WO3 material with honeycomb porous structure as well as preparation method and application of WO3 material

Abstract

The invention discloses a WO3 material with a honeycomb porous structure as well as a preparation method and application of the WO3 material. The preparation method comprises the following steps: S1, preparing WO3; and S2, mixing the WO3 obtained in the step S1 with a compound containing bivalent copper ions, and grinding to obtain the WO3 material with the honeycomb porous structure. The response value of the Cu < 2 + >-WO3 sensor to H2S is the highest, the response value of the Cu < 2 + >-WO3 sensor is 68 times that of a pure WO3 sensor at the working temperature of 200 DEG C, and due to the fact that the charge transfer efficiency and the separation degree of WO3 are greatly improved through copper ion doping, band gap energy is reduced, more electrons participate in a gas sensing reaction, and the gas sensitive performance is greatly improved. In addition, the reaction between Cu < 2 + > and reducing gas H2S is also an important factor for improving the performance of the Cu < 2 + >-WO3 sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of H2S sensors, and in particular relates to a WO3 material with a honeycomb porous structure, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen sulfide is a toxic, reducing gas with a rotten egg odor. H2S is widely used in food processing, leather and fur production, papermaking, and printing. This exogenous H2S poses a significant threat to human health, particularly the nervous system.

[0003] Early H2S detection mainly relied on chemical methods (such as the lead acetate test paper color change method) and laboratory analysis (such as gas chromatography), but these methods cannot meet the needs of real-time, online monitoring. Summary of the Invention

[0004] In view of this, the present invention aims to provide a WO3 material with a honeycomb porous structure and a preparation method and application thereof, so as to solve at least one technical problem in the background technology.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for preparing a WO3 material with a honeycomb porous structure comprises the following steps:

[0007] S1: Preparation of WO3;

[0008] S2: The WO3 obtained in step S1 is mixed with a compound containing divalent copper ions and ground to obtain a WO3 material with a honeycomb porous structure.

[0009] Furthermore, the compound containing divalent copper ions in step S2 includes copper salt or copper dioxide.

[0010] Furthermore, the copper salt includes one of copper sulfate, copper nitrate, copper chloride and copper acetate.

[0011] Furthermore, the copper salt is copper chloride.

[0012] Furthermore, in step S2, WO3 is mixed with a compound containing divalent copper ions in a molar ratio of 0.5-3%, and the grinding time is 20-40 minutes.

[0013] Furthermore, the preparation of WO3 in step S1 includes the following sub-steps: dissolving sodium tungstate and potassium chloride in a mixture of deionized water and acetone, adding concentrated hydrochloric acid dropwise under stirring to a pH of 1-2, transferring it to a reactor, hydroheating at 100°C-140°C for 10-14h, centrifuging and washing the obtained product, and drying it at 50-70°C for three days. The obtained light yellow powder is calcined at 300°C-400°C for 100-200min, with a heating rate of 1-2°C / min.

[0014] The above method for preparing a WO3 material with a honeycomb porous structure produces a WO3 material with a honeycomb porous structure.

[0015] The above-mentioned honeycomb porous structure WO3 material is used for H2S gas sensing.

[0016] Furthermore, the operating temperature of the H2S gas sensor is 180°C-220°C.

[0017] This application is dedicated to the development of a gas sensing material that can detect low concentrations of H2S gas for a long time. Tungsten oxide (WO3) nanomaterials are generally in powder form, yellow or light yellow in color, and are a polycrystalline n-type semiconductor material with a band gap energy of approximately 2.4 to 2.8 eV. Tungsten oxide of various morphologies, such as nanoplates, nanospheres, nanorods, nanowires, nanofibers, etc., are widely used in gas sensing, photocatalysis, photochromism, etc. However, pure WO3 sensing materials have disadvantages such as low sensitivity and poor selectivity, and modifying WO3 with metal salts or oxides is an effective strategy to improve the sensing performance of the material. CuO, a common p-type metal oxide semiconductor material, is often used to compound with WO3 to form a pn heterojunction to improve the gas sensing performance of WO3. This paper prepares a honeycomb porous structure WO3 composed of nanowires, and introduces a small amount of CuCl2 and CuO to modify pure WO3, and compares the Cu 2+ -WO3 and CuO / WO3 gas-sensing properties to hydrogen sulfide, and the gas sensing mechanism was proposed.

