Preparation method of composite semiconductor photocatalyst and application thereof

Abstract

The application relates to a preparation method of a composite semiconductor photocatalyst and application thereof, and comprises the following steps: preparing g-C3N4 nanosheets; dispersing the prepared g-C3N4 nanosheets into methanol at a mass fraction of 10% to 70%, then adding 750 mg of trimesic acid and 150 mg of bismuth nitrate, and ultrasonic treating for 10 min to obtain a mixed suspension; transferring the mixed suspension into a microwave reaction kettle for reaction, the reaction temperature is 90 to 130 DEG C, the reaction time is 30 to 60 min, and centrifugal drying is carried out after the reaction is completed; then g-C3N4 / Bi-MOF is obtained through anhydrous methanol washing and freeze drying; a heterostructure is constructed, the energy band structure is changed, the charge transmission resistance is reduced, the photocatalytic activity is improved, the photocatalyst has two different structure and property photocatalytic activity centers, and the photocatalytic activity is changed from the energy band structure and the catalytic activity.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photocatalysis technology, and in particular to a method for preparing a composite semiconductor photocatalyst and its application. Background Technology

[0002] Currently, many energy companies face problems such as overcapacity in low-end products and insufficient self-sufficiency in high-end chemicals. Optimizing the energy structure, utilizing low-end products in a high-end manner, and achieving clean and low-carbon development are urgent issues that domestic energy companies need to address. Fumarate monoesters are high-value-added fine chemical products with significant applications in food, pharmaceuticals, coatings, resins, and plasticizers. In particular, as a highly efficient and green antibacterial agent, its antibacterial effect is 4-5 times that of ordinary antibacterial agents, and it is non-irritating and leaves no residue, attracting considerable attention from researchers. However, traditional synthesis methods for fumarate esters generally suffer from complex processes, numerous byproducts, low yields, and highly corrosive and polluting catalysts, which do not conform to the concept of green chemical development and are difficult to industrialize. Although in recent years some researchers have used special synthesis methods such as ultraviolet light-induced synthesis and microwave radiation to synthesize fumarate monomethyl esters to address environmental issues, photochemical synthesis methods suffer from narrow spectral response ranges, high energy losses, and poor reaction selectivity, limiting the development of this technology in the industrial field.

[0003] Photocatalysis is a novel technology that converts solar energy into chemical energy. It features mild conditions, environmental friendliness, and sustainability, effectively addressing issues such as low light energy utilization and numerous side reactions in the photochemical synthesis of dimethyl fumarate. Graphite-phase nitrogen carbide (g-C3N4) possesses advantages such as high thermodynamic stability, a wide visible light response range, and high photogenerated carrier separation efficiency, making it a high-performance semiconductor photocatalyst. However, g-C3N4 has a relatively small specific surface area, and strong intermolecular forces lead to easy repolymerization during photocatalytic reactions, reducing its catalytic activity. Metal-organic frameworks (MOFs) offer advantages such as high specific surface area, abundant pore structure, and tunable alkali metal active sites, showing promising applications in adsorption and catalysis. However, they suffer from low thermal stability and a narrow spectral response range. Therefore, broadening the spectral response range and suppressing photogenerated electron recombination through composite or doping methods aims to improve the catalytic activity and quantum efficiency of photocatalysts. In particular, most composite photocatalysts are used in CO2 conversion and pollutant degradation, with few applications in improving the yield and selectivity of organic photochemical reactions. Summary of the Invention

[0004] To overcome the shortcomings of single semiconductor catalysts and the problems hindering industrial production in the synthesis of fumarate esters, this invention provides a method for preparing a composite semiconductor photocatalyst and its application. A photocatalyst material with a wide spectral response range, large specific area, and high photocatalytic activity is prepared. Furthermore, under an induced light source, the prepared catalyst material is applied to the production of monomethyl fumarate, solving problems such as long reaction times, cumbersome reaction steps, severe environmental pollution, and narrow spectral response range and low selectivity in photosynthesis.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a composite semiconductor photocatalyst, comprising the following steps:

[0006] Step 1: Prepare g-C3N4 nanosheets;

[0007] Step 2: The prepared g-C3N4 nanosheets were dispersed in methanol at a mass fraction of 10%–70%, and then 750 mg of trimesic acid and 150 mg of bismuth nitrate were added. The mixture was sonicated for 10 min to obtain a mixed suspension. The mixed suspension was transferred to a microwave reactor for reaction at a temperature of 90–130 °C for 30–60 min. After the reaction was completed, the mixture was centrifuged and dried. Then, the mixture was washed with anhydrous methanol and freeze-dried to obtain g-C3N4 / Bi-MOF.

