Laboratory of Digital Materials Science

The article was published in the journal Nanomaterials. As a result of the constant growth in the use of medicines, the accumulation of antibiotics and their decomposition products in wastewater has become a serious problem for humans and the environment. Most often, antibiotics enter rivers and groundwater as waste from pharmaceutical enterprises, medical and pharmacy institutions, and agriculture. The presence of antibiotics in water leads to an increase in the resistance of bacteria and microorganisms to them, the development of allergic reactions, and even the proliferation of dangerous bacteria. Currently, there are various methods of wastewater treatment, however, each method has its own limitations. Sorption is one of the simplest and most inexpensive cleaning methods that do not require complex production structures or additional chemical reactions. The staff of the Laboratory of Digital Materials Science and the research center "Inorganic Nanomaterials" of NUST MISIS focused on it. For the proposed method, there is no need to create special expensive equipment or artificially introduce additional chemical or biologically active components into the system that can disrupt the ecological balance. It is enough to simply pass contaminated water through a filter or a suspension of boron nitride nanoparticles. The sorbent created by the researchers on the basis of hexagonal boron nitride is able to effectively purify antibiotic wastewater. In their study, NUST MISIS staff selected three types of antibiotics, which are among the most common pollutants: ciprofloxacin, tetracycline and bicillin. In the future, scientists plan to increase the sorption capacity of nanoparticles by applying a polymer and depositing metal ions, as well as expand the range of antibiotics under study.

The article was published in Nanoscale (2022). The surface has always been of particular interest due to the wide variability of its structure and the presence of unusual properties. On the other hand, the "surface of the surface" - the edge of the nanostructure may be equally important and introduce new phenomena. The exact formation of edges on two-dimensional materials with a certain crystallographic orientation is a difficult task and requires precise knowledge of their chemical properties. In some cases, the edge shows a very specific structure. For example, the edges of multilayer graphene tend to connect to each other. The case of double-layered graphene has been studied in detail, and it has been shown that the connection of the edges does not even require overcoming any barrier, and therefore a hollow sp2-hybridized graphene structure is spontaneously formed. In our previous work, it was shown that the structure of the closed edges of bigrafen is actually strictly defined and can be represented as a curved interface between disoriented (in the general case) graphene grains. Understanding the edge structure is also important for the case of the formation of holes in a two-dimensional structure, since it is an attractive object for changing the properties of the material. For single-layer graphene, many studies have been conducted on holes for DNA sequencing, gas sensing, ion and molecular filtration (in particular, water desalination), molecular transport, etc. Several similar studies have also been conducted with hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2). The variety of hole shapes and types of passivation of their edges does not allow for systematic experimental studies. Research usually focuses on performance tests without information about edge configuration and chemical stability, which can significantly affect performance. The carbon double, boron nitride, is less studied in this regard, although it seems promising to create holes not in bigraphene, but in the double-layered h-BN. Indeed, the strong tendency of layers towards AA' packaging makes it possible to be sure that the two-layer structure will be predetermined. However, it remains completely unclear which edges of the multilayer h-BN will tend to close and what the final structure will be. The structure of the edges of multilayer h-BN is usually unknown, whereas from the general logic one can expect a similar self-passivation effect due to the close values of bending stiffness and edge energy. The presented work is devoted to the study of the edges of two-layer h-BN. It is shown that the edges tend to join regardless of the cut. A defect-free connection can be expected only in the case of a zigzag edge, in other cases a number of tetragonal and octagonal defects are formed. This result was obtained by drawing an analogy between the edge of a two-layer h-BN and the interface of a monolayer h-BN (see figure). Information about the structure and energy of the closed edges made it possible to predict the shape of the holes in h-BN, which is consistent with experimental data. Finally, it is shown that closed edges do not create states in the band gap, thereby not changing the dielectric of h-BN.

