Preparation method and application of S-shaped photocatalytic material Bi2MoO6 / CdS

Abstract

The application discloses a preparation method and application of S-type photocatalytic material Bi2MoO6 / CdS, and adopts a simple hydrothermal method to synthesize S-type Bi2MoO6 / CdS heterojunction.When the mass ratio of Bi2MoO6 to CdS is 1:4, the degradation efficiency of Cr(VI) (20 mg / L, pH=3) is 100% after 16 min of visible light irradiation, and the reaction kinetics constant (0.2339 min-1) is 334.1 and 3.5 times of single Bi2MoO6 and CdS respectively.After 5 cycles, the photocatalytic activity basically remains unchanged (<4%).Therefore, it has great application potential in photocatalytic removal of Cr(VI).

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials, specifically relating to a method for preparing an S-type photocatalytic material Bi2MoO6 / CdS and its application. Background Technology

[0002] With the development of industry, the treatment of heavy metal industrial wastewater, especially chromium-containing wastewater, has gradually become an issue that cannot be ignored. Traditional hexavalent chromium wastewater treatment methods are often characterized by high cost, complex operation, and insufficient treatment effect, and there is still room for improvement in practical applications.

[0003] Semiconductor photocatalysis technology, as an environmentally friendly, economically efficient, safe, and green treatment technology, has a very broad application prospect in the field of water pollution control. Bismuth molybdate, as a bismuth-based semiconductor material that is easy to prepare and has excellent performance, has attracted widespread attention in recent years; bismuth-containing semiconductors, due to their unique layered structure and excellent performance in promoting photocatalytic reactions, have also attracted widespread attention in the field of semiconductor photocatalysis.

[0004] Bismuth molybdate (Bi₂MoO₆) has a suitable band gap (2.5–2.8 eV) and possesses [MoO₄]₂. 2− and [Bi2O2] 2+ The alternating stacked layered structure, with its mild synthesis conditions and tunable morphology and properties, has attracted widespread attention from researchers due to its excellent performance. However, severe recombination of photogenerated carriers, narrow visible light response, and low quantum yield hinder its large-scale application in wastewater purification.

[0005] Metal sulfides are increasingly prominent in the field of photocatalysis, among which cadmium sulfide (CdS) is highly favored due to its small band gap and good band structure.

[0006] Currently, there are no reports on combining the band structure of Bi2MoO6 with that of CdS to enhance the photocatalytic reduction ability of Cr(VI). Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing the S-type photocatalytic material Bi2MoO6 / CdS.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing the S-type photocatalytic material Bi2MoO6 / CdS, comprising,

[0011] Thioacetamide and Cd(CH3COO)2∙2H2O were dissolved in ethylene glycol and stirred until homogeneous. Ethanol was then added to obtain a mixture.

[0012] Bi2MoO6 was added to the mixture, and the mixture was ultrasonically mixed until homogeneous. The mixture underwent a solvothermal reaction, and the precipitate was collected after natural cooling. The precipitate was then washed and dried to obtain Bi2MoO6 / CdS.

[0013] The theoretical mass ratio of Bi2MoO6 to CdS is 1:4, and the volume ratio of ethylene glycol to ethanol in the solvothermal reaction is 3:4.

[0014] In a preferred embodiment of the preparation method described in this invention, the preparation method of Bi2MoO6 includes:

[0015] Bi(NO)3·5H2O was dissolved in ethylene glycol to prepare a Bi(NO)3·5H2O ethylene glycol solution;

[0016] Dissolve Na2MoO6⋅2H2O in ethylene glycol to prepare a Na2MoO6⋅2H2O ethylene glycol solution.

[0017] A mixture was prepared by adding a Bi(NO)3⋅5H2O ethylene glycol solution dropwise to a Na2MoO6⋅2H2O ethylene glycol solution.

[0018] Ethanol was added to the mixture, and the mixture was heated at 160°C for 12 h. The product was then dried to obtain Bi2MoO6.

[0019] In a preferred embodiment of the preparation method described in this invention, the ratio of Bi(NO)3⋅5H2O to ethylene glycol in the Bi(NO)3⋅5H2O ethylene glycol solution is 0.9702 g: 15 mL.

