Hollow TiO2-based photocatalytic composite material for degrading Rhodamine B and its preparation method

Abstract

This invention relates to a hollow TiO2-based photocatalytic composite material for the degradation of Rhodamine B and its preparation method. By using anatase-type hollow TiO2 microspheres as the catalytic matrix, modifying their surface with aniline-based photosensitizers, and coating them with a hydrophobic crosslinking agent polymer layer formed from acrylate-based hydrophobic crosslinking agents, a novel hollow TiO2-based photocatalytic composite material is obtained. This effectively improves the problems of low catalytic efficiency, low solid-liquid separation efficiency, and poor cycle life of existing TiO2-based photocatalysts for the degradation of Rhodamine B.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic degradation materials technology, and relates to a photocatalytic material for degrading the dye Rhodamine B in wastewater, particularly a photocatalytic composite material based on hollow TiO2 microspheres. Background Technology

[0002] Rhodamine B is a cationic basic dye of the catechol class with a strong fluorescent effect. Its concentration in dyeing and printing wastewater can reach up to 100 ppm, and it is difficult to degrade. Therefore, efficient removal of the organic pollutant Rhodamine B from wastewater is necessary.

[0003] In recent years, various degradation methods, such as electrolysis, adsorption, extraction, electrochemical oxidation, and photocatalysis, have been applied to the treatment of dye wastewater. Among them, photocatalytic degradation technology, as one of the most effective methods, can effectively degrade Rhodamine B, and has the characteristics of low energy consumption, high efficiency, and no secondary pollution. TiO2-based photocatalytic materials, which have good photocatalytic activity, high conversion efficiency, and long-lasting catalytic effect, have attracted much attention.

[0004] Phongamwong et al. (Applied Catalysis B-Environment and Energy, 2022, 325:122336.) Using Au 25 Clusters, Au nanoparticles, and chlorophyll were used to functionalize anatase / rutile mixed-phase TiO2 to prepare nano-photocatalysts. The modified TiO2 catalyst achieved a 100% degradation efficiency of Rhodamine B within 60 min. Chen et al. (Environmental Research, 2023, 232: 116311.) prepared a carbon / fluorine co-doped TiO2 photocatalyst C / F-Ag-TiO2 with silver deposited on the surface using a hydrothermal method, achieving a degradation rate of 84.2% for Rhodamine B within 4 h.

[0005] However, the catalytic degradation efficiency of these existing TiO2-based photocatalysts is not high enough during the degradation process. In particular, due to the high affinity of the catalyst with the aqueous system, the solid-liquid separation efficiency of the catalyst is low after degradation, and the catalyst has a poor cycle life.

[0006] By modifying the surface of anatase-type hollow TiO2 microspheres with photosensitizers and coating them with a hydrophobic crosslinking polymer layer, a TiO2-based photocatalytic material with switchable surface wettability, high catalytic activity, high catalytic stability, and high solid-liquid separation efficiency is obtained. This material has good research and development value and application potential for improving the degradation efficiency, solid-liquid separation efficiency, and cycle life of TiO2-based photocatalysts used for the degradation of Rhodamine B in wastewater. Summary of the Invention

[0007] The purpose of this invention is to provide a hollow TiO2-based photocatalytic composite material for degrading Rhodamine B and its preparation method, so as to effectively improve the problems of low catalytic efficiency, low solid-liquid separation efficiency and poor cycle life of existing TiO2-based photocatalysts for degrading Rhodamine B.

[0008] To achieve the above-mentioned objectives, this invention prepares a novel hollow TiO2-based photocatalytic composite material by using anatase-type hollow TiO2 microspheres as the catalytic matrix, modifying their surface with aniline-based photosensitizers, and coating them with a hydrophobic crosslinking agent polymer layer formed from acrylate-based hydrophobic crosslinking agents.

[0009] First, the hollow TiO2-based photocatalytic composite material of this invention uses anatase-type hollow TiO2 microspheres as the catalytic matrix. The spherical morphology of the hollow TiO2 microspheres gives them a larger specific surface area, while the hollow structure gives them a lower density, resulting in a lower refractive index and coefficient of thermal expansion, as well as stronger light absorption. More importantly, under ultraviolet light irradiation, the valence band electrons of the hollow TiO2 microspheres are excited to the conduction band, and electrons and holes migrate to the H-TiO2 surface, causing a change in surface chemical polarity, which can improve its surface hydrophilicity and photocatalytic efficiency.

