractal clusters are objects with a branched structure: soot, colloids, various aerosols and aerogels. A fractal is such an object in which, with increasing magnification, one can see how the same structure is repeated in it at all levels and on any scale.

Molecular clusters - clusters consisting of molecules. Most clusters are molecular. Their number and variety are enormous. In particular, many biological macromolecules belong to molecular clusters.

Fullerenes are hollow particles formed by polyhedrons of carbon atoms linked by a covalent bond. A special place among fullerenes is occupied by a particle of 60 carbon atoms - C60, resembling a microscopic soccer ball.

Nanotubes are molecules that are hollow inside, consisting of approximately 1,000,000 carbon atoms and are single-layer tubes with a diameter of about a nanometer and a length of several tens of microns. On the surface of a nanotube, carbon atoms are located at the vertices of regular hexagons.

4. Types of applied use of nanochemistry

Conventionally, nanochemistry can be divided into:

1. Theoretical

2. Experimental

3. Applied

Theoretical nanochemistry develops methods for calculating the behavior of nanobodies, taking into account such parameters of the state of particles as spatial coordinates and velocities, mass, characteristics of the composition, shape and structure of each nanoparticle.

Experimental nanochemistry is developing in three directions. Within the framework of the first, supersensitive spectral methods are developed and used, which make it possible to judge the structure of molecules, including tens and hundreds of atoms. Within the framework of the second direction, phenomena are studied under local (local) electrical, magnetic, or mechanical effects on nanobodies, implemented using nanoprobes and special manipulators. Within the framework of the third direction, the macrokinetic characteristics of nanobodies collectives and the distribution functions of nanobodies in terms of state parameters are determined.

Applied nanochemistry includes:

Development of theoretical foundations for the use of nanosystems in engineering and nanotechnology, methods for predicting the development of specific nanosystems in the conditions of their use, as well as the search for optimal methods of operation (technical nanochemistry).

Creation of theoretical models of the behavior of nanosystems during the synthesis of nanomaterials and the search for optimal conditions for their production (synthetic nanochemistry).

The study of biological nanosystems and the creation of methods for using nanosystems for medicinal purposes (medical nanochemistry).

Development of theoretical models for the formation and migration of nanoparticles in the environment and methods for cleaning natural waters or air from nanoparticles (environmental nanochemistry).

5. Methods for obtaining nanoparticles

Obtaining nanoparticles in the gas phase:

1 Obtaining nanoparticles in the process of "evaporation - condensation".

In the gas phase, the following processes are most often carried out: evaporation - condensation (evaporation in an electric arc and in plasma); precipitation; topochemical reactions (reduction, oxidation, decomposition of solid phase particles). In the "evaporation - condensation" process, liquid or solid substances evaporate at a controlled temperature in an atmosphere of inert gas of low pressure, followed by condensation of the vapor in a cooling medium or on cooling devices. This method makes it possible to obtain particles ranging in size from two to several hundred nanometers. Nanoparticles smaller than 20 nm are usually spherical, while larger ones may appear faceted.

Usually, the evaporated substance is placed in a heating chamber with a heater and a hole (diaphragm), through which the evaporated particles of the substance enter the vacuum space (with a pressure of about 0.10 Pa), where the molecular beam is formed. Particles, moving almost rectilinearly, condense on a cooled substrate. Gas is pumped out of the apparatus through a valve. The source temperature is chosen depending on the required intensity of the molecular beam and the equilibrium pressure over the evaporated material. It can be above or below the melting point of the substance.

It should be noted that some substances (for example, Sn and Ge) evaporate both in the form of individual atoms and in the form of small clusters. In low-intensity molecular beams obtained by effusion flow through a hole in a heating chamber, a uniform distribution of small clusters is observed. The main advantage of the molecular beam method is the ability to accurately control the beam intensity and control the rate of particle supply to the condensation zone.

2 Gas-phase production of nanoparticles.

The low-intensity molecular beam method is often combined with chemical deposition methods. The deposition is carried out near the cold surface of the device or directly on it at a controlled temperature and reduced pressure to reduce the likelihood of particle collision.

