Composite catalyst with photocatalytic switching property as well as preparation method and application of composite catalyst

Abstract

The invention belongs to the technical field of photo-response catalysts, and particularly discloses a composite catalyst with a photo-catalytic switching property as well as a preparation method and application of the composite catalyst. The preparation method comprises the following steps: performing thermal polycondensation on dicyandiamide to obtain graphite-phase carbon nitride; and mixing vanadium pentoxide with graphite phase carbon nitride, and reacting to obtain M-phase vanadium dioxide modified graphite phase carbon nitride, namely the composite catalyst with the photocatalytic switch property. The composite catalyst prepared by the invention can reduce the appearance of a vanadium oxide impure phase, the preparation process can be shortened to one step, and the preparation cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of photoresponsive catalysts, and in particular to a composite catalyst with photocatalytic switching properties, and a preparation method and application thereof. Background Art

[0002] By integrating precious metal nanoparticles with semiconductor photocatalysts, the photocatalytic activity of the catalyst in the visible light band can be improved. However, precious metals are expensive and the physicochemical properties of some nano-precious metals are unstable. They are easily oxidized in the application environment with complex and variable temperature and pH, which affects the effect and service life of the composite photocatalyst. However, materials with surface plasmon resonance effect (SPR) are not limited to pure metals. Vanadium dioxide (VO2) has attracted widespread attention for its unique property of reversibly changing from semiconductor (M phase, space group P21 / c) to metal (R phase, space group P42 / mnm) at 68°C. This metal-semiconductor reversible phase transition (MST) of VO2 will change its physicochemical properties such as optical and electrical properties. The semiconductor and metallic properties of VO2 can form completely different heterostructures with photocatalysts, thereby changing the carrier direction in the system; more importantly, the SPR effect of R-phase VO2, which reflects the metallic properties, will also help improve the photocatalytic effect. However, the common preparation and compounding methods of VO2 are not suitable for large-scale production applications.

[0003] There are many types of vanadium oxides, including V2O3, VO2, V6O 13 , V3O7, V2O5, V5O9 and other 13 types. It is very difficult to accurately locate and prepare VO2 in complex oxide types without generating other oxides. Even if VO2 is successfully prepared, the different structures of VO2 that have been discovered include VO2(A), VO2(B), VO2(P), VO2(D), VO2(M), VO2(R) and other phases. They are typical multi-structure binary compounds, and the differences in structure make the properties of these crystal phases very different. Therefore, it is necessary to regulate the specific crystal form of VO2 to improve the physical and chemical properties of its materials. At present, the crystal form of the product is generally adjusted by controlling the concentration, temperature, time and other factors of the reactants. The commonly used preparation methods are thermal decomposition, sol-gel method, chemical vapor deposition method, reactive sputtering and hydrothermal method, which can only obtain VO2-B phase. If VO2 with reversible phase change properties is to be obtained, cumbersome additional treatment must be performed. The VO2 prepared by the above method will further undergo multiple steps of hydrothermal, ball milling or heat treatment in the process of forming a composite structure with other substances. The redox reactions occurring in this process will seriously affect the purity of VO2, thereby reducing the use effect and life of the target photocatalytic material.

[0004] Photocatalysts are often used in sewage degradation, hydrogen and oxygen production, CO2 reduction, and organic synthesis reactions. In these industries, the start and end of photocatalysis is usually regulated by turning off the lights, but this regulation method consumes a lot of energy. In the catalytic system that uses sunlight as energy, the instability of sunlight also affects the stable and widespread application of photocatalysis. And when photocatalysis is used as a coating and other film products, the highly oxidizing photocatalytic over-products will also affect the service life of the film. Therefore, it is necessary to further improve the efficiency of photocatalysis in order to complete the catalysis within the working range, and maintain catalytic inertness in the links where photocatalysis is not required, so as to protect other materials, reduce the impact on other functional processes, and improve the flexibility of catalysis.