[0008] Furthermore, the method for preparing g-C3N4 nanosheets in step 1 includes: mixing melamine and urea in a ratio of 1:2 to 1:8 to obtain a mixture, grinding the mixture and then placing it in a muffle furnace for calcination reaction, raising the temperature to 550°C at a rate of 5 to 20°C / min, annealing for 3 to 5 hours, and then grinding to obtain g-C3N4 nanosheets.

[0009] Furthermore, in step 2, the temperature at which the mixed suspension is transferred to the microwave reactor for reaction is 120°C, and the reaction time is 40 minutes.

[0010] Furthermore, the anhydrous methanol washing is performed three times, and the freeze-drying time is 12 hours.

[0011] Furthermore, melamine and urea were mixed in a 1:4 ratio to obtain a mixture.

[0012] Furthermore, melamine and urea are mixed in a 1:6 ratio to obtain a mixture.

[0013] Furthermore, the mixture was ground and then placed in a muffle furnace for calcination reaction, with the temperature increased to 550°C at a rate of 10°C / min.

[0014] Furthermore, the annealing time is 4 hours.

[0015] The application of g-C3N4 / Bi-MOF prepared by the aforementioned composite semiconductor photocatalyst in the photoinduced synthesis of monomethyl fumarate.

[0016] The light induction is achieved using a xenon lamp.

[0017] This invention uses Bi-MOF as the base material and modifies it with g-C3N4. The modified composite photocatalyst g-C3N4 / Bi-MOF is then applied to the synthesis of dimethyl fumarate to broaden the spectral response range, suppress photogenerated electron recombination, and improve photocatalytic activity and reaction selectivity.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) The g-C3N4 / Bi-MOF composite photocatalyst designed in this invention has a heterogeneous structure that changes the band structure, reduces the charge transport resistance, and improves the photocatalytic activity. Moreover, it has two major active centers, g-C3N4 and metallic Bi, with a wide light response range and high photocatalytic efficiency. This makes the photocatalyst have two photocatalytic active centers with different structures and properties, thus changing the photocatalytic activity from both the band structure and catalytic activity aspects.

[0020] (2) The optimal mass ratio of melamine and urea in the synthesis of g-C3N4 nanosheets prepared by the present invention is 1:8. Only at this ratio can g-C3N4 nanosheets be peeled off to form nanoscale g-C3N4 with rich pores, which has the narrowest band gap and the best photocatalytic activity.

[0021] (3) The g-C3N4 / Bi-MOF composite photocatalyst constructed in this invention can carry out the synthesis reaction of fumarate monomethyl ester under mild conditions. The synthesis process is simple and has low energy consumption.

[0022] (4) The prepared solid catalyst is non-corrosive and non-polluting, and is easy to separate and recover from the reaction products, making it highly valuable for industrial applications.

[0023] (5) The prepared photocatalyst enables the synthesis of monomethyl fumarate to be completed under a xenon lamp, resulting in high light energy utilization and low loss. Attached Figure Description

[0024] Figure 1 These are the PL spectra of embodiments 7-9 of the present invention;

[0025] Figure 2 This is a yield graph of monomethyl fumarate of the present invention;

[0026] Figure 3 These are SEM images of Bi-MOF in embodiments of the present invention;

[0027] Figure 4 This is a SEM image of g-C3N4 / Bi-MOF-1 prepared in Example 1 of this invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Example 1:

[0030] 11.3 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, and 750 mg of trimesic acid and 150 mg of bismuth nitrate were added sequentially. The mixture was sonicated for 10 min, and the resulting suspension was transferred to a microwave reactor. The reactor was kept at 90 °C and reacted for 30 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a g-C3N4 to Bi-MOF mass ratio of 1:10, denoted as g-C3N4 / Bi-MOF-1. The SEM image of Bi-MOF in this example is shown below. Figure 3 As shown, the SEM image of g-C3N4 / Bi-MOF-1 is as follows. Figure 4 As shown.

[0031] Example 2

[0032] 33.75 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, 750 mg of trimesic acid and 150 mg of bismuth nitrate were added, and the mixture was sonicated for 10 min. The mixed suspension was transferred to a microwave reactor, kept at 100 °C, and reacted for 40 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a mass ratio of g-C3N4 to Bi-MOF of 3:10 (mass fraction), denoted as g-C3N4 / Bi-MOF-2.

[0033] Example 3

[0034] 56.25 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, 750 mg of trimesic acid and 150 mg of bismuth nitrate were added, and the mixture was sonicated for 10 min. The mixed suspension was transferred to a microwave reactor, kept at 120 °C, and reacted for 40 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a mass ratio of g-C3N4 to Bi-MOF of 5:10 (mass fraction), denoted as g-C3N4 / Bi-MOF-3.