For the gas-phase production of nanoparticles, installations are used that differ in the methods of supplying and heating the evaporated material, the composition of the gaseous medium, the methods for implementing the condensation process and selecting the resulting powder. For example, powder is deposited on a cooled rotating cylinder or drum and scraped from it with a scraper into a receiving container.

The design scheme of the apparatus for gas-phase synthesis of metal nanopowders includes a working chamber, a cooled drum, a scraper, a funnel, a receiving container for powder, a heated tubular reactor, a device for controlled supply of the evaporated material and carrier gas. In a tubular reactor, the vaporized material is mixed with a carrier inert gas and transferred to the gas phase state.

The resulting continuous flow of clusters or nanoparticles comes from the reactor into the working chamber of the apparatus, in which a pressure of about 1–50 Pa is created. Condensation of nanoparticles and their deposition in the form of a powder occurs on the surface of a cooled rotating drum. Using a scraper, the powder is removed from the surface of the drum; then it enters the receiving tank through the funnel and is sent for further processing.

In contrast to evaporation in a vacuum, the atoms of a substance evaporated in a rarefied atmosphere lose their kinetic energy faster due to collisions with gas atoms and form crystal nuclei (clusters). When they condense, nanocrystalline particles are formed. Thus, in the process of aluminum vapor condensation in hydrogen, helium and argon at various gas pressures, particles with a size of 20 - 100 nm are obtained.

3 Obtaining nanoparticles using topochemical reactions.

Using topochemical reactions of certain gas media with metal nanoparticles at the moment of their condensation from the vapor phase, it is possible to obtain nanoparticles of desired compounds. To obtain the desired compound, the interaction of the evaporated metal with the reagent gas can also be provided directly in the gas phase.

In the method of gas-phase chemical reactions, the synthesis of nanomaterials occurs due to chemical transformations occurring in an atmosphere of vapors of volatile substances. Halides (especially metal chlorides), metal oxychlorides MeOnClm, alkoxides Me(OR)n, alkyl compounds Me(R)n, metal vapors, and so on are widely used as initial reagents. This method can be used to obtain nanomaterials of boron, carbon black, metals, alloys, nitrides, carbides, silicides, sulfides and other compounds.

In the synthesis of nanomaterials by the method under consideration, the properties of the resulting products are largely influenced by the design of the reactors, the method of heating the reagents, the temperature gradient during the process, and a number of other factors.

Gas-phase chemical reactions are usually carried out in various types of tubular flow reactors. The most widespread are reactors with external heating of the reaction zone. Quartz compounds, ceramic materials or alumina are used as structural materials for the reaction zone of apparatuses.

Topochemical interaction of the gas phase with the powder is used to apply various coatings on its particles and introduce modifying additives. In this case, it is necessary to control the degree of unevenness of the process so that the solid phase is separated only on the surface of the particles, and not in the volume between the particles. For example, topochemical reactions include the interaction of oxides with nitrogen in the presence of carbon to synthesize nitrides. In this way, powders of silicon, aluminum, titanium and zirconium nitrides are synthesized.

The composition of the inert gas affects the particle growth rate. The heavier atoms of the environment more intensively take energy from the condensed atoms and thus contribute to the growth of particles, just as a decrease in the cooling temperature also contributes to the growth of particles. By changing the gas pressure and composition of the gaseous medium in the apparatus, it is possible to obtain nanoparticles of various sizes. Thus, the replacement of helium with argon or xenon increases the size of the resulting nanoparticles by several times.

The production of nanopowders in the gas phase is facilitated by a relatively low surface tension at the solid-gas interface; an increase in surface tension leads to compaction of nanoparticles in the aggregate. At the same time, high temperature accelerates diffusion processes, which promotes particle growth and the formation of solid-state bridges between particles. The main problem of the method under consideration is the separation of nanoparticles from the gas phase under conditions when the concentration of particles in the gas flow is low and the gas temperature is sufficiently high. To capture nanoparticles, special filtering devices are used (for example, ceramic-metal filters, electrostatic precipitators), centrifugal settling of solid particles in cyclones and hydrocyclones, and special gas centrifuges.

