A vn / gan aerogel photothermal catalyst based on in-situ nitridation of vanadium in waste scr catalyst, a preparation method and applications thereof

Abstract

The present application belongs to the field of industrial hazardous waste resource utilization, photo-thermal synergistic catalytic material and VOCs treatment technology, and specifically relates to a VN / GaN aerogel photo-thermal catalyst based on in-situ nitriding of vanadium from waste SCR catalyst, a preparation method and application thereof. The preparation method comprises the following steps: selectively leaching vanadium from a waste SCR denitration catalyst; directly using a vanadium-containing DES leaching solution as a vanadium source and a spinning aid to prepare an electrostatic spinning precursor solution by compounding with gallium nitrate and a spinning aid; obtaining a precursor fiber through electrostatic spinning; calcining in an air atmosphere to obtain V2O5 / Ga2O3 nanofibers; forming VN / GaN composite nanofibers through high-temperature nitriding in ammonia; and preparing an aerogel photo-thermal catalyst through ultrasonic dispersion, aging and freeze-drying. The present application realizes green high-value closed-loop utilization of vanadium in hazardous waste, and the prepared aerogel catalyst has excellent photo-thermal conversion performance and toluene catalytic oxidation activity.

Description

Technical Field

[0001] This invention belongs to the fields of industrial hazardous waste resource utilization, nanocatalytic materials, photothermal synergistic catalysis and volatile organic compound (VOCs) treatment technology. Specifically, it relates to a VN / GaN aerogel photothermal catalyst based on in-situ vanadium nitridation of waste SCR catalyst, its preparation method and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are key precursors to regional photochemical smog, haze, and ozone pollution, posing serious threats to the atmospheric environment and human health. Benzene compounds are the main components of industrial VOC emissions, accounting for over 30%. Toluene, a typical benzene compound, is highly carcinogenic and teratogenic, and is one of the key pollutants subject to air pollution control. Photothermal synergistic catalytic degradation of VOCs offers advantages such as being environmentally friendly, energy-efficient, and operating under mild reaction conditions, making it one of the most promising VOCs treatment technologies currently available. The core of this technology lies in the photothermal catalyst, which must simultaneously possess excellent solar light absorption and photothermal conversion capabilities, highly efficient low-temperature catalytic oxidation activity, and good structural stability.

[0003] Currently, commercial toluene catalytic oxidation catalysts are mainly based on precious metals such as platinum and palladium, which suffer from drawbacks such as resource scarcity, high cost, susceptibility to sulfur water poisoning, and high-temperature sintering and deactivation. Non-precious metal oxide catalysts, on the other hand, suffer from poor catalytic activity at low temperatures, low photothermal conversion efficiency, easy agglomeration of active components, and insufficient long-term stability. Furthermore, existing photothermal catalysts are mostly nanoparticles, which present engineering application challenges such as difficult recovery, easy loss, and high bed resistance. Bulk catalysts, meanwhile, generally suffer from low specific surface area, poor mass transfer efficiency, and insufficient exposure of active sites, severely restricting the large-scale application of photothermal catalysis technology.

[0004] On the other hand, selective catalytic reduction (SCR) denitrification technology is the mainstream technology for flue gas denitrification in industries such as coal-fired power plants, cement, and steel. Waste SCR catalysts use TiO2 as a carrier, loaded with 1-5 wt% V2O5 and a small amount of WO3. Vanadium, as a scarce metal, is a secondary vanadium resource with significant recycling value. Currently, the recovery process of vanadium from waste SCR catalysts mainly relies on strong acid / strong alkali leaching, which suffers from problems such as high reagent consumption, large wastewater discharge, long process flow, and poor selectivity. Furthermore, after leaching, multiple purification steps such as extraction, back-extraction, precipitation, and calcination are required to obtain usable vanadium salts, resulting in high overall costs and hindering large-scale promotion. Eutectic solvents (DES), as a new generation of green solvents, have advantages such as low volatility, good selectivity, strong designability, and recyclability. In recent years, they have been used for the leaching of valuable metals in waste catalysts. There have been relevant studies on the selective leaching of vanadium, but existing studies have focused on the separation and purification of vanadium. There are no reports on the direct in-situ preparation of VN / GaN aerogel photothermal catalysts from vanadium-containing DES leachate without purification, nor has a fully closed-loop process of "leaching-in-situ synthesis-catalytic application" for hazardous waste vanadium been formed, which limits the large-scale application of DES in this field.

[0005] Gallium nitride (GaN) is a typical wide-bandgap III-V semiconductor with excellent electron transport properties, chemical stability, and a tunable surface nitrogen vacancy structure, making it a promising candidate for catalysis. Current technology can successfully prepare one-dimensional GaN nanofibers via electrospinning, but these are only used for photocatalytic degradation of dyes, without introducing active metal components, and lack structural and performance design for VOCs catalytic oxidation, resulting in limited catalytic activity. Existing supported GaN catalytic materials mostly employ post-loading processes such as impregnation and ion exchange, which suffer from problems such as easy aggregation of active components, poor dispersibility, weak interfacial bonding, and easy loss of active sites, severely affecting catalytic performance and lifespan.

