An industrial waste gas VOCs photocatalytic oxidation method

Abstract

The application discloses an industrial waste gas VOCs photocatalytic oxidation method and relates to the technical field of waste gas treatment. x MXene nanosheets, phosphotungstic acid are compounded in the presence of branched polyethyleneimine to obtain a surface modified dispersion liquid; then the surface modified dispersion liquid is reacted with cobalt nitrate and 2-methylimidazole to form a ZIF-67 shell layer; the photocatalytic material is prepared by heat treatment under the protection of argon; finally, the photocatalytic material is loaded on a honeycomb ceramic carrier, and VOCs are catalytically oxidized under visible light irradiation. The method significantly improves the light absorption efficiency and pollutant enrichment effect, thereby greatly improving the photocatalytic degradation performance of VOCs.

Description

Technical Field

[0001] This invention relates to the field of waste gas treatment technology, specifically to a photocatalytic oxidation method for VOCs in industrial waste gas. Background Technology

[0002] Industrial waste gases contain a wide variety of volatile organic compounds (VOCs), with benzene series compounds (benzene, toluene, xylene, etc.), esters (ethyl acetate, butyl acetate, etc.), and ketones (acetone, butanone, etc.) being typical examples. These substances possess extremely strong environmental hazards and biological toxicity. On the one hand, they pose a serious threat to human health. Long-term exposure can induce respiratory diseases and damage the immune system. Some highly toxic VOCs are also known teratogens and carcinogens. After entering the human body through airborne transmission and skin contact, they can cause irreversible damage to vital organs such as the liver and kidneys. On the other hand, as a key contributor to air pollution, VOCs are core precursors to the formation of fine particulate matter (PM2.5) and ozone. Under environmental conditions such as light and temperature, they can undergo complex photochemical reactions with nitrogen oxides to generate secondary aerosols and near-ground ozone, exacerbating regional air pollution problems such as smog and photochemical smog, seriously disrupting the ecological balance and air quality, and hindering the coordinated promotion of green industrial development and ecological environmental protection.

[0003] In the VOCs treatment technology system, semiconductor photocatalysis technology is considered one of the most promising green treatment technologies due to its outstanding advantages such as operation at room temperature and pressure, no secondary pollution, and thorough degradation. Its core principle is to utilize the photogenerated electron-hole pairs generated by semiconductor materials under light to oxidize and decompose VOCs into harmless carbon dioxide and water. However, the widely used traditional semiconductor photocatalysts (typically titanium dioxide) have many core bottlenecks, which seriously limit their practical application and large-scale promotion in industrial waste gas treatment. First, TiO2 has a narrow visible light response range. With a band gap of approximately 3.2 eV, it can only absorb a very small portion of ultraviolet light from sunlight, resulting in extremely low utilization of the visible light, which accounts for about 43% of the total, making it difficult to improve photocatalytic efficiency. Second, the high recombination rate of photogenerated carriers means that electrons and holes generated by photoexcitation can easily recombine rapidly within the semiconductor, failing to effectively migrate to the catalyst surface to participate in redox reactions, significantly reducing quantum efficiency. Furthermore, traditional TiO2 has weak adsorption capacity for low-concentration VOCs, while VOC concentrations in industrial waste gas often fluctuate significantly, frequently remaining at low ppm levels. This makes it difficult for the catalyst to effectively capture target pollutants, reducing the probability of contact between reactants and photogenerated carriers, further limiting the catalytic degradation effect. Summary of the Invention

[0004] The purpose of this invention is to provide a method for photocatalytic oxidation of VOCs in industrial waste gas, so as to solve the technical problem of poor photocatalytic oxidation performance of VOCs in industrial waste gas mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0007] S1. Dissolve bismuth nitrate in ethylene glycol to form solution A, and dissolve sodium tungstate in deionized water to form solution B. Add solution B to solution A and mix. Then add methanol solution of cerium nitrate and methanol solution of ferric nitrate, and then add sodium hydroxide solution to adjust the pH value. Heat the reaction and wash and dry the reaction product to obtain Ce-Fe co-doped Bi2WO6 nanosheets.

