GO (at) MIL-88A (Fe) / BiVO4 ternary composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a GO-coated MIL-88A (Fe) / BiVO4 ternary composite photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalysis. The preparation method of the GO-coated MIL-88A (Fe) / BiVO4 ternary composite photocatalyst comprises the following steps: sequentially adding MIL-88A (Fe) / BiVO4 and a water-soluble high-molecular compound into a GO solution, uniformly mixing the MIL-88A (Fe) / BiVO4 and the water-soluble high-molecular compound, pouring the MIL-88A (Fe) / BiVO4 and the water-soluble high-molecular compound into a mold, freezing and forming the MIL-88A (Fe) / BiVO4, drying the MIL-88A (Fe) / BiVO4, and performing heat treatment to obtain the GO-coated MIL-88A (Fe) / BiVO4 ternary composite photocatalyst. According to the invention, GO is used as a substrate, MIL-88A (Fe) / BiVO4 is loaded on the surface of the GO, the GO-coated MIL-88A (Fe) / BiVO4 ternary composite photocatalyst is constructed, and the chemical stability and recoverability of the catalyst material are obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to a GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst, a preparation method thereof, and applications thereof. Background Art

[0002] With the rapid development of industry, the problem of wastewater discharge containing heavy metal pollutants such as hexavalent chromium (Cr(VI)) is becoming increasingly serious. Photocatalytic technology is regarded as a potential solution for heavy metal pollution control due to its green, high efficiency and low energy consumption. For example, through the interfacial coupling of MIL-88A(Fe) and BiVO4 and the auxiliary effect of tartaric acid, efficient photocatalytic reduction of Cr(VI) was successfully achieved. However, the performance of powdered catalysts is easily degraded during the circulation process due to problems such as nanoparticle agglomeration and active site masking, and it is difficult to achieve efficient recovery, which restricts its practical application potential. Therefore, how to break through the stability bottleneck through material structure design while maintaining or even enhancing catalytic activity has become a key scientific issue in promoting the engineering application of photocatalytic technology. Summary of the Invention

[0003] The purpose of the present invention is to provide a GO@MIL-88A(Fe)BiVO4 ternary composite photocatalyst and its preparation method and application, in order to solve the problems existing in the above-mentioned prior art. The present invention uses GO as the structural skeleton and adopts a freezing and drying treatment method to control the stacking mode and pore structure of the GO sheets. The GO treated in this way has more active sites. By utilizing the coordination effect between the functional group active sites on the GO surface and the Fe-O clusters in MIL-88A(Fe) and the metal ions in BiVO4, the MIL-88A / BiVO4 heterojunction is loaded on its sheets, and the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained by stable compounding, which overcomes the problems of performance degradation and recovery difficulties existing in existing catalysts.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention: a method for preparing a GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst, comprising the following steps:

[0006] MIL-88A(Fe) / BiVO4 and a water-soluble polymer compound are sequentially added to a GO solution, mixed evenly, and poured into a mold. The mixture is freeze-formed, dried, and then heat-treated to obtain the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst.

[0007] Furthermore, the mass ratio of the MIL-88A(Fe) / BiVO4 and GO is (1-6):1;

[0008] The concentration of the GO solution is 5-20 mg / mL.

[0009] Furthermore, the water-soluble polymer compound includes PVP.

[0010] Furthermore, the mass ratio of the GO to the water-soluble polymer compound is (5-10):1.

[0011] Furthermore, the freezing temperature is -10°C and the freezing time is 24 hours.

[0012] Furthermore, the drying process is carried out at a temperature of -70°C and for 24 hours.

[0013] The purpose of freezing is to freeze the water in the graphene oxide aqueous solution, and the drying process is to remove the ice crystals by sublimation.

[0014] Furthermore, the heat treatment temperature is 100-150° C., and the time is 3-12 hours.

[0015] The role of heat treatment is to carbonize graphene oxide and strengthen the structural stability after molding.

