• Domestic science and medicine in the 19th - early 20th centuries Chemistry of the 19th century in medicine
• What are peptides? Types and types of peptides. All about peptides and anti-aging cosmetics with peptides Additional peptides are not formed
• Toxic effect on humans of hazardous chemicals
• Radioautography Method of autoradiography in cytology
• Identification of bacteria by antigenic structure
• Organic matter in wastewater What are organic compounds in water
• Hydrogen index (pH factor)
• What is the pH of water and why is it important to know it?
• Redox potential Redox systems
• Reversible redox system Reversible redox systems

For the concept of nanotechnology, perhaps, there is no exhaustive definition, but by analogy with the existing microtechnologies, it follows that nanotechnologies are technologies that operate on values ​​of the order of a nanometer. Therefore, the transition from "micro" to "nano" is a qualitative transition from the manipulation of matter to the manipulation of individual atoms. When it comes to the development of nanotechnologies, there are three areas in mind: the manufacture of electronic circuits (including volumetric ones) with active elements comparable in size to those of molecules and atoms; development and manufacture of nanomachines; manipulation of individual atoms and molecules and the assembly of macroobjects from them. Developments in these areas have been going on for a long time. In 1981, a tunneling microscope was created that allows the transfer of individual atoms. The tunnel effect is a quantum phenomenon of penetration of a microparticle from one classically accessible area of ​​motion to another, separated from the first by a potential barrier. The basis of the invented microscope is a very sharp needle sliding over the surface under study with a gap of less than one nanometer. In this case, electrons from the tip of the needle tunnel through this gap into the substrate.

However, in addition to studying the surface, the creation of a new type of microscope opened up a fundamentally new way for the formation of nanometer-sized elements. Unique results were obtained on the movement of atoms, their removal and deposition at a given point, as well as local stimulation of chemical processes. Since then, the technology has been greatly improved. Today, these achievements are used in everyday life: the production of any laser discs, and even more so, the production of DVDs is impossible without the use of nanotechnical control methods.

Nanochemistry is the synthesis of nanodispersed substances and materials, the regulation of chemical transformations of nanometer-sized bodies, the prevention of chemical degradation of nanostructures, methods of treating diseases using nanocrystals.

The following are the areas 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 with the formation of fractal, wireframe, tubular and columnar nanostructures.
• - 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 nanocatalysts for the chemical and petrochemical industries; study of the mechanism of catalytic reactions on nanocrystals.
• - study of nanocrystallization mechanisms in porous media in acoustic fields; synthesis of nanostructures in biological tissues; development of methods for treating diseases by forming nanostructures in tissues with pathology.
• - 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 expected result will be a functional range of machines that provides:
• - methodology for studying intramolecular rearrangements under local effects on molecules.
• - new catalysts for the chemical industry and laboratory practice;
• - oxide-rare-earth and vanadium nanocatalysts with a wide spectrum of action.
• - methodology for preventing chemical degradation of technical nanostructures;
• - Methods for predicting chemical degradation.
• - nanodrugs for therapy and surgery, preparations based on hydroxyapatite for dentistry;
• - a method for the treatment of oncological diseases by carrying out intratumoral nanocrystallization and applying an acoustic field.
• - methods for creating nanostructures by directed aggregation of nanocrystals;
• - methods for regulating the spatial organization of nanostructures.
• - new chemical sensors with ultrafine active phase; methods for increasing the sensitivity of sensors by chemical modification.

When did "nano-science" appear as a field of theoretical knowledge? Are there organic nanostructures - not synthesized, but created by nature? How can one influence a living cell with the help of mathematical models describing nanostructures? What are the "magic numbers" of nanostructures? Chemists Igor Melikhov and Viktor Bozhevolnov are talking about where the border between the physical world and the nanoworld lies.

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 instrument 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.

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Distance educational courses are a modern form of effective additional education and advanced training in the field of training specialists for the development of promising technologies for obtaining functional materials and nanomaterials. This is one of the most promising forms of modern education developing all over the world. This form of obtaining knowledge in such an interdisciplinary field as nanomaterials and nanotechnologies is especially relevant. The advantages of distance courses are their availability, flexibility in building educational routes, improving the efficiency and efficiency of the process of interaction with students, cost-effectiveness compared to full-time, which, nevertheless, can be harmoniously combined with distance learning. In the field of fundamental principles of nanochemistry and nanomaterials, video materials of the Scientific and Educational Center of Moscow State University on Nanotechnologies have been prepared:

• . Basic concepts and definitions of sciences about nanosystems and nanotechnologies. The history of the emergence of nanotechnology and the sciences of nanosystems. Interdisciplinarity and multidisciplinarity. Examples of nanoobjects and nanosystems, their features and technological applications. Objects and methods of nanotechnologies. Principles and prospects for the development of nanotechnologies.
• . Basic principles for the formation of nanosystems. Physical and chemical methods. Processes for obtaining nano-objects "from top to bottom". Classical, "soft", microsphere, ion-beam (FIB), AFM - lithography and nanoindentation. Mechanoactivation and mechanosynthesis of nanoobjects. Processes for obtaining nano-objects "bottom-up". Nucleation processes in gaseous and condensed media. Heterogeneous nucleation, epitaxy and heteroepitaxy. Spinodal collapse. Synthesis of nanoobjects in amorphous (glassy) matrices. Chemical homogenization methods (coprecipitation, sol-gel method, cryochemical technology, aerosol pyrolysis, solvothermal treatment, supercritical drying). Classification of nanoparticles and nanoobjects. Techniques for obtaining and stabilizing nanoparticles. Aggregation and disaggregation of nanoparticles. Synthesis of nanomaterials in one and two-dimensional nanoreactors.
• . Statistical physics of nanosystems. Features of phase transitions in small systems. Types of intra- and intermolecular interactions. hydrophobicity and hydrophilicity. Self-assembly and self-organization. Micellization. Self-assembled monolayers. Langmuir-Blodgett films. Supramolecular organization of molecules. Molecular recognition. Polymer macromolecules, methods for their preparation. Self-organization in polymer systems. Microphase separation of block copolymers. Dendrimers, polymer brushes. Layered self-assembly of polyelectrolytes. supramolecular polymers.
• . Substance, phase, material. Hierarchical structure of materials. Nanomaterials and their classification. Inorganic and organic functional nanomaterials. Hybrid (organo-inorganic and inorganic-organic) materials. Biomineralization and bioceramics. Nanostructured 1D, 2D and 3D materials. mesoporous materials. Molecular sieves. Nanocomposites and their synergistic properties. Structural nanomaterials.
• . Catalysis and nanotechnology. Basic principles and concepts in heterogeneous catalysis. Influence of preparation and activation conditions on the formation of the active surface of heterogeneous catalysts. Structure-sensitive and structure-insensitive reactions. Specificity of thermodynamic and kinetic properties of nanoparticles. Electrocatalysis. Catalysis on zeolites and molecular sieves. membrane catalysis.
• . Polymers for structural materials and for functional systems. "Smart" polymer systems capable of performing complex functions. Examples of "smart" systems (polymer fluids for oil production, smart windows, nanostructured membranes for fuel cells). Biopolymers as the most "smart" systems. biomimetic approach. Sequence design for optimizing the properties of "smart" polymers. Problems of molecular evolution of sequences in biopolymers.
• . The current state and problems of creating new materials for chemical current sources: solid oxide fuel cells (SOFC) and lithium batteries are considered. The key structural factors that affect the properties of various inorganic compounds, which determine the possibility of their use as electrode materials, are analyzed: complex perovskites in SOFCs and compounds of transition metals (complex oxides and phosphates) in lithium batteries. The main anode and cathode materials used in lithium batteries and recognized as promising are considered: their advantages and limitations, as well as the possibility of overcoming the limitations by a directed change in the atomic structure and microstructure of composite materials by nanostructuring in order to improve the characteristics of current sources.

Some issues are discussed in the following chapters of the books (Binom publishing house):

Illustrative materials on nanochemistry, self-assembly and nanostructured surfaces:

Scientific - popular "video books":

Selected Chapters of Nanochemistry and Functional Nanomaterials.

As stated above, due to the location of the nanoworld on the borders of classical physics and quantum mechanics, its objects can no longer be considered as absolutely identical and statistically indistinguishable. All of them are individual, and one nanoparticle differs from another in composition, structure, and many other parameters (for example, C 60 and C 70 fullerenes). It is impossible to ignore the presence of inhomogeneities and irregularities in the structure of an object and use average, integral characteristics to describe it, as is customary in classical physics. The peculiarity of nano-objects lies in the fact that their size is commensurate with the radius of action of the forces of interatomic interaction, i.e. with the distance at 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 science that studies the properties of various nanostructures, as well as the development of new ways to obtain, study and modify them, is called nanochemistry. It explores 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 in the range of 0.1-100 nm.

