Homojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalyst preparation, in particular to a homojunction photocatalyst as well as a preparation method and application thereof.The cyano and nitrogen defect co-modified C3N4 / C3N5 homojunction photocatalyst is constructed through simple mixing, grinding and thermal polymerization, and the C3N4 / C3N5 homojunction photocatalyst shows excellent catalytic performance in the aspect of photocatalytic production of H2O2 and has a good application prospect. The industrialization requirement of photocatalytic synthesis of H2O2 is expected to be met. The C3N4 / C3N5 homojunction photocatalyst containing the nitrogen defect and the cyano group provided by the invention has the advantages of simple preparation method, low raw material price, high stability and high hydrogen peroxide synthesis efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly relates to a homojunction photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] H2O2 is a green oxidant and energy carrier. Since its decomposition products are only water and oxygen, it is widely used in fields such as rocket fuel, bleaching, fuel cells, chemical synthesis, medicine, and environmental remediation. However, the synthesis of H2O2 relies on the energy-consuming and highly polluting anthraquinone oxidation process. This process emits 1.2 tons of CO2 into the atmosphere when producing 1 ton of H2O2. At the same time, the anthraquinone oxidation process also requires the use of precious metals as catalysts, which are not only expensive but also pose risks of gas explosion and hazardous waste emissions. Therefore, developing an environmentally friendly, safe, and low-cost method for synthesizing H2O2 has important economic value.

[0003] Semiconductor photocatalytic technology has become a highly promising alternative due to its unique advantages. This technology uses solar energy as the energy source, water and oxygen as raw materials, and generates H2O2 through photocatalytic reactions. Currently, commercial photocatalysts include TiO2, ZnO, MOF, etc. However, traditional oxide photocatalysts have certain catalytic activities in fields such as photocatalytic degradation of organic pollutants and CO2 reduction, but generally have very low activities in photocatalytic synthesis of H2O2. And the carefully designed MOF-based catalysts have considerable catalytic activities, but the synthesis of MOF faces problems such as complex processes, high ligand prices, and poor material stability, which limit its commercialization. At the same time, non-metal carbon nitride materials have broad application prospects in the fields of energy and environmental catalysis due to their high stability, easy adjustment of molecular structure, simple preparation, and wide raw material sources. As photocatalytic materials, carbon nitride materials have many remarkable advantages. First, carbon nitride materials are completely composed of carbon, nitrogen, and hydrogen elements, avoiding the problem of secondary pollution to the environment caused by metal ions. Second, the raw materials for preparing carbon nitride are widely available and inexpensive. In addition, the conjugated polymer network in carbon nitride endows it with excellent physical and chemical stability. This makes the material have broad application prospects in fields such as optoelectronics and photocatalysis.

[0004] However, the carbon nitride obtained by conventional thermal polymerization is usually in bulk form, so the carrier recombination rate is high and the surface active sites are few. In addition, the unmodified carbon nitride has a narrow spectral absorption range and can only absorb sunlight with a wavelength less than 460 nm, resulting in insufficient utilization of visible light. Finally, as the main raw material for photocatalytic reactions, oxygen molecules are difficult to effectively adsorb and activate on the surface of carbon nitride. These factors above lead to the low efficiency of photocatalytic synthesis of H2O2 by the currently prepared carbon nitride materials, making it difficult to meet practical applications. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a homojunction photocatalyst and its preparation method and application. The present invention constructs a cyanide group and nitrogen defect co-modified C3N4 / C3N5 homojunction photocatalyst through thermal polymerization and simple mixing and grinding, and shows excellent catalytic performance in photocatalytic production of H2O2, and is expected to meet the industrial demand for photocatalytic synthesis of H2O2. The C3N4 / C3N5 homojunction containing nitrogen defects and cyanide groups provided by the present invention has the advantages of simple preparation method, cheap raw materials, non-toxicity, and high efficiency in synthesizing hydrogen peroxide.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A preparation method of a homojunction photocatalyst, comprising the following steps: Mix urea and an alkali with water, stir evenly, and dry to obtain a urea crystal precursor uniformly mixed with the alkali.

