A TiO2 inorganic semiconductor nanofiber aerogel, its preparation and application

Abstract

This invention relates to a TiO2 inorganic semiconductor nanofiber aerogel, its preparation, and its application. The method involves mixing a TiO2 semiconductor nanofiber membrane with composite carbon and water to obtain a dispersion, then adding a crosslinking agent and a catalyst to obtain a mixed solution. The mixed solution is then subjected to vertically oriented freeze-drying, followed by heat treatment to obtain the TiO2 inorganic semiconductor nanofiber aerogel. The crosslinking agent comprises polyvinyl alcohol and citric acid, with a dispersion mass percentage of 0.8% and a citric acid to polyvinyl alcohol mass ratio of 1:1. The TiO2 inorganic semiconductor nanofiber aerogel prepared by this invention constructs a highly ordered three-dimensional porous network structure, exhibiting high catalytic activity, good stability, and maintaining resilience even after multiple cyclic compression tests.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials, and specifically relates to a TiO2 inorganic semiconductor nanofiber aerogel, its preparation and application. Background Technology

[0002] The excessive consumption of traditional fossil fuels has led to a continuous rise in atmospheric CO2 concentrations, causing serious problems such as frequent extreme weather events and ecosystem imbalances. Therefore, achieving CO2 emission reduction and efficient conversion has become a key area of ​​scientific research. Photothermal catalysis technology can utilize solar energy, combining the advantages of photocatalysis and thermocatalysis to drive the activation of CO2 molecules and convert them into fuels or chemicals such as CO, CH4, and CH3OH. This not only mitigates the greenhouse effect but also enables resource recycling, making it an effective strategy for green CO2 emission reduction.

[0003] Traditional photothermal catalysts are semiconductor metal oxides, mostly in powder form, which suffer from problems such as low spectral utilization, difficulty in recycling, and poor catalytic activity. In recent years, graphene aerogel-supported semiconductor metal oxide catalysts have been widely used in photocatalysis and photothermal catalysis due to their high specific surface area and three-dimensional porous structure. However, because their pore structure is mostly disordered macropores with a wide pore size distribution and a lack of directional transport channels, the light scattering efficiency inside the material is low, which greatly limits the spectral utilization. At the same time, the active components of the catalyst supported in it are prone to agglomeration, migration, and even detachment within the macroporous structure, which seriously affects the efficiency and stability of the photothermal catalytic reaction and hinders the large-scale application of this technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a TiO2 inorganic semiconductor nanofiber aerogel and its preparation and application, which overcomes the shortcomings of low spectral utilization rate of powder photothermal catalysts in the prior art.

[0005] This invention provides a method for preparing TiO2 inorganic semiconductor nanofiber aerogel, comprising:

[0006] Step (1) The precursor TiO2 semiconductor nanofiber membrane is calcined in an inert atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane; wherein the precursor TiO2 semiconductor nanofiber membrane is obtained by electrospinning with a spinning solution containing isopropyl titanate, anhydrous ethanol, acetic acid and polyvinylpyrrolidone; the mass ratio of the isopropyl titanate, anhydrous ethanol, acetic acid and polyvinylpyrrolidone is 0.2:3.16:2:1.5;

[0007] Step (2) The composite carbon TiO2 semiconductor nanofiber membrane is mixed with water to obtain a dispersion, and then a crosslinking agent and a catalyst are added to obtain a mixture; wherein the crosslinking agent components include polyvinyl alcohol and citric acid, and the mass percentage of the dispersion is 0.8%; the mass ratio of citric acid to polyvinyl alcohol is 1:1; the mass fraction of polyvinyl alcohol relative to the dispersion is 0.4%, and the mass fraction of citric acid relative to the dispersion is 0.4%;

[0008] Step (3) The mixture is vertically oriented frozen, freeze-dried, and then heat-treated to obtain TiO2 inorganic semiconductor nanofiber aerogel.

[0009] In step (1), the inert atmosphere is nitrogen; the calcination is carried out at 600 °C for 1 hour.

[0010] In step (1), isopropyl titanate, anhydrous ethanol, acetic acid and polyvinylpyrrolidone are stirred for 2-6 hours to obtain spinning solution.

[0011] The electrospinning process parameters in step (1) include: the propulsion speed of the spinning solution is 0.8~1 ml / h, the spinning distance between the spinning needle and the roller collector is 15 cm, and the applied electric field is 14~18 KV.

[0012] Preferably, the catalyst in step (2) is polyphosphoric acid, which promotes the cross-linking reaction.

