A g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst and preparation method

Abstract

The present invention discloses a g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst and its preparation method. The solid-state Z-type photocatalyst uses g-C3N4 as the PS I end, Bi2WO6 as the PS II end, and a conductive polymer, polypyrrole, as an electron mediator. The g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst is synthesized hydrothermally by encapsulating polypyrrole with g-C3N4 and then adding it to a Bi2WO6 solution. The g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst is stable and highly reusable, and exhibits excellent degradation effects on dyes and phenolic compounds.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and in particular to a solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 and a preparation method thereof. Background Art

[0002] Numerous modification studies have significantly improved the performance of g-C3N4 photocatalysts, but their visible light utilization range still has much room for expansion. Doping modification alone cannot solve the problem of easy electron-hole recombination in g-C3N4 itself. Overcoming the inherent limitations of semiconductors requires two approaches: on the one hand, reducing the semiconductor's band gap can broaden the spectral response range. On the other hand, making the conduction band potential more negative and the valence band potential more positive. Z-type photocatalytic materials, composed of multiple components, can simultaneously meet these two requirements. When g-C3N4 is combined with another photocatalyst to form a Z-type structure, the problems of high electron-hole recombination rate and poor cyclic stability originally existing in g-C3N4 are overcome, and the results show even better photocatalytic performance.

[0003] Bi2WO6 has a perovskite-type WO6 layered and octahedral structure, resulting in a narrow bandgap and a high recombination rate for photogenerated electrons and holes. To improve its catalytic performance, many studies have combined Bi2WO6 with materials such as g-C3N4 and graphene to prepare photocatalytic materials. However, the development of all-solid-state Z-scheme photocatalysts is limited. Furthermore, no all-solid-state Z-scheme photocatalysts using conductive polymers such as polypyrrole (PPY) as electron mediators have been reported. Summary of the Invention

[0004] The present invention addresses these shortcomings by providing a g-C3N4 / ppy / Bi2WO6 solid-state Z-scheme photocatalyst and its preparation method. The solid-state Z-scheme photocatalyst utilizes g-C3N4 as the PS I end, Bi2WO6 as the PS II end, and a conductive polymer, polypyrrole, as the electron mediator. The g-C3N4 / ppy / Bi2WO6 solid-state Z-scheme photocatalyst is synthesized hydrothermally by encapsulating polypyrrole with g-C3N4 and then adding it to a Bi2WO6 solution. The catalyst is stable, highly reusable, and exhibits excellent degradation properties against dyes and phenolic compounds.

[0005] The technical solution of the solid-state Z-type photocatalyst and preparation method of the present invention is a g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst, with g-C3N4 as the PSⅠ end of the solid-state Z-type photocatalyst, Bi2WO6 as the PSⅡ end of the solid-state Z-type photocatalyst, and a conductive polymer polypyrrole as an electron mediator.

[0006] The preparation method of the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 is as follows: polypyrrole is wrapped with g-C3N4 and then added to a Bi2WO6 solution to synthesize the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 by a hydrothermal method.

[0007] The preparation method of the g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst comprises the following steps:

[0008] (1) Preparation of g-C3N4: Grind the precursor of g-C3N4 for 30-40 min, heat to 500-550 °C and calcine for 5-6 h to obtain a yellow solid powder;

[0009] (2) Preparation of g-C3N4 / ppy: g-C3N4 was added to ammonia water, and pyrrole was added under magnetic stirring. The mixture was stirred in an ice-water bath for 0.4-0.8 h to obtain a pyrrole ammonia solution. Sodium persulfate was added to ammonia water to form an APS ammonia solution, and the mixture was stirred in an ice-water bath for 0.4-0.8 h. The APS ammonia solution was added to the pyrrole ammonia solution and stirred in an ice-water bath for 20-28 h. After filtration and washing, the mixture was dried at 50-60°C to obtain a black g-C3N4 / ppy powder.

[0010] (3) Preparation of g-C3N4 / ppy / Bi2WO6: Prepare Bi(NO3)3 and Na2WO4 solutions separately. Take g-C3N4 / ppy and add Na2WO4 solution and stir thoroughly. Then slowly add Bi(NO3)3 solution. Transfer the mixture to a hydrothermal reactor and react at 170-190℃ for 23-25h. Filter and wash the product to obtain g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst.

[0011] In step (1), g-C3N4 is obtained by high-temperature calcination of a precursor, which is at least one of urea, dicyandiamide, and thiourea. The precursor is heated to 500-550°C at a rate of 2°C / min-5°C / min and calcined for 4-4.5h, and then kept warm for 2-3h.

[0012] In step (1), the heating rate is 2°C / min-5°C / min.

[0013] In step (2), the concentration of the ammonia water is 0.01 mol / L.

[0014] In step (2), the concentration of the pyrrole ammonia solution is 0.06-0.07 (V / V), the concentration of the APS ammonia solution is 133-155 g / L, and the solid-liquid ratio of the mixed solution of g-C3N4, pyrrole ammonia solution and APS ammonia solution is 0.912-9.15 g / L.