[0007] Perform the first thermal polymerization on the urea crystal precursor in an oxygen-deficient environment. The OH released by the melting of the alkali - Reacts with the amino group in urea to generate a cyanide group. At the same time, the addition of the alkali causes a reduction in the ordered structure of nitrogen atoms in the g-C3N4 structure, thereby forming nitrogen defects, and obtaining C3N4 containing nitrogen defects.

[0008] Mix 3-amino-1,2,4-triazole and an alkali with water, stir evenly, and dry to obtain a 3-amino-1,2,4-triazole precursor containing the alkali.

[0009] Grind and mix the C3N4 containing nitrogen defects with the 3-amino-1,2,4-triazole precursor containing the alkali, and perform the second thermal polymerization. The OH released by the melting of the alkali - Reacts with the amino group in 3-amino-1,2,4-triazole to form a cyanide group, and at the same time destroys the ordered structure in the C3N5 structure, and forms C3N5 on the surface of the C3N4 containing nitrogen defects, obtaining a homojunction photocatalyst doped with nitrogen defects and cyanide groups.

[0010] The present invention uses urea and 3-amino-1,2,4-triazole as raw materials to prepare a carbon nitride homojunction material through two-step thermal polymerization. By adding a small amount of alkali to react with the amino group in the derivative intermediate of urea and 3-amino-1,2,4-triazole, a cyanide group is generated. At the same time, the addition of the alkali reduces the ordered structure of nitrogen atoms during the polymerization of the precursor, thereby forming nitrogen defects, and finally realizing the simultaneous introduction of nitrogen defects and cyanide groups into the homojunction. The C3N4 / C3N5 homojunction modified with nitrogen defects and cyanide groups improves the light utilization rate of visible light, significantly enhances the visible light absorption ability of the material and the separation efficiency of photogenerated carriers, and is applied to photocatalytic synthesis of H2O2, having the advantages of high H2O2 synthesis efficiency, high catalyst stability, simple preparation method, and low cost.

[0011] In a preferred embodiment of the present invention, the mass ratio of urea to the base is 20-100:1.

[0012] In a preferred embodiment of the present invention, the first thermal polymerization temperature is 490 °C - 550 °C, and the thermal polymerization time is 3 h - 4 h.

[0013] In a preferred embodiment of the present invention, the mass ratio of 3-amino-1,2,4-triazole to the base is 20-100:1.

[0014] In a preferred embodiment of the present invention, the mass ratio of nitrogen-deficient C3N4 to the 3-amino-1,2,4-triazole precursor containing the base is 1.5-6:1.

[0015] In a preferred embodiment of the present invention, the second thermal polymerization temperature is 490 °C - 550 °C, and the thermal polymerization time is 3 h - 4 h.

[0016] In a preferred embodiment of the present invention, the base is NaOH or KOH.

[0017] Another object of the present invention is to provide a homojunction photocatalyst prepared by the preparation method described in any one of the above.

[0018] The third object of the present invention is to provide an application of the homojunction photocatalyst described above in photocatalytic production of H2O2.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The preparation method of the homojunction photocatalyst of the present invention is to mix urea and the base to prepare a urea crystal precursor uniformly mixed with the base, and perform the first thermal polymerization. The OH - released by the melting of the base reacts with the amino group in urea to generate a cyano group. At the same time, the addition of the base causes a reduction in the ordered structure of nitrogen atoms in the C3N4 structure, thereby forming nitrogen defects to obtain nitrogen-deficient C3N4; mix 3-amino-1,2,4-triazole and the base to obtain a 3-amino-1,2,4-triazole precursor containing the base, grind and mix the nitrogen-deficient C3N4 with the 3-amino-1,2,4-triazole precursor containing the base, and perform the second thermal polymerization. The OH -React with the amino group in 3-amino-1,2,4-triazole to form a cyano group, while destroying the ordered structure in the C3N5 structure, forming C3N5 on the surface of nitrogen-deficient C3N4, and obtaining a homojunction photocatalyst doped with nitrogen defects and cyano groups. The present invention uses urea and 3-amino-1,2,4-triazole as raw materials to prepare a carbon nitride homojunction material through two-step thermal polymerization. By adding a small amount of base to react with the amino group in the derivative intermediate of urea and 3-amino-1,2,4-triazole, a cyano group is generated. At the same time, the addition of the base reduces the ordered structure of nitrogen atoms during the polymerization of the precursor, thereby forming nitrogen defects, and finally realizing the simultaneous introduction of nitrogen defects and cyano groups into the homojunction. The C3N4 / C3N5 homojunction modified with nitrogen defects and cyano groups improves the light utilization rate of visible light, significantly enhances the visible light absorption ability of the material and the separation efficiency of photogenerated carriers, and is applied to the photocatalytic synthesis of H2O2, with the advantages of high H2O2 synthesis efficiency, high catalyst stability, simple preparation method and low cost.