[0008] S2. The Ce-Fe co-doped Bi2WO6 nanosheets are dispersed in deionized water containing branched polyethyleneimine and sodium nitrate, and then Ti3C2T is added. x The MXene nanosheet dispersion and phosphotungstic acid solution were ultrasonically treated, centrifuged, washed with hot deionized water, washed with anhydrous methanol, and finally redispersed in anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0009] S3. The surface-modified nanosheet dispersion is mixed with a methanol solution of cobalt nitrate and stirred. Then, a methanol solution of 2-methylimidazole is added to react. The reaction product is washed with methanol and dried to obtain a composite material with a ZIF-67 shell.

[0010] S4. The composite material with the ZIF-67 shell is heat-treated under argon protection and then cooled to obtain the photocatalytic material.

[0011] S5. The photocatalytic material is loaded onto a honeycomb ceramic carrier to form a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction in the photocatalytic reactor.

[0012] This invention improves the photocatalytic oxidation performance of VOCs in industrial waste gas from the following aspects: Firstly, through Ce-Fe co-doping and PEI surface-oriented modification, the intrinsic band structure and physical dispersion state of the material are deeply optimized. The co-doping of Ce and Fe introduces a synergistic effect of fd orbitals in Bi2WO6, which not only broadens the absorption bandwidth of the material to visible light, but also induces a large number of lattice oxygen vacancies, constructing effective electron trapping centers, thereby suppressing the internal recombination of photogenerated carriers at the source. Then, surface charge modification using low-concentration PEI eliminates the aggregation of nanosheets through electrostatic repulsion, ensuring that the catalyst has a very high effective active surface area in the reaction system. This combination of intrinsic energy level regulation and macroscopic dispersion optimization provides the system with a higher flux of photogenerated free radicals, thereby significantly improving the photocatalytic oxidation performance of VOCs in industrial waste gas from the perspective of increasing the number of photogenerated carriers and effective reaction sites. On the other hand, by constructing an ultra-thin ZIF-67 shell in situ and activating it at an ultra-low temperature of 250℃, the core bottlenecks of low pollutant contact probability and high charge migration resistance in waste gas treatment were solved. The ZIF-67 ultra-thin shell utilizes its highly developed porosity to produce a "pre-concentration" effect on dilute VOCs molecules, forcibly enriching pollutant molecules around the catalytic active center, overcoming the problem of slow reaction kinetics in low-concentration waste gas. The most critical technological breakthrough lies in the formation of Co-O-Bi interfacial bridging chemical bonds induced by ultra-low temperature heat treatment. This strong chemical coupling transforms the original physical contact into a low-impedance electron transport channel, generating a powerful "charge pump" effect that drives photogenerated electrons to migrate instantaneously to the outer active center to participate in the oxidation reaction. This synergistic mechanism of adsorption concentration and efficient charge transfer greatly extends the carrier lifetime and reduces the reaction activation energy, thereby significantly enhancing the photocatalytic oxidation performance of industrial waste gas VOCs from the perspectives of accelerating the interfacial reaction rate and improving deep mineralization capacity.

[0013] Preferably, in step S1, the mass ratio of bismuth nitrate to sodium tungstate is 5:(1-2).

[0014] Preferably, in step S1, the pH value is adjusted to 8.0-8.5 using sodium hydroxide solution.

[0015] Preferably, in step S1, the heating reaction temperature is 150–160°C and the heating reaction time is 16–20 h.

[0016] Preferably, in step S2, Ce-Fe co-doped Bi2WO6 nanosheets and Ti3C2T x The mass ratio of MXene nanosheets is 1:(0.02~0.05).