[0010] Secondly, the hollow TiO2-based photocatalytic composite material of the present invention uses aniline compounds as photosensitizers. Modifying the surface of hollow TiO2 microspheres with photosensitizers not only does not affect the internal crystal structure of TiO2, but also promotes light-induced charge separation and improves the recombination of photogenerated electron-hole pairs, thereby improving the overall catalytic degradation efficiency of the hollow TiO2-based photocatalytic composite material.

[0011] Third, the outer layer of the hollow TiO2-based photocatalytic composite material of the present invention is a hydrophobic crosslinking agent polymer layer. The hydrothermal method can promote the formation of a three-dimensional network hydrophobic polymer outer layer. The hydrophobic outer layer works synergistically with the inner layer of photo-induced hydrophilic hollow TiO2 microspheres, so that the composite material as a whole can achieve surface wettability switching between hydrophilic and hydrophobic under ultraviolet light irradiation / dark conditions, thereby improving the solid-liquid separation efficiency and cycle life of the composite material.

[0012] Furthermore, the present invention also provides a suitable method for preparing the hollow TiO2-based photocatalytic composite material for degrading Rhodamine B. This method involves modifying hollow TiO2 microspheres with a silane coupling agent to obtain silanized hollow TiO2 microspheres. Then, aniline-based photosensitizers, acrylate-based hydrophobic crosslinking agents, and initiators are added to a toluene solvent system. An in-situ hydrothermal reaction is carried out under an inert atmosphere to form a three-dimensional network of hydrophobic crosslinked polymer layers coating the surface of the hollow TiO2 microspheres, thus obtaining the hollow TiO2-based photocatalytic composite material of the present invention.

[0013] In this invention, there are no particular limitations on the hollow TiO2 microspheres used as the catalytic matrix; hollow TiO2 microspheres prepared by various methods reported in the literature can be used.

[0014] However, preferably, the present invention selects anatase-type hollow TiO2 microspheres as the catalytic matrix of the hollow TiO2-based photocatalytic composite material.

[0015] Furthermore, the anatase-type hollow TiO2 microspheres of the present invention are more preferably obtained by using carbon microspheres prepared by hydrothermal method as hard templates, performing solvothermal self-assembly reaction on the surface of carbon microspheres with tetrabutyl titanate, and then calcining at high temperature in air to remove the internal hard template carbon microspheres.

[0016] Similarly, the present invention does not have any particular limitation on the silane coupling agent used for silanization modification. It can be any commonly used trimethoxysilane coupling agent, which increases the surface activity of the hollow TiO2 microspheres and facilitates the subsequent grafting and coating of the hydrophobic crosslinked polymer layer.

[0017] Preferably, the present invention uses (3-mercaptopropyl)trimethoxysilane as a silane coupling agent, and its amount is preferably 4 to 8 times the mass of the hollow TiO2 microspheres.

[0018] Specifically, this invention uses aniline compounds that can promote charge separation as photosensitizers. Preferably, o-phenylenediamine is used as a photosensitizer, and its amount is 3 to 5 times the mass of the silanized hollow TiO2 microspheres.

[0019] The acrylate-based hydrophobic crosslinking agent described in this invention can be any acrylate-based crosslinking agent that can undergo a self-polymerization reaction under the action of an initiator to form a hydrophobic crosslinked polymer layer, such as trimethylolpropane-trimethacrylate, pentaerythritol triacrylate, ethyl methacrylate, etc. Its function is to form a hydrophobic crosslinked polymer coating layer on the surface of silanized hollow TiO2 microspheres.

[0020] Furthermore, the present invention preferably uses trimethylolpropane-trimethacrylate as a hydrophobic crosslinking agent, and its amount is 20 to 55 times the mass of the silanized hollow TiO2 microspheres.

[0021] Furthermore, the initiator is used to initiate the self-polymerization of acrylate hydrophobic crosslinking agents. Various conventional low-activity azo initiators can be used, including but not limited to 2,2′-azobis(2-methylpropionitrile), azobisisoheptanenitrile, etc., or conventional inorganic persulfate initiators, including but not limited to ammonium persulfate, potassium persulfate, etc.

