Gas-sensitive sensing analysis method based on metal modified BN nanotube

Abstract

The invention provides a gas-sensitive sensing analysis method based on a metal modified BN nanotube. The gas-sensitive sensing analysis method comprises the following steps: acquiring a pre-constructed decomposition product model of environment-friendly insulating gas C4F7N and a metal modified BN nanotube model; calculating an electron energy band structure and state density of an adsorption system formed by the decomposition product model acting on the BN nanotube model, and obtaining a first analysis result of the adsorption system on an electron state level; calculating adsorption energy and electron transfer of the adsorption system, and obtaining a second analysis result; calculating molecular orbital change conditions of the adsorption system, and performing consistency analysis based on the molecular orbital change conditions to obtain adsorption performance and electronic behavior analysis results of the adsorption system. Through a series of calculation and analysis steps, the analysis results of the adsorption system in the aspects of electronic state and adsorption behavior can be effectively obtained, the analysis results of adsorption performance and electronic behavior can be obtained through consistency analysis, and powerful support is provided for related research and application of gas-sensitive sensing.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials and gas sensors, and in particular relates to a gas sensing analysis method based on metal-modified BN nanotubes, which is used for detecting discharge decomposition gas of environmentally friendly insulating gas C4F7N. Background Art

[0002] In the field of insulation of high-voltage electrical equipment, traditional insulating media such as SF6 (sulfur hexafluoride) are widely used due to their excellent insulation performance and arc extinguishing characteristics. However, as a potent greenhouse gas, SF6 has a global warming potential (GWP) that is 23,500 times that of carbon dioxide (CO2), causing serious impacts on the environment. Therefore, finding environmentally friendly alternative gases has become an important task for the power industry.

[0003] As a potential SF6 substitute gas, C4F7N (heptafluoroisobutyronitrile) not only has higher insulation performance than pure SF6, but also has a global warming potential of only 2100, which is much lower than SF6. In addition, C4F7N may produce toxic decomposition products such as CF4 and COF2 during decomposition, and the presence of these gases may pose a threat to the safe operation of equipment and the surrounding environment. Therefore, the development of a sensor technology that can effectively detect C4F7N decomposition gas is crucial to ensure the safe and stable operation of the power system.

[0004] The existing gas sensors have many limitations in detecting C4F7N decomposition gas. On the one hand, their selectivity is generally not high, and it is difficult to accurately distinguish the various gases produced by the decomposition of C4F7N. On the other hand, some sensors have too strong adsorption capacity, which makes recovery difficult, while some have too weak adsorption capacity and cannot produce sufficient response signals to the gas. In addition, in practical application scenarios, these sensors often lack the ability to respond quickly to specific gases and high sensitivity detection performance. Although two-dimensional materials such as graphene and hexagonal boron nitride (h-BN) have become a hot topic in gas sensor research due to their unique physical and chemical properties, such as high carrier mobility, high mechanical strength, good photocatalytic performance and large specific surface area, and the adsorption capacity of gas molecules and the overall performance of the sensor can be improved to a certain extent by introducing defects or doping metal atoms in them, there is still a lack of efficient and highly selective detection methods for C4F7N decomposition gases, especially CF4 and COF2, which have similar structures and properties. Therefore, the development of new metal-modified BN nanotube gas sensors for C4F7N decomposition gas detection has become an important research topic and development direction that needs to be tackled in this field. Summary of the invention

[0005] In view of this, the present invention aims to provide a gas-sensitive sensing analysis method of metal-modified BN nanotubes for detecting the discharge decomposition gas of the environmentally friendly insulating gas C4F7N, which is helpful to study the modification behavior of metals on BN nanotubes and is of great significance for further expanding the use of metal-modified BN nanotubes as gas-sensitive materials for high-performance gas sensors for the detection of C4F7N discharge decomposition gas.

[0006] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0007] A gas sensing analysis method based on metal-modified BN nanotubes comprises the following steps:

[0008] Get pre-built decomposition product models of environmentally friendly insulating gas C4F7N and metal-modified BN nanotube models;

[0009] The electronic band structure and state density of the adsorption system formed by the decomposition product model acting on the BN nanotube model are calculated, and the first analysis result of the adsorption system at the electronic state level is obtained based on the electronic band structure and state density;

[0010] Calculate the adsorption energy and electron transfer of the adsorption system, and obtain the second analysis result of the adsorption system at the adsorption behavior level based on the adsorption energy and electron transfer;

[0011] The molecular orbital changes of the adsorption system are calculated, and the consistency analysis of the first analysis result and the second analysis result is performed based on the molecular orbital changes to obtain the adsorption performance and electronic behavior analysis results of the adsorption system when the decomposition product model acts on the metal-modified BN nanotube model.

[0012] Furthermore, in the BN nanotube model, the metal atoms used for metal modification include: cobalt Co, rhodium Rh, or a combination of cobalt Co and rhodium Rh.

[0013] Furthermore, the decomposition product models of the environmentally friendly insulating gas C4F7N include: a carbon tetrafluoride CF4 gas model and a carbon difluoride monoxide COF2 gas model.