[0018] Compared with the prior art, the honeycomb porous structured WO3 material and its preparation method and application described in the present invention have the following advantages:

[0019] Cu of this application 2+ -WO3 sensor has the highest response value to H2S. At the working temperature of 200℃, Cu 2+ The response value of the -WO3 sensor is 68 times that of the pure WO3 sensor. This may be because copper ion doping greatly improves the charge transfer efficiency and separation degree of WO3, reduces the band gap energy, and causes more electrons to participate in the gas sensing reaction, which greatly improves the gas sensing performance. In addition, Cu 2+The reaction with reducing gas H2S also increases the 2+ -An important factor in the performance of WO3 sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 The scanning electron microscope images of the samples described in the embodiment of the present invention ((A) WO3, (B) Cu 2+ -SEM image of WO3 sample, Cu 2+ -WO3 sample (C) TEM and (D) HRTEM images and Cu 2+ -elemental mapping of WO3 samples);

[0022] Figure 2 The XRD patterns of the samples described in the embodiment of the present invention ((A) WO3, CuO, Cu 2+ -WO3 and CuO-WO3 samples, (B) XRD pattern magnified in the diffraction angle range of 20-30°);

[0023] Figure 3 The Cu 2+ -XPS spectrum of WO3 sample;

[0024] Figure 4 Response graphs of samples described in an embodiment of the present invention ((A) Response values of three sensors to 5.5 ppm H2S gas at different operating temperatures; (B) Selective responses to seven different gases at 200°C; (C) Relationship curves between the response values of the three sensors and H2S gas concentration at 200°C; (D) A partial enlargement of the response values of Figure C to 0.02-0.14 ppm H2S).

[0025] Figure 5 Temperature diagram of the Cu2+-WO3 sensor for 5.5ppm H2S gas at an operating temperature of 200℃ ((A) Cyclic stability after five consecutive cycles; (B) Long-term stability after 56 days of intermittent detection);

[0026] Figure 6 UV-visible diffuse reflectance spectra of the samples ((A) electrochemical impedance spectroscopy of three samples; (B) WO3 and Cu 2 + -UV-visible diffuse reflectance spectrum of WO3 sample; (C) Mott-Schottky curve);

[0027] Figure 7 Cu 2+ -Schematic diagram of the sensing mechanism of WO3 sensor for H2S gas. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0030] Example

[0031] 1. Synthesis of WO3

[0032] 0.01 mol of sodium tungstate and 0.01 mol of potassium chloride were dissolved in a mixture of 60 mL of deionized water and 10 mL of acetone, stirred for 30 minutes until the solution was clear, and then concentrated hydrochloric acid was added dropwise under stirring to pH = 1.5. The mixture was transferred to a reactor and hydroheated at 120°C for 12 hours. The obtained product was centrifuged and washed three times with anhydrous ethanol and deionized water respectively, and dried in a vacuum drying oven at 60°C for three days. The obtained light yellow powder was calcined at 350°C for 150 minutes with a heating rate of 1.5°C / min.

[0033] 2. Synthesis of CuO

[0034] 1 g of CuSO4·5H2O was dissolved in 20 mL of concentrated ammonia water and ultrasonicated for 30 min. The resulting mixed solution was added to a reactor and hydrothermally treated at 150°C for 12 h. The product was centrifuged, washed three times with anhydrous ethanol and three times with deionized water, and finally dried in a vacuum drying oven at 60°C for 3 days.

[0035] 3. Cu 2+ Preparation of -WO3 and CuO-WO3

[0036] WO3 was mixed with 1% molar ratio of CuCl2 and CuO respectively and ground in a mortar for 30 minutes to obtain two composite materials. The color of the sample did not change during the grinding process.

[0037] Depend on Figure 1 (A) It can be seen that pure WO3 is a honeycomb porous structure composed of nanowires. After grinding with CuCl2, the porous structure of WO3 disappears and becomes granular, such as Figure 1 (B) shows that the nanowires broke during the grinding process. 2+ -The microstructure of WO3 was tested by transmission electron microscopy (TEM) images, such as Figure 1As shown in (C, D). As can be seen from Figure C, the particle size of the WO3 nanoparticles is approximately 10nm, with clear lattice fringes, indicating high crystallinity. The HRTEM image shows that the lattice spacing of 0.384nm corresponds to the (002) plane of WO3, and the lattice spacing of 0.231nm corresponds to the (111) plane of CuO, indicating that a CuO-WO3 complex was successfully obtained. This indicates that CuCl2 combines with oxygen in the air during the grinding process with WO3 to form CuO. There is a clear boundary between the lattice fringes of WO3 and CuO, indicating the formation of a CuO / WO3 p-n heterojunction.