[0016] Graphene oxide (GO) has a high specific surface area and excellent mechanical strength. The oxygen-containing functional groups (such as hydroxyl and carboxyl) rich on its surface can be used as anchoring sites to fix nanoparticles by chemical bonding or physical adsorption, effectively inhibiting the agglomeration of active components. In addition, the two-dimensional sheet structure of GO can form a three-dimensional cross-linked network through π-π stacking or hydrogen bonding, while enhancing the structural stability, it exposes more active sites. The present invention utilizes the unique π-π stacking network of GO, surface carboxyl coordination and other effects to firmly anchor the MIL-88A (Fe) / BiVO4 heterojunction particles on the GO sheet, solving the problem of performance degradation (i.e., poor stability) caused by the agglomeration of the powdered MIL-88A (Fe) / BiVO4 photocatalyst and the masking of active sites; through the cross-linking effect of water-soluble polymer compounds (such as PVP), the problem of GO structural collapse is suppressed, and the stability of the photocatalyst is enhanced.

[0017] In addition, GO has high carrier mobility, which can optimize the electron transfer path and can serve as an electron transfer bridge to optimize the charge separation efficiency of the heterojunction interface. The functional groups on its surface can also regulate the redox characteristics of the metal active center through coordination, thereby improving the catalytic performance in multiple dimensions and providing a new solution for building an efficient and stable photocatalytic system.

[0018] The second technical solution of the present invention: a GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared by the above preparation method.

[0019] The third technical solution of the present invention: an application of the above-mentioned GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst in Cr(VI) reduction.

[0020] The fourth technical solution of the present invention: A method for treating Cr(VI)-containing wastewater, comprising the following steps: adding the above-mentioned GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst to the Cr(VI)-containing wastewater, then adding tartaric acid (TA), placing it in a dark place and stirring it for 20 to 30 minutes, and then performing photocatalytic reduction.

[0021] Tartaric acid acts as a hole trapping agent, interacting with holes through electron transfer, filling the holes and restoring the electronic balance of the composite photocatalyst in water.

[0022] Furthermore, the illumination current of the photocatalytic reduction is 15A, and the illumination time is 15 minutes; the light source used in the photocatalytic reduction is a 220W xenon lamp.

[0023] Furthermore, the dosage ratio of the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst and Cr(VI)-containing wastewater is 1 cm 3 :50mL; the amount of tartaric acid added to the Cr(VI)-containing wastewater is 2mM; the concentration of Cr(VI) in the Cr(VI)-containing wastewater is 10-20mg / L; the pH of the Cr(VI)-containing wastewater is 2.

[0024] The present invention discloses the following technical effects:

[0025] (1) The present invention uses GO as the substrate and loads MIL-88A(Fe) / BiVO4 on its surface to construct a GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst, which significantly improves the chemical stability and recyclability of the catalyst material.

[0026] (2) The three-dimensional skeleton of the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared by the present invention increases the active sites through π-π stacking and carboxyl coordination, which can enhance the adsorption performance under dark reaction, promote the directional migration of photogenerated electrons absorbed and excited by BiVO4, and strengthen the Fe 3+ / Fe 2+ The redox cycle improves the Cr(VI) reduction efficiency. At the same time, the three-dimensional network can inhibit the migration and agglomeration of nanoparticles and improve the mechanical stability of the catalyst.

[0027] (3) The GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared in the present invention constructs a directional charge separation network for MIL-88A(Fe) / BiVO4. In this network, BiVO4 is mainly responsible for light absorption and electron excitation, while the Fe-O clusters in MIL-88A(Fe) enhance the redox cycle. The three-dimensional skeleton and chemical bonding of GO effectively inhibit the degradation of active components, ensuring the long-term maintenance of catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a physical picture of PGO@M2B1-4 prepared in Example 1;

[0030] Figure 2 The scanning electron micrographs of the photocatalysts in the examples and comparative examples are shown, wherein (a) is the M2B1 photocatalyst prepared in comparative example 1, (b) is the PGO prepared in comparative example 2, (c) is the PGO@M2B1-4 prepared in example 1, and (d) is the scanning electron micrograph of the catalyst obtained in example 10;

[0031] Figure 3 XRD diffraction patterns of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1, M2B1 prepared in Comparative Example 1, and PGO prepared in Comparative Example 2;

[0032] Figure 4 IR spectra of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1, M2B1 prepared in Comparative Example 1, and PGO prepared in Comparative Example 2;

[0033] Figure 5 Performance curves of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1, M2B1 prepared in Comparative Example 1, and PGO prepared in Comparative Example 2 for photocatalytic reduction of Cr(VI) in water;