[0015] In step (3), the molar ratio of Bi(NO3)3 and Na2WO4 is 2:1, and the solid-liquid ratio of g-C3N4 / ppy to Bi2WO6 solution is 0.274-2.74 g / L.

[0016] Evaluation method of photocatalytic performance:

[0017] The entire photocatalytic reaction was carried out in a photocatalytic reactor using a mercury lamp as the light source. 50 mL of a 20 mg / L pollutant was added to a photocatalytic test tube, along with 0.01 g of a g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst. Adsorption was performed in the dark for the first 30 minutes, followed by photocatalytic degradation. Samples were taken every 5 minutes and the absorbance was measured using a UV-visible spectrophotometer. The concentration change over time was recorded.

[0018] The beneficial effects of the present invention are as follows: the present invention utilizes a conductive polymer polypyrrole having a conjugated π structure as a g-C3N4 / Bi2WO6 solid-state Z-type photocatalytic electron mediator, aiming to accelerate the electron migration rate and promote the effective separation of electrons and holes. Traditional electron mediators of Z-type photocatalysts use ionic redox electron pairs in liquid solutions, but there are problems such as the concentration requirements for the ion pairs and the fact that the ion pairs themselves can react with photoelectrons. The all-solid-state Z-type photocatalyst introduces a solid conductor as an electron mediator to overcome the shortcomings of liquid-phase ion pairs. Solid-state electron mediators mostly use high-conductivity metals (Au, Ag, and Cd) and graphene. As a conductive polymer, polypyrrole has a large π conjugated electron cloud in its molecule, which is beneficial as an electron mediator to improve electron mobility. The g-C3N4 / ppy / Bi2WO6 solid-state Z-type photocatalyst of the present invention is stable and highly reusable, and has a good degradation effect on both dyes and phenolic compounds.

[0019] Figure 1 This is a TEM transmission image of the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 prepared in the present invention. It can be seen from the figure that the rod-shaped Bi2WO6 is tightly combined with the block-shaped g-C3N4. Figure 2 Shown is the SEM electron microscope image of the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6. It can be seen that a dense ppy spherical particle layer is formed on the surface of the block material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown is the TEM transmission image of the solid-state Z-scheme photocatalyst of g-C3N4 / ppy / Bi2WO6;

[0021] Figure 2 Shown is the SEM electron microscope image of the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6;

[0022] Figure 3 Shown is the cyclic photodegradation curve of rhodamine by the solid Z-scheme photocatalyst g-C3N4 / ppy / Bi2WO6;

[0023] Figure 4 Shown is the photodegradation curve of p-nitrophenol by solid-state Z-scheme photocatalyst g-C3N4 / ppy / Bi2WO6. DETAILED DESCRIPTION

[0024] In order to better understand the present invention, the technical solutions of the present invention are described in detail below with specific examples, but the present invention is not limited thereto.

[0025] Example 1

[0026] Grind 10 g of dicyandiamide for 30-40 minutes and then put it into a crucible. Heat it to 550°C in a muffle furnace at a rate of 2°C / min and calcine it for 4 hours. Then, keep it at 550°C for 2 hours to obtain yellow solid powder of g-C3N4.

[0027] Weigh 0.274g of g-C3N4 and add it to 30ml of 0.01mol / L ammonia. While stirring magnetically, add 1.5ml of pyrrole and stir in an ice-water bath for 0.5h. Weigh 4.564g of ammonium persulfate and add it to 30ml of 0.01mol / L ammonia to form an APS solution. Incubate the solution in an ice-water bath for 0.5h. Then, combine the two solutions and stir in an ice-water bath for 24h. Filter, wash, and oven-dry the black product at 50-60°C.

[0028] Weigh 4.8507g of Bi(NO3)3·5H2O and dissolve it in 10ml of nitric acid. Weigh 1.6493g of Na2WO4 and dissolve it in 40ml of water. Add 0.0685g of g-C3N4 / ppy to the Na2WO4 and stir evenly. Slowly add the Bi(NO3)3 solution and stir evenly. Transfer the mixture to a hydrothermal reactor and react at 180°C for 24h.

[0029] The product is filtered and washed to obtain the g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst.

[0030] Add 50mL of 20mg / L rhodamine solution to a photocatalytic test tube, add 0.01g of g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst, and perform adsorption under dark conditions for the first 30min. Then turn on the light source for photocatalytic degradation. Take samples every 5 minutes and measure the absorbance using a UV-visible spectrophotometer. Record the change in absorbance over time. After low-temperature drying, the used 0.01g g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst is placed back into a new 50mL of 20mg / L rhodamine solution and the photodegradation process is repeated. Repeat the operation 5 times, record the change in absorbance over time, and draw a photodegradation curve, as shown in the figure. Figure 3 It can be seen that the performance of the g-C3N4 / ppy / Bi2WO6 sample is very stable, and the degradation rate of 5 photodegradation cycles can reach more than 90%. Its activity does not change significantly after 5 cycles.