[0014] Furthermore, the metal-modified BN nanotube model was constructed according to the following steps:

[0015] The exchange and correlation of electrons in the metal-modified BN nanotube model are approximated based on density functional theory;

[0016] Eliminate the relativistic effects of metal atoms in the metal-modified BN nanotube model after approximation;

[0017] The hydrogen bonds in the metal-modified BN nanotube model were calculated using p orbital double value plus polarization function as the atomic orbital basis set;

[0018] Density functional theory-dispersion correction was performed on the metal-modified BN nanotube model using a semi-empirical dispersion correction method;

[0019] The van der Waals force correction method based on density functional theory is used to correct the intermolecular forces and long-range interactions of the metal-modified BN nanotube model;

[0020] The set global orbital cutoff radius and the set smearing area are used to perform smooth convergence of the single-layer structure to obtain the metal-modified BN nanotube single-layer structure, thereby completing the construction of the metal-modified BN nanotube model.

[0021] Furthermore, before the decomposition product model is applied to the BN nanotube model to form an adsorption system, the method further includes:

[0022] The gas molecular structure of the decomposition product model and the single-layer structure of the BN nanotube model were geometrically optimized to obtain the optimized molecular structure and single-layer structure, and analysis was performed based on the optimized molecular structure and single-layer structure.

[0023] Furthermore, in the cobalt (Co)-modified BN nanotube model, the cobalt (Co) atom is placed above the center of the hexagonal ring of the BN nanotube, and the lengths of the Co-N bonds are all equal, with an average length of the Co-B bond of 1.86 Å.

[0024] Furthermore, the binding energy of Co atoms modified onto the BN nanotube monolayer is calculated using the following formula:

[0025]

[0026] In the formula, E Co-BNNT 、E Co and E BNNT represent the energies of Co-BN nanotube monolayer, Co atoms and intrinsic BN nanotube monolayer, respectively.

[0027] Furthermore, the energy of the most stable configuration of gas molecules adsorbing cobalt Co atoms modified onto the BN nanotube monolayer is calculated using the following formula:

[0028]

[0029] E Co-BNNT / gas is the total energy of the adsorption system, and E Co-BNNT and E gas are the energies of the Co-BN nanotube monolayer and the gas molecules, respectively.

[0030] Furthermore, the density of states includes: total density of states and partial-wave density of states;

[0031] The total density of states is used to give a macroscopic description of the overall electronic structure of the adsorption system;

[0032] The partial-wave density of states is used to decompose the total density of states according to the contribution of atomic orbitals or specific atoms, and to describe the contribution of each decomposed part to the total density of states.

[0033] Furthermore, the molecular orbital changes are represented by the highest occupied molecular orbital distribution, the lowest unoccupied molecular orbital distribution and the energy gap.

[0034] In summary, the present invention provides a gas sensing analysis method based on metal-modified BN nanotubes, including obtaining a pre-constructed decomposition product model of environmentally friendly insulating gas C4F7N and a metal-modified BN nanotube model; calculating the electronic band structure and state density of the adsorption system formed by the decomposition product model acting on the BN nanotube model, and obtaining the first analysis result of the adsorption system at the electronic state level based on the electronic band structure and state density; calculating the adsorption energy and electron transfer of the adsorption system, and obtaining the second analysis result of the adsorption system at the adsorption behavior level based on the adsorption energy and electron transfer; calculating the molecular orbital changes of the adsorption system, and performing consistency analysis on the first analysis result and the second analysis result based on the molecular orbital changes, and obtaining the adsorption performance and electronic behavior analysis results of the adsorption system when the decomposition product model acts on the metal-modified BN nanotube model. The present invention can effectively obtain the analysis results of the adsorption system at the electronic state and adsorption behavior level through a series of calculation and analysis steps, and obtain the adsorption performance and electronic behavior analysis results through consistency analysis, providing strong support for gas sensing related research and applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 A flow chart of a gas sensing analysis method based on metal-modified BN nanotubes provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1 The embodiment of the present invention provides a gas sensing analysis method based on metal-modified BN nanotubes, comprising the following steps:

[0039] Step 1: Obtain the pre-built decomposition product model of the environmentally friendly insulating gas C4F7N and the metal-modified BN nanotube model.

[0040] It should be noted that BN nanotubes, or boron nitride nanotubes, are a type of nanomaterial with a structure similar to carbon nanotubes. They are composed of boron (B) atoms and nitrogen (N) atoms and have good mechanical properties, thermal stability, and chemical stability. Metal modification is achieved by introducing metal atoms into BN nanotubes to change their electronic structure and surface properties, thereby giving them new functional properties. For example, the introduction of metal atoms may enhance their adsorption capacity or catalytic performance for certain gases.

[0041] This step can provide a basic model for the subsequent analysis of the interaction between gas decomposition products and metal-modified BN nanotubes.