[0006] Vanadium nitride (VN) is a typical metallic transition metal nitride with a platinum-like electronic structure and catalytic activity. It also possesses excellent visible-near-infrared light absorption and photothermal conversion performance, making it an ideal photothermal catalytic active component. However, existing VN-based catalysts generally suffer from problems such as easy aggregation, low specific surface area, and weak interfacial bonding with the support. Furthermore, there are no reports on technologies combining vanadium recovery from spent SCR catalysts with in-situ preparation of VN / GaN aerogel catalysts. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a VN / GaN aerogel photothermal catalyst based on in-situ vanadium nitridation of waste SCR catalysts, its preparation method, and its applications. This invention uses waste SCR hazardous waste as the vanadium source, employs selective leaching of vanadium using DES, and directly prepares VN / GaN aerogel in situ, achieving green and high-value closed-loop utilization of hazardous waste vanadium. The resulting catalyst possesses both excellent photothermal conversion performance and toluene catalytic oxidation activity, solving the core problems of existing catalysts such as easy agglomeration of active components, poor low-temperature activity, low photothermal efficiency, and difficult recovery. It achieves efficient, stable, and low-energy-consumption photothermal catalytic oxidation degradation of low-concentration toluene. This invention has broad application prospects in industrial VOCs waste gas treatment and indoor air purification.

[0008] The technical solution of the present invention is described in detail below.

[0009] A method for preparing a VN / GaN aerogel photothermal catalyst based on in-situ vanadium nitridation of spent SCR catalyst includes the following steps: (1) Selective vanadium leaching: The waste SCR denitration catalyst was leached using the choline chloride-oxalic acid eutectic solvent DES. After solid-liquid separation, a vanadium-containing eutectic solvent DES leachate was obtained. (2) In-situ preparation of spinning solution: The vanadium-containing eutectic solvent DES leaching solution obtained in step (1) is directly mixed with gallium source, spinning aid and anhydrous ethanol-deionized water mixed solvent, and magnetically stirred to obtain a uniform and transparent electrospinning precursor solution. (3) Electrospinning: The electrospinning precursor liquid obtained in step (2) is electrospinned to obtain precursor nanofibers. (4) Air precalcination: The precursor nanofibers obtained in step (3) are placed in an air atmosphere for calcination to remove organic components and obtain V2O5 / Ga2O3 composite nanofibers. (5) Ammonia nitriding treatment: The V2O5 / Ga2O3 composite nanofibers obtained in step (4) are placed in an ammonia atmosphere and nitrided at high temperature to convert Ga2O3 into hexagonal wurtzite GaN and V2O5 is nitrided in situ to generate VN, thus obtaining VN / GaN composite nanofibers. (6) Aerogel forming: The VN / GaN composite nanofibers obtained in step (5) are added to the dispersion solvent and ultrasonically dispersed in an ice bath to obtain a uniform fiber dispersion; sealed and aged at room temperature, then pre-frozen, freeze-dried and dried at low temperature to obtain VN / GaN aerogel photothermal catalyst.

[0010] In this invention, in step (1), the molar ratio of choline chloride to oxalic acid in the eutectic solvent DES is 1:1 to 1:2; the waste SCR denitration catalyst is pre-ground to below 200 mesh, the solid-liquid ratio of the waste SCR denitration catalyst to DES is 1:5 to 1:20 g / mL, the leaching temperature is 100 to 140℃, the leaching time is 2 to 4 hours, and solid-liquid separation is performed by filtration. During the leaching process, oxalate ions and vanadium ions form a stable V(IV) / V(V) vanadium oxychloride chelate, achieving highly selective leaching of vanadium, with a vanadium leaching rate ≥95% and a TiO2 and Al2O3 support leaching rate ≤3%.

[0011] In this invention, in step (2), the gallium source is gallium nitrate nonahydrate; the spinning aid is polyvinylpyrrolidone (PVP) with a number average molecular weight of 1,300,000; in the anhydrous ethanol-deionized water mixed solvent, the volume ratio of anhydrous ethanol to deionized water is 4:1 to 10:1; the magnetic stirring temperature is room temperature, and the magnetic stirring time is 6 to 12 hours. In the obtained electrospinning precursor solution, the vanadium-containing eutectic solvent DES leaching solution accounts for 8 wt% to 20 wt%, gallium nitrate nonahydrate accounts for 2.5 wt% to 5.0 wt%, polyvinylpyrrolidone (PVP) accounts for 6 wt% to 10 wt%, and the remainder is the anhydrous ethanol-deionized water mixed solvent. In this step, the choline chloride-oxalic acid eutectic solvent DES has three functions in the spinning solution: vanadium source, co-solvent, and dispersant. It can effectively control the viscosity of the spinning solution and inhibit the aggregation of vanadium species.

[0012] In this invention, the process parameters for electrospinning in step (3) are: spinning voltage of 15~20kV, feed speed of 0.5~1.5mL / h, receiving distance of 12~18cm, ambient humidity of 20~30%, and ambient temperature of 20~25℃.

