Silver-doped composite photocatalyst, and preparation method and application thereof

Abstract

The application discloses a silver-doped composite photocatalyst and a preparation method and application thereof, and belongs to the technical field of greenhouse gas treatment. In the synthesis process of CuInS2 nanosheets, Ag single atoms are doped in situ to prepare the silver-doped composite photocatalyst. Ag single atoms are introduced in situ by doping different amounts of noble metal Ag in the synthesis process of CuInS2. CuInS2 is a kind of catalyst with excellent visible light response capability. After being combined with noble metal Ag, the photo-generated electrons in CuInS2 are more inclined to be transferred from CuInS2 to Ag, greatly enhancing the separation and transfer capability of photo-generated charges. The catalyst significantly improves the carbon dioxide photoreduction reaction activity. The prepared silver-doped composite photocatalyst has good stability.

Description

Technical Field

[0001] This invention belongs to the field of greenhouse gas treatment technology, and in particular relates to a silver-doped composite photocatalyst, its preparation method, and its application. Background Technology

[0002] As a traditional greenhouse gas control technology, photocatalytic carbon dioxide reduction is one of the main technologies for carbon dioxide control. This technology involves passing pollutant gases through a catalyst bed, converting them into high-value-added hydrocarbons in a directed and efficient manner at room temperature. By adding a catalyst, the reaction process is altered, and the activation energy of the reaction is lowered. This not only helps achieve the goal of "artificial carbon cycle" to solve the increasingly serious environmental problems, but also holds promise for alleviating the current energy shortage. The development of highly efficient photocatalytic materials is a key link and also a bottleneck in current research and application.

[0003] Copper indium sulfide (CuInS2) is a direct bandgap semiconductor (I-III-IV) free of any toxic heavy metals, typically existing in the form of nanosheets or quantum dots. CuInS2 not only possesses a narrow direct bandgap of 1.50 eV, close to the optimal bandgap for solar energy harvesting (1.45 eV), but also exhibits an ultra-high absorption coefficient, relatively high carrier mobility, and tunable bandgap, making it a highly attractive candidate. However, due to its inherent limitations, the visible-light photocatalytic activity of pure ternary chalcogenides is not satisfactory. Summary of the Invention

[0004] The purpose of this invention is to provide a silver-doped composite photocatalyst, its preparation method, and its applications, thereby addressing the problems existing in the prior art. This invention solves the carbon-carbon coupling problem in current photocatalytic carbon dioxide reduction research, providing a method for achieving the photocatalytic reduction of carbon dioxide to prepare the high-value-added two-carbon product ethylene through silver-doped CuInS2. Maintaining the unique structure and electronic properties of ternary chalcogenides, the key to solving the problem lies in constructing effective carbon dioxide reactive sites through efficient strategies to enhance the adsorption and activation capacity of carbon dioxide, thereby improving the photocatalyst activity and achieving product selectivity.

[0005] One of the technical solutions provided by this invention:

[0006] A method for preparing a silver-doped composite photocatalyst involves in-situ doping with Ag single atoms during the synthesis of CuInS2 to obtain the silver-doped composite photocatalyst.

[0007] Analysis showed that silver exists in the form of single atoms; secondly, the presence of silver improved the efficiency of photogenerated charge separation, increased the carbon dioxide reduction rate, promoted the occurrence of carbon-carbon coupling reaction, and achieved selective transformation of reduction products. The final product was mainly high-value-added ethylene, with a selectivity of up to 98.8%.

[0008] A method for preparing a silver-doped composite photocatalyst includes the following steps: InCl3·4H2O and Cu(CH3COO)2·H2O are added to ethylene glycol, and after complete dissolution, precious metal silver is added. After vigorous stirring, thioacetamide is added, and vigorous stirring is continued. The resulting mixed solution is heated and cooled to room temperature, filtered, the precipitate is washed, and dried to prepare the silver-doped composite photocatalyst.

[0009] Preferably, the stirring time is 30 minutes.

[0010] Preferably, the mass ratio of InCl3·4H2O to Cu(CH3COO)2·H2O is 7:4.

