Carbon nitride photocatalyst with strong built-in electric field, high specific surface area and wide spectral absorption, and preparation method and application thereof

Abstract

The invention discloses a carbon nitride photocatalyst with a strong built-in electric field, a high specific surface area and wide spectral absorption, and a preparation method and application thereof, and belongs to the technical field of photocatalyst preparation. The carbon nitride photocatalyst with strong built-in electric field, high specific surface area and wide spectrum absorption is obtained by self-assembling 2, 3-diamino piperazine and carrying out high-intensity ultrasonic field treatment and fused salt auxiliary calcination. 2, 2, 3-diamino piperazine is doped into carbon nitride, n-pi * electron transition is successfully activated, and capture of visible light with the wavelength of 500 nm or above is achieved; due to the existence of a strong built-in electric field, the separation and migration efficiency of photon-generated carriers is improved; ultrasonic treatment and molten salt assistance effectively increase the specific surface area, more active sites are exposed, formation of a quasi-homogeneous photocatalytic system is facilitated, and finally the yield of hydrogen peroxide is remarkably improved. The technological process is simple, the preparation cost is low, operation is safe, and the prepared carbon nitride photocatalyst with the strong built-in electric field, the high specific surface area and the wide spectrum absorption is high in stability and catalytic activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalyst preparation, and particularly relates to a carbon nitride photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is well-known for its versatility and environmentally friendly oxidation properties, and has shown excellent efficacy in many fields such as water treatment, pulp bleaching, healthcare, and the food industry. The synthesis of H2O2 from H2O and O2 using semiconductor photocatalysts through artificial photosynthesis has received extensive attention due to its potential to greatly improve safety, reduce pollution, and lower energy consumption. The key to realizing this process lies in the development of cost-effective and highly active photocatalysts. As a typical metal-free organic semiconductor photocatalyst, carbon nitride (CN or g-C3N4) has been highly regarded for its stable physical and chemical properties, suitable bandgap, and easy preparation, and has become a promising catalyst for photocatalytic synthesis of H2O2. Unfortunately, CN has a narrow response range to visible light, few exposed active sites, and extremely easy recombination of photo-generated carriers, which seriously hinder the application of CN in photocatalytic synthesis of H2O2.

[0003] Currently, researchers mainly overcome the deficiencies of single CN through strategies such as doping, constructing heterojunctions, and regulating morphology. Although the catalytic performance of CN has been improved through the above modification methods, some modification means are costly, the process is complex, and the performance improvement after modification is not obvious. Currently, technologies for improving the catalytic performance of CN from multiple dimensions through simple and low-cost methods are scarce. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned existing technologies: the modification cost of CN photocatalyst is relatively high and the performance improvement after modification is not obvious, the purpose of the present invention is to provide a carbon nitride photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption, a preparation method thereof, and an application thereof. The CN photocatalyst prepared by the present invention has a powerful built-in electric field, significantly improved charge behavior of CN (KPFM test proves that the surface potential difference increases from 5.8 mV to 20.1 mV, and the surface photovoltage increases from 0.00128 mV to 0.34 mV); broadened spectral absorption (the absorption edge increases from 468 nm to above 500 nm); rich exposed active sites (the specific surface area increases from 61.1025 m 2 g -1 to 130.9698 m 2 g -1 ). Finally, its photocatalytic H2O2 production performance is significantly improved, and this method has not been reported yet.

[0005] The specific technical solution of the present invention is as follows:

[0006] A preparation method of a CN photocatalyst with a strong built-in electric field, high specific surface area and wide spectral absorption, comprising the following steps:

[0007] (1) Preparation of 2,3-diaminopiperazine-urea self-assembled mixture:

[0008] Put urea, 2,3-diaminopiperazine, absolute ethanol and deionized water in a crucible in a certain proportion, heat the mixture at a certain temperature to obtain a uniform clear solution, and cool it to room temperature to obtain a 2,3-diaminopiperazine-urea self-assembled mixture;

[0009] (2) Preparation of 2,3-diaminopiperazine-doped CN photocatalyst:

