Preparation method and application of sulfur cadmium zinc quantum dots / mesoporous silica composite photocatalyst

Abstract

The present invention belongs to the field of photocatalysis technology and discloses a preparation method and application of a sulfur-cadmium zinc quantum dot / mesoporous silica composite photocatalyst. The preparation steps are: (1) preparing mesoporous silica (mesop-SiO2); (2) preparing sulfur-cadmium zinc quantum dots (ZnCdS QDs); (3) MUA-modified sulfur-cadmium zinc quantum dots; (4) compounding the sulfur-cadmium zinc quantum dots and mesoporous silica in proportion to obtain a sulfur-cadmium zinc quantum dot / mesoporous silica (MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst. The sulfur-cadmium zinc quantum dot / mesoporous silica composite photocatalyst prepared by the present invention utilizes the advantages of mesoporous silica's high specific area to capture CO2 and the advantages of the sulfur-cadmium zinc quantum dots having a suitable energy band position to achieve efficient conversion of CO2. The present invention is simple to operate and effectively achieves the purpose of converting CO2 into renewable fuels.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalysis and relates to a preparation method and application of a sulfur-cadmium zinc quantum dot / mesoporous silica composite photocatalyst. Background Art

[0002] With the growth of the global population and rapid economic development, humanity's consumption of fossil fuels such as coal, oil, and natural gas has increased dramatically, causing serious environmental pollution and an energy crisis. Excessive greenhouse gas emissions are also contributing to global warming. Currently, global CO2 concentrations have reached 420 ppm, forcing the world to seek effective means of converting greenhouse gases like CO2 into renewable energy. Capturing CO2 and converting it into usable, high-value-added compounds has become an effective means of reducing CO2 concentrations. Among these, the main methods being developed include electrochemical catalysis, thermochemical catalysis, biocatalysis, and photochemical catalysis. Photochemical catalysis is widely used for CO2 conversion due to its high efficiency, environmental friendliness, simplicity, and low cost.

[0003] Researchers have found that zero-dimensional quantum dots (QDs) materials have been widely studied in the components of photocatalysts due to their special quantum size effect, electron transfer characteristics and effective absorption of visible light. Ternary ZnCdS has a high absorption coefficient, which creates good conditions for regulating optical properties from the ultraviolet to the visible light range, and can adjust the appropriate band gap range. In the field of photocatalytic reduction of CO2, ZnCdS QDs have shown high catalytic activity. However, due to the low porosity of the quantum dot surface, it is difficult to capture CO2 and reaction intermediates, which greatly limits the improvement of the catalytic performance of quantum dots. Therefore, the introduction of a catalyst carrier with a high specific surface area and the ability to efficiently capture CO2 is of positive significance for improving the catalytic activity of quantum dots in the photoreduction of CO2.

[0004] In recent years, mesoporous silica nanoparticles (mesop-SiO2) have become a research hotspot in the catalysis community due to their large open pore structure, high specific surface area, excellent solvent dispersibility, and good biocompatibility. These advantages have enabled mesoporous silica to achieve significant progress in the capture and catalytic conversion of CO2. However, mesoporous silica itself lacks photocatalytic activity and cannot convert CO2 into renewable fuels. Therefore, a strategy to achieve efficient CO2 photoreduction by combining zinc cadmium sulfate quantum dots (ZnCdS QDs) and mesoporous silica (mesop-SiO2) to form a composite photocatalyst is feasible. However, no relevant reports have been reported to date. Summary of the Invention

[0005] The present invention utilizes hydrothermal and hot injection methods to prepare a sulfur-cadmium zinc quantum dot / mesoporous silica composite photocatalyst, which is used for efficient photocatalytic conversion of CO2 to CO. The photocatalytic activity is greatly enhanced, and the composite photocatalyst has good practical application value. A method for preparing a sulfur-cadmium zinc quantum dot / mesoporous silica composite photocatalyst comprises the following steps:

[0006] (1) Preparation of mesoporous silica (mesop-SiO2)

[0007] Dissolve cetyltrimethylammonium bromide (CTAB) and butyraldehyde in water, pour into a sealed bottle, and stir at room temperature for 5-10 minutes. Quickly add ammonia water and stir for 30-60 minutes. Then add tetraethyl silicate (TEOS) and stir at room temperature for 12-24 hours. Centrifuge and dry the product, and finally calcine in air.