[0020] In a preferred embodiment of the preparation method described in this invention, the ratio of the Na2MoO6⋅2H2O ethylene glycol solution is 0.2425 g: 15 mL.

[0021] In a preferred embodiment of the preparation method described in this invention, the ratio of Bi(NO)3⋅5H2O to Na2MoO6⋅2H2O in the mixture is 0.9702 g: 0.2425 g.

[0022] In a preferred embodiment of the preparation method described in this invention, ethanol is added to the mixture, wherein the volume ratio of ethylene glycol to ethanol is 3:4, and the dropping rate of the Bi(NO)3⋅5H2O ethylene glycol solution is 1 mL / min.

[0023] In a preferred embodiment of the preparation method described in this invention, the mixture comprises thioacetamide, Cd(CH3COO)2∙2H2O, ethylene glycol, and ethanol in a ratio of 0.5638 g : 1 g : 30 mL : 40 mL.

[0024] In a preferred embodiment of the preparation method described in this invention, the solvothermal reaction is carried out at a temperature of 180°C for 12 hours.

[0025] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing the S-type photocatalytic material Bi2MoO6 / CdS.

[0026] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of the S-type photocatalytic material Bi2MoO6 / CdS in the photocatalytic degradation of Cr(VI) in wastewater, comprising,

[0027] 10 mg of photocatalytic material Bi2MoO6 / CdS was suspended in 50 mL of 20 mg / L Cr(VI). Before light exposure, the suspension was stirred in the dark for 1 h to reach adsorption-desorption equilibrium.

[0028] After adsorption-desorption equilibrium is reached, turn on the light to irradiate the reaction for 16 min.

[0029] The reaction conditions were as follows: irradiation with a 300 W xenon lamp at room temperature under visible light radiation.

[0030] Beneficial effects of this invention:

[0031] (1) This invention provides a method for preparing the S-type photocatalytic material Bi2MoO6 / CdS. Bi(NO)3⋅5H2O ethylene glycol solution is added dropwise to Na2MoO6⋅2H2O ethylene glycol solution. Then the mixture is transferred to a 100ml Teflon autoclave and 40 mL of ethanol is added. That is, the volume ratio of ethylene glycol to ethanol is 3:4, which can form special micro-reaction conditions, which helps to form nanosheets Bi2MoO6 and has excellent degradation effect on Cr(VI).

[0032] (2) When the amount of Bi2MoO6 / CdS is small, when it is 0.2 g / L, after 16 min of visible light irradiation, the degradation efficiency of Cr(VI) 20 mg / L pH = 3 is 100%, and the reaction kinetic constants are 334.1 and 3.5 times that of Bi2MoO6 and CdS, respectively.

[0033] (3) In the preparation of Bi2MoO6 / CdS in this invention, the theoretical mass ratio of Bi2MoO6:CdS is preferably 1:4, which has the best catalytic effect and shows excellent stability. After 5 cycles, the reduction efficiency is still maintained at 96.2%. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0035] Figure 1 The image shows the XRD pattern of the S-type Bi2MoO6 / CdS heterojunction obtained in an embodiment of the present invention.

[0036] Figure 2 This is a SEM image of the S-type Bi2MoO6 / CdS heterojunction obtained in an embodiment of the present invention.

[0037] Figure 3 This is an EDS image of the S-type Bi2MoO6 / CdS heterojunction obtained in an embodiment of the present invention.

[0038] Figure 4 This is a TEM image of the S-type Bi2MoO6 / CdS heterojunction prepared in an embodiment of the present invention.

[0039] Figure 5 The image shows the reduction diagrams of Cr(VI) in the S-type Bi2MoO6, CdS and Bi2MoO6 / CdS heterojunctions obtained in the embodiments of the present invention.

[0040] Figure 6 The image shows the stability of the S-type Bi2MoO6 / CdS heterojunction obtained in the embodiments of the present invention after five cycles.

[0041] Figure 7 This is a graph showing the effect of the mass ratio of Bi2MoO6 / CdS on the Cr(VI) removal performance in an embodiment of the present invention.

