Preparation method of defect-rich Bi4NbO8Cl-C composite photocatalyst

Abstract

Hexavalent chromium (Cr (VI)) is widely applied to the industries of electroplating, spinning, leather tanning and chromium product manufacturing, and Cr (VI)-containing sewage has very strong biotoxicity and mutagenicity. Therefore, effective removal of Cr (VI) in industrial wastewater has important significance for protecting ecological environment and human health. As a novel bismuth-based oxychloride photocatalyst, the Bi4NbO8Cl material with the Aurivillius-Sillen structure has the advantages that the unique layered molecular structure of the Bi4NbO8Cl material is beneficial to the separation of photon-generated carriers, and the Bi4NbO8Cl material has good photocatalytic performance. On the basis of a Bi4NbO8Cl visible light response photocatalyst, the concentration of a glucose solution is regulated and controlled, carbon shell layers with different thicknesses are loaded, meanwhile, oxygen vacancy defects with different concentrations are formed, the visible light response Bi4NbO8Cl (at) C composite photocatalyst is obtained, and a good effect is achieved when the visible light response Bi4NbO8Cl (at) C composite photocatalyst is used for treating Cr (VI)-containing wastewater under the acidic condition.

Description

Technical field:

[0001] The present invention relates to a method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst. Specifically, a Bi4NbO8Cl layered structure is prepared using a molten salt method as a matrix. A glucose solution is used as a carbon source, and the glucose is carbonized using a hydrothermal method. A carbon coating is then formed in situ on the surface of the Bi4NbO8Cl matrix. By controlling the concentration of the glucose solution to achieve varying carbon coating amounts, the resulting Bi4NbO8Cl@C exhibits acid resistance and is capable of effectively treating acidic hexavalent chromium-containing industrial wastewater. This technology relates to the field of photocatalytic material preparation. Background technology:

[0002] Hexavalent chromium (Cr(VI)), mostly present in oxygen anions (CrO4 2- 、HCrO4 - 、Cr2O7 2- It is widely used in the electroplating, textile, leather tanning, and chromium product manufacturing industries. The high solubility of Cr(VI)-containing oxyanions makes them easily diffuse into natural water bodies and thus absorbed by plants, animals, and humans. Cr(VI) is highly biotoxic and mutagenic. Therefore, the effective removal of Cr(VI) from industrial wastewater is of great significance for protecting the ecological environment and human health.

[0003] Semiconductor photocatalysts generate charge carriers under sunlight. These photogenerated electrons convert the more toxic Cr(VI) into the less toxic Cr(III), which is then precipitated as Cr(OH)3 in an alkaline environment, thereby recycling chromium resources and protecting the environment. Traditional semiconductor catalysts, such as TiO2 and ZnO, only respond to ultraviolet light, which accounts for approximately 5% of the solar spectrum, and are unresponsive to visible and near-infrared light, which account for approximately 49% and 46%, respectively. Therefore, the development of efficient visible-light-responsive catalysts has long been a sought-after goal.

[0004] Recent studies have found that Bi4NbO8Cl material with Aurivilius-Sillén structure is a new type of bismuth-based chloride oxide photocatalyst, which is composed of [Bi2O2] 2+ layer, [NbO4] 3- layer and [Cl] -This unique layered molecular structure facilitates the separation of photogenerated charge carriers, thereby enhancing the photocatalytic performance of the catalyst. Because both the valence and conduction bands of Bi4NbO8Cl exhibit strong hybridization between Bi 6s and O 2p orbitals, this property narrows the band gap, providing visible light absorption and high photostability. However, similar to most single-component photocatalysts, Bi4NbO8Cl suffers from a high recombination rate of photogenerated charge carriers, significantly limiting its application in the photocatalytic reduction of Cr(VI). Therefore, improving the photogenerated charge separation efficiency of Bi4NbO8Cl photocatalysts through modification is imperative to enhance the quantum yield.