[0013] Preferably, in step (2), the mass fraction of the catalyst relative to the dispersion is 0.2%.

[0014] In step (2), the mixing is homogenous mixing, and the speed of the homogenizer is 4000~5000 rpm / min, and the time is 30~60 min.

[0015] After adding the crosslinking agent and catalyst in step (2), the homogenizer is homogenized at a speed of 4000~5000 rpm / min for 30~60 min.

[0016] In step (3), the copper mold used for vertical directional freezing has a core composed of a polytetrafluoroethylene plastic main cavity and a copper bottom substrate. Liquid nitrogen is used as the cold source. Copper has extremely high thermal conductivity (about 394 W / (m·K)) and can quickly conduct the energy of the external cold source to the cavity, ensuring the formation of a stable vertical temperature gradient. This allows ice crystals to pass vertically through the TiO2 fiber mixture to construct a hierarchical porous framework structure. Then, the ice crystals are removed by freeze drying to obtain uncrosslinked composite nanofiber aerogel. The uncrosslinked composite nanofiber aerogel is placed in an air circulation oven for heat treatment to achieve the crosslinking esterification reaction of the crosslinking agent, resulting in a TiO2 inorganic semiconductor nanofiber aerogel with a hierarchical porous framework structure with stable connection points.

[0017] Preferably, the vertical directional freezing in step (3) includes directional freezing under liquid nitrogen conditions for 15 min.

[0018] Preferably, the freeze-drying process parameters in step (3) include: freezing temperature of -65 ~ -55 ℃, vacuum degree of 5 ~ 10 Pa, and time of 3 days.

[0019] Preferably, the heat treatment in step (3) is performed under air circulation conditions at 95~105 ℃ for 60 min.

[0020] For example, heat treatment is carried out in a forced-air drying oven.

[0021] This invention provides a TiO2 inorganic semiconductor nanofiber aerogel prepared by the method described above, wherein the TiO2 inorganic semiconductor nanofiber aerogel has a composite hierarchical porous framework structure with stable connection points.

[0022] This invention provides an application of the TiO2 inorganic semiconductor nanofiber aerogel in photothermal CO2 conversion.

[0023] The TiO2 inorganic semiconductor nanofiber aerogel prepared in this invention constructs a highly ordered three-dimensional porous network structure. Its unique pore structure provides efficient diffusion channels for reactants and products in the CO2 conversion reaction. By calcining in an inert gas to prepare a composite carbon semiconductor fiber material, the material's light absorption capacity is enhanced, enabling efficient utilization of the full spectrum of sunlight and significantly improving photothermal conversion capabilities. Combining the high porosity and low thermal conductivity of the aerogel, absorbed light energy can be efficiently converted into heat energy, achieving uniform heat distribution within the material and providing a stable thermodynamic environment for the CO2 reduction reaction.

[0024] Furthermore, this invention utilizes a chemical crosslinking process between polyvinyl alcohol and citric acid to give the aerogel excellent compressive resilience, achieving a compressive strength of 1.41 kPa at a 20% compression distance. This endows the material with superior mechanical properties, providing a solid material foundation for the industrial application of photothermal catalytic CO2 conversion technology.

[0025] Beneficial effects

[0026] The preparation process of this invention is simple and inexpensive, and it is a convenient and efficient preparation method.

[0027] The TiO2 inorganic semiconductor nanofiber aerogel prepared by this invention constructs a highly ordered three-dimensional porous network structure, realizes full-spectrum solar light utilization through composite carbon materials, introduces crosslinking agents to improve the strength and resilience of TiO2 inorganic semiconductor nanofiber aerogel, has high catalytic activity and good stability, and can maintain resilience even after multiple cyclic compression tests. Attached Figure Description

[0028] Figure 1 Scanning electron microscope (SEM) images (a) of the composite carbon TiO2 semiconductor nanofiber membrane of Comparative Example 5 and (b) of the TiO2 inorganic semiconductor nanofiber aerogel of Example 1.

[0029] Figure 2 The UV-Vis diffuse reflectance spectra of Example 1 and Comparative Example 6 are shown below.

[0030] Figure 3 The temperature change of the sample surface over time under 300 W xenon lamp irradiation for Example 1 and Comparative Example 6;

[0031] Figure 4 The compressive stress-strain curves of Example 1 and Comparative Examples 1-4 at a 20% compression distance are shown.

