A composite photocatalytic material, its preparation method and application

Abstract

The present invention belongs to the technical field of catalysts. In order to solve the problems of secondary pollution, low photocatalytic efficiency and non-reusability existing in the existing photocatalysts for the degradation of unsymmetrical dimethylhydrazine wastewater, a composite photocatalytic material is proposed. This material is a supported three-dimensional core-shell structure TiO2 / CeO2, denoted as CC / TiO2NRs@CeO2NPs. The TiO2 nanorods supported by this material can not only be reused, but also greatly increase the active area. The CeO2 nanoparticles are introduced in the form of coating the nanorod arrays, ensuring the structural stability. When irradiated with ultraviolet-visible light, the photo-generated electrons transfer to the valence band of TiO2, while the photo-generated holes transfer to the conduction band of CeO2, thereby increasing the yield of photo-generated carriers. The photo-generated electrons react with the oxygen molecules adsorbed on the surface of the acceptor to form superoxide radicals, and the photo-generated holes react with water molecules to generate hydroxyl radicals. These strongly oxidizing radicals can directly oxidize the organic pollutant molecules and mineralize them into water molecules and carbon dioxide, realizing the photocatalytic degradation of unsymmetrical dimethylhydrazine.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a composite photocatalytic material, a preparation method thereof and an application thereof. Background Art

[0002] Unsymmetrical dimethylhydrazine has advantages such as high specific impulse, low cost and easy storage, and is widely used as a high-energy liquid rocket fuel in the aerospace field. During the processes of space launch, engine test, fuel storage, etc., a large amount of unsymmetrical dimethylhydrazine waste gas and waste liquid will be generated, which are likely to induce cancer and cause gene mutations. The environmental problems caused thereby cannot be ignored and need to be solved urgently.

[0003] At present, photocatalytic technology has been applied to the treatment process of unsymmetrical dimethylhydrazine wastewater due to its advantages such as environmental friendliness, safety and reliability, and low energy consumption. TiO2 is favored in the field of photocatalytic water purification because of its non-direct human toxicity, stable physical and chemical properties, easy batch synthesis, etc. However, its relatively wide band gap enables it to only utilize ultraviolet light in sunlight, and the too strong electron-hole recombination level greatly reduces the photocatalytic efficiency. In addition, the use mode of powder also makes the catalyst not convenient for recycling and reuse, and is likely to cause secondary pollution. These two problems seriously limit its practical application feasibility, and a suitable modification method and loading means must be found.

[0004] Rare earth oxide CeO2 is low in cost, can absorb visible light, has a relatively narrow band gap (2.8 eV) and appropriate band edge potential. Combining nano-TiO2 and CeO2 to form a heterojunction can effectively expand the light response range of the TiO2 photocatalytic material, enhance the light absorption ability of the TiO2 photocatalytic material in the ultraviolet and visible light regions, improve the light utilization efficiency, and can inhibit the recombination of photo-generated electrons and holes, thereby improving the photocatalytic performance.

[0005] However, the existing TiO2 / CeO2 heterojunction powder structure has a low active area and cannot be recycled, and a stable structure loading material with a high active area should be further developed.

[0006] The photocatalyst for degrading unsymmetrical dimethylhydrazine wastewater disclosed in CN201210073295.6 is noble metal-doped ZnO nanoparticles. Noble metals such as Ag and Pd are doped in the photocatalyst, and photocatalytic reaction can be carried out in the visible light range. However, the prepared photocatalyst is high in cost, and the noble metals in the catalyst may cause secondary pollution.

[0007] The disclosed immobilized unsymmetrical dimethylhydrazine photocatalytic material, such as the three-dimensional macroporous carbon / carbon nanotube / titanium dioxide / silver composite material disclosed in CN201510212240.2 for photocatalytic degradation of unsymmetrical dimethylhydrazine wastewater, can only carry out photocatalytic degradation under the condition of ultraviolet light, and requires an ultraviolet lamp tube as the required excitation light source, consuming a large amount of electric energy and increasing the cost.

[0008] CN110368919A prepared TiO2 nanorod arrays by a hydrothermal method and loaded them on a conductive glass substrate, and doped with a mixture of iron, nickel, and zinc for modification, achieving the degradation of unsymmetrical dimethylhydrazine under simulated sunlight conditions. Under visible light irradiation with an intensity of 60 mW / cm 2 for 180 min, the degradation rate of 15 ml of unsymmetrical dimethylhydrazine with a concentration of 20 mg / L was only 32%, and the photocatalytic efficiency was relatively low.

[0009] The CeO2 / TiO2 heterojunction micro-nano material disclosed in CN110605111A is a micron-scale microsphere structure, which is prone to agglomeration when used in wastewater solutions. Under visible light irradiation for 120 min, the degradation rate of a 14 mg / L methyl orange solution was only 70%. Its photocatalytic efficiency under visible light is relatively low, and the recovery of the micron-scale microsphere structure is difficult and not convenient for repeated use. Summary of the Invention

[0010] In order to comprehensively solve the above problems, the present invention proposes a composite photocatalytic material, which is specifically a supported core-shell structure TiO2 / CeO2 composite photocatalytic material. Its application to the treatment of unsymmetrical dimethylhydrazine wastewater can make up for the deficiencies of the existing technology, is green and environmentally friendly, has high photocatalytic efficiency, stable performance, and is convenient for repeated use.