[0008] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0009] First, sulfur powder was added to octadecene ODE and heated under nitrogen until dissolved to prepare an S precursor. Then, cadmium oxide (CdO) and zinc acetate (Zn(OAc)2) were added to a mixture of octadecene ODE and oleic acid (OA) and heated under nitrogen until dissolved to prepare a ZnCd precursor. Finally, the S precursor was injected into the ZnCd precursor and cooled to room temperature. The resulting sulfur-cadmium zinc quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0010] (3) MUA-modified cadmium zinc sulfate quantum dots

[0011] Dissolve 11-mercaptoundecanoic acid MUA in methanol, and adjust the pH of the solution to 9-12 with tetramethylammonium hydroxide pentahydrate to obtain a MUA mixed solution;

[0012] Under dark conditions, the zinc cadmium sulfate quantum dots ZnCdS QDs obtained in step (2) were dispersed in the MUA mixture, and the container was placed under N2 flow. The mixture was heated under reflux at 60-80°C overnight, precipitated with ethyl acetate and diethyl ether, washed with acetone and dispersed in water, and recorded as MUA-ZnCdS QDs.

[0013] (4) Preparation of zinc cadmium sulfate quantum dots / mesoporous silica composite photocatalyst

[0014] The MUA-ZnCdS QDs obtained in step (3) and the mesoporous silica mesop-SiO2 obtained in step (1) are dispersed in deionized water, stirred in the dark for 12-24 hours, and a zinc cadmium sulfate quantum dot / mesoporous silica composite photocatalyst is obtained, which is recorded as MUA-ZnCdS QDs / mesop-SiO2.

[0015] In step (1), the usage ratio of cetyltrimethylammonium bromide, butyraldehyde, ammonia water and tetraethyl silicate is 0.64 g:15.0 mL:6.0 mL:2.8 mL; wherein the concentration of ammonia water is 25-28 wt %.

[0016] The calcination temperature is 550°C and the calcination time is 6 hours.

[0017] In step (2), the molar ratio of sulfur powder, CdO and Zn(OAc)2 is 2:1:1; in the mixture of octadecene ODE and oleic acid OA, the volume ratio of ODE:OA is 13:6;

[0018] In step (3), the mass ratio of MUA and ZnCdS QDs was 1:1;

[0019] In step (4), the mass ratio of MUA-ZnCdS QDs to mesoporous silica (mesop-SiO2) is 1:1.7-19.

[0020] The prepared zinc cadmium sulfate quantum dots / mesoporous silica (MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst is used for photocatalytic reduction of CO2 to CO.

[0021] The above technical analysis test method is specifically as follows:

[0022] (1) The photocatalytic performance of different photocatalysts was tested in a quartz glass reactor. The generated CO was analyzed using a gas chromatograph. The specific experimental steps are as follows: 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto quartz glass and then dried at 60 °C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 min to completely remove the air. During the reaction, a xenon lamp was used to pass through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0023] (2) The light source uses a light power density of 1000mW cm -2 300W Xe lamp. Analysis was performed every 60 minutes.

[0024] Technical advantages of the present invention

[0025] (1) The present invention synthesizes a photocatalytic composite material using a hydrothermal method and a hot injection method. This synthesis method results in a uniform distribution of mesoporous silica pores and highly dispersed quantum dots of uniform size. Furthermore, after the quantum dots undergo MUA ligand exchange, they possess surface groups with enhanced reactivity, allowing for uniform dispersion in aqueous solution and facilitating their composite formation with mesoporous silica.

[0026] (2) The photocatalytic composite material prepared by the present invention achieves efficient photoreduction of CO2, and the photocatalytic activity of the composite material reaches 898.6 μmol g -1 h -1 .

