A NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide and its application

Abstract

This invention discloses an Al-doped thin-layer manganese dioxide (MnO) NO2 adsorption-sensing structure and its applications. The Al-doped MnO NO2 adsorption-sensing structure comprises a two-dimensional manganese dioxide monolayer as a substrate, to which Al is doped either through modification or substitution doping at a concentration of 2% to 4%. The Al-modified doped structure forms a strong adsorption interface with NO2, dominated by ionic interactions, suitable for NO2 capture, enrichment, immobilization, and one-time detection. The Al-substituted doped structure forms a gas-sensitive interface with reversible adsorption-desorption, suitable for high-sensitivity NO2 gas detection. Depending on the Al doping method, the adsorption-sensing structure can be used for NO2 gas detection, capture, enrichment, and immobilization applications.

Description

Technical Field

[0001] This application relates to the field of gas adsorption and gas-sensitive detection technology, and in particular to a NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide and its application. Background Technology

[0002] With the acceleration of industrialization and the continuous growth of motor vehicle ownership, nitrogen oxides (NOx) have increased significantly. x Nitrogen dioxide (NO2) has become one of the major air pollutants. It is a typical toxic and harmful gas, a significant precursor to photochemical smog, acid rain, and ozone, posing a serious challenge to the ecological environment and public safety. Inhaling certain amounts of NO2 can severely damage the human respiratory tract, easily causing fainting and potentially increasing the risk of asthma, chronic obstructive pulmonary disease (COPD), and cardiovascular disease. Controlling NO2 faces two core needs: real-time and sensitive monitoring of NO2 concentrations in the environment, and efficient fixation and enrichment of this toxic gas.

[0003] In the field of gas monitoring, researchers have been dedicated to developing sensors capable of accurately identifying toxic gases. Traditional chemical, optical, and electrochemical sensors generally suffer from high cost, complex structures, or poor portability. In recent years, two-dimensional layered materials (such as graphene and transition metal sulfides) have been widely studied as novel gas-sensitive materials due to their unique specific surface area and electronic properties. These materials primarily utilize the change in conductivity before and after gas adsorption to achieve sensing, offering advantages such as high sensitivity, fast response, and room-temperature operation. However, ideal sensor materials typically require gas molecules to have a moderate adsorption strength on their surface so that they can be rapidly desorbed after detection for repeated use. Conversely, in the field of gas capture and treatment, materials are required to have extremely strong chemical adsorption of gas molecules to achieve efficient capture and prevent gas escape. How to simultaneously meet the differentiated requirements of "highly sensitive reversible detection" and "efficient irreversible capture" within the same material structure through precise microstructural control remains a challenge in current materials science research.

[0004] Two-dimensional manganese dioxide (MnO) possesses a unique layered structure and abundant surface active sites. Its monolayer structure exhibits excellent chemical stability and tunable electronic properties, offering significant advantages in gas sensing and sparking considerable interest in its applications in electronic and optoelectronic devices. Currently, MnO demonstrates superior electrochemical performance and has been applied in energy storage, catalysis, and other fields. In recent years, researchers have synthesized well-structured and uniformly surfaced MnO monolayer structures using methods such as chemical exfoliation and hydrothermal synthesis, laying a solid foundation for comprehensive research combining simulation and experimental work. Existing studies on two-dimensional MnO and its doped structures mostly focus on describing macroscopic properties such as bandgap modulation, adsorption energy changes, or overall conductivity changes to determine gas adsorption. However, systematic studies on the effects of different doping methods on gas sensing characteristics such as interfacial bonding types, adsorption reversibility and sensitivity, and response recovery time for Al-doped MnO structures are relatively scarce. Furthermore, the basis for structural optimization for high-intensity adsorption capture / enrichment and single-use detection applications remains insufficient.

[0005] The shortcomings of existing technologies and research include:

[0006] 1. There is limited research on Al-doped manganese dioxide, and there is a lack of systematic research and summarization on the effects of different doping methods on NO2 adsorption strength, adsorption reversibility and electrical response characteristics.

[0007] 2. The electronic structure analysis of interfacial bonding characteristics is insufficient. There are few technical solutions that comprehensively adopt ELF, mIGM, Promolecular-RDG, DOS and other methods to accurately distinguish the interaction type of gas-material interface from the microscopic bonding nature of ionic or covalent bonds.

[0008] 3. The correspondence between microscopic mechanisms and macroscopic performance is insufficient. In the existing technology, a theoretical framework for unified analysis of "interface bonding type" and "macroscopic gas-sensitive index" has not yet been established.