[0022] Furthermore, the present invention preferably uses 2,2′-azobis(2-methylpropionitrile) as an initiator, and its amount is 0.3 to 0.7 times the mass of the silanized hollow TiO2.

[0023] Furthermore, the in-situ hydrothermal polymerization process is carried out under an inert atmosphere and stirring conditions, with the preferred in-situ hydrothermal reaction temperature being 60–80°C and the preferred reaction time being 6–14 h.

[0024] Furthermore, the reaction product was thoroughly washed with anhydrous ethanol and deionized water, and then vacuum dried to finally obtain the hollow TiO2-based photocatalytic composite material described in this invention.

[0025] The hollow TiO2-based photocatalytic composite material of this invention is a dark brownish-red powder. Under ultraviolet light irradiation, its surface becomes hydrophilic and can be fully dispersed in an aqueous solution containing Rhodamine B to catalytically degrade Rhodamine B, exhibiting strong light absorption and fast catalytic degradation efficiency. After catalytic degradation, the surface of the composite material becomes hydrophobic after the dispersion is placed in the dark, making it easy to settle and separate from the liquid phase, thereby achieving effective purification of water and recovery of the catalyst.

[0026] The hollow TiO2-based photocatalytic composite material of this invention exhibits strong catalytic degradation ability for Rhodamine B, high solid-liquid separation efficiency, and long cycle life. The material preparation method is simple, low-cost, convenient to use, and highly practical, and can be widely applied in photocatalysis, degradation, water treatment, and other fields. Attached Figure Description

[0027] Figure 1 These are field emission scanning electron microscope images of hollow TiO2 microspheres (a) and hollow TiO2-based photocatalytic composite materials (b).

[0028] Figure 2 The infrared spectrum (a) and X-ray diffraction pattern (b) of hollow TiO2 microspheres and hollow TiO2-based photocatalytic composite materials are shown.

[0029] Figure 3 The water contact angle of the hollow TiO2-based photocatalytic composite material changes with UV irradiation time (a) and the wettability switching performance under UV irradiation and dark conditions (b).

[0030] Figure 4 The UV absorbance of the aqueous solution during the degradation of Rhodamine B by hollow TiO2-based photocatalytic composite material changes over time (a) and the degradation curve (b).

[0031] Figure 5 It is the regeneration performance of hollow TiO2-based photocatalytic composite materials in degrading Rhodamine B.

[0032] Figure 6 The UV absorbance of the aqueous solution during the degradation of Rhodamine B by hollow TiO2 microspheres changes over time (a) and the degradation curve (b).

[0033] Figure 7 It is the regeneration performance of hollow TiO2 microspheres in degrading Rhodamine B.

[0034] Figure 8 The UV absorbance of the aqueous solution of Rhodamine B as a function of time (a) and the degradation curve (b) are shown in the image. Implementation

[0035] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0036] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0037] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art.

[0038] This invention provides a method for preparing hollow TiO2-based photocatalytic composite materials, specifically including: Using glucose as a carbon source, carbon microspheres were prepared by conventional hydrothermal method as a hard template. Tetrabutyl titanate was used as a titanium source and was self-assembled on the surface of carbon microspheres by solvothermal method to obtain a TiO2 core-shell structure composite containing hard template carbon microspheres. The hard template carbon microspheres were removed by high-temperature calcination, and hollow TiO2 microspheres were obtained after cooling.

[0039] Hollow TiO2 microspheres were modified by silane coupling agent, and then photosensitizer, hydrophobic crosslinking agent and initiator were added with toluene as solvent. The reaction was carried out in situ under N2 inert atmosphere to form a three-dimensional network of hydrophobic crosslinked polymer layer on the surface of hollow TiO2 microspheres. The washed product was centrifuged and dried to obtain the hollow TiO2-based photocatalytic composite material of the present invention.

[0040] In this invention, (3-mercaptopropyl)trimethoxysilane is preferably used as a silane coupling agent, and its amount is 4 to 8 times the mass of the hollow TiO2 microspheres.

[0041] Furthermore, in the in-situ hydrothermal reaction polymerization process described in this invention, hollow TiO2 microspheres, photosensitizers, hydrophobic crosslinking agents, and initiators are all indispensable.