[0011] The composite photocatalytic material prepared by the present invention has TiO2 nanorods loaded on carbon cloth, which are convenient for repeated use and form a three-dimensional interface structure, greatly increasing the active area. CeO2 nanoparticles are introduced in the form of coating the nanorod array. The formed core-shell structure heterojunction not only promotes the separation and export of electron-hole pairs but also ensures the stability of the structure. When irradiated with ultraviolet-visible light, photo-generated electrons transfer to the valence band of TiO2, while photo-generated holes transfer to the conduction band of CeO2, thereby increasing the yield of photo-generated carriers. The photo-generated electrons react with oxygen molecules adsorbed on the surface of the acceptor to form superoxide radicals (·O2-), and the photo-generated holes react with water molecules to generate hydroxyl radicals (·OH). These strongly oxidizing radicals can directly oxidize organic pollutant molecules and mineralize them into water molecules and carbon dioxide, achieving the purpose of photocatalytic degradation of unsymmetrical dimethylhydrazine.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0013] A composite photocatalytic material, which is a supported three-dimensional core-shell structure TiO2 / CeO2, denoted as CC / TiO2 NRs@CeO2 NPs.

[0014] A preparation method of a composite photocatalytic material, including

[0015] Step 1: Prepare CC / TiO2;

[0016] Step 2: Prepare CC / TiO2 NRs based on CC / TiO2;

[0017] Step 3: Prepare CC / TiO2 NRs@CeO2 NPs based on CC / TiO2 NRs.

[0018] Preferably, Step 1 includes:

[0019] Step 1.1: Dropwise add tetrabutyl titanate into an anhydrous ethanol solution under vigorous stirring to prepare a mixed solution;

[0020] Step 1.2: Immerse the washed carbon cloth in the mixed solution for 10 min to 30 min for seeding;

[0021] Step 1.3: Heat-treat the seeded carbon cloth in a muffle furnace, and then cool it to room temperature in the furnace after completion;

[0022] Step 1.4: Wash the heat-treated carbon cloth with anhydrous ethanol and ultrapure water, and dry it to obtain a carbon cloth loaded with a titanium dioxide seed layer, denoted as CC / TiO2.

[0023] Preferably, Step 2 includes:

[0024] Step 2.1: Prepare a mixed solution of concentrated hydrochloric acid, ultrapure water and tetrabutyl titanate, place the carbon cloth loaded with the titanium dioxide seed layer obtained in Step 1 in the mixed solution, and transfer it to a high-pressure reactor;

[0025] Step 2.2: Place the high-pressure reactor in a muffle furnace for hydrothermal reaction;

[0026] Step 2.3: Wash the hydrothermal reaction product with anhydrous ethanol and ultrapure water, and dry it to obtain a carbon cloth loaded with a titanium dioxide nanorod array, denoted as CC / TiO2 NRs.

[0027] Preferably, Step 3 includes:

[0028] Step 3.1: Prepare a mixed solution of cerium nitrate solution and anhydrous ethanol, immerse the carbon cloth loaded with the titanium dioxide nanorod array obtained in Step 2 in the mixed solution for 30 min to 60 min, place it in a muffle furnace for heat treatment, and then cool it to room temperature in the furnace after completion;

[0029] Step 3.2: Wash the heat-treated TiO2 nanorod array modified carbon cloth three times with deionized water and anhydrous ethanol, and dry it to obtain a supported three-dimensional core-shell structure TiO2 / CeO2 composite photocatalytic material, denoted as CC / TiO2 NRs@CeO2 NPs.

[0030] Preferably, in Step 1.1, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:50 to 100; the heat treatment process in Step 1.3 is: heating to 400°C to 600°C at a heating rate of 5°C / min and holding for 6 h to 10 h.

[0031] Preferably, in Step 2.1, the volume ratio of tetrabutyl titanate, concentrated hydrochloric acid and ultrapure water is 1:50 to 100:100 to 200; the hydrothermal reaction process in Step 2.2 is: reacting at 150°C to 300°C for 10 h to 15 h.

[0032] Preferably, in Step 3, the concentration of cerium nitrate solution is 5 to 10 mmol / L, and the molar ratio of cerium nitrate to tetrabutyl titanate in Step 2.1 is 1:2; the heat treatment process is: heating to 400°C to 600°C at a heating rate of 5°C / min and holding for 4 h to 8 h.