[0020] 2. The present invention constructs a homojunction photocatalyst through thermal polymerization and simple mixing and grinding methods, and uses alkali to dope and modify the homojunction, which not only improves the spectral absorption range, carrier separation efficiency and H2O2 selectivity of the homojunction, but also promotes the adsorption and activation of oxygen molecules, thereby significantly improving the photocatalytic synthesis performance of H2O2. Compared with the traditional synthesis scheme, the present invention uses raw materials with low price and simple synthesis, has high product synthesis yield, low investment cost, and high photocatalytic synthesis efficiency of H2O2. Brief Description of the Drawings

[0021] Figure 1 It is a flowchart for preparing the homojunction photocatalyst of the present invention.

[0022] Figure 2 Among them, (A) - (C) are SEM images of the homojunction photocatalyst prepared in Example 1 at different magnifications.

[0023] Figure 3 Among them, (A) - (C) are TEM images of the homojunction photocatalyst prepared in Example 1 at different magnifications.

[0024] Figure 4 It is an XRD pattern of the homojunction photocatalyst prepared in Example 1.

[0025] Figure 5 It is an FTIR pattern of the homojunction photocatalyst prepared in Example 1.

[0026] Figure 6 It is an EPR spectrum of the homojunction photocatalyst prepared in Example 1.

[0027] Figure 7 It is a diffuse reflection image of the homojunction photocatalyst prepared in Example 1.

[0028] Figure 8 Transient photocurrent response diagram of the homojunction photocatalyst prepared in Example 1.

[0029] Figure 9 Impedance spectrum diagram of the homojunction photocatalyst prepared in Example 1.

[0030] Figure 10 Among them, (A) - (C) are the photocatalytic performance diagrams of the homojunction photocatalyst prepared in Example 1.

[0031] Figure 11 H2O2 synthesis stability test diagram of the homojunction photocatalyst prepared in Example 1.

[0032] Figure 12 H2O2 selectivity test diagram of the homojunction photocatalyst prepared in Example 1.

[0033] Figure 13 Apparent quantum yield diagram of the homojunction photocatalyst prepared in Example 1. Detailed implementation manners

[0034] The following combines the embodiments of the present invention and uses preferred embodiments and accompanying drawings for detailed description. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods.

[0036] The preparation flow chart of the homojunction photocatalyst of the present invention is as Figure 1 shown. Mix urea and NaOH, calcine at 500 °C for 4 h for the first thermal polymerization to obtain C3N4 with nitrogen defects, denoted as DC3N4; mix 3 - amino - 1,2,4 - triazole and NaOH to obtain a 3 - amino - 1,2,4 - triazole precursor containing NaOH. Grind and mix the C3N4 with nitrogen defects and the 3 - amino - 1,2,4 - triazole precursor containing NaOH, and calcine at 500 °C for 3 h for the second thermal polymerization to obtain a homojunction photocatalyst containing nitrogen defects and cyano groups, denoted as DC3N4 / DC3N5.

