Design and preparation method of high-performance VOCs gas-sensitive material

Abstract

The invention discloses a design and preparation method of a high-performance VOCs gas-sensitive material, and relates to the technical field of gas-sensitive material development. The method comprises the following steps: selecting a metal oxide substrate material, and selecting different metal types as alternatives of dopants; selecting and calculating a descriptor depicting the interaction strength of the material formula and the target gas, and selecting a proper metal doping type according to the calculation result of the descriptor; a simple solvothermal method and a high-temperature treatment method are combined to synthesize materials with different proportions of doping amounts of selected metals; the material is prepared into a gas sensitive sensor, the gas sensitive performance is tested, and the optimal doping proportion is determined; and characterizing the optimal formula material, and verifying the change of the doped metal on the material characteristics. According to the method disclosed by the invention, calculation and experiment are organically combined through the descriptor of the interaction strength of the gas molecules and the material surface, so that the defects of blindness of the traditional experiment and difficulty in describing the influence of trace doping by numerical calculation can be effectively overcome, and the development of the high-performance VOCs gas-sensitive material is accelerated.

Description

Technical Field

[0001] The present invention belongs to the field of gas-sensitive materials, and specifically relates to a design and preparation method of a high-performance VOCs gas-sensitive nanomaterial. Background Art

[0002] Volatile organic compounds (VOCs) are a general term for volatile organic compounds (VOCs) with melting points below room temperature and boiling points between 50 and 260°C. They are commonly found in industrial production processes such as petrochemicals, paint manufacturing, and pharmaceutical manufacturing. In recent years, the demand for VOC detection has increased significantly due to the significant harm they pose to human health, particularly for VOCs such as benzene and aldehydes.

[0003] Metal oxide semiconductor (MOS), as an important sensing material in chemiresistive gas sensors, occupies 60% of the sensing market and is widely used in the detection of VOCs. However, for some gases, it still has the disadvantages of slow response speed and low sensitivity. In recent years, nanotechnology has developed rapidly, and nanoparticles have shown excellent sensing characteristics due to their extremely strong adsorption capacity, chemical reactivity and excellent catalytic properties. In addition, doping / loading precious metals or transition metals is also one of the methods to improve the sensitivity of gas-sensitive materials through electronic sensitization and chemical sensitization effects. Most of the existing metal loading / doping sensitization methods are based on experience or a lot of trial and error, and lack rational material design and targeted synthesis methods. In recent years, some numerical calculation methods such as first-principles calculations have gradually been introduced into the field of material design, which to a certain extent compensated for the blindness of experiments. However, it is still difficult to describe the impact of trace doping on gas-sensing performance. Summary of the Invention

[0004] In light of the aforementioned and / or existing issues in the prior art, the present invention provides a method for designing and preparing a high-performance VOCs gas-sensing material based on MOS-doped metals. This invention is applicable to the formulation optimization and targeted synthesis of a variety of VOCs gas-sensing materials, aiming to provide a rational design approach and preparation method for VOCs-based gas-sensing materials.

[0005] The technical solution adopted in the present invention is:

[0006] For the target VOCs gas, metal oxide semiconductor (MOS) material is selected as the substrate, and different metal doping modifications are selected as alternative formulas to improve the sensing performance; descriptors that characterize the interaction strength between the material formula and the target gas, such as adsorption energy, nucleophilicity index, etc., are selected and calculated as the basis for pre-screening of high-sensitive material formulas, providing rational design guidance for material selection and formula optimization, and reducing experimental costs; a large absolute value of adsorption energy or a large nucleophilicity is used as selection index, and the appropriate metal doping type is selected according to the descriptor calculation results; since the descriptors obtained by numerical calculation are difficult to accurately compare the advantages and disadvantages of formulas doped with different trace proportions after the selected metal, a simple solvent thermal method and high-temperature treatment method are combined to directionally synthesize materials with different metal doping amounts; the material is prepared into a gas sensor, and the gas-sensing performance, such as response value, detection limit, response / recovery time, selectivity, etc., is tested to screen the optimal formula for the target VOCs; the optimal formula material is characterized to verify the changes in material characteristics caused by doping metals.