[0017] Preferably, in step S2, the mass ratio of Ce-Fe co-doped Bi2WO6 nanosheets to phosphotungstic acid is 1:(0.01~0.02).

[0018] To induce the orderly growth of the ZIF-67 shell, polyethyleneimine must be used as an organic linker layer for surface functionalization. However, polyethyleneimine is inherently an insulating long-chain organic polymer. Researchers discovered in experiments that polyethyleneimine residues at the heterojunction form a physical barrier similar to a "thermal insulation layer," significantly hindering the migration of photogenerated electrons from the internal Bi2WO6 substrate to the active centers of the ZIF-67 surface. This results in a situation where, although the production of photogenerated electrons is significantly increased and the capture sites for VOCs molecules are enhanced, the charge transfer pathway between the two is severely "blocked" by the insulating polyethyleneimine layer. This leads to violent recombination of charge carriers during cross-interface migration, preventing the full release of the synergistic effect due to low interfacial transport efficiency, thus reducing the synergistic photocatalytic oxidation performance of industrial waste gas. To further address this technical problem, this invention, during the interface functionalization pretreatment process, synergistically introduces two-dimensional MXene nanosheets with metallic conductivity and phosphotungstic acid with molecular-level redox activity, constructing a "three-dimensional charge relay network" within the insulating polyethyleneimine layer. Specifically, this invention utilizes the electrostatic anchoring effect of polyethyleneimine chain segments to flatly attach highly conductive two-dimensional MXene nanosheets onto the surface of a Bi2WO6 substrate, constructing a large-area surface contact lateral "electron collection highway." Simultaneously, phosphotungstic acid molecules are used as "electron shuttles" to embed into the long chain gaps of polyethyleneimine, forming a longitudinal "charge tunnel." During the subsequent interface activation process, MXene and phosphotungstic acid jointly induce local polarization and energy level rearrangement in the polyethyleneimine layer, successfully transforming the originally insulating organic layer into a charge relay channel with high carrier flux. This improved scheme produced unexpected technical effects: MXene enabled rapid lateral spread of charge on the two-dimensional interface, while phosphotungstic acid, utilizing its reversible redox energy level, acted like a "charge pump" to actively pump electrons longitudinally to the cobalt active center of the outer ZIF-67 through the tunneling effect. This "interwoven" charge transfer network completely eliminated the physical shielding effect of the polyethyleneimine layer, significantly reduced the cross-interface migration resistance, and enabled the high-flux photogenerated electrons generated in the first aspect to instantly reach the surface of VOCs molecules enriched in the second aspect. This achieved lossless synergy throughout the entire process from charge generation and directional transport to efficient capture and degradation, thereby nonlinearly improving the photocatalytic oxidation performance and deep mineralization rate of industrial waste gas VOCs.

[0019] Preferably, in step S3, the mass ratio of cobalt nitrate to 2-methylimidazole is 1:(2-3).

[0020] Preferably, in step S3, the reaction temperature is 25–30°C and the reaction time is 4–6 hours.

[0021] Preferably, in step S4, the heat treatment temperature is 250–260°C and the heat treatment time is 3–5 hours.

[0022] Preferably, in step S5, the loading amount of photocatalytic material on the honeycomb ceramic support is controlled at 4–6 mg / cm³. 2 .

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. By co-doping Bi2WO6 with Ce-Fe, the visible light absorption range is broadened and lattice oxygen vacancies are generated, effectively suppressing the recombination of photogenerated electron-hole pairs; at the same time, PEI surface modification is used to improve the dispersibility of nanosheets and increase the effective active surface area of ​​the catalyst.

[0025] 2. The ZIF-67 ultrathin shell has a "pre-concentration" effect on low-concentration VOCs molecules, increasing the local reaction concentration; through low-temperature heat treatment, Co-O-Bi interface chemical bonds are formed, constructing a low-impedance electron transport channel and accelerating charge migration to active sites.