[0042] Preferably, the present invention uses o-phenylenediamine as a photosensitizer to promote charge separation, and its amount is 3 to 5 times the mass of the silanized hollow TiO2 microspheres.

[0043] In this invention, trimethylolpropane-trimethacrylate is preferred as a hydrophobic crosslinking agent, and its amount is 20 to 55 times the mass of the silanized hollow TiO2 microspheres.

[0044] In this invention, 2,2′-azobis(2-methylpropionitrile) is preferably used as an initiator, and its amount is 0.3 to 0.7 times the mass of the silanized hollow TiO2 microspheres. Its function is to initiate the self-polymerization of the hydrophobic crosslinking agent to form a three-dimensional network of hydrophobic crosslinked polymer coating layer on the surface of the silanized hollow TiO2 microspheres.

[0045] Furthermore, the in-situ hydrothermal reaction polymerization process must be carried out under an inert N2 atmosphere and magnetic stirring conditions. The preferred in-situ hydrothermal reaction temperature is 60–80°C, and the preferred reaction time is 6–14 h.

[0046] Furthermore, the present invention preferably uses anhydrous ethanol and deionized water to thoroughly wash the reaction product, and then vacuum-drys it at 60°C for 12 hours to obtain the hollow TiO2-based photocatalytic composite material of the present invention. Example

[0047] Example 1

[0048] Weigh 4.95g of glucose and place it in a beaker containing 50mL of deionized water. Disperse the glucose evenly by sonication at 25℃ for 2min. Transfer the glucose to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven for hydrothermal reaction at 180℃ for 10h.

[0049] After the reaction was completed, the reaction product was cooled to room temperature in the furnace, thoroughly washed with anhydrous ethanol and deionized water, dried under vacuum at 60°C for 12 hours, and then thoroughly ground to obtain carbon microspheres.

[0050] Measure 2 mL of tetrabutyl titanate and slowly add it to 20 mL of anhydrous ethanol at a rate of 1 drop per second. After the addition is complete, stir magnetically for 30 min.

[0051] Weigh 0.4g of carbon microspheres as a hard template and add them to the above mixed solution of tetrabutyl titanate and anhydrous ethanol. Stir magnetically for 30min to form a homogeneous mixed solution. Place the solution in a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Solvothermal reaction at 220℃ for 20h allows tetrabutyl titanate to react on the surface of the carbon microspheres.

[0052] After the reaction was completed, the reaction product was thoroughly washed with deionized water and anhydrous ethanol, and then dried under vacuum at 60°C for 12 h to obtain a TiO2 core-shell structured composite containing hard template carbon microspheres.

[0053] The core-shell composite was placed in a tube furnace and heated to 550°C at a rate of 5°C / min. It was then calcined in air for 2 hours to remove the internal hard template carbon microspheres. After cooling, hollow TiO2 microspheres were obtained.

[0054] Example 2

[0055] Weigh 0.1 g of hollow TiO2 microspheres and 0.53 g of silane coupling agent (3-mercaptopropyl)trimethoxysilane, add them to 60 mL of anhydrous ethanol / water (3:1, v:v) mixed solution, and carry out silanization grafting reaction by continuous stirring at 65 °C for 2 h.

[0056] After the reaction was completed, the microspheres were dried under vacuum at 60°C for 12 hours to obtain silanized hollow TiO2 microspheres.

[0057] Weigh 0.1g of silanized hollow TiO2 microspheres and add them together with 0.32g of photosensitizer o-phenylenediamine into 30mL of toluene solvent and mix thoroughly. Then add 3.18g of hydrophobic crosslinking agent trimethylolpropane-trimethacrylate and 0.05g of initiator 2,2′-azobis(2-methylpropionitrile). Under an inert N2 atmosphere and with magnetic stirring, carry out in-situ hydrothermal polymerization at 70℃ for 8h to form a three-dimensional network of hydrophobic crosslinked polymer coating on the surface of the silanized hollow TiO2 microspheres.

[0058] After the reaction was completed, the reaction product was thoroughly washed with anhydrous ethanol and deionized water, and then dried under vacuum at 60°C for 12 h to obtain a hollow TiO2-based photocatalytic composite material.