[0033] The composite photocatalytic material is applied to the treatment of unsymmetrical dimethylhydrazine wastewater, and the application method includes:

[0034] S1: Prepare 40 ml of unsymmetrical dimethylhydrazine wastewater with a concentration of 100 mg / L to 110 mg / L;

[0035] S2: Add the supported three-dimensional core-shell structure TiO2 / CeO2 composite photocatalytic material of 4 cm 2 ~9 cm 2 to the unsymmetrical dimethylhydrazine wastewater in Step 1, place it in a light-shielded reaction box and let it stand for reaction for 30 min;

[0036] S3: Use a xenon lamp light source, place the quartz tube 10 cm away from the lamp light source, start the photocatalytic reaction, sample and analyze every 1 h, and set the lamp radiation power to 100 W / cm 2 ;

[0037] S4: During the photocatalytic reaction, sample and analyze every 1 h to measure the concentration of unsymmetrical dimethylhydrazine in the wastewater.

[0038] The concentrations of unsymmetrical dimethylhydrazine in the wastewater in S1, S2 and S3 are all measured by the sodium nitroferricyanide spectrophotometric method.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. The supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material proposed by the present invention can directly obtain CC / TiO2 NRs@CeO2 NPs through the impregnation-calcination-solvent hydrothermal-impregnation-calcination method. The TiO2 nanorod arrays supported on the carbon cloth form a three-dimensional interface structure, greatly increasing the reactive area and providing more active reaction sites. The CeO2 nanoparticles are tightly wrapped on the surface of the TiO2 nanorods. The core-shell structured heterojunction formed by highly crystalline TiO2 and CeO2 promotes the separation and export of electron-hole pairs, thereby improving the photocatalytic activity and being more convenient for recycling compared to powder materials.

[0041] 2. The supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material of the present invention combines CeO2 and TiO2, effectively expanding the light response range of the TiO2 photocatalytic material and enhancing the light absorption ability of the TiO2 photocatalytic material in the ultraviolet and visible light regions. Compared with the traditional unmodified TiO2 photocatalytic material that only responds to ultraviolet light with a wavelength less than 380 nm, the supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material of the present invention can not only respond to ultraviolet light but also respond in the visible light region of 380 - 780 nm. The degradation rate of UDMH can reach 97.5% under simulated sunlight conditions for 210 min. Therefore, it has high photocatalytic activity and efficiency.

[0042] 3. The CC / TiO2 NRs@CeO2 NPs prepared by the present invention has the best photocatalytic performance. The degradation rate of UDMH is 97.5% under simulated sunlight conditions, and the degradation rate can still reach 95% after 5 cycles under xenon lamp illumination. The degradation efficiency only decreases by 2.5% after five cycles. Thus, it can be seen that the composite photocatalytic material has stable performance and good recyclability.

[0043] 4. The preparation process of the supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material of the present invention is simple and low-cost (conventional methods such as chemical treatment methods load copper and iron hydroxides on certain oxide carriers to make catalysts, and use H2O2 and oxygen in the air to oxidize and remove UDMH in water. Such methods are costly and energy-consuming. In the experiment, excessive H2O2 needs to be degraded with substances such as MnO2. The tetrabutyl titanate of this method is 8000 yuan / ton, and cerium nitrate is 14000 yuan / ton.). The materials used are all common industrial raw materials that can be purchased on the market and produced on a large scale. The preparation process is simple and there are no harsh preparation conditions, effectively solving the problems of difficult recycling of TiO2 powder materials, low photocatalytic efficiency, and easy agglomeration during the photocatalytic reaction process (a three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material is loaded on the carbon cloth through the impregnation-calcination-solvent hydrothermal-repeated calcination method. This supported photocatalytic material does not agglomerate compared to TiO2 powder materials), and has broad market application prospects. Description of the Drawings

[0044] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0045] In the drawings:

[0046] Figure 1 Scanning electron microscope (SEM) morphology of the composite photocatalytic material: (a) and (b) are both carbon cloth fibers CC; (c) and (d) are both CC / TiO2; (e) and (f) are both CC / TiO2NRs; (g) and (h) are both CC / TiO2NRs@CeO2NPs

[0047] Figure 2 High-resolution transmission electron microscope (HRTEM) morphology diagram of the composite photocatalytic material;

[0048] Figure 3 X-ray electron diffraction (XRD) diagram of the composite photocatalytic material: (a) component powders (TiO2, TiO2NRs, CeO2NPs) of the composite photocatalytic material; (b) composite photocatalytic materials (samples CC, CC / TiO2, CC / TiO2NRs, CC / TiO2NRs@CeO2NPs);

[0049] Figure 4 Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis) diagram of the component powders of the composite photocatalytic material (TiO2, TiO2NRs, CeO2NPs, TiO2 / CeO2);

[0050] Figure 5 I-t curve of the composite photocatalytic material under light and dark conditions (samples CC / TiO2, CC / TiO2NRs, CC / TiO2NRs@CeO2NPs);

[0051] Figure 6 Electrochemical impedance spectroscopy of the composite photocatalytic material (samples CC / TiO2, CC / TiO2NRs, CC / TiO2NRs@CeO2NPs);