[0042] Figure 8The figures shown are the performance test results of Bi2MoO6 / CdS in Example 5 of this invention; where a is the band gap diagram obtained by converting the diffuse reflectance test data of Bi2MoO6 solid using the Kubelka-Munk function, b is the band gap diagram obtained by converting the diffuse reflectance test data of CdS solid using the Kubelka-Munk function, c is the valence band diagram of Bi2MoO6 and CdS obtained by VB-XPS test, d is the work function of Bi2MoO6 obtained by theoretical simulation calculation and then the Femi level position diagram obtained, e is the work function of CdS obtained by theoretical simulation calculation and then the Femi level position diagram obtained, and f is a schematic diagram of the band structure and interface electron transfer path of the Bi2MoO6 / CdS photocatalytic material.

[0043] Figure 9 This is an electron paramagnetic resonance (EPR) image of hydroxyl radicals and superoxide radicals in an embodiment of the present invention. Detailed Implementation

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0046] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. All raw materials used in this invention are common commercially available products.

[0047] Example 1

[0048] This embodiment provides a method for preparing Bi2MoO6, the main steps of which are as follows:

[0049] (1) Dissolve 0.9702 g of Bi(NO)3⋅5H2O in 15 mL of ethylene glycol for 30 min;

[0050] Dissolve 0.2425 g Na2MoO6⋅2H2O in 15 mL of ethylene glycol for 30 min;

[0051] Subsequently, the Bi(NO)3⋅5H2O ethylene glycol solution was added dropwise to the Na2MoO6⋅2H2O ethylene glycol solution at a dropping rate of 1 ml / min to obtain a mixture;

[0052] (2) Transfer the mixture into a 100ml Teflon autoclave, add 40 mL of ethanol, i.e., the volume ratio of ethylene glycol to ethanol is 3:4, continue stirring for 30 min, then heat at 160℃ for 12 h. After the solvothermal reaction, cool naturally and collect the precipitate, and wash it alternately with distilled water and ethanol.

[0053] (3) Finally, the product was dried at 80°C for 6 h to obtain Bi2MoO6.

[0054] Example 2

[0055] (1) Dissolve 0.5638 g of thioacetamide and 1 g of Cd(CH3COO)2∙2H2O in 30 mL of ethylene glycol and stir for 30 min, then add 40 mL of ethanol;

[0056] (2) Pour the mixture into a 100 mL Teflon-lined autoclave, add 0.1355 g of Bi2MoO6 prepared in Example 1, the theoretical mass ratio of Bi2MoO6 to CdS is 1:4, sonicate for 0.5 h, heat at 180℃ for 12 h, and collect the precipitate after natural cooling.

[0057] (3) Finally, rinse with deionized water and ethanol, and dry at 80°C for 6 hours. The catalyst Bi2MoO6 / CdS was obtained by solvothermal method for later use.

[0058] The XRD pattern of the S-type Bi2MoO6 / CdS heterojunction prepared in this embodiment can be found in [reference]. Figure 1 ;from Figure 1 As can be seen from the data, the prepared Bi2MoO6 / CdS heterojunction material corresponds one-to-one with the standard card numbers of Bi2MoO6 and CdS, proving that the Bi2MoO6 / CdS heterojunction material was successfully prepared.

[0059] SEM image of the S-type Bi2MoO6 / CdS heterojunction prepared in this embodiment, see [link to SEM image]. Figure 2 Scanning electron microscopy (SEM) analysis shows that Bi₂MoO₆ and CdS are uniformly mixed together.

[0060] The EDS image of the S-type Bi2MoO6 / CdS heterojunction obtained in this embodiment is shown in the figure. Figure 3 The EDS analysis by scanning electron microscopy shows that the elemental mass ratio of the prepared Bi2MoO6 / CdS 1:4 is basically consistent with the theoretical value.

[0061] TEM image of the S-type Bi2MoO6 / CdS heterojunction prepared in this embodiment, see [link to TEM image]. Figure 4Transmission electron microscopy (TEM) results show that Bi₂MoO₆ and CdS are arranged in nanosheets and uniformly composited together, forming a Bi₂MoO₆ and CdS interface, which provides an effective foundation for the S-type electron transfer pathway.

[0062] Example 3

[0063] Dissolve 0.5638 g of thioacetamide and 1 g of Cd(CH3COO)2∙2H2O in 30 mL of ethylene glycol for 30 min, then add 40 mL of ethanol, pour the mixture into a 100 mL Teflon autoclave, and treat at 180 °C for 12 h.