[0059] Figure 1 Field emission scanning electron microscope (FESEM) images of hollow TiO2 microspheres (a) prepared in Example 1 and hollow TiO2-based photocatalytic composite materials (b) prepared in Example 2 are provided. It can be seen that the hollow TiO2 microspheres are hollow spheres with a size of approximately 1–2 μm. After in-situ hydrothermal encapsulation with a hydrophobic crosslinked polymer layer, the product still maintains its spherical shape, but the surface becomes relatively rough, exhibiting a velvety texture and multiple protrusions. This is due to the incomplete and uniform coating of the polymer on the surface of the hollow TiO2 microspheres, demonstrating the composite formation of the hollow TiO2-based photocatalytic composite material.

[0060] Figure 2 The images show the infrared spectrum (a) and X-ray diffraction pattern (b) of the hollow TiO2 microspheres from Example 1 and the hollow TiO2-based photocatalytic composite material from Example 2. In the infrared spectrum, the hollow TiO2 microspheres are only visible at 500 cm⁻¹. -1 A strong characteristic absorption peak of Ti−O bond appeared at [value missing], while the hollow TiO2-based photocatalytic composite material, in addition to this strong characteristic absorption peak, also showed strong absorption peaks at 1700 and 3450 cm⁻¹. -1 The presence of C=O and N−H characteristic peaks from the photosensitizer o-phenylenediamine and the hydrophobic crosslinking agent trimethylolpropane-trimethacrylate indicates that the hydrophobic crosslinking polymer layer has achieved the intended coating composite with the hollow TiO2 microspheres. Furthermore, the X-ray diffraction pattern shows that the hollow TiO2 microspheres possess anatase phase (PDF No. 21-1272) crystal structure, and the coating of the surface with the hydrophobic crosslinking polymer layer does not affect the crystal structure of the hollow TiO2 microspheres. This allows the composite material to be excited under ultraviolet irradiation, achieving catalytic degradation and wettability switching.

[0061] Figure 3 Figure (a) shows the relationship between the water contact angle of the hollow TiO2-based photocatalytic composite material and the duration of ultraviolet (UV) irradiation. Initially, the hollow TiO2-based photocatalytic composite material exhibits a hydrophobic surface with a water contact angle of 113° (as shown in the upper inset), indicating that the hydrophobic crosslinking agent layer on the surface of the composite material plays a dominant role at this stage. However, after irradiation with UV light at 200–275 nm for 0.5 h, the water contact angle of the composite material rapidly decreases to 21° (as shown in the lower inset), exhibiting high hydrophilicity. This demonstrates that after UV irradiation, the TiO2 inside the hollow TiO2-based photocatalytic composite material is excited, releasing hydrophilic hydroxyl groups, which play a dominant role through the crosslinking agent network, thus making the composite material hydrophilic.

[0062] Figure 3 (b) further shows that the surface wettability of the hollow TiO2-based photocatalytic composite material can reversibly switch between hydrophilic and hydrophobic under repeated alternating ultraviolet irradiation and dark treatment. This indicates that the hydrophobic outer layer of the hollow TiO2-based photocatalytic composite material works synergistically with the photo-induced hydrophilic hollow TiO2 inner layer to achieve the switching of its surface wettability between hydrophilic and hydrophobic under ultraviolet irradiation / dark treatment conditions, thereby improving the solid-liquid separation efficiency and cycle life of the composite material.

[0063] Example 3

[0064] Weigh 0.1 g of hollow TiO2 microspheres and 0.45 g of silane coupling agent (3-mercaptopropyl)trimethoxysilane, add them to 60 mL of anhydrous ethanol / water (3:1, v:v) mixed solution, and carry out silanization grafting reaction by continuous stirring at 65 °C for 2 h.

[0065] After the reaction was completed, the microspheres were dried under vacuum at 60°C for 12 hours to obtain silanized hollow TiO2 microspheres.

[0066] Weigh 0.1g of silanized hollow TiO2 microspheres and add them together with 0.48g of photosensitizer o-phenylenediamine into 30mL of toluene solvent and mix thoroughly. Then add 2.52g of hydrophobic crosslinking agent trimethylolpropane-trimethacrylate and 0.03g of initiator 2,2′-azobis(2-methylpropionitrile). Under an inert N2 atmosphere and with magnetic stirring, carry out in-situ hydrothermal polymerization at 60℃ for 10h to form a three-dimensional network of hydrophobic crosslinked polymer coating layer on the surface of the silanized hollow TiO2 microspheres.