[0009] Therefore, in this application, based on simulation calculation results, the NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide was studied, and its feasibility in NO2 adsorption, gas sensing detection and capture applications was verified. Summary of the Invention

[0010] The purpose of this invention is to provide an Al-doped thin-layer manganese dioxide NO2 adsorption-sensing structure and its application, in order to improve the shortcomings and defects of the prior art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] This invention provides an NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide, comprising a two-dimensional manganese dioxide substrate. The two-dimensional manganese dioxide substrate has a monolayer structure, which is an O-Mn-O three-atom layer structure with a thickness of 1.963 Å. The two-dimensional manganese dioxide substrate is doped with Al element, and the Al element in the two-dimensional manganese dioxide substrate is doped by modification doping or substitution doping, with a doping concentration ratio of 2% to 4%. The Al-doped thin-layer manganese dioxide substrate constitutes an adsorption and gas-sensing response functional layer for NO2 gas, which is used to adsorb NO2 gas and cause a detectable change in electrical signal during the adsorption process, so as to realize the adsorption and detection of NO2 gas.

[0013] The Al element is incorporated into any surface of the two-dimensional manganese dioxide substrate in a modified doping manner.

[0014] The Al element is introduced into the two-dimensional manganese dioxide substrate by substitution doping, replacing the lattice positions occupied by Mn or O atoms in the two-dimensional manganese dioxide substrate lattice. The Al element is preferably introduced by substitution doping to replace the manganese atoms in the middle layer of the two-dimensional manganese dioxide substrate.

[0015] The Al-modified doped two-dimensional manganese dioxide substrate forms a strong chemisorption interface with NO2 gas, and the adsorption process of NO2 under room temperature conditions is irreversible, making it suitable for the capture, enrichment and immobilization of NO2 gas.

[0016] The Al-substituted doped two-dimensional manganese dioxide substrate forms a chemisorption interface with reversible adsorption-desorption between itself and NO2 gas, which can be used for repeatable NO2 gas sensing detection.

[0017] The modified doped configuration produces a detectable electrical response to NO2 gas at room temperature, with a response sensitivity greater than 7.5.

[0018] The substitution-doped configuration produces a detectable electrical response to NO2 gas at room temperature, with a response sensitivity greater than 100.

[0019] Preferably, the doping concentration of Al element incorporated into the two-dimensional manganese dioxide substrate in a modified doping manner is 3.5%.

[0020] Preferably, the doping concentration of Al element incorporated into the two-dimensional manganese dioxide substrate in a substitution doping manner is 3.7%.

[0021] Preferably, the Al element is incorporated into the top atomic layer of the two-dimensional manganese dioxide substrate in a modified doping manner.

[0022] Preferably, the Al element replaces the lattice positions of manganese atoms in the intermediate layer of the two-dimensional manganese dioxide substrate by substitution doping.

[0023] Preferably, the Al-modified doped manganese dioxide substrate forms a chemisorption with an adsorption energy of -3.689 eV with NO2 molecules.

[0024] Preferably, the Al-substituted doped manganese dioxide substrate forms a chemisorption with an adsorption energy of -1.133 eV with NO2 molecules.

[0025] Preferably, the Al-modified doped manganese dioxide substrate has a room temperature response sensitivity of up to 7.68 to NO2 gas.

[0026] Preferably, the Al-substituted doped manganese dioxide substrate has a room temperature response sensitivity of up to 114.73 to NO2 gas.

[0027] Preferably, the Al-substituted doped manganese dioxide substrate exhibits a response recovery time as low as 8.81 × 10⁻⁶ for NO₂ detection under mild heating conditions (358 K). -1 s.

[0028] Compared with the prior art, the NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide provided by the present invention has the following beneficial effects, including:

[0029] 1. This invention constructs a strong adsorption interface and a reversible gas-sensitive interface in thin-layer manganese dioxide through two methods: Al modification doping and Al substitution doping. The modified doping structure is suitable for NO2 capture, enrichment and one-time detection, while the substitution doping structure is suitable for repeatable NO2 gas-sensitive detection.

[0030] 2. This invention reveals the influence of different Al doping methods on the NO2 adsorption mechanism and gas sensing performance, and clarifies the structure-performance relationship between modified doping and strong adsorption, and substitution doping and moderate adsorption strength, high sensitivity and easy recovery.

[0031] 3. This invention proposes a NO2 adsorption-sensing structure that can be selected according to application requirements: the modified doped structure is used for NO2 capture, enrichment and one-time detection, and the replacement doped structure is used for reversible and highly sensitive NO2 gas detection. Attached Figure Description

[0032] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings:

[0033] Figure 1 A simulation flowchart of a NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide and its application is shown.

[0034] Figure 2 A schematic diagram of the geometrically optimized intrinsic manganese dioxide structure and doping sites is shown, including a top view and a side view.

[0035] Figure 3 a~f show schematic diagrams of the geometrically optimized manganese dioxide monolayer after Al element is modified and substituted at different sites. Figure 3 a~c represents Al at sites H and T. Mn T O Modified and doped manganese dioxide monolayer structure Figure 3 d~f represents the manganese dioxide monolayer structure after Al substitution and doping at sites T1, T2, and T3.