[0034] Figure 6 The performance curves of the ternary composite photocatalysts prepared in Examples 1 to 6 for photocatalytic reduction of Cr(VI) in water are shown;

[0035] Figure 7 The cyclic stability test results of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1;

[0036] Figure 8 Performance curves of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1 for the photocatalytic reduction of Cr(VI) in water under different conditions, where (a) represents different TA dosages, (b) represents different Cr(VI) solution concentrations, (c) represents different pH values, and (d) represents different temperatures. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0039] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0040] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0042] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0043] In a first aspect of the present invention, a method for preparing a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is provided, comprising the following steps:

[0044] MIL-88A(Fe) / BiVO4 and a water-soluble polymer compound are sequentially added to a GO solution, mixed evenly, and poured into a mold. The mixture is freeze-formed, dried, and then heat-treated to obtain the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst.

[0045] In a specific embodiment of the present invention, the mass ratio of MIL-88A(Fe) / BiVO4 and GO is (1-6):1; the concentration of the GO solution is 5 mg / mL.

[0046] In a specific embodiment of the present invention, the water-soluble polymer compound includes PVP.

[0047] In a specific embodiment of the present invention, the mass ratio of GO to the water-soluble polymer compound is 5:1.

[0048] In a specific embodiment of the present invention, the freezing temperature is -10°C and the freezing time is 24 hours.

[0049] In a specific embodiment of the present invention, the drying temperature is -70°C and the drying time is 24 hours.

[0050] In a specific embodiment of the present invention, the heat treatment temperature is 150° C. and the time is 3 hours.

[0051] In a specific embodiment of the present invention, the preparation method of MIL-88A(Fe) / BiVO4 comprises the following steps:

[0052] (1) Preparation of MIL-88A(Fe) powder: Fumaric acid and ferric chloride hexahydrate were mixed in the form of a solution, stirred at 600 r / min for 30 min, and then placed in an oil bath at 100°C for 4 h to obtain MIL-88A(Fe). The MIL-88A(Fe) was washed with ultrapure water (electrical impedance greater than 18Ω), then dried at 60°C and ground to 5-10 μm to obtain MIL-88A(Fe) powder.

[0053] (2) Preparation of MIL-88A(Fe) / BiVO4: dissolving bismuth nitrate pentahydrate in a dilute nitric acid solution to obtain a bismuth nitrate pentahydrate solution; dissolving ammonium metavanadate in a sodium hydroxide solution to obtain an ammonium metavanadate solution; adding the ammonium metavanadate solution dropwise to the bismuth nitrate pentahydrate solution under magnetic stirring to obtain a BiVO4 solution, then adding MIL-88A(Fe) powder to the BiVO4 solution, adjusting the pH to 1, and stirring to obtain a mixed solution;

[0054] The mixed solution was transferred into a reactor and subjected to hydrothermal reaction at 180°C for 15 h. After cooling to room temperature, the solution was repeatedly washed with ethanol and deionized water for three times and dried at 60°C for 12 h to obtain MIL-88A(Fe) / BiVO4.

[0055] In a second aspect, the present invention provides a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared by the above preparation method.

[0056] In a third aspect, the present invention provides an application of the above-mentioned PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst in Cr(VI) reduction.

[0057] In a fourth aspect, the present invention provides a method for treating Cr(VI)-containing wastewater, comprising the following steps: adding the above-mentioned PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst to the Cr(VI)-containing wastewater, then adding tartaric acid, placing it in a dark place and stirring for 20 to 30 minutes before photocatalytic reduction.

[0058] Furthermore, the illumination intensity of the photocatalytic reduction is 15A, and the illumination time is 15 minutes; the light source used in the photocatalytic reduction is a 220W xenon lamp.

[0059] Furthermore, the dosage ratio of the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst and Cr(VI)-containing wastewater is 1 cm 3 :50mL; the amount of tartaric acid added to the Cr(VI)-containing wastewater is 2mM; the concentration of Cr(VI) in the Cr(VI)-containing wastewater is 10-20mg / L; the pH of the Cr(VI)-containing wastewater is 2.

[0060] Unless otherwise specified, the equipment, reagents, processes, parameters, etc. involved in the specific embodiments of the present invention are conventional equipment, reagents, processes, parameters, etc.

[0061] All ranges recited in the detailed description of the present invention include all points within that range.

[0062] In the specific embodiment of the present invention, "room temperature" refers to the normal ambient temperature, which can be 10-30°C.