The work was published in the journal Science 374, 1616-1620 (2021) This work was done in collaboration with a number of foreign institutes, the main experiment in which was conducted at NIMS (Tsukuba, Japan), Prof. D.M.Tang. Experimental measurements of chirality during stretching of carbon nanotubes (CNTs) and heating to 2000 K showed that plastic deformation occurred in its central section, while a clear tendency to increase the chiral angle was observed. Interestingly, this contradicted the previous theoretical model describing plastic deformation through the movement of dislocation nuclei (defects 5/7, adjacent pentagon and heptagon) arising from high deformations in CNTs from the Stone-Wales defect, and predicting a gradual decrease in the chiral angle. Experimental conditions allowed us to assume that due to the extremely slow elongation of the heated nanotube, the formation of Stone-Wales defects (and their further transformation into dislocation nuclei 5/7) cannot be the main reason for the change in chirality, since the process of formation of such defects under these conditions is reversible. To solve this problem, we proposed and theoretically described a new mechanism according to which dislocations are formed as a result of evaporation of carbon dimers (C2) and the associated formation of defects 5/8/5. This defect can split into dislocations 5/7, both as a result of the rotation of bonds, and due to further evaporation of carbon (Fig. (d,e)). The calculated defect formation energy of 5/8/5, depending on the chirality angles, using density functional theory methods shows that in CNTs with a small chiral angle, it is energetically more advantageous for dislocations with the Burgers vector (1.0) to appear, which increase the chiral angle as a result of movement through the structure. We also calculated the ratio of the probabilities of dislocation formation (1.0) and (0.1) to predict the chirality trend according to our model. The result (Fig. (f)) made it possible to accurately describe experimental observations and explain the nature of the mechanism of plastic deformation of nanotubes at high temperatures and slow stretching. Thus, we have studied the method of local chirality change, which allows us to implement metal-semiconductor-metal contact in single-walled carbon nanotubes, that is, to create an intramolecular transistor based on nanotubes.

The project is dedicated to the development of new means of obtaining nanostructured materials and the study of new graphene-based materials with electrical, mechanical and optical properties promising for various applications. The study of the created materials will be carried out not only experimentally, but also using numerical modeling methods. For the successful development of graphene electronics, it is extremely important to understand the physics of the influence of various structural features of a material on its electrical and optical properties. Such features may include edges, interfaces between regions with different lattice parameters, and mechanical stresses.

The project will study the stability and properties of a new class of nanomaterials with a special atomic structure determined by low dimensionality. The novelty of the project is primarily due to the choice of research objects, the systematic study and description of which (despite their prospects) has not yet been carried out. We propose to investigate for the first time two families of materials, each of which has its own attractive properties: films of monoatomic thickness based on a number of metals and quasi-one-dimensional structures of binary M2X3 and ternary M2X3Y8 compositions. The project will carry out a comprehensive theoretical study of the structure and physico-chemical properties of such objects, as well as predict the mechanisms of their production and identify potential applications. The obtained data will significantly expand the fundamental knowledge about low-dimensional nanomaterials, will allow a comprehensive description of their potential properties, and the results of the project will become the basis for further controlled synthesis of nanostructures with the necessary composition and properties, which will undoubtedly arouse the interest of the scientific community in this problem and can take the development of the field of synthesis of low-dimensional materials to a new level.

Controlled change in the structure of nanomaterials at the atomic level is the most important task of modern materials science. The influence of the surface is expressed in the need to take into account the size of nanostructures when describing their stability. This problem is especially clearly manifested in the study of the phase transformation of nanomaterials, when their energy begins to depend not only on external conditions, but also on the contribution of surface effects. For example, the classical carbon Bandy phase diagram changes as the thickness of the carbon film decreases, the pressure of the graphite-diamond phase transition increases, which reflects an increase in the instability of the diamond as its size decreases. Upon reaching atomic thickness, diamond films should exhibit a number of extremely attractive physical properties, but their synthesis requires fundamentally different approaches. Two ways of synthesizing nanomaterials seem natural for today's science: top-down and bottom-up methods. The top-down method, when the macroscopic material is separated to the required nanostructure, was not considered, since it is probably impossible to obtain diamond films of nanometer thickness by separating a diamond crystal. The bottom-up method (the necessary nanostructure is synthesized from smaller nanostructures) seems to be the most attractive for this case, although it certainly requires overcoming a number of non-trivial scientific problems. The traditional method of chemical deposition from the gas phase is not applicable to solving the problem of obtaining diamonds of atomic thickness due to the high growth rate of diamond layers and their heterogeneity at the atomic level. Therefore, in this paper, we will consider another option for producing diamond films, when the starting material is not steam, but a two-layer graphene film. The formation of diamond films occurs through a controlled chemical reaction of two graphene sheets with third–party atoms, mainly hydrogen or fluorine. We will test this method experimentally, and theoretically we will study in detail the mechanism of transformation of graphene layers not only in the case of bilayer graphene, but also other structures based on weakly bonded layers – double-layered carbon nanotubes and related nanomaterials.