[0031] Example 2

[0032] Grind 10 g of thiourea for 30-40 min and then put it into a crucible. Heat it to 550 °C in a muffle furnace at a rate of 2 °C / min and calcine it for 4 h. Keep it at 550 °C for 2 h to obtain yellow solid powder of g-C3N4.

[0033] Weigh 0.274g of g-C3N4 and add it to 30ml of 0.01mol / L ammonia. While stirring magnetically, add 1.5ml of pyrrole and stir in an ice-water bath for 0.5h. Weigh 4.564g of sodium persulfate and add it to 30ml of 0.01mol / L ammonia to form an APS solution. Incubate the solution in an ice-water bath for 0.5h. Then, combine the two solutions and stir in an ice-water bath for 24h. Filter, wash, and oven-dry the black product at 50-60°C.

[0034] Weigh 4.8507g of Bi(NO3)3·5H2O and dissolve it in 10ml of nitric acid. Weigh 1.6493g of Na2WO4 and dissolve it in 40ml of water. Randomly add 1#, 2#, 3#, and 4# g-C3N4 / ppy from a minimum of 0.0137g to the Na2WO4 solution, stirring evenly. Slowly add the Bi(NO3)3 solution, stirring evenly, and transfer the mixture to a hydrothermal reactor and react at 180°C for 24h. Filter and wash the products to obtain 1#, 2#, 3#, and 4# g-C3N4 / ppy / Bi2WO6 solid-state Z-scheme photocatalysts, respectively. The corresponding solid-to-liquid ratios of g-C3N4 / ppy to Bi2WO6 solutions are 0.274, 0.548, 1.096, and 2.74g / L, respectively.

[0035] 50 mL of 20 mg / L p-nitrophenol was added to a photocatalytic test tube, followed by 0.01 g of 1#-4#g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst sample. Adsorption was performed in the dark for the first 30 minutes, and then the light source was turned on for photocatalytic degradation. Samples were taken every 5 minutes and the absorbance was measured using a UV-visible spectrophotometer. The relationship between the absorbance and time was recorded, and a photodegradation curve was plotted, as shown in Figure 1. Figure 4 As shown, it can be seen that the 1-4#g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalysts have a very fast degradation rate for p-nitrophenol, and the degradation rate is above 90%.

Claims

1. A solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6, characterized in that: The PSⅠend and PSⅡend of the solid Z-scheme photocatalyst are g-C3N4 and Bi2WO6, respectively, and the conductive polymer polypyrrole is used as the electron mediator. The preparation method of the solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 comprises the following steps: (1) Preparation of g-C3N4: Grind the precursor of g-C3N4 for 30-40 min, then heat to 500-550 °C and calcine for 5-6 h to obtain a yellow solid powder; (2) Preparation of g-C3N4 / ppy: Add g-C3N4 to ammonia water, add pyrrole under magnetic stirring, and stir in an ice-water bath for 0.4-0.8 h to obtain a pyrrole ammonia solution; add ammonium persulfate to ammonia water to form an APS ammonia solution, and stir in an ice-water bath for 0.4-0.8 h; add the APS ammonia solution to the pyrrole ammonia solution and stir in an ice-water bath for 20-28 h; filter, wash, and dry at 50-60°C to obtain a black g-C3N4 / ppy powder; (3) Preparation of g-C3N4 / ppy / Bi2WO6: Prepare Bi(NO3)3 and Na2WO4 solutions respectively. Take g-C3N4 / ppy and add Na2WO4 solution and stir thoroughly. Then slowly add Bi(NO3)3 solution. Transfer the mixture to a hydrothermal reactor and react at 170-190℃ for 23-25h. Filter and wash the product to obtain g-C3N4 / ppy / Bi2WO6 solid Z-type photocatalyst.

2. The solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 according to claim 1, characterized in that In step (1), g-C3N4 is obtained by high-temperature calcination of a precursor, wherein the precursor is at least one of urea, dicyandiamide, and thiourea. The precursor is heated to 500-550°C at a rate of 2°C / min-5°C / min and calcined for 4 hours, and then kept warm for 2 hours.

3. The solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 according to claim 1, characterized in that In step (1), the heating rate is 2°C / min-5°C / min.

4. The solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 according to claim 1, characterized in that In step (2), the concentration of the ammonia water is 0.01 mol / L.

5. The solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 according to claim 1, characterized in that In step (2), the volume ratio of the pyrrole ammonia aqueous solution is 0.05, the concentration of the APS ammonia aqueous solution is 133-155 g / L, and the solid-liquid ratio of the mixed solution of g-C3N4, pyrrole ammonia aqueous solution and APS ammonia aqueous solution is 0.912-9.15 g / L.

6. The solid Z-type photocatalyst of g-C3N4 / ppy / Bi2WO6 according to claim 1, characterized in that In step (3), the molar ratio of Bi(NO3)3 and Na2WO4 is 2:1, and the solid-liquid ratio of g-C3N4 / ppy to Bi2WO6 solution is 0.274-2.74 g / L.

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