RU2389536C1 - Active molecular sieve - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to production of molecular sieves. Proposed active molecular sieve comprises multiple pores with their extension in at least one measure, making less than 100 nm. Each said pore comprises at least one electrode connected with shift strain measuring appliance. Said electrode comprises at least one nano tube or nano wire. Electric field of preset magnitude and spatial configuration is maintained in molecular sieve pores to amplify differences in efficient linear sizes of molecules and their Van Der Waals interaction with pores walls and add to variety of pore permeability for molecules of different types.

EFFECT: efficient tool in treatment of fluid and gaseous media, membrane catalytic reactor.

9 cl, 10 dwg

Description

The invention relates to molecular sieves intended for the selective separation of multicomponent media, as well as to perform the functions of nanomembrane reactors, providing enhanced opportunities for chemical reactions and separation of their products.

Molecular sieves have a wide range of end applications. In recent years, in connection with the growth of environmental and energy problems, a complex of technologies has appeared - “combustion of fuel with zero emissions”, where the most promising is the combustion of oxygen in the atmosphere (complete combustion). There are already several projects of thermal power plants focused on burning coal in oxygen diluted with CO ₂ (www.inno.ru/projects/23440/project23590.shtml). With increasing oxygen concentration, the combustion process intensifies, so even low-quality fuels burn well in pure oxygen. This allows not only the complete combustion of traditional fuels, but also opens up the possibility of using various new types of biofuels and garbage without significant preparatory transformations. Obtained by the most common cryogenic method, oxygen (freezing air below -150 ° C), according to some estimates, will increase the cost of generating electricity by 30%. In addition, this method involves a separate oxygen plant, which may be appropriate for large-scale consumers, but unacceptable for small ones. A solution is sought in the development of membrane air separation technologies. According to estimates, the development of new complex technologies for resource conservation becomes economically feasible already at a cost of a barrel of oil from $ 40. Thus, we can conclude that these technologies are in great demand both at the current moment and in the foreseeable future.

Currently, only 4-5% of the global oxygen demand is met using molecular sieves (RU 2297276, 04.20.2007). A small fraction of the distribution of molecular sieves in the problem of air separation is due to the following factors. The basis of existing systems of this type are sorbents based on zeolites or related materials. Since the principle of their operation is based on the sorption of nitrogen from the air stream, the possible productivity achievable within such systems is significantly limited. The adsorption capacity of commercial zeolites ranges from 3 cm ³ / g (US 5266102, 11/30/1993, and 6087289, 07/11/2000) to 15-20 cm ³ / g (RU 2297276 and IN 181823, 10.30.1998). Thus, to ensure the production of oxygen in industrial volumes (several tens of tons per day and above), either thousands of tons of sorbent or regular implementation of the regeneration of spent sorbent are required. As a result, under the conditions of industrial production volumes, this method loses in efficiency to cryogenic air fractionation. In addition, such disadvantages of air separation sorbents that are part of the state of the art, such as moisture sensitivity, the need for a sorbent activation procedure involving many hours of slow heating to avoid hydroxylation, limited selectivity with respect to oxygen (2-7 under normal conditions (US 4481018, 11/06/1984, 5114440, 05/19/1992, 5174979, 12/29/1992, IN 181823, RU 2297276)), a limited degree of purification of the resulting oxygen, which is usually 95-96%, etc.

In addition to energy, molecular sieves are widely used in the chemical industry (selective gas separation, selective evaporation of liquids; in particular, environmentally friendly and resource-saving processes for producing valuable oil products from natural and associated gases, selective biogas separation in the processing of organic waste, etc.) , in the food industry (in particular, processing of secondary food raw materials with the release of valuable components), in medicine (membrane dispensers and drug prolongators Paratov apparatus for plasmapheresis and blood oxygenation, artificial pancreas, artificial kidney etc.). Such applications as energy-saving desalination, wastewater treatment with the release of valuable components in industry and utilities, oxygen decontamination of wastewater, air conditioning, storage in an atmosphere of nitrogen to prevent spoilage and fire, etc. can also be noted.

Molecular sieves are also of interest from the point of view of the implementation of nanomembrane reactors. These systems form an extremely promising approach to solving the problems of large-capacity industrial chemistry and provide both efficient synthesis, separation and purification of the resulting chemical compounds (in particular, aromatic hydrocarbons) with low energy consumption. Each pore of a nanomembrane structure plays the role of a reactor in which a single cycle of chemical transformations and separation of reaction products takes place.

A common drawback of molecular sieves that are part of the state of the art is that their selectivity is based solely on steric effects, such as differences in the size and shape of the molecules being separated (for this reason, existing molecular sieves can be described as passive). In order to ensure high selectivity to target type molecules, it is necessary to ensure high accuracy of the geometric parameters and elemental composition of pores to the kinetic diameter and parameters of the electron shell of the target molecules. Such powerful and universal methods of pore engineering for the parameters of target molecules are currently absent. Moreover, for a number of molecules, the factor of their spatial orientation near the entrance to the pore is essential, which is not amenable to control in the case of passive molecular sieves. This narrows the range of media suitable for separation and reduces the overall efficiency of such systems. It should be noted that in the case of molecular sieves constituting the current state of the art, which are made, as a rule, of dielectric materials, pore cleaning is also one of the significant problems. To solve it, special mechanical (washing), thermal (heating the sieves by an external source) and chemical (chemically active washing) methods are used, which makes the operation of systems based on passive molecular sieves more expensive and complicated.

The problem to which the present invention is directed, is to create a molecular sieve of a new, active type, which eliminates the above disadvantages of molecular sieves.

The technical result achieved by the implementation of the invention is to provide a molecular sieve of a new, active type, characterized by the following functionality:

1) an electric field is maintained in the pores of the molecular sieve with a given value, spatial configuration, and time dependence. Maintaining a given electric field provides redistribution of the electron density of molecules entering the pores. Since the parameters of this redistribution depend on the type of molecule, the differences in the effective linear sizes of the molecules and their Van der Waals interaction with the pore walls can thus be enhanced. This contributes to the difference in pore permeability for molecules of various types. If an alternating electric field is created in the pores, kinetic effects associated with the difference in the characteristic time of transport through the pore for molecules of various types can be used. These factors allow you to control the selectivity of the molecular sieve;

2) polarized molecules of the shared medium experience orientation along the field lines of the field. This provides control of the spatial orientation of the molecules inside the pore, as well as in the area near the entrance of the pore, which is essential for extended molecules and complex molecules. Polarized molecules also experience translational motion in the direction of the field gradient, which allows one to organize directed transport of molecules inside the pore, as well as in the area near the entrance of the pore;

3) in contrast to the case of passive molecular sieves, the parameters of which are fixed and determined by the capabilities of the used formation technology, the proposed active molecular sieves allow you to continuously adjust their functional parameters to target molecules by changing the parameters of the electric field in the pores. Note that this functionality is significant, because in many practically important applications the sizes of the molecules being separated are only slightly different from each other (for example, the kinetic diameter of the oxygen molecule is 0.346 nm, and the kinetic diameter of the molecules of the main component of air - nitrogen, is 0.364 nm);

4) in the case of one aspect of the invention, it is possible to change in situ the effective geometry of the pores as a result of the Coulomb interaction of the components of the pore. This allows you to change the steric interaction of the pore with the molecules of the shared medium, and use the effects of resonant and wave mechanical motion to transport molecules;

5) in the case of one aspect of the invention, a self-cleaning pore mode is provided, in particular, by controlled local heating of each pore by an electric current passing through certain pore components. This allows you to control the desorption of molecules and particles through thermal and current activation of the desorption process. In addition, within the framework of local heating of the pore, it is possible to achieve a rapid expansion of the medium filling the pore (in particular, accompanied by a liquid-gas phase transition) with mechanical expulsion of the pore contents. The intensity of this process can be controlled within wide limits;

6) the creation of a controlled electric field in the pores makes it possible to exert an additional influence both on the transport and on the reactivity of chemical reactions agents located in the pores, and thereby provides access to chains of chemical transformations that are not realized under ordinary conditions. This is relevant for the application of molecular sieves as a nanomembrane catalytic reactor.