[0013] In this invention, in step (4), the calcination process conditions are as follows: under an air atmosphere, the air flow rate is controlled at 100~300 sccm, the temperature is raised to 500~900℃ at a heating rate of 1~3℃ / min, held for 1~3h, and then naturally cooled to room temperature. During the calcination process, organic components such as PVP and DES are completely thermally decomposed and removed, gallium nitrate is completely decomposed into β-Ga2O3, the vanadium precursor is completely oxidized into V2O5, and the fiber morphology remains intact.

[0014] In this invention, in step (5), the high-temperature nitriding process conditions are as follows: under an ammonia atmosphere, the ammonia flow rate is controlled at 150~250 sccm, the temperature is raised to 800~900℃ at a heating rate of 1~3℃ / min, held for 1~3h, and then naturally cooled to room temperature.

[0015] In this invention, in step (6), the dispersing solvent is a mixture of anhydrous ethanol and tert-butanol with a volume ratio of 2:1 to 1:2; the mass concentration of the fiber dispersion is 5 to 15 mg / mL; the ice bath ultrasonic treatment adopts an intermittent pulse mode, with a single ultrasonic treatment lasting 3 to 5 seconds and an interval of 2 to 4 seconds, a power of 180 to 220 W, and a dispersion time of 30 to 60 min; the mixture is sealed and aged at room temperature for 12 to 24 h; the pre-freezing temperature is -40 to -60 °C, and the pre-freezing time is 2 to 4 h; the freeze-drying cold trap temperature is < -60 °C, the vacuum degree is < 15 Pa, and the drying time is 24 to 48 h; finally, the mixture is dried at 60 to 80 °C for 2 to 6 h to remove residual solvent.

[0016] This invention also provides a VN / GaN aerogel photothermal catalyst prepared by the above method, wherein the catalyst has a three-dimensional continuous nanofiber network and a mesoporous-macroporous hierarchical porous structure, with a specific surface area of ​​200~350 m². 2 / g, with a pore size distribution ranging from 1.5 to 40 nm and a VN content of 30 wt% to 50 wt%. VN and GaN are uniformly distributed inside the nanofibers, with fiber diameters ranging from 150 to 250 nm. A stable Schottky heterojunction can be formed at the VN-GaN interface, exhibiting strong interfacial electronic interactions.

[0017] Furthermore, this invention provides an application of the above-mentioned VN / GaN aerogel photothermal catalyst in the photothermal catalytic oxidation of VOCs. In a specific embodiment, the VOCs are toluene.

[0018] In this invention, when the VN / GaN aerogel photothermal catalyst is applied in the photothermal catalytic oxidation of VOCs, VN, as the main photothermal conversion host and the main catalytic active site, has excellent visible-near-infrared light absorption capabilities. Under sunlight irradiation, it can rapidly achieve photothermal conversion, raising the catalyst surface temperature to 120-220℃ and initiating the low-temperature catalytic oxidation of toluene. GaN, as the electronic regulator and structural framework, has nitrogen vacancies on its surface that can assist in the adsorption and activation of oxygen. At the same time, it can directionally transport electrons to the VN interface through Schottky heterojunctions, enhancing the activation ability of VN for oxygen and toluene molecules, forming a strong synergistic catalytic effect. The three-dimensional aerogel structure provides abundant mass transfer channels and a high specific surface area, significantly improving gas contact efficiency and active site exposure rate. Meanwhile, the macroscopic bulk structure facilitates catalyst recovery and reuse, solving the engineering application problems of powder catalysts.

[0019] Compared with the prior art, the present invention has the following beneficial effects: ① This invention realizes the green and high-value closed-loop utilization of vanadium in waste SCR hazardous waste. After selective leaching of vanadium using DES, the leachate is directly used for in-situ catalyst preparation without separation and purification, eliminating the high-pollution and high-cost processes such as extraction, precipitation, and purification in traditional vanadium recovery processes. The comprehensive utilization rate of vanadium is ≥90%. DES has three functions: leaching agent, spinning aid solvent, and vanadium dispersant. It can be recycled and reused, and there is no secondary pollution in the entire process.

[0020] ② This invention can construct a VN / GaN metal-semiconductor Schottky heterojunction through an in-situ nitridation process, solving the problems of easy aggregation of active components, weak interfacial bonding, and low electron transport efficiency in traditional supported catalysts; VN and GaN are uniformly distributed inside the nanofibers; the built-in electric field formed by the Schottky heterojunction can achieve efficient carrier separation, promote the directional migration of interfacial electrons, significantly enhance the activation ability of oxygen molecules, greatly reduce the energy barrier of toluene oxidation reaction, and achieve low-temperature and high-efficiency catalysis.

[0021] ③ The catalyst prepared by this invention has both excellent photothermal conversion performance and catalytic oxidation activity. The metallic plasmon effect of VN endows the material with full-spectrum solar light absorption capability and high photothermal conversion efficiency. Under sunlight driving, the surface temperature can reach 220℃, which is higher than the catalyst's own T90 (below 172℃). Low-temperature and efficient catalytic oxidation of toluene can be achieved without additional heating, resulting in low energy consumption. GaN and VN form dual active sites for synergistic catalysis, and the toluene T90 (90% conversion temperature) can be as low as below 172℃, which is far superior to traditional transition metal oxide catalysts. At the same time, it has excellent resistance to poisoning and long-term stability in water-containing and sulfur-containing atmospheres.