[0036] Figure 4 The band structure diagrams of intrinsic manganese dioxide monolayers, Al-modified doped manganese dioxide monolayers, and Al-substituted doped manganese dioxide monolayers are shown. Figure 4 a is the band structure diagram of an intrinsic manganese dioxide unimolecular molecule. Figure 4 b is the band structure diagram of the H-Al-MnO2 modified and doped structure. Figure 4 c is the band structure diagram of the T2-Al-MnO2 substitution doped structure.

[0037] Figure 5 The density of states diagrams of geometrically optimized Al-modified and Al-substituted doped manganese dioxide monolayers versus intrinsic manganese dioxide are shown. Figure 5 a is the total density of states diagram of the H-Al-MnO2 modified and doped structure and the intrinsic structure. Figure 5 b is the total density of states diagram of the T2-Al-MnO2 substituted doped structure and the intrinsic structure. Figure 5 c is the partial density of states diagram of the H-Al-MnO2 modified and doped structure. Figure 5 d is the partial density of states diagram of the T2-Al-MnO2 substitution-doped structure.

[0038] Figure 6 The electronic localization function (ELF) plots of Al-modified and Al-substituted doped manganese dioxide monolayers are shown. Figure 6 a is the ELF diagram of the Al-modified doped monolayer manganese dioxide structure. Figure 6 b is the ELF diagram of the Al-substituted doped monolayer manganese dioxide structure.

[0039] Figure 7 The RDG plots based on promolecular density for Al-modified and Al-substituted doped manganese dioxide monolayers are shown, including top and front views. Figure 7 a is the RDG diagram of the Al-modified doped monolayer manganese dioxide structure based on the promolecular density. Figure 7 b is the RDG diagram of the Al-substituted doped monolayer manganese dioxide structure based on the Promolecular density.

[0040] Figure 8 The bond order analysis diagrams of Al-modified and Al-substituted doped manganese dioxide monolayers are shown.

[0041] Figure 9 The geometrically optimized NO2 molecular structure model is shown.

[0042] Figure 10 The diagram shows the optimal structure for NO2 molecule adsorption on the surface of intrinsic manganese dioxide monolayer, Al-modified doped and Al-substituted doped manganese dioxide monolayer. Figure 10 a represents the intrinsic manganese dioxide monolayer adsorption structure. Figure 10 b is a NO2-H-Al-MnO2 modified and doped adsorption structure. Figure 10 c is a NO2-T2-Al-MnO2 substitution-doped adsorption structure.

[0043] Figure 11 The differential charge density (CDD) is shown when Al-modified and Al-substituted doped manganese dioxide monolayers adsorb NO2 gas molecules. Figure 11 a is a CDD with a NO2-H-Al-MnO2 modified and doped adsorption structure. Figure 11 b is a CDD with a NO2-T2-Al-MnO2 substituted doped adsorption structure.

[0044] Figure 12 The electron localization function (ELF) of intrinsic manganese dioxide monolayers, Al-modified doped and Al-substituted doped manganese dioxide monolayers adsorbing NO2 gas molecules is shown. Figure 12 a represents an intrinsic manganese dioxide monolayer adsorption structure of ELF. Figure 12 b is an ELF with a NO2-H-Al-MnO2 modified and doped adsorption structure. Figure 12 c represents an ELF with a NO2-T2-Al-MnO2-substituted doped adsorption structure.

[0045] Figure 13 An improved independent gradient model (mIGM) analysis of the adsorption of NO2 gas molecules in intrinsic manganese dioxide monolayers and Al-modified and Al-substituted manganese dioxide monolayers is shown, including top and front views. Figure 13 a represents mIGM, which is the intrinsic manganese dioxide monolayer adsorption structure. Figure 13 b represents mIGM with a NO2-H-Al-MnO2 modified and doped adsorption structure. Figure 13 c represents mIGM with a NO2-T2-Al-MnO2 substitution-doped adsorption structure.

[0046] Figure 14 The analysis of NO2 gas molecules adsorbed by intrinsic manganese dioxide monolayers and Al-modified and Al-substituted manganese dioxide monolayers is shown using a reduced density gradient model based on promolecular density, including top and front views. Figure 14 a is a diagram of the reduced density gradient model based on promolecular density for the intrinsic manganese dioxide monolayer adsorption structure. Figure 14 b is a diagram of the reduced density gradient model based on promolecular density for the NO2-H-Al-MnO2 modified doped adsorption structure. Figure 14 c represents the reduced density gradient plot based on Promolecular density for the NO2-T2-Al-MnO2 substituted doped adsorption structure.