[0037] Example 1 A preparation method of a heterojunction catalyst, comprising the following steps: (1) Mix urea and NaOH with deionized water at a mass ratio of 50:1, stir evenly, and dry at 60 °C for 24 h to obtain a urea crystal precursor uniformly mixed with NaOH.

[0038] (2) Grind the urea crystal precursor uniformly mixed with NaOH, put it into a muffle furnace, heat it to 500 °C at a heating rate of 2 °C per minute in an anoxic environment, and keep it warm for 4 h. The product undergoes thermal polymerization to obtain C3N4 with nitrogen defects, denoted as DC3N4.

[0039] (3) Mix 3-amino-1,2,4-triazole and NaOH with deionized water at a mass ratio of 50:1, stir evenly, and dry at 60 °C for 24 h to obtain a 3-amino-1,2,4-triazole precursor containing NaOH.

[0040] (4) Grind and mix DC3N4 and the 3-amino-1,2,4-triazole precursor containing NaOH evenly at a mass ratio of 3:1, heat it to 500 °C at a heating rate of 5 °C per minute in an anoxic environment, and keep it warm for 3 h to obtain a homojunction photocatalyst containing nitrogen defects and cyanide groups, denoted as DC3N4 / DC3N5.

[0041] Example 2 A preparation method of a heterojunction catalyst, comprising the following steps: (1) Mix urea and NaOH with deionized water at a mass ratio of 20:1, stir evenly, and dry at 60 °C for 24 h to obtain a urea crystal precursor uniformly mixed with NaOH.

[0042] (2) Grind the urea crystal precursor uniformly mixed with NaOH, put it into a muffle furnace, heat it to 500 °C at a heating rate of 2 °C per minute in an anoxic environment, and keep it warm for 3 h. The product undergoes thermal polymerization to obtain C3N4 with nitrogen defects, denoted as DC3N4.

[0043] (3) Mix 3-amino-1,2,4-triazole and NaOH with deionized water at a mass ratio of 20:1, stir evenly, and dry at 60 °C for 24 h to obtain a 3-amino-1,2,4-triazole precursor containing NaOH.

[0044] (4) Grind and mix DC3N4 and the 3-amino-1,2,4-triazole precursor containing NaOH evenly at a mass ratio of 1.5:1, heat it to 500 °C at a heating rate of 5 °C per minute in an anoxic environment, and keep it warm for 3.5 h to obtain a homojunction photocatalyst containing nitrogen defects and cyanide groups.

[0045] Example 3 A preparation method of a heterojunction catalyst, comprising the following steps: (1) Mix urea and NaOH with deionized water according to a mass ratio of 100:1, stir evenly, and dry at 60 °C for 24 h to obtain a urea crystal precursor uniformly mixed with NaOH.

[0046] (2) Grind the urea crystal precursor uniformly mixed with NaOH and put it into a muffle furnace. Heat it to 500 °C at a heating rate of 2 °C per minute in an anoxic environment, and keep it warm for 3.5 h. The product is thermally polymerized to obtain C3N4 with nitrogen defects, denoted as DC3N4.

[0047] (3) Mix 3-amino-1,2,4-triazole and NaOH with deionized water according to a mass ratio of 100:1, stir evenly, and dry at 60 °C for 24 h to obtain a 3-amino-1,2,4-triazole precursor containing NaOH.

[0048] (4) Grind and mix DC3N4 and the 3-amino-1,2,4-triazole precursor containing NaOH evenly according to a mass ratio of 6:1, heat it to 500 °C at a heating rate of 5 °C per minute in an anoxic environment, and keep it warm for 4 h to obtain a homojunction photocatalyst containing nitrogen defects and cyano groups.

[0049] Comparative Example 1 A preparation method of a catalyst, comprising the following steps: (1) Mix urea and NaOH with deionized water according to a mass ratio of 50:1, stir evenly, and dry at 60 °C for 24 h to obtain a urea crystal precursor uniformly mixed with NaOH.