[0026] 3. By introducing MXene nanosheets and phosphotungstic acid, transverse conductive channels and longitudinal "electron shuttle" paths are formed in the PEI modified layer, transforming the insulating interface into a high-efficiency charge transport network, enabling rapid and non-destructive transfer of photogenerated electrons from the substrate to the surface active center. Attached Figure Description

[0027] Figure 1 This is a SEM image of the surface of the photocatalytic material prepared in Example 4 of the present invention.

[0028] Figure 2 The image shows the XPS spectrum of the photocatalytic material prepared in Example 4 of this invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0032] Step 1: Dissolve 5.0 g of bismuth nitrate in 30 mL of ethylene glycol to form solution A, and dissolve 1.8 g of sodium tungstate in 30 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A, then add 4.3 mL of 10 mg / mL cerium nitrate methanol solution and 4.0 mL of 10 mg / mL ferric nitrate methanol solution sequentially. Adjust the pH of the system to 8.3 using sodium hydroxide solution. Transfer the mixture to a high-pressure reactor and heat at 155 °C for 18 h. After washing with deionized water and ethanol and drying, Ce-Fe co-doped Bi₂WO₆ nanosheets are obtained.

[0033] Step 2: Disperse 1.0 g of Ce-Fe co-doped Bi₂WO₆ nanosheets in 100 mL of deionized water containing 0.1 wt% branched polyethyleneimine (PEI) and 0.1 M sodium nitrate, stir for 1 h, and then add 40 mL of 2.0 mg / mL Ti₃C₂T₆. x MXene nanosheet dispersion and 3.5 mL of 5.0 mg / mL phosphotungstic acid solution were ultrasonicated for 1 h and then centrifuged. The mixture was first washed with 80 °C hot deionized water to remove excess PEI, then washed with anhydrous methanol for dehydration, and finally redispersed in 40 mL of anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0034] Step 3: Add 0.29 g of cobalt nitrate to the above surface-modified nanosheet dispersion and stir for 1 h. Then add 100 mL of a methanol solution containing 0.7 g of 2-methylimidazole. Continue the reaction at 28 °C for 5 h. The reaction product is washed three times by centrifugation with anhydrous methanol and dried under vacuum at 50 °C to obtain a composite material with a ZIF-67 shell.

[0035] Step 4: Place the composite material in a tube furnace and heat it to 255°C at a rate of 0.5°C / min under the protection of high-purity argon gas, then maintain the temperature for 4 hours. Cool the furnace to room temperature to obtain the final photocatalytic material.

[0036] Step 5: The prepared photocatalytic material is formulated into a slurry and loaded onto a honeycomb ceramic support using an impregnation method, with the loading amount controlled at 5.5 mg / cm³. 2 After drying, the material is loaded into a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is simultaneously irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction within the photocatalytic reactor.

[0037] Example 2

[0038] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0039] Step 1: Dissolve 5.0 g of bismuth nitrate in 30 mL of ethylene glycol to form solution A, and dissolve 1.3 g of sodium tungstate in 30 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A, then add 4.3 mL of 10 mg / mL cerium nitrate methanol solution and 4.0 mL of 10 mg / mL ferric nitrate methanol solution sequentially. Adjust the pH of the system to 8.3 using sodium hydroxide solution. Transfer the mixture to a high-pressure reactor and heat at 155 °C for 18 h. After washing with deionized water and ethanol and drying, Ce-Fe co-doped Bi₂WO₆ nanosheets are obtained.