[0047] Figure 15 The band structure diagrams of the adsorption of NO2 gas molecules by Al-modified and Al-substituted doped manganese dioxide monolayers are shown. Figure 15 a is the band structure diagram of the NO2-H-Al-MnO2 modified and doped adsorption structure. Figure 15 b is the band structure diagram of the NO2-T2-Al-MnO2 substitution-doped adsorption structure.

[0048] Figure 16 The density of states diagram of NO2 gas molecules adsorbed in an Al-modified manganese dioxide monolayer is shown. Figure 16 a is the total density of states (TDOS) diagram of the NO2-H-Al-MnO2 modified doped adsorption structure. Figure 16 b is the partial density of states (PDOS) diagram of the NO2-H-Al-MnO2 modified doped adsorption structure.

[0049] Figure 17 The density of states diagram of NO2 gas molecules adsorbed in an Al-substituted doped manganese dioxide monolayer is shown. Figure 17 a is the total density of states (TDOS) diagram of the NO2-T2-Al-MnO2 substitution-doped adsorption structure. Figure 17 b is the partial density of states (PDOS) diagram of the NO2-T2-Al-MnO2 substituted doped adsorption structure.

[0050] Figure 18 The response recovery times of Al-modified and Al-substituted doped manganese dioxide monolayers adsorbing NO2 gas molecules at different temperatures are shown. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0052] In this invention, the term "modification doping" refers to introducing Al atoms into specific sites on or near the surface of a manganese dioxide monolayer, such as the H site at the center of the hexagonal plane of the top O atom or the T site above the Mn atoms in the middle layer. Mn The top T position above the O atom O The doping method, which involves Mn–O interlayer bridge sites B1 and B2, to regulate the electronic structure and electrical properties of a manganese dioxide monolayer by forming a stable surface / near-surface interstitial configuration, is described. The term "substitution doping" refers to Al atoms occupying lattice positions in the manganese dioxide monolayer that were originally occupied by Mn or O atoms, thereby controlling the lattice and electronic structure. The substituted lattice sites can be Al atoms replacing the T1 site of the top-layer O atom, Al atoms replacing the T2 site of the middle-layer Mn atom, and Al atoms replacing the T3 site of the bottom-layer O atom. These terms should not be construed as limiting the invention. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0053] Example 1:

[0054] This application provides an NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide and its application. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide includes a two-dimensional manganese dioxide substrate doped with Al. The Al doping method in the two-dimensional manganese dioxide substrate is modification doping and substitution doping. The Al modification doping concentration is 2% to 4%. The effectiveness of the NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide is calculated using simulation. The calculation process includes the following steps:

[0055] Step S1: For the toxic and harmful gas NO2, a molecular structure model is established using Materials Studio, and the geometry of the gas molecules is optimized.

[0056] Step S2: Construct a monolayer structure of manganese dioxide and perform geometry optimization to obtain the most stable thin-layer manganese dioxide.

[0057] Step S3: Modify and substitute intrinsic manganese dioxide with Al element at multiple sites and perform geometry optimization to obtain the most stable doping configuration under different doping methods.

[0058] Step S4: Calculate the optimal adsorption structure of NO2 on the surface of Al-modified and Al-substituted doped manganese dioxide monolayers using different placement methods;

[0059] Step S5: By calculating its electrical properties, the adsorption and gas-sensitive response mechanism of Al-modified and Al-substituted doped manganese dioxide monolayers for NO2 is revealed at the microscopic level, and the response sensitivity and response recovery time after NO2 adsorption are determined at the macroscopic level.

[0060] In this embodiment, the specific parameter settings for gas molecule geometry optimization in step S1 are as follows:

[0061] The CASTEP module was used to build a structural model of gas molecules in a periodic box, and single-point energy calculations were performed, with the energy tolerance set to 1×10⁻⁶. -5 The convergence tolerances for maximum force and maximum displacement are 0.01 eV / Å and 1×10 eV / Å, respectively. -3 Å.

[0062] In this embodiment, the method for establishing a manganese dioxide monolayer in step S2 is as follows:

[0063] A single-cell structure of a manganese dioxide monolayer was obtained by cutting the surface of a manganese dioxide crystal (001), and a 3×3×1 supercell was established as the adsorption substrate structure. It is a 3-atom-layer structure containing 18 O atoms and 9 Mn atoms, with a lattice constant of 8.56 Å×8.56 Å. The thickness of the monolayer structure is 1.963 Å. The optimal thickness of the vacuum layer of the supercell structure is 15 Å to avoid the interaction between adjacent molecular layers.