[0005] Graphite carbon nitride (g-C3N4), which is composed mainly of C, H, N and a small amount of O, has the advantages of easy preparation, non-toxicity, low cost and high catalytic performance. It is widely studied as a photocatalyst with great application prospects. However, its catalytic effect still cannot meet the needs of a wide range of application scenarios. Its catalytic potential can be further released by increasing the degree of polymerization and constructing a composite structure. Summary of the invention

[0006] In view of this, the present invention provides a composite catalyst with photocatalytic switching properties and a preparation method and application thereof, in order to solve the problems that the existing VO2-M@g-C3N4 preparation steps are complicated and require the use of toxic organic solvents, and the existing photocatalysts have poor catalytic effects and require light or sunlight regulation, and have high energy consumption or instability.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing a composite catalyst having photocatalytic switching properties comprises the following steps:

[0009] 1) subjecting dicyandiamide to thermal polycondensation to obtain graphite phase carbon nitride;

[0010] 2) mixing vanadium pentoxide with graphite-phase carbon nitride and reacting them to obtain M-phase vanadium dioxide-modified graphite-phase carbon nitride;

[0011] The M-phase vanadium dioxide-modified graphite-phase carbon nitride is a composite catalyst with photocatalytic switching properties.

[0012] Preferably, the thermal polycondensation in step 1) is first maintained at 500-510° C. for 3.5-4 hours, and then heated to 520-530° C. for 0.4-0.6 hours.

[0013] Preferably, the mass ratio of vanadium pentoxide to graphite carbon nitride in step 2) is 1:9.5-10.5.

[0014] Preferably, the reaction temperature in step 2) is 550-570° C., the reaction time is 1.8-2.2 h, and the reaction pressure is 10-25 Pa.

[0015] Another object of the present invention is to provide a composite catalyst having photocatalytic switching properties prepared by the above preparation method.

[0016] Another object of the present invention is to provide a composite catalyst with photocatalytic switching properties for use in surface coating / film of smart glass, degradation of printing and dyeing wastewater, or photolysis of water to produce hydrogen.

[0017] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The composite catalyst with photocatalytic switching properties prepared by the present invention is recorded as VO2-M@g-C3N4. The preparation advantages of VO2-M@g-C3N4 include: the conventional method (such as hydrothermal method, sol-gel method, etc.) for preparing VO2 composite system can only obtain the composite material of VO2 B phase and carbon nitride. The process usually requires a long reaction time or uses toxic organic solvents, and is accompanied by the generation of impurities, such as V2O3, V6O 13 etc.; and the obtained VO2-B@g-C3N4 needs to be subjected to phase change treatment in a high vacuum or inert gas atmosphere above 450°C to obtain M-phase VO2 with phase change properties. The present invention reduces the appearance of vanadium oxide impurities by accurately adjusting the mass ratio of g-C3N4 to V2O5, while weakening the vacuum requirement, shortening the usual 2-3 step composite process to 1 step, and reducing the preparation cost.

[0019] 2. The present invention uniformly mixes V2O5 with graphite phase carbon nitride and performs heat treatment under a weak vacuum environment at a specific temperature. In the treatment process disclosed in the present invention, carbon nitride can uniformly and gently generate a reducing atmosphere to convert V 5+ Restore to V 4+ , and under the reaction conditions of the present invention, a weak vacuum low oxygen environment will be continuously maintained, which prevents the generated VO2 from being further reduced to products such as V2O3, and at the reaction temperature disclosed in the present invention, the most stable phase of VO2 is the R phase, and a single VO2-M can be obtained after cooling to room temperature, thereby ensuring the uniformity, singleness and mildness of VO2 generation.

[0020] 3. The VO2-M@g-C3N4 composite catalytic material prepared by the present invention solves water pollution problems in industry and life, such as inorganic pollution and microbial pollution. The main sources include industrial wastewater, the use of pesticides and fertilizers, oil spills, etc., which lead to the presence of various organic compounds in the water, such as benzene, phenol, pesticides and organic solvents. And after the composite material is matched with phosphorescent materials, the non-uniformity of sunlight in terms of region, time, climate, etc. can be ignored, and catalysis can be carried out stably and efficiently for a long time.