The specified technical result is achieved in a molecular sieve, including many pores, the length of which in at least one dimension is less than 100 nm, and each of these pores includes at least 1 electrode, electrically connected to bias voltage control means, to the composition of the specified electrode at least one nanotube or nanowire is included.

The set of pores is divided into one or more subsets, and the same type of electrodes that are part of the pores of a common subset are electrically connected to each other.

At least one of the electrodes of each specified pore is made of a material that provides elastic deformation of the electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or a combination of pore electrodes.

At least one of the electrodes of each specified pore is made of a material that provides plastic or elasto-plastic deformation of this electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or a combination of pore electrodes.

The specified electrode is a carbon nanotube.

Each pore contains two electrodes, the first electrode is part of a conductive layer of amorphous carbon or a chemically inert metal in which the sieve pores are made, and the second electrode is a carbon nanotube, the first and second electrodes being spatially separated and not touching each other.

Said second electrode is a multilayer carbon nanotube with at least one outer outer layer removed, where said removal is accomplished by local anodic oxidation, and a chemically inert metal is selected as the material of said first electrode.

The surface of said carbon nanotube and the surface of said first electrode form a gap whose width is less than 0.4 nm.

The gap between the surface of said carbon nanotube and the surface of said first electrode is formed by local anodic oxidation of a portion of the material of the first electrode.

The invention is illustrated by drawings, where figure 1 shows a schematic representation of the structure corresponding to the intermediate step of forming one of the options for implementing an active molecular sieve; figure 2 is a schematic representation corresponding to an intermediate step of the process of forming a variant of the pores of the active molecular sieve, where this step precedes the formation of the working volume of the pore; figure 3 is a schematic diagram corresponding to an intermediate step of the process of forming a variant of the pores of the active molecular sieve, where the working volume of the pore is formed; figure 4 is a schematic representation corresponding to an intermediate step of the process of forming a variant of the pores of the active molecular sieve, where the pore electrodes are transferred to the state of mechanical contact; 5 is a schematic diagram corresponding to an intermediate step in the process of forming a variant of the pore of an active molecular sieve, where the output electrode is coated with an insulating or conductive layer; Fig.6 is a schematic diagram corresponding to an intermediate step of the pore formation process of an active molecular sieve for a variant corresponding to the presence of an additional electrode in the pore; Fig. 7 shows a schematic illustration of one embodiment of an active molecular sieve; on Fig shows a schematic representation of a variant of the through pores of the active molecular sieve; figure 9 shows a schematic illustration of a variant of the through pores of the active molecular sieve, where the pore electrodes are transferred into a state of mechanical contact; figure 10 shows the distribution of the electric field strength (left) and potential (right) in the pore when applying a positive potential of 0.01 V to the nanotube (the model was obtained in the ElCut medium and demonstrates the effect of pore closure by the Coulomb umbrella, which is formed due to the concentration of the electric nanotube fields).

The molecular sieve includes many pores, the length of which in at least one dimension is less than 100 nm, and each of these pores includes at least 1 electrode 2, 4, electrically connected to bias voltage control means, the specified electrode includes at least one nanotube or nanowire (figure 1-9).

The set of pores is divided into one or more subsets, with the same type of electrodes 2, 4, which are part of the pores of a common subset, are electrically connected to each other.

At least one of the electrodes 2, 4 of each specified pore is made of a material that provides elastic deformation of this electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or a combination of pore electrodes.

At least one of the electrodes 2, 4 of each indicated pore is made of a material that provides plastic or elasto-plastic deformation of this electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or a combination of pore electrodes.

The specified electrode 2 is a carbon nanotube.

The composition of each indicated pore includes two electrodes 2, 4, the first electrode 4 is part of a conductive layer of amorphous carbon or a chemically inert metal in which the sieve pores are made, and the second electrode 2 is a carbon nanotube, the first 4 and second 2 electrodes being spatially separated and do not touch each other.

Said second electrode 2 is a multilayer carbon nanotube with at least one outer outer layer removed, where said removal is accomplished by local anodic oxidation, and a chemically inert metal is selected as the material of said first electrode 4.

The surface of said carbon nanotube 2 and the surface of said first electrode 4 form a gap whose width is less than 0.4 nm.

The gap between the surface of said carbon nanotube 2 and the surface of said first electrode 4 is formed by local anodic oxidation of a portion of the material of the first electrode 4.

Detailed description

As already noted in the section "background to the invention", the currently existing systems of the type of "molecular sieve" are passive structures made in the form of a porous bulk or thin-film material, and dielectrics such as silicon oxide are usually used as the material titanium oxide, aluminosilicates, etc. (patents CN 1341551, 03/27/2002, CN 1341550, 03/27/2002, RU 2278818, 09/10/2004, etc.). The principle of operation of such porous structures is based on steric effects associated with a difference in the size and shape of the molecules being separated. Thus, there is a certain analogy with the principle of operation of ordinary macroscopic sieves. This circumstance implies a number of significant limitations that were considered in the previous section.

The present invention proposes to take a cardinal step in the development of molecular sieve systems and to replace each sieve pore with an electric or electromechanical device that has certain functionality when manipulating a substance at the nanoscale. In one aspect of the invention, this functionality is reduced to creating a given electric field in the pore using stationary electrodes located therein. In another aspect of the invention, a portion of the electrodes is capable of performing mechanical movement and thus performing mechanical work. The Coulomb force acting on the side of the stationary pore electrodes acts as a drive for the moving electrodes. In addition, the functionality of electromechanical structures that play the role of pores allows one to reach the realization of the regime of self-cleaning of pores (regeneration of sorption ability), as well as the manipulation of molecules in the region near the entrance to the pore. Consider the design and operation of the proposed active molecular sieves in more detail.

The number of electrodes and their location in the pore can be different. In particular, the electrodes can be located on opposite sides of the side walls of the pore or have a nested structure (for example, coaxial). Note that these electrodes, in addition to the function of creating an electric field, can also play a structural function, that is, form the working surface of the pore. The composition of the electrodes can be used carbon nanotubes or other extended nanoobjects obtained by the method of self-organization (in this description, the generic term "nanowire" is used to denote them).

