Biocl modified bivo4 composite photocatalyst and preparation method thereof

Abstract

The application discloses a BiOCl modified BiVO4 composite photocatalyst and a preparation method thereof, and belongs to the field of bismuth vanadate photocatalysts. The preparation method of the BiOCl modified BiVO4 composite photocatalyst is as follows: bismuth nitrate pentahydrate is added into ethylene glycol to form a solution A; ammonium metavanadate, sodium hydroxide and potassium chloride are added into deionized water to form a solution B; the solution A is added into the solution B, pH is adjusted to 6-7, and constant temperature reaction is carried out in a 70-90 DEG C water bath for at least 1 h; the precipitate is obtained by cooling and filtration; the precipitate is kept at 400-500 DEG C for at least 4 h, and the BiOCl modified BiVO4 composite photocatalyst is obtained by cooling and grinding. The composite photocatalyst has a photodegradation rate of 100%, and is beneficial to industrial application.

Description

Technical Field

[0001] This invention belongs to the field of bismuth vanadate photocatalysts, specifically relating to a BiOCl-modified BiVO4 composite photocatalyst and its preparation method. Background Technology

[0002] BiVO4 is a visible-light photocatalyst that can directly degrade organic pollutants using sunlight and is applied in wastewater treatment. The photocatalytic activity of BiVO4 is strongly dependent on its crystal structure, with three main crystal structures: monoclinic scheelite, tetragonal zircon, and tetragonal scheelite. Monoclinic scheelite BiVO4 exhibits higher photocatalytic performance than the other two tetragonal phases. This is due to the relatively narrow band gap of the monoclinic structure and the internal electric field generated by the distortion of the VO4 tetrahedra, which facilitates the separation of electron-hole pairs. However, single BiVO4 suffers from poor photogenerated electron-hole mobility, rapid recombination, and poor adsorption, resulting in low photocatalytic efficiency. Researchers mainly use methods such as semiconductor composites, elemental doping, and noble metal deposition to modify BiVO4, constructing composite materials to improve its photocatalytic performance.

[0003] BiOCl is an environmentally friendly new material, due to its special composition of Cl... - and [Bi2O2] 2+ BiOCl exhibits unique optochemical properties due to its interlaced polar two-dimensional layered structure, self-generated internal electric field, and short carrier transfer distance. However, BiOCl has a wide band gap (approximately 3.2 eV) and can only absorb ultraviolet light, which severely limits its utilization of sunlight. Studies have shown that constructing heterojunctions by combining BiVO4 and BiOCl is an effective way to enhance the visible light photocatalytic activity of BiVO4.

[0004] CN106391062A discloses a BiVO4 / BiOCl heterojunction photocatalyst, which consists of microspheres with BiVO4 nanosheets encapsulated around a BiOCl core, the microspheres having a diameter of 1-5 μm. The BiVO4 / BiOCl photocatalyst synthesized in this invention exhibits high crystallinity and high photocatalytic degradation activity for organic dyes, reaching up to 98%. CN115254151A discloses a core-shell structured BiVO4@BiOCl heterojunction, its preparation method, and its applications. This core-shell structured BiVO4@BiOCl heterojunction exhibits enhanced photocatalytic performance across the entire UV-Vis-NIR spectrum, with a maximum photocatalytic degradation rate of 90.32% under visible light.

[0005] However, most of the existing literature reports on the preparation of BiOCl / BiVO4 composite materials using hydrothermal methods, which often require high pressure reactors, high temperatures, long synthesis times, or complex processes, making them unsuitable for industrial production. Summary of the Invention

[0006] The technical problem to be solved by this invention is the high production cost of BiOCl / BiVO4 composite materials.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for preparing BiOCl-modified BiVO4 composite photocatalyst, comprising the following steps:

[0008] a. Add bismuth nitrate pentahydrate to ethylene glycol and stir until completely dissolved to obtain solution A. Add ammonium metavanadate, sodium hydroxide, and potassium chloride to deionized water and stir until completely dissolved to obtain solution B.