Nanoparticles can be formed from high temperature decomposition of solids containing metal cations, molecular anions, or organometallic compounds. This process is called thermolysis. For example, small particles of lithium can be obtained by decomposition of lithium azide LiN. The substance is placed in an evacuated quartz tube and heated to 400 C in the apparatus. At a temperature of about 370 C, azide decomposes with the release of gaseous N2, which can be determined by the increase in pressure in the evacuated space. After a few minutes, the pressure drops to its original level, indicating that all N2 has been removed. The remaining lithium atoms combine into small colloidal metal particles. This method can be used to obtain particles with sizes less than 5 nm. Particles can be passivated by introducing an appropriate gas into the chamber.

Obtaining nanoparticles in the liquid phase:

1 Chemical condensation.

Chemical methods for obtaining nanoparticles and ultrafine systems have been known for a long time. A colloidal solution of a gold sol (red) with a particle size of 20 nm was obtained in 1857. M. Faraday. The aggregative stability of the sol is explained by the formation of a double electric layer on the solid-solution interface and the appearance of the electrostatic component of the disjoining pressure, which is the main factor in stabilizing this system.

The simplest and most frequently used method is the synthesis of nanoparticles in solutions during various reactions. To obtain metal nanoparticles, reduction reactions are used, in which aluminum and borohydrides, tetraborates, hypophosphites, and many other inorganic and organic compounds are used as a reducing agent.

Nanosized particles of salts and metal oxides are obtained most often in exchange and hydrolysis reactions. For example, a gold sol with a particle size of 7 nm can be obtained by reducing gold chloride with sodium borohydride using dodecanethiol as a stabilizer. Thiols are widely used to stabilize semiconductor nanoparticles. This method has extremely broad possibilities and makes it possible to obtain materials containing biologically active macromolecules.

2 Precipitation in solutions and melts.

Precipitation in solutions.

The general laws governing the formation of nanoparticles in liquid media depend on many factors: the composition and properties of the initial substance (solution, melt); the nature of the equilibrium diagram of the phases of the system under consideration; a method for creating supersaturation of a solution or melt; equipment used and how it works.

In the case of the synthesis of the necessary phases, the powder is heat-treated after it is dried, or these phases are combined into one. After heat treatment, the aggregates are disaggregated to the size of nanoparticles.

The starting materials and solvent are chosen so that by-products can be completely removed from the target product during washing and subsequent heat treatment without environmental pollution. For effective mixing of reagents, mixing devices with various types of agitators (propeller, rod, turbine), circulation mixing using pumps (centrifugal and gear), dispersing devices (nozzles, nozzles, injectors, rotating disks, acoustic sprayers, etc.) are used.

On the one hand, to increase the productivity of the reactor, the solubility of the starting materials must be high. However, when obtaining nanoparticles, this will increase their mass content in the resulting suspension and the probability of combining into aggregates.

On the other hand, to ensure a high degree of nonequilibrium in the formation of a solid phase, it is necessary to use saturated solutions of the initial substances. In order to retain a small fraction of nanoparticles in suspension, it is expedient to use poorly soluble initial substances. In this case, the productivity of the reactor will decrease. Another possibility is to use a small amount of precipitant and a large excess of precipitant. When precipitation in aqueous solutions, solutions of ammonia, ammonium carbonate, oxalic acid, or ammonium oxalate are most often used as precipitants. Highly soluble salts of nitric, hydrochloric or acetic acids are chosen as starting materials during precipitation.

By adjusting the pH and temperature of the solution, it is possible to create conditions for obtaining highly dispersed hydroxides. The product is then calcined and, if necessary, reduced. The resulting metal powders have a size of 50 - 150 nm spherical or close to the shape of the sphere. The deposition method can be used to obtain oxide metal and metal oxide materials, compositions based on them, various ferrites and salts.

The responsible stage that determines the properties of the resulting powder is its separation from the liquid phase. With the appearance of a gas-liquid interface, the Laplace forces and compressible particles sharply increase. As a result of the action of these forces, compressive pressures of the order of megapascals arise in particles of the nanoscale spectrum, which are used when compacting macroparticles into monolithic porous products. In this case, hydrothermal conditions are created in the pores of the aggregate, leading to an increase in the solubility of particles and the strengthening of aggregates due to the dissolution-condensation mechanism. Particles are combined into a strong aggregate, and then into a separate crystal.