[0064] In this embodiment, step S3 is used to determine the most stable doping configuration of Al element under both modification and substitution doping methods. The specific method is as follows:

[0065] Al atoms were selected to perform site-specific doping on a manganese dioxide monolayer using two different doping methods: modification doping and substitution doping. Modification doping involves adsorbing Al atoms onto specific sites (H, T) on the surface of a two-dimensional manganese dioxide substrate. Mn T O By replacing atoms at different doping sites (T1, T2, T3), a doping concentration of 3.5% (1 / 28 atomic ratio) was achieved. By replacing atoms at different doping sites (T1, T2, T3), a doping concentration of 3.7% (1 / 27 atomic ratio) was achieved. By comparing the influence of different doping structures on the bond length of surrounding atoms and calculating their formation energy, binding energy, and cohesive energy, the doping structure that is easiest to form and has higher stability was determined. The structural stability was further ensured by using the density of states, the reduced density gradient RDG model based on Promolecular density, Mulliken population analysis, and bond order calculation.

[0066] In this embodiment, steps S2 and S3 perform geometric optimization on the intrinsic and Al-doped manganese dioxide monolayers. The specific parameter settings during optimization are as follows:

[0067] First-principles calculations were performed using a CASTEP package, with an energy tolerance of 1×10⁻⁶. -5 The convergence tolerances for maximum force and maximum displacement are set to 0.01 eV / Å and 1×10 eV, respectively. -3 The exchange correlation energy between electrons was corrected using the Perdew-Burke-Ernzerhof (PBE) function of the generalized gradient approximation (GGA). After convergence testing, structural relaxation was performed on the Brillouin zone (BZ) integral using a 6×6×1 k-point grid, and property calculations were performed using a 12×12×1 k-point grid. The OTFG-Ultrasoft pseudopotential was used, and the cutoff energy was set to 580 eV. In addition, for the system of unpaired electrons, spin polarization calculations were introduced. Each unit cell of this two-dimensional material has a magnetic moment of 3 μB, which is mainly contributed by Mn atoms. For the 3d orbitals of the transition metal Mn, the Hubbard-U correction was considered, with an effective U value of 3.9 eV, to more accurately describe the strong correlation effect of electrons in the MnO2 system.

[0068] In this embodiment, step S4 simulates the adsorption process of NO2 gas molecules on the surface of Al-doped modified manganese dioxide monolayer. The specific steps are as follows:

[0069] In the Geometry Optimization task, all other settings are the same as in steps S2 and S3. In addition, TS's DFT-D is used to accurately describe the long-range van der Waals interactions between the manganese dioxide monolayer and the gas.

[0070] In this embodiment, step S4, which determines the optimal adsorption structure corresponding to the Al-modified doped and Al-substituted doped manganese dioxide monolayer structures, is as follows:

[0071] First, the adsorption structure was geometrically optimized. NO2 approached the surface of the Al-doped manganese dioxide monolayer in different ways, mainly perpendicular or horizontally to the manganese dioxide monolayer. The adsorption energy was then calculated. , transfer charge Size and adsorption distance Determine the optimal adsorption structure. Adsorption energy. The calculation method is as follows:

[0072]

[0073] in , and These represent the total energy of the doped adsorption structure, the total energy of the doped structure, and the total energy of the isolated gas molecules, respectively. A negative adsorption energy indicates that the gas adsorption process is exothermic and can occur spontaneously. Transfer charge. Used to study the magnitude of charge transfer in adsorption structures. A positive value indicates that the gas molecules act as electron donors, consuming charge. A negative value indicates that the gas molecule acts as an electron acceptor, accumulating charge; parameter Defined by the shortest distance between atoms in the gas and atoms in the doped substrate. , The larger, Smaller adsorption structures indicate stronger interactions and represent the optimal adsorption structure.

[0074] In this embodiment, step S5 calculates its electrical properties using a 10 × 10 × 1 k-point grid. The electrical properties include the band structure diagram, density of states diagram, differential charge density, and electron localization function, which need to be preset when calculating the properties.

[0075] In this embodiment, step S5 response sensitivity The calculation method is as follows:

[0076]

[0077] in and The values ​​represent the conductivity of the doped adsorption structure and the doped structure, respectively, which can be used to obtain the response sensitivity of the structure to the detected gas at room temperature.

[0078] In this embodiment, step S5 response recovery time The calculation method is as follows:

[0079]

[0080] in For the frequency of attempts ( =10 12 Hz), For adsorption energy, Boltzmann constant ( =8.62×10 -5 eV / K), The operating temperature (in Kelvin).

[0081] The band structure diagram and density of states diagram of the Al-modified and Al-substituted doped structures in this embodiment were obtained through simulation calculations. The adsorption energy, transfer charge, adsorption distance, band structure diagram, density of states diagram, differential charge density, electronic localization function, improved independent gradient model diagram, and reduced density gradient model diagram based on promolecular density of the optimal adsorption structure of Al doped structures were also obtained. At the same time, the response sensitivity curves and response recovery time of Al-modified and Al-substituted doped thin-layer manganese dioxide to NO2 were calculated.