The whole set of pores of a molecular sieve can be divided into separate subsets, the electrodes of the same type being electrically connected to each other. Thus, pores belonging to a common subset can work only in a single mode, since the bias voltage of the electrodes included in these pores will coincide at each moment in time. Pores included in different subsets can work in independent modes.

The principle of operation of the described pores is based on the fundamental effect of the redistribution of the electron density of molecular orbitals in an external electric field. This change in the electron density distribution is individual for each type of molecule. In a first approximation, the tendency of a molecule to redistribute its electron density in an external field can be characterized by the magnitude of the polarizability of the molecule (in the general case, by the polarizability tensor). The magnitude of the polarizability varies significantly for molecules of various types. Differences in the degree of polarization of the molecules that have fallen into the inner region of the pore will determine the differences in the Van der Waals interaction of these molecules with the walls of the pore. This difference is further enhanced if the pore wall in contact with the molecule is formed by one of the electrodes and thus has a substantially uncompensated surface charge. The differences in the van der Waals interaction, in turn, directly determine the differences in the mobility of molecules in the pore. This ensures the implementation of the Coulomb mechanism of selectivity, that is, the mechanism of selective pore permeability for molecules of certain types.

In contrast to the steric mechanism of selectivity associated with the geometry of the pore, which is fixed, the Coulomb mechanism allows you to continuously change the transport parameters of the pore and its selectivity to molecules of certain types. This is an important advantage, since in the general case it is not known how to ensure the geometry and elemental composition of the passive pore with such accuracy that effective use of the characteristic steric features of the target molecules is ensured. So, for example, in one of the most developed tasks for systems of the "molecular sieve" type - the problem of air separation by the method of selective nitrogen sorption, the best achieved selectivity parameter under normal conditions is 5. That is, for every five sorbed nitrogen molecules, one oxygen molecule is sorbed ( RU 2297276). In the case of the described Coulomb mechanism of selectivity, the parameters of the electric field in the pore can vary continuously, which ensures high accuracy of tuning the effective pore parameters to the characteristics of the target molecules.

The described Coulomb selectivity mechanism may also have the functionality of a steric mechanism, since the polarization of molecules provides a change in their linear dimensions. For extended molecules, which, due to their length, have a significant polarizability, this effect will be especially relevant. Considering that the deformation of molecules can reach 30% or more without breaking the interatomic bonds, one can expect a significant role of this effect for simple molecules, for example, molecules of the main components of air. The case when the Coulomb force causes deformation not only of manipulated molecules, but also of structural elements of the pore itself, will be considered below. The possibility of continuous changes in the parameters of the electric field in the pores is also essential for the described steric aspects of the Coulomb selectivity mechanism (adjusting the sizes of pores and molecules for each other). Note that the current level of technology includes a molecular sieve, which also allows for continuous change in the parameters of their pores (US patent No. 2008184883). The principle of operation of the molecular sieve proposed in the aforementioned patent is based on a change in the effective pore cross section with a change in temperature. This is achieved by using organic molecules in the sieve material, characterized by a large temperature coefficient of expansion.

While the magnitude of the electric field strength in the pore determines the degree of polarization of the molecule, the spatial configuration of the field determines the magnitude and direction of the uncompensated force acting on the side of the field on the molecule. As is known, an electric dipole placed in an inhomogeneous electric field is subjected to the action of a force directed along the field gradient. Since nanoscale electrodes are capable of creating a highly inhomogeneous electric field (the so-called emitter effect), this factor can play a significant role in the transport of the molecule, not only inside the pore, but also in the region located at the entrance to the pore. Depending on the geometry and location of the pore electrodes, as well as the ratio of the bias voltage supplied to them, the electric field lines emerging from the pore can have a different spatial configuration. In the particular case corresponding to the general electrical neutrality of the pore, the outgoing lines of force will quickly cancel each other away from the pore, however, in a certain effective region near the pore, a highly inhomogeneous electric field will remain. Molecules in this region will experience polarization and orientation along the lines of force, as well as translational displacement in the direction of the field gradient. Thus, directed transport of target molecules towards the pore can be organized, as well as their preliminary orientation. The latter is especially relevant for extended molecules and molecules of complex shape, since the result of interaction with the input pore aperture can completely depend on their spatial orientation.

If the pore contains at least two electrodes, the spatial configuration of the field inside the pore can be controlled. By changing the ratio of electric potentials supplied to these electrodes, it is possible to provide a different picture of the lines of force of the resulting electric field, and both the shape and direction of the lines of force can change. By changing the ratio of the indicated electric potentials in time, it is possible to organize the movement of electric field lines, in particular their rotation. The indicated regime of an alternating electric field expands the possibilities of the Coulomb mechanism of selectivity. This is possible due to the use of kinetic effects associated with the difference in the temporal characteristics of the transport process in the pore of various types of molecules (here it is appropriate to draw an analogy with the principle of operation of the so-called time-of-flight mass spectrometer (see, for example, Ageev V.N., Kutsenko E.N. . // ZhTF. 1969. T. 39. S.1275), which in this case was implemented on a nanoscale). Theoretically, in the case of a sufficiently high frequency of an alternating field, differences in the characteristic time of their polarization or charge exchange can also contribute to the difference in the mobility of molecules.

The change in the electric field can be provided not only in time, but also along the pore. For this, it is necessary to use additional electrodes. The presence along the pore of sections with different magnitude and direction of the electric field allows for multi-stage separation of molecules, which implies sequential separation of certain types of molecules in the pore sections.

In addition to stationary electrodes, the pore may also contain electrodes capable of performing mechanical movement. To bring the electrodes into motion, it is necessary to apply a force in the form of a Coulomb force acting on the side of other pore electrodes. In the case of the implementation of the moving pore electrodes in the form of elastic elements, they return to their original state as the deflecting forces decrease due to the action of the elastic forces. In the case of the implementation of movable electrodes in the form of plastic or elasto-plastic elements, in order to return to the initial state, it is necessary to apply the Coulomb force of the opposite direction to the electrodes.

The technical result of the implementation of the described pores with moving electrodes is as follows. Changing the geometry of the moving electrodes allows in situ to change the geometry and effective cross section of the pore and thereby change the steric interaction of this pore with the molecules of the shared medium. In addition, in this way, an additional technical result can also be achieved. In the case when the movable electrodes are elastic elements, they can perform mechanical vibrations at natural frequencies. Since these electrodes are made on a nanoscale, the upper limit of the frequency of their oscillations can reach units of THz (Tsu-Wei Chou, Zhifeng Ren, Rod Ruoff, Hai Wang. NSF Nanoscale Science and Engineering Grantees Conference. 2003) and more. This frequency range can intersect with the range of natural frequencies of vibrations of the mechanical system of the target molecules - the pore walls. In this case, resonance effects of mass transfer will arise that can significantly affect the transport of molecules in the pore (in the extreme case, turn pore permeability on or off for certain molecules). This mechanism based on vibrations can be generalized for the case of a coordinated propagation of these vibrations in space, which makes it possible to organize wave processes of mass transfer along the pore.