[0035] Example 4

[0036] 78.75 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, 750 mg of trimesic acid and 150 mg of bismuth nitrate were added, and the mixture was sonicated for 10 min. The mixed suspension was transferred to a microwave reactor, kept at 100 °C, and reacted for 60 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a mass ratio of g-C3N4 to Bi-MOF of 7:10 (mass fraction), denoted as g-C3N4 / Bi-MOF-4.

[0037] Example 5

[0038] 33.75 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, 750 mg of trimesic acid and 150 mg of bismuth nitrate were added, and the mixture was sonicated for 10 min. The mixed suspension was transferred to a microwave reactor, kept at 120 °C, and reacted for 40 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a mass ratio of g-C3N4 to Bi-MOF of 3:10 (mass fraction), which was denoted as g-C3N4 / Bi-MOF-5.

[0039] Implementation Case 6

[0040] 56.25 mg of g-C3N4 nanosheets were dispersed in a certain amount of methanol, 750 mg of trimesic acid and 150 mg of bismuth nitrate were added, and the mixture was sonicated for 10 min. The mixed suspension was transferred to a microwave reactor, kept at 130 °C, and reacted for 40 min. After centrifugation and drying, the mixture was washed three times with anhydrous methanol and then freeze-dried for 12 h to obtain a composite material with a mass ratio of g-C3N4 to Bi-MOF of 5:10 (mass fraction), which was denoted as g-C3N4 / Bi-MOF-6.

[0041] Example 7

[0042] The method for preparing g-C3N4 nanosheets based on Examples 1-6 is as follows: 1g of melamine and 8g of urea are mixed evenly, ground, transferred to a crucible, placed in a muffle furnace for calcination reaction, heated to 550℃ at a rate of 10℃ / min, and annealed for 3.5h to obtain a light yellow powder, which is then ground to obtain g-C3N4-1.

[0043] Example 8

[0044] 1g of melamine and 6g of urea were mixed evenly, ground, transferred to a crucible, and placed in a muffle furnace for calcination. The temperature was increased to 550℃ at a rate of 5℃ / min, and after annealing for 4 hours, a light yellow powder was obtained. After grinding, g-C3N4-2 was obtained.

[0045] Example 9

[0046] 1g of melamine and 4g of urea were mixed evenly, ground, transferred to a crucible, and placed in a muffle furnace for calcination. The temperature was increased to 550℃ at a rate of 10℃ / min, and after annealing for 4 hours, a light yellow powder was obtained. After grinding, g-C3N4-3 was obtained.

[0047] like Figure 1 The image shown is the PL spectrum of g-C3N4 prepared in Examples 7-9. Figure 1 It can be seen that the g-C3N4-1 obtained in Example 1 has the lowest fluorescence intensity, indicating that it has the best efficiency in inhibiting electron-hole separation and enhanced photocatalytic activity. Therefore, g-C3N4-1 prepared in Example 6 is preferred when selecting g-C3N4.

[0048] Example 10

[0049] The application of g-C3N4 / Bi-MOF prepared in Examples 1-5 in the photoinduced synthesis of monomethyl fumarate was investigated. Specifically, 100 mg of the g-C3N4 / Bi-MOF catalyst prepared in Examples 1-5 was added to 100 ml of a mixed solution of anhydrous methanol and maleic anhydride, respectively. The solution was purged with nitrogen for 20 min to ensure air removal, and irradiated with a 300 W xenon lamp for 4 h at a controlled temperature of 20 °C. After filtration, vacuum distillation, washing, and drying, samples of the six target products were obtained. The reaction equations are as follows:

[0050]

[0051] The purity and yield of the five prepared samples were statistically analyzed as follows: Figure 2 As shown:

[0052] In Example 1, the g-C3N4 / Bi-MOF-1 prepared for the production of monomethyl fumarate resulted in a sample with a yield of 58% and a purity of 78% for monomethyl fumarate.

[0053] In Example 2, the g-C3N4 / Bi-MOF-2 prepared for the production of monomethyl fumarate yielded a sample with a purity of 91% and a yield of 70% monomethyl fumarate.

[0054] In Example 3, the g-C3N4 / Bi-MOF3 prepared for the application of producing monomethyl fumarate resulted in a sample with a yield of 62.5% and a purity of 91.5% for monomethyl fumarate.

[0055] In Example 4, the g-C3N4 / Bi-MOF-4 prepared for the application of producing monomethyl fumarate resulted in a sample with a yield of 62% and a purity of 92% for monomethyl fumarate.

[0056] In Example 5, the g-C3N4 / Bi-MOF-5 prepared for the application of producing monomethyl fumarate showed a yield of 77.64% and a yield of 97.5% of monomethyl fumarate in the prepared sample.