[0010] Put the 2,3-diaminopiperazine-urea self-assembled mixture obtained in step (1) into a muffle furnace, heat it at a fixed heating rate, and heat it at a certain temperature for a period of time; after naturally cooling to room temperature, grind the product into powder;

[0011] (3) Preparation of a CN photocatalyst with a strong built-in electric field, high specific surface area and wide spectral absorption:

[0012] Grind the 2,3-diaminopiperazine-doped CN prepared in step (2) evenly with a certain mass and a fixed proportion of molten salt and place it in a strong ultrasonic field for a certain time; after freeze-drying the mixture, put it into a tube furnace, heat it at a fixed heating rate in an inert gas atmosphere, and heat it at a certain temperature for a period of time; after naturally cooling to room temperature, wash and dry the product and grind it into powder to obtain a CN photocatalyst with a strong built-in electric field, high specific surface area and wide spectral absorption.

[0013] Preferably, in step (1), the mass ratio of the urea to the 2,3-diaminopiperazine is 1 g: 1-4 mg.

[0014] Preferably, in step (1), the volume ratio of the absolute ethanol to the water is 2-2.5: 1 mL.

[0015] Preferably, in step (1), the heating temperature of the 2,3-diaminopiperazine-urea self-assembled mixture is 75-85 °C.

[0016] Preferably, in step (2), the heating rate of the 2,3-diaminopiperazine-urea self-assembled mixture in the muffle furnace is 4-6 °C / min -1 .

[0017] Preferably, in step (2), the holding temperature of the 2,3-diaminopiperazine-urea self-assembled mixture in the muffle furnace is 520-570 °C.

[0018] Preferably, in step (2), the holding time of the 2,3-diaminopiperazine-urea self-assembly mixture in the muffle furnace is 2.8 to 3.2 h.

[0019] Preferably, in step (3), the molten salt is potassium chloride and lithium chloride.

[0020] Preferably, in step (3), the mass of the molten salt is 4.8 to 5.2 times that of the 2,3-diaminopiperazine-doped CN photocatalyst.

[0021] Preferably, in step (3), the molar ratio of the molten salt is potassium chloride: lithium chloride = 41:59.

[0022] Preferably, in step (3), the ultrasonic time is 30 to 60 min.

[0023] Preferably, in step (3), the drying method is freeze-drying.

[0024] Preferably, in step (3), the gas environment of the mixture in the tube furnace is one of argon or nitrogen.

[0025] Preferably, in step (3), the heating rate of the mixture in the tube furnace is 4 to 6 °C / min -1 .

[0026] Preferably, in step (3), the holding temperature of the mixture in the tube furnace is 520 to 570 °C.

[0027] Preferably, in step (3), the holding time of the mixture in the tube furnace is 2.8 to 3.2 h.

[0028] Another object of the present invention is to provide an application of a CN photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption in the preparation of H2O2, which specifically includes the following steps: using a xenon lamp with a certain wattage and a cut-off filter with a certain wavelength to filter out ultraviolet light as a visible light source, mixing a certain mass of the catalyst and a certain volume of the mixed solvent in the dark and stirring for a certain time and introducing oxygen to reach the adsorption-desorption equilibrium, stopping introducing oxygen after turning on the light, sucking out a part of the liquid at regular intervals, filtering, and adding a certain volume and concentration of sulfuric acid and potassium oxalotitanate solution to the filtrate respectively, and analyzing the change of the absorbance value at a certain wavelength using a UV-2700 ultraviolet-visible spectrophotometer.