[0027] (3) The photocatalytic composite material prepared by the present invention has high catalytic stability and still has 91% catalytic activity after a 20-hour cycle test. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Nitrogen adsorption / desorption spectra (BET) of Examples 1-5;

[0029] Figure 2 This is a morphology characterization diagram of the composite photocatalyst obtained in Example 5;

[0030] Figure 3 This is a test diagram of the photocatalytic reduction of CO2 performance of the composite photocatalyst obtained in Examples 1-5;

[0031] Figure 4 This is a photocatalytic cycle test of the composite photocatalyst obtained in Example 5. DETAILED DESCRIPTION

[0032] The technology of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0033] Example 1

[0034] A method for preparing a composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (5% MUA-ZnCdS QDs / mesop-SiO2) comprises the following steps:

[0035] (1) Preparation of mesoporous silica (mesop-SiO2)

[0036] Combine 0.64 g of hexadecyltrimethylammonium bromide (CTAB), 12.0 mL of deionized water, and 15.0 mL of butyraldehyde in a sealed bottle and stir at 27°C for 5 minutes. Rapidly add 6.0 mL of aqueous ammonia (25-28 wt%) and stir for 30 minutes. Then add 2.8 mL of tetraethyl orthosilicate (TEOS) and stir at 27°C for 24 hours. The product is filtered, washed, dried at 100°C for 12 hours, and finally calcined in air at 550°C for 6 hours.

[0037] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0038] First, 0.51g of sulfur powder was added to 16ml of octadecene (ODE) and heated to 150°C under nitrogen until dissolved, preparing the sulfur precursor. Next, 0.256g of cadmium oxide (CdO) and 0.368g of zinc acetate (Zn(OAc)2) were added to a mixture of 13ml of octadecene (ODE) and 6ml of oleic acid (OA), and heated to 300°C under nitrogen until dissolved, preparing the zinc cadmium dextrose (ZnCd) precursor. Finally, 4ml of the sulfur precursor was injected into the ZnCd precursor for 10 minutes. After cooling to room temperature, the quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0039] (3) MUA-modified cadmium zinc sulfate quantum dots

[0040] 20 mg of 11-mercaptoundecanoic acid (MUA) was placed in a reaction vessel, 15 ml of methanol (11.85 g) was added, and the pH was adjusted to greater than 10 with tetramethylammonium hydroxide pentahydrate. In the dark, 20 mg of zinc cadmium sulfate quantum dots (ZnCdS QDs) were dispersed in the mixture, and the vessel was placed under a flow of nitrogen. The mixture was heated under reflux at 60°C overnight. The quantum dots were precipitated with ethyl acetate and diethyl ether, washed with acetone, and dispersed in water. These were designated MUA-ZnCdS QDs.

[0041] (4) Preparation of 5% MUA-ZnCdS QDs / mesoporous silica composite photocatalyst

[0042] 5 mg of zinc cadmium sulfate quantum dots (MUA-ZnCdS QDs) and 95 mg of mesoporous silica (mesop-SiO2) were dispersed in 10 ml of deionized water and stirred in the dark for 24 hours to obtain zinc cadmium sulfate quantum dots / mesoporous silica (5% MUA-ZnCdSQDs / mesop-SiO2) composite photocatalyst.

[0043] (5) Photocatalytic reduction of CO2 experiments were carried out on the composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (5% MUA-ZnCdS QDs / mesop-SiO2).

[0044] 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto a quartz glass and then dried at 60°C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 minutes to completely remove air. During the reaction, a xenon lamp was passed through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0045] Depend on Figure 1 The specific surface area is calculated to be 232.4m 2 g-1 .Depend on Figure 3 It can be seen that the CO production rate was measured to be 325.7 μmol g -1 h -1 .

[0046] Example 2

[0047] A method for preparing a composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (10% MUA-ZnCdS QDs / mesop-SiO2) comprises the following steps:

[0048] (1) Preparation of mesoporous silica (mesop-SiO2)

[0049] Combine 0.64 g of hexadecyltrimethylammonium bromide (CTAB), 12.0 mL of deionized water, and 15.0 mL of butyraldehyde in a sealed bottle and stir at 27°C for 5 minutes. Rapidly add 6.0 mL of aqueous ammonia (25-28 wt%) and stir for 30 minutes. Then add 2.8 mL of tetraethyl orthosilicate (TEOS) and stir at 27°C for 24 hours. The product is filtered, washed, dried at 100°C for 12 hours, and finally calcined in air at 550°C for 6 hours.