By organizing a certain movement of the electric field lines or a certain movement of the pore electrodes, it is possible to ensure the reverse movement of molecules or particles that have fallen into the pore, that is, to ensure the regeneration of the sorption ability of the pores (self-cleaning of the pores). However, the effect of thermal and current activation of desorption of molecules or particles can also be used to clean pores. By passing a high-density electric current through certain pore electrodes, local heating of the pore to a temperature above the threshold temperature of adsorption of the target molecules or particles is ensured, which leads to the desorption of the latter. In addition to thermal activation of desorption, current activation can also take place, associated with the transfer of momentum by drifting charge carriers to adsorbed molecules, followed by desorption of the latter. In addition, within the framework of local pore heating, it is possible to achieve a rapid expansion of the medium filling the pore (in particular, accompanied by a liquid-gas phase transition), with mechanical expulsion of the pore contents (in a sense, it is an analogue of the process of sneezing in humans). The intensity of this process can be controlled within wide limits. To ensure the effective release of Joule heat in the pore, a detachable connection of movable electrodes can be used, in the contact patch of which the required level of energy dissipation is achieved by charge carriers.

The minimum number of electrodes in each pore is one electrode. In this case, only the sign and magnitude of the electric field strength in the pores can vary, while keeping the pattern of the lines of force constant. Note that due to the Coulomb repulsion of the parts of one electrode from each other, a mechanism for changing the effective pore cross section can be realized. An example is the increase in the diameter of the holes made in a conductive material when a sufficient electric potential is applied to this material. In this case, the role of the electrodes is played by the pore walls themselves. Each pore, therefore, contains one electrode, and the electrodes of all pores are electrically connected to each other. From a technological point of view, this is the easiest way to implement an active molecular sieve.

As you know, in the pores of a molecular sieve not only can the separation of molecules by types occur, but conditions can also be provided for chemical reactions to occur. In this case, the molecular sieve acts as a so-called membrane reactor. Nanomembrane reactors provide both efficient synthesis and separation of the resulting chemical compounds at low energy consumption. Each pore of the nanomembrane structure plays the role of a microreactor, in which a single cycle of chemical transformations and separation of reaction products takes place. This approach to solving the problems of large-capacity industrial chemistry seems extremely promising.

The creation of a controlled electric field in the pores makes it possible to exert an additional influence both on transport and on the reactivity of chemical reaction agents and thereby provides access to chains of chemical transformations that are not feasible under ordinary conditions. New opportunities that active nanomembranes provide (in this context, active nanoreactors) relative to traditional bulk and membrane reactors can be formulated as follows:

1) new mechanisms for the transport of reagents, which allow controlled activation of the kinetics of chemical processes. Input and output of reagents can be carried out:

a) diffusion;

b) directional drift transport due to the movement of polarized molecules in an inhomogeneous field induced by nanoscale pore electrodes can be used to introduce reagents;

c) stimulation of the withdrawal of matter from the pores of the nanoreactor can be achieved by rapidly increasing the pressure in them (heating nanoscale electrodes by passing electric current through them) or by mechanical movement of nanoscale electrodes (for example, cyclic bending of the electrode, including resonance, resulting from an alternating Coulomb interaction with another pore electrode).

2) An electric field is provided in active nanoreactors, the intensity of which can reach extremely large values (comparable to intra atomic ones). The electron shells of reagent molecules in such fields undergo severe deformation, which directly affects their reactivity.

3) The electric field lines induced by a nanoscale electrode may have a beam configuration. Polarized reagent molecules will tend to form compound bridges along the lines of force (see the results of applicants' studies of the effect of the formation of molecular bridges between the tunnel probe and the substrate: Reports of the Academy of Sciences, 2007, vol. 412, No. 6, pp. 1-4), vol. e. mutual orientation and rapprochement of molecules is ensured (in a certain sense, consistent with the concept of mechanosynthesis). Thus, in particular, the probability of the occurrence of the target reaction can be increased and the course of competing reactions is suppressed. The range of target reactions carried out under the indicated conditions is also expanding.

4) In an active nanoreactor, it is easy to achieve ultrahigh pressures both by the Coulomb forces (the outer layers of polarized molecules drifting into the nanopore press on the inner ones) and mechanical (through the movement of nanoscale electrodes).

5) The electrodes of each pore of the active nanoreactor can be controlled to heat to a high temperature. A specific system can be obtained - the cold surface of an active nanomembrane containing individual hot spots, and the sizes of these points can be up to one nanometer. As an example, we note that extended molecules located on such a surface will be activated only in their individual areas.

6) A direct electrical interface is provided to the reagent molecules placed in the pores of the active nanoreactor, and an electric current can be passed through them. The reception by the molecules of electrons external to themselves is a factor in the change in their reaction properties. In particular, the conformation of molecules can be changed in this way.

7) Sensing of reagent molecules (study of the features of electron transport through molecules in a reactor in order to identify their state).

8) The magnetic field can be regulated in the pores of the nanoreactor. A magnetic field is induced by an electric current passing through nanoscale electrodes. Given the small pore volume of the nanoreactor, the reagent molecules will be in the closest proximity to the source of the magnetic field. This simplifies the task of creating a high magnetic field.

9) As in conventional membrane reactors, the role of the surface can be effectively used in active nanoreactors (provided by a large specific surface area). A distinctive feature of the proposed active nanoreactors is the ability to accurately control their geometry in situ (provided in the aspect of the invention, the presence of moving electrodes in the pores, the mechanical state of which is controlled by the Coulomb effect from other pore electrodes). The effective sizes of nanopores can be adjusted so that a specific fragment of the target molecules is placed in them in order to activate this fragment, or vice versa, to shield it from external reactions. Note that this functionality is relevant, for example, for DNA technology (the removal of single nucleotides from the end of a DNA molecule).

The described functionality of active nanoreactors is also included in the claimed technical result of the invention.

Execution example

First, we consider the structure corresponding to the intermediate stage of formation of one of the options for the implementation of an active molecular sieve. A schematic representation of this structure is shown in figure 1. The specified structure contains a conductive substrate 1 (figure 1) with an array of vertical carbon nanotubes 2 penetrating the layers of dielectric 3 and amorphous carbon 4, and the layer of amorphous carbon is separated from the nanotubes by cylindrical coaxial gaps.

The method of forming this intermediate structure involves the use of self-alignment techniques based on the effect of local anodic oxidation and includes the following steps (the method described in more detail is disclosed in RF patent No. 2349542). Catalytic nanoparticles (for example, nickel clusters) are formed on the surface of the conductive substrate 1, which plays the role of an input electrode (Fig. 2) using the sol-gel method. The process of growth of carbon nanotubes in an electric field is carried out by the method of catalytic pyrolysis of carbon-containing gas vapors (for example, butane-propane mixture). The result of this process is to obtain many vertically oriented carbon nanotubes 2. A dielectric layer 3, for example, an alumina layer, is deposited by magnetron or ion sputtering. A cathode sputtering method is applied to apply a layer of amorphous carbon 4, which plays the role of an output electrode. By thermal annealing, the conductivity of the amorphous carbon layer 4 is increased. A potential difference of at least 3 V is applied between the input 1 and output 4 electrodes, so that the output electrode 4 is an anode. Moreover, in the region localized around the nanotube 2, the carbon layer 4 is oxidized with the formation of gaseous CO ₂ , which leads to the formation of a gap between the nanotube 2 and the electrode 4 (Fig. 3). The oxidation process occurs until the nanotube 2 is completely isolated from the output electrode 4. The atmosphere in which the oxidation process is carried out must contain oxygen or water vapor. The length of the gap between the nanotube 2 and the electrode 4 depends on such parameters of the local anodic oxidation as the bias voltage of the nanotube 2 — electrode 4, the time dependence of this bias voltage, the concentration of oxygen and / or water vapor in the atmosphere, the temperature of the atmosphere and the oxidized sample, and photostimulation parameters oxidation process.

