A composite photocatalyst and preparation method thereof

Abstract

The invention relates to a composite photocatalyst and a preparation method thereof, and belongs to the technical field of semiconductor photocatalysis. The invention uses nano titanium dioxide and a self-made organic semiconductor as raw materials to prepare a composite photocatalyst. The invention prepares a tetrahydrofuran mixed solution of an organic semiconductor and an ethanol dispersion of nano titanium dioxide in sequence, then drops the mixed solution into the ethanol dispersion of nano titanium dioxide, and stirs and mixes in the dark to obtain an organic semiconductor / nano titanium dioxide heterojunction composite photocatalyst. The preparation of the invention uses the self-made organic semiconductor composite nano titanium dioxide to improve the visible light utilization rate of the nano titanium dioxide, and a synergistic effect is generated in the prepared composite photocatalyst, which can effectively improve charge separation and light stability, and improve photocatalytic efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor photocatalysis, and in particular, relates to a composite photocatalyst and a preparation method thereof. Background Art

[0002] In recent years, semiconductor catalysts have made important breakthroughs in treating wastewater contaminated by macromolecular organic matter. Chinese researchers have successfully synthesized a series of new photocatalytic materials using a variety of methods, including solid-phase synthesis, semiconductor composites, and doping with transition metal ions and non-metallic ions. These new materials can photocatalytically degrade organic macromolecules into non-toxic carbon dioxide, water, and some small molecules under ultraviolet light.

[0003] Traditional titanium dioxide is a widely used photocatalytic material. It shows high stability in acids, alkalis and most solvents, is suitable for a variety of environments, and is low-cost, rich in raw materials, non-toxic and environmentally friendly. Under ultraviolet light, it can effectively degrade organic pollutants and kill microorganisms. However, titanium dioxide can only absorb ultraviolet light, which accounts for only 5% of sunlight, and has an extremely low utilization rate of visible light. The titanium dioxide photocatalytic system in the prior art generally uses artificial ultraviolet lamps as light sources and has no use value. Extending the available spectral range to the visible light region and using sunlight as a light source are key factors that determine whether it can be applied on a large scale in practice. Based on this, the present invention provides a composite photocatalyst and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a composite photocatalyst and a preparation method thereof, so as to solve the problems mentioned in the above background technology.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A composite photocatalyst comprising nano-titanium dioxide and a self-made organic semiconductor;

[0007] A method for preparing a composite photocatalyst comprises the following steps:

[0008] The first step: dissolving the organic semiconductor in tetrahydrofuran, stirring and mixing evenly at room temperature to obtain a mixed solution for use;

[0009] Step 2: Add nano-titanium dioxide into anhydrous ethanol, and mix by ultrasonic dispersion at room temperature to obtain an ethanol dispersion of nano-titanium dioxide;

[0010] Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir and mix evenly, remove the solvent by rotary evaporation, and dry in an oven to constant weight to obtain a composite photocatalyst of any proportion.

[0011] Furthermore, the crystal structure of the nano titanium dioxide is one of anatase type and rutile type.

[0012] Furthermore, the stirring and mixing in the first step is performed at a rotation speed of 300-400 rpm and for a time of 20-30 min.

[0013] Furthermore, the mass ratio of the organic semiconductor to tetrahydrofuran in the mixed solution in the first step is 3:(80-100).

[0014] Furthermore, the ultrasonic dispersion time in the second step is 40-60 min.

[0015] Furthermore, in the second step, the mass ratio of nano-titanium dioxide to ethanol in the ethanol dispersion of nano-titanium dioxide is 1:(160-200).

[0016] Furthermore, in the third step, the stirring condition is light-proof condition, the stirring speed condition is 600-800 rpm, and the stirring time condition is 100-120 min.

[0017] Furthermore, the drying temperature in the third step is 40-50°C.

[0018] Preferably, the mass fraction of the organic semiconductor accounts for 15-25% of the composite photocatalyst.