[0050] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0051] First, 0.51g of sulfur powder was added to 16ml of octadecene (ODE) and heated to 150°C under nitrogen until dissolved, preparing a sulfur precursor. Next, 0.256g of cadmium oxide (CdO) and 0.368g of zinc acetate (Zn(OAc)2) were added to a mixture of 13ml of octadecene (ODE) and 6ml of oleic acid (OA), and heated to 300°C under nitrogen until dissolved, preparing a zinc cadmium dextrose (ZnCd) precursor. Four milliliters of the sulfur precursor was injected into the ZnCd precursor for 10 minutes. After cooling to room temperature, the quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0052] (3) MUA-modified cadmium zinc sulfate quantum dots

[0053] 20 mg of 11-mercaptoundecanoic acid (MUA) was placed in a reaction vessel, 15 ml of methanol (11.85 g) was added, and the pH was adjusted to greater than 10 with tetramethylammonium hydroxide pentahydrate. In the dark, 20 mg of zinc cadmium sulfate quantum dots (ZnCdS QDs) were dispersed in the mixture, and the vessel was placed under a flow of nitrogen. The mixture was heated under reflux at 60°C overnight. The quantum dots were precipitated with ethyl acetate and diethyl ether, washed with acetone, and dispersed in water. These were designated MUA-ZnCdS QDs.

[0054] (4) Preparation of 10% MUA-ZnCdS QDs / mesoporous silica composite photocatalyst

[0055] 10 mg of zinc cadmium sulfate quantum dots (MUA-ZnCdS QDs) and 90 mg of mesoporous silica (mesop-SiO2) were dispersed in 10 ml of deionized water and stirred in the dark for 24 hours to obtain zinc cadmium sulfate quantum dots / mesoporous silica (10% MUA-ZnCdSQDs / mesop-SiO2) composite photocatalyst.

[0056] (5) Photocatalytic reduction of CO2 experiments were carried out on the composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (10% MUA-ZnCdS QDs / mesop-SiO2).

[0057] 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto a quartz glass and then dried at 60°C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 minutes to completely remove air. During the reaction, a xenon lamp was passed through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0058] Depend on Figure 1 The specific surface area calculated from b is 225m 2 g -1 ,Depend on Figure 3 The CO production rate was found to be 358.3 μmol g -1 h -1 .

[0059] Example 3

[0060] A method for preparing a composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (18% MUA-ZnCdS QDs / mesop-SiO2) comprises the following steps:

[0061] (1) Preparation of mesoporous silica (mesop-SiO2)

[0062] Combine 0.64 g of hexadecyltrimethylammonium bromide (CTAB), 12.0 mL of deionized water, and 15.0 mL of butyraldehyde in a sealed bottle and stir at 27°C for 5 minutes. Rapidly add 6.0 mL of aqueous ammonia (25-28 wt%) and stir for 30 minutes. Then add 2.8 mL of tetraethyl orthosilicate (TEOS) and stir at 27°C for 24 hours. The product is filtered, washed, dried at 100°C for 12 hours, and finally calcined in air at 550°C for 6 hours.

[0063] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0064] First, 0.51g of sulfur powder was added to 16ml of octadecene (ODE) and heated to 150°C under nitrogen until dissolved, preparing a sulfur precursor. Next, 0.256g of cadmium oxide (CdO) and 0.368g of zinc acetate (Zn(OAc)2) were added to a mixture of 13ml of octadecene (ODE) and 6ml of oleic acid (OA), and then heated to 300°C under nitrogen until dissolved. 4ml of the sulfur precursor was injected into the ZnCd precursor for 10 minutes. After cooling to room temperature, the quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0065] (3) MUA-modified cadmium zinc sulfate quantum dots

[0066] 20 mg of 11-mercaptoundecanoic acid (MUA) was placed in a reaction vessel, 15 ml of methanol (11.85 g) was added, and the pH was adjusted to greater than 10 with tetramethylammonium hydroxide pentahydrate. In the dark, 20 mg of zinc cadmium sulfate quantum dots (ZnCdS QDs) were dispersed in the mixture, and the vessel was placed under a flow of nitrogen. The mixture was heated under reflux at 60°C overnight. The quantum dots were precipitated with ethyl acetate and diethyl ether, washed with acetone, and dispersed in water. These were designated MUA-ZnCdS QDs.