[0052] Figure 7 Degradation effect diagram of unsymmetrical dimethylhydrazine wastewater by the composite photocatalytic material under xenon lamp source radiation conditions (samples CC / TiO2, CC / TiO2NRs, CC / TiO2NRs@CeO2NPs);

[0053] Figure 8 Reusability effect diagram of the composite photocatalytic material (CC / TiO2NRs@CeO2NPs);

[0054] Figure 9 This is the flowchart of the preparation method of the composite photocatalytic material of the present invention. Specific embodiments

[0055] The following will describe the preferred embodiments of the present invention with reference to the attached Figures 1-9 It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0056] Example 1:

[0057] As Figure 9 shown, a preparation method of a composite photocatalytic material includes

[0058] Step 1: Prepare CC / TiO2. Specifically, it includes:

[0059] Step 1.1: Add tetrabutyl titanate dropwise to an anhydrous ethanol solution under vigorous stirring to prepare a mixed solution; wherein, the volume ratio of tetrabutyl titanate to anhydrous ethanol is 1:100.

[0060] Step 1.2: Immerse the washed carbon cloth (denoted as CC) in the mixed solution for 30 minutes for inoculation;

[0061] Step 1.3: Heat-treat the inoculated carbon cloth in a muffle furnace at a heating rate of 5 °C / min to 400 °C, hold for 6 hours, and then cool it to room temperature with the furnace after the heat treatment is completed;

[0062] Step 1.4: Wash the heat-treated carbon cloth three times with anhydrous ethanol and ultrapure water, and dry it to obtain carbon cloth loaded with a titanium dioxide seed layer, denoted as CC / TiO2.

[0063] Step 2: Prepare CC / TiO2 NRs based on CC / TiO2. Specifically, it includes:

[0064] Step 2.1: Prepare a mixed solution according to the volume ratio of tetrabutyl titanate, concentrated hydrochloric acid and ultrapure water of 1:50:100, stir it vigorously, place the carbon cloth loaded with the titanium dioxide seed layer in Step 1 in the mixed solution, and transfer it to a high-pressure reaction kettle;

[0065] Step 2.2: Place the high-pressure reaction kettle in a muffle furnace and react at 150 °C for 10 hours for hydrothermal reaction;

[0066] Step 2.3: After the reaction is completed, wash the hydrothermal reaction product with anhydrous ethanol and ultrapure water, and dry it to obtain carbon cloth loaded with a titanium dioxide nanorod array, denoted as CC / TiO2 NRs. (NRs represents nanorods)

[0067] Step 3: Prepare CC / TiO2 NRs@CeO2 NPs based on CC / TiO2 NRs. Specifically, it includes:

[0068] Step 3.1: Vigorously stir the cerium nitrate solution (concentration 5 mmol / L) with absolute ethanol to prepare a mixed solution. The molar ratio of cerium nitrate to tetrabutyl titanate in Step 2.1 is 1:2. Immerse the carbon cloth loaded with titanium dioxide nanorod arrays obtained in Step 2 in the mixed solution for 60 min, and place it in a muffle furnace for heat treatment. The heat treatment process is: heat to 400 °C at a heating rate of 5 °C / min, hold for 4 h, and then cool to room temperature with the furnace after completion;

[0069] Step 3.2: Wash the heat-treated TiO2 nanorod array modified carbon cloth three times with deionized water and absolute ethanol, and dry it to obtain a supported three-dimensional core-shell structure TiO2 / CeO2 composite photocatalytic material, denoted as CC / TiO2 NRs@CeO2 NPs. (NRs represents nanoparticles)

[0070] Example 2:

[0071] A preparation method of a composite photocatalytic material, including

[0072] Step 1: Prepare CC / TiO2. Specifically, it includes:

[0073] Step 1.1: Dropwise add tetrabutyl titanate into the absolute ethanol solution under vigorous stirring to prepare a mixed solution; among them, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:100.

[0074] Step 1.2: Immerse the washed carbon cloth (denoted as CC) in the mixed solution for 30 min for inoculation;

[0075] Step 1.3: Heat-treat the inoculated carbon cloth in a muffle furnace, heat to 400 °C at a heating rate of 5 °C / min, hold for 6 h, and cool to room temperature with the furnace after completion of heat treatment;

[0076] Step 1.4: Wash the heat-treated carbon cloth three times with absolute ethanol and ultrapure water, and dry it to obtain a carbon cloth loaded with a titanium dioxide seed layer, denoted as CC / TiO2.