[0021] As a surface coating / film for smart glass: it takes into account both temperature control and cleaning functions. First, in a humid environment (such as rainy and foggy days), the composite photocatalyst film can clean the surface of the glass. In a dry and high-temperature environment, VO2 changes from a low-temperature semiconductor state to a high-temperature metal state, and its effect on infrared light also changes from high transmittance at low temperatures to high barrier at high temperatures. The transmittance in the visible light region remains almost unchanged, and the barrier to the ultraviolet light region is always high. Therefore, by attaching VO2 material to the glass surface, it is possible to control solar heat in different seasons and achieve an energy-saving mode of warm in winter and cool in summer.

[0022] Used for photolysis of water to produce hydrogen: The production process can be adjusted in stages. When VO2 is metallic, it assists the main catalyst to produce hydrogen quickly and efficiently, while the M phase inhibits the catalytic effect. At the same time, a narrow-wavelength cold light source or phosphorescent material corresponding to the SPR effect of the VO2 metal phase can be used as a light source for photocatalysis at night, greatly extending the service life, flexibility, net working time and working efficiency of the composite photocatalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 XRD spectrum (Intensity——intensity, Theta——θ) of the VO2-M@g-C3N4 composite catalyst prepared in Example 1 of the present invention;

[0025] Figure 2 XRD patterns (Intensity, Theta) of graphite carbon nitride obtained in Example 1 and Comparative Example 1 of the present invention;

[0026] Figure 3 The photodegradation curves of the graphite phase carbon nitride obtained in Example 1 and Comparative Example 1 of the present invention in the photocatalytic reaction;

[0027] Figure 4 The photodegradation curves of the composite catalyst prepared in Example 1 of the present invention under photocatalytic reaction at different temperatures. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a composite catalyst having photocatalytic switching properties, comprising the following steps:

[0029] 1) subjecting dicyandiamide to thermal polycondensation to obtain graphite phase carbon nitride;

[0030] 2) Mixing vanadium pentoxide with graphite-phase carbon nitride and reacting them to obtain M-phase vanadium dioxide-modified graphite-phase carbon nitride, recorded as VO2-M@g-C3N4;

[0031] The M-phase vanadium dioxide-modified graphite-phase carbon nitride is a composite catalyst with photocatalytic switching properties.

[0032] In the present invention, the thermal polycondensation in step 1) is specifically first maintained at 500-510°C for 3.5-4h, and the maintaining temperature can be specifically 502°C, 504°C, 505°C, 506°C, 508°C, and the maintaining time can be specifically 3.6h, 3.7h, 3.8h, 3.9h; then the temperature is raised to 520-530°C and maintained for 0.4-0.6h, and the maintaining temperature can be specifically 522°C, 524°C, 525°C, 526°C, 528°C, and the maintaining time can be specifically 0.42h, 0.45h, 0.48h, 0.5h, 0.52h, 0.55h, 0.58h.

[0033] In the present invention, the temperature difference in the process of preparing graphite phase carbon nitride by thermal polycondensation will greatly affect the yield of carbon nitride. In the same time (4h as an example), the yield of carbon nitride is 67.7% when the thermal polycondensation temperature is 500°C in an air atmosphere, and 26.4% at 520°C; but the carbon nitride obtained by thermal polycondensation at 520°C has a higher lattice integrity. The present invention chooses to continue to heat up to 520-530°C after calcination at 500-510°C and continue to keep warm, so that carbon nitride with a higher degree of polycondensation can be obtained while retaining a higher yield of about 51.2%.

[0034] In the present invention, the mixing in step 2) is preferably performed by first crushing the obtained graphite phase carbon nitride and then mixing it with vanadium pentoxide.

[0035] In the present invention, the mass ratio of vanadium pentoxide to graphite carbon nitride in step 2) is 1:9.5-10.5, preferably 1:9.8-10.2, and more preferably 1:10.

[0036] In the present invention, by accurately adjusting the mass ratio of g-C3N4 to V2O5, the appearance of vanadium oxide impurities is reduced, and the vacuum requirement is weakened.