There is a possibility of additional broadening of the gap between the nanotube 2 and the output electrode 4. For this, the nanotube 2 is transferred to the state of mechanical contact with the output electrode 4 by means of the Coulomb force (Fig. 4), after which the local anode oxidation process of the output electrode 4 is repeated. This procedure can be carried out the required number of times. In order to prevent the undesired oxidation of the output electrode 4 during the operation of the obtained structure in the case of the transition of the nanotube 2 to the state of mechanical contact, it is necessary either to ensure the corresponding polarity and the range of the working bias voltage, or to apply an additional layer of chemically inert conductive material 5 to the surface of the output electrode 4 (figure 5).

We note the presence of the problem of the interaction of a carbon nanotube with particles of a substance sprayed during the formation of dielectric layer 3. These particles should form layer 3 and at the same time leave the surface of nanotube 2 free from any coatings. For this, the applied materials and the conditions for their application should be chosen so that it is energetically disadvantageous for the substance to remain on the surface of the nanotube in the form of a continuous or even dispersed coating. Small diameter carbon nanotubes (single-walled or with a small number of layers) have a small radius of curvature of the surface and, accordingly, a large surface energy and thereby contribute to the fulfillment of this condition. In order to meet the requirement in question, the following two methods can additionally be applied. In the case of high anisotropy of the deposition, the direction of which coincides with the longitudinal axis of the nanotube, the side surface of the nanotube will experience a minimum of interactions with particles of the sprayed substance, which will help maintain the purity of the side surface of the nanotube. The second mechanism is based on the Coulomb repulsion of sprayed particles and carbon nanotubes. To do this, the sprayed particles are electrically charged (for example, as a result of ionization under the influence of the plasma), and the same potential is applied to the nanotubes.

The elimination of the risk of the formation of a dielectric layer 2 on the surface of carbon nanotubes 2 can also be achieved by eliminating the operation of dielectric deposition. In this case, the formation of a dielectric layer 3 separating the input 1 and controlling 4 electrodes can be carried out by oxidation or nitridation of the surface of the input electrode 1.

In a similar way, a structure with an additional output electrode 6 can be obtained (Fig.6). For this, after the operation of forming a gap between the nanotube 2 and the output electrode 4, the following additional operations are carried out: applying a second dielectric layer 5, applying a second layer of amorphous carbon 6, local oxidation of the second layer of amorphous carbon 6. In the structure thus obtained, electrode 4 can be used, in particular, to excite oscillations of a nanotube 2, which is in a state of mechanical contact with the electrode 6.

To go from the described intermediate structure to the finished molecular sieve, it is necessary to determine the following. Firstly, a conductive mesoporous membrane acts as a substrate 1 (Figs. 1-6), formed according to one of the known technologies (by the technology of sintering of powders, by the sol-gel method, etc.). The requirements for pore sizes and their dispersion for the underlying membrane 1 can be significantly underestimated. Secondly, the dielectric layer 3, which serves as a support for the upper layer of amorphous carbon 4, is removed by selective liquid etching (the etchant is accessible to the removed layer from the side of the mesoporous substrate 1). In order for the amorphous carbon layer 4 suspended in this way to be spatially fixed, it is necessary that the length of the grown carbon nanotubes 2 gravitates to two significantly different values (Fig. 7). Longer nanotubes 2 should penetrate the amorphous carbon layer 4 and ensure the initiation of LAO of this layer (that is, ensure the formation of pores). A significant part of the shorter nanotubes 2 should enter the amorphous carbon layer 4, but not penetrate it. The initiation of LAO layer of amorphous carbon 4 by such nanotubes 2 will be excluded (the LAO process is initiated only in the region of exit of nanotubes 2 from the layer of amorphous carbon 4). These nanotubes will serve as mechanical clamps supporting the amorphous carbon layer 4. The growth of nanotubes 2, distributed in lengths into two groups, can be carried out using two types of catalyst particles that differ significantly in size or dissolution parameters of carbon.

Since the short nanotubes 2 will be in mechanical contact with the amorphous carbon layer 4, an electrical contact will also exist between them. From an electrical point of view, this case is equivalent to connecting a shunt resistor to the circuit formed by the pore electrodes. When a bias voltage is applied between pore electrodes, this resistor will play the role of an ohmic load. To avoid energy dissipation at the ohmic load, it is possible to replace short carbon nanotubes that perform the function of supporting the amorphous carbon layer 4 with some non-conductive nanowires, for example, nanorods made of titanium oxide or zinc oxide. From the point of view of simplifying the technology of molecular sieve formation, it is more preferable to isolate short carbon nanotubes 2 from the mesoporous substrate 1. A particular case of realizing this insulation is provided by using as catalyst clusters that provide the growth of short nanotubes 2 metal particles coated with a dielectric shell and not having by virtue of this electrical contact with the surface of the mesoporous substrate 1.

An interesting opportunity opens up if metal (for example, gold) is used as the material of the output electrode 4, and a multilayer carbon nanotube is used as the carbon nanotube 2. Then, by changing the polarity of the applied voltage so that the carbon nanotube 2 is the anode, it is possible to initiate anodic oxidation of at least one outer layer of the nanotube 2 (according to the studies conducted by the applicant, the threshold voltage of the LAO carbon nanotube exceeded the threshold voltage of amorphous carbon and amounted to about 6 V (Chaplygin Yu.A., Nevolin V.K., Khartov S.V. Reports of the Academy of Sciences, 2007, vol. 412, No. 6, pp. 1-4.)). The minimum value of the gap thus obtained separating the nanotube 2 from the gold electrode 4 will correspond to the distance between the layers in the carbon nanotube, which is about 0.33 nm. The gap thus obtained, in addition to the small width, will also be characterized by perfect geometry. This embodiment is of interest for applications of molecular sieves focused on the separation of media with small molecules. By increasing the number of oxidizable outer layers of multilayer carbon nanotubes 2, it is possible to change the effective pore size with a step of 0.33 nm.

The examples given describe the formation of a gap between a carbon nanotube and an output electrode by means of local anodic oxidation of the output electrode or by local anodic oxidation of the outer layers of a carbon nanotube. These examples can be summarized as follows.

In the case of the formation of a gap by means of local anodic oxidation of the output electrode, any material capable of oxidizing due to the effect of local anodic oxidation (for example, Ti, Ta, etc.) can be selected as the material of the output electrode. Similarly, if a gap is formed by local anodic oxidation of a carbon nanotube, instead of a carbon nanotube, any other object (hereinafter referred to as the controlled element) can be used, at least part of which is made of material capable of oxidizing due to the effect of local anodic oxidation (for example, nanorods and nanotubes made of Si, W, Ti, etc.).