[0064] The resulting yellow CdS was rinsed four times alternately with deionized water and ethanol;

[0065] The product was dried overnight in an oven at 80°C to obtain CdS.

[0066] In this embodiment of the invention, the photocatalytic reaction conditions were as follows: all batches of photoreduction experiments were conducted at room temperature using a 300 W xenon lamp system equipped with a 420 nm cutoff filter as a visible light source, and the experiments were carried out under visible light source radiation.

[0067] The specific steps are as follows:

[0068] 10 mg of sample was suspended in 50 mL of 20 mg / L Cr(VI). Before light exposure, the suspension was stirred in the dark for 1 h to reach adsorption-desorption equilibrium.

[0069] After adsorption-desorption equilibrium was reached, the lamp was turned on, and 5 ml of solution was taken out every 4 minutes; the concentration of Cr(VI) was detected at 542 nm using the diphenylurea (DPC) colorimetric method.

[0070] from Figure 5 It can be seen that when the input amount of Bi2MoO6 / CdS is 0.2 g / L, after 16 min of visible light irradiation, the degradation efficiency of Cr(VI) 20 mg / L at pH = 3 is 100%, and the reaction kinetic constant is 0.2339 min. −1 These are 334.1 and 3.5 times that of Bi2MoO6 and CdS, respectively.

[0071] from Figure 6 It can be seen that Bi2MoO6 / CdS exhibits excellent stability, and the reduction efficiency remains at 96.2% after 5 cycles.

[0072] Example 4

[0073] Dissolve 0.5638 g of thioacetamide and 1 g of Cd(CH3COO)2∙2H2O in 30 mL of ethylene glycol and stir for 30 min. Then add 40 mL of ethanol and pour the mixture into a 100 mL Teflon-lined autoclave.

[0074] Different masses of Bi2MoO6 (Bi2MoO6 / CdS mass ratio of 1:1, 1:2, 1:3, 1:4, 1:5) were added, ultrasonicated for 0.5 h, heated at 180℃ for 12 h, collected after natural cooling, and finally washed with deionized water and ethanol and dried at 80℃ for 6 h.

[0075] The above-mentioned catalysts Bi2MoO6 / CdS with different mass ratios were obtained by solvothermal method for later use, and their performance in removing Cr(VI) was tested.

[0076] See results Figure 7 It can be seen that the photocatalytic activity of Bi2MoO6 / CdS increases with the increase of CdS mass, and the catalytic effect is best at a mass ratio of 1:4. After 16 min of visible light irradiation, the degradation efficiency of Cr(VI) 20 mg / L at pH = 3 is 100%. The reaction kinetic constant of Bi2MoO6 / CdS 1:4 is 0.2339 min−1, which is 334.1 and 3.5 times that of Bi2MoO6 and CdS alone, respectively. After 5 cycles, the reduction efficiency is still maintained at 96.2%. The catalytic activity decreases when the mass ratio is 1:5, which may be due to the excessive CdS covering the active sites.

[0077] Example 5

[0078] The performance of the Bi2MoO6 / CdS heterojunction prepared in Example 2 was determined, see [reference needed]. Figure 8 , Figure 9 ,from Figure 8 As can be seen from a and b, the band gaps of Bi₂MoO₆ and CdS obtained by transforming the solid diffuse reflectance test data using the Kubelka-Munk function are 2.64 eV and 2.3 eV, respectively. Figure 8 In the figure, c represents the valence bands of Bi₂MoO₆ and CdS obtained by VB-XPS testing, which are 2.43 eV and 1.44 eV, respectively. Figure 8 The work functions of Bi₂MoO₆ and CdS were obtained through theoretical simulations using d and e, and the Femi energy levels were found to be 1.797 and 1.146 eV, respectively. The Femi energy level of CdS is higher than that of Bi₂MoO₆. Figure 8When Bi₂MoO₆ and CdS are in uniform contact, interfacial electrons flow from CdS to Bi₂MoO₆, forming a built-in electric field at the interface. Under visible light irradiation, electrons in the conduction band of Bi₂MoO₆ transfer to the valence band of CdS under the influence of this built-in electric field, forming an S-type electron transfer mechanism. This helps improve the separation efficiency of photogenerated carriers and maintain the original high oxidizing and reducing properties. Figure 8 As can be seen from f, under the influence of the built-in electric field, photogenerated carriers form an S-type electron transfer mode, maintaining the original high oxidizing and reducing properties, thereby effectively improving photocatalytic activity.