[0011] Preferably, the precious metal silver is AgNO3, and the amount of AgNO3 used accounts for 0.5-1.6% of the sum of the masses of InCl3·4H2O and Cu(CH3COO)2·H2O.

[0012] Preferably, the heating temperature is 180°C.

[0013] Preferably, the drying temperature is 60°C.

[0014] The method for preparing the silver-doped composite photocatalyst provided by this invention is a method for photocatalytic reduction of carbon dioxide to ethylene through in-situ silver doping of CuInS2. The specific operation is as follows: First, 70 mg InCl3·4H2O and 40 mg Cu(CH3COO)2·H2O are added to 40 mL of ethylene glycol, then AgNO3 is added, and the mixture is stirred vigorously for 30 min. Then, 72 mg thioacetamide is added, and the mixture is stirred vigorously again. The reaction is carried out at 180 °C for 24 h in a solvothermal manner. During the reaction, silver will be doped into the CuInS2 bulk phase in the form of single atoms. After naturally cooling to room temperature, the precipitate obtained by centrifugation is washed continuously with deionized water and ethanol to remove residual ions. Finally, it is dried at 60 °C.

[0015] This invention obtains composite photocatalysts with different Ag doping amounts by changing the Ag doping amount during the synthesis of CuInS2, introducing single Ag atoms in situ into CuInS2 without destroying its inherent ternary chalcogenide structure.

[0016] The second technical solution provided by this invention:

[0017] A silver-doped composite photocatalyst prepared by the above preparation method, wherein the silver doping amount is 1-3 wt% based on the mass ratio of silver atoms to the composite photocatalyst, preferably 2 wt%.

[0018] The third technical solution provided by this invention:

[0019] Application of the above-mentioned silver-doped composite photocatalyst in the photocatalytic reduction of carbon dioxide to ethylene.

[0020] The fourth technical solution provided by this invention:

[0021] A method for photocatalytic reduction of carbon dioxide to ethylene using the aforementioned silver-doped composite photocatalyst, wherein the reactants are carbon dioxide and gaseous water, and the reaction condition is visible light excitation.

[0022] The beneficial effects of this invention are:

[0023] This invention prepares a series of visible light-driven silver-doped composite photocatalysts by doping CuInS2 with different amounts of Ag single atoms during the synthesis process, thereby improving the photocatalytic reduction performance of carbon dioxide and regulating product selectivity. While maintaining the unique structure and electronic properties of ternary chalcogenides, an effective strategy is employed to construct active sites for carbon dioxide reactivity, enhancing the composite photocatalyst's adsorption and activation capabilities for carbon dioxide, thus achieving improved photocatalyst activity and a shift in product selectivity. The presence of Ag improves the photogenerated charge separation efficiency, increases the carbon dioxide reduction rate, and promotes carbon-carbon coupling reactions. Compared with pure CuInS2 photocatalyzed carbon dioxide, the reduction performance is improved by 90 times, achieving a selective shift in reduction products. The final product is mainly high-value-added ethylene, with a selectivity as high as 98.8%. The introduction of silver improves the photogenerated charge separation efficiency of CuInS2, allowing more photogenerated carriers to participate in the carbon dioxide reduction reaction.

[0024] The present invention provides a method for preparing an Ag-doped composite photocatalyst, which requires simple reaction equipment, has a short reaction time, and is easy to operate. The reaction raw materials are readily available, and the raw material and reaction costs are low, which is conducive to large-scale production. No toxic or harmful substances are used or generated during the entire reaction process, which fully meets the requirements of clean production. By doping different amounts of noble metal Ag during the synthesis of CuInS2 nanosheets, Ag single atoms are introduced in situ. CuInS2, as a catalyst with excellent visible light response, tends to transfer photogenerated electrons from CuInS2 to Ag after combining with noble metal Ag. This greatly enhances the separation and transfer ability of photogenerated charges. The composite catalyst significantly improves the activity of carbon dioxide photoreduction reaction. In addition, the composite photocatalyst has a stable structure and stable catalytic performance after multiple full uses. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. 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.