[0032] Figure 5 The compression stress-strain curve of Example 1 during 45 cycles of compression testing;

[0033] Figure 6 The graphs show the photothermal CO2 conversion reaction performance test results for Examples 1, 1-3, and 5-6.

[0034] Figure 7 This is a schematic diagram of vertically oriented freezing in the preparation method of TiO2 inorganic semiconductor nanofiber aerogel of the present invention;

[0035] Figure 8 This is a scanning electron microscope image of the TiO2 inorganic semiconductor nanofiber aerogel of Comparative Example 4. Detailed Implementation

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The final materials obtained in the examples and comparative examples were used as samples for relevant tests.

[0038] Test standards and methods involved in the examples and comparative examples:

[0039] Photothermal CO2 conversion reaction performance testing: In a closed vacuum system, 50 mg of sample was used as the catalyst, and 80 kPa pure CO2 and 5 mL of deionized water were used as the reaction system. The 50 mg catalyst was placed on a custom tripod inside the reactor to avoid direct contact with water. A 300 W xenon lamp (PLS-SXE300+, Beijing POLIFIL Technology Co., Ltd.) was used as the light source; the product (CO) was analyzed by gas chromatography (Fuli GC9790II, Fuli Analytical Instruments Co., Ltd.) equipped with a flame ionization detector (FID).

[0040] Mechanical property testing: The stress-strain properties of the samples were tested using an Instron 5969 electronic universal testing machine. The testing process strictly followed the relevant provisions for compression testing of non-metallic materials in GB / T 16491-2022 "Electronic Universal Testing Machine" standard. The test parameters were set as follows: compression rate of 2 mm / min, and strain set to 20% per compression. The number of compression cycles in the cyclic test was 45.

[0041] Scanning electron microscopy (SEM) testing: The microscopic surface morphology of the sample was characterized using a field emission scanning electron microscope (TESCAN / MAIA3).

[0042] UV-Vis absorption testing: The light absorption performance of the samples was analyzed using a Shimadzu UV-2600 spectrophotometer. Pure BaSO4 was used as the reflectance standard sample for light absorption performance analysis.

[0043] Sample surface temperature test: A 300 W xenon lamp (PLS-SXE300+, Beijing Pofilai Technology Co., Ltd.) was used as the light source to irradiate the sample, and an infrared thermal imager (model: UNI-T, Uni-Trend Technology (China) Co., Ltd.) was used simultaneously to monitor the sample surface temperature changes in real time. The xenon lamp power was kept stable at 300 W, the irradiation time was 1 min, and temperature data was recorded every 10 s to record the temperature changes of the sample surface.

[0044] In the vertically oriented freezing copper mold, the core is composed of a polytetrafluoroethylene plastic main cavity and a copper bottom substrate.

[0045] Polyvinylpyrrolidone (Mw = 1300000) and citric acid were both purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] Isopropyl titanate and polyphosphate were both purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0047] Acetic acid (99.5%) and anhydrous ethanol (99.7%) were both purchased from Sinopharm Chemical Reagent Co., Ltd.

[0048] Polyvinyl alcohol was purchased from Anaiji (Shanghai) Pharmaceutical Chemicals Co., Ltd.

[0049] Example 1

[0050] (1) TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. Based on this TiO2 fiber spinning solution, a precursor TiO2 semiconductor nanofiber membrane was prepared by electrospinning. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spinning distance between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined at 600 ℃ for 1 h in a N2 atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0051] (2) The composite carbon TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a dispersion of 15 g of composite carbon TiO2 semiconductor nanofiber membrane with a mass fraction of 0.8%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.4%, the mass fraction of citric acid relative to the dispersion was 0.4%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0052] (3) Pour the mixture into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and use liquid nitrogen for vertical directional freezing for 15 min. Then place it in a freeze dryer with a vacuum degree of 5-10 Pa at -60±5 ℃ for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0053] (4) The uncrosslinked composite nanofiber aerogel was placed in an air circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking esterification reaction of the crosslinking agent and obtain TiO2 inorganic semiconductor nanofiber aerogel with a hierarchical porous framework structure with stable connection points.

[0054] Example 1 exhibited high catalytic activity in the photothermal CO2 to CO conversion reaction: the CO yield reached 379.44 μmol g after 5 hours. catalyst -1 This indicates that it has good conversion efficiency in photothermal driven carbon emission reduction reactions.

[0055] Mechanical strength: In the compression test, when the compression distance is 20%, the material can withstand a compressive stress of 1.41 kPa, demonstrating a certain structural load-bearing capacity. Compression resilience stability: After 45 compression-rebound cycles, the material can still maintain its compression resilience, indicating that it has excellent structural fatigue resistance and mechanical stability.