[0050] (2) Grind the urea crystal precursor uniformly mixed with NaOH and put it into a muffle furnace. Heat it to 500 °C at a heating rate of 2 °C per minute in an anoxic environment, and keep it warm for 4 h. The product is thermally polymerized to obtain C3N4 with nitrogen defects, denoted as DC3N4.

[0051] Comparative Example 2 A preparation method of a catalyst, comprising the following steps: Mix 3-amino-1,2,4-triazole and NaOH with deionized water according to a mass ratio of 50:1, stir evenly, and dry at 60 °C for 24 h to obtain a 3-amino-1,2,4-triazole precursor containing NaOH, denoted as DC3N5.

[0052] The preparation methods of Example 2 and Example 3 are the same as that of Example 1, except that the reaction conditions and the dosages of some raw materials are changed. The obtained homojunction photocatalysts have the same effects as those of Example 1, and both can improve the efficiency of photocatalytic synthesis of H2O2.

[0053] Result Analysis Figure 2 In (A)-(C), SEM images of the homojunction photocatalyst prepared in Example 1 at different magnifications are shown. Figure 3 In (A)-(C), TEM images of the homojunction photocatalyst prepared in Example 1 at different magnifications are shown. It can be seen from the SEM and TEM images that the homojunction exhibits relatively loose characteristics and obvious wrinkled sheet-like structures, and the wrinkled DC3N5 nanosheets are tightly anchored on the surface of DC3N4. This unique morphology is crucial for the separation and transport of photo-generated carriers. It can be seen from the XRD pattern that C3N4 and C3N5 show two characteristic peaks, located at 13.1° and 27.7° respectively. These peaks are due to the in-plane stacking of heptazine units and the interlayer stacking of conjugated aromatic structures. After adding sodium hydroxide, the full width at half maximum of the diffraction peaks of DC3N4 and DC3N5 decreases significantly, indicating that alkali etching can destroy the in-plane stacking of heptazine units and the interlayer stacking of conjugated aromatic structures.

[0054] Figures 4 to 6 They are the XRD pattern, FTIR pattern and EPR spectrum of the homojunction photocatalyst prepared in Example 1 respectively. In the infrared spectrum, absorption peaks appear at the positions of 810 cm -1 , 1000 cm -1 ~1800 cm -1 and 3000 cm -1 ~3600 cm -1 respectively, which come from the breathing vibration of heptazine rings, the stretching vibration of heterocycles and the stretching vibration of N-H in carbon nitride. Compared with C3N4, C3N5 and C3N4 / C3N5, an absorption peak located at 2165 cm -1 is detected in DC3N4, DC3N5 and DC3N4 / DC3N5, which is due to the stretching vibration peak of the generated cyano group. The above results show that NaOH etching can effectively introduce cyano groups. Figure 6 In, characteristic EPR signals with a g value of 2.0038 are detected in both C3N4 / C3N5 and DC3N4 / DC3N5, which originate from sp in the π-conjugated network 2Unpaired electrons on carbon atoms. The signal intensity of DC3N4 / DC3N5 is significantly stronger than that of C3N4 / C3N5. This is because the introduction of cyano groups causes the delocalization and aggregation of isolated valence electrons in the π-conjugated network. At the same time, the absence of nitrogen atoms leads to the redistribution of electrons to adjacent carbon atoms in the π-conjugated network, resulting in more unpaired electrons in DC3N4 / DC3N5.

[0055] Figures 7 to 9 They are the diffuse reflectance diagram, transient photocurrent response diagram, and impedance spectrum diagram of the homojunction photocatalyst prepared in Example 1, respectively. Figure 10 Among them, (A) - (C) are the photocatalytic performance diagrams of the homojunction photocatalyst prepared in Example 1. Figures 11 to 13 They are the H2O2 synthesis stability test diagram, H2O2 selectivity test diagram, and apparent quantum yield diagram of the homojunction photocatalyst prepared in Example 1. It can be seen from the figures that compared with the unmodified C3N4, C3N5, and C3N4 / C3N5, the nitrogen-deficient and cyano-modified C3N4 / C3N5 homojunction of the present invention improves the light utilization rate of visible light, significantly enhances the visible light absorption ability of the material, the separation efficiency of photo-generated carriers, and the photocatalytic performance. The catalytic results show that the modified homojunction photocatalyst exhibits excellent performance in photocatalytic production of H2O2, and its generation rate reaches 7.64 mmol g -1 h -1 −1, which are 6.24 and 1.91 times that of single C3N4 and C3N5, respectively. The apparent quantum yield reaches 7.36% (400 nm), and the selectivity of H2O2 exceeds 90%.