[0063] Example 1

[0064] A preparation method of PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst:

[0065] (1) Dissolve 10 mmol of fumaric acid and 10 mmol of ferric chloride hexahydrate in 100 mL of deionized water to obtain a fumaric acid solution and a ferric chloride hexahydrate solution, respectively;

[0066] At room temperature, an aqueous solution of ferric chloride hexahydrate was quickly added to the fumaric acid solution, and the mixture was vigorously stirred at 600 r / min for 30 min to obtain solution A.

[0067] (2) Solution A was transferred to a three-necked flask and treated in an oil bath at 100°C for 4 h to obtain MIL-88A(Fe). After cooling to room temperature, the orange precipitate of MIL-88A(Fe) was collected by centrifugation and washed with ultrapure water (electrical impedance greater than 18Ω). It was then vacuum-dried at 60°C for 12 h to obtain the MIL-88A(Fe) orange photocatalyst, which was ground to 5-10 μm to obtain MIL-88A(Fe) powder.

[0068] (3) dissolving 1 mmol of bismuth nitrate pentahydrate in 30 mL of a 2 M dilute nitric acid solution to obtain a bismuth nitrate pentahydrate solution; dissolving 1 mmol of ammonium metavanadate in 30 mL of a 2 M sodium hydroxide solution to obtain an ammonium metavanadate solution;

[0069] Under magnetic stirring, the ammonium metavanadate solution was added dropwise to the bismuth nitrate pentahydrate solution at a rate of 5 mL / min until the solution became clear and transparent, thereby obtaining solution B, namely, BiVO4 solution.

[0070] (4) To 0.3 g of solution B obtained in step (3), 0.6 g of MIL-88A(Fe) powder obtained in step (2) was added (the mass ratio of MIL-88A(Fe) powder to BiVO4 solution was 2:1), and the pH was adjusted to 1. The mixture was stirred for 1 h to obtain a mixed solution; the mixed solution was transferred to a reactor and hydrothermally reacted at 180°C for 15 h. After cooling to room temperature, the mixture was repeatedly washed with ethanol and deionized water for 3 times, and dried at 60°C for 12 h to obtain MIL-88A(Fe) / BiVO4, which was recorded as M2B1.

[0071] (5) Add 20 mg of M2B1 to 1 mL of GO solution (5 mg / mL), stir evenly (stir for 1 h), then add 1 mg of PVP and mix evenly. Pour the mixture into a 1 cm × 1 cm × 1 cm polyethylene mold coated with dimethyl silicone oil, and then freeze it in a refrigerator for 24 h (freezing temperature is -10 ° C). After taking it out, immediately transfer it to a freeze dryer (-70 ° C) and keep it for 24 h. After taking it out and demolding it, place it in an oven and heat it to 150 ° C and keep it for 3 h to obtain the PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst, named PGO@M2B1-4 (also known as PGO@M2B1).

[0072] The actual picture of PGO@M2B1-4 prepared in this example is shown in Figure 1 .

[0073] Example 2

[0074] The same as Example 1, except that in step (5), the amount of M2B1 used is 25 mg, and a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained, named PGO@M2B1-5.

[0075] Example 3

[0076] The same as Example 1, except that in step (5), the amount of M2B1 used is 5 mg, and a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained, named PGO@M2B1-1.

[0077] Example 4

[0078] The same as Example 1, except that in step (5), the amount of M2B1 used is 10 mg, and a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained, named PGO@M2B1-2.

[0079] Example 5

[0080] The same as Example 1, except that in step (5), the amount of M2B1 used is 15 mg, and a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained, named PGO@M2B1-3.

[0081] Example 6

[0082] The same as Example 1, except that in step (5), the amount of M2B1 used is 30 mg, and a PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst is obtained, which is named PGO@M2B1-6.

[0083] Example 7

[0084] The same as Example 1, except that the ternary composite photocatalyst prepared in Example 1 was taken out from the solution after one photocatalytic reduction and placed in an oven at 60° C. to dry for 12 hours.

[0085] The method of primary photocatalytic reduction is: take 1cm 3The PGO@M2B1 prepared in Example 1 was added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst adsorption to reach equilibrium. Then, a light source (220 W xenon lamp, light source current 15 A) was turned on and irradiated for 15 min.