The following level of generalization is also justified: instead of the local anodic oxidation reaction, in the considered cases, any other chemical or physical effect from the side of the controlled element / output electrode can be applied, causing local physical or chemical changes in the material of the output electrode / controlled element. The controlled element / output electrode can induce changes in the material of the output electrode / controlled element by electric current, electric field, thermal or chemical effects (in particular, the controlled element / output electrode can act as a catalyst for a chemical reaction). Examples of chemical reactions that allow local activation include oxidation, nitridation, halogenation, catalytic reactions, etc. Further, the material of the controlled element / output electrode, whose properties have been changed, can be removed by selective etching, and thus a gap can be formed between the controlled element and the output electrode (i.e., the pore volume of the active molecular sieve is formed).

The spatial separation of the controlled element (in particular, a carbon nanotube) and the output electrode can be achieved both by the described method of local change in the properties of the material of the control electrode / controlled element, and by pre-coating the controlled element with a conformal layer of a special material, onto which the control electrode material is then applied . The formation of a gap between the controlled element and the output electrode is ensured by the subsequent selective removal of this layer, which thus plays the function of the so-called sacrificial layer. The requirements for the material of the sacrificial layer in this case are determined both by the possibility of its selective removal, and by its ability to conformally cover the controlled element. From this point of view, the coating of a controlled element with a molecular monolayer formed as a result of self-organization seems to be very promising. The main factor determining the self-ordering of molecules on the surface of an object is the so-called diphilicity of molecules. Diphilicity suggests that the properties of one end of the molecule are different from the properties of its other end, and this difference is such that it is energetically advantageous for the molecule to adsorb onto the surface of the object at one end and not at the other (Zhou C., Deshpande MR, Reedb MA Applied physics letters. 1997 Vol. 71, No. 5, p. 611-613). As a result, an ordered layer with a thickness of one molecule is formed on the surface, characterized by high structural perfection. In the General case, using the described mechanism, it is possible to ensure the formation on the surface of a controlled number of molecular layers.

In the case of application of the described method of the sacrificial layer, conductive materials of almost any chemical composition and structure can be used as materials of the controlled element and the output electrode (or their individual parts), since these materials should not provide physical or chemical transformations.

Thus, the above examples of the implementation of the invention have been considered, which ensure the achievement of the claimed technical result - due to the presence in each pore of two independent electrodes (a conductive wall of the pore 4 and a controlled element, in which, in particular, can be a carbon nanotube 2) in the pores An electric field is maintained with a controlled magnitude, spatial configuration and their time dependence. This provides the following functionality:

1) redistribution of the electron density of molecules entering the pores (stimulated polarization). The parameters of this redistribution depend on the type of molecule. Thus, differences in the effective diameter of molecules and their Van der Waals interaction with pore walls can be enhanced. Both of these factors contribute to the difference in pore permeability for molecules of various types. If an alternating electric field is created between the walls of the pores 4 and the controlled elements (in particular, the central nanotubes 2), kinetic effects associated with the difference in the characteristic time of transport through the pores for molecules of various types can be used. These factors allow you to control the selectivity of the molecular sieve;

2) in the structure under consideration, the polarized molecules of the shared medium are oriented along the field lines of force. This provides control of the spatial orientation of the molecules inside the pore, as well as in the area near the entrance of the pore, which is essential for extended molecules and complex molecules. Polarized molecules also experience translational motion in the direction of the field gradient, which allows one to organize directed transport of molecules inside the pore, as well as in the area near the entrance of the pore;

3) in contrast to the case of passive molecular sieves, the parameters of which are fixed and determined by the capabilities of the formation technology, the parameters of the considered structure can be tuned to target molecules by changing the magnitude, spatial configuration, and time dependence of the electric field in the pores;

4) since the controlled element (in particular, carbon nanotube 2) is able to bend under the influence of the Coulomb force applied from the side of the pore wall 4, it is possible to change in situ the effective cross section of the pores. In the case of the wave motion of a controlled element (in particular, a carbon nanotube 2 fixed cantilever (Fig. 3) or in a state of mechanical contact with the electrode 6 (Fig. 6)), the effect of wave mass transfer through the pore can be ensured;

5) since an electric current can be passed through a controlled element (in particular, a carbon nanotube 2), which is a part of each pore, a self-cleaning pore mode is implemented, which assumes a controlled local heating of each pore. This allows you to control the desorption of molecules and particles through thermal and current activation of the desorption process;

6) the possibility of creating a controlled electric field structure in the pores of the considered structure allows one to exert an additional influence both on the transport and on the reactivity of chemical reactions in the pores of the agents and thereby provides access to chains of chemical transformations that are not realized under ordinary conditions. This is relevant for the application of molecular sieves as a nanomembrane catalytic reactor.

The described technical result determines the macroeconomic potential of the “active molecular sieves” line of the present invention.

Application example in the air separation problem

Let us consider an example of the use of an active molecular sieve in the problem of oxygen evolution from air. We assume that in the example of the sieve described above, an option was chosen that involves the formation of the electrode 4 in the form of a metal layer. In this case, a multilayer carbon nanotube is used as the carbon nanotube 2, and the gap between the nanotube 2 and the output electrode 4 is formed by local anodic oxidation of at least one outer layer of the nanotube 2. Let us assume that one outer layer of the nanotube 2 was oxidized, due to which the gap between the nanotube 2 and the output electrode 4 is 0.33 nm (corresponds to the distance between the layers in a multilayer carbon nanotube). We also assume that Ti is selected as the material of the output electrode 4, and an additional operation is carried out, which consists in nitridizing the surface of the specified electrode. As a result, a dielectric layer 5 is formed on the surface of the electrode 4 (Fig. 8). Note that due to the excess of the titanium density value of the density of titanium nitride, the gap between the nanotube and the surface of the dielectric layer 5 may deviate from the indicated 0.33 nm downward. It will be shown below that in the considered example this is not of fundamental importance. In the general case, the initial gap between the nanotube 2 and the output electrode 4 can be set at 0.66 nm (involves the sequential removal of the two outer layers of the carbon nanotube 2). By setting the nitridization depth of the output electrode 4, it is possible to vary the amount of decreasing the length of the resulting gap, including reducing the specified gap to a value close to 0.3 nm. Instead of the nitridation method for applying a dielectric coating 5, an atomic layering method can be used. The advantage of this method is that it guarantees the atomic accuracy of the thickness of the formed layers.