[0005] Carbon materials, especially graphene-like carbon layer structures, have sp 2 The hybrid carbon hexagonal structure has excellent conductivity and can act as an electron acceptor, enhancing the spatial separation of photogenerated charges on the photocatalyst surface. Therefore, we designed a method to prepare a carbon-coated Bi4NbO8Cl composite photocatalyst. In a hydrothermal reaction environment, glucose exhibits a certain degree of reducing activity, creating oxygen vacancies within the Bi4NbO8Cl structure, which extends the composite photocatalyst's absorption in the visible light region. Simultaneously, the photogenerated electrons in the Bi4NbO8Cl migrate to the carbon layer, enhancing the spatial separation of photogenerated charge carriers and improving the efficiency of the photocatalytic reduction of Cr(VI) under acidic conditions. Summary of the invention:

[0006] The present invention adopts a hydrothermal method to prepare a defect-rich Bi4NbO8Cl@C composite photocatalyst with excellent performance.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst is carried out according to the following steps:

[0009] (1) Preparation of Bi4NbO8Cl powder: At room temperature, weigh 0.1 mol of NaCl and KCl respectively and put them into an agate mortar; then weigh 0.01 mol of BiOCl, 0.005 mol of Nb2O5 and 0.015 mol of Bi2O3 in turn and add them to the agate mortar; grind the above mixture in the agate mortar for 15 min until there is no obvious graininess; further transfer the above mixture to an agate ball mill, add 10 mm agate balls, seal the ball mill and place it in a planetary ball mill for 2 h at a speed of 300 rpm; transfer the ball-milled powder to a corundum crucible and calcine it in a muffle furnace for a certain time while maintaining a certain heating rate; take out the calcined product and wash it with 300 mL of 80°C hot water five times without grinding, paying attention to ultrasound during the process; check the residual Cl with 0.1 mol / L AgNO3 - concentration; the above product was dried in an oven at 60°C for 12 h and ground to obtain Bi4NbO8Cl powder;

[0010] (2) Prepare glucose solution: weigh a certain amount of glucose (C6O6H 12 ·H2O) powder was added to a polytetrafluoroethylene liner containing 40 mL of deionized water and stirred magnetically for 10 min to form a uniform glucose solution;

[0011] (3) Preparation of Bi4NbO8Cl@C powder: 1.09 g of the Bi4NbO8Cl powder prepared in step (1) was added to the glucose solution in step (2), and the mixture was stirred for 30 min. The inner liner was then sealed in a stainless steel hydrothermal kettle and placed in a forced air drying oven, where it was heated at a certain temperature and maintained for a period of time. After the reaction was completed, the reactor was cooled to room temperature.

[0012] (4) The suspension in (3) was centrifuged at 6000 rpm, and the precipitate was collected and washed three times with deionized water and ethanol respectively; the collected precipitate was dried in a forced air drying oven at 60°C for 24 h, and the powder was collected to obtain dry Bi4NbO8Cl@C powder.

[0013] Preferably, the calcination temperature in step (1) is 600-800° C., the calcination time is 0.5-5 h, and the heating rate is 2-5° C. / min.

[0014] Preferably, the mass of the glucose powder described in step (2) is 396 mg-3.96 g.

[0015] Preferably, the hydrothermal temperature in step (3) is 160-200° C., and the holding time is 2-12 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention uses a Bi4NbO8Cl sheet structure prepared by a molten salt method as a matrix and utilizes the reducing property of glucose in a hydrothermal reaction to prepare a defect-rich Bi4NbO8Cl material. Simultaneously, glucose molecules are thermally decomposed, forming an in-situ carbon coating on the surface of the Bi4NbO8Cl material, expanding the photocatalytic material's absorption of visible light and enhancing the efficiency of photogenerated carrier separation. Based on the Bi4NbO8Cl visible-light-responsive photocatalyst, the present invention modulates the concentration of the glucose solution to load carbon shells of varying thicknesses while simultaneously forming oxygen vacancy defects of varying concentrations, resulting in a visible-light-responsive Bi4NbO8Cl@C composite photocatalyst. This composite photocatalyst achieves excellent results in treating Cr(VI)-containing wastewater under acidic conditions. When the glucose addition amount is 1.584 g, the hydrothermal temperature is 180°C, and the reaction time is 6 h, the Bi4NbO8Cl@C achieves optimal photocatalytic treatment efficiency for the target pollutant Cr(VI). Description of the drawings:

[0018] Figure 1 This is the Raman graph of the Bi4NbO8Cl@C composite photocatalyst prepared by the present invention with different glucose addition amounts.

[0019] Figure 2 This is the SEM image of the sample prepared in Example 1.

[0020] Figure 3 ESR graph of Bi4NbO8Cl@C composite photocatalyst with different glucose addition amounts prepared by the present invention

[0021] Figure 4 DRS diagram of the Bi4NbO8Cl@C composite photocatalyst prepared in the present invention with different glucose addition amounts.