[0042] For the decomposition product model of C4F7N, it is necessary to use theoretical calculation tools to simulate its atomic structure and chemical bonds based on its possible decomposition reaction pathways, the chemical composition of the products, etc. For the metal-modified BN nanotube model, it is necessary to consider the doping method, position, concentration, etc. of the metal atoms, and combine the structural characteristics of the BN nanotubes themselves to determine the changes in its electronic structure and geometric structure through calculation.

[0043] Step 2: Calculate the electronic band structure and state density of the adsorption system formed by the decomposition product model acting on the BN nanotube model, and obtain the first analysis result of the adsorption system at the electronic state level based on the electronic band structure and state density.

[0044] It should be noted that the electronic band structure is a way to describe the energy distribution of electrons in solids. In crystals, the energy of electrons is not continuous, but is divided into a series of energy bands. These energy bands include the valence band (the highest energy band filled with electrons, in which electrons are usually relatively stable), the conduction band (the energy band that is not filled with electrons, and electrons can gain enough energy to jump to the conduction band so that the material has properties such as conductivity), and the band gap that may exist between them (the energy gap, in which it is difficult for electrons to exist, which determines whether the material is a conductor, semiconductor or insulator). By calculating the electronic band structure, we can understand important information such as the distribution of electronic states and conductivity of the material.

[0045] The state density indicates the number of electronic states in a unit energy interval. It reflects the distribution of electronic states of a material in different energy intervals.

[0046] This step can provide an in-depth understanding of the properties of the adsorption system from the electronic state level, including judging its conductive properties, electronic state distribution, etc., providing an important basis for the subsequent comprehensive analysis of the adsorption system.

[0047] In this step, quantum mechanical calculation methods such as density functional theory (DFT) can be used to calculate the electronic band structure and state density. DFT converts multi-electron problems into single-electron problems and uses exchange-correlation functionals to approximately describe the interactions between electrons, thereby solving the electronic band structure and state density. Based on the calculated electronic band structure, it is possible to determine whether the adsorption system has an energy gap, the position of the Fermi level, etc., and then determine its conductive properties (such as whether it is a conductor, semiconductor or insulator). Through state density analysis, whether it is the total state density or the partial wave state density, we can understand the energy distribution characteristics of the electronic state and the contribution of different atomic orbitals to the electronic state density, so as to further analyze the relationship between processes such as chemical bond formation and electron transfer and the electronic state distribution, and obtain the first analysis result at the electronic state level.

[0048] Step 3: Calculate the adsorption energy and electron transfer of the adsorption system, and obtain the second analysis result of the adsorption system at the adsorption behavior level based on the adsorption energy and electron transfer.

[0049] It should be noted that adsorption energy refers to the energy released when gas molecules are adsorbed onto the solid surface. It reflects the thermodynamic stability of the adsorption process. The higher the adsorption energy, the more stable the adsorption of gas molecules on the solid surface. Calculating the adsorption energy can determine whether the adsorption is physical adsorption (relatively low adsorption energy, mainly due to van der Waals forces) or chemical adsorption (relatively high adsorption energy, involving the formation of chemical bonds), as well as understand the strength of the adsorption process.

[0050] In the adsorption system, electron transfer refers to the movement of electrons between gas molecules and adsorbents (such as metal-modified BN nanotubes). When gas molecules are adsorbed onto the surface of the adsorbent, electrons may be transferred from one side to the other due to factors such as the difference in electronegativity of the atoms on both sides and the characteristics of the electronic structure, thereby changing the electronic structure and chemical properties of both sides. This is very important for understanding the chemical reactions and physical changes during the adsorption process.

[0051] This step can be used to analyze the adsorption system from the perspective of adsorption behavior, clarify the stability of adsorption, the type of adsorption (physical adsorption or chemical adsorption), and the transfer of electrons during the adsorption process, so as to have a more comprehensive understanding of the adsorption process.

[0052] The calculation of adsorption energy in this step can be achieved by comparing the total energy difference of the system before and after adsorption. When gas molecules are adsorbed onto metal-modified BN nanotubes, the total energy of the system will change, and this energy difference is the adsorption energy. For the calculation of electron transfer, the transfer of electrons from gas molecules to metal-modified BN nanotubes or vice versa can be analyzed by quantum mechanical calculation methods based on factors such as the difference in atomic electronegativity and the overlap of molecular orbitals. The adsorption type can be determined based on the size of the adsorption energy. A higher adsorption energy may be chemical adsorption, and a lower adsorption energy may be chemical adsorption or an adsorption type between the two. Combined with the electron transfer situation, the various characteristics of the adsorption system at the adsorption behavior level can be further analyzed to obtain the second analysis result.

[0053] Step 4: Calculate the molecular orbital changes of the adsorption system, and perform consistency analysis on the first analysis result and the second analysis result based on the molecular orbital changes to obtain the adsorption performance and electronic behavior analysis results of the adsorption system when the decomposition product model acts on the metal-modified BN nanotube model.

[0054] It should be noted that molecular orbitals are wave functions that describe the motion state of electrons in molecules. In the adsorption system, after gas molecules are adsorbed onto metal-modified BN nanotubes, the electronic structure of the molecules will change, which is manifested in changes in the energy level, shape, and overlap of the molecular orbitals. By calculating the changes in molecular orbitals, we can gain a deeper understanding of the impact of the adsorption process on the electronic structure of the molecule, as well as the relationship between this change and other properties of the adsorption system (such as electronic energy band structure, adsorption energy, etc.).