Since the kinetic diameter of the oxygen and nitrogen molecules is 0.346 nm and 0.364 nm, respectively, the gap between the nanotube 2 and the dielectric layer 5, whose value is 0.33 nm (or less), will not provide conditions for the efficient transport of these molecules. That is, the transport of molecules through the pore formed by the gap between the nanotube 2 and the dielectric layer 5 will be eliminated or at least substantially hindered. Next, a bias voltage is applied between the nanotube 2 and the output electrode 4, which increases until the nanotube 2 passes into a state of contact with the pore wall (i.e., with the dielectric layer 5, Fig. 9). The action of the van der Waals forces in the contact patch of the nanotube 2 and the dielectric layer 5 ensures the stability of this state of the system. The cross section of the pore thus increases. The degree of this increase is determined by such a geometric parameter of the system as the ratio of the total thickness of the output electrode 4 and the dielectric layer 5 and the gap between the underlying membrane 1 and the output electrode 4 (this ratio determines the amount of deflection of the cantilevered nanotube in the area of exit from the pore). If the ratio of the total thickness of the output electrode 4 and the dielectric layer 5 to the gap between the underlying membrane 1 and the output electrode 4 is set sufficiently large, then the increase in the pore cross section will still be insufficient for efficient transport of molecules with a kinetic diameter of 0.346 nm and 0.364 nm. The action of the Coulomb attraction force between the nanotube 2 and the output electrode 4 causes elastic deformation of the dielectric layer 5 separating them. The deformation of the dielectric layer 5 provides an increase in the deflection of the nanotube 2 in the area of its contact with the dielectric layer 5 and, accordingly, an increase in the deflection of the nanotube 2 in the region of exit from the pore . In the described manner, a continuous increase in the pore cross section is achieved in accordance with a continuous increase in the Coulomb force. Note that when the thickness of the dielectric layer 5 is 4 nm and the relative deformation of the specified layer is 5% (lies in the range of elastic deformation of titanium nitride), the magnitude of the deflection of the nanotube in the region of its contact with the dielectric layer 5 will increase by 0.2 nm . Thus, at a certain magnitude of the Coulomb force and, therefore, a bias voltage applied between the nanotube 2 and the output electrode 5, the through passage of the pore will reach 0.346 nm and will be equal to the kinetic diameter of the oxygen molecule. This will provide conditions for the efficient transport of oxygen molecules through the pore, while the transport of nitrogen molecules having a kinetic diameter of 0.364 nm will be difficult. In the described manner, the solution to the problem of selective separation of oxygen and nitrogen is achieved. The magnitude of the bias voltage corresponding to the transition of the active molecular sieve to the state of effective oxygen transport is determined empirically in the process of gradually increasing the bias voltage. With a further increase in the bias voltage, a sieve state is achieved that corresponds to the effective transport of both oxygen and nitrogen with the retention of other possible fractions of the mixture to be separated, which have a larger kinetic diameter. With a decrease in the bias voltage, the sieve successively passes through the states corresponding to a decrease in the output pore cross section. First, nitrogen transport stops, then oxygen. In the general case, if plastic deformation is also added to the elastic deformation of the dielectric layer 5, then the effect of a hysteresis of the sieve states will be observed (the dependence of the output pore cross section on the bias voltage corresponding to the forward voltage sweep will not coincide with a similar dependence corresponding to the reverse sweep by voltage).

Application example in the task of desalination of water

Let us also consider an example of the use of an active molecular sieve in the problem of desalination of sea water. The current state of the art includes the so-called electrodialysis systems based on the spatial redistribution of impurity salt ions in an external electric field. In the general case, the total energy spent transporting one ion to the surface of the electrode is determined by the bias voltage applied to the electrodes. The electric field strength determines the magnitude of the Coulomb force acting on the ion, and, accordingly, the rate of extraction of this ion from the volume of water. As is known, at a given bias voltage, the electric field strength is inversely proportional to the distance between the electrodes. From here it is easy to see that in order to increase the energy efficiency of electrodialysis systems, it is necessary to break the treated water into layers of minimum thickness. The thinnest one-dimensional “layers” of water (that is, capillaries) can be obtained inside molecular sieves (nanomembranes). These molecular sieves have through pores, the diameter of which lies in the nanometer range, which provides an ultra-high degree of dispersion of water: bulk water is divided into a system of nanocapillaries penetrating the pores. Further, to implement the electrodialysis method, it is necessary that each pore of a molecular sieve contains two independent electrodes. There is a need for technology for the industrial production of molecular sieves with such pores.

Above was an example of the implementation of active molecular sieves, providing through pores, the geometry of which is controlled in the range from 100 to 0.33 nm. Each pore contains a central electrode (carbon nanotube) and a cylindrical electrode coaxial to it (lateral surface of the pore). It should be noted separately the ordering of the resulting pores in the monolayer, which is essential. In the task of desalination, these systems have the following functionality. The carbon nanotube present in each pore is a concentrator of the electric field. As is known, the electric field induced by the needle electrode can be approximately estimated by the formula U / r, where U is the bias voltage applied to the needle electrode, r is the radius of curvature of this electrode. Thus, a single-walled carbon nanotube, characterized by a diameter of ~ 1 nm, when a bias voltage of 0.01 V is applied to it, provides an electric field concentration of up to 2 · 10 ⁷ V / m. To form such fields in a macroscopic capacitor, the distance between the plates of which is 1 cm, a voltage of 200 kV would have to be applied. The above estimate demonstrates the effect of strengthening the Coulomb forces acting on ions, which is achieved when the described active pores are used. However, this high-intensity field is localized in small areas of space, namely, in the immediate vicinity of carbon nanotubes inducing it. Therefore, the presence of self-aligned pores with nanotubes plays a decisive role. These pores bring treated water precisely to those areas of space in which the field is localized and exclude the possibility of water transport “bypassing the field”.

Since the energy of thermal motion per one degree of freedom (in this case, in the direction of the longitudinal axis of the pore) is about 0.013 eV at room temperature, the potential of 0.01 V can be considered a threshold value: a positive potential of 0.01 V is applied to nanotubes blocks (average) access to the cations of salts dissolved in water at the time (Fig. 10).

Chlorine anions, on the contrary, tend to the surface of the nanotube, where, having given an extra electron, they go into a neutral state and leave the system in the form of gaseous chlorine. To increase the degree of purification, it is possible to increase the blocking voltage on the nanotube to a value of 0.01 · (1 + 3σ), where σ is the standard deviation of the distribution of thermal energy, the value of which is approximately KT, i.e., 0.01 eV. Thus, the extraction of one anion from water requires energy from 0.01 to 0.04 eV, which for desalination of a liter of water gives a value from 0.5 to 2 kJ (0.14-0.56 kWh / m ³ ) . Salt cations by means of diffuse transport go into the brine located above the membrane and are removed from the system of the horizontal component of the flow. This component of the flow can be very intense, since the brine remains cold and its removal from the system is not associated with energy loss (in contrast, for example, from distillation desalination methods). A large brine flow and, accordingly, its poor enrichment also eliminates the difficulties associated with precipitation and the disposal / discharge of concentrated brine.