To remove the liquid phase from the sediment, the processes of filtration, centrifugation, electrophoresis, and drying are used. The probability of formation of strong aggregates can be reduced by replacing water with organic solvents, as well as the use of surfactants, freeze drying, and the use of a drying agent under supercritical conditions.

A variation of the technology for obtaining nanoparticles in liquid media is the controlled dissolution of larger particles in suitable solvents. To do this, it is necessary to slow down or even stop the process of their dissolution in the nanosize range. In the same way, it is possible to carry out the correction of the sizes of the particles obtained by the listed methods in cases where their size turned out to be larger than necessary.

Precipitation in melts.

With this method, the liquid medium is molten salts or metals (most often molten salts are used). The formation of a solid phase occurs at a sufficiently high temperature, when diffusion processes cause a high rate of crystal growth. The main problem in this case is the exclusion of the capture by the synthesized powder of the components of side compounds. To isolate the synthesized powder after cooling, the salt is dissolved in suitable solvents.

By changing the degree of non-equilibrium of the process, it is possible to control the structure of the material. If the process is stopped at the stage when the solid phase has nanosizes, it is possible to obtain a nanomaterial. However, it is very difficult to do this because of the high rate of diffusion mass transfer at a sufficiently high temperature of the medium.

This method is more promising for obtaining nanoparticles by dissolving initial larger particles. In this case, one can immediately obtain a nanocomposite if the dissolving medium, for example, glassy, ​​plays the role of a matrix for nanoparticles.

3 Sol-gel method.

The sol-gel method includes several main technological phases. Initially, aqueous or organic solutions of the starting materials are obtained. Sols (colloidal systems) with a solid dispersed phase and a liquid dispersion medium are formed from solutions to obtain a sol, for example, hydrolysis of salts of weak bases or alcoholates is used. You can use other reactions leading to the formation of stable and concentrated sols (for example, the use of peptizers - substances that prevent the decomposition of particle aggregates in dispersed systems). It is effective to apply a protective layer of water-soluble polymers or surfactants to nanoparticles during hydrolysis, which are added together with water during hydrolysis.

Subsequently, the sol is converted into a gel when part of the water is removed from it by heating, extraction with an appropriate solvent. In some cases, an aqueous sol is sprayed into a heated water-immiscible organic liquid.

By converting a sol into a gel, structured colloidal systems are obtained. The solid particles of the dispersed phase are interconnected into a loose spatial grid, which contains a liquid dispersion medium in its cells, depriving the system as a whole of fluidity. Contacts between particles are easily and reversibly destroyed under mechanical and thermal influences. Gels with an aqueous dispersion medium are called hydrogels, and those with a hydrocarbon dispersion medium are called organogels.

By drying the gel, it is possible to obtain aerogels or xerogels - fragile microporous bodies (powders). Powders are used for product molding, plasma spraying, and so on. The gel can be used directly to produce films or monolithic articles. Currently, the sol-gel method is widely used to obtain nanoparticles from inorganic non-metallic materials.

4 Electrochemical method for obtaining nanoparticles.

The electrochemical method is associated with the release of a substance at the cathode during the electrolysis of simple and complex cations and anions. If a system consisting of two electrodes and an electrolyte solution (melt) is included in a direct electric current circuit, then oxidation-reduction reactions will occur at the electrodes. At the anode (positive electrode), anions donate electrons and are oxidized; at the cathode (negative electrode), cations gain electrons and are reduced. The precipitate formed on the cathode as a result of, for example, electrocrystallization, in morphological terms, can be either a loose or a dense layer of many microcrystallites.

The texture of the deposit is influenced by many factors, such as the nature of the substance and solvent, the type and concentration of ions of the target product and foreign impurities, the adhesive properties of the deposited particles, the temperature of the medium, the electric potential, diffusion conditions, and others. One of the promising scientific directions is the use of electrochemical synthesis for the design of nanostructured materials. Its essence lies in the formation of two-dimensional (Langmuir) monolayers of metal nanoparticles under monolayer surfactant matrices during kinetically controlled electroreduction. The main advantages of the method are the experimental availability and the ability to control and manage the process of obtaining nanoparticles.