[0067] After the reaction was completed, the reaction product was thoroughly washed with anhydrous ethanol and deionized water, and then dried under vacuum at 60°C for 12 h to obtain a hollow TiO2-based photocatalytic composite material.

[0068] Example 4

[0069] Weigh 0.1 g of hollow TiO2 microspheres and 0.67 g of silane coupling agent (3-mercaptopropyl)trimethoxysilane, add them to 60 mL of anhydrous ethanol / water (3:1, v:v) mixed solution, and carry out silanization grafting reaction by continuous stirring at 65 °C for 2 h.

[0070] After the reaction was completed, the microspheres were dried under vacuum at 60°C for 12 hours to obtain silanized hollow TiO2 microspheres.

[0071] Weigh 0.1g of silanized hollow TiO2 microspheres and add them together with 0.30g of photosensitizer o-phenylenediamine into 30mL of toluene solvent and mix thoroughly. Then add 5.28g of hydrophobic crosslinking agent trimethylolpropane-trimethacrylate and 0.07g of initiator 2,2′-azobis(2-methylpropionitrile). Under an inert N2 atmosphere and with magnetic stirring, carry out an in-situ hydrothermal polymerization reaction at 80℃ for 6h to form a three-dimensional network of hydrophobic crosslinked polymer coating layer on the surface of the silanized hollow TiO2 microspheres.

[0072] After the reaction was completed, the reaction product was thoroughly washed with anhydrous ethanol and deionized water, and then dried under vacuum at 60°C for 12 h to obtain a hollow TiO2-based photocatalytic composite material.

[0073] Comparative Example

[0074] Without adding photosensitizers, a hollow TiO2-based photocatalytic composite material was prepared by coating the surface of hollow TiO2 microspheres with a hydrophobic crosslinked polymer coating layer.

[0075] Weigh 0.1 g of hollow TiO2 microspheres and 0.53 g of silane coupling agent (3-mercaptopropyl)trimethoxysilane, add them to 60 mL of anhydrous ethanol / water (3:1, v:v) mixed solution, and carry out silanization grafting reaction by continuous stirring at 65 °C for 2 h.

[0076] After the reaction was completed, the microspheres were dried under vacuum at 60°C for 12 hours to obtain silanized hollow TiO2 microspheres.

[0077] Weigh 0.1g of silanized hollow TiO2 microspheres and mix them thoroughly in 30mL of toluene solvent. Then add 3.18g of hydrophobic crosslinking agent trimethylolpropane-trimethacrylate and 0.05g of initiator 2,2′-azobis(2-methylpropionitrile). Under the conditions of N2 inert atmosphere and magnetic stirring, the reaction temperature is controlled at 70℃ for in-situ hydrothermal polymerization reaction for 8h, forming a three-dimensional network of hydrophobic crosslinked polymer coating layer on the surface of silanized hollow TiO2 microspheres.

[0078] After the reaction was completed, the reaction product was thoroughly washed with anhydrous ethanol and deionized water, and then dried under vacuum at 60°C for 12 h to obtain a hollow TiO2-based photocatalytic composite material without photosensitizer.

[0079] Testing revealed that this photosensitizer-free hollow TiO2-based photocatalytic composite material, like the product in the examples, possesses an anatase-type hollow TiO2 core and an outer hydrophobic crosslinking agent layer. The synergistic effect of these two elements allows the composite material to exhibit the same characteristics as... Figure 3 The ability to switch between consistent surface wettability under varying UV light / dark conditions.

[0080] Application examples

[0081] Hollow TiO2 microspheres were prepared using Example 1, hollow TiO2-based photocatalytic composite materials were prepared using Example 2, and hollow TiO2-based photocatalytic composite materials without photosensitizers were prepared using a comparative example. These materials were used to degrade Rhodamine B in aqueous solutions.

[0082] Specifically, 20 mL of a 10 mg / L Rhodamine B aqueous solution was taken, and 10 mg of each of the above photocatalytic materials were added. The degree of catalytic degradation of the solution was measured with time (0.5, 1, 2, 3, 4 h) using an ultraviolet spectrophotometer.