[0007] Preferably, when the adsorption energy is selected as the calculation indicator, the calculation of the adsorption energy needs to go through the following processes: modeling the oxide substrate, cutting the crystal surface, expanding the cell, optimizing the structure, setting the doping elements and the corresponding proportions, optimizing the structure of the target VOCs, adsorbing the target VOCs on the surface of the doped material, and optimizing the structure;

[0008] Among them, the cut crystal plane refers to the high crystal energy plane of the exposed oxide. Its crystal plane coordination saturation is low, exposing more active sites, making it easier to adsorb reactant molecules and promote effective carrier separation, such as the {110} plane of SnO2;

[0009] Among them, cell expansion refers to setting a sufficiently thick vacuum layer to ensure that the interaction between adjacent repeating units can be ignored, accurately simulating the actual properties of the material;

[0010] Among them, all structural optimizations are aimed at finding the most stable structure, that is, the lowest energy state;

[0011] Among them, the adsorption energy calculation refers to the difference between the system energy after adsorbing VOCs and the sum of the two initial system energies;

[0012] Preferably, under the premise of no experience in substrate selection, the substrate can be selected from one or more of SnO2, ZnO, WO3, In2O3, CuO, Fe2O3, or Co3O4;

[0013] Preferably, the doping metal may be one or more of Au, Pt, Cu, Cr, Ni or Ir;

[0014] Preferably, the increase in the absolute value of adsorption energy before and after doping is selected as a sign of excellent metal doping performance;

[0015] Preferably, the adsorption energy calculation can be performed using Monte Carlo annealing or first principles calculation (DFT);

[0016] Preferably, the trace doping amount is 0.1% to 1.5%.

[0017] The directional synthesis process of the material includes: synthesizing a homogeneous precursor solution; transferring the solution to a Teflon-lined stainless steel autoclave, sealing and maintaining the solution at a constant temperature for more than 12 hours; naturally cooling the solution to room temperature, centrifuging, washing, drying, and heat treating the solution to obtain a precursor material; and then mixing the metal-doped solution with the precursor in different proportions, heat treating the solution, and grinding the solution to obtain the gas-sensitive material.

[0018] Preferably, the centrifugal washing is to adjust the centrifuge speed to 2000 r / min, separate the precipitate after 5 minutes, and rinse it alternately with distilled water and an organic solvent;

[0019] Preferably, the drying refers to drying in a vacuum drying oven at 80°C for not less than 12 hours;

[0020] Preferably, the heat treatment is performed in a muffle furnace in an air atmosphere. The heat treatment time and temperature vary depending on the specific situation. The heat treatment heating rate is 5°C / min.

[0021] The gas sensing test includes synthesis of gas sensors and gas sensing performance evaluation;

[0022] Preferably, the synthetic gas sensor comprises adding a sample to deionized water and grinding the mixture to form a paste, then uniformly applying the paste to the outer edge of the gas sensor substrate and completely covering the electrode, drying the mixture at 60° C. for 2 h to form a gas-sensitive coating, and allowing the mixture to stand at room temperature for 24 h.

[0023] Preferably, the gas-sensitive test refers to connecting a load resistor in series with the obtained gas-sensitive sensor, connecting an external constant 3.3V voltage, passing air into the sensor cavity for a certain period of time to restore the sensor to the baseline, and then passing the test gas. When the gas passes through the gas-sensitive material, the sensor resistance changes, causing the circuit voltage to change, and the resistance change of the sensor is indirectly obtained by detecting the voltage change across the load resistor.

[0024] For n-type semiconductors, the response value is defined as:

[0025] K=R a / R g ,

[0026] The response value for p-type semiconductor is defined as:

[0027] K=R g / R a ,

[0028] Among them, R a is the baseline resistance, R g is the response resistance.

[0029] The beneficial effects of the present invention are:

[0030] The present invention introduces a descriptor that characterizes the interaction strength between gas molecules and material surfaces, organically combining calculation and experiment, and provides a new idea for the design and preparation of high-performance VOCs gas-sensitive materials. The theoretical a priori metal doping types of the material formula and the experimental a posteriori material formula with the optimal doping ratio can effectively make up for the blindness of traditional experiments and the defects that numerical calculations are difficult to describe the effects of trace doping, thereby accelerating the development of high-performance VOCs gas-sensitive materials; the present invention can overcome the problems of large experimental workload and waste in existing material development methods, and provide a descriptor that characterizes the interaction strength between gas molecules and material surfaces to guide the optimal design of the formula, thereby reducing experimental costs; it can overcome the deficiency that existing numerical calculations are difficult to accurately describe the effects of trace doping, and provide a formula scheme for optimizing the doping ratio combined with gas-sensitive testing to find the optimal material formula. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, wherein:

[0032] Figure 1 This is a design flow chart of the high-performance VOCs gas-sensitive material of the present invention;

[0033] Figure 2 This is the modeling and calculation process of Pt and Ni doped SnO2 in the material studio of the present invention;

