Preparation methods and applications of cadmium sulfide-cobalt hydroxide-graphene photocatalysts

Abstract

This invention proposes a method for preparing and applying a cadmium sulfide-cobalt hydroxide-graphene photocatalyst. The method includes: first, preparing CdS nanocubes; then, sequentially adding a graphene oxide solution, CdS nanocubes, and cobalt nitrate hexahydrate to deionized water to obtain a mixed solution; finally, adding a solution containing trisodium citrate and hexamethylenetetramine to the mixed solution; and then sequentially subjecting the mixture to oil bath heating and freeze-drying to obtain a cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst. This invention introduces dual auxiliary catalysts, combining CdS with GR and Co(OH)2 cocatalysts in an appropriate manner to promote charge separation / transfer and inhibit photocorrosion, thereby improving the overall photocatalytic hydrogen production coupled with benzyl alcohol oxidation to benzaldehyde performance, and effectively enhancing the performance of CdS.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, and particularly to a method for preparing and applying a cadmium sulfide-cobalt hydroxide-graphene photocatalyst. Background Technology

[0002] The photocatalytic conversion of aromatic alcohols into various value-added products is of great significance in chemical synthesis. Benzaldehyde, one of the main oxidation products of aromatic alcohols, is widely used in the synthesis of various organic compounds, from pharmaceuticals to plastic additives. Traditional synthetic strategies employ a series of reagents and oxidants to achieve the coupling of benzyl alcohol, but these methods are time-consuming, have poor selectivity, and involve expensive / toxic reagents. Therefore, it is urgent to develop a photocatalytic method that is highly selective, environmentally friendly, low-cost, and fully utilizes electrons and holes for clean hydrogen fuels and high-value-added fine chemicals.

[0003] Cadmium sulfide has attracted widespread attention due to its relatively narrow band gap optical absorption properties and favorable band edge position, meeting the thermodynamic requirements of many mainstream photocatalytic reactions. However, due to the rapid recombination of photogenerated carriers, the instability of photocatalytic activity, and the lack of reactive sites, the photocatalytic activity of cadmium sulfide remains at a low conversion efficiency. Summary of the Invention

[0004] In view of the above, the main objective of this invention is to provide a method for preparing and applying a cadmium sulfide-cobalt hydroxide-graphene photocatalyst to solve the aforementioned technical problems.

[0005] This invention proposes a method for preparing a cadmium sulfide-cobalt hydroxide-graphene photocatalyst, wherein the method includes the following steps:

[0006] Step 1: Dissolve Cd(Ac)2·2H2O, polyvinylpyrrolidone, and C6H5Na3O7 in a first deionized water to obtain a first solution. Dissolve K3(Co(CN)6) in a second deionized water to obtain a second solution. Add the second solution dropwise to the first solution while stirring. After the dropwise addition is complete, stir for the first time. After stirring, perform an aging operation to obtain a suspension. Centrifuge the suspension to collect the product. Then, wash the obtained product for the first time to obtain the sample.

[0007] Step 2: Mix water and ethanol to obtain a first mixed solution. Disperse the sample into the first mixed solution to obtain a Cd-PBA cubic solution. Add Na2S solution to the Cd-PBA cubic solution to carry out the reaction. After the reaction is completed, centrifuge to collect the product. Then wash the obtained product a second time. After washing, vacuum dry to obtain CdS nanocubes.

[0008] Step 3: Add the graphene oxide solution to the third deionized water for the first ultrasonic dispersion to obtain the graphene oxide dispersion. Then add the CdS nanocubes to the graphene oxide dispersion for the second ultrasonic dispersion. After ultrasonic dispersion, add cobalt nitrate hexahydrate and stir for the second time to obtain the third solution. Add the second mixed solution containing trisodium citrate and hexamethylenetetramine to the third solution and stir for the third time to obtain the third mixed solution.

[0009] Step 4: Heat the third mixed solution in an oil bath and stir vigorously under constant temperature. After stirring, wait for the solution temperature to drop to room temperature, wash the collected solution with deionized water by centrifugation, and then freeze-dry it to finally obtain the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst.

[0010] This invention also proposes an application of a cadmium sulfide-cobalt hydroxide-graphene photocatalyst. The cadmium sulfide nanocubic block-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared by the above preparation method is used for liquid-phase visible light photocatalytic reduction of benzyl alcohol.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. Under mild reaction conditions, this invention significantly improves the yield of benzaldehyde and hydrogen, with a hydrogen production efficiency 6.6 times that of blank CdS and a benzaldehyde selectivity of up to 99.6%. The method is simple to operate and has broad application prospects.

