Preparation method and application of ZIF-8 coated heterojunction photocatalyst

Abstract

The invention relates to the technical field of photocatalysis, in particular to a preparation method and application of a ZIF-8 wrapped heterojunction photocatalyst, cadmium nitrate tetrahydrate, thiourea, ethidene diamine and potassium permanganate are used as raw materials, and a sulfur-manganese-cadmium solid solution is prepared by a hydrothermal method; adding the linear catalyst into a zinc nitrate and dimethylimidazole methanol solution through a low-temperature in-situ growth method; the preparation method has the advantages that the prepared ZIF-8 coated MnxCd1-xS heterojunction photocatalyst has a larger specific surface area, and potential difference can exist between the two materials due to the difference of energy bands, so that an interface electric field is constructed, the purpose of accelerating the carrier migration rate is achieved, the service life of carriers is further prolonged, and the photocatalytic activity is improved. And the whole preparation process has no special requirements on equipment, has extremely high yield, is simple to operate, easy to control and good in repeatability, and is beneficial to industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to a preparation method and application of a ZIF-8 wrapped heterojunction photocatalyst. Background Art

[0002] As a green, environmentally friendly and sustainable energy conversion technology, photocatalysis has received extensive attention in the field of energy and environment in recent years. Among them, n-type semiconductor CdS, as a typical narrow-bandgap semiconductor, has shown great application potential in the field of photocatalytic water splitting due to its excellent photochemical properties and high quantum efficiency. The conduction band and valence band of CdS span the hydrolysis site, providing a good potential range for photocatalytic water separation, enabling it to effectively absorb sunlight and generate photogenerated electrons and holes, thereby driving the water splitting reaction.

[0003] However, despite the many advantages mentioned above, CdS still faces some challenges in its practical application. First, the photoelectron migration rate of CdS is relatively slow, which limits the improvement of its photocatalytic efficiency. Secondly, CdS is prone to severe photocorrosion during the photocatalytic process, resulting in insufficient stability of the catalyst and difficulty in maintaining efficient catalytic activity for a long time. These problems have seriously hindered the large-scale application of CdS in the field of photocatalysis. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method and application of a ZIF-8 wrapped heterojunction photocatalyst, which solves the problems of slow photoelectron migration rate and insufficient stability caused by severe photocorrosion of CdS photocatalyst.

[0005] To achieve the above object, the present invention provides a method for preparing a ZIF-8-wrapped heterojunction photocatalyst and its application, comprising the following steps:

[0006] placing cadmium nitrate tetrahydrate and thiourea in ethylenediamine and dispersing them by magnetic stirring to obtain a first mixed solution, adding potassium permanganate aqueous solution to the first mixed solution, and dispersing them by magnetic stirring to obtain a second mixed solution;

[0007] The second mixed solution is transferred to a hydrothermal reactor for reaction to obtain a first reaction product, and the first reaction product is allowed to stand, then centrifuged, washed, and dried to obtain a sulfur-manganese-cadmium solid solution;

[0008] Zinc nitrate hexahydrate and dimethylimidazole are placed in methanol and dispersed and reacted by magnetic stirring to obtain a reaction solution;

[0009] The sulfur-manganese-cadmium solid solution is added to the reaction solution to react to obtain a second reaction product. The second reaction product is allowed to stand, centrifuged, washed, and dried to obtain ZIF-8 encapsulated Mnx Cd 1-x S heterojunction photocatalyst.

[0010] Among them, in “putting cadmium nitrate tetrahydrate and thiourea in ethylenediamine and dispersing them by magnetic stirring to obtain a first mixed solution, adding potassium permanganate aqueous solution to the first mixed solution, and dispersing them by magnetic stirring to obtain a second mixed solution”, the method further includes:

[0011] The mass of cadmium nitrate tetrahydrate is 0.4-0.6 g, the mass of thiourea is 0.2-0.4 g, the amount of ethylenediamine is 5-15 mL, the concentration of potassium permanganate aqueous solution is 20-30 mg / mL, the amount is 1-3 mL, and the stirring time is 5-30 min.