Obtaining nanoparticles using plasma:

1 Plasma chemical synthesis.

One of the most common chemical methods for obtaining ultrafine powders of metals, nitrides, carbides, oxides, borides, and their mixtures is plasma-chemical synthesis. This method is characterized by a very fast (in 10.3 - 10.6 s) reaction proceeding far from equilibrium and a high rate of formation of a new phase at a relatively low rate of their growth.

In plasma-chemical synthesis, low-temperature (400 - 800 K) nitrogen, ammonia, hydrocarbon, argon plasma is used, which is created using an electric arc, an electromagnetic high-frequency field, or a combination of them in reactors called plasmatrons. In them, the flow of initial substances (gaseous, liquid or solid) quickly flies through the zone where the plasma is maintained, receiving energy from it for carrying out chemical transformation reactions. The source substance itself can also be a plasma-forming gas.

The reactor includes the following main components: electrodes, nozzles for the inlet of plasma-forming gas, electromagnet coils for maintaining the plasma arc, nozzles for introducing reagents, cold gas inlet devices, and a receiver for synthesis products. The arc column formed between the electrodes forms a plasma flow, while a temperature of 1200–4500 K is reached in the reactor. The resulting products are quenched in various ways: in tubular heat exchangers, by flooding the reacting mixture flow with jets of cold gases or liquids, in cooled Laval nozzles.

The characteristics of the resulting powders depend on the raw materials used, the synthesis technology, and the type of plasma torch; their particles are single crystals and have dimensions of 10 - 100 nm or more. The processes occurring during plasma-chemical synthesis and the gas-phase method for obtaining nanoparticles are close to each other. After interaction in the plasma, the formation of active particles in the gas phase occurs. In the future, it is necessary to preserve their nanosizes and separate them from the gas phase.

Powders of plasma-chemical synthesis are characterized by a wide size distribution of nanoparticles and, as a consequence, the presence of rather large (up to 1–5 μm) particles, that is, low selectivity of the process, as well as a high content of impurities in the powder.

To obtain nanoparticles, one can use not only the method of their growth, but also the dissolution of larger particles in plasma. In practice, reactors are used, in the working volume of which laser radiation is introduced through a special window and the flow of the reaction mixture. In the area of ​​their intersection, a reaction zone appears, where the formation of particles occurs. The particle size depends on the pressure of the reactor and the intensity of the laser radiation. The parameters of laser radiation are much easier to control (than high-frequency or arc plasma), which makes it possible to obtain a narrower particle size distribution. In this way, silicon nitride powder with a particle size of 10 - 20 nm was obtained.

2 Electroerosive method.

The essence of the method is the formation of an arc between electrodes immersed in a bath of liquid. Under these conditions, the substance of the electrodes is partially dispersed and interacts with the liquid to form a dispersed powder. For example, electrical erosion of aluminum electrodes in water results in the formation of aluminum hydroxide powder.

The resulting solid precipitate is separated from the liquid phase by filtration, centrifugation, electrophoresis. The powder is then dried and, if necessary, pre-crushed. In the process of subsequent heat treatment, the target product is synthesized from the powder, from which particles of the desired size are obtained in the process of deaggregation. This method can be used to obtain nanosized particles if large particles are placed in the liquid phase.

3 Shock-wave or detonation synthesis.

By this method, nanoparticles are obtained in plasma formed during the explosion of high explosives (HEs) in an explosion chamber (detonation tube).

Depending on the power and type of explosive device, shock-wave interaction on the material is carried out in a very short period of time (tenths of microseconds) at a temperature of more than 3000 K and a pressure of several tens of hectopascals. Under such conditions, a phase transition is possible in substances with the formation of ordered dissipative nanoscale structures. The shock wave method is most effective for materials synthesized at high pressures, such as diamond powders, cubic boron nitrate, and others.

During the explosive transformation of condensed explosives with a negative oxygen balance (a mixture of TNT and RDX), carbon is present in the reaction products, from which a diamond dispersed phase is formed with a particle size of the order of 4–5 nm.