[0029] Preferably, the wattage of the xenon lamp is 300 W; the wavelength of the cut-off filter is 420 nm; the mixed solvent is anhydrous ethanol and water with a volume ratio of 1:8 - 9 mL; the volume ratio of the catalyst to the mixed solvent is 1 mg:2 - 2.5 mL; the stirring time for the photocatalyst to reach the adsorption - desorption equilibrium with oxygen is 25 - 35 min; the sampling interval after turning on the lamp is 10 - 20 min; the amount of each sample taken after turning on the lamp is 1 mL; the concentration of sulfuric acid is 3 mol / L -1 and the concentration of potassium titanyl oxalate solution is 0.05 mol / L -1 ; the volumes of both the sulfuric acid and the potassium titanyl oxalate solution are 0.5 mL; the wavelength of the ultraviolet - visible spectrophotometer is 400 nm.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] 1. The synthesis method is simple and easy to operate;

[0032] 2. The raw materials are only low - cost urea, 2,3 - diamino - piperazine, potassium chloride and lithium chloride, without using expensive or environmentally harmful reagents such as organic solvents or protective gases, and there are basically no risk factors;

[0033] 3. It has a strong built - in electric field and significant spatial charge separation, significantly improving the charge behavior of CN;

[0034] 4. The lone pair electrons of the piperazine ring and rich edge - NH2 are easy to induce n - π* electron transitions, achieving visible light capture above 500 nm.

[0035] 5. The strong ultrasonic field and molten salt - assisted calcination increase the specific surface area from 61.1 m 2 / g -1 to 130.66 m 2 / g -1 , and the fully exposed active sites and rich edge - NH2 are conducive to the formation of a quasi - homogeneous photocatalytic system.

[0036] 6. It has high cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention, the following will briefly introduce the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0038] Figure 1X-ray diffraction patterns of x-FDACN prepared in Examples 1-4 and pure CN prepared in Example 7. Obviously, two distinct CN characteristic peaks appear at around 13.2° (100) and 27.2° (002) for all samples, indicating that CN was successfully prepared and its crystal structure was well retained.

[0039] Figure 2 FT-IR spectra of x-FDACN prepared in Examples 1-4 and pure CN prepared in Example 7. Functional group analysis of CN and x-FDACN was carried out by FT-IR. The typical peaks of CN and x-FDACN at 3000 - 3600, 1200 - 1700 and 810 cm -1 correspond to the stretching vibration peaks of -O-H / -N-H, aromatic CN heterocyclic units and triazine units respectively. The peaks at 924, 1000 and 2190 cm -1 correspond to the C-N bond, N-K bond and cyano group of the piperazine structure respectively. It is proved that the piperazine ring, cyano group and potassium ions were successfully introduced into the photocatalyst.

[0040] Figure 3 Scanning electron microscope images and catalyst thickness measured by atomic force microscope of 40-FDACN (b, d) prepared in Example 2 and pure CN (a, c) prepared in Example 7. Compared with CN, 40-FDACN presents a thinner and smaller structure, which is very beneficial for the exposure of photocatalytic active sites, the expansion of light absorption and the rapid migration of photo-generated carriers.

[0041] Figure 4 Nitrogen adsorption-desorption isotherms of 40-FDACN prepared in Example 2, 40-DACN prepared in Example 5 and pure CN prepared in Example 7. As shown in the figure, the specific surface area increases from 61.1025 m 2 g -1 (CN) to 83.1595 m 2 g -1 (40-DACN), and after ultrasonic treatment, the specific surface area further increases to 130.6598 m 2 g -1 (40-FDACN). The increased specific surface area can provide sufficient active sites for redox reactions, enhance the internal reflectivity to accommodate additional light, and is beneficial for improving photocatalytic activity.

[0042] Figure 5Solid-state UV diffuse reflectance images of 40-FDACN prepared in Example 2 and pure CN prepared in Example 7. Compared with CN, the synthesized 40-FDACN exhibits a significant red shift and significantly improved visible light response. The absorption edge of 40-FDACN broadens to over 500 nm, likely due to activated n-π* electron transitions. This demonstrates that the designed strategy effectively improves the visible light responsiveness of CN catalysts.

[0043] Figure 6 PL spectra of 40-FDACN prepared in Example 2 and pure CN prepared in Example 7. Compared with CN, 40-FDACN shows significantly quenched photoluminescence intensity, indicating that the design scheme can accelerate charge transfer and effectively suppress carrier recombination.