[0057] In Example 6, the g-C3N4 / Bi-MOF-5 prepared for the application of producing monomethyl fumarate showed a yield of 60.16% and a yield of 80.3% of monomethyl fumarate in the prepared sample.

[0058] pass Figure 2 It can be seen that g-C3N4 / Bi-MOF-5 (the mass ratio of g-C3N4 to Bi-MOF is 3:10) has the best catalytic activity for the synthesis of monomethyl fumarate, with a product purity of 97.6% and a yield of 77.64%.

[0059] Comparative Examples

[0060] Bi4O5Br2 / g-C3N4 was synthesized via a hydrothermal method. 100 mg of Bi4O5Br2 / g-C3N4 was added to a mixed solution of anhydrous methanol and maleic anhydride in 100 mL. The solution was purged with nitrogen for 20 min to ensure air removal, and then irradiated with a 300 W xenon lamp for 4 h at a controlled temperature of 20 °C. The reaction solution was filtered, distilled under reduced pressure, washed, and dried to obtain monomethyl fumarate product with a purity of 40.36% and a yield of 20.7%.

[0061] Comparing the photocatalytic conversion yields of the composite catalysts prepared in Examples 1, 2, 3, 4, and 5 to monomethyl fumarate and the yield of monomethyl fumarate by Bi4O5Br2 / g-C3N4 in Examples 5, it can be seen that the composite photocatalysts g-C3N4 / Bi-MOF-1, g-C3N4 / Bi-MOF-2, g-C3N4 / Bi-MOF-3, g-C3N4 / Bi-MOF-4, and g-C3N4 / Bi-MOF-4 prepared in any of Examples 1, 2, 3, 4, 5, and 6 provided by this invention are superior. A comparison of the purity and yield of fumarate monoesters obtained from MOF-5 and g-C3N4 / Bi-MOF-6 with the current process in the comparative examples shows that the purity and yield of fumarate monoesters prepared by g-C3N4 / Bi-MOF in Examples 1, 2, 3, 4, 5, and 6 of this invention are higher than those prepared in the comparative examples. Furthermore, the solid-phase catalysts prepared in the examples of this invention are non-corrosive, non-polluting, and easily separated and recovered from the reactants, making them highly valuable for industrial applications. In addition, through… Figure 2 It can be seen that Implementation Case 5 is the preferred scheme, and the yield and purity of the g-C3N4 / Bi-MOF-5 photocatalytic conversion product, monomethyl fumarate, are the highest.

[0062] The above embodiments are merely illustrative examples of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. The application of a composite semiconductor photocatalyst in the photoinduced synthesis of monomethyl fumarate; characterized in that, A method for preparing a composite semiconductor photocatalyst includes the following steps: Step 1: Prepare g-C3N4 nanosheets; Step 2: The prepared g-C3N4 nanosheets were dispersed in methanol at a mass fraction of 10%~70%, and then 750 mg of trimesic acid and 150 mg of bismuth nitrate were added. The mixture was sonicated for 10 min to obtain a mixed suspension. The mixed suspension was transferred to a microwave reactor for reaction at a temperature of 100~130 ℃ for 30~60 min. After the reaction was completed, the mixture was centrifuged and dried. Then, the mixture was washed with anhydrous methanol and freeze-dried to obtain g-C3N4 / Bi-MOF.

2. The application according to claim 1, characterized in that, The method for preparing g-C3N4 nanosheets in step 1 includes: mixing melamine and urea in a ratio of 1:2 to 1:8 to obtain a mixture; grinding the mixture and then calcining it in a muffle furnace; heating the temperature to 550℃ at a rate of 5 to 20 ℃ / min; annealing for 3 to 5 h; and then grinding to obtain g-C3N4 nanosheets.

3. The application according to claim 1, characterized in that, In step 2, the temperature at which the mixed suspension is transferred to the microwave reactor is 120°C and the reaction time is 40 minutes.

4. The application according to claim 1, characterized in that, The anhydrous methanol washing was performed three times, and the freeze-drying time was 12 hours.

5. The application according to claim 2, characterized in that, Melamine and urea are mixed in a 1:4 ratio to obtain a mixture.

6. The application according to claim 2, characterized in that, Melamine and urea are mixed in a 1:6 ratio to obtain a mixture.

7. The application according to claim 2, characterized in that, The mixture was ground and then placed in a muffle furnace for calcination reaction, with the temperature increased to 550°C at a rate of 10 °C / min.

8. The application according to claim 2 or 7, characterized in that, The annealing time is 4 hours.

9. The application according to claim 1, characterized in that, The light induction is achieved using a xenon lamp.

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