[0037] In the present invention, the reaction temperature in step 2) is 550-570°C, specifically 552°C, 555°C, 558°C, 560°C, 562°C, 565°C, 568°C; the reaction time is 1.8-2.2h, specifically 1.9h, 2h, 2.1h; the reaction pressure is 10-25Pa, specifically 12Pa, 14Pa, 15Pa, 16Pa, 18Pa, 20Pa, 22Pa, 24Pa.

[0038] The present invention also provides a composite catalyst having photocatalytic switching properties prepared by the above preparation method.

[0039] The present invention also provides an application of a composite catalyst with photocatalytic switching properties in the surface coating / film of smart glass, the degradation of printing and dyeing wastewater, or the photolysis of water to produce hydrogen.

[0040] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] Take 6g of dicyandiamide (DICY, C2H4N4) and put it into a clean porcelain boat and keep it evenly distributed. Then put the porcelain boat into a tube furnace and perform thermal polycondensation under air atmosphere. The thermal polycondensation is heated from room temperature to 500℃ at a heating rate of 10℃ / min for 4h, and then heated to 520℃ for 0.5h, and then cooled to room temperature with the furnace to obtain a graphite phase carbon nitride (g-C3N4) sample. The original carbon nitride is a block solid. After grinding into a fine and uniform powder, it is washed with deionized water, anhydrous ethanol, and ethylene glycol as washing solvents in sequence. The washed powder is placed in a vacuum oven and dried at 70℃ for 6h to obtain graphite phase carbon nitride (g-C3N4) with a yield of 58.89%.

[0043] 0.12 g of vanadium pentoxide (V2O5) and 1.2 g of g-C3N4 powder were uniformly mechanically mixed (mass ratio V2O5:g-C3N4=1:10) and evenly spread into a porcelain boat. In a vacuum atmosphere of 10 Pa, the temperature was raised from room temperature to 560°C at a heating rate of 10°C / min and kept for 2 h. Then, the temperature was cooled to room temperature with the furnace to obtain M-phase VO2-modified g-C3N4 (VO2-M@g-C3N4).

[0044] The obtained VO2-M@g-C3N4 was subjected to XRD detection, and the XRD spectrum is shown as follows Figure 1 As shown, the characteristic peak of VO2 is consistent with the standard card JCPDS#01-072-0514, which can determine that the material obtained by the present invention is VO2-M.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that the operation of heating the temperature to 520° C. and maintaining it for 0.5 h is deleted, and graphite phase carbon nitride is obtained. The yield of graphite phase carbon nitride is 67.7%.

[0047] The g-C3N4 obtained in Example 1 and Comparative Example 1 was subjected to XRD detection (Example 1 was recorded as 500-5204+0.5h, Comparative Example 1 was recorded as 500-4h), and the detection results are as follows: Figure 2 As shown, through Figure 2 It can be seen that the (002) peak representing the interlayer order of graphite phase carbon nitride is the highest peak and is also an important indicator for judging the degree of polymerization of g-C3N4. From the PDF standard card (JCPDS#01-087-1526), ​​it can be seen that the peak is located at 26.505°. By comparison, it can be seen that the g-C3N4 polymerized under the conditions of Example 1 has a higher degree of polymerization.

[0048] Then, the graphite phase carbon nitride of Example 1 and Comparative Example 1 were used as catalysts to perform a photocatalytic test on Rhodamine B for 2 hours under 450 nm light. The photodegradation curve of the catalytic reaction is shown in FIG. Figure 3 As shown, through Figure 3 It can be seen that the VO2-M@g-C3N4 catalyst obtained in Example 1 of the present invention has a higher photocatalytic efficiency.