[0012] Wherein, in “transferring the second mixed solution to a hydrothermal reactor for reaction to obtain a first reaction product”, the method further comprises:

[0013] The reaction temperature in the hydrothermal reactor is 140°C-200°C, and the reaction time is 36-48h.

[0014] Among them, in “placing zinc nitrate hexahydrate and dimethylimidazole in methanol, stirring and dispersing them under magnetic force, and reacting them to obtain a reaction solution”, the method further includes:

[0015] The mass of zinc nitrate hexahydrate is 0.2-0.4 g, the mass of dimethylimidazole is 0.1-0.2 g, the amount of methanol is 20-40 mL, and the reaction time is 0.5-1.5 h.

[0016] Wherein, in “adding the sulfur-manganese-cadmium solid solution to the reaction solution to react and obtain a second reaction product”, the method further includes:

[0017] The dosage of sulfur, manganese and cadmium is 20-70 mg, the temperature is -15°C, and the reaction time is 0.5-1.5 h.

[0018] The ZIF-8 prepared in the present invention encapsulates Mn x Cd 1-x S heterojunction photocatalysts can be applied to photocatalytic hydrogen production.

[0019] The invention discloses a preparation method and application of a ZIF-8 wrapped heterojunction photocatalyst, wherein tetrahydrated cadmium nitrate, thiourea, ethylenediamine and potassium permanganate are used as raw materials, and a sulfur-manganese-cadmium solid solution is prepared by a hydrothermal method; the linear catalyst is added to a zinc nitrate and dimethylimidazole methanol solution by a low-temperature in-situ growth method, and finally a ZIF-8 wrapped Mn x Cd 1- x The advantages of the present invention are that the prepared ZIF-8 wrapped Mn xCd 1-x S heterojunction photocatalyst has a larger specific surface area, and due to the difference in energy bands, there can be a potential difference between the two materials, thereby constructing an interfacial electric field to accelerate the carrier migration rate, further extend the carrier life, and improve the photocatalytic activity. In addition, the entire preparation process has no special requirements for equipment, has extremely high yield, simple operation, easy control, good repeatability, and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0021] Figure 1 The ZIF-8 encapsulated Mn prepared in the first embodiment of the present invention x Cd 1-x X-ray diffraction pattern of S heterojunction photocatalyst.

[0022] Figure 2 The ZIF-8 encapsulated Mn prepared in the first embodiment of the present invention x Cd 1-x Scanning electron microscope image of S heterojunction photocatalyst.

[0023] Figure 3 The ZIF-8 encapsulated Mn prepared in the first embodiment of the present invention x Cd 1-x Solid UV diffuse reflectance image of S heterojunction photocatalyst.

[0024] Figure 4 The ZIF-8 encapsulated Mn prepared in the first embodiment of the present invention x Cd 1-x Electrochemical impedance spectroscopy of S heterojunction photocatalyst.

[0025] Figure 5 The ZIF-8 encapsulated Mn prepared in the first embodiment of the present invention x Cd 1-x Schematic diagram of hydrogen production activity of S heterojunction photocatalyst.

[0026] Figure 6 It is a flow chart of the preparation method of the ZIF-8 wrapped heterojunction photocatalyst according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0028] First embodiment:

[0029] See also Figures 1 to 6 ,in Figure 1 The prepared ZIF-8 encapsulated Mn x Cd 1-x X-ray diffraction pattern of S heterojunction photocatalyst, Figure 2 The prepared ZIF-8 encapsulated Mn x Cd 1-x SEM image of S heterojunction photocatalyst. Figure 3 The prepared ZIF-8 encapsulated Mn x Cd 1-x Solid UV diffuse reflectance image of S heterojunction photocatalyst, Figure 4 The prepared ZIF-8 encapsulated Mn x Cd 1-x Electrochemical impedance spectroscopy of S heterojunction photocatalyst, Figure 5 The prepared ZIF-8 encapsulated Mn x Cd 1-x The hydrogen production activity diagram of S heterojunction photocatalyst, Figure 6 It is a flow chart of the preparation method of ZIF-8 wrapped heterojunction photocatalyst.