[0044] Figure 7 Electrochemical impedance spectroscopy (a) and photocurrent spectra (b) of 40-FDACN prepared in Example 2 and pure CN prepared in Example 7. The electrochemical impedance radius of 40-FDACN is significantly smaller than that of CN, indicating that 40-FDACN has lower resistance and easier charge transfer. The significantly higher photocurrent intensity is highly beneficial for charge separation and transfer.

[0045] Figure 8 Photovoltage spectra (a) and KPFM spectra (b, c) of 40-FDACN prepared in Example 2 and pure CN prepared in Example 7. The photovoltage value and potential difference of 40-FDACN are significantly higher than those of CN, indicating that a strong built-in electric field exists in 40-FDACN, which promotes charge behavior and enhances photocatalytic activity.

[0046] Figure 9 The photocatalytic H2O2 production performance of x-FDACN, 40-DACN, 40-DCN and pure CN prepared in Examples 1-7 is shown in the figure. The H2O2 production rate of CN is only 600 μmol·g -1 After doping with 2,3-diaminopiperazine (40-DCN), the H2O2 yield increased slightly to 1525 μmol·g -1 With the assistance of molten salt (40-DACN), the H2O2 yield was further increased to 5616.67 μmol·g -1 After adding a strong ultrasonic field, the H2O2 yield (40-FDACN) reached 8075 μmol·g -1 , which is 13.5 times that of pure CN and surpasses most CN-based photocatalysts.

[0047] Figure 10Performance graph of the cyclic preparation of H2O2 by 40-FDACN prepared in Example 2. After five consecutive H2O2 preparation experiments, the yield of 40-FDACN did not decrease significantly, indicating that the catalyst has good cyclic stability. Detailed implementation mode

[0048] The present invention will be further described below in conjunction with examples and drawings:

[0049] Example 1

[0050] Put 20 g of urea, 20 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water into a crucible, heat to 80 °C to obtain a uniform clear solution. After cooling to room temperature, put it into a muffle furnace and heat at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After naturally cooling to room temperature, grind the product into powder. Grind the powder evenly with 5 times its mass of potassium chloride and lithium chloride (molar ratio of KCl:LiCl is 41:59) and put it into a strong ultrasonic field for 30 min; after freeze-drying the mixture, put it into a tubular furnace, and under an argon atmosphere, heat at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h; after naturally cooling to room temperature, wash, dry and grind the product into powder and label it as 20-FDACN.

[0051] Example 2

[0052] Put 20 g of urea, 40 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water into a crucible, heat to 80 °C to obtain a uniform clear solution. After cooling to room temperature, put it into a muffle furnace and heat at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After naturally cooling to room temperature, grind the product into powder. Grind the powder evenly with 5 times its mass of potassium chloride and lithium chloride (molar ratio of KCl:LiCl is 41:59) and put it into a strong ultrasonic field for 30 min; after freeze-drying the mixture, put it into a tubular furnace, and under an argon atmosphere, heat at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h; after naturally cooling to room temperature, wash, dry and grind the product into powder and label it as 40-FDACN.

[0053] Example 3

[0054] Put 20 g of urea, 60 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water into a crucible, heat to 80 °C to obtain a uniform clear solution. After cooling to room temperature, put it into a muffle furnace and heat at a heating rate of 5 °C / min -1Heat to 550 °C and hold for 3 h. After natural cooling to room temperature, grind the product into powder. Grind the powder evenly with 5 times its mass of potassium chloride and lithium chloride (KCl:LiCl molar ratio is 41:59) and place it in a strong ultrasonic field for 30 min; after freeze-drying the mixture, put it into a tube furnace, and under an argon atmosphere, at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h; after natural cooling to room temperature, wash, dry, grind the product into powder and label it as 60-FDACN.

[0055] Example 4

[0056] Place 20 g of urea, 80 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water in a crucible, heat to 80 °C to obtain a homogeneous clear solution, and after cooling to room temperature, put it into a muffle furnace, at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After natural cooling to room temperature, grind the product into powder. Grind the powder evenly with 5 times its mass of potassium chloride and lithium chloride (KCl:LiCl molar ratio is 41:59) and place it in a strong ultrasonic field for 30 min; after freeze-drying the mixture, put it into a tube furnace, and under an argon atmosphere, at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h; after natural cooling to room temperature, wash, dry, grind the product into powder and label it as 80-FDACN.