[0055] By analyzing the changes in molecular orbitals and comparing the consistency with the results of the first two steps, the adsorption performance and electronic behavior analysis results of the adsorption system are comprehensively and accurately obtained, and the overall performance of the adsorption system in the physical and chemical process is comprehensively evaluated.

[0056] Quantum mechanics calculation methods (such as DFT) are also used to calculate the changes in molecular orbitals. By analyzing the energy level movement of molecular orbitals before and after adsorption, changes in the degree of orbital overlap, etc., we can gain a deeper understanding of the impact of the adsorption process on the molecular electronic structure. These molecular orbital changes are then analyzed for consistency with the first analysis results (based on the electronic band structure and state density) and the second analysis results (based on adsorption energy and electron transfer). For example, if the changes in the electronic state distribution caused by the molecular orbital changes are consistent with the results in the electronic band structure analysis, and the molecular orbital changes match the adsorption behavior reflected by the adsorption energy and electron transfer, then the analysis results can be considered consistent, thereby more accurately obtaining the adsorption performance (such as adsorption stability, adsorption capacity, etc.) and electronic behavior (such as electron transfer direction, range of electron activity in the adsorption system, etc.) analysis results.

[0057] This embodiment provides a gas sensing analysis method based on metal-modified BN nanotubes. The entire process is based on quantum mechanics calculation methods, especially density functional theory (DFT) and its related extension methods. First, a C4F7N decomposition product model and a metal-modified BN nanotube model are constructed, which is the basis. Then, DFT is used to calculate important physical and chemical parameters such as the electronic band structure, state density, adsorption energy, electron transfer, and molecular orbital changes of the adsorption system. These parameters reflect the characteristics of the adsorption system from the electronic state level, adsorption behavior level, and molecular electronic structure level. Finally, the analysis results at different levels are comprehensively compared through consistency analysis to obtain comprehensive and accurate adsorption performance and electronic behavior analysis results of the adsorption system.

[0058] This embodiment focuses on multiple aspects of the adsorption system, and conducts a comprehensive analysis from multiple levels, such as the electronic state level, the adsorption behavior level, and the molecular electronic structure level. By calculating different physical and chemical parameters and performing consistency analysis, the overall performance and behavior of the adsorption system can be understood more comprehensively and accurately, which is relatively rare in previous gas-sensitive sensing analysis methods. In addition, through consistency analysis, the analysis results at different levels are mutually verified and comprehensively evaluated, which improves the reliability and accuracy of the analysis results, thereby obtaining adsorption performance and electronic behavior analysis results of the adsorption system that are more in line with the actual situation.

[0059] In one embodiment, for the BN nanotube model, the metal atoms used as metal modification include: cobalt Co, rhodium Rh, or a combination of cobalt Co and rhodium Rh.

[0060] Cobalt is a transition metal element with multiple oxidation states, the most common of which are +2 and +3. Its atomic structure characteristics enable it to change the electronic structure and surface properties of BN nanotubes by transferring or sharing electrons when combined with BN nanotubes for modification. For example, cobalt atoms can provide empty d orbitals to form coordination bonds or other chemical bonds with atoms in BN nanotubes, thereby affecting the adsorption performance of BN nanotubes for gas molecules and electronic conductivity.

[0061] Rhodium is also a transition metal, and it mainly exists in the +3 oxidation state. It is relatively stable in chemical properties, but has unique properties in catalysis and other aspects. When used to modify BN nanotubes, rhodium atoms can interact with BN nanotubes by virtue of their own electronic structure characteristics, such as unfilled d orbitals, which may enhance the adsorption capacity of BN nanotubes for specific gases, change their electronic state density distribution, and thus give BN nanotubes new physical and chemical properties.

[0062] In one embodiment, the decomposition product model of the environmentally friendly insulating gas C4F7N includes: a carbon tetrafluoride CF4 gas model and a carbon difluoride monoxide COF2 gas model.

[0063] CF4 is a relatively stable compound, and its molecule is a tetrahedral structure, with the central carbon atom (C) connected to four fluorine atoms (F) by covalent bonds. It is a colorless, tasteless, and odorless gas at room temperature and pressure, and has a low boiling point, mainly because the intermolecular force is a weak van der Waals force. The chemical bond characteristic of CF4 is that the C-F bond has a strong polarity, and because the fluorine atom has a strong electronegativity, the electron cloud is biased toward the fluorine atom. In the C4F7N decomposition product model, the appearance of CF4 may have an impact on subsequent gas-sensitive sensing analysis. For example, its adsorption with metal-modified BN nanotubes may be mainly based on van der Waals forces, and its molecular structure and electronic structure will affect the electron transfer and energy changes during the adsorption process.