[0030] The present invention provides a method for preparing a ZIF-8 wrapped heterojunction photocatalyst, comprising the following steps:

[0031] S101: placing cadmium nitrate tetrahydrate and thiourea in ethylenediamine and dispersing them by magnetic stirring to obtain a first mixed solution, adding potassium permanganate aqueous solution to the first mixed solution, and dispersing them by magnetic stirring to obtain a second mixed solution.

[0032] Specifically: 0.5 g of cadmium nitrate tetrahydrate and 0.4 g of thiourea were placed in 10 mL of ethylenediamine, and dispersed by magnetic stirring at 25° C. for 10 min to obtain a first mixed solution, and then 2.1 mL of 30 mg / mL potassium permanganate solution was added to the first mixed solution, and magnetic stirring was performed at 25° C. for 10 min to obtain a second mixed solution.

[0033] S102: transferring the second mixed solution to a hydrothermal reactor for reaction to obtain a first reaction product, allowing the first reaction product to stand, then centrifugally separating, washing, and drying to obtain a sulfur-manganese-cadmium solid solution.

[0034] Specifically: the second mixed solution was transferred to a 25 mL hydrothermal reactor, placed in a constant temperature oven, and reacted at 160° C. for 48 h; then the reactor was cooled to 25° C., and the obtained precipitate (the first reaction product) was washed alternately with deionized water and ethanol for 3 times, and dried to obtain the Mn x Cd 1-xS sample (sulfur, manganese and cadmium solid solution).

[0035] S103: zinc nitrate hexahydrate and dimethylimidazole are placed in methanol, dispersed and reacted by magnetic stirring to obtain a reaction solution.

[0036] Specifically: 0.3 g of zinc nitrate hexahydrate (named as solution A) and 0.16 g of dimethylimidazole (named as solution B) were respectively placed in 15 mL of methanol, dispersed by magnetic stirring at 25° C., and after complete dissolution, solution B was added to solution A, and the mixture was reacted at 25° C. for 1 hour to obtain the reaction solution.

[0037] S104: adding the sulfur-manganese-cadmium solid solution to the reaction solution to react, obtaining a second reaction product, and centrifuging, washing, and drying the second reaction product to obtain ZIF-8 encapsulated Mn x Cd 1-x S heterojunction photocatalyst.

[0038] Specifically: 50 mg of the Mn x Cd 1-x S sample (sulfur manganese cadmium solid solution) was added to the mixed solution and reacted at -15°C for 1 hour to obtain a second reaction product; the second reaction product was washed with methanol three times and finally dried at 60°C to obtain the ZIF-8 encapsulated Mn x Cd 1-x S photocatalyst.

[0039] For further information, see Figure 1 , the figure shows that ZIF-8 encapsulates Mn x Cd 1-x The S heterojunction photocatalyst did not change, but compared with the characteristic diffraction peaks of MCS, ZIF-8 encapsulated Mn x Cd 1-x The characteristic diffraction peak intensity of S heterojunction photocatalyst is weak. And because the content of ZIF-8 is low, there is no characteristic peak corresponding to ZIF-8 in the X-ray diffraction diagram.

[0040] For further information, see Figure 2 , the figure shows that the prepared sample is a nanowire with a relatively rough surface.

[0041] For further information, see Figure 3 , the figure shows that ZIF-8 encapsulates Mn x Cd 1-x The S heterojunction photocatalyst image has a slight red shift.

[0042] For further information, see Figure 4 , compared to Mn x Cd 1-xS, ZIF-8 wrapped Mn x Cd 1-x The electron transfer rate of S heterojunction photocatalyst is greatly improved.

[0043] For further information, see Figure 5 , the figure shows that compared with Mn x Cd 1-x S, ZIF-8 wrapped Mn x Cd 1-x The hydrogen production capacity of the S heterojunction photocatalyst was significantly improved. After 5 hours of illumination, the photocatalytic hydrogen production reached 11.78mmol g-1h-1, achieving efficient hydrogen production.