One of the priority tasks of this area of ​​knowledge is to establish a relationship between the size of a nanoparticle and its properties. In nanochemistry, the role of quantum size effects, causing a change in the properties of a substance depending on the size of the particles and the number of atoms or molecules in them. The role of size effects is so great that attempts are being made to create tables of dependence of the properties of clusters and nanoparticles on their size and geometry, similar to the Periodic Table. Quantum size effects determine such properties of a substance as heat capacity, electrical conductivity, some optical properties, and so on.

Changes in characteristics are associated with two main reasons: an increase in the surface fraction and a change in the electronic structure due to quantum effects. The properties of atoms located near the surface differ from the properties of atoms located in the bulk of the material; therefore, the particle surface can be considered as a special state of matter. The larger the proportion of atoms located on the surface, the stronger the effects associated with the surface (Fig. 9).

Rice. 9. Change in the ratio of "surface" atoms (1) and those in the bulk of the material (2) depending on the particle size.

Features of the electronic structure of nanoobjects are explained by the enhancement of quantum properties associated with a decrease in size. The unusual properties of nanostructures hinder their trivial technical use and at the same time open up completely unexpected technical prospects.

Significant differences in the properties of nanoparticles begin to appear at particle sizes below 100 nm. From an energy point of view, a decrease in particle size leads to an increase in the role of surface energy, which leads to a change in the physical and chemical properties of small objects.

Nanochemistry Research Objects are bodies with such a mass that their equivalent size (the diameter of a sphere, the volume of which is equal to the volume of the body) remains within the nanointerval (0.1 - 100 nm). Conventionally, nanochemistry can be divided into theoretical, experimental, and applied (Fig. 10).

Rice. 10. Structure of nanochemistry

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 develops in three directions. As part of first, which is quite consistent with the section of analytical chemistry, supersensitive physical and chemical methods are being developed and used that make it possible to judge the structure of molecules and clusters, including tens and hundreds of atoms. Second direction explores phenomena under local (local) electrical, magnetic or mechanical effects on nanobodies, implemented with the help of nanoprobes and special manipulators. In this case, the goal is to study the interaction of individual gas molecules with nanobodies and nanobodies with each other, to reveal the possibility of internal rearrangements without destruction of molecules and clusters and with their decay. This area is also interested in the possibility of "atomic assembly" of a nanobody of the desired appearance when atoms move over the surface of the substrate (the base material, the surface of which is subjected to various types of processing, resulting in the formation of layers with new properties or the growth of a film of another material). As part of third directions determine the macrokinetic characteristics of nanobodies collectives and their distribution functions according to state parameters.

Applied Nanochemistry includes: the 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); study of biological nanosystems and 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 purifying natural waters or air from nanoparticles ( ecological nanochemistry).

Speaking about the sizes of the objects of study, it should be taken into account that 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 is assumed to be 100 nm.

In a given interval, any property specifically depends on its mass and volume. Therefore, the object of nanochemistry can be considered objects in which interactions each atom with all other atoms are significant.

Nanochemistry objects can be classified according to different features. For example, by phase state(Table 1).

Geometrically(dimensions) nano-objects can be classified in different ways. Some researchers propose to characterize the dimensionality of an object by the number of dimensions in which the object has macroscopic dimensions. Others take as a basis the number of nanoscopic measurements.

In table. Table 2 lists the main objects of nanochemical research (nanoparticles and their corresponding nanosystems).

The classification of nanoobjects according to their dimension is important not only from a formal point of view. Geometry significantly affects their physicochemical properties. Let us consider some of the most priority objects of nanochemistry research.

Nanoparticles from atoms of inert gases. They 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 spheres is used (Fig. 11). The binding energy, that is, the energy spent on detaching an individual atom from a nanoparticle, is very small, so the particles exist at temperatures not higher than 10–100 K.

Rice. 11. Nanoparticles of 16 argon atoms.

Metal nanoparticles. In metal clusters of several atoms, both covalent and metallic types of bonds can be realized (Fig. 12). Metal nanoparticles are highly reactive and are often used as catalysts. Metal nanoparticles can take the correct shape - octahedron, icosahedron, tetradecahedron.

Rice. 12. Nanoparticles consisting of atoms of platinum (white spheres) and copper (gray)

Fullerenes. They are particles hollow inside, formed by polyhedrons of carbon atoms bound by a covalent bond. A special place among fullerenes is occupied by a particle of 60 carbon atoms - C 60 , resembling a microscopic soccer ball (Fig. 13).