[0064] The structure of the COF2 molecule can be roughly described as a planar triangle, with the central carbon atom (C) connected to an oxygen atom (O) and two fluorine atoms (F), where the carbon atom forms a double bond with the oxygen atom and is connected to each fluorine atom by a single bond. It is also a colorless gas at room temperature and pressure, but may have a slight odor. The chemical bond characteristics of COF2 are that the C-O double bond consists of a σ bond and a π bond, and both the C-F bond and the C-O bond have a certain polarity, making the molecule as a whole have a significant polarity. In the C4F7N decomposition product model, the presence of COF2 makes the adsorption process more complicated, because its polar molecular structure may produce a stronger interaction with the metal-modified BN nanotubes, such as through electrostatic attraction, and its double bond structure makes it more active in chemical reactivity than CF4, which may make it easier to transfer electrons, form or break chemical bonds during the adsorption process.

[0065] In one embodiment, the metal-modified BN nanotube model is constructed according to the following steps:

[0066] (1) Based on density functional theory, the exchange and correlation of electrons in the metal-modified BN nanotube model are approximated.

[0067] Density functional theory is used to perform all spin polarization calculations in this example in the quantum mechanics calculation tool, and the Perdew-Burke-Ernzerhof (PBE) function of the generalized gradient approximation method (GGA) is selected to approximate the exchange and correlation of electrons. The PBE functional performs well in calculating the structure and properties of materials. It is widely used in dealing with various material systems, such as metals, semiconductors, insulators, and molecular systems. When calculating structural parameters such as lattice constants and elastic constants of solid materials, the PBE functional can give results that are consistent with experimental values. In the study of molecular adsorption, the PBE functional can better describe the interaction between the adsorbed molecules and the substrate, as well as the electron transfer during the adsorption process.

[0068] (2) Eliminate the relativistic effects of metal atoms in the metal-modified BN nanotube model after approximate treatment.

[0069] In order to ensure that the obtained model is in a stable state and facilitate subsequent calculations and analysis, DFT Semi-core Pseudopots (DSPP) is selected to eliminate the relativistic effect of Co atoms in the kernel processing. DSPP is a pseudopotential method used to simplify the treatment of atomic electronic structure in DFT calculations. When dealing with systems containing heavy atoms (such as transition metal atoms Co), considering all electrons (including inner-shell electrons) will make the calculation extremely complex and computationally intensive. DSPP replaces the complex potential of semi-core electrons (electronic states between the inner and outermost electrons of an atom) with pseudopotentials, greatly reducing the number of electrons that need to be considered, thereby significantly reducing the computational cost. At the same time, for heavy atoms, the relativistic effect will have a significant impact on the electronic structure, such as increasing the mass of electrons and shrinking orbits. These changes will affect the energy and distribution of electrons. DSPP can effectively eliminate the relativistic effect of Co atoms in the kernel processing, making the calculated electronic structure more consistent with the actual physical and chemical process, ensuring that the model is in a stable state, and facilitating the subsequent accurate calculation of various physical and chemical properties of the system, such as the geometric structure and adsorption performance.

[0070] (3) The p orbital double value plus polarization function is used as the atomic orbital basis set to calculate the hydrogen bonds in the metal-modified BN nanotube model.

[0071] The p-orbital Double-Numerical plusPolarization function (DNP) is used as the atomic orbital basis set to make the calculation of hydrogen bonds more accurate.

[0072] As an atomic orbital basis set, DNP plays an important role in calculating the electronic structure and related properties of molecules and materials. It is a relatively sophisticated basis set that further improves the description of electronic wave functions by adding polarization functions on the basis of dual numerical basis sets. When dealing with systems involving hydrogen bonds, the DNP basis set can more accurately capture the changes in the distribution of electrons and the interactions between atoms during the formation of hydrogen bonds.

[0073] (4) Density functional theory-dispersion correction was performed on the metal-modified BN nanotube model using a semi-empirical dispersion correction method.

[0074] The DFT-D correction of the Co-modified BN nanotube model was performed using the Grimme method.

[0075] The Grimme method is a commonly used semi-empirical dispersion correction method for considering the van der Waals forces (dispersion forces) between molecules in DFT calculations. In traditional DFT calculations, the van der Waals forces between molecules are often not handled well, and this force plays an important role in many systems (such as gas adsorption, molecular aggregation, etc.). The Grimme method considers the van der Waals interactions between molecules by adding an empirical dispersion correction term to the DFT energy expression. For the Co-modified BN nanotube model, when studying its interaction with other molecules (such as gas molecules), DFT-D correction can more accurately describe the adsorption energy, intermolecular distance and other properties of the model.

[0076] (5) The van der Waals force correction method based on density functional theory is used to correct the intermolecular forces and long-range interactions of the metal-modified BN nanotube model.

[0077] In the framework of density functional theory, van der Waals force correction methods are designed to make up for the shortcomings of traditional DFT calculations in dealing with intermolecular van der Waals forces and long-range interactions. Intermolecular van der Waals forces include dispersion forces, inductive forces, and orientation forces, which play a key role in many physical and chemical processes of material systems (such as gas adsorption, molecular self-assembly, etc.). Van der Waals force correction methods such as the Grimme method can more accurately describe intermolecular interactions by adding specific correction terms to the DFT energy expression.