[0040] Step 2: Disperse 1.0 g of Ce-Fe co-doped Bi₂WO₆ nanosheets in 100 mL of deionized water containing 0.1 wt% branched polyethyleneimine (PEI) and 0.1 M sodium nitrate, stir for 1 h, and then add 20 mL of 2.0 mg / mL Ti₃C₂T₆. x MXene nanosheet dispersion and 2.5 mL of 5.0 mg / mL phosphotungstic acid solution were ultrasonicated for 1 h and then centrifuged. The mixture was first washed with 80 °C hot deionized water to remove excess PEI, then washed with anhydrous methanol for dehydration, and finally redispersed in 40 mL of anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0041] Step 3: Add 0.29 g of cobalt nitrate to the above surface-modified nanosheet dispersion and stir for 1 h. Then add 100 mL of a methanol solution containing 0.60 g of 2-methylimidazole. Continue the reaction at 28 °C for 5 h. The reaction product is washed three times by centrifugation with anhydrous methanol and dried under vacuum at 50 °C to obtain a composite material with a ZIF-67 shell.

[0042] Step 4: Place the composite material in a tube furnace and heat it to 255°C at a rate of 0.5°C / min under the protection of high-purity argon gas, then maintain the temperature for 4 hours. Cool the furnace to room temperature to obtain the final photocatalytic material.

[0043] Step 5: The prepared photocatalytic material is formulated into a slurry and loaded onto a honeycomb ceramic support by impregnation, with the loading amount controlled at 4.5 mg / cm³. 2 After drying, the material is loaded into a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is simultaneously irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction within the photocatalytic reactor.

[0044] Example 3

[0045] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0046] Step 1: Dissolve 5.0 g of bismuth nitrate in 30 mL of ethylene glycol to form solution A, and dissolve 1.5 g of sodium tungstate in 30 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A, then add 4.3 mL of 10 mg / mL cerium nitrate methanol solution and 4.0 mL of 10 mg / mL ferric nitrate methanol solution sequentially. Adjust the pH of the system to 8.3 using sodium hydroxide solution. Transfer the mixture to a high-pressure reactor and heat at 155 °C for 18 h. After washing with deionized water and ethanol and drying, Ce-Fe co-doped Bi₂WO₆ nanosheets are obtained.

[0047] Step 2: Disperse 1.0 g of Ce-Fe co-doped Bi₂WO₆ nanosheets in 100 mL of deionized water containing 0.1 wt% branched polyethyleneimine (PEI) and 0.1 M sodium nitrate, stir for 1 h, and then add 30 mL of 2.0 mg / mL Ti₃C₂T₆. x MXene nanosheet dispersion and 3 mL of 5.0 mg / mL phosphotungstic acid solution were ultrasonicated for 1 h and then centrifuged. The mixture was first washed with 80 °C hot deionized water to remove excess PEI, then washed with anhydrous methanol for dehydration, and finally redispersed in 40 mL of anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0048] Step 3: Add 0.29 g of cobalt nitrate to the above surface-modified nanosheet dispersion and stir for 1 h. Then add 100 mL of a methanol solution containing 0.65 g of 2-methylimidazole. Continue the reaction at 28 °C for 5 h. The reaction product is washed three times by centrifugation with anhydrous methanol and dried under vacuum at 50 °C to obtain a composite material with a ZIF-67 shell.

[0049] Step 4: Place the composite material in a tube furnace and heat it to 255°C at a rate of 0.5°C / min under the protection of high-purity argon gas, then maintain the temperature for 4 hours. Cool the furnace to room temperature to obtain the final photocatalytic material.

[0050] Step 5: The prepared photocatalytic material is formulated into a slurry and loaded onto a honeycomb ceramic support by impregnation, controlling the loading amount to be 5 mg / cm³. 2 After drying, the material is loaded into a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is simultaneously irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction within the photocatalytic reactor.

[0051] Example 4

[0052] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0053] Step 1: Dissolve 5.0 g of bismuth nitrate in 30 mL of ethylene glycol to form solution A, and dissolve 2 g of sodium tungstate in 30 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A, then add 4.3 mL of 10 mg / mL cerium nitrate methanol solution and 4.0 mL of 10 mg / mL ferric nitrate methanol solution sequentially. Adjust the pH of the system to 8.5 using sodium hydroxide solution. Transfer the mixture to a high-pressure reactor and heat at 160 °C for 20 h. After washing with deionized water and ethanol and drying, Ce-Fe co-doped Bi₂WO₆ nanosheets are obtained.