[0083] After degradation, the photocatalytic material is left in the dark to make its surface hydrophobic, so that it can be easily separated and recovered from the solution by centrifugation. After drying, it can be used again for the degradation of Rhodamine B in aqueous solution.

[0084] Figure 4 The changes in UV absorbance of the aqueous solution of Rhodamine B over time and the degradation curve (b) are shown in Example 2 using the hollow TiO2-based photocatalytic composite material. In the absorbance spectrum of (a), the absorbance peak near 550 nm is the characteristic peak of Rhodamine B in aqueous solution. It can be seen that the characteristic peak of Rhodamine B decreases most significantly in the first 0.5 h, and the height of this characteristic peak continuously decreases with increasing degradation time. Further quantitative analysis of the Rhodamine B degradation curve shown in (b) reveals that Rhodamine B is rapidly degraded within the first 0.5 h, with a degradation rate reaching 80%. As the degradation time continues to increase, the degradation rate of Rhodamine B reaches 92% after 4 h, demonstrating the highly efficient degradation ability of the hollow TiO2-based photocatalytic composite material in Example 2 for Rhodamine B.

[0085] Figure 5 This study demonstrates the regeneration performance of the hollow TiO2-based photocatalytic composite material in degrading Rhodamine B in Example 2. It shows that the degradation rate reached 92% when the hollow TiO2-based photocatalytic composite material was first used to degrade Rhodamine B. After degradation, the composite material was left in the dark to make its surface hydrophobic. After centrifugation and drying, the degradation rate remained unchanged when it was used a second time to degrade Rhodamine B in aqueous solution. Repeating this recycling process, the composite material still achieved a 90% degradation rate for Rhodamine B on the fifth use, which is 97.8% of the initial degradation rate. This indicates that the hollow TiO2-based photocatalytic composite material, due to its switchable wettability surface, promotes material separation and regeneration, and has a good cycle life.

[0086] The catalytic degradation effect and recycling of Rhodamine B by the hollow TiO2-based photocatalytic composite materials in the products of Examples 3 and 4 were tested using the same method, and the results were consistent with those of the product in Example 2.

[0087] Figure 6 This example illustrates the use of hollow TiO2 microspheres as a photocatalyst for the degradation of Rhodamine B in Example 1. From the UV absorbance curve of the aqueous solution in (a) over time, it can be seen that the characteristic peak of Rhodamine B near 550 nm decreases continuously with increasing degradation time, but the decrease is limited. Furthermore, quantitative analysis of the degradation curve in (b) shows that Rhodamine B is rapidly degraded at the initial 0.5 and 1 h, with a degradation rate of 46%; however, as the degradation time continues to increase, the degradation rate of Rhodamine B at 4 h only reaches 48%. (Comparison) Figure 4 In Example 2, the degradation of Rhodamine B by the hollow TiO2-based photocatalytic composite material shows that, due to the lack of photosensitizer modification, the ability of hollow TiO2 microspheres to catalytically degrade Rhodamine B is significantly lower than that of the hollow TiO2-based photocatalytic composite material.

[0088] Figure 7 The regeneration performance of hollow TiO2 microspheres in Rhodamine B degradation in Example 1 was compared. The initial degradation rate was only 48%, and the surface of the hollow TiO2 microspheres without the composite hydrophobic crosslinking agent remained hydrophilic, requiring multiple, time-consuming centrifugation separations for complete recovery. After drying, they were reused for Rhodamine B degradation in aqueous solution. Repeating this recycling process, the degradation rate of Rhodamine B by the hollow TiO2 microspheres on the fifth use had dropped to 30%, only 62.5% of the initial degradation rate. This was significantly lower than the degradation rate maintained on the fifth reuse of the hollow TiO2-based photocatalytic composite material in Example 2 (97.8%). This indicates that the hollow TiO2 microspheres without surface modification and coating lack a switchable wettability surface, hindering material separation and regeneration, resulting in a poorer cycle life.

[0089] The above comparison shows that by modifying the surface of hollow TiO2 microspheres with the photosensitizer o-phenylenediamine and coating them with a hydrophobic crosslinking agent polymer layer, the catalytic activity, catalytic efficiency, and cycle life of the photocatalytic material can be significantly improved.