[0077] Step 2: Prepare CC / TiO2 NRs based on CC / TiO2. Specifically, it includes:

[0078] Step 2.1: Prepare a mixed solution according to the volume ratio of tetrabutyl titanate, concentrated hydrochloric acid and ultrapure water of 1:50:100, and vigorously stir it. Place the carbon cloth loaded with the titanium dioxide seed layer in Step 1 in the mixed solution, and transfer the mixed solution containing the carbon cloth to a high-pressure reaction kettle;

[0079] Step 2.2: Place the high-pressure reactor in a muffle furnace and carry out hydrothermal reaction at 150 °C for 10 h;

[0080] Step 2.3: After the reaction, wash the hydrothermal reaction product with absolute ethanol and ultrapure water, and after drying, obtain carbon cloth loaded with titanium dioxide nanorod arrays, denoted as CC / TiO2 NRs. (NRs represents nanorods)

[0081] Step 3: Prepare CC / TiO2 NRs@CeO2 NPs based on CC / TiO2 NRs. Specifically, it includes:

[0082] Step 3.1: Vigorously stir the cerium nitrate solution (concentration 5 mmol / L) with absolute ethanol to prepare a mixed solution. The molar ratio of cerium nitrate to tetrabutyl titanate in Step 2.1 is 1:4. Immerse the carbon cloth loaded with titanium dioxide nanorod arrays obtained in Step 2 in the mixed solution for 60 min, and place it in a muffle furnace for heat treatment. The heat treatment process is: heat to 400 °C at a heating rate of 5 °C / min, hold for 4 h, and then cool to room temperature with the furnace;

[0083] Step 3.2: Wash the heat-treated TiO2 nanorod array modified carbon cloth three times with deionized water and absolute ethanol, and dry it to obtain a supported three-dimensional core-shell structure TiO2 / CeO2 composite photocatalytic material, denoted as CC / TiO2 NRs@CeO2 NPs. (NRs represents nanoparticles)

[0084] Example 3:

[0085] A preparation method of a composite photocatalytic material, including

[0086] Step 1: Prepare CC / TiO2. Specifically, it includes:

[0087] Step 1.1: Dropwise add tetrabutyl titanate into the absolute ethanol solution under vigorous stirring to prepare a mixed solution; wherein, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:100.

[0088] Step 1.2: Immerse the washed carbon cloth (denoted as CC) in the mixed solution for 30 min for inoculation;

[0089] Step 1.3: Carry out heat treatment on the inoculated carbon cloth in a muffle furnace, heat to 400 °C at a heating rate of 5 °C / min, hold for 6 h, and after the heat treatment is completed, cool to room temperature with the furnace;

[0090] Step 1.4: Wash the heat-treated carbon cloth three times with absolute ethanol and ultrapure water, and after drying, obtain carbon cloth loaded with titanium dioxide seed layers, denoted as CC / TiO2.

[0091] Step 2: Prepare CC / TiO2 NRs based on CC / TiO2. Specifically, it includes:

[0092] Step 2.1: Prepare a mixed solution according to the volume ratio of tetrabutyl titanate, concentrated hydrochloric acid and ultrapure water of 1:50:100, and stir it vigorously. Place the carbon cloth loaded with the titanium dioxide seed layer in Step 1 into the mixed solution and transfer it to a high-pressure reaction kettle.

[0093] Step 2.2: Place the high-pressure reaction kettle in a muffle furnace and carry out a hydrothermal reaction at 150 °C for 10 h.

[0094] After the reaction, wash the hydrothermal reaction product with absolute ethanol and ultrapure water, and after drying, obtain a carbon cloth loaded with titanium dioxide nanorod arrays, denoted as CC / TiO2 NRs. (NRs represents nanorods)

[0095] Step 3: Prepare CC / TiO2 NRs@CeO2 NPs based on CC / TiO2 NRs. Specifically, it includes:

[0096] Step 3.1: Vigorously stir a cerium nitrate solution (concentration 5 mmol / L) and absolute ethanol to prepare a mixed solution. The molar ratio of cerium nitrate to tetrabutyl titanate in Step 2.1 is 1:8. Immerse the carbon cloth loaded with titanium dioxide nanorod arrays obtained in Step 2 in the mixed solution for 60 min, and place it in a muffle furnace for heat treatment. The heat treatment process is: heat it to 400 °C at a heating rate of 5 °C / min, hold for 4 h, and then cool it to room temperature with the furnace.

[0097] Wash the heat-treated TiO2 nanorod array modified carbon cloth three times with deionized water and absolute ethanol, and after drying, obtain a supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material, denoted as CC / TiO2 NRs@CeO2 NPs. (NRs represents nanoparticles)

[0098] The photocatalyst inoculates a TiO2 seed layer on the surface of the carbon cloth, hydrothermally grows TiO2 nanorod arrays on the seed layer, and CeO2 nanoparticles tightly coat the TiO2 nanorod arrays to form a three-dimensional core-shell structured heterojunction.

[0099] The diameter of the carbon cloth fiber is 5 - 10 μm, the thickness of the TiO2 seed layer inoculated on the surface of the carbon cloth by the photocatalyst is 100 nm - 300 nm, the crystal form of the TiO2 seed layer is anatase type, the length of the TiO2 nanorod arrays hydrothermally grown on the seed layer of the supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material is 500 nm - 1000 nm, the diameter is 50 nm - 100 nm, and the crystal form of the TiO2 nanorod arrays is rutile type.