[0022] ④ The three-dimensional aerogel catalyst prepared by this invention has a hierarchical porous structure and ultra-high specific surface area, resulting in high mass transfer efficiency and large gas contact area. At the same time, the macroscopic bulk structure can be directly packed into a fixed-bed reactor without secondary molding, which solves the engineering application problems of traditional nanopowder catalysts, such as difficult recovery, easy loss, and high bed resistance. It has significant application advantages and industrialization prospects in fields such as industrial VOCs waste gas treatment and indoor air purification. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 : Schematic diagram of the preparation process of the VN / GaN aerogel photothermal catalyst of the present invention.

[0025] Figure 2 SEM image of the VN / GaN composite nanofibers prepared in Example 1.

[0026] Figure 3 TEM images of the VN / GaN composite nanofibers prepared in Example 2 and the corresponding EDX elemental distribution mapping results; (a) is a TEM image of a single composite nanofiber, and (b), (c), and (d) are the elemental distribution mapping diagrams of Ga, V, and N, respectively.

[0027] Figure 4 XRD diffraction patterns of VN / GaN aerogel prepared in Example 3; (a) XRD pattern of precursor nanofibers after air precalcination, corresponding to V2O5 and Ga2O3 phases; (b) XRD pattern of VN / GaN aerogel obtained after ammonia nitridation treatment.

[0028] Figure 5 Infrared thermal images of the VN / GaN aerogel prepared in Example 1 under irradiation with a 500 W xenon lamp; (a) is the initial temperature photo before irradiation (0 min), and (b), (c), and (d) are infrared thermal images at irradiation time of 5 min, 10 min, and 30 min, respectively.

[0029] Figure 6 The toluene catalytic performance curves of the VN / GaN aerogel catalyst prepared in Example 1 are shown in (a) and (b). (a) shows the toluene conversion rate as a function of reaction time, and (b) shows the toluene conversion rate as a function of temperature. Detailed Implementation

[0030] This invention elaborates on the preparation method and performance characterization of VN / GaN aerogel photothermal catalyst through the following embodiments. The parameters of each embodiment are optimized and adjusted within the scope defined in the claims to form a three-dimensional aerogel photothermal catalyst with controllable structure and excellent performance, thereby achieving the application effect of efficient photothermal catalytic oxidation of toluene.

[0031] like Figure 1 As shown, this invention provides a method for preparing a VN / GaN aerogel photothermal catalyst based on in-situ vanadium nitridation of spent SCR catalyst, comprising the following steps: The spent SCR denitration catalyst was leached using choline chloride-oxalic acid eutectic solvent DES, and the resulting vanadium-containing eutectic solvent DES leachate was obtained after solid-liquid separation. The vanadium-containing eutectic solvent DES leachate was directly mixed with gallium source, spinning aid PVP and anhydrous ethanol-deionized water mixed solvent, and magnetically stirred to obtain a uniform and transparent electrospinning precursor solution. PVP / gallium nitrate / vanadium-DES precursor nanofibers were prepared by electrospinning the electrospinning precursor solution. The precursor nanofibers were calcined in an air atmosphere to remove organic components, resulting in V2O5 / Ga2O3 composite nanofibers. V2O5 / Ga2O composite nanofibers were nitrided at high temperature in an ammonia atmosphere to convert Ga2O3 into hexagonal wurtzite GaN and V2O5 was nitrided in situ to generate VN, thus obtaining VN / GaN composite nanofibers. VN / GaN composite nanofibers were added to a dispersion solvent and ultrasonically dispersed in an ice bath to obtain a uniform fiber dispersion. The dispersion was then sealed and aged at room temperature, followed by pre-freezing, freeze-drying, and low-temperature drying to obtain a VN / GaN aerogel photothermal catalyst.

[0032] The following are specific examples.

[0033] Example 1

[0034] Choline chloride and oxalic acid were mixed at a molar ratio of 1:1.5 and stirred at 100℃ for 1 hour to obtain a homogeneous and transparent eutectic solvent DES. Waste SCR denitrification catalyst from a power plant was ground to below 200 mesh and added to the eutectic solvent DES at a solid-liquid ratio of 1:10 g / mL. The mixture was stirred at 120℃ for 3 hours to leach, and the TiO2 support residue was removed by filtration to obtain a vanadium-containing eutectic solvent DES leachate. ICP analysis showed that the vanadium leaching rate was 96.2%, the TiO2 leaching rate was 2.1%, the Al2O3 leaching rate was 2.4%, and the vanadium concentration in the leachate was 0.78 mol / L.