[0034] Figure 3 Response curves of the SnO2 sensor with different Pt doping ratios to xylene;

[0035] Figure 4 This is the temperature response curve of the 0.5% Pt-doped SnO2 sensor of the present invention to xylene;

[0036] Figure 5 This is the FESEM image of 0.5% Pt-doped SnO2 at 500nm and 2μm;

[0037] Figure 6 The electron image and element mapping of O, Sn, Pt and EDS spectrum of the 0.5% Pt-doped SnO2 material of the present invention are shown;

[0038] Table 1 shows the calculation process of the adsorption energy of xylene on Pt and Ni-doped SnO2 surfaces in the present invention. Table 1 DETAILED DESCRIPTION

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention is further described below in conjunction with the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto. In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any formal modifications and / or changes made to the present invention will fall within the scope of protection of the present invention. Secondly, "one embodiment" or "embodiment" referred to herein refers to specific features, structures or characteristics that can be included in at least one implementation method of the present invention. "In one embodiment" appearing in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0040] The chemical raw materials required for the present invention can all be purchased from the market.

[0041] Example

[0042] The target VOCs was selected as p-xylene, the substrate oxide was selected as SnO2, and the doping metals Pt and Ni were compared. The theoretical calculations of the examples were all performed in Material Studio. The following are the specific steps for calculating the adsorption energy using the first principles (DFT) method using the DMol3 module.

[0043] Model SnO2, cut the {110} crystal plane and relax the surface, set the vacuum layer to 10A, optimize the structure, and obtain the lowest energy state, which is recorded as E a =-546.058636Ha;

[0044] Load Pt and optimize the structure to obtain the lowest energy state, denoted as E a1 =-546.0586357Ha;

[0045] Load Ni and optimize the structure to obtain the lowest energy state, denoted as E a1 =-546.0534943Ha;

[0046] Model and optimize the structure of xylene to obtain the lowest energy state, denoted as E b =-310.575338Ha;

[0047] Xylene was adsorbed onto the optimized SnO2 surface and the structure was optimized again. After reaching convergence, the lowest energy state was obtained, which was recorded as Ec =-856.643173Ha; then the adsorption energy of xylene on the SnO2 surface is ΔE = E c –E b –E a =-5.77246449 kcal / mol;

[0048] Finally, xylene was adsorbed onto the optimized Pt-SnO2 surface and the structure was optimized again. After reaching convergence, the lowest energy state was obtained, which was recorded as E c1 =-856.651761Ha; the adsorption energy of xylene on the Pt-doped SnO2 surface is ΔE = E c1 -E a1 -E b =-11.16170862 kcal / mol;

[0049] Finally, xylene was adsorbed onto the optimized Ni-SnO2 surface and the structure was optimized again. After reaching convergence, the lowest energy state was obtained, which was recorded as E c1 =-856.6425467Ha; the adsorption energy of xylene on the Ni-doped SnO2 surface is ΔE = E c1 -E a1 -E b =-8.605923144 kcal / mol;

[0050] The calculation shows that both Pt and Ni doping improve the performance of SnO2 in adsorbing xylene, and Pt doping has a greater improvement on the performance. The experimental formula Pt-doped SnO2 was selected;

[0051] Dissolve tin chloride dihydrate (SnCl2·2H2O) and sodium citrate monohydrate (Na3C6H5O7·H2O) in distilled water, stir until completely dissolved, then add sodium hydroxide (NaOH) solution and continue stirring for 5 minutes to form a homogeneous solution;

[0052] The solution was transferred to a Teflon-lined stainless steel autoclave, sealed, and maintained at 180°C for 12 hours. After cooling naturally to room temperature, the resulting precipitate was separated by centrifugation and rinsed several times with distilled water and acetone. It was then vacuum-dried at 60°C for 12 hours. It was then calcined in a muffle furnace at 400°C in air for 4 hours. Hexahydrated platinic acid (HPtCl6·6H2O) was mixed with the above powder in atomic ratios of 0%, 0.1%, 0.5%, and 2.0%. Finally, it was calcined again in a muffle furnace at 300°C in air for 1 hour to obtain the pure SnO2, 0.1% Pt-doped SnO2, 0.5% Pt-doped SnO2, and 2.0% Pt-doped SnO2 nanomaterials.

[0053] The product is added to deionized water and ground into a paste, which is then evenly applied to the outer edge of the gas sensor substrate and completely covers the electrode. It is dried at 60°C for 2 hours to form a gas-sensitive coating, and allowed to stand at room temperature for 24 hours to obtain the pure SnO2, 0.1% Pt-doped SnO2, 0.5% Pt-doped SnO2 and 2.0% Pt-doped SnO2 gas sensors.