[0044] The present invention provides a method for preparing a ZIF-8 wrapped heterojunction photocatalyst. The method firstly obtains nanowires with regular morphology by a hydrothermal method, and then obtains a ZIF-8 supported sulfur-manganese-cadmium heterojunction by low-temperature in-situ growth. x Cd 1-x The physical and chemical properties of S itself and the high specific surface area of ​​ZIF-8 can expose more active sites.

[0045] The present invention has the following beneficial effects:

[0046] 1. Due to the introduction of ZIF-8 into the inventive material, the specific surface area of ​​the material finally prepared is increased, and more active sites can be exposed.

[0047] 2. The preparation method of the inventive material has no special requirements for equipment, has high output, is simple to operate, easy to control, has good repeatability, and is conducive to large-scale industrial production.

[0048] Second embodiment:

[0049] The prepared ZIF-8 encapsulated Mn x Cd 1-x S heterojunction photocatalysts are used for photocatalytic hydrogen production.

[0050] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A method for preparing a ZIF-8-wrapped heterojunction photocatalyst, characterized in that: The following steps are involved: placing cadmium nitrate tetrahydrate and thiourea in ethylenediamine and dispersing them by magnetic stirring to obtain a first mixed solution, adding potassium permanganate aqueous solution to the first mixed solution, and dispersing them by magnetic stirring to obtain a second mixed solution; The second mixed solution is transferred to a hydrothermal reactor for reaction to obtain a first reaction product, and the first reaction product is allowed to stand, then centrifuged, washed, and dried to obtain a sulfur-manganese-cadmium solid solution; Zinc nitrate hexahydrate and dimethylimidazole are placed in methanol and dispersed and reacted by magnetic stirring to obtain a reaction solution; The sulfur-manganese-cadmium solid solution is added to the reaction solution to react to obtain a second reaction product. The second reaction product is allowed to stand, centrifuged, washed, and dried to obtain ZIF-8 encapsulated Mn x Cd 1-x S heterojunction photocatalyst.

2. The method for preparing a ZIF-8-wrapped heterojunction photocatalyst according to claim 1, characterized in that: In "putting cadmium nitrate tetrahydrate and thiourea in ethylenediamine and dispersing them by magnetic stirring to obtain a first mixed solution, adding potassium permanganate aqueous solution to the first mixed solution, and dispersing them by magnetic stirring to obtain a second mixed solution", the method further includes: The mass of cadmium nitrate tetrahydrate is 0.4-0.6 g, the mass of thiourea is 0.2-0.4 g, the amount of ethylenediamine is 5-15 mL, the concentration of potassium permanganate aqueous solution is 20-30 mg / mL, the amount is 1-3 mL, and the stirring time is 5-30 min.

3. The method for preparing a ZIF-8-wrapped heterojunction photocatalyst according to claim 1, characterized in that: In "transferring the second mixed solution to a hydrothermal reactor for reaction to obtain a first reaction product", the method further includes: The reaction temperature in the hydrothermal reactor is 140°C-200°C, and the reaction time is 36-48h.

4. The method for preparing a ZIF-8-wrapped heterojunction photocatalyst according to claim 1, characterized in that: In "placing zinc nitrate hexahydrate and dimethylimidazole in methanol, dispersing them with magnetic stirring and reacting them to obtain a reaction solution", the method further includes: The mass of zinc nitrate hexahydrate is 0.2-0.4 g, the mass of dimethylimidazole is 0.1-0.2 g, the amount of methanol is 20-40 mL, and the reaction time is 0.5-1.5 h.

5. The method for preparing a ZIF-8-wrapped heterojunction photocatalyst according to claim 1, characterized in that: In "adding the sulfur-manganese-cadmium solid solution to the reaction solution for reaction to obtain a second reaction product", the method further includes: The dosage of sulfur, manganese and cadmium is 20-70 mg, the temperature is -15°C, and the reaction time is 0.5-1.5 h.

6. ZIF-8 encapsulated Mn prepared by any one of the preparation methods of claims 1 to 5 x Cd 1-x S heterojunction photocatalyst, characterized in that Applied in photocatalytic hydrogen production.

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