[0035] Take 15g of the above-mentioned vanadium-containing eutectic solvent DES leaching solution, add 50g of gallium nitrate stock solution (8% by mass), 10g of polyvinylpyrrolidone (PVP) (Mw=1300000), 42mL of anhydrous ethanol, and 8mL of deionized water, and stir magnetically at room temperature for 10h to obtain a homogeneous and transparent electrospinning precursor solution. Inject the precursor solution into a 10mL spinning syringe equipped with a No. 21 stainless steel flat-tipped needle, set the spinning voltage to 18kV, the feed rate to 1mL / h, the receiving distance to 15cm, the ambient humidity to 25%, and the ambient temperature to 22℃, and continuously spin for 4h to obtain PVP / gallium nitrate / vanadium-DES composite precursor nanofibers.

[0036] Precursor fibers were laid flat in an alumina crucible and placed in a tube furnace. The temperature was increased to 900°C at a rate of 2°C / min under an air atmosphere and held for 2 hours at an air flow rate of 200 sccm. The mixture was then allowed to cool naturally to room temperature to obtain V₂O₅ / Ga₂O₃ composite nanofibers. These composite fibers were then laid flat in an alumina ceramic boat and placed in a tube furnace. The temperature was increased to 850°C at a rate of 2°C / min under an ammonia atmosphere and held for 2 hours at an ammonia flow rate of 200 sccm. After nitriding, ammonia was continuously purged, and the mixture was allowed to cool naturally to room temperature to obtain VN / GaN composite nanofibers.

[0037] 1g of the above VN / GaN composite nanofibers were added to 100mL of a 1:1 mixture of anhydrous ethanol and tert-butanol. The mixture was ultrasonically dispersed in an ice bath for 40min using an intermittent pulse mode, with a 4s interval between each ultrasonic session and a 3s interval, at a power of 190W, resulting in a uniform fiber dispersion of 10mg / mL. The dispersion was completely sealed with a sealing film and aged at room temperature for 18h to allow the fibers to fully overlap and self-assemble into a robust three-dimensional network structure. The aged dispersion was then poured into a polytetrafluoroethylene mold and pre-frozen at -60℃ for 3h. It was then placed in a freeze dryer at -65℃ under a vacuum of 10Pa for 36h to obtain a cylindrical VN / GaN aerogel photothermal catalyst with a VN content of 40.1wt%. The specific surface area of ​​the catalyst was measured to be 312m² using an Autosorb-1 fully automated surface area and pore size analyzer from Quantachrome (USA). 2 / g, with an average pore size of 18nm, exhibiting a mesoporous-macroporous hierarchical porous structure; SEM analysis revealed that the aerogel is composed of regularly morphologically regular nanofibers with an average diameter of approximately 240nm. Figure 2 ).

[0038] Example 2

[0039] Choline chloride and oxalic acid were mixed at a molar ratio of 1:1 and stirred at 100℃ for 1 h to obtain a homogeneous and transparent DES. Waste SCR denitrification catalyst was ground to below 200 mesh and added to DES at a solid-liquid ratio of 1:15 g / mL. The mixture was stirred at 130℃ for 2 h to leach. The TiO2 support residue was removed by filtration to obtain a vanadium-containing DES leachate. ICP analysis showed that the vanadium leaching rate was 95.1%, the TiO2 leaching rate was 2.3%, the Al2O3 leaching rate was 2.6%, and the vanadium concentration in the leachate was 0.76 mol / L.

[0040] Take 16g of the above-mentioned vanadium-containing DES leaching solution, add 40g of 10% gallium nitrate stock solution, 9g of PVP (Mw=1300000), 44mL of anhydrous ethanol, and 7mL of deionized water, and stir magnetically at room temperature for 10h to obtain a homogeneous and transparent electrospinning precursor solution. Inject the precursor solution into a spinning injector, set the spinning voltage to 16kV, the feed rate to 0.8mL / h, the receiving distance to 16cm, the ambient humidity to 28%, and the ambient temperature to 23℃, and continuously spin for 4h to obtain composite precursor nanofibers.

[0041] Precursor fibers were placed in a tube furnace and heated to 850°C at a rate of 2°C / min under an air atmosphere, held for 3 hours at an air flow rate of 200 sccm, and then naturally cooled to room temperature to obtain V₂O₅ / Ga₂O₃ composite nanofibers. The composite fibers were then placed in a tube furnace under an ammonia atmosphere and heated to 900°C at a rate of 2°C / min, held for 3 hours at an ammonia flow rate of 200 sccm, and then naturally cooled to room temperature to obtain VN / GaN composite nanofibers.

[0042] 0.8 g of the above VN / GaN composite nanofibers were added to 100 mL of a 1:1 mixture of anhydrous ethanol and tert-butanol. The mixture was ultrasonically dispersed in an ice bath for 35 min using an intermittent pulse mode, with a 3-second interval between each sonication and a 2-second interval, at a power of 180 W, resulting in a uniform fiber dispersion of 8 mg / mL. The dispersion was completely sealed with a sealing film and aged at room temperature for 18 h to allow the fibers to fully overlap and self-assemble into a robust three-dimensional network structure. The aged dispersion was then poured into a polytetrafluoroethylene mold, pre-frozen at -55°C for 3.5 h, and then freeze-dried at -65°C under a vacuum of 12 Pa for 48 h to obtain the VN / GaN aerogel photothermal catalyst. The specific surface area of ​​the catalyst was measured to be 287 m² using an Autosorb-1 fully automated surface area and pore size distribution analyzer from Quantachrome (USA). 2 / g, with an average pore size of 22nm. The average fiber diameter is 230nm, and the VN content is 39.7wt%. Figure 3 shows the TEM morphology image and corresponding EDX elemental distribution mapping results of the VN / GaN composite nanofibers prepared in Example 2, where (a) is the TEM image of a single composite nanofiber, and (b), (c), and (d) are the distribution mapping diagrams of Ga, V, and N elements, respectively. As can be seen from the figure, Ga, V, and N elements are uniformly distributed along the fiber direction, indicating that VN and GaN have been uniformly composited inside the nanofibers through the in-situ nitriding process.