[0100] Ellipsoidal CeO2 nanoparticles with uniform height, a major axis of 20 nm to 30 nm, and a minor axis of 10 nm to 20 nm tightly coat the TiO2 nanorod arrays to form a three-dimensional core-shell structure TiO2 / CeO2 heterojunction.

[0101] Example 1 Experiment:

[0102] 1) The scanning electron microscope (SEM) morphology of the composite photocatalytic material is shown in Figure 1 ;

[0103] 2) The high-resolution transmission electron microscope (HRTEM) morphology of the composite photocatalytic material is shown in Figure 2 ;

[0104] 3) The X-ray electron diffraction (XRD) of the composite photocatalytic material is shown in Figure 3 ;

[0105] 4) The ultraviolet-visible diffuse reflectance spectrum (UV-vis) of the component powder of the composite photocatalytic material is shown in Figure 4 ;

[0106] 5) The I-t curve of the composite photocatalytic material under light and dark conditions is shown in Figure 5 ;

[0107] 6) The electrochemical impedance spectrum of the composite photocatalytic material is shown in Figure 6 .

[0108] Result Analysis:

[0109] (1) Morphology Analysis

[0110] From Figure 1 The scanning electron microscope (SEM) morphology diagram of the composite photocatalytic material shown:

[0111] (a), (b): The carbon cloth fiber CC is a carbon cloth woven into a cloth shape with a diameter of 5 μm to 10 μm;

[0112] (c), (d): CC / TiO2 refers to the TiO2 seed layer with a thickness of 100 nm to 300 nm attached to the surface of the carbon cloth. The loading of the TiO2 seed layer on the carbon cloth surface provides a basis for the subsequent growth of the nanorod array and the formation of the heterojunction; the crystal form of the TiO2 seed layer is anatase.

[0113] (e), (f): CC / TiO2 NRs are TiO2 nanorod arrays densely grown on the surface of the carbon cloth with a length of 500 nm to 1000 nm and a diameter of 50 nm to 100 nm. The orderly grown TiO2 nanorod arrays greatly increase the active area of the material and provide a stable support for the subsequent coating structure. The crystal form of the TiO2 nanorod arrays is rutile.

[0114] (g), (h): CC / TiO2 NRs@CeO2 NPs shows that ellipsoidal CeO2 nanoparticles tightly coat the TiO2 nanorod array, forming a three-dimensional core-shell structure TiO2 / CeO2 heterojunction.

[0115] It should be noted that the crystal form of the seed layer refers to the crystal form of the first layer of TiO2 seed layer grown on the carbon cloth, and its crystal form is anatase TiO2, that is, the crystal form of the first layer of TiO2 coating. The TiO2 nanorod array is a TiO2 array structure grown on the seed layer, and its crystal form is rutile TiO2. The determination of this crystal form can be seen in the XRD pattern of the present invention. The difference between the two crystal forms is that one is the crystal structure. Anatase is a tetragonal crystal system with high atomic symmetry and has good optoelectronic properties and photocatalytic properties. The crystal structure of rutile is a hexagonal crystal system, and its physical properties such as thermal stability, acid and alkali resistance, and hardness are superior.

[0116] (2) HRTEM detection

[0117] From Figure 2 As can be seen from the high-resolution transmission electron microscopy (HRTEM) morphology map of the composite photocatalytic material CC / TiO2 NRs@CeO2 NPs shown, CeO2 nanoparticles tightly coat the TiO2 nanorod array to form a three-dimensional core-shell structure heterojunction. The local enlarged image of HRTEM shows that CeO2 nanoparticles closely adhere to the surface of TiO2 nanorods, and their particles are highly uniform, with an ellipsoidal shape with a major axis of 20 nm to 30 nm and a minor axis of 10 nm to 20 nm.

[0118] Figure 2 The lattice fringe spacings of TiO2 NRs and CeO2 NPs in (c) are 0.327 nm and 0.311 nm respectively, corresponding to the (110) crystal orientation of the titanium dioxide card PDF#77-0443 and the (111) crystal orientation of the cerium dioxide card PDF#81-0792, which proves the formation of the heterojunction of CC / TiO2 NRs@CeO2 NPs. It is difficult to observe an amorphous layer between highly crystalline TiO2 and CeO2, which means that the carrier migration within the core-shell structure heterojunction is easier.

[0119] (3) XRD pattern

[0120] Figure 3(a) The XRD patterns of the component powders (TiO2, TiO2 NRs, CeO2 NPs) of the composite photocatalytic material show that TiO2, TiO2 NRs and CeO2 NPs have different characteristic diffraction peaks, and their corresponding PDF card numbers are PDF#78-2486, PDF#77-0443 and PDF#81-0792 respectively. The crystal form of the TiO2 seed layer is anatase, and the crystal form of the TiO2 nanorod array is rutile, which is consistent with the results of high-resolution transmission electron microscopy. Figure 3 (b) The spectra of the composite photocatalytic materials (samples CC, CC / TiO2, CC / TiO2NRs, CC / TiO2 NRs@CeO2 NPs) further prove the formation of the heterojunction of CC / TiO2 NRs@CeO2 NPs.