[0026] Figure 1 XRD patterns of 2% Ag / CIS prepared in Example 1 and CIS prepared in Comparative Example 1 are shown in comparison.

[0027] Figure 2 TEM comparison images of 2% Ag / CIS prepared in Example 1 and CIS prepared in Comparative Example 1;

[0028] Figure 3 The graph shows a comparison of the catalytic performance of 2% Ag / CIS, 1% Ag / CIS, 3% Ag / CIS and CIS prepared in Examples 1-3 and Comparative Example 1.

[0029] Figure 4 Results of the effect of illumination time on the catalytic performance of 2% Ag / CIS:

[0030] Figure 5 The results of catalytic performance tests of 2% Ag / CIS under different catalytic conditions;

[0031] Figure 6 The results are for the stability determination of the catalytic performance of 2% Ag / CIS. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] The room temperature in this invention refers to 25±2℃.

[0038] This invention provides a method to enhance the photocatalytic performance of carbon dioxide reduction and adjust product selectivity by doping CuInS2 with different amounts of Ag single atoms during the synthesis process. Firstly, during the preparation of the ternary chalcogenide material, different amounts of AgNO3 are added, and a hydrothermal reaction is carried out at 180°C for 24 hours. After cooling to room temperature, the product is washed several times with deionized water and ethanol, and then vacuum dried at 60°C for 12 hours. The in-situ introduction of Ag single atoms into CuInS2 makes carbon dioxide more easily activated, ultimately causing a change in the reduction product selectivity from CH4 to C2H4. In the activity evaluation of the catalyst provided by this invention, its catalytic activity is significantly improved, and the reduction product changes from CH4 to the high-value-added hydrocarbon product C2H4.

[0039] Example 1

[0040] 70 mg of InCl3·4H2O and 40 mg of Cu(CH3COO)2·H2O were weighed and dissolved thoroughly in 40 mL of ethylene glycol solution. Then, 1.3 mg of AgNO3 was added, and the mixture was stirred vigorously for 30 min. Next, 72 mg of thioacetamide was added to the mixture, and stirring was continued vigorously for another 30 min. The resulting mixture was then poured into a 50 mL stainless steel autoclave lined with polytetrafluoroethylene (PTFE), and reacted at 180 °C for 24 h. After cooling the autoclave to room temperature in air, the mixture was filtered. The resulting precipitate was washed continuously with deionized water and ethanol to remove residual ions, and finally dried at 60 °C for 24 h to prepare a silver-doped composite photocatalyst. The Ag content of the photocatalyst was 2 wt% (2% Ag / CIS).

[0041] Example 2

[0042] 70 mg of InCl3·4H2O and 40 mg of Cu(CH3COO)2·H2O were weighed and dissolved thoroughly in 40 mL of ethylene glycol solution. Then, 0.67 mg of AgNO3 was added, and the mixture was stirred vigorously for 30 min. Next, 72 mg of thioacetamide was added to the mixture, and stirring was continued vigorously for another 30 min. The resulting mixture was then poured into a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 24 h. After cooling the autoclave to room temperature in air, the mixture was filtered. The resulting precipitate was washed continuously with deionized water and ethanol to remove residual ions. Finally, it was dried at 60 °C for 24 h to prepare a silver-doped composite photocatalyst. The Ag content of the photocatalyst was 1 wt% (referred to as 1% Ag / CIS).

[0043] Example 3

[0044] 70 mg of InCl3·4H2O and 40 mg of Cu(CH3COO)2·H2O were weighed and dissolved thoroughly in 40 mL of ethylene glycol solution. Then, 1.7 mg of AgNO3 was added, and the mixture was stirred vigorously for 30 min. Next, 72 mg of thioacetamide was added to the mixture, and stirring was continued vigorously for another 30 min. The resulting mixture was then poured into a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 24 h. After cooling the autoclave to room temperature in air, the mixture was filtered. The resulting precipitate was washed continuously with deionized water and ethanol to remove residual ions. Finally, it was dried at 60 °C for 24 h to prepare a silver-doped composite photocatalyst. The Ag content of the photocatalyst was 3 wt%, denoted as 3% Ag / CIS.