[0054] Step 2: Disperse 1.0 g of Ce-Fe co-doped Bi₂WO₆ nanosheets in 100 mL of deionized water containing 0.1 wt% branched polyethyleneimine (PEI) and 0.1 M sodium nitrate, stir for 1 h, and then add 50 mL of 2.0 mg / mL Ti₃C₂T₆. x MXene nanosheet dispersion and 4 mL of 5.0 mg / mL phosphotungstic acid solution were ultrasonicated for 1 h and then centrifuged. The mixture was first washed with 80 °C hot deionized water to remove excess PEI, then washed with anhydrous methanol for dehydration, and finally redispersed in 40 mL of anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0055] Step 3: Add 0.29 g of cobalt nitrate to the above surface-modified nanosheet dispersion and stir for 1 h. Then add 100 mL of a methanol solution containing 0.87 g of 2-methylimidazole. Continue the reaction at 30 °C for 6 h. The reaction product is washed three times by centrifugation with anhydrous methanol and dried under vacuum at 50 °C to obtain a composite material with a ZIF-67 shell.

[0056] Step 4: Place the composite material in a tube furnace and heat it to 260°C at a rate of 0.5°C / min under the protection of high-purity argon gas, then maintain the temperature for 5 hours. Cool the furnace to room temperature to obtain the final photocatalytic material.

[0057] Step 5: The prepared photocatalytic material is formulated into a slurry and loaded onto a honeycomb ceramic support by impregnation, controlling the loading amount to 6 mg / cm³. 2 After drying, the material is loaded into a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is simultaneously irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction within the photocatalytic reactor.

[0058] Example 5

[0059] A method for photocatalytic oxidation of VOCs in industrial waste gas includes the following steps:

[0060] Step 1: Dissolve 5.0 g of bismuth nitrate in 30 mL of ethylene glycol to form solution A, and dissolve 1 g of sodium tungstate in 30 mL of deionized water to form solution B. Slowly add solution B dropwise to solution A, then add 4.3 mL of 10 mg / mL cerium nitrate methanol solution and 4.0 mL of 10 mg / mL ferric nitrate methanol solution sequentially. Adjust the pH of the system to 8.0 using sodium hydroxide solution. Transfer the mixture to a high-pressure reactor and heat at 150 °C for 16 h. After washing with deionized water and ethanol and drying, Ce-Fe co-doped Bi₂WO₆ nanosheets are obtained.

[0061] Step 2: Disperse 1.0 g of Ce-Fe co-doped Bi₂WO₆ nanosheets in 100 mL of deionized water containing 0.1 wt% branched polyethyleneimine (PEI) and 0.1 M sodium nitrate, stir for 1 h, and then add 10 mL of 2.0 mg / mL Ti₃C₂T₆. x MXene nanosheet dispersion and 2 mL of 5.0 mg / mL phosphotungstic acid solution were ultrasonicated for 1 h and then centrifuged. The mixture was first washed with 80℃ hot deionized water to remove excess PEI, then washed with anhydrous methanol for dehydration, and finally redispersed in 40 mL of anhydrous methanol to obtain a surface-modified nanosheet dispersion.

[0062] Step 3: Add 0.29 g of cobalt nitrate to the above surface-modified nanosheet dispersion and stir for 1 h. Then add 100 mL of a methanol solution containing 0.58 g of 2-methylimidazole. Continue the reaction at 25 °C for 4 h. The reaction product is washed three times by centrifugation with anhydrous methanol and dried under vacuum at 50 °C to obtain a composite material with a ZIF-67 shell.