[0019] Further, the organic semiconductor is prepared by the following steps:

[0020] Step 1, 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, dimethyl malonate, piperidine and anhydrous ethanol are mixed in a three-necked flask, a condenser and a thermometer are installed, magnetic stirring is turned on, the system temperature is raised to 80°C, and after reacting at 80°C for 2h, a 20% by mass aqueous sodium hydroxide solution is added to the three-necked flask, and the reaction is continued at 80°C for 2h. After the reaction is completed, 10-20% by mass dilute hydrochloric acid is added to the three-necked flask to adjust the pH of the system to 4-5, and the mixture is extracted with dichloromethane. After separating the organic layer with a separatory funnel, the intermediate 1 is obtained by rotary evaporation;

[0021] Step 2, intermediate 1, N-bromosuccinimide and tetrahydrofuran were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 70°C for 3-4 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 2;

[0022] Step 3, under nitrogen protection, the intermediate 2, 2,5-bis(trimethyltinyl)thiophene and bromobenzene are mixed in a three-necked flask, a condenser and a thermometer are installed, and magnetic stirring is turned on. Then, tetrakis(triphenylphosphine)palladium is added to the three-necked flask, and the mixture is reacted at a temperature of 140-150° C. for 48 hours. After the reaction is completed, the solvent is removed by rotary evaporation, and isopropanol and petroleum ether are added in sequence for washing using a Soxhlet extraction apparatus. The target product is collected with dichloromethane and the organic semiconductor is obtained by spin drying.

[0023] Furthermore, the amount ratio of 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, dimethyl malonate, piperidine, anhydrous ethanol, and sodium hydroxide aqueous solution used in step 1 is 20 mmol: (20-25) mmol: (4-6) mmol: (30-40) mL: (15-20) mL.

[0024] Furthermore, the usage ratio of the intermediate 1, N-bromosuccinimide and tetrahydrofuran used in step 2 is 15 mmol:30 mmol:(20-30) mL.

[0025] Furthermore, the usage ratio of the intermediate 2, 2,5-bis(trimethyltinyl)thiophene, bromobenzene, and tetrakis(triphenylphosphine)palladium used in step 3 is 10 mmol: 10 mmol: (40-50) mL: (25-35) mg.

[0026] Beneficial effects of the present invention:

[0027] The invention uses nano titanium dioxide and a self-made organic semiconductor as raw materials to prepare a composite photocatalyst. The invention prepares a tetrahydrofuran mixed solution of an organic semiconductor and an ethanol dispersion of nano titanium dioxide in sequence, then drops the mixed solution into the ethanol dispersion of nano titanium dioxide, and stirs and mixes in the dark to obtain an organic semiconductor / nano titanium dioxide heterojunction composite photocatalyst. The preparation of the invention uses the self-made organic semiconductor composite nano titanium dioxide to improve the visible light utilization rate of the nano titanium dioxide, and a synergistic effect is generated in the prepared composite photocatalyst, which can effectively improve charge separation and light stability, and improve the photocatalytic efficiency.

[0028] The invention uses 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one and dimethyl malonate as raw materials, utilizes the carbonyl group of 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one and the active methylene group of dimethyl malonate to undergo Knoevenagel reaction under the catalytic action of piperidine, and then hydrolyzes with sodium hydroxide and acidifies to obtain intermediate 1, then uses intermediate 1 as raw material and uses N-bromosuccinimide as bromination reagent to cause halogenation reaction on the α-carbon atom of the thiophene ring of intermediate 1 to obtain intermediate 2, and finally uses intermediate 2 and 2,5-bis(trimethyltinyl)thiophene as raw materials, utilizes the bromine atom of the intermediate and the trimethyltin group of 2,5-bis(trimethyltinyl)thiophene to undergo Stiller coupling reaction to obtain an organic semiconductor; the organic semiconductor of the invention is a A novel polythiophene polymer is disclosed. The present invention introduces a new heterocycle and a cis double bond into the polymer main chain of an organic semiconductor, changes the conjugation length and the energy band structure of the organic semiconductor, reduces the band gap, regulates the photocatalytic performance of the organic semiconductor, and makes the absorption spectrum of the organic semiconductor closer to the visible light region, thereby improving the photocatalytic efficiency of the composite photocatalyst. In addition, a polar carboxyl group is introduced into the polymer main chain of the organic semiconductor of the present invention, which improves the solubility of the organic semiconductor in a polar solvent and improves the interface bonding performance between the organic semiconductor and nano-titanium dioxide, thereby improving the stability of the composite photocatalyst. Moreover, the improvement of the interface bonding performance can also shorten the distance of electron transmission between heterojunctions, improve the migration efficiency of photogenerated carriers, and further enhance the photocatalytic activity of the composite photocatalyst. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0030] Example 1

[0031] A composite photocatalyst comprising nano-titanium dioxide and a self-made organic semiconductor;

[0032] Wherein, the organic semiconductor is prepared by the following steps:

[0033] Step 1, 20mmol 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, 20mmol dimethyl malonate, 4mmol piperidine, and 30mL anhydrous ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, the system temperature was raised to 80°C, and after reacting at 80°C for 2h, 15mL of a 20% by mass sodium hydroxide aqueous solution was added to the three-necked flask, and the reaction was continued at 80°C for 2h. After the reaction was completed, 10% by mass dilute hydrochloric acid was added to the three-necked flask to adjust the pH of the system to 4, and extracted with dichloromethane, and the organic layer was separated by a separatory funnel, and then rotary evaporated to obtain intermediate 1;

[0034] Step 2, 15 mmol of intermediate 1, 30 mmol of N-bromosuccinimide and 20 mL of tetrahydrofuran were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 70°C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 2;

[0035] Step 3. Under nitrogen protection, 10 mmol of intermediate 2, 10 mmol of 2,5-bis(trimethyltinyl)thiophene and 40 mL of bromobenzene were mixed in a three-necked flask, a condenser and a thermometer were installed, and magnetic stirring was turned on. Then, 25 mg of tetrakis(triphenylphosphine)palladium was added to the three-necked flask, and the mixture was reacted at a temperature of 140°C for 48 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and isopropanol and petroleum ether were added in turn for washing using a Soxhlet extraction apparatus. The target product was collected with dichloromethane and the organic semiconductor was obtained by spin drying.

[0036] A method for preparing a composite photocatalyst comprises the following steps:

[0037] Step 1: Dissolve 3 parts of organic semiconductor in 80 parts of tetrahydrofuran by weight, stir at room temperature and 300 rpm for 20 minutes to obtain a mixed solution for use;

[0038] Step 2: Add 17 parts of anatase nano-titanium dioxide by mass to 2720 parts of anhydrous ethanol, and ultrasonically disperse for 40 minutes at room temperature to obtain an ethanol dispersion of nano-titanium dioxide;

[0039] Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir for 100 minutes at 600 rpm in a dark environment, remove the solvent by rotary evaporation, and dry in an oven at 40°C to constant weight to obtain a composite photocatalyst. The mass fraction of organic semiconductors in the composite photocatalyst prepared in this embodiment accounts for 15% of the composite photocatalyst.

[0040] Example 2

[0041] A composite photocatalyst comprising nano-titanium dioxide and a self-made organic semiconductor;

[0042] Wherein, the organic semiconductor is prepared by the following steps:

[0043] Step 1, 20mmol 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, 22.5mmol dimethyl malonate, 5mmol piperidine, and 35mL anhydrous ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, the system temperature was raised to 80°C, and after reacting at 80°C for 2h, 17.5mL of a 20% by mass sodium hydroxide aqueous solution was added to the three-necked flask, and the reaction was continued at 80°C for 2h. After the reaction was completed, 15% by mass dilute hydrochloric acid was added to the three-necked flask to adjust the pH of the system to 4.5, and extracted with dichloromethane, and the organic layer was separated by a separatory funnel, and then rotary evaporated to obtain intermediate 1;

[0044] Step 2, 15 mmol of intermediate 1, 30 mmol of N-bromosuccinimide and 25 mL of tetrahydrofuran were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 70°C for 3.5 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 2;

[0045] Step 3. Under nitrogen protection, 10 mmol of intermediate 2, 10 mmol of 2,5-bis(trimethyltinyl)thiophene and 45 mL of bromobenzene were mixed in a three-necked flask, a condenser and a thermometer were installed, and magnetic stirring was turned on. Then, 30 mg of tetrakis(triphenylphosphine)palladium was added to the three-necked flask, and the mixture was reacted at a temperature of 145°C for 48 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and isopropanol and petroleum ether were added in sequence for washing using a Soxhlet extraction apparatus. The target product was collected with dichloromethane and the organic semiconductor was obtained by spin drying.

[0046] A method for preparing a composite photocatalyst comprises the following steps:

[0047] Step 1: Dissolve 3 parts of organic semiconductor in 90 parts of tetrahydrofuran by weight, stir at room temperature and 300-400 rpm for 20-30 minutes to obtain a mixed solution for use;

[0048] Step 2: Add 12 parts of anatase nano-titanium dioxide by mass to 2280 parts of anhydrous ethanol, and ultrasonically disperse for 50 minutes at room temperature to obtain an ethanol dispersion of nano-titanium dioxide;

[0049] Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir for 110 minutes at 700 rpm in a dark environment, remove the solvent by rotary evaporation, and dry in an oven at 45°C to constant weight to obtain a composite photocatalyst. The mass fraction of organic semiconductors in the composite photocatalyst prepared in this embodiment accounts for 20% of the composite photocatalyst.