By subjecting porous structures of various metals and their salts, gels of metal hydroxides to shock-wave action from an explosive charge, nanopowders of oxides of Al, Mg, Ti, Zn, Si, and others can be obtained.

The advantage of the shock-wave synthesis method is the possibility of obtaining nanopowders of various compounds not only of ordinary phases, but also of high-pressure phases. However, the practical application of the method requires special facilities and technological equipment for blasting.

Mechanochemical synthesis.

With this method, mechanical processing of solids is provided, as a result of which grinding and plastic deformation of substances occur. The grinding of materials is accompanied by the breaking of chemical bonds, which predetermines the possibility of the subsequent formation of new chemical bonds, that is, the occurrence of mechanochemical reactions.

The mechanical action during the grinding of materials is pulsed; in this case, the appearance of the stress field and its subsequent relaxation do not occur during the entire time the particles stay in the reactor, but only at the moment of particle collision and in a short time after it. The mechanical action is not only impulsive, but also local, since it does not occur in the entire mass of a solid, but only where a stress field arises and then relaxes.

The impact of energy released at a high degree of non-equilibrium during impact or abrasion, due to the low thermal conductivity of solids, leads to the fact that some part of the substance is in the form of ions and electrons - in the plasma state. Mechanochemical processes in a solid can be explained using the phonon theory of the destruction of brittle bodies (a phonon is an energy quantum of elastic vibrations of a crystal lattice).

Mechanical grinding of solid materials is carried out in ultrafine grinding mills (ball, planetary, vibration, jet). When the working bodies interact with the crushed material, its local short-term heating to high (plasma) temperatures is possible, which are obtained under normal conditions at high temperatures.

Mechanically, it is possible to obtain nanopowders with a particle size of 200 to 5 - 10 nm. So, when grinding a mixture of metal and carbon for

48 hours were obtained particles of TiC, ZrC, VC and NbC with a size of 7 - 10 nm. In a ball mill, from a mixture of tungsten carbon and cobalt powders with an initial particle size of about 75 μm, WC-Co nanocomposite particles with a particle size of 11-12 nm were obtained in 100 hours.

Biochemical methods for obtaining nanomaterials.

Nanomaterials can also be produced in biological systems. In many cases, living organisms, such as some bacteria and protozoa, produce minerals with particles and microscopic structures in the nanometer size range.

Biomineralization processes operate with fine biochemical control mechanisms, resulting in the production of materials with well-defined characteristics.

Living organisms can be used as a direct source of ultrafine materials whose properties can be changed by varying the biological conditions of synthesis or processing. Ultrafine materials obtained by biochemical synthesis methods can be used as starting materials for some of the already tested and known methods for the synthesis and processing of nanomaterials, as well as in a number of technological processes. So far, there are few works in this direction of research, but it is already possible to point out a number of examples of the production and use of biological nanomaterials.

At present, ultrafine materials can be obtained from a number of biological objects, for example, ferritins and related proteins containing iron, magnetic bacteria, and others. Thus, ferritins (a type of protein) provide living organisms with the ability to synthesize particles of iron hydroxides and oxyphosphates of nanometer size. The ability of magnetotactic bacteria to use the lines of the Earth's magnetic field for their own orientation makes it possible to have chains of nanosized (40 - 100 nm) single-domain magnetite particles.

It is also possible to obtain nanomaterials using microorganisms. At present, bacteria have been discovered that oxidize sulfur, iron, hydrogen and other substances. With the help of microorganisms, it became possible to carry out chemical reactions to extract various metals from ores, bypassing traditional technological processes. An example is the technology of bacterial leaching of copper from sulfide materials, uranium from ores, separation of arsenic impurities from tin and gold concentrates.

In some countries, at present, up to 5% of copper, a large amount of uranium and zinc are obtained by microbiological methods. There are good prerequisites, confirmed by laboratory studies, for the use of microbiological processes for the extraction of manganese, bismuth, lead, germanium from poor carbonate ores. With the help of microorganisms, it is possible to open finely disseminated gold in arsenopyrite concentrates. Therefore, a new direction has appeared in technical microbiology, which is called microbiological hydrometallurgy.

cryochemical synthesis.