[0038] To further observe Cu 2+ -The distribution of each element in the WO3 composite material, this application conducted element mapping characterization analysis on the sample. Figure 1 It can be seen that Cu 2+ Cu is indeed present in the -WO3 sample. The density of the dots corresponds to the Cu concentration in the sample. The sparse distribution of dots indicates a low Cu content, which corresponds to the amount of copper source introduced during sample synthesis. The primary source of C is exogenous contamination. The relatively uniform distribution of O, W, and Cu enhances its gas sensing performance.

[0039] Figure 2 A is WO3, CuO, Cu 2+ -WO3 and CuO-WO3 samples XRD patterns. All diffraction peaks of WO3-based samples can be attributed to monoclinic WO3. The sharp diffraction peaks indicate that the sample has a high degree of crystallinity. No diffraction peaks of Cu and its oxides were observed, which may be due to the small content of CuCl2 and CuO. In order to clearly observe the changes in the diffraction peaks of WO3 between 2θ angles of 20-30° after the addition of CuCl2 and CuO, the XRD pattern was partially enlarged, as shown in the figure below. Figure 2 As shown in B, it can be found that after adding CuCl2 and CuO, the diffraction peaks are obviously shifted to the left, indicating that the lattice spacing of WO3 becomes larger. This may be due to the larger radius of Cu 2+ (0.073nm) replaces the slightly smaller radius W 6+ (0.065nm), further proving that Cu 2+ -WO3 and CuO-WO3 samples were successfully synthesized.

[0040] To further determine the Cu 2+ -WO3 sample's surface element composition and valence state, and its XPS spectrum was tested. Figure 3 The XPS fine spectra of W, O and Cu elements are shown. After peak fitting, it is found that the O1s spectrum ( Figure 3A) consists of a strong peak and a weak peak. The characteristic peaks at 530.4eV and 531.8eV can be attributed to the lattice oxygen of WO3 and O 2- , and surface adsorbed oxygen, the content of surface adsorbed oxygen is about 28%. According to the surface resistance control principle, the influence of surface adsorbed oxygen in gas-sensitive materials on gas-sensitive performance is dominant. Figure 3 B is the XPS spectrum of W 4f, W 4f 7 / 2 The characteristic peak of the orbital is located at 35.7eV, while the W 4f 5 / 2 The characteristic peak of W is located at 37.5 eV, corresponding to 6+ The weak peak at 41.4 eV belongs to W 5p 3 / 2 track. Figure 3 The XPS spectrum of C is Cu 2p, and the characteristic peaks at 933.7eV and 953.5eV are attributed to Cu 2+ Cu 2p 3 / 2 and Cu 2p 1 / 2 orbital, and the two peaks at 951.9eV and 932.0eV are attributed to Cu + The characteristic peaks of Cu 2+ Gain electrons and turn into Cu + This may be due to the lower Fermi level of the n-type semiconductor WO3, and the electrons flow to the p-type semiconductor CuO with a higher Fermi level, which further proves the formation of the pn heterojunction.

[0041] First, this application studies the optimal operating temperature of the three sensors. Figure 4 As can be seen from A, as the operating temperature increases from 180℃ to 260℃, the sensor's response to 5.5ppm H2S gas increases first and then decreases. The response value is the largest at 200℃, indicating that the optimal operating temperature is 200℃. At this operating temperature, Cu 2+ The response values of CuO-WO3, CuO-WO3 and pure WO3 sensors to 5.5ppm H2S are 67.6, 24.5 and 2.8 respectively. 2+ The response value of the -WO3 sensor is significantly higher than that of the pure WO3 sensor, about 24 times, while the response value of the CuO-WO3 sensor to H2S gas is improved, but significantly lower than that of the Cu 2+ -WO3 sensor, so this application systematically studied Cu 2+ -Gas sensing performance of WO3 sensor.

[0042] At an operating temperature of 200°C, the selective responses of the three sensors to 5.5ppm H2S gas and 100ppm other reducing gases were tested, such as Figure 4 B. Cu 2+-WO3 sensor's response to 5.5ppm H2S gas is much higher than its response to 100ppm of the other six common gases, indicating that Cu 2+ -WO3 sensor has excellent selectivity for H2S detection. Comparing the response values in the figure, it can be seen that Cu 2+ -WO3 sensor has significantly improved selectivity to H2S gas compared to pure WO3 sensor. 2+ -The response value of the WO3 sensor to 5.5ppm H2S gas is about 10 times the response value of 100ppm other gases (ethylene glycol, ethanol, methanol, acetone, benzene, ammonia). This may be due to the Cu 2+ Can react with H2S, thereby improving selectivity.