[0078] (6) Using the set global orbital cutoff radius and the set smearing area, the single-layer structure is smoothly converged to obtain the metal-modified BN nanotube single-layer structure, thereby completing the construction of the metal-modified BN nanotube model.

[0079] Static calculations with a self-consistent field convergence accuracy of 10^-6 Ha were used, and the global orbital cutoff radius and 0.005Ha smearing were used to ensure smooth convergence of the entire system. According to the principle of eliminating boundary effects by periodic boundary conditions, a BN nanotube monolayer was constructed in a 4×4×1 supermonomer, containing 16 B atoms and 16 N atoms, and a vacuum gap was used to avoid mutual influence between adjacent layers.

[0080] Self-consistent field (SCF) calculation is a key step in DFT calculation, which solves the wave function and energy of electrons through continuous iteration until the set convergence criteria are reached.

[0081] In DFT calculations, the global orbital cutoff radius is used to limit the extension range of the electron wave function, avoiding the calculation of unnecessary long-distance electron wave functions, thereby reducing the amount of calculation. Smearing is a technique used to handle the transition between occupied and unoccupied electron states. By setting a certain smearing area (such as 0.005Ha), the calculation process can be smoother and numerical instability can be avoided.

[0082] The Co-BN nanotube monolayer is defined as the modification of Co atoms on the surface of the original BN nanotube, on which there are four possible modification sites, namely TH (located above the center of the hexagonal ring of the BN nanotube), TB (located on the top of the B atom), TN (located on the top of the N atom) and TB (the bridge between two N atoms). In one embodiment, the binding energy (E) of the Co atom modified onto the BN nanotube monolayer is b ) The formula is defined as:

[0083]

[0084] E Co-BNNT 、E Co and E BNNT represent the energies of Co-BN nanotube monolayer, Co atoms and intrinsic BN nanotube monolayer, respectively.

[0085] In one embodiment, before applying the decomposition product model to the BN nanotube model to form an adsorption system, the method further includes:

[0086] The gas molecular structure of the decomposition product model and the single-layer structure of the BN nanotube model were geometrically optimized to obtain the optimized molecular structure and single-layer structure, and analysis was performed based on the optimized molecular structure and single-layer structure.

[0087] In this embodiment, the geometric optimization of the gas molecular structure of the decomposition product model and the single-layer structure of the BN nanotube model is to optimize the structures of the intrinsic BN nanotube single-layer film, Co atoms, and CF4 and COF2 gas molecules respectively.

[0088] The intrinsic BN nanotube monolayer structure is composed of a hexagonal pattern of cross-arranged B atoms and N atoms. The BN bond length of the unmodified BN nanotube monolayer structure is 1.47Å. The CF4 gas molecule has a regular tetrahedral spatial configuration. The C atom at the center is bonded to the remaining four F atoms by σ bonds, so that the FCF structure forms an angle of 109.49° and a CF bond length of 1.34Å. The COF2 gas molecule belongs to a three-dimensional spatial structure. The bond lengths of the CF bond and the C=O bond are 1.34Å and 1.18Å respectively, and the angle of the O=C=O structure is 126.19°. The planar triangular structure and high electronegativity make the COF2 gas molecule very stable.

[0089] In a further embodiment, for metal modification atoms such as Co, the preferred modification site is tracked as the TH site (located above the center of the hexagonal ring of the BN nanotube), and the Co atom can be placed at the TH site for geometry optimization.

[0090] In a further embodiment, the optimized Co atom forms three bonds with three adjacent N atoms, resulting in a certain degree of structural distortion in each system, but in the optimized configuration, the lengths of the three Co-N bonds are equal to some extent. The average length of the Co-B bonds in the Co-modified BN nanotube model is 1.86 Å.

[0091] After obtaining the most stable Co-BN nanotube monolayer structure, in order to study the adsorption behavior of C4F7N decomposition gases CF4 and COF2 on them, the initial distance of the gas molecules close to the Co atoms of the Co-BN nanotube monolayer was selected as a specific value. All possible positions for gas molecule adsorption were considered. After completing the geometry optimization, some gas molecules that were not determined to be in the most stable configuration were significantly displaced and moved to the position determined to have the highest stability. In one embodiment, the most stable configuration (MSC) of gas molecule adsorption is determined by the lowest energy (E ads ) is determined and calculated as follows:

[0092]

[0093] E Co-BNNT / gas is the total energy of the adsorption system, and E Co-BNNT and E gas are the energies of the Co-BN nanotube monolayer and the gas molecules, respectively. By using the Mulliken atomic charges method to analyze the atomic and molecular charge transfer of Co atoms and gas molecules, the above calculations will not be affected by the basic calculation set, thus ensuring good accuracy of the results. According to the known definition, negative values ​​represent the electron acceptance behavior of the analyzed Co atoms or gas molecules.

[0094] In one embodiment, the calculation of the density of states distribution of C4F7N discharge decomposition gas molecules on the Co-doped BN nanotube monolayer includes a total density of states (TDOS) distribution and a partial-wavelength density of states (PDOS) distribution.