[0022] Figure 5 This is a graph showing the reduction curve of Cr(VI) by the Bi4NbO8Cl@C composite photocatalyst prepared in the present invention with different glucose addition amounts. Specific implementation method:

[0023] Example 1:

[0024] At room temperature, 0.1 mol of NaCl and KCl were weighed and placed in an agate mortar. 0.01 mol of BiOCl, 0.005 mol of Nb2O5, and 0.015 mol of Bi2O3 were weighed and added to the agate mortar in sequence. The mixture was ground in the agate mortar for 15 min until no obvious graininess was observed. The mixture was further transferred to an agate ball mill, and 10 mm agate balls were added. The sealed ball mill was placed in a planetary ball mill and milled for 2 h at 300 rpm. The milled powder was transferred to a corundum crucible and calcined at 750 °C in a muffle furnace for 1 h, maintaining a heating rate of 3 °C / min. The calcined product was taken out and washed with 300 mL of 80 °C hot water five times without grinding, paying attention to ultrasound during the washing process. Residual Cl was tested with 0.1 M AgNO3. - The above product was dried in an oven at 60°C for 12 h and ground to obtain Bi4NbO8Cl powder. 1.584 g of glucose (C6O6H 12 ·H2O) powder was added to a polytetrafluoroethylene liner previously filled with 40 mL of deionized water and magnetically stirred for 10 minutes to form a uniform glucose solution. 1.09 g of Bi4NbO8Cl powder was added to the glucose solution, and the mixture was stirred for another 30 minutes. The liner was then sealed in a stainless steel hydrothermal autoclave and placed in a forced air drying oven, where it was heated at 180°C for 6 hours. After the reaction was completed, the autoclave was cooled to room temperature. The suspension in the hydrothermal autoclave liner was centrifuged at 6000 rpm, and the precipitate was collected and washed three times with deionized water and three times with ethanol. The collected precipitate was dried in a forced air drying oven at 60°C for 24 hours, and the powder was collected to obtain dry Bi4NbO8Cl@C powder, designated as BNC@C-1.584.

[0025] Example 2:

[0026] This embodiment differs from embodiment 1 in that:

[0027] The mass of the added glucose powder was 3.96 g, so the sample obtained in this example was labeled BNC@C-3.96.

Claims

1. A method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst, characterized in that: Follow these steps: (1) Preparation of Bi4NbO8Cl powder: At room temperature, weigh 0.1 mol of NaCl and KCl respectively and put them into an agate mortar; then weigh 0.01 mol of BiOCl, 0.005 mol of Nb2O5 and 0.015 mol of Bi2O3 in turn and add them to the agate mortar; grind the above mixture in the agate mortar for 15 min until there is no obvious graininess; further transfer the above mixture to an agate ball mill, add 10 mm agate balls, seal the ball mill and place it in a planetary ball mill for 2 h at a speed of 300 rpm; transfer the ball-milled powder to a corundum crucible and calcine it in a muffle furnace for a certain time while maintaining a certain heating rate; take out the calcined product and wash it with 300 mL of 80°C hot water five times without grinding, paying attention to ultrasound during the process; check the residual Cl with 0.1 mol / L AgNO3 - concentration; the above product was dried in an oven at 60°C for 12 h and ground to obtain Bi4NbO8Cl powder; (2) Prepare glucose solution: weigh a certain amount of glucose (C6O6H 12 ·H2O) powder was added to a polytetrafluoroethylene liner containing 40 mL of deionized water and stirred magnetically for 10 min to form a uniform glucose solution; (3) Preparation of Bi4NbO8Cl@C powder: 1.09 g of the Bi4NbO8Cl powder prepared in step (1) was added to the glucose solution in step (2), and the mixture was stirred for 30 min. The inner lining was then encapsulated with a stainless steel hydrothermal reactor shell and placed in a forced air drying oven, where it was heated at a certain temperature and maintained for a period of time. After the reaction was completed, the reactor was cooled to room temperature. (4) The suspension in (3) was centrifuged at 6000 rpm, the precipitate was collected, and the precipitate was washed three times with deionized water and ethanol respectively; the collected precipitate was dried in a forced air drying oven at 60°C for 24 h, and the powder was collected to obtain dry Bi4NbO8Cl@C powder.

2. The method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst according to claim 1, wherein: The mass of glucose in step (2) is 0.396g-3.96g.

3. The method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst according to claim 1, wherein: The temperature of the hydrothermal reaction in step (3) is 160-200°C.

4. The method for preparing a defect-rich Bi4NbO8Cl@C composite photocatalyst according to claim 1, wherein: The holding time of the hydrothermal reaction in step (3) is 2-12 hours.

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