Rice. 13. Fullerene C 60 molecule

Fullerenes are widely used: in the creation of new lubricants and anti-friction coatings, new types of fuel, ultra-hard diamond-like compounds, sensors and paints.

carbon nanotubes. These are hollow molecular objects consisting of approximately 1,000,000 carbon atoms and representing single-layer or multilayer tubes with a diameter of 1 to 30 nm and a length of several tens of microns. On the nanotube surface, carbon atoms are located at the vertices of regular hexagons (Fig. 14).

Rice. 14. Carbon nanotubes.

Nanotubes have a number of unique properties, due to which they are widely used mainly in the creation of new materials, electronics, and scanning microscopy. The unique properties of nanotubes: high specific surface area, electrical conductivity, and strength make it possible to create effective catalyst carriers for various processes on their basis. For example, nanotubes are used to make new energy sources - fuel cells that can last many times longer than simple batteries of a similar size. For example, nanotubes with palladium nanoparticles can compactly store hydrogen thousands of times their volume. Further development of fuel cell technology will allow them to store hundreds and thousands of times more energy than modern batteries.

Ionic clusters. They represent a classic picture characteristic of an ionic bond in the crystal lattice of sodium chloride (Fig. 15). If an ionic nanoparticle is large enough, then its structure is close to that of a bulk crystal. Ionic compounds are used in the creation of high-resolution photographic films, molecular photodetectors, and in various fields of microelectronics and electro-optics.

Rice. 15. NaCl cluster.

fractal clusters. These are objects with a branched structure (Fig. 16): soot, colloids, various aerosols and aerogels. A fractal is 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.

Fig.16. fractal cluster

Molecular clusters(supramolecular systems). Clusters of molecules. Most clusters are molecular. Their number and variety is enormous. In particular, many biological macromolecules belong to molecular clusters (Figs. 17 and 18).

Rice. 17. Molecular cluster of ferredoxin protein.

Rice. 18. High spin molecular clusters

Course Curriculum

newspaper number	Educational material
17	Lecture number 1. What is hidden behind the prefix "nano"? Nanoscience and nanochemistry. size effect. Classification of nanoobjects.(Eremin V.V., Drozdov A.A.)
18	Lecture number 2. Methods for the synthesis and study of nanoparticles. Classification of methods for the synthesis of nanoparticles. Chemical methods of synthesis ("bottom up"). Methods of visualization and research of nanoparticles.(Eremin V.V., Drozdov A.A.)
19	Lecture number 3. Nanotechnology. Fundamental and applied research: connection between nanoscience and nanotechnology. Mechanical nanodevices. Magnetic nanomaterials. Nanotechnologies in medicine. Development of nanotechnologies.(Eremin V.V., Drozdov A.A.) Test No. 1(Deadline - November 25, 2009)
20	Lecture number 4. Carbon nanomaterials. Allotropic forms of carbon are "nano" and not "nano". Nanodiamonds. Fullerenes and their derivatives. Nanotubes, their classification and properties. General properties of carbon nanoforms.(Eremin V.V.)
21	Lecture number 5. Nanomaterials for energy. Traditional and alternative energy sources. Nanomaterials in fuel cells. Nanomaterials for hydrogen storage.(Eremin V.V.)
22	Lecture number 6. Nanocatalysis. General properties of catalysts. Classification of catalytic reactions. Principles of structural and energy correspondence. Catalysis on nanoparticles and zeolites.(Eremin V.V.) Test No. 2(deadline - until December 30, 2009)
23	Lecture number 7. Nanochemistry in Olympiad problems. 1. Simple tasks. Methods for obtaining nanoparticles. Structure of nanoparticles. Properties of nanoparticles.(Eremin V.V.)
24	Lecture number 8. Nanochemistry in Olympiad problems. 2. Complex combined problems. (Eremin V.V.)
Final work. A brief report on the final work, accompanied by a certificate from the educational institution, must be sent to the Pedagogical University no later than February 28, 2010. (More details about the final work will be published after Lecture No. 8.)

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 the chemical laboratory, but also in the 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)

Number of atoms in a nanocluster	Diameter, nm	Fraction of atoms on the surface, %	Number of inner layers	Cluster type
1	0,24 – 0,34	100	0	–
2	0,45 – 0,60	100	0	–
3 – 12	0,55 – 0,80	100	0	Small
13 – 100	0,8 – 2,0	92 – 63	1 – 3	Average
10 2 – 10 4	2 – 10	63 – 15	4 – 18	Big
10 4 – 10 5	10 – 30	15 – 2	> 18	Giant
> 10 6	> 30	< 2	a lot of	colloidal particle

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.

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