[0043] Example 3

[0044] Choline chloride and oxalic acid were mixed at a molar ratio of 1:2 and stirred at 100℃ for 1 h to obtain homogeneous and transparent DES. Waste SCR denitration catalyst was ground to below 200 mesh and added to DES at a solid-liquid ratio of 1:8 g / mL. The mixture was stirred at 110℃ for 4 h to leach. The TiO2 support residue was removed by filtration to obtain vanadium-containing DES leachate. ICP analysis showed that the vanadium leaching rate was 95.7%, the TiO2 leaching rate was 1.8%, the Al2O3 leaching rate was 2.2%, and the vanadium concentration in the leachate was 0.79 mol / L.

[0045] Take 14g of the above-mentioned vanadium-containing DES leaching solution, add 33g of 12% gallium nitrate stock solution, 11g of PVP (Mw=1300000), 40mL of anhydrous ethanol, and 9mL of deionized water, and magnetically stir at room temperature for 11h to obtain a homogeneous and transparent electrospinning precursor solution. Inject the precursor solution into a spinning injector, set the spinning voltage to 20kV, the feed rate to 1.2mL / h, the receiving distance to 14cm, the ambient humidity to 22%, and the ambient temperature to 20℃, and continuously spin for 4h to obtain composite precursor nanofibers. Place the precursor fibers in a tube furnace, heat to 900℃ at a heating rate of 3℃ / min under air atmosphere, hold for 2h, with an air flow rate of 250sccm, and naturally cool to room temperature to obtain V2O5 / Ga2O3 composite nanofibers. The composite fibers were placed in a tube furnace and heated to 880°C at a rate of 3°C / min under an ammonia atmosphere. The temperature was maintained for 1.5 hours with an ammonia flow rate of 250 sccm. The mixture was then allowed to cool naturally to room temperature to obtain VN / GaN composite nanofibers.

[0046] 1.2 g of the above VN / GaN composite nanofibers were added to 100 mL of a 1:1 mixture of anhydrous ethanol and tert-butanol. The mixture was ultrasonically dispersed in an ice bath for 50 min using an intermittent pulse mode, with a 5-second interval between each sonication and a 4-second interval, at a power of 210 W, resulting in a uniform fiber dispersion of 12 mg / mL. The dispersion was completely sealed with a sealing film and aged at room temperature for 18 h to allow the fibers to fully overlap and self-assemble into a robust three-dimensional network structure. The aged dispersion was then poured into a polytetrafluoroethylene mold, pre-frozen at -60°C for 2.5 h, and then freeze-dried at -65°C under a vacuum of 8 Pa for 24 h to obtain the VN / GaN aerogel photothermal catalyst. The specific surface area of ​​the catalyst was measured to be 335 m² using an Autosorb-1 fully automated surface area and pore size distribution analyzer from Quantachrome (USA). 2 / g, with an average pore size of 16nm. The GaN fiber has an average diameter of 210nm and a VN content of 40.5wt%, with VN and GaN uniformly distributed within the nanofibers. Figure 4 shows the XRD diffraction pattern of the VN / GaN aerogel prepared in Example 3, where (a) is the XRD pattern of the precursor nanofibers after air pre-calcination, corresponding to the phases V2O5 and Ga2O3; (b) is the XRD pattern of the VN / GaN aerogel obtained after ammonia nitridation treatment. The nitrided sample contains characteristic diffraction peaks of hexagonal wurtzite GaN and cubic VN, indicating that V2O5 and Ga2O3 are completely nitrided into VN and GaN at a nitriding temperature of 850℃.

[0047] Example 4 (Catalytic Performance Test) The VN / GaN aerogel catalysts prepared in Examples 1-3 were cut into cylindrical shapes matching the inner diameter of the reactor and packed into a fixed-bed photothermal reactor. A 500W xenon lamp (simulating sunlight, wavelength range 300-2500 nm) was used as the light source to test the photothermal catalytic oxidation performance of toluene. The test conditions were: initial toluene concentration of 100 mg / m³. 3 The total gas flow rate is 50 mL / min. -1 The oxygen volume fraction was 20%, nitrogen was used as the balance gas, the reaction system was at atmospheric pressure, and the air humidity was approximately 50%. Gas chromatography was used to monitor the concentrations of toluene and CO2 at the reactor inlet and outlet online, and toluene conversion and CO2 selectivity were calculated. Simultaneously, long-term stability and sulfur and water resistance tests were conducted.