[0063] Step 4: Place the composite material in a tube furnace and heat it to 250°C at a rate of 0.5°C / min under the protection of high-purity argon gas, then maintain the temperature for 3 hours. Cool the furnace to room temperature to obtain the final photocatalytic material.

[0064] Step 5: The prepared photocatalytic material is formulated into a slurry and loaded onto a honeycomb ceramic support by impregnation, controlling the loading amount to 4 mg / cm³. 2 After drying, the material is loaded into a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is simultaneously irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction within the photocatalytic reactor.

[0065] Comparative Example 1 (Conventional Semiconductor Control): The difference between Comparative Example 1 and Example 1 is the use of commercially available titanium dioxide (P25) as the photocatalyst. It was formulated into a slurry and loaded onto a honeycomb ceramic support of the same specifications at a loading rate of 5.5 mg / cm³. 2 Toluene waste gas degradation experiments were conducted under the same conditions.

[0066] Comparative Example 2 (Ce-Fe Co-doping Control): The difference between Comparative Example 2 and Example 1 is that cerium nitrate methanol solution and ferric nitrate methanol solution are not added in step 1 to prepare pure phase Bi2WO6 nanosheets.

[0067] Comparative Example 3 (without MXene and phosphotungstic acid control): The difference between Comparative Example 3 and Example 1 is that in step 2, after adding PEI and sodium nitrate and stirring, Ti3C2T is not added. x The MXene nanosheet dispersion and phosphotungstic acid solution were directly centrifuged and washed, and the remaining steps were exactly the same.

[0068] Comparative Example 4 (without ZIF-67 shell control): The difference between Comparative Example 4 and Example 1 is that after the preparation of the surface-modified nanosheet dispersion in step 2 is completed, it is directly dried and heat-treated, without step 3 (i.e. without the ZIF-67 shell).

[0069] 1. VOCs Degradation Rate Test: A dynamic photocatalytic reaction system was used for testing. The system consists of a gas generator, a photocatalytic reactor, a light source system, and a gas detection device. The photocatalytic reactor has an effective volume of 5L and contains the honeycomb ceramic supported catalysts corresponding to the examples and comparative examples. A 500W xenon lamp (equipped with a 420nm cutoff filter to ensure only visible light irradiation) was used as the light source. The vertical distance between the light source and the catalyst surface was 15cm, and the irradiation intensity was consistently 100mW / cm². 2 During the test, toluene was used as the target VOC, and a concentration of 300 mg / m³ was prepared using a gas generator. 3 Toluene waste gas was discharged, with a flow rate controlled at 1 L / min, ensuring a residence time of 5 s in the reactor. After the reaction started, gas samples were collected from the reactor inlet and outlet every 30 min using an automatic gas sampling valve. The toluene concentration was determined using a gas chromatograph (GC-FID, detection limit 0.1 mg / m³), with three parallel samples taken at each time point. The degradation rate was calculated using the formula: "Degradation rate (%) = (Inlet toluene concentration - Outlet toluene concentration) / Inlet toluene concentration × 100%". The final result was the average value after 2 hours of reaction, which was taken as the VOCs degradation performance index for this group of samples. The test results are shown in Table 1.

[0070] 2. VOCs Mineralization Rate Test: The mineralization rate test and degradation rate test were conducted simultaneously in the same dynamic reaction system to assess the extent to which VOCs were completely oxidized to CO2 and H2O. The test conditions were exactly the same as those for the degradation rate test. After 2 hours of reaction, inlet and outlet exhaust gases were collected simultaneously. The total organic carbon (TOC) content in the gases was determined using a total organic carbon analyzer (TOC-VCPH), and the CO2 generation in the outlet gas was determined using an infrared gas analyzer. The mineralization rate was calculated using the formula: "Mineralization rate (%) = (Carbon content in CO2 generated by the reaction / Carbon content in the inlet toluene) × 100%". The carbon content in the inlet toluene was derived from the initial concentration, and the carbon content in CO2 was calculated from the detected CO2 concentration. Each group was tested in parallel three times, and the average value was taken as the final mineralization rate data. The test results are shown in Table 1.