[0057] Example 5 (Comparative Example 1: Without the action of a strong ultrasonic field)

[0058] Place 20 g of urea, 40 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water in a crucible, heat to 80 °C to obtain a homogeneous clear solution, and after cooling to room temperature, put it into a muffle furnace, at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After natural cooling to room temperature, grind the product into powder. Grind the powder evenly with 5 times its mass of potassium chloride and lithium chloride (KCl:LiCl molar ratio is 41:59) and place it in a tube furnace, and under an argon atmosphere, at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h; after natural cooling to room temperature, wash, dry, grind the product into powder and label it as 40-DACN.

[0059] Example 6 (Comparative Example 2: Without molten salt and without strong ultrasonic field assistance)

[0060] Put 20 g of urea, 40 mg of 2,3-diaminopiperazine, 10 mL of absolute ethanol and 5 mL of deionized water in a crucible, heat to 80 °C to obtain a homogeneous clear solution. After cooling to room temperature, put it into a muffle furnace and heat it at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After natural cooling to room temperature, grind the product into powder and label it as 40-DCN

[0061] Example 7 (Comparative Example 3: without molten salt, without strong ultrasonic field assistance and without doping 2,3-diaminopiperazine)

[0062] Put 20 g of urea, 10 mL of absolute ethanol and 5 mL of deionized water in a crucible, heat to 80 °C to obtain a homogeneous clear solution. After cooling to room temperature, put it into a muffle furnace and heat it at a heating rate of 5 °C / min -1 Heat to 550 °C and hold for 3 h. After natural cooling to room temperature, grind the product into powder and label it as CN.

[0063] Example 8

[0064] Application of a CN photocatalyst with strong built-in electric field, high specific surface area and wide-spectrum absorption in the preparation of H2O2 is as follows: Use a 300 W xenon lamp and a 420 nm cut-off filter to filter out ultraviolet light (λ < 420 nm) as the visible light source. Mix 20 mg of the photocatalyst and 50 mL of a mixed solvent (45 mL of deionized water and 5 mL of ethanol) in the dark and stir for 30 min, and then introduce O2 to reach the adsorption-desorption equilibrium. Stop introducing O2 after turning on the light. Take 1 mL of the liquid every 15 min, and after filtration, add 0.5 mL of H2SO4 solution (3 mol / L -1 ) and 0.5 mL of C4H2K2O 10 Ti solution (0.05 mol / L -1 ) to the filtrate, and analyze the change of absorbance value at 400 nm using a UV-2700 ultraviolet-visible spectrophotometer.

[0065] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0066] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0067] In addition, any combination can be made among various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of a CN photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption, characterized in that It includes the following steps: (1) Preparation of 2,3-diaminopiperazine-urea self-assembled mixture: Urea, 2,3-diaminopiperazine, absolute ethanol and deionized water are placed in a crucible in a certain proportion, and the mixture is heated at a certain temperature to obtain a uniform clear solution, which is cooled to room temperature to obtain a 2,3-diaminopiperazine-urea self-assembled mixture; (2) Preparation of 2,3-diaminopiperazine-doped CN photocatalyst: The 2,3-diaminopiperazine-urea self-assembled mixture obtained in step (1) is put into a muffle furnace and heated at a fixed heating rate, and heated at a certain temperature for a certain period of time; after naturally cooling to room temperature, the product is ground into powder; (3) Preparation of a CN photocatalyst with strong built-in electric field, high specific surface area and wide spectral absorption: The 2,3-diaminopiperazine-doped CN prepared in step (2) is ground evenly with a certain mass and fixed proportion of molten salt and placed in a strong ultrasonic field for a certain time; after the mixture is freeze-dried, it is put into a tubular furnace and heated at a fixed heating rate under an inert gas atmosphere, and heated at a certain temperature for a certain period of time; after naturally cooling to room temperature, the product is washed, dried and ground into powder to obtain a CN photocatalyst with strong built-in electric field, high specific surface area and wide spectral absorption.