[0049] Photocatalytic test conditions: The mass of graphite carbon nitride is 35 mg, which is poured into 35 mL of 5×10 -5 mol / L dye (Rhodamine B, RhB) solution. The detection system was placed on a magnetic stirring table with continuous stirring, first stirred for 30 minutes in a dark environment to allow the system to reach adsorption and desorption equilibrium, and then subjected to a 2-hour photodegradation test under 50W 365nm (±5nm) LED cold light source irradiation. 3mL of the suspension was taken out every 20 minutes, and the supernatant was taken after centrifugation and the absorption spectrum was detected in a UV-vis spectrophotometer. The concentration of the dye was determined by monitoring the change in the maximum absorbance intensity of different dye solutions. Using the Beer-Lambert method, the absorbance is proportional to the concentration of the diluted solution, from which the photodegradation percentage can be calculated using the following formula:

[0050]

[0051] η represents the degradation rate, C0 is the initial concentration of the RhB solution, C is the concentration at a certain irradiation time, and the photodegradation curve is drawn by the degradation percentage. After each test, the sample will be poured back into the photodegradation system.

[0052] Example 2

[0053] Take 6g of dicyandiamide (DICY, C2H4N4) and put it into a clean porcelain boat and keep it evenly distributed. Then put the porcelain boat into a tube furnace and perform thermal polycondensation under air atmosphere. The thermal polycondensation is heated from room temperature to 500℃ at a heating rate of 10℃ / min for 4h, and then heated to 520℃ for 0.6h. Then cool it to room temperature with the furnace to obtain a graphite phase carbon nitride (g-C3N4) sample. The original carbon nitride is a block solid. After grinding into a fine and uniform powder, it is washed with deionized water, anhydrous ethanol, and ethylene glycol as washing solvents in sequence. The washed powder is placed in a vacuum oven and dried at 70℃ for 6h to obtain graphite phase carbon nitride (g-C3N4) with a yield of 56.16%.

[0054] 0.117 g of vanadium pentoxide (V2O5) and 1.2 g of g-C3N4 powder were uniformly mechanically mixed (mass ratio V2O5:g-C3N4=1:10.2) and evenly spread into a porcelain boat. In a vacuum atmosphere of 10 Pa, the temperature was increased from room temperature to 570°C at a heating rate of 10°C / min and kept for 2 h. Then, the temperature was cooled to room temperature with the furnace to obtain M-phase VO2-modified g-C3N4 (VO2-M@g-C3N4).

[0055] Example 3

[0056] Take 6g of dicyandiamide (DICY, C2H4N4) and put it into a clean porcelain boat and keep it evenly distributed. Then put the porcelain boat into a tube furnace and perform thermal polycondensation under air atmosphere. The thermal polycondensation is heated from room temperature to 508℃ at a heating rate of 10℃ / min for 4h, and then heated to 520℃ for 0.45h, and then cooled to room temperature with the furnace to obtain a graphite phase carbon nitride (g-C3N4) sample. The original carbon nitride is a block solid. After grinding into a fine and uniform powder, it is washed with deionized water, anhydrous ethanol, and ethylene glycol as washing solvents in sequence. The washed powder is placed in a vacuum oven and dried at 70℃ for 6h to obtain graphite phase carbon nitride (g-C3N4) with a yield of 61.2%.

[0057] 0.12 g of vanadium pentoxide (V2O5) and 1.14 g of g-C3N4 powder were uniformly mechanically mixed (mass ratio V2O5:g-C3N4=1:9.5) and evenly spread into a porcelain boat. In a vacuum atmosphere of 20 Pa, the temperature was increased from room temperature to 560°C at a rate of 10°C / min and kept for 2.2 h. Then, the temperature was cooled to room temperature with the furnace to obtain M-phase VO2-modified g-C3N4 (VO2-M@g-C3N4).