[0013] 2. This invention introduces a dual auxiliary catalyst, combining CdS with GR and Co(OH)2 co-catalysts in an appropriate manner to promote charge separation / transfer and inhibit photocorrosion, thereby helping to improve the overall catalytic performance and effectively enhancing the performance of CdS.

[0014] 3. The highly selective cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared by this invention has a more obvious catalytic effect. It can selectively convert benzyl alcohol into benzaldehyde through photocatalysis and couple to generate hydrogen, providing a sustainable way to obtain high-value benzaldehyde. It also has the advantages of low preparation cost, environmental friendliness, and full utilization of electrons and holes.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments of the invention. Attached Figure Description

[0016] Figure 1This is a SEM image of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared in this invention.

[0017] Figure 2 XPS image of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared in this invention;

[0018] Figure 3 XRD patterns of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared in this invention before and after photocatalytic reaction.

[0019] Figure 4 This is a comparison diagram of the photocatalytic hydrogen production activities of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared in this invention, compared with those of cadmium sulfide cubes, cadmium sulfide graphene, and cadmium sulfide cobalt hydroxide. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0022] Example 1

[0023] Please see Figures 1 to 2 The specific preparation methods include:

[0024] Step 1: Dissolve 0.1156g of Cd(Ac)2·2H2O, 0.8248g of polyvinylpyrrolidone, and 0.0854g of C6H5Na3O7 in 30mL of first deionized water to obtain the first solution. Dissolve 0.13g of K3(Co(CN)6) in 30mL of second deionized water to obtain the second solution. Add the second solution dropwise to the first solution while stirring. After the dropwise addition is complete, stir for the first time for 30min. After stirring, age for 1h to obtain a suspension. Centrifuge the suspension to collect the product. Wash the obtained product with ethanol for the first time. After washing 3 times, obtain the sample.

[0025] Step 2: Mix 50 mL of water and 50 mL of ethanol to obtain a first mixed solution. Disperse the sample into the first mixed solution to obtain a Cd-PBA (Cd Prussian blue analogue) cubic solution. Add 20 mL / 90 mM Na2S solution to the Cd-PBA cubic solution to react. After reacting for 2 h, centrifuge to collect the product. Then wash the obtained product a second time with ethanol. After washing 3 times, vacuum dry at 60 °C for 12 h to obtain CdS (cadmium sulfide) nanocubes.

[0026] Step 3: First, sonicate 4 ml of graphene oxide solution with a concentration of 2.5 mg / mL for 2 h. Then, add the graphene oxide (GO) solution to 50 mL of third deionized water for the first ultrasonic dispersion for 0.5 h to obtain the graphene oxide dispersion. Then, add CdS nanocubes to the graphene oxide dispersion for the second ultrasonic dispersion for 30 min. After ultrasonic dispersion, add 1.8 mmol of cobalt nitrate hexahydrate and stir for the second time for 30 min to obtain the third solution. Add 50 mL of the second mixed solution containing 0.19 mmol of trisodium citrate (C6H5O7Na3) and 1.8 mmol of hexamethylenetetramine (HMTA) to the third solution and stir for the third time with magnetic stirring for 1 h to obtain the third mixed solution.

[0027] Step 4: The third mixed solution is heated to 90°C in an oil bath and stirred vigorously for 10 hours under constant temperature conditions. After stirring, the solution temperature is allowed to drop to room temperature. The collected solution is centrifuged and washed three times with deionized water and then freeze-dried to finally obtain CdS-Co(OH)2-GR, namely cadmium sulfide nanocubic blocks-cobalt hydroxide nanosheet array-graphene composite photocatalyst (CCG).

[0028] Example 2

[0029] Please see Figures 1 to 2 This embodiment provides a method for preparing a cadmium sulfide-cobalt hydroxide-graphene photocatalyst, the method comprising the following steps:

[0030] Step 1: Dissolve 0.1383g of Cd(Ac)2·2H2O, 1.00g of polyvinylpyrrolidone (PVP), and 0.10g of C6H5Na3O7 in 30mL of first deionized water to obtain the first solution. Dissolve 0.13g of K3(Co(CN)6) in 30mL of second deionized water to obtain the second solution. Add the second solution dropwise to the first solution while stirring. After the dropwise addition is complete, stir for the first time for 30min. After stirring, age for 1h to obtain a suspension. Centrifuge the suspension to collect the product. Wash the obtained product with ethanol for the first time. After washing 3 times, obtain the sample.