2. The preparation method of a CN photocatalyst with strong built-in electric field, high specific surface area and wide spectral absorption according to claim 1, characterized in that, In step (1), the mass ratio of urea to 2,3-diaminopiperazine is 1 g: 1-4 mg; The volume ratio of absolute ethanol to water is 2-2.5: 1 mL; The heating temperature of the 2,3-diaminopiperazine-urea self-assembled mixture is 75-85 °C.

3. The preparation method of a CN photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption according to claim 1, characterized in that, In step (2), the heating rate of the 2,3-diaminopiperazine-urea self-assembly mixture in the muffle furnace is 4 to 6 °C min -1 ; The holding temperature of the 2,3-diaminopiperazine-urea self-assembled mixture in the muffle furnace is 520-570 °C; The holding time of the 2,3-diaminopiperazine-urea self-assembled mixture in the muffle furnace is 2.8-3.2 h.

4. The preparation method of a CN photocatalyst with a strong built-in electric field, a high specific surface area, and wide-spectrum absorption according to claim 1, characterized in that, In step (3), the molten salt is potassium chloride and lithium chloride; The mass of the molten salt is 4.8-5.2 times that of the 2,3-diaminopiperazine-doped CN photocatalyst; The molar ratio of the molten salt is potassium chloride: lithium chloride = 41:

59.

5. The preparation method of a CN photocatalyst with a strong built-in electric field, a high specific surface area, and a wide spectral absorption as claimed in claim 1, characterized in that, In step (3), the ultrasonic time is 30-60 min; The drying method is freeze-drying; The gas environment of the mixture in the tubular furnace is one of argon or nitrogen.; The heating rate of the mixture in the tubular furnace is 4-6 °C / min -1 ; The holding temperature of the mixture in the tubular furnace is 520-570 °C; The holding time of the mixture in the tubular furnace is 2.8-3.2 h.

6. A CN photocatalyst with a strong built-in electric field, high specific surface area, and wide spectral absorption, characterized in that, Prepared by the method according to any one of claims 1-5.

7. Use of a CN photocatalyst with a strong built-in electric field, high specific surface area, and wide spectral absorption in the preparation of H2O2, characterized in that, Specifically, it includes the following steps: Use a xenon lamp with a certain wattage and a cut-off filter with a certain wavelength to filter out ultraviolet light as a visible light source, mix a certain mass of catalyst and a certain volume of mixed solvent in the dark and stir for a certain time and introduce oxygen to reach adsorption-desorption equilibrium, stop introducing oxygen after turning on the light, absorb a part of the liquid every once in a while, filter, and then add a certain volume and concentration of sulfuric acid and potassium oxalotitanate solution to the filtrate respectively, and analyze the change of absorbance value at a certain wavelength using a UV-2700 ultraviolet-visible spectrophotometer.

8. Use of a CN photocatalyst with a strong built-in electric field, high specific surface area, and wide spectral absorption in the preparation of H2O2, characterized in that, The wattage of the xenon lamp is 300 W; the wavelength of the cut-off filter is 420 nm; the mixed solvent is anhydrous ethanol and water with a volume ratio of 1:8 - 9 mL; the volume ratio of the catalyst to the mixed solvent is 1 mg:2 - 2.5 mL; the stirring time for the photocatalyst and oxygen to reach the adsorption-desorption equilibrium is 25 - 35 min; the sampling interval after turning on the lamp is 10 - 20 min; the amount of each sample taken after turning on the lamp is 1 mL; the concentration of sulfuric acid is 3 mol / L -1 , and the concentration of potassium titanyl oxalate solution is 0.05 mol / L -1 , and the volumes of both the sulfuric acid and the potassium titanyl oxalate solution are 0.5 mL; the wavelength of the ultraviolet-visible spectrophotometer is 400 nm.

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