[0048] The test results are as follows: Photothermal performance: The catalyst prepared in Example 1, after being irradiated with a 500W xenon lamp for 10 minutes, had a surface temperature that rose to 168°C, and after irradiation for 30 minutes, the temperature stabilized at 195°C. Figure 5 The catalyst prepared in Example 2 stabilized at a surface temperature of 192℃ after irradiation for 30 min; the catalyst prepared in Example 3 stabilized at a surface temperature of 187℃ after irradiation for 30 min. All catalysts prepared in the three examples exhibited excellent photothermal conversion performance. Figure 5 shows the infrared thermal imaging results of the VN / GaN aerogel prepared in Example 1 under irradiation with a 500W xenon lamp. (a) is the initial temperature photograph before irradiation (0 min), with a sample temperature of 294 K; (b), (c), and (d) are infrared thermal imaging photographs after irradiation for 5 min, 10 min, and 30 min, respectively, with corresponding maximum sample temperatures of 376 K, 441 K, and 468 K.

[0049] Catalytic activity: Figure 6 shows the toluene catalytic performance curve of the VN / GaN aerogel catalyst prepared in Example 1. (a) is the curve of toluene conversion rate as a function of reaction time. The results show that the toluene conversion rate under photothermal catalysis is 93.1%, which is significantly higher than that of thermal catalysis alone (49.6%). (b) is the curve of toluene conversion rate as a function of temperature. The T10 and T90 under photothermal catalysis and thermal catalysis conditions are compared. It can be seen from the figure that the T90 of photothermal catalysis is lower than that of thermal catalysis, indicating that the catalyst significantly reduces the temperature of toluene oxidation reaction under the synergistic effect of photothermal catalysis, and achieves low-temperature and high-efficiency catalytic oxidation. In this example, the toluene ignition temperature T10 (10% conversion rate) was 126℃, T90 was 167℃, and CO2 selectivity was ≥95%. The catalyst prepared in Example 2 showed a toluene conversion rate of 94.5%, which was significantly higher than that of the single-heat thermal catalysis (45.3%). The T10 was 134℃, T90 was 168℃, and CO2 selectivity was ≥93%. The catalyst prepared in Example 3 showed a toluene conversion rate of 92.7%, which was significantly higher than that of the single-heat thermal catalysis (46.4%). The T10 was 130℃, T90 was 172℃, and CO2 selectivity was ≥96%.

[0050] Stability test: The catalyst prepared in Example 1 showed a toluene conversion rate decrease of only 7.2% after 100 hours of continuous operation; the catalyst in Example 2 showed a conversion rate decrease of 6.8% after 100 hours of continuous operation; and the catalyst in Example 3 showed a conversion rate decrease of 8.5% after 100 hours of continuous operation, all of which showed excellent long-term stability.

[0051] Anti-poisoning performance: After adding 50ppmSO2 and 5vol%H2O to the reaction gas and running continuously for 24h, the toluene conversion rate of the catalyst prepared in Example 1 was 87.7%, that in Example 2 was 89.5%, and that in Example 3 was 85.8%, showing excellent anti-sulfur and anti-water performance.

[0052] Comparative Example 1 (Preparation of VN / GaN catalyst by conventional impregnation method) The spent SCR catalyst, identical to that in Example 1, was treated using the traditional sulfuric acid leaching method. V₂O₅ powder was obtained through P₂O₄ extraction, sulfuric acid back-extraction, ammonia precipitation, and calcination at 500°C. Pure Ga₂O₃ nanofibers were prepared following the steps in Example 1, and then the same amount of V₂O₅ powder was loaded onto them using an equal-volume impregnation method. After nitriding under the same conditions as in Example 1, a VN / GaN powder catalyst was obtained, without the preparation of an aerogel. Testing showed that the catalyst had a toluene T90 of 260°C, and after 100 hours of continuous operation, the conversion rate decreased by 21.7%. The conversion rate retention rate after 24 hours at 50 ppm SO₂ + 5% H₂O was only 68.3%, significantly lower than that of the embodiments of this invention.

[0053] Comparative Example 2 (Pure GaN Aerogel Catalyst) Without adding vanadium-containing DES leachate, the remaining spinning, pre-calcination, nitriding, and aerogel preparation steps were completely consistent with Example 1, yielding a pure GaN aerogel catalyst. Testing revealed that this catalyst exhibited no photothermal conversion performance, with a toluene conversion rate of less than 20% at 350°C, indicating almost no toluene catalytic oxidation activity.

[0054] The above test results show that the VN / GaN aerogel photothermal catalyst prepared in this invention has excellent photothermal conversion performance, low-temperature catalytic oxidation activity of toluene, long-term stability and anti-poisoning performance, realizing the green and high-value utilization of vanadium in waste SCR hazardous waste, solving the core defects of existing catalysts, and has broad application prospects in the field of VOCs photothermal catalytic treatment.