[0031] Step 2: Mix 50 mL of water and 50 mL of ethanol to obtain a first mixed solution. Disperse the sample into the first mixed solution to obtain a Cd-PBA (Cd Prussian blue analogue) cubic solution. Add 20 mL / 100 mM Na2S solution to the Cd-PBA cubic solution to react. After reacting for 2 h, centrifuge to collect the product. Then wash the obtained product a second time with ethanol. After washing 3 times, vacuum dry at 60 °C for 12 h to obtain CdS (cadmium sulfide) nanocubes.

[0032] Step 3: First, sonicate 4 ml of graphene oxide solution with a concentration of 3 mg / mL for 2 h. Then, add 50 mL of deionized water to the graphene oxide (GO) solution for the first ultrasonic dispersion for 0.5 h, and then add CdS nanocubes to the graphene oxide dispersion for the second ultrasonic dispersion for 30 min. After ultrasonic dispersion, add 2.5 mmol of cobalt nitrate hexahydrate and stir for the second time for 30 min to obtain the third solution. Add 50 mL of the second mixed solution containing 0.25 mmol of trisodium citrate (C6H5O7Na3) and 2.5 mmol of hexamethylenetetramine (HMTA) to the third solution and stir for the third time with magnetic stirring for 1 h to obtain the third mixed solution.

[0033] Step 4: The third mixed solution is heated to 90°C in an oil bath and stirred vigorously for 10 hours under constant temperature conditions. After stirring, the solution temperature is allowed to drop to room temperature. The collected solution is washed three times by centrifugation with deionized water and then freeze-dried to finally obtain CdS-Co(OH)2-GR, namely cadmium sulfide nanocubic blocks-cobalt hydroxide nanosheet array-graphene composite photocatalyst.

[0034] Example 3

[0035] Please see Figures 1 to 2 Step 1: Dissolve 0.1532g of Cd(Ac)2·2H2O, 1.1054g of polyvinylpyrrolidone (PVP), and 0.1312g of C6H5Na3O7 in 30mL of first deionized water to obtain the first solution. Dissolve 0.13g of K3(Co(CN)6) in 30mL of second deionized water to obtain the second solution. Add the second solution dropwise to the first solution while stirring. After the dropwise addition is complete, stir for the first time for 30min. After stirring, age for 1h to obtain a suspension. Centrifuge the suspension to collect the product. Then wash the obtained product with ethanol for the first time. After washing 3 times, obtain the sample.

[0036] Step 2: Mix 50 mL of water and 50 mL of ethanol to obtain a first mixed solution. Disperse the sample into the first mixed solution to obtain a Cd-PBA (Cd Prussian blue analogue) cubic solution. Add 20 mL / 110 mM Na2S solution to the Cd-PBA cubic solution to react. After reacting for 2 h, centrifuge to collect the product. Then wash the obtained product a second time with ethanol. After washing 3 times, vacuum dry at 60 °C for 12 h to obtain CdS (cadmium sulfide) nanocubes.

[0037] Step 3: First, sonicate 4 ml of graphene oxide solution with a concentration of 4 mg / mL for 2 h. Then, add 50 mL of deionized water to the graphene oxide (GO) solution for the first ultrasonic dispersion for 0.5 h, and then add CdS nanocubes to the graphene oxide dispersion for the second ultrasonic dispersion for 30 min. After ultrasonic dispersion, add 3.1 mmol of cobalt nitrate hexahydrate and stir for the second time for 30 min to obtain the third solution. Add 50 mL of the second mixed solution containing 0.33 mmol of trisodium citrate (C6H5O7Na3) and 3.3 mmol of hexamethylenetetramine (HMTA) to the third solution and stir for the third time with magnetic stirring for 1 h to obtain the third mixed solution.

[0038] Step 4: The third mixed solution is heated to 90°C in an oil bath and stirred vigorously for 10 hours under constant temperature conditions. After stirring, the solution temperature is allowed to drop to room temperature. The collected solution is washed three times by centrifugation with deionized water and then freeze-dried to finally obtain CdS-Co(OH)2-GR, namely cadmium sulfide nanocubic blocks-cobalt hydroxide nanosheet array-graphene composite photocatalyst.

[0039] from Figure 1 Observations revealed that the prepared CdS-Co(OH)2-GR sample had a cubic nanosheet array structure, which proved that graphene coating on the cadmium sulfide surface could provide growth sites for the cobalt hydroxide nanosheet array structure, further promoting the construction of the nanosheet array structure.