The high activity of metal atoms and clusters in the absence of stabilizers causes the reaction into larger particles. The process of aggregation of metal atoms proceeds practically without activation energy. The stabilization of active atoms of almost all elements of the periodic system was achieved at low (77 K) and ultralow (4 - 10 K) temperatures by the matrix isolation method. The essence of this method is the use of inert gases at ultralow temperatures. Most often, argon and xenon are used as a matrix. Pairs of metal atoms are condensed with a large, usually a thousandfold, excess of inert gas onto a cooled surface up to 10 - 12 K. Significant dilution of inert gases and low temperatures practically exclude the possibility of diffusion of metal atoms, and they are stabilized in the condensate. The physicochemical properties of such atoms are studied by various spectral and radio spectral methods.

The main processes of cryochemical nanotechnology:

1 Preparation and dispersion of solutions.

As a result of the dissolution of the initial substance or substances in one or another solvent, it is possible to achieve the highest possible degree of mixing of the components in a homogeneous solution, in which a high degree of accuracy of matching the specified composition is guaranteed. The most commonly used solvent is water; however, it is possible to use other solvents that are easily frozen and sublimated.

Then the resulting solution is dispersed into separate drops of the required size, and they are cooled until the moisture is completely frozen. The process of hydrodynamic dispersion is carried out due to the expiration of the solution through various nozzles and filters, as well as using nozzles.

Similar Documents

General information about methods for obtaining nanoparticles. Basic processes of cryochemical nanotechnology. Preparation and dispersion of solutions. Biochemical methods for obtaining nanomaterials. Freezing liquid droplets. Supersonic outflow of gases from a nozzle.

term paper, added 11/21/2010


Basic concepts of nanotechnology and the development of nanochemistry. The role of carbon in the nanoworld. Discovery of fullerenes as a form of existence of carbon. Types of smart nanomaterials: biomimetic, biodegradable, ferrofluid, software and hardware complex.

presentation, added 08/12/2015


The main aspects that relate to the field of nanochemistry. Classification of size effects according to Mayer, the reasons for their occurrence. Scheme of work and general view of the atomic force microscope. Classification of nanomaterials by dimension. Properties of carbon nanotubes.

presentation, added 07/13/2015


Properties and classification of nanoparticles: nanoclusters and nanoparticles proper. Cell cultures used for in vitro toxicity studies: lung, amnion and human lymphocyte carcinomas, rat cardiomyocytes. Study of the cytotoxicity of nanomaterials.

term paper, added 05/14/2014


Application of nanotechnologies in medicine. The impact of nanoparticles on the human body. Medical applications of scanning probe microscopes. Obtaining single crystals in a two-layer bath. Devices for obtaining drugs with whiskers.

thesis, added 06/04/2015


Features of obtaining silver nanoparticles by the method of chemical reduction in solutions. The principle of radiation-chemical reduction of metal ions in aqueous solutions. Formation of metal sols. Study of the effect of pH on the magnitude of the plasmon peak.

term paper, added 12/11/2008


Influence of excess surface energy on the adhesion interaction of nanoparticles. Surfactant adsorption monolayer. Local concentration and formation of an island nanoscale structure. Influence of surfactants on surface forces and stability of lyophobic nanosystems.

test, added 02/17/2011


Characterization of silver nanoparticles. Their influence on the viability of human lymphocytes according to the results of the MTT test. Cell cultures used for in vitro toxicity studies. Study of the cytotoxicity of nanomaterials in mammalian cell cultures.

term paper, added 05/04/2014


Patterns of nanophase formation in solution. Method for the preparation of catalysts. Method for preparing palladium nanoparticles stabilized in ultrathin layers of chitosan deposited on alumina. Physical and chemical properties of nanocomposites.

thesis, added 12/04/2014


Magnetic nanoparticles of metals. Physico-chemical properties of micellar solutions. Conductometric study, synthesis of cobalt nanoparticles in direct micelles. Obtaining a Langmuir-Blodgett film, scanning electron and atomic force microscopy.