[0079] from Figure 9 Electron paramagnetic resonance (EPR) tests of hydroxyl radicals and superoxide radicals can prove that hydroxyl radical and superoxide radical signals are present under light irradiation and increase with the duration of light irradiation. The charge carriers undergo S-type electron transfer. Otherwise, according to the traditional II-type electron transfer method, there would be no hydroxyl radical and superoxide radical signals under light irradiation.

[0080] In summary, this invention provides a method for preparing the S-type photocatalytic material Bi2MoO6 / CdS. A Bi(NO)3⋅5H2O ethylene glycol solution is dropwise added to a Na2MoO6⋅2H2O ethylene glycol solution. The mixture is then transferred to a 100ml Teflon autoclave, and 40 mL of ethanol is added, resulting in an ethylene glycol:ethanol volume ratio of 3:4. This creates specific micro-reaction conditions that facilitate the formation of Bi2MoO6 nanosheets and exhibit excellent degradation effects on Cr(VI). When the ethylene glycol:ethanol volume ratio is not 3:4, the effect is poor.

[0081] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing an S-type photocatalytic material Bi2MoO6 / CdS, characterized in that: include, Thioacetamide and Cd(CH3COO)2∙2H2O were dissolved in ethylene glycol and stirred until homogeneous. Ethanol was then added to obtain a mixture in which the ratio of thioacetamide, Cd(CH3COO)2∙2H2O, ethylene glycol and ethanol was 0.5638 g : 1 g : 30 mL : 40 mL. Bi2MoO6 was added to the mixture, and the mixture was ultrasonically mixed until homogeneous. The mixture underwent a solvothermal reaction, and the precipitate was collected after natural cooling. The precipitate was then washed and dried to obtain Bi2MoO6 / CdS. The theoretical mass ratio of Bi2MoO6 to CdS is 1:4, and the volume ratio of ethylene glycol to ethanol in the solvothermal reaction is 3:

4. The preparation method of Bi2MoO6 includes dissolving Bi(NO)3·5H2O in ethylene glycol to obtain a Bi(NO)3·5H2O ethylene glycol solution; Dissolve Na2MoO6⋅2H2O in ethylene glycol to prepare a Na2MoO6⋅2H2O ethylene glycol solution. A mixture was prepared by adding Bi(NO)3⋅5H2O ethylene glycol solution dropwise to Na2MoO6⋅2H2O ethylene glycol solution. The dropping rate of Bi(NO)3⋅5H2O ethylene glycol solution was 1 mL / min. Ethanol was added to the mixture, and the mixture was heated at 160°C for 12 h. The product was then dried to obtain Bi2MoO6, wherein the volume ratio of ethylene glycol to ethanol in the mixture was 3:

4. The solvothermal reaction was carried out at a temperature of 180°C for 12 hours.

2. The preparation method according to claim 1, characterized in that: The ratio of Bi(NO)3⋅5H2O to ethylene glycol in the Bi(NO)3⋅5H2O ethylene glycol solution is 0.9702 g: 15 mL.

3. The preparation method according to claim 1 or 2, characterized in that: The ratio of the Na2MoO6⋅2H2O ethylene glycol solution is 0.2425 g: 15 mL.

4. The preparation method according to claim 3, characterized in that: The ratio of Bi(NO)3⋅5H2O to Na2MoO6⋅2H2O in the mixture is 0.9702 g: 0.2425 g.

5. The S-type photocatalytic material Bi2MoO6 / CdS prepared by any of the preparation methods described in claims 1 to 4.

6. The application of the S-type photocatalytic material Bi2MoO6 / CdS as described in claim 5 in the photocatalytic degradation of Cr(VI) in wastewater, characterized in that: include, 10 mg of photocatalytic material Bi2MoO6 / CdS was suspended in 50 mL of 20 mg / L Cr(VI). Before light exposure, the suspension was stirred in the dark for 1 h to reach adsorption-desorption equilibrium. After adsorption-desorption equilibrium is reached, turn on the light to irradiate the reaction for 16 min. The reaction conditions were as follows: irradiation with a 300 W xenon lamp at room temperature under visible light radiation.

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