[0040] Figure 2 The XPS spectrum of CdS-Co(OH)2-GR prepared in this invention is shown in the figure. (a) Full spectrum; (b) C1s; (c) Cd3d; (d) Co 2p; (e) S2p; (f) O1s. The chemical elemental composition and valence state of CdS-Co(OH)2-GR were measured by X-ray photoelectron spectroscopy (XPS). In the Cd 3d spectrum of the ternary CdS-Co(OH)2-GR, the two peaks at 405.0 eV and 411.8 eV belong to Cd 3d5 / 2 and Cd 3d, respectively. 3 / 2This indicates that it exists in the form of a +2 valence. Figure 2 In the Co 2p spectrum of (d), Co 2p 3 / 2 and Co2p 1 / 2 The binding energies were 781.8 eV and 797.6 eV, respectively, indicating the presence of Co in the ternary sample. 2+ Furthermore, two peaks at 786.6 eV and 803.1 eV correspond to Co 2p ions. 3 / 2 and Co 2p 1 / 2 The satellite peaks are related. For the S2p XPS spectrum, the S2p peak at 161.3 eV is... 3 / 2 and S2p at 163.2 eV 1 / 2 The binding energy can be attributed to S in CdS 2- .from Figure 2 (f) The 1s spectrum shows that the peak at 531.7 eV corresponds to the Co-OH bond in the composite material, while the peak at 533.5 eV is due to the presence of H2O molecules adsorbed on the sample surface.

[0041] Example 4

[0042] Please see Figure 3 This embodiment provides an application of a cadmium sulfide-cobalt hydroxide-graphene photocatalyst. The cadmium sulfide nanocubic block-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared by the above preparation method is used for liquid phase visible light photocatalytic reduction of benzyl alcohol.

[0043] Photocatalysis mainly involves the selective conversion of benzyl alcohol into benzaldehyde under visible light irradiation, using benzyl alcohol as the reaction solution, and the subsequent coupling to produce hydrogen gas. The specific steps are as follows:

[0044] Photocatalytic oxidation of benzyl alcohol was performed under 2 hours of 420 nm xenon lamp irradiation. The benzyl alcohol-coupled hydrogen production reaction was carried out in a 50 mL sealed quartz reactor. 5 mg of catalyst was added to the quartz reactor containing 10 mL of benzyl alcohol solution. Before the reaction, high-purity Ar gas was introduced for 30 minutes in a dark environment to purge residual air from the reactor and ensure the reaction was conducted under Ar gas conditions. A 300 W 420 nm xenon lamp was used as the light source. After 2 hours of irradiation, 1 mL of gas was extracted and analyzed by gas chromatography (thermal conductivity detector TCD) to obtain the hydrogen production. Simultaneously, after the reaction, the solid catalyst was filtered out using a 0.22 μm filter membrane, and the concentration changes of benzyl alcohol and benzaldehyde solutions during the reaction were analyzed by high-performance liquid chromatography (HPLC).

[0045] from Figure 3As can be seen, the XRD results of CdS-Co(OH)2-GR before the reaction are the same as those after the reaction, and there is no change in the phase structure. This indicates that CdS-Co(OH)2-GR has good stability in the benzyl alcohol coupled hydrogen production reaction.

[0046] Please see Figure 4 To verify the effectiveness of the present invention, the photocatalytic performance of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst prepared in Example 2 of the present invention was compared with that of cadmium sulfide (CdS) cubes, cadmium sulfide graphene (CG), and cadmium sulfide cobalt hydroxide (CC).

[0047] Based on the aforementioned photocatalytic process, the catalyst was placed in an aqueous solution of benzyl alcohol under visible light irradiation. The photocatalytic activity of the catalyst was investigated through experiments on the selective oxidation of benzaldehyde by benzyl alcohol coupled with hydrogen production. The liquid product benzaldehyde was detected by high-performance liquid chromatography (HPLC), and the gaseous product H2 was detected by gas chromatography (GC). Figure 4 (a) is a graph showing the hydrogen production activity of cadmium sulfide cubes, cadmium sulfide graphene, cadmium sulfide cobalt hydroxide, and CCG. It can be observed from the graph that the hydrogen production activity of the unary catalyst cadmium sulfide cubes is lower than that of the binary and ternary catalysts. Furthermore, the hydrogen production efficiency of the ternary catalyst CdS-Co(OH)2-GR reaches 3180 μmol / g / h, which is 6.6 times that of the unary catalyst cadmium sulfide cubes. Figure 4 (b) is a graph showing the conversion rates of benzyl alcohol in cadmium sulfide cubes, cadmium sulfide graphene, cadmium sulfide cobalt hydroxide, and CdS-Co(OH)2-GR. The graph shows that the conversion rate of benzyl alcohol in CdS-Co(OH)2-GR reaches 71%, which is significantly higher than that of mono- and binary materials.