[0009] b. Slowly add solution A obtained in step a to solution B, mix well and adjust the pH to 6-7. React at a constant temperature of 70-90℃ until complete. After cooling, filtration, washing and drying, the precipitate is obtained.

[0010] c. Calcine the precipitate obtained in step b at 400-500℃ for at least 4 hours, then cool and grind it to obtain the BiOCl-modified BiVO4 composite photocatalyst.

[0011] In step a above, the molar ratio of bismuth nitrate pentahydrate in solution A to the total molar amounts of ammonium metavanadate and potassium chloride in solution B is 1:1.

[0012] In step a above, the concentration of solution A is 0.3-0.7 mol / L.

[0013] In step a above, the molar ratio of ammonium metavanadate to potassium chloride in solution B is 0.1-0.9:1.

[0014] In step a above, the concentration of ammonium metavanadate is 0.01-0.4 mol / L.

[0015] In step b above, the reaction is carried out at a constant temperature of 70-90℃ in a water bath for at least 1 hour.

[0016] A BiOCl-modified BiVO4 composite photocatalyst is prepared by the above-mentioned method for preparing BiOCl-modified BiVO4 composite photocatalyst.

[0017] The above-mentioned BiOCl-modified BiVO4 composite photocatalyst has a crystal form that is a mixed phase of monoclinic BiVO4 and BiOCl or a mixed phase of monoclinic BiVO4, tetragonal BiVO4 and BiOCl.

[0018] The beneficial effects of this invention are: This invention overcomes the shortcomings of the prior art and provides a method for preparing BiOCl-modified BiVO4 composite photocatalyst. The method uses liquid-phase precipitation, which is simple and mild. The photodegradation rate of the composite catalyst of this invention is as high as 100%, which is beneficial for industrial application. Attached Figure Description

[0019] Figure 1 The change in the removal rate of Rhodamine B by BiVO4 prepared at different calcination temperatures over time;

[0020] Figure 2 The change in the removal rate of Rhodamine B by BiOCl / BiVO4 prepared at different calcination temperatures over time. Detailed Implementation

[0021] The technical solution of the present invention can be implemented in the following manner.

[0022] A method for preparing a BiOCl-modified BiVO4 composite photocatalyst includes the following steps: adding pentahydrate and bismuth nitrate to ethylene glycol and stirring until dissolved to form solution A; adding ammonium metavanadate, sodium hydroxide, and potassium chloride to deionized water and stirring until dissolved to form solution B; slowly adding solution A to solution B, adjusting the pH of the solution to 6-7, reacting at a constant temperature of 70-90℃ in a water bath for at least 1 hour, cooling, filtering, washing, and drying to obtain a precipitate; keeping the above precipitate at 400-500℃ for at least 4 hours, cooling and grinding to obtain the BiOCl-modified BiVO4 composite photocatalyst.

[0023] The sum of the molar amounts of ammonium metavanadate and potassium chloride in the solution is equal to the molar ratio of bismuth pentahydrate and bismuth nitrate, and the molar ratio of ammonium metavanadate to potassium chloride is 0.1-0.9:1. The concentration of solution A is 0.3-0.7 mol / L, and the concentration of ammonium metavanadate is 0.01-0.4 mol / L.

[0024] The BiOCl-modified BiVO4 composite photocatalyst obtained by the above preparation method is a mixed phase of monoclinic BiVO4 and BiOCl or a mixed phase of monoclinic BiVO4, tetragonal BiVO4 and BiOCl.

[0025] The technical solution and effects of the present invention will be further explained below through practical examples.

[0026] Example

[0027] 1. Sample preparation

[0028] Example: 5 mmol of Bi(NO3)3·5H2O was weighed and added to 20 mL of ethylene glycol, stirred until dissolved to form solution A. 2.5 mmol of NH4VO3, 2.5 mmol of NaOH, and 2.5 mmol of KCl were weighed and added to 20 mL of deionized water, stirred until dissolved to form solution B. Solution A was slowly added to solution B, the pH of the solution was adjusted to 7, and the reaction was carried out at an 80°C water bath for 1 hour. After cooling and filtration, the solution was washed repeatedly with deionized water and anhydrous ethanol at least three times, and dried in an oven at 110°C for 1 hour. A suitable amount of sample was incubated at 400°C, 450°C, and 500°C for 4 hours respectively, cooled, and ground into a fine powder to obtain the BiOCl / BiVO4 catalyst sample.