[0056] In summary, the present invention uses urea and 3-amino-1,2,4-triazole as raw materials to prepare a carbon nitride homojunction material through two-step thermal polymerization. By adding a small amount of base to react with the amino groups in the urea and the derivative intermediate of 3-amino-1,2,4-triazole, cyano groups are generated. At the same time, the addition of the base reduces the ordered structure of nitrogen atoms during the polymerization of the precursor, thereby forming nitrogen defects, and finally realizing the simultaneous introduction of nitrogen defects and cyano groups into the homojunction. The C3N4 / C3N5 homojunction modified with nitrogen defects and cyano groups improves the light utilization rate of visible light, significantly enhances the visible light absorption ability of the material and the separation efficiency of photo-generated carriers, and is applied to photocatalytic synthesis of H2O2, having the advantages of high H2O2 synthesis efficiency, high catalyst stability, simple preparation method, and low cost.

[0057] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods adopted are the same as those in the embodiments, in order to prevent redundancy, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the scope of protection attached is intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the protection of the present invention and the scope of equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A preparation method of a homogeneous junction photocatalyst, characterized in that, It includes the following steps: Mix urea and an alkali with water, stir evenly, and dry to obtain a urea crystal precursor uniformly mixed with the alkali; Perform the first thermal polymerization on the urea crystal precursor in an anoxic environment, and the OH released by the alkali melting reacts with the amino group in urea to generate a cyano group. At the same time, the addition of alkali leads to a reduction in the ordered structure of nitrogen atoms in the C3N4 structure, thereby forming nitrogen defects to obtain C3N4 containing nitrogen defects; - ​ Mix 3-amino-1,2,4-triazole and an alkali with water, stir evenly, and dry to obtain a 3-amino-1,2,4-triazole precursor containing the alkali; Mix C3N4 with nitrogen defects and the 3-amino-1,2,4-triazole precursor containing an alkali by grinding, and perform a second thermal polymerization. The OH released by the melting of the alkali - reacts with the amino group in 3-amino-1,2,4-triazole to form a cyano group, and at the same time destroys the ordered structure in the C3N5 structure to form C3N5 on the surface of C3N4 with nitrogen defects, obtaining a homojunction photocatalyst doped with nitrogen defects and cyano groups.

2. The preparation method of the homogeneous junction photocatalyst according to claim 1, characterized in that, The mass ratio of urea to the alkali is 20~100:

1.

3. The preparation method of the homogeneous junction photocatalyst according to claim 1, characterized in that, The first thermal polymerization temperature is 490 °C~550 °C, and the thermal polymerization time is 3 h~4 h.

4. The preparation method of the homogeneous junction photocatalyst according to claim 1, characterized in that, The mass ratio of 3-amino-1,2,4-triazole to the alkali is 20~100:

1.

5. The preparation method of the homogeneous junction photocatalyst according to claim 1, characterized in that, The mass ratio of nitrogen-deficient C3N4 to the 3-amino-1,2,4-triazole precursor containing the alkali is 1.5~6:

1.

6. The preparation method of the homogeneous junction photocatalyst according to claim 1, wherein, The second thermal polymerization temperature is 490 °C~550 °C, and the thermal polymerization time is 3 h~4 h.

7. The preparation method of the homogeneous junction photocatalyst according to claim 1, characterized in that, The alkali is NaOH or KOH.

8. A homojunction photocatalyst prepared by the preparation method according to any one of claims 1~7.

9. An application of the homojunction photocatalyst according to claim 8 in photocatalytic production of H2O2.

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