[0058] Experimental Example 1

[0059] In order to measure the photocatalytic degradation of RhB aqueous solution with and without visible light irradiation, VO2-M@g-C3N4 prepared in Example 1 was weighed as a photocatalyst and added together with 0.35 g of strontium aluminate long afterglow luminescent powder to 35 mL of 5×10 -5 mol / L dye solution. The resulting suspension was magnetically stirred in a dark photochemical reaction box for 30 min to ensure the adsorption and desorption equilibrium between the dye and the photocatalyst. In order to carry out photocatalytic degradation with long afterglow as the light source, a 365nm (±5nm) LED light source was used for 20 min to achieve a stable photocatalytic degradation reaction. At the same time, it will ensure that the long afterglow photoluminescent agent SrAl2O4:Eu 2+ ,Dy 3+ It can capture and store excitation / light energy for continuous photocatalytic degradation reactions in a sunless environment. In addition, 3 mL of the suspension was taken out from the reactor, and the supernatant was taken after centrifugation and the concentration of the dye was measured in real time using a UV-vis spectrophotometer. Then the visible light source was turned off, and degradation was carried out for 20 minutes under the action of long afterglow. 3 ml of the suspension was taken out from the reactor, and the dye concentration was detected after centrifugation. After each detection, the sample was poured back into the photodegradation system. The above photocatalytic degradation reaction was repeated alternately 3 times for a total of 2 hours. The above experiments were carried out at different temperatures (converted to VO2-R@g-C3N4 at 70°C, recorded as VO2-R@g-C3N4; kept at 25°C for VO2-M@g-C3N4, recorded as VO2-M@g-C3N4), and the time-concentration photocatalytic effect diagram was drawn as shown in the figure Figure 4 shown.

[0060] Figure 4 The two data are from the same sample (composite catalyst prepared in Example 1) at different temperatures, before and after VO2 undergoes metal (R 68°C)-semiconductor (M 25°C) phase transition, and catalysis of the same dye under the same illumination conditions. Since the R phase VO2 in the sample has an SPR (surface plasmon resonance) absorption effect on the phosphorescence wavelength, the photocatalysis of the material is promoted, so a catalytic effect of 90.2% is obtained; while the M phase VO2 forms an energy band mismatch with the graphite phase carbon nitride, inhibiting the catalytic effect, so it is shown as no catalysis. The present invention can turn on or off the photocatalytic reaction by controlling the temperature.

[0061] When the specific "switch" is on (VO2-R), the catalytic rate is greatly improved within 2 hours, and when the "switch" is off (VO2-M), there is almost no photocatalytic effect within 2 hours, and catalysis can be selectively promoted or inhibited efficiently. Vanadium dioxide (VO2) with metal-semiconductor reversible phase transition properties (MST) exhibits completely different optical and electrical properties in two phases, and accordingly, the SPR effect of VO2 metal R phase and the full light absorption effect of narrow bandgap semiconductor M phase will also form two completely different matches with g-C3N4. Therefore, the present invention starts from the MST theory, introduces VO2 with isomeric properties into g-C3N4, and constructs a metal-carbon nitride or semiconductor-carbon nitride isomorphic composite structure in situ, and obtains a catalytic system with a "photoswitch" effect.

[0062] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0063] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite catalyst having photocatalytic switching properties, characterized in that: The steps include: 1) subjecting dicyandiamide to thermal polycondensation to obtain graphite phase carbon nitride; 2) mixing vanadium pentoxide with graphite-phase carbon nitride and reacting them to obtain M-phase vanadium dioxide-modified graphite-phase carbon nitride; The M-phase vanadium dioxide-modified graphite-phase carbon nitride is a composite catalyst with photocatalytic switching properties.

2. The method for preparing a composite catalyst having photocatalytic switching properties according to claim 1, characterized in that: The thermal polycondensation in step 1) is specifically first maintained at 500-510° C. for 3.5-4 hours, and then heated to 520-530° C. for 0.4-0.6 hours.

3. A method for preparing a composite catalyst having photocatalytic switching properties according to claim 1 or 2, characterized in that: The mass ratio of vanadium pentoxide to graphite carbon nitride in step 2) is 1:9.5-10.

5.

4. The method for preparing a composite catalyst having photocatalytic switching properties according to claim 3, characterized in that: The reaction temperature in step 2) is 550-570° C., the reaction time is 1.8-2.2 h, and the reaction pressure is 10-25 Pa.

5. A composite catalyst having photocatalytic switching properties prepared by the preparation method according to any one of claims 1 to 4.

6. Application of the composite catalyst with photocatalytic switching properties as claimed in claim 5 in surface coating / film of smart glass, degradation of printing and dyeing wastewater or photolysis of water to produce hydrogen.

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