[0048] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. Use of a cadmium sulfide-cobalt hydroxide-graphene photocatalyst, characterized in that, The cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst is used in the simultaneous photocatalytic hydrogen production and benzaldehyde preparation reaction by oxidation of benzyl alcohol. The preparation process of the cadmium sulfide nanocubic block-cobalt hydroxide nanosheet array-graphene composite photocatalyst is as follows: Step 1: Dissolve Cd(Ac)2·2H2O, polyvinylpyrrolidone, and C6H5Na3O7 in a first deionized water to obtain a first solution. Dissolve K3(Co(CN)6) in a second deionized water to obtain a second solution. Add the second solution dropwise to the first solution while stirring. After the dropwise addition is complete, stir for the first time. After stirring, perform an aging operation to obtain a suspension. Centrifuge the suspension to collect the product. Then, wash the obtained product for the first time to obtain the sample. Step 2: Mix water and ethanol to obtain a first mixed solution. Disperse the sample into the first mixed solution to obtain a Cd-PBA cubic solution. Add Na2S solution to the Cd-PBA cubic solution to carry out the reaction. After the reaction is completed, centrifuge to collect the product. Then wash the obtained product a second time. After washing, vacuum dry to obtain CdS nanocubes. Step 3: Add the graphene oxide solution to the third deionized water for the first ultrasonic dispersion to obtain the graphene oxide dispersion. Then add the CdS nanocubes to the graphene oxide dispersion for the second ultrasonic dispersion. After ultrasonic dispersion, add cobalt nitrate hexahydrate and stir for the second time to obtain the third solution. Add the second mixed solution containing trisodium citrate and hexamethylenetetramine to the third solution and stir for the third time to obtain the third mixed solution. Step 4: The third mixed solution is heated in an oil bath and stirred vigorously under constant temperature conditions. After stirring, the solution temperature is allowed to drop to room temperature. The collected solution is washed by centrifugation with deionized water and then freeze-dried to finally obtain the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst. In this process, graphene is wrapped on the surface of cadmium sulfide to provide growth sites, and cobalt hydroxide is grown on the surface of cadmium sulfide in the form of a nanosheet array. Under visible light irradiation, a cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst was placed in a benzyl alcohol aqueous solution. During the selective oxidation of benzaldehyde by benzyl alcohol coupled with hydrogen production, the following process was observed: The hydrogen production efficiency of the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst reached 3180 μmol / g / h, which is 6.6 times that of the unary catalyst cadmium sulfide cubic hydrogen production activity. The conversion rate of benzyl alcohol in the cadmium sulfide nanocube-cobalt hydroxide nanosheet array-graphene composite photocatalyst reached 71%.

2. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 1, characterized in that, In step 1, the mass of Cd(Ac)2·2H2O is 0.1156~0.1532 g, the mass of polyvinylpyrrolidone is 0.8248~1.1054 g, the mass of C6H5Na3O7 is 0.0854~0.1312 g, and the preset volume of the first deionized water is 30 mL.

3. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 2, characterized in that, In step 1, the first stirring time is 30 minutes, the aging time is 1 hour, the first washing is done with ethanol, and the washing is performed 3 times.

4. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 2, characterized in that, In step 2, the mixed solution of water and ethanol is obtained by mixing 50 mL of water and 50 mL of ethanol, the amount of Na2S solution added is 20 mL / 90~110 mM, and the reaction time is 2 h.

5. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 2, characterized in that, In step 2, the second washing is performed with ethanol, and the washing is repeated 3 times. The vacuum drying temperature is 60°C, and the drying time is 12 hours.

6. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 5, characterized in that, In step 3, the graphene oxide solution is first sonicated for 2 h, and then the graphene oxide (GO) solution is added to 50 mL of third deionized water for the first ultrasonic dispersion.

7. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 6, characterized in that, In step 3, the concentration of graphene oxide solution is 2.5~4 mg / mL, the amount added is 4 ml, the first ultrasonic dispersion time is 0.5 h, the second ultrasonic dispersion time is 30 min, the amount of cobalt nitrate hexahydrate added is 1.8~3.1 mmol, and the second stirring time is 30 min.

8. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 7, characterized in that, In step 3, the volume of the second mixed solution is 50 mL, the content of trisodium citrate is 0.19~0.33 mmol, the content of hexamethylenetetramine is 1.8~3.3 mmol, and the third stirring is carried out by magnetic stirring for 1 h.

9. The application of the cadmium sulfide-cobalt hydroxide-graphene photocatalyst according to claim 7, characterized in that, In step 4, the deionized water is centrifuged and washed 3 times, the oil bath temperature is 90℃, and the vigorous stirring time is 10 h under constant temperature conditions.

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