[0090] Figure 8 The figures (a) and (b) show the UV absorbance of the aqueous solution of the comparative hollow TiO2-based photocatalytic composite material without photosensitizer during the degradation of Rhodamine B. As shown in the UV absorbance variation graph (a), the characteristic peak height of Rhodamine B near 550 nm decreases continuously with increasing degradation time. Further quantitative analysis of the Rhodamine B degradation curve in (b) reveals that the comparative composite material, lacking the photosensitizer o-phenylenediamine, achieves a final Rhodamine B degradation rate of only 46%, consistent with the degradation rate of the hollow TiO2 microspheres in Example 1, both lower than the hollow TiO2-based photocatalytic composite material containing o-phenylenediamine photosensitizer in the example.

[0091] Furthermore, unlike the degradation curve trends of Examples 1 and 2, the degradation curve of the comparative product when degrading Rhodamine B under the same conditions was significantly flatter and failed to complete the degradation rapidly within 1 hour. This is partly because the coating of the surface hydrophobic crosslinking agent slightly hindered the absorption of ultraviolet light by the hollow TiO2 microspheres, and partly because the lack of photosensitizer to promote the separation and transport efficiency of photogenerated carriers failed to improve the degradation efficiency.

[0092] This demonstrates that photosensitizers play a crucial role in hollow TiO2-based photocatalytic composite material systems.

[0093] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hollow TiO2-based photocatalytic composite material for degrading Rhodamine B is prepared by using anatase-type hollow TiO2 microspheres as the catalytic matrix, modifying their surface with o-phenylenediamine photosensitizer, and completely coating them with a hydrophobic crosslinking agent polymer layer formed from acrylate hydrophobic crosslinking agents. The hydrophobic crosslinking agent polymer layer is formed by in-situ polymerization on the surface of hollow TiO2 microspheres pretreated with silane coupling agent, which is used to fix the photosensitizer and endow the composite material with the property of switching between hydrophilic and hydrophobic surface wettability under ultraviolet light / dark conditions.

2. The method for preparing the hollow TiO2-based photocatalytic composite material for degrading Rhodamine B as described in claim 1 comprises: modifying anatase-type hollow TiO2 microspheres with a silane coupling agent to obtain silanized hollow TiO2 microspheres; adding o-phenylenediamine photosensitizer, acrylate hydrophobic crosslinking agent, and initiator to a toluene solvent system; and carrying out an in-situ hydrothermal reaction under an inert atmosphere to form a three-dimensional network-like hydrophobic crosslinked polymer layer coating the surface of the hollow TiO2 microspheres, thereby obtaining the hollow TiO2-based photocatalytic composite material.

3. The preparation method according to claim 2, characterized in that: The anatase-type hollow TiO2 microspheres are obtained by using carbon microspheres prepared by hydrothermal method as hard templates, performing a solvothermal self-assembly reaction on the surface of carbon microspheres with tetrabutyl titanate, and then calcining at high temperature in air to remove the internal hard template carbon microspheres.

4. The preparation method according to claim 2, characterized in that: The silane coupling agent is (3-mercaptopropyl)trimethoxysilane, and the amount used is 4 to 8 times the mass of the hollow TiO2 microspheres.

5. The preparation method according to claim 2, characterized in that: The amount of the o-phenylenediamine photosensitizer is 3 to 5 times the mass of the silanized hollow TiO2 microspheres.

6. The preparation method according to claim 2, characterized in that: The acrylate-based hydrophobic crosslinking agent is trimethylolpropane-trimethylacrylate, and its dosage is 20 to 55 times the mass of the silanized hollow TiO2 microspheres.

7. The preparation method according to claim 2, characterized in that: The initiator is a low-activity azo initiator or an inorganic persulfate initiator.

8. The preparation method according to claim 2, characterized in that: The initiator is 2,2′-azobis(2-methylpropionitrile), and the amount used is 0.3 to 0.7 times the mass of the silanized hollow TiO2.

9. The preparation method according to claim 2, characterized in that: The in-situ hydrothermal reaction temperature is 60–80℃, and the reaction time is 6–14 h.

10. The application of the hollow TiO2-based photocatalytic composite material of claim 1 in the catalytic degradation of Rhodamine B in water.

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