[0050] Example 3

[0051] A composite photocatalyst comprising nano-titanium dioxide and a self-made organic semiconductor;

[0052] Wherein, the organic semiconductor is prepared by the following steps:

[0053] Step 1, 20mmol 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, 25mmol dimethyl malonate, 6mmol piperidine, and 40mL anhydrous ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, the system temperature was raised to 80°C, and after reacting at 80°C for 2h, 20mL of a 20% by mass sodium hydroxide aqueous solution was added to the three-necked flask, and the reaction was continued at 80°C for 2h. After the reaction was completed, 20% by mass dilute hydrochloric acid was added to the three-necked flask to adjust the pH of the system to 5, and extracted with dichloromethane, and the organic layer was separated by a separatory funnel, and then rotary evaporated to obtain intermediate 1;

[0054] Step 2, 15 mmol of intermediate 1, 30 mmol of N-bromosuccinimide and 30 mL of tetrahydrofuran were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 70°C for 4 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 2;

[0055] Step 3. Under nitrogen protection, 10 mmol of intermediate 2, 10 mmol of 2,5-bis(trimethyltinyl)thiophene and 50 mL of bromobenzene were mixed in a three-necked flask, a condenser and a thermometer were installed, and magnetic stirring was turned on. Then, 35 mg of tetrakis(triphenylphosphine)palladium was added to the three-necked flask, and the mixture was reacted at a temperature of 150° C. for 48 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and isopropanol and petroleum ether were added in sequence for washing using a Soxhlet extraction apparatus. The target product was collected with dichloromethane and the organic semiconductor was obtained by spin drying.

[0056] A method for preparing a composite photocatalyst comprises the following steps:

[0057] Step 1: Dissolve 3 parts of organic semiconductor in 100 parts of tetrahydrofuran by weight, stir at room temperature and 400 rpm for 30 minutes to obtain a mixed solution for use;

[0058] Step 2: Add 9 parts of rutile nano-titanium dioxide by mass into 1800 parts of anhydrous ethanol, and ultrasonically disperse for 60 minutes at room temperature to obtain an ethanol dispersion of nano-titanium dioxide;

[0059] Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir for 120 minutes at 800 rpm in a dark environment, remove the solvent by rotary evaporation, and dry in an oven at 50°C to constant weight to obtain a composite photocatalyst. The mass fraction of organic semiconductors in the composite photocatalyst prepared in this embodiment accounts for 25% of the composite photocatalyst.

[0060] Comparative Example 1

[0061] The organic semiconductor used in the raw material was replaced by polythiophene, and the remaining preparation steps were the same as in Example 3.

[0062] A method for preparing a composite photocatalyst comprises the following steps:

[0063] Step 1: Disperse 3 parts of polythiophene in 100 parts of tetrahydrofuran by weight, stir for 30 minutes at room temperature and a speed of 400 rpm to obtain a mixed solution for use;

[0064] Step 2: Add 9 parts of rutile nano-titanium dioxide by mass into 1800 parts of anhydrous ethanol, and ultrasonically disperse for 60 minutes at room temperature to obtain an ethanol dispersion of nano-titanium dioxide;

[0065] Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir for 120 minutes at 800 rpm in a dark environment, remove the solvent by rotary evaporation, and dry in an oven at 50°C to constant weight to obtain a composite photocatalyst. The mass fraction of polythiophene in the composite photocatalyst prepared in this embodiment accounts for 25% of the composite photocatalyst.

[0066] Experimental Example 1

[0067] The photocatalytic performance of the composite photocatalysts in Examples 1-3 and Comparative Example 1 was tested by degrading Rhodamine B at room temperature:

[0068] Under light-proof conditions, 50 mg of the composite photocatalysts obtained in Examples 1-3 and Comparative Example 1 were added to 50 mL of a 10 mg / L rhodamine B solution, stirred and mixed evenly, and then illuminated with a 300 W xenon lamp, using a filter to provide visible light with a wavelength of λ ≥ 400 nm. After the illumination began, 4 mL of the sample was taken every 20 min, and the supernatant was taken after centrifugation and analyzed with a UV-visible spectrophotometer and the characteristic peak signal intensity of rhodamine B was recorded, and the photodegradation efficiency % = C was calculated. 实时浓度 / C 初始浓度, the test results are shown in Table 1:

[0069] Table 1

[0070]

[0071] It can be seen from Table 1 that the degradation efficiency of the composite photocatalyst of the present invention in Examples 1-3 for Rhodamine B in water is much better than that of the composite photocatalyst in Comparative Example 1. The reason is that after the homemade organic semiconductor of the present invention is replaced with polythiophene, conventional polythiophene is infusible and insoluble, and has a poor dispersion effect in the solution, making it difficult to form a good interface bonding force with nano-titanium dioxide.