[0067] (4) Preparation of zinc cadmium sulfate quantum dots / mesoporous silica (18% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst

[0068] 18 mg of zinc cadmium sulfate quantum dots (MUA-ZnCdS QDs) and 82 mg of mesoporous silica (mesop-SiO2) were dispersed in 10 ml of deionized water and stirred in the dark for 24 hours to obtain zinc cadmium sulfate quantum dots / mesoporous silica (18% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst.

[0069] (5) Photocatalytic reduction of CO2 experiments were carried out on the composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (18% MUA-ZnCdS QDs / mesop-SiO2).

[0070] 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto a quartz glass and then dried at 60°C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 minutes to completely remove air. During the reaction, a xenon lamp was passed through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0071] Depend on Figure 1The specific surface area calculated from c is 222.1m 2 g -1 ,Depend on Figure 3 The CO production rate was found to be 545.3 μmol g -1 h -1 .

[0072] Example 4

[0073] A method for preparing a composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (23% MUA-ZnCdS QDs / mesop-SiO2) comprises the following steps:

[0074] (1) Preparation of mesoporous silica (mesop-SiO2)

[0075] Combine 0.64 g of hexadecyltrimethylammonium bromide (CTAB), 12.0 mL of deionized water, and 15.0 mL of butyraldehyde in a sealed bottle and stir at 27°C for 5 minutes. Rapidly add 6.0 mL of aqueous ammonia (25-28 wt%) and stir for 30 minutes. Then add 2.8 mL of tetraethyl orthosilicate (TEOS) and stir at 27°C for 24 hours. The product is filtered, washed, dried at 100°C for 12 hours, and finally calcined in air at 550°C for 6 hours.

[0076] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0077] First, 0.51g of sulfur powder was added to 16ml of octadecene (ODE) and heated to 150°C under nitrogen until dissolved, preparing a sulfur precursor. Next, 0.256g of cadmium oxide (CdO) and 0.368g of zinc acetate (Zn(OAc)2) were added to a mixture of 13ml of octadecene (ODE) and 6ml of oleic acid (OA), and then heated to 300°C under nitrogen until dissolved. 4ml of the sulfur precursor was injected into the ZnCd precursor for 10 minutes. After cooling to room temperature, the quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0078] (3) MUA-modified cadmium zinc sulfate quantum dots

[0079] 20 mg of 11-mercaptoundecanoic acid (MUA) was placed in a reaction vessel, 15 ml of methanol (11.85 g) was added, and the pH was adjusted to greater than 10 with tetramethylammonium hydroxide pentahydrate. In the dark, 20 mg of zinc cadmium sulfate quantum dots (ZnCdS QDs) were dispersed in the mixture, and the vessel was placed under a flow of nitrogen. The mixture was heated under reflux at 60°C overnight. The quantum dots were precipitated with ethyl acetate and diethyl ether, washed with acetone, and dispersed in water. These were designated MUA-ZnCdS QDs.

[0080] (4) Preparation of zinc cadmium sulfate quantum dots / mesoporous silica (23% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst

[0081] 23 mg of zinc cadmium sulfate quantum dots (MUA-ZnCdS QDs) and 77 mg of mesoporous silica (mesop-SiO2) were dispersed in 10 ml of deionized water and stirred in the dark for 24 hours to obtain zinc cadmium sulfate quantum dots / mesoporous silica (23% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst.

[0082] (5) Photocatalytic reduction of CO2 experiments were carried out on the composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (23% MUA-ZnCdS QDs / mesop-SiO2).