[0086] Example 8

[0087] The same as Example 7, except that the catalyst obtained in Example 7 was taken out from the solution after undergoing one more photocatalytic reduction and placed in an oven at 60° C. to dry for 12 h.

[0088] Example 9

[0089] The same as Example 8, except that the catalyst obtained in Example 8 was taken out from the solution after undergoing one more photocatalytic reduction and placed in an oven at 60° C. to dry for 12 h.

[0090] Example 10

[0091] The same as Example 9, except that the catalyst obtained in Example 9 was taken out from the solution after undergoing one more photocatalytic reduction and dried in an oven at 60° C. for 12 h.

[0092] Comparative Example 1

[0093] Preparation method of M2B1 photocatalyst:

[0094] (1) Dissolve 10 mmol of fumaric acid and 10 mmol of ferric chloride hexahydrate in 100 mL of deionized water to obtain a fumaric acid solution and a ferric chloride hexahydrate solution, respectively;

[0095] At room temperature, an aqueous solution of ferric chloride hexahydrate was quickly added to the fumaric acid solution, and the mixture was vigorously stirred at 600 r / min for 30 min to obtain solution A.

[0096] (2) Solution A was transferred to a three-necked flask and treated in an oil bath at 100°C for 4 h to obtain MIL-88A(Fe). After cooling to room temperature, the orange precipitate of MIL-88A(Fe) was collected by centrifugation and washed with ultrapure water (electrical impedance greater than 18Ω). It was then vacuum-dried at 60°C for 12 h to obtain the MIL-88A(Fe) orange photocatalyst, which was ground to 5-10 μm to obtain MIL-88A(Fe) powder.

[0097] (3) dissolving 1 mmol of bismuth nitrate pentahydrate in 30 mL of a 2 M dilute nitric acid solution to obtain a bismuth nitrate pentahydrate solution; dissolving 1 mmol of ammonium metavanadate in 30 mL of a 2 M sodium hydroxide solution to obtain an ammonium metavanadate solution;

[0098] Under magnetic stirring, the ammonium metavanadate solution was added dropwise to the bismuth nitrate pentahydrate solution at a rate of 5 mL / min until the solution became clear and transparent, thereby obtaining solution B, namely, BiVO4 solution.

[0099] (4) To 0.3 g of solution B obtained in step (3), 0.6 g of MIL-88A(Fe) powder obtained in step (2) was added (the mass ratio of MIL-88A(Fe) powder to BiVO4 solution was 2:1), and the pH was adjusted to 1. The mixture was stirred for 1 h to obtain a mixed solution; the mixed solution was transferred to a reactor and hydrothermally reacted at 180°C for 15 h. After cooling to room temperature, the mixture was repeatedly washed with ethanol and deionized water for 3 times, and dried at 60°C for 12 h to obtain MIL-88A(Fe) / BiVO4, which was recorded as M2B1.

[0100] Comparative Example 2

[0101] Preparation method of PGO:

[0102] To 1 mL of GO solution (5 mg / mL), 1 mg of PVP was added and mixed thoroughly. The mixture was then poured into a 1 cm × 1 cm × 1 cm polyethylene mold coated with dimethyl silicone oil and placed in a refrigerator for 24 hours (freezing temperature: -10°C). Immediately after removal, the mold was transferred to a freeze dryer (-70°C) and held for 24 hours. After removal and demolding, the mold was placed in an oven heated to 150°C and held for 3 hours to obtain PGO.

[0103] Effect Example 1

[0104] 1. Scanning electron microscope image

[0105] The scanning electron microscope images of the photocatalysts in the examples and comparative examples are shown in FIG. Figure 2 , where (a) is M2B1 prepared in comparative example 1, (b) is PGO prepared in comparative example 2, (c) is PGO@M2B1-4 prepared in example 1, and (d) is a scanning electron microscope image of the catalyst obtained in example 10.

[0106] from Figure 2 As can be seen from Figure (a), the M2B1 prepared in Comparative Example 1 has a spindle morphology with irregular cylindrical particles dotted on the surface; Figure 2 As can be seen from Figure (b), the PGO prepared in Comparative Example 2 is stacked in layers, with a large number of interpenetrating pores between the layers. Figure 2 As can be seen from Figure (c), the PGO@M2B1-4 prepared in Example 1 combines the morphological characteristics of M2B1 and PGO, and the surface of the PGO nanosheet layer is evenly loaded with complete M2B1 crystal particles, which indicates that the PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst (i.e., PGO@M2B1-4) was successfully prepared.