[0043] Depend on Figure 4 It can be seen that the response values of the three gas sensors increase with the increase of H2S concentration, especially Cu 2+ -WO3 sensor, its response value is the highest in the entire concentration range of detection, so it is linearly fitted. In the concentration range of 0.02-0.14ppm, its fitting equation is y=22.67x+3.8(R 2 =0.89), when the concentration is greater than 0.14 ppm, the fitting equation is y=6.04x+21.29(R 2 =0.97). Since the data points overlap and are unclear between 0.02ppm and 0.14ppm, the data in this range are magnified. Figure 4 D. It can be seen that different linear laws are followed in the low concentration range and high concentration range, respectively. This good linear relationship is suitable for practical applications. It is worth noting that Cu 2+ The WO3 sensor has a significant response value of 1.46 to a low concentration of 20 ppb H2S gas, indicating that this sensor has an ultra-low detection limit for H2S gas detection, making it possible to use this sensor to detect trace H2S gas.

[0044] The cyclic stability and long-term stability of the sensor are also important indicators for evaluating the performance of the sensor. Therefore, this application tested the Cu 2+ -Dynamic response and recovery of WO3 sensor to 5.5ppm H2S gas for five cycles. As shown in the figure, the resistance value remains almost unchanged after five cycles at 200℃, indicating that Cu 2+ -WO3 sensor has good cycle stability. In addition, this application also 2+ -WO3 sensor was tested for 56 days to explore its long-term stability, such as Figure 5 As shown in B, Cu 2+The response value of the Cu-WO3 sensor to hydrogen sulfide gas only decreased slightly within 56 days, from 69 to 65, and still maintained a high response value, indicating that the sensor has good long-term stability. 2+ -WO3 sensor has greatly improved sensitivity (24 times), has an ultra-low detection limit (20ppb), excellent selectivity and stability, and has high practical application value.

[0045] In order to study Cu 2+ -The sensing mechanism of WO3 sensor for H2S gas, this application tests the electrochemical impedance spectroscopy of three materials, such as Figure 6 As shown in A. It can be seen from the figure that after doping with CuO or CuCl2, the arc radius of the electrochemical impedance spectrum is reduced, especially Cu 2+ The -WO3 sample has the smallest arc radius, indicating the highest charge transfer efficiency and the greatest separation between electrons and holes. This suggests that the charge transfer efficiency and separation on the material's surface may be important factors influencing its gas-sensing performance. The presence of the heterojunction may be a key factor in the significant improvement in charge transfer efficiency.

[0046] The band gap energy of semiconductor materials determines the number of electrons generated by thermal excitation. The smaller the band gap energy, the more electrons are generated by thermal excitation. After O2 is adsorbed on the WO3 surface, it is easier for it to obtain electrons and generate more active oxygen O2. - / O - , used for gas sensing reactions, the better the gas sensing performance of the material, for this purpose this application tested WO3 and Cu 2+ -The UV-visible diffuse reflectance spectrum of WO3, such as Figure 6 As shown in B. WO3 and Cu were obtained by making the edge tangent line. 2+ -WO3 band gap energy is 2.59 and 2.15eV respectively. WO3 doped with Cu 2+ After that, the band gap energy becomes smaller, indicating that Cu 2+ -WO3 sample surface has more electrons participating in the gas sensing process, resulting in better gas sensing performance. This result shows that the band gap energy is also an important factor affecting Cu 2+ -WO3 sensing performance. In order to judge the 2+ -The conductivity type of WO3 samples, the present application tested their Mott-Schottky curves, such as Figure 6 As shown in C, the slopes are all positive, indicating that both samples are n-type semiconductors, and their Fermi levels are -0.303eV (WO3) and -0.238eV (Cu 2 + -WO3). Therefore, Cu 2+ / Cu +The surface state formed is located below the conduction band of WO3, such as Figure 7 shown.

[0047] At the working temperature of 200℃, the electrons in the WO3 valence band absorb heat energy and are excited to the conduction band. 2+ / Cu + The potential energy of the surface state is higher than the conduction band potential energy of WO3, and some electrons will jump to the surface state of copper, Cu 2+ After gaining electrons, it becomes Cu + , Cu + The reducing property is strong, and it is easier to react with O2 adsorbed on the surface to generate Cu 2+ and O2 - Formula (1, 2), there will also be a part of the surface adsorbed O2 directly obtain electrons from the WO3 conduction band to form O2 - (Formula 3), at a high temperature of 200℃, O2 - Further electron decomposition to O - (Equation 4), as electrons continue to lose, the WO3 electron depletion layer continues to thicken, and the resistance gradually increases, which is manifested as a higher initial resistance of the sensor. When it comes into contact with the target gas H2S, the H2S molecules are adsorbed on the WO3 surface (Equation 5), and then react with O - Reacts with H2S to produce SO2, while releasing electrons to WO3, which recombine with holes in the valence band (Formula 6). 2+ Reacts with adsorbed oxygen and H2S to generate Cu + (Formula 7) enables the recycling of copper ions, which is probably Cu 2+ -WO3 sensor has a significantly improved gas sensing performance compared to pure WO3 sensor. When n-type semiconductor sensor detects reducing gas, its sensitivity is defined as S=Ra / Rg. The change of resistance in air and gas to be measured generates a signal, and the greater the change of resistance, the higher the sensitivity. 2+ -WO3 sensor has a higher initial resistance, Ra, due to its greatly thickened electron depletion layer, so its sensitivity S value is much higher than that of pure WO3 sensor.