[0082] Comparative Example 1:

[0083] The comparative simulation process is the same as in Example 1, except that no element is doped in the manganese dioxide monolayer substrate. The adsorption performance parameters of the intrinsic manganese dioxide structure for NO2 adsorption are calculated, and the band structure diagram, density of states diagram, adsorption energy, transfer charge, adsorption distance, improved independent gradient model diagram, and reduced density gradient model diagram based on promolecular density of the intrinsic manganese dioxide structure for NO2 adsorption are obtained.

[0084] Based on the results of the above embodiments and comparative examples, a theoretical analysis was conducted on the NO2 adsorption-sensing structure of Al-doped thin-layer manganese dioxide.

[0085] By calculating the intrinsic band structure diagrams and the band structure diagrams of manganese dioxide monolayers after Al modification and Al substitution doping, the band structure changes under different doping methods are compared. By calculating the intrinsic band structure diagrams and the density of states diagrams of manganese dioxide monolayers after Al modification and Al substitution doping, the density of states changes under different doping methods are compared, thus obtaining the influence of Al modification and substitution doping on the electrical properties of manganese dioxide monolayers.

[0086] By calculating the optimal structures for NO2 adsorption in intrinsic manganese dioxide monolayers and Al-modified and Al-substituted manganese dioxide monolayers, the corresponding charge density difference (CDD) was obtained. Combined with the electronic localization function (ELF), improved independent gradient model (mIGM), and reduced density gradient map (RDG) based on promolecular density of intrinsic and Al-substituted manganese dioxide monolayers before and after adsorption, the strength and type of interfacial interactions between NO2 molecules and different substrates were compared and analyzed. Furthermore, by examining the band structure diagrams and density of states (DOS) diagrams of Al-modified and Al-substituted manganese dioxide monolayers after NO2 adsorption, the influence of different doping methods on the electrical response behavior and gas-sensing mechanism during NO2 adsorption was further revealed.

[0087] Specifically, the present invention will be further illustrated below by referring to the simulation data in the embodiments and comparative examples:

[0088] First, from the perspective of geometric structure and macroscopic stability, such as Figure 3 As shown, various modified and substituted doped configurations were constructed in a manganese dioxide monolayer. Al atoms were placed at H and T atoms in the modified doping configurations. Mn T O Surface sites such as B1 and B2 are placed at lattice sites such as T1, T2, and T3 during substitution doping. Notably, Al atoms initially located at sites B1 and B2 migrate to lattice sites T1, T2, and T3 after relaxation. Mn And H sites, therefore the modified doping configuration ultimately retains only H and T sites. Mn and T O Three representative sites. Table 1 compares the formation energy, binding energy, and cohesive energy of each configuration. It can be seen that both H-site modification doping and T2-site substitution doping have low formation energies and large negative binding energies, while maintaining a high cohesive energy. This indicates that both are easy to form and can provide strong doping bonding while maintaining overall lattice stability.

[0089] Table 1 shows the eight doping sites (H, T) of Al atoms under both modification doping and substitution doping methods. Mn T O Formation energy, binding energy, and cohesive energy of manganese dioxide structure after doping with B1, B2, T1, T2, and T3, in eV.

[0090]

[0091] Table 1

[0092] Based on this, the effect of doping on electrical properties is further analyzed using band structure and density of states. For example... Figure 4 and Figure 5 As shown, the intrinsic MnO2 monolayer band gap is 2.128 eV. After H-site modification and doping, the conduction band shifts significantly downward, the band gap decreases to 0.489 eV, and a higher density of electronic states accumulates near the Fermi level. Electrons transition from the valence band to the conduction band more easily, thus improving the material's conductivity and enhancing its metallic properties. This provides a basis for changes in electrical parameters caused by NO2 adsorption and interfacial electron transfer. After T2 site substitution doping, the band gap only slightly decreases to 2.066 eV, while the conductivity is improved to some extent. Therefore, different doping methods effectively control the band structure and conductivity of the substrate while ensuring structural stability, providing a good foundation for subsequent electrical changes caused by gas adsorption.

[0093] To further reveal the bonding nature after doping, this invention characterizes the Al-O bond by combining the electronic localization function (ELF), a reduced density gradient model based on promolecular density, and bond order calculations. For example... Figure 6 and Figure 7 As shown, in Al-modified and substituted doped structures, a fully delocalized electron region with an ELF approaching 0 appears around the Al atoms, while a closed RDG isosurface with an "inner blue and outer red" appearance is formed near the Al-O bond, indicating the existence of a strong attractive nucleus surrounded by a repulsive potential. Combined with... Figure 8 The bond order analysis shown indicates that the Al-O bond order in both doped configurations is approximately 0.24, which is significantly lower than that of a typical covalent bond but greater than that of a pure electrostatic interaction. This suggests that the Al-O bond is predominantly ionic with some covalent component. This indicates that the Al-doped structure can exist stably, providing a structural basis for the interfacial interactions and electronic structure changes during the subsequent NO2 adsorption process.