Claims

1. A method for preparing a VN / GaN aerogel photothermal catalyst based on in-situ vanadium nitridation of spent SCR catalyst, characterized in that, The specific steps are as follows: (1) Selective vanadium leaching: The waste SCR denitration catalyst was leached using the choline chloride-oxalic acid eutectic solvent DES. After solid-liquid separation, a vanadium-containing eutectic solvent DES leachate was obtained. (2) In-situ preparation of spinning solution: The vanadium-containing eutectic solvent DES leaching solution obtained in step (1) is directly mixed with gallium source, spinning aid and anhydrous ethanol-deionized water mixed solvent, and magnetically stirred to obtain a uniform and transparent electrospinning precursor solution. (3) Electrospinning: The electrospinning precursor liquid obtained in step (2) is electrospinned to obtain precursor nanofibers. (4) Air precalcination: The precursor nanofibers obtained in step (3) are placed in an air atmosphere for calcination to remove organic components and obtain V2O5 / Ga2O3 composite nanofibers. (5) Ammonia nitriding treatment: The V2O5 / Ga2O3 composite nanofibers obtained in step (4) are placed in an ammonia atmosphere and nitrided at high temperature to convert Ga2O3 into hexagonal wurtzite GaN and V2O5 is nitrided in situ to generate VN, thus obtaining VN / GaN composite nanofibers. (6) Aerogel forming: The VN / GaN composite nanofibers obtained in step (5) are added to the dispersion solvent and ultrasonically dispersed in an ice bath to obtain a uniform fiber dispersion; sealed and aged at room temperature, then pre-frozen, freeze-dried and dried at low temperature to obtain VN / GaN aerogel photothermal catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), in the choline chloride-oxalic acid eutectic solvent DES, the molar ratio of choline chloride to oxalic acid is 1:1 to 1:2; the waste SCR denitrification catalyst is pre-ground to below 200 mesh, the solid-liquid ratio of the waste SCR denitrification catalyst to DES is 1:5 to 1:20 g / mL, the leaching temperature is 100 to 140℃, the leaching time is 2 to 4 h, and solid-liquid separation is carried out by filtration.

3. The preparation method according to claim 1, characterized in that, In step (2), the gallium source is gallium nitrate nonahydrate; the spinning aid is polyvinylpyrrolidone (PVP) with a number average molecular weight of 1,300,000; in the anhydrous ethanol-deionized water mixed solvent, the volume ratio of anhydrous ethanol to deionized water is 4:1 to 10:1; the magnetic stirring temperature is room temperature, and the magnetic stirring time is 6 to 12 hours. In the obtained electrospinning precursor solution, the vanadium-containing eutectic solvent DES leaching solution accounts for 8 wt% to 20 wt%, gallium nitrate nonahydrate accounts for 2.5 wt% to 5.0 wt%, polyvinylpyrrolidone (PVP) accounts for 6 wt% to 10 wt%, and the balance is the anhydrous ethanol-deionized water mixed solvent.

4. The preparation method according to claim 1, characterized in that, In step (3), the electrospinning process parameters are: spinning voltage of 15~20kV, feed speed of 0.5~1.5mL / h, receiving distance of 12~18cm, ambient humidity of 20~30%, and ambient temperature of 20~25℃.

5. The preparation method according to claim 1, characterized in that, In step (4), the calcination process conditions are as follows: under an air atmosphere, the air flow rate is controlled at 100~300 sccm, the temperature is raised to 500~900℃ at a heating rate of 1~3℃ / min, held for 1~3h, and then naturally cooled to room temperature.

6. The preparation method according to claim 1, characterized in that, In step (5), the high-temperature nitriding process conditions are as follows: under an ammonia atmosphere, the ammonia flow rate is controlled at 150~250 sccm, the temperature is raised to 800~900℃ at a heating rate of 1~3℃ / min, held for 1~3h, and then naturally cooled to room temperature.

7. The preparation method according to claim 1, characterized in that, In step (6), the dispersion solvent is a mixture of anhydrous ethanol and tert-butanol with a volume ratio of 2:1 to 1:2; the mass concentration of the fiber dispersion is 5 to 15 mg / mL; the ice bath ultrasonication adopts an intermittent pulse mode, with a single ultrasonication of 3 to 5 seconds and an interval of 2 to 4 seconds, a power of 180 to 220 W, and a dispersion time of 30 to 60 min; the mixture is sealed and aged at room temperature for 12 to 24 h; the pre-freezing temperature is -40 to -60℃, and the pre-freezing time is 2 to 4 h; the freeze-drying cold trap temperature is < -60℃, the vacuum degree is < 15 Pa, and the drying time is 24 to 48 h; finally, the mixture is dried at 60 to 80℃ for 2 to 6 h to remove residual solvent.

8. A VN / GaN aerogel photothermal catalyst prepared by the method according to any one of claims 1 to 7, characterized in that, The catalyst possesses a three-dimensional continuous nanofiber network and a mesoporous-macroporous hierarchical porous structure with a specific surface area of ​​200-350 m². 2 / g, pore size distribution range is 1.5~40nm, VN content is 30wt%~50wt%.

9. The application of the VN / GaN aerogel photothermal catalyst according to claim 8 in the photothermal catalytic oxidation of VOCs.

10. The application according to claim 9, characterized in that, VOCs are toluene.

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