[0072] A composite photocatalyst and a preparation method thereof provided by the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combination method. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention can be used in combination with each other in any way. The fact that these combinations are not exhaustively described in this specification is only for the purpose of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A composite photocatalyst, characterized in that: It includes nano-titanium dioxide and a homemade organic semiconductor; Wherein, the organic semiconductor is prepared by the following steps: Step 1, 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, dimethyl malonate, piperidine and anhydrous ethanol are mixed in a container, stirred evenly, the system temperature is raised to 80°C, and the reaction is carried out at a temperature of 80°C for 2h, then a 20% by mass aqueous sodium hydroxide solution is added to the container, and the reaction is continued at a temperature of 80°C for 2h. After the reaction is completed, a 10-20% by mass dilute hydrochloric acid is added to the container to adjust the pH of the system to 4-5 to obtain an intermediate 1; Step 2, intermediate 1, N-bromosuccinimide and tetrahydrofuran are mixed in a container, stirred evenly, and reacted at 70° C. for 3-4 hours to obtain intermediate 2; Step 3, under nitrogen protection, the intermediate 2, 2,5-bis(trimethyltinyl)thiophene and bromobenzene are mixed in a container, stirred evenly, tetrakis(triphenylphosphine)palladium is added to the container, and reacted at a temperature of 140-150° C. for 48 hours to obtain the organic semiconductor; The preparation method of the composite photocatalyst comprises: The first step is to dissolve the organic semiconductor in tetrahydrofuran, stir and mix evenly at room temperature to obtain a mixed solution for use; Step 2: Add nano-titanium dioxide into anhydrous ethanol, and mix by ultrasonic dispersion at room temperature to obtain an ethanol dispersion of nano-titanium dioxide; Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir and mix evenly, remove the solvent by rotary evaporation, and dry in an oven to constant weight to obtain the composite photocatalyst.

2. A composite photocatalyst according to claim 1, characterized in that: The amount ratio of 4H-cyclopenta[2,1-B:3,4-B']dithiophene-4-one, dimethyl malonate, piperidine, anhydrous ethanol and sodium hydroxide aqueous solution used in step 1 is 20 mmol: 20-25 mmol: 4-6 mmol: 30-40 mL: 15-20 mL.

3. A composite photocatalyst according to claim 1, characterized in that: The amount ratio of the intermediate 1, N-bromosuccinimide and tetrahydrofuran used in step 2 is 15 mmol: 30 mmol: 20-30 mL.

4. A composite photocatalyst according to claim 1, characterized in that: The usage ratio of intermediate 2, 2,5-bis(trimethyltinyl)thiophene, bromobenzene and tetrakis(triphenylphosphine)palladium used in step 3 is 10 mmol: 10 mmol: 40-50 mL: 25-35 mg.

5. A method for preparing a composite photocatalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: The first step is to dissolve the organic semiconductor in tetrahydrofuran, stir and mix evenly at room temperature to obtain a mixed solution for use; Step 2: Add nano-titanium dioxide into anhydrous ethanol, and mix by ultrasonic dispersion at room temperature to obtain an ethanol dispersion of nano-titanium dioxide; Step 3: drop the mixed solution into the ethanol dispersion of nano-titanium dioxide, stir and mix evenly, remove the solvent by rotary evaporation, and dry in an oven to constant weight to obtain the composite photocatalyst.

6. The method for preparing a composite photocatalyst according to claim 5, characterized in that: The crystal structure of the nano titanium dioxide is anatase type or rutile type.

7. The method for preparing a composite photocatalyst according to claim 5, characterized in that: The stirring and mixing in the first step is carried out at a rotation speed of 300-400 rpm and a time of 20-30 min. The mass ratio of the organic semiconductor to tetrahydrofuran in the mixed solution is 3:80-100.

8. The method for preparing a composite photocatalyst according to claim 5, characterized in that: The time of the second step of ultrasonic dispersion is 40-60 minutes, and the mass ratio of nano-titanium dioxide to ethanol in the nano-titanium dioxide ethanol dispersion is 1:160-200.

9. The method for preparing a composite photocatalyst according to claim 5, characterized in that: In the third step, the stirring condition is light-proof condition, the stirring speed condition is 600-800 rpm, the stirring time condition is 100-120 min, and the drying temperature condition is 40-50°C.

10. The method for preparing a composite photocatalyst according to claim 5, characterized in that: The mass fraction of organic semiconductors accounts for 15-25% of the composite photocatalyst.

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