[0121] (4) UV-Vis diffuse reflectance spectra

[0122] From Figure 4 The UV-Vis diffuse reflectance spectra (UV-vis) of the component powders of the composite photocatalytic material show that compared with the component powders TiO2, TiO2 NRs, CeO2 NPs of the composite photocatalytic material, the TiO2 / CeO2 composite material has a larger light response range and stronger ultraviolet and visible light absorption ability.

[0123] (5) I-t curve of light and dark condition changes

[0124] From Figure 5 The I-t curve of light and dark condition changes of the composite photocatalytic material shown can be seen that the photocurrent magnitudes of CC / TiO2, CC / TiO2 NRs, CC / TiO2 NRs@CeO2 NPs are 0.2 - 0.3 μA / cm 2 , 0.8 - 1.0 μA / cm 2 , 1.4 - 1.6 μA / cm 2 respectively. This is because the photo-generated electrons and holes of CC / TiO2 and CC / TiO2NRs are easily recombined, while the formation of the core-shell structure heterojunction of CC / TiO2 NRs@CeO2 NPs is beneficial to the separation of electron-hole pairs, can generate more photo-generated electrons and holes, and improve the photocatalytic efficiency.

[0125] (6) Electrochemical impedance spectroscopy

[0126] From Figure 6It can be seen from the electrochemical impedance spectra of the composite photocatalytic materials shown that the arc radius of CC / TiO2NRs@CeO2 NPs is smaller than that of CC / TiO2 and CC / TiO2 NRs, indicating that the charge transfer resistance at the interface is smaller. This shows that the core-shell structure heterojunction formed by CC / TiO2NRs@CeO2 NPs is conducive to the charge transfer at the interface, thereby promoting the photocatalytic activity.

[0127] Example 4

[0128] The photocatalytic degradation experiment of unsymmetrical dimethylhydrazine was carried out under the radiation condition of a xenon lamp (simulating sunlight). The content of unsymmetrical dimethylhydrazine was detected by the sodium aminoferrocyanide spectrophotometry (GB / T14376-93), and the degradation rate was calculated. The specific experiment is as follows.

[0129] S1: Prepare 40 ml of unsymmetrical dimethylhydrazine simulated wastewater with a concentration between 100 mg / L and 110 mg / L in a beaker;

[0130] S2: Add the CC / TiO2, CC / TiO2 NRs, and CC / TiO2 NRs@CeO2 NPs prepared in Examples 1, 2, and 3 with a size of 4 cm 2 ~9 cm 2 to the beaker in step 1 respectively, and place it in a light-shielded reaction box and let it stand for reaction for 30 min;

[0131] S3: Use a xenon light source, place the quartz tube 10 cm away from the light source, start the photocatalytic reaction, sample and analyze every 1 h, and set the light radiation power to 100 W / cm 2 .

[0132] S4: During the photocatalytic reaction, sample and analyze every 1 h, and use the sodium aminoferrocyanide spectrophotometry to measure the concentration of unsymmetrical dimethylhydrazine in the wastewater.

[0133] In S1, S2, and S3, the concentration of unsymmetrical dimethylhydrazine in the wastewater was measured by the sodium aminoferrocyanide spectrophotometry.

[0134] Results:

[0135] (1) Photocatalytic degradation

[0136] From Figure 7It can be seen that under simulated sunlight conditions within 210 min, in Example 1, Example 2, and Example 3, the degradation rate of UDMH by CC / TiO2 was 24.4%, and the degradation rate of UDMH by CC / TiO2 NRs was 47.3%. The photocatalytic performance of CC / TiO2 NRs@CeO2 NPs in Example 1 was the best, with a degradation rate of 97.5% for UDMH under simulated sunlight conditions. The photocatalytic degradation rate of UDMH by CC / TiO2 NRs@CeO2 NPs in Example 2 was 83.4% under simulated sunlight conditions, and the photocatalytic degradation rate of UDMH by CC / TiO2 NRs@CeO2 NPs in Example 3 was 73.2% under simulated sunlight conditions.

[0137] (2) Reuse of the composite photocatalytic material

[0138] From Figure 8 It can be seen that the degradation rate of the sample CC / TiO2 NRs@CeO2 NPs composite photocatalytic material obtained in Example 1 was still up to 95% after 5 cycles under xenon lamp illumination conditions. The degradation efficiency only decreased by 2.5% after five cycles. Thus, it can be seen that the composite photocatalytic material has stable performance and good recyclability.