[0048] O2(gas)→O2(adsorbed)(1)

[0049] O2(adsorbed)+Cu + →O2 - (adsorbed)+Cu 2+ (2)

[0050] O2(adsorbed)+e - →O2 - (adsorbed)(3)

[0051] O2 - (adsorbed)+e - →2O - (adsorbed)(4)

[0052] H2S(gas)→H2S(adsorbed)(5)

[0053] H2S(adsorbed)+3O - (adsorbed)→SO2+H2O+3e - (6)

[0054] H2S(adsorbed)+Cu 2+ +O2→Cu + +2H + +SO2+e - (7)

[0055] In this paper, a simple grinding method was used to successfully prepare Cu 2+ -WO3 and CuO / WO3 composite materials, the sensing performance of the three samples to H2S gas was investigated, and the gas sensing mechanism was proposed. The results showed that CuCl2 doped Cu 2+ There are two copper ions with different valence states in the WO3 sample, Cu + and Cu 2+ The sensor has significantly improved the sensing performance of hydrogen sulfide gas compared with pure WO3 sensor. Its response value is 24 times that of pure WO3, and its selectivity for H2S gas is also greatly improved. It has a lower detection limit (20ppb). This may be because copper ion doping improves the charge transfer efficiency and separation degree of WO3, and the band gap energy is reduced, resulting in more electrons participating in the gas sensing reaction, which improves the gas sensing performance. In addition, Cu with strong oxidizing properties 2+ The redox reaction between Cu and H2S gas also increases 2+ -WO3 sensor sensitivity and selectivity are important factors, Cu 2+ With Cu + The cyclic conversion between Cu and H2S is beneficial to long-term detection of H2S gas and improves stability. 2+ -WO3 sensor has high sensitivity, high stability and low detection limit for hydrogen sulfide gas detection, which is beneficial for practical application.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a WO3 material with a honeycomb porous structure, characterized by: The steps include: S1: Preparation of WO3; S2: The WO3 obtained in step S1 is mixed with a compound containing divalent copper ions and ground to obtain a WO3 material with a honeycomb porous structure.

2. The method for preparing a WO3 material with a honeycomb porous structure according to claim 1, characterized in that: The compound containing divalent copper ions in step S2 includes copper salt or copper dioxide.

3. The method for preparing a WO3 material with a honeycomb porous structure according to claim 1, wherein: The copper salt includes one of copper sulfate, copper nitrate, copper chloride and copper acetate.

4. The method for preparing a WO3 material with a honeycomb porous structure according to claim 1, characterized in that: The copper salt is copper chloride.

5. The method for preparing a WO3 material with a honeycomb porous structure according to claim 1, characterized in that: In step S2, WO3 is mixed with a compound containing divalent copper ions in a molar ratio of 0.5-3%, and the grinding time is 20-40 minutes.

6. The method for preparing a WO3 material with a honeycomb porous structure according to claim 1, characterized in that: The preparation of WO3 in step S1 includes the following steps: dissolving sodium tungstate and potassium chloride in a mixture of deionized water and acetone, adding concentrated hydrochloric acid dropwise under stirring to a pH of 1-2, transferring the mixture to a reactor, and hydroheating at 100°C-140°C for 10-14 hours. The obtained product is centrifuged and washed, and dried at 50-70°C for three days. The obtained light yellow powder is calcined at 300°C-400°C for 100-200 minutes at a heating rate of 1-2°C / min.

7. A WO3 material with a honeycomb porous structure prepared by the method for preparing a WO3 material with a honeycomb porous structure according to any one of claims 1 to 6.

8. The WO3 material with a honeycomb porous structure as claimed in claim 7 is used for H2S gas sensing.

9. The use according to claim 8, characterized in that: The operating temperature of H2S gas sensor is 180℃-220℃.

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