[0029] Comparative example: Undoped pure BiVO4 was selected as the comparative example, i.e., pure BiVO4 catalyst sample.

[0030] 2. Performance Testing

[0031] 0.2 g of each of the example and comparative samples were weighed and added to 200 mL of Rhodamine B solution of different concentrations. The mixture was stirred in the dark for 30 min to reach adsorption / desorption equilibrium. The samples were then irradiated under simulated sunlight. At regular intervals, 10 mL of the solution was taken out and centrifuged at 3000 r / min for 5 min. The absorbance of the supernatant was measured, and the photodegradation rate D was calculated.

[0032] For a single BiVO4, such as Figure 1 As shown, the adsorption rates of Rhodamine B in samples at different calcination temperatures were all low, ranging from 15.84% to 19.00%, and the degradation rates after 3 hours of photocatalytic reaction were only 28.43% to 38.11%, indicating poor overall photocatalytic performance.

[0033] For binary BiOCl / BiVO4, such as Figure 2 As shown, the removal rate of Rhodamine B by BiOCl / BiVO4 prepared at different calcination temperatures varies with time. The adsorption rates of samples at 400℃ and 450℃ are relatively close, at 47.39% and 43.81%, respectively, while the adsorption rate of the sample at 500℃ is only 21.87%. The degradation rates of Rhodamine B by samples at 400℃ and 450℃ after 1.5h of light irradiation can reach 97.15% and 99.05%, respectively, and Rhodamine B can be completely degraded after 2h, while the degradation rate of the sample at 500℃ after 3h is 93.82%.

Claims

1. A method for preparing BiOCl-modified BiVO4 composite photocatalyst, characterized in that... Includes the following steps: a. Add bismuth nitrate pentahydrate to ethylene glycol and stir until completely dissolved to obtain solution A. The molar ratio of bismuth nitrate pentahydrate in solution A to the total molar amounts of ammonium metavanadate and potassium chloride in solution B is 1:

1. Add ammonium metavanadate, sodium hydroxide, and potassium chloride to deionized water and stir until completely dissolved to obtain solution B. The molar ratio of ammonium metavanadate to potassium chloride in solution B is 0.1-0.9:

1. b. Slowly add solution A obtained in step a to solution B, mix well and adjust the pH to 6-7. React at a constant temperature of 70-90℃ until complete. After cooling, filtration, washing and drying, the precipitate is obtained. c. Calcine the precipitate obtained in step b at 400-500℃ for at least 4 hours, then cool and grind it to obtain the BiOCl-modified BiVO4 composite photocatalyst.

2. The preparation method of the BiOCl-modified BiVO4 composite photocatalyst according to claim 1, characterized in that: In step a, the concentration of solution A is 0.3-0.7 mol / L.

3. The preparation method of the BiOCl-modified BiVO4 composite photocatalyst according to claim 1, characterized in that: In step a, the concentration of ammonium metavanadate is 0.01-0.4 mol / L.

4. The preparation method of the BiOCl-modified BiVO4 composite photocatalyst according to claim 1, characterized in that: In step b, the reaction is carried out at a constant temperature of 70-90℃ in a water bath for at least 1 hour.

5. A BiOCl-modified BiVO4 composite photocatalyst, prepared by the preparation method of the BiOCl-modified BiVO4 composite photocatalyst according to any one of claims 1-4.

6. The BiOCl-modified BiVO4 composite photocatalyst according to claim 5, characterized in that: Its crystal form is a mixture of monoclinic BiVO4 and BiOCl or a mixture of monoclinic BiVO4, tetragonal BiVO4 and BiOCl.

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