It is important to note that in the case of active membranes, it becomes possible to control the pore wettability. The water molecule, as you know, is an electric dipole. When a strongly inhomogeneous electric field is induced by a nanotube, water dipoles will experience the effect of an uncompensated Coulomb force directed along the field gradient, i.e., to the nanotube. This provides the effect of directed drift pulling of water molecules into the pore (the pore goes into a hydrophilic state). Since the intensity in the focus of the electric field reaches 10 ⁷ V / m or more, this effect will be very significant. Together with the factor of pore organization into the system of the most permeable geometry (monolayer) and the factor of ultrahigh degree of pore integration (up to 10 ¹⁶ m ^-2 or more), this provides a significant margin of productivity. According to estimates, the productivity is at least 4-5 orders of magnitude higher than that for existing systems based on semipermeable cellulose acetate membranes and reaches 300 m ³ / h of water per square meter of membrane. This performance value is theoretical and applies only to the pore monolayer itself, not including, in particular, the substrate in the form of a classical mesoporous membrane (note that the requirements for pore sizes and their spread for the underlying membrane can be significantly underestimated and, accordingly, can be reduced its resistance to flow; to reduce the latter, it is advisable to use an underlying membrane with a large pore size gradient in the direction from the working surface). However, this value can be considered as a demonstration at a qualitative level of the high potential of the method in terms of productivity. A value of 30 m ³ / h or more should be considered as practically achievable performance.

Regarding performance, we also note the following fact. The central electrode in each pore is an elastic element (carbon nanotube) and can undergo cyclic deflection by the Coulomb force acting from the side of the pore wall. The inner surface of the pores can be made in the form of a cone expanding in the direction of exit from the pore (the technology of pore formation allows this effect to be achieved). The combination of these factors allows for the operation of an active molecular sieve, in which each pore implements a nanoscale analogue of a pump with a variable volume of working chambers. This makes it possible to transport water through the membrane not only at zero, but also at a negative pressure difference between the inlet and outlet flows. In this mode, the entire membrane is a “surface distributed pump”.

One of the main factors affecting the overall performance of membrane systems is their resistance to contamination. In the case of the proposed system, the mechanism for increasing the resistance to pollution is, firstly, the extremely small pore size (up to 0.33 nm wide), due to which the contaminants will accumulate on the surface without penetrating into the inner region of the pores. At the surface of the membrane, these contaminants will form a colloidal solution with water and can be removed from the system with a longitudinal component of the flow. Secondly, a monolayer pore form factor (there is no stochastically percolated pore labyrinth that can trap particles of contaminants). Those particles that were able to penetrate into the pore will freely enter the outlet water stream. And finally, thirdly, the possibility of active pore self-cleaning. Let us briefly describe the mechanism of such self-cleaning. A high-density electric current can be passed through a carbon nanotube, which will lead to its heating (for this, in particular, the closure of the nanotube to the pore wall can be applied; in addition to closing the circuit, this will also increase the input cross section of the pore). As a result, desorption of molecules and particles by the mechanism of thermal and current (analogue of electromigration) activation of desorption will occur. In the case of the aquatic environment, it is possible to enhance this effect. As a result of heating the nanotube around it, water will transfer to the gaseous phase. The rapid explosive growth of a water vapor bubble will lead to the expulsion of the medium from the pore and to mechanical separation and entrainment of even relatively massive polluting formations from the surface. Note that by stopping the heating in time, the collapse of the bubble can be achieved instead of breaking it off. The intensity of these processes can be controlled within wide limits.

The described factors of increasing productivity, on the one hand, and the possibility of obtaining pores with a diameter of up to 0.33 nm, on the other hand, provide conditions for the effective operation of the system in a mode below a threshold voltage of 0.01 V, which provides “reflection of cations” from the pore entrance. Since cations do not occur at voltages below the indicated “reflection” value and the latter can fall into the region close to the pore entrance, it is necessary that the cation penetration into the pore is blocked by the steric effect, that is, the cation must not penetrate into the pore due to its geometrical dimensions . The kinetic diameter of the sodium cation is 0.09 nm, which is significantly less than the kinetic diameter of the water molecule (0.28 nm). However, each cation, being in water, attracts polar water molecules to itself and thereby forms a “shirt” of these molecules around itself. Such a stable design is already significantly larger in size than a single water molecule. In the same way, stable associates based on anions arise. As a result, it is possible to choose pore sizes so that single water molecules pass through them, and associates based on anions and impurity cations do not. The principle of operation of traditional semi-permeable reverse osmosis membranes (for example, membranes made from cellulose acetate) is based on this effect. These membranes have pores with a diameter of 0.5-1 nm, which, as practice shows, is sufficient to realize the separation effect of water molecules and their associates. However, since the existing semipermeable membranes are bulky materials with randomly percolated pores, their permeability is extremely low. In practice, this leads to low resulting performance of desalination systems, as well as their vulnerability to pollution. The above-mentioned feature of the proposed active membranes associated with the organization of pores in a monolayer, as well as with the presence of a mechanism for controlling the wettability of pores and a self-cleaning mechanism, can drastically increase productivity relative to traditional reverse osmosis membranes. In the case of applying the mechanism of accelerating the transport of water molecules through the pores associated with the modulation of the geometry of the pores ("distributed pump" mode), the resulting productivity can be further increased.

The operating mode of the active molecular sieve, corresponding to a bias voltage below the threshold value of 0.01 V, is an analog of reverse osmosis. This operating mode provides a further increase in the energy efficiency of desalination (less than 0.5 kJ per liter or less than 0.14 kWh / m ³ ). To use it, pores of an extremely small size (0.33-1 nm) are required. When using larger pores (1-100 nm), it is necessary to use the first of the described modes, which is an indirect analog of electrodialysis (corresponds to a bias voltage exceeding the threshold value of 0.01 V). In this mode, power consumption is increased, however, by increasing the pore size, a further increase in the resulting system performance can be achieved. Proposed in the invention of active molecular sieves can be focused on both the first and second mode of operation.

Thus, desalination of water, based on the use of active molecular sieves, allows 2 or more orders of magnitude to increase energy efficiency relative to existing desalination systems and significantly increase their productivity.

Claims (9)

1. A molecular sieve, comprising many pores, the length of which in at least one dimension is less than 100 nm, each of these pores includes at least one electrode electrically connected to bias voltage control means, at least one of these electrodes nanotube or nanowire. 2. The sieve of claim 1, wherein the plurality of pores is divided into one or more subsets, the same type of electrodes included in the pores of the common subset being electrically connected to each other. 3. The sieve according to claim 1, in which at least one of the electrodes of each specified pore is made of a material that provides elastic deformation of the electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or combination of pore electrodes. 4. The sieve according to claim 1, in which at least one of the electrodes of each specified pore is made of a material that provides plastic or elastoplastic deformation of this electrode in response to the effect exerted by the Coulomb force from the side of the other pore electrode or a combination of pore electrodes. 5. The sieve of claim 1, wherein said electrode is a carbon nanotube. 6. The sieve according to claim 1, in which each of the specified pores includes two electrodes, the first electrode is part of a conductive layer of amorphous carbon or a chemically inert metal in which the pores of the sieve are made, and the second electrode is a carbon nanotube, the first and second the electrodes are spatially separated and do not touch each other. 7. The sieve of claim 6, wherein said second electrode is a multilayer carbon nanotube with at least one outer outer layer removed, where said removal is accomplished by local anodic oxidation, and a chemically inert metal is selected as the material of said first electrode. 8. The sieve according to claim 6, in which the surface of the specified carbon nanotube and the surface of the specified first electrode form a gap whose width is less than 0.4 nm. 9. The sieve of claim 6, wherein a gap between the surface of said carbon nanotube and the surface of said first electrode is formed by local anodic oxidation of a portion of the material of the first electrode.

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