[0107] from Figure 1 As can be seen in Figure (d), after the PGO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared in Example 1 undergoes Cr(VI) reduction reaction, the surface micromorphology of the graphene sheet does not change significantly. Based on this, it can be preliminarily inferred that the ternary composite photocatalyst exhibits good structural stability in the photocatalytic reaction system.

[0108] 2. XRD diffraction pattern

[0109] The XRD diffraction patterns of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1, M2B1 prepared in Comparative Example 1, and PGO prepared in Comparative Example 2 are shown in FIG. Figure 3 .

[0110] from Figure 3 It can be seen that the M2B1 prepared in Comparative Example 1 observed the (002) crystal plane belonging to MIL-88A(Fe) at 2θ=12.1°, and the (121) and (040) crystal planes belonging to BiVO4 at 2θ=28.8° and 30.5°. A broadened diffraction peak was observed near 2θ=24.9° in the PGO prepared in Comparative Example 2, which is attributed to the characteristic signal of the (002) crystal plane of graphite carbon, indicating the successful preparation of graphene oxide. The PGO@M2B1 prepared in Example 1 observed characteristic peaks belonging to M2B1 at 2θ=12.1°, 28.8° and 30.5°, and the peak value of the characteristic peak belonging to M2B1 showed a slight decrease. This may be because graphene is coated on the surface of M2B1 in an amorphous state, slightly reducing the crystallinity of MIL-88A(Fe) / BiVO4. The presence of each characteristic peak indicates the successful preparation of the PGO@M2B1 photocatalytic material.

[0111] 3. Infrared spectrum

[0112] The infrared spectra of PGO@M2B1-4 (i.e., PGO@M2B1) prepared in Example 1, M2B1 prepared in Comparative Example 1, and PGO prepared in Comparative Example 2 are shown in FIG. Figure 4 .

[0113] from Figure 4 It can be seen that the M2B1 prepared in Comparative Example 1 is located at 490 cm -1 and 621cm -1 The absorption peak at 562 cm belongs to the stretching vibration absorption peak of VO. -1 The peak at 1627cm is the stretching vibration peak of Fe-O. -1 The peak at 1355 cm-1 is attributed to the C=C bond stretching vibration associated with unoxidized graphite. -1The stretching vibration of the C=O bond of the carboxyl group is 1110 cm -1 The peak at 40° is attributed to the COC vibration absorption in GO. In the infrared spectrum of PGO@M2B1 prepared in Example 1, functional groups belonging to M2B1 and PGO were also found, and the VO stretching vibration peak of M2B1 shifted to a lower wavenumber after recombination. This may be due to the interaction between the π electrons of graphene and the metal ions of BiVO4. The interfacial chemical interaction is expected to improve the photogenerated charge separation efficiency of the material.

[0114] 4. Test of Photocatalytic Reduction of Cr(VI) in Water

[0115] The M2B1 photocatalyst prepared in Comparative Example 1, the PGO photocatalyst prepared in Comparative Example 2, and the PGO@M2B1 ternary composite photocatalyst prepared in Example 1 were tested for photocatalytic reduction of Cr(VI) in water, and the following steps were performed:

[0116] M2B1 treatment group: 20 mg of the M2B1 photocatalyst prepared in Comparative Example 1 was weighed and added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). Tartaric acid (TA) was then added at a 2 mM amount for coupling. The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst to reach adsorption equilibrium. The light source (220 W xenon lamp, light source current 15 A) was then turned on for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0117] PGO treatment group: 1cm 3 The PGO photocatalyst prepared in Comparative Example 2 was added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)), and then tartaric acid (TA) was added in an amount of 2 mM for coupling. The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 minutes to allow the catalyst to reach adsorption equilibrium. Then, a light source (220 W xenon lamp, light source current 15 A) was turned on for 15 minutes. Samples were taken every 3 minutes and the absorbance was measured using a UV spectrophotometer.

[0118] PGO@M2B1 treated group: 1cm 3 The PGO@M2B1 prepared in Example 1 was added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst to reach adsorption equilibrium. The reaction was then irradiated with a light source (220 W xenon lamp, light source current 15 A) for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0119] The performance curves of photocatalytic reduction of Cr(VI) in water for each treatment group are shown in Figure 5 .