[0054] 50 ppm of xylene was introduced by adjusting the flow meter, and the response of the above sensor was measured. Figure 3 The response curve of the above sensor to 50 ppm xylene at 300°C and 17.3% RH is shown.

[0055] Compared with the pure SnO2 sensor, the Pt-doped SnO2 sensor has a faster response speed and a higher response value. It can be seen that Pt doping can indeed improve the sensing performance of the SnO2 sensor for xylene.

[0056] Among sensors with different Pt doping, the 0.5% Pt-doped SnO2 sensor has the fastest response and the highest response value compared with the others. It can be seen that 0.5% Pt doping can most significantly improve the sensing performance of SnO2 sensor for xylene.

[0057] 50 ppm of xylene was introduced by adjusting the flow meter, and the ambient temperature was adjusted to 100°C, 200°C, 300°C, and 400°C, respectively, and the response of the above-mentioned sensor was measured. Figure 4 The temperature response curve of 0.5% Pt-doped SnO2 sensor to 50 ppm xylene at 17.3% RH is shown.

[0058] Among them, the 0.5% Pt-doped SnO2 sensor responds most quickly and has the highest response value at 300°C compared with other temperatures. It can be seen that within the above temperature range, 300°C is the optimal response temperature of the 0.5% Pt-doped SnO2 sensor.

[0059] FESEM characterization of the 0.5% Pt-doped SnO2 gas-sensing material revealed irregularly aggregated Pt-doped SnO2 ellipsoids with a fuzzy surface structure. Their average diameter was micrometer-scale, approximately 0.5-1.5 μm. Agglomeration is a common phenomenon in nanoscale SnO2. This demonstrates that rational material design and targeted synthesis methods reduced unnecessary experimental effort, developed a new formulation for 0.5% doped SnO2 specifically for xylene, and explored novel morphologies of Pt-doped SnO2 ellipsoids.

[0060] The present invention has been described in detail above with reference to the embodiments. However, the contents described above are only specific embodiments of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, any modifications and improvements made within the scope of the present invention without departing from the concept of the present invention should still fall within the scope of the present invention.

Claims

1. A design and preparation method of a high-performance VOCs gas-sensitive material, characterized in that: The following steps are involved: Step S1. For the target VOCs gas, a metal oxide semiconductor (MOS) material is selected as the substrate, and different metal doping modifications are selected as alternative formulations to improve sensing performance; Step S2. Select and calculate a descriptor that characterizes the interaction strength between the material formulation and the target gas as a basis for pre-screening of highly sensitive material formulations; Step S3. Selecting a suitable metal doping formula based on the descriptor calculation results; Step S4. Since the numerically calculated descriptors are unable to accurately simulate the advantages and disadvantages of the formulations doped with different trace proportions of the selected metal, materials with different metal doping amounts are synthesized in a targeted manner; Step S5. Testing the gas-sensing properties of the synthesized material to screen the optimal formulation for the target VOCs; Step S6: Characterize the optimal formula material to verify the changes in material characteristics caused by the doped metal.

2. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: In step S1, the MOS material substrate is selected. Under the premise of no experience in substrate selection, the substrate can be selected from one or more of SnO2, ZnO, WO3, In2O3, CuO, Fe2O3 or Co3O4.

3. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: The doping metal in step S1 is one or more of Au, Pt, Cu, Cr, Ni or Ir.

4. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: In step S2, the descriptor for describing the interaction strength between the material formulation and the target gas is adsorption energy, nucleophilicity index, or a combination thereof, and the calculation method is Monte Carlo annealing or first principles calculation.

5. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: The metal doping formula in step S3 is determined based on increasing the absolute value of the material-gas adsorption energy or affinity index.

6. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: The directional synthesis method in step S4 is a combination of a simple solvent thermal synthesis method and a high temperature heat treatment method, with trace amounts of different metals doped, with the doped metal amount being 0.1% to 1.5%.

7. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: The gas-sensing performance indicators used to screen the formulations in step S5 are response value, detection limit, response / recovery time, and selectivity.

8. The method for designing and preparing a high-performance VOCs gas-sensitive material according to claim 1, characterized in that: The material characterization method in step S6 uses XRD, XPS, SEM and TEM characterization methods to obtain the material morphology, metal doping amount, doping uniformity and microstructural changes caused by doping, and verify the effect of doping on improving the gas-sensing performance of the material.

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