[0071] 3. Long-term operational stability test: The materials from the examples and comparative examples were placed in the reactor and operated continuously for 100 hours under the same toluene exhaust gas environment and light conditions. The toluene degradation rate was recorded every 10 hours, and the activity retention rate after 100 hours was calculated (degradation rate at 100 hours / initial stable degradation rate). The test results are shown in Table 1.

[0072] Table 1:

[0073] Toluene degradation rate (%) VOCs mineralization rate (%) 100h stability performance (%) Example 1 98.0 81.7 98.7 Example 2 96.3 80.6 98.2 Example 3 97.5 81.1 98.5 Example 4 98.6 82.4 99.1 Example 5 95.1 79.5 97.6 Comparative Example 1 22.3 12.5 92.0 Comparative Example 2 56.4 38.2 94.2 Comparative Example 3 71.2 45.6 90.5 Comparative Example 4 68.5 42.3 93.8

[0074] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for photocatalytic oxidation of VOCs in industrial waste gas, characterized in that, Includes the following steps: S1. Dissolve bismuth nitrate in ethylene glycol to form solution A, and dissolve sodium tungstate in deionized water to form solution B; Solution B was added to solution A and mixed. Then, methanol solutions of cerium nitrate and ferric nitrate were added, followed by sodium hydroxide solution to adjust the pH value. The reaction was heated and the reaction product was washed and dried to obtain Ce-Fe co-doped Bi2WO6 nanosheets. S2. The Ce-Fe co-doped Bi2WO6 nanosheets are dispersed in deionized water containing branched polyethyleneimine and sodium nitrate, and then Ti3C2T is added. x The MXene nanosheet dispersion and phosphotungstic acid solution were ultrasonically treated, centrifuged, washed with hot deionized water, washed with anhydrous methanol, and finally redispersed in anhydrous methanol to obtain a surface-modified nanosheet dispersion. S3. The surface-modified nanosheet dispersion is mixed with a methanol solution of cobalt nitrate and stirred. Then, a methanol solution of 2-methylimidazole is added to react. The reaction product is washed with methanol and dried to obtain a composite material with a ZIF-67 shell. S4. The composite material with the ZIF-67 shell is heat-treated under argon protection and then cooled to obtain the photocatalytic material. S5. The photocatalytic material is loaded onto a honeycomb ceramic carrier to form a photocatalytic reactor. Industrial waste gas VOCs are introduced into the photocatalytic reactor, and the photocatalytic material is irradiated with a visible light source. The industrial waste gas VOCs undergo an oxidation reaction in the photocatalytic reactor.

2. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S1, the mass ratio of bismuth nitrate to sodium tungstate is 5:(1-2).

3. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S1, the pH value is adjusted to 8.0-8.5 using sodium hydroxide solution.

4. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S1, the heating reaction temperature is 150–160°C, and the heating reaction time is 16–20 h.

5. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S2, Ce-Fe co-doped Bi2WO6 nanosheets and Ti3C2T x The mass ratio of MXene nanosheets is 1:(0.02~0.05).

6. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S2, the mass ratio of Ce-Fe co-doped Bi2WO6 nanosheets to phosphotungstic acid is 1:(0.01~0.02).

7. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S3, the mass ratio of cobalt nitrate to 2-methylimidazole is 1:(2-3).

8. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S3, the reaction temperature is 25–30°C and the reaction time is 4–6 hours.

9. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S4, the heat treatment temperature is 250–260°C and the heat treatment time is 3–5 hours.

10. The method for photocatalytic oxidation of VOCs in industrial waste gas according to claim 1, characterized in that, In step S5, the loading amount of photocatalytic material on the honeycomb ceramic support is controlled at 4–6 mg / cm³. 2 .

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