[0094] Regarding gas molecules, such as Figure 9 As shown, the geometry of the NO2 molecule was first constructed and optimized to ensure its molecular configuration was reasonable in subsequent adsorption simulations. Then, the optimized NO2 was placed at multiple initial positions on intrinsic MnO2, H-site modified doped, and T2-site substituted doped surfaces, respectively, and geometric optimization was performed to obtain the desired results. Figure 10 The optimal adsorption configurations are shown in Table 2, with corresponding adsorption energies, transfer charges, and adsorption distances. The results indicate that the intrinsic MnO2 surface exhibits only a weak interaction with NO2, with an adsorption energy of approximately -0.401 eV, a charge transfer of approximately +0.03 e, and an adsorption distance of approximately 3.286 Å, which is typical physisorption. However, both H-Al-MnO2 and T2-Al-MnO2 surfaces significantly increase the adsorption energy, increase the charge transfer amplitude, and significantly shorten the adsorption distance, indicating that NO2 adsorption transforms from physisorption to chemisorption on both doped structures. Modification doping corresponds to strong adsorption, while substitution doping corresponds to moderate adsorption.

[0095] Table 2 shows the adsorption energies of intrinsic manganese dioxide monolayers, Al-modified and Al-substituted manganese dioxide monolayers for NO2 adsorption. , transfer charge Adsorption distance Related covalent radius .

[0096]

[0097] Table 2

[0098] To distinguish the direction of electron gain and loss at the interface and their interaction types, this invention combines differential charge density (CDD) analysis, such as... Figure 11 As shown. Figure 11a represents the CDD of the NO2-H-Al-MnO2 adsorption structure. Blue represents electron accumulation, and yellow represents electron dissipation. It can be seen that a large area of ​​electrons accumulates around the NO2 molecule while electrons are significantly dissipated on the substrate surface, indicating that NO2 acts as an electron acceptor, acquiring electrons from the doped substrate. 2- T2-Al-MnO2 adsorption structure ( Figure 11 In b), the opposite is true: electrons dissipate near the NO2 molecule while electrons accumulate in the substrate region, indicating that NO2 acts as an electron donor, releasing electrons to the substrate. There is an essential difference between the two doping methods in the direction of interfacial charge transfer.

[0099] Furthermore, by jointly characterizing the adsorbed structure using ELF, mIGM, and Promolecular-RDG, the dominant type of interfacial bonding can be analyzed from an electronic structure perspective. For example... Figures 12-14 As shown, when NO2 is adsorbed on the intrinsic MnO2 surface, the localized electron regions are basically separated before and after adsorption. Only scattered light green van der Waals interaction regions appear in the mIGM and RDG diagrams, indicating weak physical adsorption characteristics. In the NO2-H-Al-MnO2 adsorption structure, a large area of ​​completely delocalized electron regions exists near Al. The mIGM and RDG isosurfaces show continuous blue bridge-shaped attraction regions. Combined with the aforementioned charge transfer results, this indicates that the interface is dominated by strong electrostatic attraction driven by ionic bonds. In the NO2-T2-Al-MnO2 adsorption structure, locally compact "blue inside, red outside" blue attraction nuclei appear in the mIGM and RDG diagrams. The electron clouds between gas molecules and the substrate clearly overlap, indicating a bonding mechanism dominated by covalent bond electron sharing. Thus, this invention clearly distinguishes between ionic bond-dominated chemisorption at modified and doped interfaces and covalent bond-dominated chemisorption at substituted and doped interfaces.

[0100] The aforementioned interfacial interactions are ultimately reflected in the changes in energy bands and density of states before and after adsorption. For example... Figure 15 As shown, after NO2 adsorbs on the H-Al-MnO2 surface, the band gap increases from 0.489 eV to 0.600 eV, and the density of states near the Fermi level decreases; while after NO2 adsorbs on the T2-Al-MnO2 surface, the band gap decreases from 2.066 eV to 1.822 eV, and the density of states near the Fermi level increases. Figure 16 and Figure 17The total density of states (TDOS) and partial density of states (PDOS) distributions shown reveal the following: In the NO2-H-Al-MnO2 structure, the O(NO2)-p orbitals on the valence band side and the Al states on the conduction band side exhibit energy level separation and charge localization, corresponding to a charge flow primarily from the substrate to the gas. In the NO2-T2-Al-MnO2 structure, the substrate Op orbitals and the Np and Op orbitals in NO2 show significant hybridization and overlap across multiple energy regions, demonstrating substantial electron sharing and bond reconstruction. This difference in band structure and density of states directly reflects the aforementioned differences in interfacial bonding types in electrical properties: the former shows a slightly increased band gap and decreased conductivity, corresponding to a negative response; the latter shows a decreased band gap and increased conductivity, corresponding to a positive response.