[0120] from Figure 5 It can be seen that the adsorption performance of the PGO prepared in Comparative Example 2 and the PGO@M2B1 samples prepared in Example 1 within 30 minutes of the dark reaction is improved by about 10% compared with the M2B1 in Comparative Example 1. This is due to the larger specific surface area between the PGO sheets, which provides more active sites. Under visible light, the photocatalytic performance of PGO is not ideal, which may be attributed to the rapid recombination of photogenerated carriers. After the introduction of M2B1, this problem is effectively solved, and the performance of the catalyst material for photocatalytic reduction of Cr(VI) is greatly improved. Although the performance of PGO@M2B1 is slightly inferior to that of M2B1, PGO@M2B1 can still maintain its morphology intact after the reaction ( Figure 5 ), indicating that it has good stability and recycling performance.

[0121] The same method as the PGO@M2B1 treatment group was used to test the photocatalytic reduction of Cr(VI) in water on PGO@M2B1-1, PGO@M2B1-2, PGO@M2B1-3, PGO@M2B1-4, PGO@M2B1-5 and PGO@M2B1-6 prepared in Examples 1 to 6. The test results are shown in Table 1. Figure 6 .

[0122] from Figure 6 As can be seen from the figure, the dark reaction adsorption performance of the composite photocatalysts at various ratios is essentially the same, while the reduction effect of PGO@M2B1 on Cr(VI) generally shows an increasing trend with increasing M2B1 mass ratio. For example, PGO@M2B1-1 can only reduce about 60% of Cr(VI) within 15 minutes, PGO@M2B1-2 can reduce about 70% of Cr(VI) within 15 minutes, and PGO@M2B1-3 can reduce about 83% of Cr(VI) within 15 minutes. However, under the same conditions, PGO@M2B1-4 and PGO@M2B1-5 have excellent photocatalytic performance, reducing 100% of Cr(VI) within 15 minutes.

[0123] The same method as the PGO@M2B1 treatment group was used to test the photocatalytic reduction of Cr(VI) in water by PGO@M2B1-4 with different photocatalytic reactions prepared in Example 1 (1 time) and Examples 7 to 10 (2 times, 3 times, 4 times and 5 times, respectively). The test results are shown in Table 1. Figure 7 .

[0124] from Figure 7As can be seen, within 15 minutes, Example 1 achieved 100% reduction of Cr(VI); Example 7 achieved an efficiency exceeding 95%; Example 8 achieved a reduction efficiency of approximately 90%; Example 9 achieved a reduction efficiency exceeding 85%; and Example 10 still achieved a reduction efficiency of 80%. In summary, after five cycles, PGO@M2B1 maintained approximately 80% photocatalytic activity, with the reduction efficiency decreasing by only approximately 5% per cycle, demonstrating the material's structural stability. This is due to the conductivity of graphene, which anchors the MIL-88A(Fe) / BiVO4 nanoparticles, preventing aggregation and dissolution, thereby improving stability. This demonstrates the excellent stability and reproducibility of PGO@M2B1.

[0125] V. Test of Photocatalytic Reduction of Cr(VI) in Water by PGO@M2B1 Prepared in Example 1 under Different Conditions

[0126] Taking PGO@M2B1 prepared in Example 1 as the object, the effects of TA dosage, Cr(VI) solution concentration, pH value and temperature on the removal of Cr(VI) were investigated. Specifically:

[0127] (1) Take 1cm 3 Example 1 PGO@M2B1 was prepared and added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). Tartaric acid (TA) was then added in amounts of 1.2, 1.6, 2.0, and 2.4 mM for coupling. The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst to reach adsorption equilibrium. The light source (220 W xenon lamp, light source current 15 A) was then turned on for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0128] To 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)), tartaric acid (TA) was added at 1.2, 1.6, 2.0, and 2.4 mM, respectively. The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed for 30 minutes to allow the catalyst to reach adsorption equilibrium. Then, a light source (220 W xenon lamp, light source intensity 15A) was turned on for 15 minutes. Samples were taken every 3 minutes and the absorbance was measured using a UV spectrophotometer.