[0056] Comparative Example 1

[0057] (1) A TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. A precursor TiO2 semiconductor nanofiber membrane was then prepared by electrospinning based on the TiO2 fiber spinning solution. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spinning distance between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined at 600 ℃ for 1 h in a N2 atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0058] (2) The composite carbon TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a dispersion of 15 g of composite carbon TiO2 semiconductor nanofiber membrane with a mass fraction of 0.8%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.4%, the mass fraction of citric acid relative to the dispersion was 0.8%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0059] (3) Pour the mixture into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and use liquid nitrogen for vertical directional freezing for 15 min. Then place it in a freeze dryer with a vacuum degree of 5-10 Pa at -60±5 ℃ for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0060] (4) The uncrosslinked composite nanofiber aerogel was placed in an air circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking esterification reaction of the crosslinking agent and obtain TiO2 inorganic semiconductor nanofiber aerogel with a hierarchical porous framework structure with stable connection points.

[0061] In Comparative Example 1, the CO yield reached 298.17 μmol g in the photothermal CO2 to CO conversion reaction after 5 hours. catalyst -1Mechanical strength: In compression tests, the material can withstand a compressive stress of 0.92 kPa when the compression distance is 20%.

[0062] Comparative Example 2

[0063] (1) A TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. A precursor TiO2 semiconductor nanofiber membrane was then prepared by electrospinning based on the TiO2 fiber spinning solution. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spinning distance between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined at 600 ℃ for 1 h in a N2 atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0064] (2) The composite carbon TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a dispersion of 15 g of composite carbon TiO2 semiconductor nanofiber membrane with a mass fraction of 0.8%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.6%, the mass fraction of citric acid relative to the dispersion was 0.6%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0065] (3) Pour the mixture into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and use liquid nitrogen for vertical directional freezing for 15 min. Then place it in a freeze dryer with a vacuum degree of 5-10 Pa at -60±5 ℃ for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0066] (4) The uncrosslinked composite nanofiber aerogel was placed in an air circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking esterification reaction of the crosslinking agent and obtain TiO2 inorganic semiconductor nanofiber aerogel with a hierarchical porous framework structure with stable connection points.

[0067] In Comparative Example 2, the CO yield reached 175.76 μmol g in the photothermal CO2 to CO conversion reaction after 5 hours. catalyst -1 Mechanical strength: In compression tests, the material can withstand a compressive stress of 0.31 kPa when the compression distance is 20%.

[0068] Comparative Example 3

[0069] (1) A TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. A precursor TiO2 semiconductor nanofiber membrane was then prepared by electrospinning based on the TiO2 fiber spinning solution. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spinning distance between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined at 600 ℃ for 1 h in a N2 atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0070] (2) The composite carbon TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a dispersion of 15 g of composite carbon TiO2 semiconductor nanofiber membrane with a mass fraction of 0.8%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.6%, the mass fraction of citric acid relative to the dispersion was 1.2%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0071] (3) Pour the mixture into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and use liquid nitrogen for vertical directional freezing for 15 min. Then place it in a freeze dryer with a vacuum degree of 5-10 Pa at -60±5 ℃ for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0072] (4) The uncrosslinked composite nanofiber aerogel was placed in an air circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking esterification reaction of the crosslinking agent and obtain TiO2 inorganic semiconductor nanofiber aerogel with a hierarchical porous framework structure with stable connection points.

[0073] Comparative Example 3 showed a CO yield of 298.17 μmol g in the photothermal CO2 to CO conversion reaction after 5 hours. catalyst -1 Mechanical strength: In compression tests, the material can withstand a compressive stress of 0.33 kPa when the compression distance is 20%.

[0074] Comparative Example 4

[0075] (1) A TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. A precursor TiO2 semiconductor nanofiber membrane was then prepared by electrospinning based on the TiO2 fiber spinning solution. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spinning distance between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined in N2 at 600 ℃ for 1 h to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0076] (2) The composite carbon TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a 15 g dispersion of composite carbon TiO2 semiconductor nanofiber membrane with a mass fraction of 0.4%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.4%, the mass fraction of citric acid relative to the dispersion was 0.4%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0077] (3) Pour the mixture into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and use liquid nitrogen for vertical directional freezing for 15 min. Then place it in a freeze dryer with a vacuum degree of 5-10 Pa at -60±5 ℃ for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0078] (4) The uncrosslinked composite nanofiber aerogel was placed in an air-circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking and esterification reaction of the crosslinking agent, resulting in an incomplete TiO2 inorganic semiconductor nanofiber aerogel. Figure 8 As shown, the reduced proportion of TiO2 fiber membrane matrix in this fiber aerogel resulted in insufficient fiber support to form the aerogel wall during the aerogel preparation process, causing structural collapse, and the fiber surface was covered by crosslinking agent.