[0139] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. Application of a composite photocatalytic material in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: The composite photocatalytic material is a supported three-dimensional core-shell structured TiO₂ / CeO₂, denoted as CC / TiO₂ NRs@CeO₂ NPs, which means that a TiO₂ seed layer is inoculated on the surface of carbon cloth, TiO₂ nanorod arrays are hydrothermally grown on the seed layer, and CeO₂ nanoparticles closely coat the TiO₂ nanorod arrays to form a three-dimensional core-shell structured heterojunction; The specific application method includes: S1: Prepare 40 ml of unsymmetrical dimethylhydrazine wastewater with a concentration of 100 mg / L - 110 mg / L; S2: Add 4 cm² - 9 cm² of the supported three-dimensional core-shell structured TiO₂ / CeO₂ composite photocatalytic material to the unsymmetrical dimethylhydrazine wastewater in step 1, and place it in a light-shielded reaction box for static reaction for 30 min; S3: Use a xenon lamp light source, place the quartz tube 10 cm away from the lamp light source, and start the photocatalytic reaction; S4: During the photocatalytic reaction, sample and analyze every 1 h to measure the concentration of unsymmetrical dimethylhydrazine in the wastewater.

2. The application of a composite photocatalytic material according to claim 1 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: The preparation method of the composite photocatalytic material includes: Step 1: Immerse the carbon cloth in a mixed solution of tetrabutyl titanate and absolute ethanol for inoculation, and the inoculated carbon cloth is heat-treated in a muffle furnace to obtain a carbon cloth loaded with a titanium dioxide seed layer, denoted as CC / TiO₂; Step 2: Place the carbon cloth loaded with the titanium dioxide seed layer in a mixed solution of tetrabutyl titanate, concentrated hydrochloric acid and ultrapure water, and prepare a carbon cloth loaded with titanium dioxide nanorod arrays through a hydrothermal reaction, denoted as CC / TiO₂ NRs; Step 3: Place the carbon cloth loaded with titanium dioxide nanorod arrays in a mixed solution of cerium nitrate solution and absolute ethanol, and obtain the supported three-dimensional core-shell structured TiO₂ / CeO₂ composite photocatalytic material through heat treatment, denoted as CC / TiO₂ NRs@CeO₂ NPs.

3. The application of a composite photocatalytic material according to claim 2 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: Step 1 includes: Step 1.1: Drop tetrabutyl titanate into the absolute ethanol solution under stirring conditions to prepare a mixed solution; Step 1.2: Immerse the carbon cloth in the mixed solution for 10 min - 30 min to complete TiO₂ inoculation; Step 1.3: Heat-treat the inoculated carbon cloth in a muffle furnace; Step 1.4: Wash the heat-treated carbon cloth with absolute ethanol and ultrapure water, and dry it to obtain a carbon cloth loaded with a titanium dioxide seed layer, denoted as CC / TiO₂.

4. Use of a composite photocatalytic material according to claim 3 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: Step 2 includes: Step 2.1: Prepare a mixed solution of concentrated hydrochloric acid, ultrapure water and tetrabutyl titanate, place the carbon cloth loaded with the titanium dioxide seed layer in step 1 in the mixed solution, and transfer it to a high-pressure reaction kettle; Step 2.2: Place the high-pressure reaction kettle in a muffle furnace for hydrothermal reaction; Step 2.3: Wash the hydrothermal reaction product with absolute ethanol and ultrapure water, and dry it to obtain a carbon cloth loaded with titanium dioxide nanorod arrays, denoted as CC / TiO₂ NRs.

5. Use of a composite photocatalytic material according to claim 4 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: Step 3 includes: Step 3.1: Prepare a mixed solution of cerium nitrate solution and absolute ethanol, immerse the carbon cloth loaded with titanium dioxide nanorod arrays obtained in step 2 in the mixed solution for 30 min - 60 min, place it in a muffle furnace for heat treatment, and cool it to room temperature with the furnace after completion; Step 3.2: Wash the heat-treated carbon cloth loaded with titanium dioxide nanorod arrays with deionized water and absolute ethanol, and dry it to obtain a supported three-dimensional core-shell structured TiO2 / CeO2 composite photocatalytic material, denoted as CC / TiO2 NRs@CeO2 NPs.

6. The application of a composite photocatalytic material according to claim 5 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: In Step 1.1, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:50 - 100; the heat treatment process in Step 1.3 is: maintain at 400°C - 600°C for 6 h - 10 h.

7. Use of a composite photocatalytic material according to claim 6 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: In Step 2.1, the volume ratio of tetrabutyl titanate, concentrated hydrochloric acid, and ultrapure water is 1:50 - 100:100 - 200; the hydrothermal reaction process in Step 2.2 is: react at 150°C - 300°C for 10 h - 15 h.

8. Use of a composite photocatalytic material according to claim 7 in the treatment of unsymmetrical dimethylhydrazine wastewater, characterized in that: In Step 3.1, the concentration of cerium nitrate solution is 5 - 10 mmol / L, and the molar ratio of cerium nitrate to tetrabutyl titanate in Step 2.1 is 1:2; the heat treatment process is: maintain at 400°C - 600°C for 4 h - 8 h.

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