[0129] (2) Take 1cm 3Example 1 PGO@M2B1 was prepared and added to 50 mL of water containing 10, 15, 20, and 25 mg / L hexavalent chromium (Cr(VI)), respectively. Tartaric acid (TA) was then added in an amount of 2 mM for coupling. The pH was adjusted to 2 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst to reach adsorption equilibrium. The light source (220 W xenon lamp, light source current 15 A) was then turned on for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0130] (3) Take 1cm 3 Example 1 PGO@M2B1 was prepared and added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). Tartaric acid (TA) was then added in an amount of 2 mM for coupling. The pH was adjusted to 2, 3, 4, 6, and 8 with dilute nitric acid. A dark reaction was performed at 20-30°C for 30 min to allow the catalyst to reach adsorption equilibrium. The light source (220 W xenon lamp, light source current 15 A) was then turned on for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0131] (4) Take 1cm 3 Example 1: PGO@M2B1 was prepared and added to 50 mL of water containing 20 mg / L hexavalent chromium (Cr(VI)). Tartaric acid (TA) was then added in an amount of 2 mM for coupling. The pH was adjusted to 2 with dilute nitric acid. The dark reaction was carried out for 30 min at 5, 10, 15, 20, 25, and 30 °C to allow the catalyst adsorption to reach equilibrium. Then, the light source (220 W xenon lamp, light source current 15 A) was turned on for 15 min. Samples were taken every 3 min and the absorbance was measured using a UV spectrophotometer.

[0132] The test results of photocatalytic reduction of Cr(VI) in water are shown in Figure 8 , Figure 8 In the figure, (a) is different TA dosage, (b) is different Cr(VI) solution concentration, (c) is different pH value, and (d) is different temperature.

[0133] from Figure 8 As can be seen from Figure (a), when TA = 2mM, PGO@M2B1 has the best performance. Figure 8 As can be seen in Figure (b), when the Cr(VI) concentration is 10, 15, and 20 mg / L, PGO@M2B1 can completely reduce Cr(VI) to Cr(III) within 9 minutes. When the concentration rises to 25 mg / L, PGO@M2B1 can only reduce about 90% of Cr(VI) within 15 minutes. Figure 8As can be seen in Figure (c) when pH = 2, PGO@M2B1 can completely reduce Cr(VI) to Cr(III) within 9 minutes. Figure 8 Figure (d) shows that under illumination, the Cr(VI) reduction efficiency increases with increasing temperature. At 5°C, the reduction effect is poor, due to the low temperature suppressing the activity of photogenerated carriers. When T > 20°C, PGO@M2B1 completely reduces Cr(VI) within 9 minutes. In summary, PGO@M2B1 achieves its strongest photocatalytic activity at room temperature.

[0134] Combined with the above results, it can be seen that the present invention successfully loaded M2B1 onto the PGO surface and constructed a new ternary composite photocatalyst material. This material has good chemical stability, excellent adsorption and electron transfer capabilities, can greatly accelerate the photocatalytic Cr(VI) reduction reaction, and exhibits good repeatability and recyclability.

[0135] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst, characterized in that: The following steps are involved: MIL-88A(Fe) / BiVO4 and a water-soluble polymer compound are sequentially added to a GO solution, mixed evenly, and poured into a mold. The mixture is freeze-formed, dried, and then heat-treated to obtain the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst.

2. The preparation method according to claim 1, characterized in that The mass ratio of the MIL-88A(Fe) / BiVO4 and GO is (1-6):1; And / or, the concentration of the GO solution is 5 to 20 mg / mL.

3. The preparation method according to claim 1, characterized in that The water-soluble high molecular compound includes PVP.

4. The preparation method according to claim 1, characterized in that The mass ratio of the GO to the water-soluble polymer compound is (5-10):

1.

5. The preparation method according to claim 1, characterized in that The heat treatment temperature is 100-150° C., and the time is 3-12 hours.

6. A GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst according to claim 6 in Cr(VI) reduction.

8. A method for treating wastewater containing Cr(VI), characterized in that: The method comprises the following steps: adding the GO@MIL-88A(Fe) / BiVO4 ternary composite photocatalyst described in claim 6 into Cr(VI)-containing wastewater, and then adding tartaric acid for photocatalytic reduction.

9. The method for treating Cr(VI)-containing wastewater according to claim 8, wherein: The photocatalytic reduction had a light irradiation current of 15 A and a light irradiation time of 15 min.

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