[0101] Finally, this invention evaluates the practical application performance of the two doped structures by calculating the response sensitivity and response recovery time at different temperatures. (See Table 3 and...) Figure 18 As shown, at 298 K, both the H-Al-MnO2 modified doped structure and the T2-Al-MnO2 substituted doped structure exhibit a response sensitivity greater than 7.5 for NO2. The modified doped structure achieves a negative response sensitivity of 7.68, while the substituted doped structure achieves a positive response sensitivity as high as 114.73, indicating that both can achieve high-sensitivity detection. However, there is a significant difference in response recovery time: the recovery time of the NO2-H-Al-MnO2 structure reaches 10 at room temperature. 26 The adsorption time is on the order of s, and even with heating, desorption is difficult to complete in a short time, exhibiting almost irreversible strong adsorption characteristics; the NO2-T2-Al-MnO2 structure requires 1.43 × 10⁻⁶ K to recover. 3 Furthermore, with a gradual increase in temperature, its recovery time significantly shortens (at 358 K and 398 K, the recovery times are 8.81 × 10⁻⁶ s, respectively). -1 s and 2.20×10 -2 The modified doped structure exhibits excellent controllable recovery characteristics and adsorption-desorption reversibility. Therefore, the modified doped structure of this invention is more suitable as a material for capturing, enriching, and detecting NO2 in one-time or long-term exposure, while the replaced doped structure is more suitable as a sensitive layer for a room-temperature reversible, highly sensitive NO2 sensor for environmental monitoring and safety early warning, realizing the application strategy of "selecting the structure according to the interface bonding type and adsorption intensity within the same material structure".

[0102] Table 3 shows the response sensitivity of H-Al-MnO2 and T2-Al-MnO2 doped structures after NO2 adsorption at 298 K, 358 K and 398 K.

[0103]

[0104] Table 3

[0105] Finally, it should be noted that the above-described embodiments are merely preferred examples for clearly illustrating the present invention, but they are not intended to limit the implementation of the present invention. Those skilled in the art should understand that the technical features in the above solutions can be arbitrarily combined, and other modifications or equivalent substitutions can be made to some technical features based on the above specific implementation methods. It is impossible to exhaustively list all implementation methods here. Therefore, any modifications, improvements, equivalent substitutions, etc., derived from the technical solutions of the present invention within the spirit and principles of the present invention should be within the scope of protection claimed by the present invention.

Claims

1. A NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide, characterized in that, The device includes a two-dimensional manganese dioxide substrate, wherein the two-dimensional manganese dioxide substrate has a monolayer structure, wherein the monolayer structure is an O-Mn-O three-atom layer structure, and the thickness of the monolayer structure is 1.963 Å; the two-dimensional manganese dioxide substrate is doped with Al element, wherein the Al element in the two-dimensional manganese dioxide substrate is doped by modification doping or substitution doping, and the doping concentration ratio is 2% to 4%; the Al-doped thin layer of manganese dioxide constitutes a functional layer for NO2 gas adsorption and gas-sensitive response, which is used to adsorb NO2 gas and cause a detectable change in electrical signal during the adsorption process, so as to realize the adsorption and gas-sensitive detection of NO2 gas.

2. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 1, characterized in that, The Al element is incorporated into any surface of the two-dimensional manganese dioxide substrate in a modified doping manner.

3. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 1, characterized in that, The Al element is introduced into the two-dimensional manganese dioxide substrate by substitution doping, replacing the lattice positions occupied by Mn or O atoms in the two-dimensional manganese dioxide substrate lattice.

4. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 2, characterized in that, The two-dimensional manganese dioxide substrate modified and doped with Al forms a strong chemisorption interface with NO2 gas, and the adsorption process of NO2 under room temperature conditions is irreversible, making it suitable for the capture, enrichment and immobilization of NO2 gas.

5. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 3, characterized in that, The two-dimensional manganese dioxide substrate, which is doped with Al, forms a chemisorption interface with reversible adsorption-desorption between itself and NO2 gas, which is used for reproducible NO2 gas-sensitive detection.

6. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 4, characterized in that, The two-dimensional manganese dioxide substrate modified and doped with Al exhibits a detectable electrical response to NO2 gas at room temperature, with a response sensitivity greater than 7.

5.

7. The NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide according to claim 5, characterized in that, The two-dimensional manganese dioxide substrate doped with Al exhibits a detectable electrical response to NO2 gas at room temperature, with a response sensitivity greater than 100.

8. The application of the NO2 adsorption-sensing structure based on Al-doped thin-layer manganese dioxide as described in any one of claims 1 to 7 in the detection, capture, enrichment or immobilization of NO2.

9. The application according to claim 8, characterized in that, The detection of NO2 is a gas-sensitive detection of NO2.

Images