[0079] Mechanical strength of Comparative Example 4: In the compression test, when the compression distance is 20%, the material can withstand a compressive stress of 0.86 kPa. However, it does not possess compressive resilience.

[0080] Comparative Example 5

[0081] TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. Based on this TiO2 fiber spinning solution, a precursor TiO2 semiconductor nanofiber membrane was prepared by electrospinning. During electrospinning, the spinning solution feed rate was 1 ml / h, the spinning needle-to-collector distance was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined at 600 °C for 1 h in a N2 atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane.

[0082] Comparative Example 5: The TiO2 semiconductor nanofiber film with composite carbon achieved a CO yield of 15 μmol g / L in the photothermal CO2 to CO conversion reaction after 5 hours. catalyst -1 .

[0083] Comparative Example 6

[0084] (1) A TiO2 fiber spinning solution was prepared by mixing isopropyl titanate, anhydrous ethanol, acetic acid, and polyvinylpyrrolidone in a mass ratio of 0.2:3.16:2:1.5 and stirring for 6 h. A precursor TiO2 semiconductor nanofiber membrane was then prepared by electrospinning based on the TiO2 fiber spinning solution. During electrospinning, the feed rate of the spinning solution was 1 ml / h, the spacing between the spinning needle and the roller collector was 15 cm, and the applied electric field was 15 kV. The precursor TiO2 semiconductor nanofiber membrane was calcined in air at 600 ℃ for 1 h to obtain the TiO2 semiconductor nanofiber membrane.

[0085] (2) The TiO2 semiconductor nanofiber membrane was immersed in deionized water to prepare a TiO2 semiconductor nanofiber membrane dispersion with a mass fraction of 0.8%. The dispersion was homogenized at a high speed of 5000 rpm / min for 1 min using a high-speed homogenizer. A crosslinking agent and polyphosphoric acid were added, wherein the mass fraction of polyvinyl alcohol relative to the dispersion was 0.4%, the mass fraction of citric acid relative to the dispersion was 0.4%, and the mass fraction of polyphosphoric acid relative to the dispersion was 0.2%. The mixture was then homogenized at a high speed of 5000 rpm / min for 1 h to obtain a mixed solution.

[0086] (3) The mixture was poured into a cylindrical mold with a diameter of 3 cm and a height of 5 cm and vertically oriented for freezing with liquid nitrogen for 15 min. Then it was freeze-dried in a freeze dryer at -60±5 ℃ and a vacuum degree of 5-10 Pa for 3 days to obtain uncrosslinked composite nanofiber aerogel.

[0087] (4) The uncrosslinked composite nanofiber aerogel was placed in an air circulating oven at 100±5 ℃ for heat treatment for 60 min to achieve the crosslinking esterification reaction of the crosslinking agent and obtain TiO2 inorganic semiconductor nanofiber aerogel without carbon elements.

[0088] Comparative Example 6 showed that in the photothermal CO2 to CO conversion reaction, the CO yield reached 8 μmol g in 5 hours. catalyst -1 .

[0089] like Figure 1 Image a shows a scanning electron microscope (SEM) image of the composite carbon TiO2 semiconductor nanofiber film of Comparative Example 5, with fiber diameters ranging from 400 to 900 nm. Figure 1 Image b shows a scanning electron microscope (SEM) image of the TiO2 inorganic semiconductor nanofiber aerogel from Example 1. As can be seen from the image, the TiO2 inorganic semiconductor nanofiber aerogel prepared in Example 1 has a composite hierarchical porous framework structure, and the nanofibers are tightly bound together by a crosslinking agent. The TiO2 inorganic semiconductor nanofiber aerogel prepared in Example 1 has a relatively ordered three-dimensional spatial structure.

[0090] like Figure 2 The UV-Vis diffuse reflectance spectra of Example 1 and Comparative Example 6 are shown. The figures show that the material calcined in air only exhibits absorption in the ultraviolet region, while the sample of Example 1 shows absorption across the entire spectrum. This indicates that the TiO2 inorganic semiconductor nanofiber aerogel prepared in Example 1 can utilize the full spectrum of sunlight.