[0083] 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto a quartz glass and then dried at 60°C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 minutes to completely remove air. During the reaction, a xenon lamp was passed through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0084] Depend on Figure 1 The specific surface area calculated from d is 201.8m 2 g -1 ,Depend on Figure 3 The CO production rate was found to be 723.9 μmol g -1 h -1 .

[0085] Example 5

[0086] A method for preparing a composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (37% MUA-ZnCdS QDs / mesop-SiO2) comprises the following steps:

[0087] (1) Preparation of mesoporous silica (mesop-SiO2)

[0088] Combine 0.64 g of hexadecyltrimethylammonium bromide (CTAB), 12.0 mL of deionized water, and 15.0 mL of butyraldehyde in a sealed bottle and stir at 27°C for 5 minutes. Rapidly add 6.0 mL of aqueous ammonia (25-28 wt%) and stir for 30 minutes. Then add 2.8 mL of tetraethyl orthosilicate (TEOS) and stir at 27°C for 24 hours. The product is filtered, washed, dried at 100°C for 12 hours, and finally calcined in air at 550°C for 6 hours.

[0089] (2) Preparation of zinc cadmium sulfur quantum dots (ZnCdS QDs)

[0090] First, 0.51g of sulfur powder was added to 16ml of octadecene (ODE) and heated to 150°C under N2 until dissolved. Then, 0.256g of cadmium oxide (CdO) and 0.368g of zinc acetate (Zn(OAc)2) were added to a mixture of 13ml of octadecene (ODE) and 6ml of oleic acid (OA), and then heated to 300°C under N2 until dissolved. 4ml of the S precursor was injected into the ZnCd precursor for 10 minutes. After cooling to room temperature, the quantum dots were precipitated with acetone and then dispersed in n-hexane.

[0091] (3) MUA-modified cadmium zinc sulfate quantum dots

[0092] 20 mg of 11-mercaptoundecanoic acid (MUA) was placed in a reaction vessel, 15 ml of methanol (11.85 g) was added, and the pH was adjusted to greater than 10 with tetramethylammonium hydroxide pentahydrate. In the dark, 20 mg of zinc cadmium sulfate quantum dots (ZnCdS QDs) were dispersed in the mixture, and the vessel was placed under a flow of nitrogen. The mixture was heated under reflux at 60°C overnight. The quantum dots were precipitated with ethyl acetate and diethyl ether, washed with acetone, and dispersed in water. These were designated MUA-ZnCdS QDs.

[0093] (4) Preparation of zinc cadmium sulfate quantum dots / mesoporous silica (37% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst

[0094] 37 mg of zinc cadmium sulfate quantum dots (MUA-ZnCdS QDs) and 63 mg of mesoporous silica (mesop-SiO2) were dispersed in 10 ml of deionized water and stirred in the dark for 24 hours to obtain zinc cadmium sulfate quantum dots / mesoporous silica (37% MUA-ZnCdS QDs / mesop-SiO2) composite photocatalyst.

[0095] (5) Photocatalytic reduction of CO2 experiments were carried out on the composite photocatalyst of zinc cadmium sulfate quantum dots / mesoporous silica (37% MUA-ZnCdS QDs / mesop-SiO2).

[0096] 10 mg of catalyst was dispersed in 3 ml of deionized water. The resulting mixture was dropped onto a quartz glass and then dried at 60°C. The dried catalyst was placed in a quartz reactor containing 1 mL of water. Carbon dioxide was then introduced into the reactor for 30 minutes to completely remove air. During the reaction, a xenon lamp was passed through a quartz window (22.1 cm 2 ) illuminates the catalyst sample.

[0097] Depend on Figure 1The specific surface area can be calculated as 50.7m 2 g -1 .

[0098] Transmission images such as Figure 2 As shown, the morphology of the sulfur-cadmium zinc quantum dots is particles with a diameter of 8 nm, which are evenly dispersed and uniform in size. The morphology of the mesoporous silica is nanospheres with a diameter of about 120 nm, and the surface has an obvious mesoporous structure. The morphology of the sulfur-cadmium zinc quantum dots / mesoporous silica composite photocatalyst shows that the mesoporous silica is evenly covered with quantum dots, indicating that the sulfur-cadmium zinc quantum dots / mesoporous silica composite photocatalyst was successfully prepared.