[0095] For the adsorption system, it can be seen that when CF4 and COF2 gas molecules are adsorbed on the Co-doped BN nanotube monolayer, the total density of states (TDOS) distribution of the system changes significantly. Specifically, the TDOS curve after adsorption moves to the right as a whole, indicating an increase in electronic states near the Fermi level, which is usually associated with an increase in the conductivity of the system. This phenomenon shows that the introduction of Co atoms enhances the chemical activity of the BN nanotube monolayer, thereby improving its adsorption capacity for C4F7N decomposition gas molecules. More specifically, after the adsorption of COF2 gas molecules, the TDOS distribution of the Co-BN nanotube monolayer shows a continuous new peak in the energy range of -10eV to -5eV. This may be due to the strong interaction between the highly active oxygen atoms in the COF2 molecules and the Co atoms, resulting in a significant change in the electronic state. This change is the most significant in all adsorption systems, suggesting that significant charge transfer may have occurred during the adsorption process. In addition, on the right side of the Fermi level, the TDOS distribution of the Co-BN nanotube monolayer decreases after the adsorption of CF4 gas. This indicates that the number of electronic states above the Fermi level is reduced, which may be due to the redistribution of electronic states caused by the transfer of electrons from CF4 molecules to the Co-BN nanotube monolayer during the adsorption process.

[0096] In order to understand the electronic behavior of Co-BN nanotube monolayer when adsorbing CF4 and COF2 gases, further PDOS analysis was performed, and it was found that the 3d orbital of Co atom has a great influence on the respective TDOS distribution due to its metal activity. From the PDOS distribution of each adsorption system, it can be seen that the d orbital of Co atom is highly hybridized with the p orbital of C or O atom in the adsorbed CF4 gas molecule and COF2 gas molecule. This finding confirms the stable formation of Co-C or Co-O bonds in the Co-BN nanotube adsorption system.

[0097] These orbital interactions suggest that CF4 and COF2 gases have ideal adsorption on the Co-BN nanotube monolayer, leading to electron redistribution on the substrate and thus affecting its conductivity to a great extent.

[0098] This example mainly focuses on the state density distribution (including TDOS and PDOS) analysis of C4F7N discharge decomposition gas molecules (CF4 and COF2) on Co-doped BN nanotube monolayers. By observing the movement of the TDOS curve, the change in peak value, etc., the relationship between the change in electronic state and the system conductivity, chemical activity, adsorption capacity, and charge transfer is inferred; the relationship between orbital hybridization and chemical bond formation is obtained through PDOS analysis, thereby forming the first analysis result.

[0099] In one embodiment, the adsorption behaviors of CF4 and COF2 gas molecules on the most stable Co-BN nanotube monolayer structure are analyzed based on adsorption energy and electron transfer.

[0100] For the adsorption of COF2 molecules on Co-modified surfaces, the preferred configuration is to approach Co atoms through the O atoms of COF2 molecules, which may be because the unique molecular configuration of COF2 makes the O atoms in it more multivalent. Table 1 lists the adsorption energy and charge transfer in the system of CF4 and COF2 gas molecules adsorbed on Co-BN nanotubes. The calculated E ads The range of QT is from -0.81 to -0.36 eV, which confirms that all Co-BN nanotube gas adsorption systems are mainly physical adsorption. The range of QT is from 0.04 e to 0.04 e, and the negatively charged gas molecules in all adsorption systems indicate the charge transfer path from Co atoms to gas molecules.

[0101] Table 1 Adsorption energy and electron transfer of gas molecules on Co-BN nanotubes

[0102]

[0103] This example analyzes the adsorption behavior of CF4 and COF2 gas molecules on the most stable Co-BN nanotube monolayer structure based on adsorption energy and electron transfer. By determining the adsorption configuration, listing the data of adsorption energy (Eads) and charge transfer (QT), judging that the adsorption type is mainly physical adsorption and clarifying the charge transfer path, the second analysis result is obtained.

[0104] In one embodiment, the molecular orbital change is represented by the highest occupied molecular orbital distribution, the lowest unoccupied molecular orbital distribution and the energy gap. The adsorption of CF4 and COF2 gases in the Co-BN nanotube monolayer was analyzed by molecular orbital analysis, and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) distribution of the adsorption system were calculated according to the molecular orbital theory. As shown in Table 2, the Eg between HOMO and LUMO was calculated to evaluate the conductivity change.

[0105] Table 2 Molecular orbitals and energy gaps before and after adsorption

[0106]

[0107] Molecular orbitals are an effective method to evaluate the probability of electron transfer between characteristic molecules and the surface of Co-BN nanotubes. In all Co-BN nanotube adsorption systems, spin-up and spin-down are symmetrical. This confirms the previous state density distribution analysis that CF4 and COF2 gas molecules become non-magnetic molecules after adsorption. At the same time, with the adsorption of gas molecules, the energy gap of the Co-BN nanotube monolayer also changes, and this change can be clearly observed in Table 2. In other words, the conductivity of the Co-BN nanotube monolayer changes after interacting with CF4 and COF2 gases. The adsorption of CF4 and COF2 gases causes the electrons in the Co-BN nanotubes to be redistributed, thereby changing the energy of HOMO and LUMO accordingly, and the changing trend of the molecular orbitals matches the energy gap.