[0091] like Figure 3 The figure shows the temperature change of the sample surface over time under 300 W xenon lamp irradiation for Examples 1 and Comparative Example 6. It can be seen from the figure that the sample surface temperature treated in an air atmosphere tends to stabilize around 100 °C, while the sample surface temperature treated in an N2 atmosphere tends to stabilize around 160 °C. This indicates that the TiO2 inorganic semiconductor nanofiber aerogel material prepared in Example 1 has better photothermal conversion performance.

[0092] like Figure 4 The figures show the compressive stress-strain curves of Example 1 and Comparative Examples 1-4 at a 20% compression distance. It can be seen from the figures that Example 1 exhibits good mechanical properties, able to withstand a compressive stress of 1.41 kPa at a 20% compression distance, and is able to recover well.

[0093] like Figure 5 The figure shows the compressive stress-strain curves (compression distance 20%) of Example 1 during 45 fatigue cycles. After 45 compression recovery cycles, only 9.1% plastic deformation occurred. This indicates that the TiO2 inorganic semiconductor nanofiber aerogel material prepared in Example 1 can be reused multiple times.

[0094] like Figure 6 The figures show the photocatalytic CO2 conversion performance test results for Example 1, Comparative Examples 1-3, and Comparative Examples 5-6. As can be seen from the figures, the photothermal CO2 to CO conversion yield of Example 1 can reach 379.44 μmol g within 5 h. catalyst -1 The TiO2 inorganic semiconductor nanofiber aerogel of Example 1 exhibits excellent photothermal CO2 conversion performance, which is significantly higher than that of other comparative materials.

[0095] like Figure 7 This is a schematic diagram of the vertically oriented freezing process in the preparation method of TiO2 inorganic semiconductor nanofiber aerogel of the present invention. As can be seen from the diagram, vertically oriented freezing is used to allow ice crystals to grow vertically and construct a composite hierarchical porous framework structure.

Claims

1. A method for preparing TiO2 inorganic semiconductor nanofiber aerogel, characterized in that, include: Step (1) The precursor TiO2 semiconductor nanofiber membrane is calcined in an inert atmosphere to obtain a composite carbon TiO2 semiconductor nanofiber membrane; wherein the precursor TiO2 semiconductor nanofiber membrane is obtained by electrospinning with a spinning solution containing isopropyl titanate, anhydrous ethanol, acetic acid and polyvinylpyrrolidone; the mass ratio of the isopropyl titanate, anhydrous ethanol, acetic acid and polyvinylpyrrolidone is 0.2:3.16:2:1.5; Step (2) The composite carbon TiO2 semiconductor nanofiber membrane is mixed with water to obtain a dispersion, and then a crosslinking agent and a catalyst are added to obtain a mixture; wherein the crosslinking agent components include polyvinyl alcohol and citric acid, and the mass percentage of the dispersion is 0.8%; the mass ratio of citric acid to polyvinyl alcohol is 1:1; the mass fraction of polyvinyl alcohol relative to the dispersion is 0.4%, and the mass fraction of citric acid relative to the dispersion is 0.4%; Step (3) The mixture is vertically oriented frozen, freeze-dried, and then heat-treated to obtain TiO2 inorganic semiconductor nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that, In step (1), the inert atmosphere is nitrogen; the calcination is carried out at 600 °C for 1 hour.

3. The preparation method according to claim 1, characterized in that, The catalyst in step (2) is polyphosphoric acid.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of the catalyst relative to the dispersion is 0.2%.

5. The preparation method according to claim 1, characterized in that, The vertical directional freezing in step (3) includes directional freezing under liquid nitrogen conditions for 15 min.

6. The preparation method according to claim 1, characterized in that, The process parameters for freeze drying in step (3) include: freezing temperature of -65 ~ -55 ℃, vacuum degree of 5 ~ 10 Pa, and time of 3 days.

7. The preparation method according to claim 1, characterized in that, In step (3), the heat treatment is carried out under air circulation conditions at 95~105 ℃ for 60 min.

8. A TiO2 inorganic semiconductor nanofiber aerogel, characterized in that, The TiO2 inorganic semiconductor nanofiber aerogel is prepared by any one of the methods described in claims 1-7.

9. An application of the TiO2 inorganic semiconductor nanofiber aerogel according to claim 8, characterized in that, Application of TiO2 inorganic semiconductor nanofiber aerogel in photothermal CO2 conversion.

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