[0099] Depend on Figure 3 The measured CO production rate is 898.6 μmol g -1 h -1 .

[0100] The results of the cycle test are as follows Figure 4 As shown in Figure 2, after 20 h of circulation, the CO production rate can reach 816.7 μmol g -1 h -1 .

Claims

1. A method for preparing a zinc cadmium sulfate quantum dot / mesoporous silica composite photocatalyst, characterized in that: Here are the steps: (1) Preparation of mesoporous silica mesop-SiO2: Dissolve cetyltrimethylammonium bromide (CTAB) and butyraldehyde in water and pour into a sealed bottle, stir at room temperature for the first time, quickly add ammonia water, stir for the second time, then add tetraethyl silicate (TEOS), stir for the third time at room temperature, centrifuge and dry the product, and finally calcine in air atmosphere; (2) Preparation of zinc cadmium sulfur quantum dots ZnCdS QDs: First, sulfur powder was added to octadecene ODE and heated under nitrogen until dissolved to prepare an S precursor. Then, cadmium oxide (CdO) and zinc acetate (Zn(OAc)2) were added to a mixture of octadecene ODE and oleic acid (OA) and heated under nitrogen until dissolved to prepare a ZnCd precursor. Finally, the S precursor was injected into the ZnCd precursor and cooled to room temperature. The resulting sulfur-cadmium zinc quantum dots were precipitated with acetone and then dispersed in n-hexane. (3) MUA-modified cadmium zinc sulfate quantum dots Dissolve 11-mercaptoundecanoic acid MUA in methanol, and adjust the pH of the solution to 9-12 with tetramethylammonium hydroxide pentahydrate to obtain a MUA mixed solution; Under dark conditions, the zinc cadmium sulfate quantum dots ZnCdS QDs obtained in step (2) were dispersed in the MUA mixture, and the container was placed under N2 flow. The mixture was heated under reflux overnight, precipitated with ethyl acetate and diethyl ether, washed with acetone and dispersed in water, and recorded as MUA-ZnCdS QDs; (4) Preparation of zinc cadmium sulfate quantum dots / mesoporous silica composite photocatalyst The MUA-ZnCdS QDs obtained in step (3) and the mesoporous silica mesop-SiO2 obtained in step (1) are dispersed in deionized water, stirred in the dark for 12-24 hours, and a zinc cadmium sulfate quantum dot / mesoporous silica composite photocatalyst is obtained, which is recorded as MUA-ZnCdS QDs / mesop-SiO2; The mass ratio of MUA-ZnCdS QDs and mesoporous silica mesop-SiO2 is 1:1.7-19.

2. The preparation method according to claim 1, wherein In step (1), the usage ratio of cetyltrimethylammonium bromide, butyraldehyde, ammonia water and tetraethyl silicate is 0.64 g:15.0 mL:6.0 mL:2.8 mL; wherein the concentration of ammonia water is 25-28 wt %.

3. The preparation method according to claim 1, wherein In step (1), the first stirring time is 5-10 min, the second stirring time is 30-60 min, the third stirring time is 12-24 h, the calcination temperature is 550° C., and the calcination time is 6 h.

4. The preparation method according to claim 1, wherein In step (2), the molar ratio of sulfur powder, CdO and Zn(OAc)2 is 2:1:1; in the mixture of octadecene ODE and oleic acid OA, the volume ratio of ODE:OA is 13:

6.

5. The preparation method according to claim 1, wherein In step (3), the mass ratio of MUA and ZnCdS QDs was 1:

1.

6. The preparation method according to claim 1, wherein In step (3), the reflux temperature is 60-80°C.

7. Use of the sulfur cadmium zinc quantum dot / mesoporous silica composite photocatalyst prepared by the method according to any one of claims 1 to 6 for photocatalytic reduction of CO2 to CO.

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