[0108] By analyzing the above-mentioned adsorption structure, adsorption energy, charge transfer, adsorption distance, TDOS, PDOS and molecular orbital, such as the consistency analysis of the state density and molecular orbital energy gap on the conductivity analysis, the consistency analysis of the adsorption energy and state density on the adsorption capacity and type analysis, the consistency analysis of the state density, adsorption energy and molecular orbital on the charge transfer analysis, etc., the adsorption performance and electronic behavior of Co-BN nanotube monolayer for CF4 and COF2 gases were explored.

[0109] Based on the above analysis results, the following conclusions can be drawn:

[0110] The adsorption energies of Co-BN nanotube monolayers for CF4 and COF2 gases are moderate, which indicates that they are suitable gas-sensitive materials for detecting CF4 and COF2 gases.

[0111] The adsorption of CF4 and COF2 gases on the Co-BN nanotube monolayer leads to the redistribution of electrons on the substrate, which in turn greatly affects its conductivity.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas sensing analysis method based on metal-modified BN nanotubes, characterized in that: The steps include: Get pre-built decomposition product models of environmentally friendly insulating gas C4F7N and metal-modified boron nitride BN nanotube models; Calculating the electronic band structure and state density of the adsorption system formed by the decomposition product model acting on the BN nanotube model, and obtaining a first analysis result of the adsorption system at the electronic state level based on the electronic band structure and the state density; Calculating the adsorption energy and electron transfer of the adsorption system, and obtaining a second analysis result of the adsorption system at the adsorption behavior level based on the adsorption energy and the electron transfer; The molecular orbital changes of the adsorption system are calculated, and the first analysis result and the second analysis result are analyzed for consistency based on the molecular orbital changes to obtain the adsorption performance and electronic behavior analysis results of the adsorption system when the decomposition product model acts on the metal-modified BN nanotube model.

2. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: In the BN nanotube model, the metal atoms used for metal modification include cobalt Co, rhodium Rh, or a combination of cobalt Co and rhodium Rh.

3. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: The decomposition product models of the environmentally friendly insulating gas C4F7N include: carbon tetrafluoride CF4 gas model and carbon difluoride monoxide COF2 gas model.

4. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: The metal-modified BN nanotube model is constructed according to the following steps: The exchange and correlation of electrons in the metal-modified BN nanotube model are approximated based on density functional theory; Eliminating the relativistic effect of metal atoms in the BN nanotube model modified by metal after approximation treatment; The hydrogen bonds in the metal-modified BN nanotube model are calculated using p orbital double value plus polarization function as the atomic orbital basis set; Density functional theory-dispersion correction is performed on the metal-modified BN nanotube model using a semi-empirical dispersion correction method; The intermolecular forces and long-range interactions of the metal-modified BN nanotube model are corrected using a van der Waals force correction method based on density functional theory; The set global orbital cutoff radius and the set smearing area are used to perform smooth convergence of the single-layer structure to obtain the metal-modified BN nanotube single-layer structure, thereby completing the construction of the metal-modified BN nanotube model.

5. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: Before the decomposition product model acts on the BN nanotube model to form the adsorption system, the method further includes: The gas molecular structure of the decomposition product model and the single-layer structure of the BN nanotube model are geometrically optimized to obtain optimized molecular structures and single-layer structures, and analysis is performed based on the optimized molecular structures and single-layer structures.

6. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 5, characterized in that: In the cobalt (Co)-modified BN nanotube model, the cobalt (Co) atom is placed above the center of the hexagonal ring of the BN nanotube, and the lengths of the Co-N bonds are all equal, with an average length of the Co-B bond of 1.86Å.

7. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 5, characterized in that: The binding energy of Co atoms modified onto the BN nanotube monolayer is calculated using the following formula: In the formula, E Co-BNNT 、E Co and E BNNT represent the energies of Co-BN nanotube monolayer, Co atoms and intrinsic BN nanotube monolayer, respectively.

8. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 6, characterized in that: The energy of the most stable configuration of gas molecules adsorbing cobalt Co atoms modified onto the BN nanotube monolayer is calculated using the following formula: E Co-BNNT / gas is the total energy of the adsorption system, and E Co-BNNT and E gas are the energies of the Co-BN nanotube monolayer and the gas molecules, respectively.

9. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: The state density includes: total state density and partial wave state density; The total density of states is used to macroscopically describe the overall electronic structure of the adsorption system; The partial-wave state density is used to decompose the total state density according to the contribution of atomic orbitals or specific atoms, and to describe the contribution of each decomposed part to the total state density.

10. The gas sensing analysis method based on metal-modified BN nanotubes according to claim 1, characterized in that: The molecular orbital changes are represented by the highest occupied molecular orbital distribution, the lowest unoccupied molecular orbital distribution and the energy gap.

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