[0045] Comparative Example 1

[0046] Same as Example 1, except that AgNO3 was not added. The preparation method is as follows:

[0047] 70 mg of InCl3·4H2O and 40 mg of Cu(CH3COO)2·H2O were weighed and dissolved thoroughly in 40 mL of ethylene glycol solution. After vigorous stirring for 30 min, 72 mg of thioacetamide was added to the mixture, and vigorous stirring was continued for another 30 min. The resulting mixture was then poured into a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 24 h. After cooling the autoclave to room temperature in air, the mixture was filtered. The resulting precipitate was washed continuously with deionized water and ethanol to remove residual ions. Finally, it was dried at 60 °C for 24 h to prepare undoped silver CuInS2 material, denoted as CIS.

[0048] Performance testing experiments:

[0049] 1. Crystal structure and crystal form analysis

[0050] The 2% Ag / CIS prepared in Example 1 and the CIS prepared in Comparative Example 1 were analyzed by X-ray diffraction. Figure 1 XRD patterns of 2% Ag / CIS and CIS were obtained by... Figure 1 It can be seen that the crystal structure of CuInS2 did not change after Ag doping, and there were no Ag NPs. Ag atoms were highly dispersed in the CuInS2 support. Among them, the diffraction peaks of the (112), (220), and (312) crystal planes of CuInS2 in 2% Ag / CIS showed a slight tendency to shift to a smaller angle due to the doping of Ag atoms. This is because Ag with a larger atomic radius was doped into the CuInS2 support, which also indicates the successful doping of Ag atoms.

[0051] 2. Microstructure and morphology analysis

[0052] The 2% Ag / CIS prepared in Example 1 and the CIS prepared in Comparative Example 1 were analyzed by transmission electron microscopy. Figure 2 TEM spectra of 2% Ag / CIS and CIS, by Figure 2 It can be seen that the Ag atoms were successfully doped and highly uniformly dispersed in the CuInS2 material without destroying the inherent structure of the ternary chalcogenide.

[0053] 3. Photocatalytic carbon dioxide reduction performance test

[0054] The photocatalytic carbon dioxide reduction performance of the composite photocatalysts prepared in Examples 1-3 and Comparative Example 1 was evaluated under the following conditions: 2% Ag / CIS, 1% Ag / CIS, 3% Ag / CIS, and CIS were ground in a mortar, and 5 mg of each was weighed and placed in 2.0 mL of deionized water. The mixtures were then ultrasonically dispersed, and the resulting solutions were uniformly dropped onto glass fiber membranes with a radius of 2.5 cm and a pore size of 0.1 μm. The membranes were then dried in an oven at 60 °C for 20 min. Before illumination, 2 mL of ultrapure water was injected into the bottom of the reactor. The glass fiber membranes with the composite photocatalysts were then placed on polytetrafluoroethylene triangular supports in the reactor. Air was completely removed from the system through vacuum treatment, and then high-purity carbon dioxide was introduced to bring the internal pressure of the device to 0.08 MPa. A 300W Xe lamp with a 420nm cutoff filter was positioned 5cm above the reactor as a visible light source. Liquid ultrapure water was converted to gaseous state by xenon lamp irradiation for 4 hours. The resulting products were then measured. The reduction efficiency of the composite photocatalyst for carbon dioxide is shown in Table 1. The yield was defined as the standard volumetric flow rate of the reactant gas entering the reaction system per hour divided by the mass of the catalyst, in μmol·g. -1 ·h -1 The selectivity of reduction is defined as the percentage of carbon dioxide entering the reactor that is converted into different hydrocarbons (such as CO, CH4, C2H4, etc.), expressed as %; see the comparison chart of catalytic performance. Figure 3 ,pass Figure 3 As shown in Table 1, the photocatalytic reduction of carbon dioxide by CIS (pure phase CuInS2) produces one-carbon products (CO and CH4). After silver doping, the main product of CuInS2 is ethylene. The amount of silver doping has a great influence on the photocatalytic activity and product selectivity of CuInS2 for carbon dioxide reduction. The photocatalytic performance is best when the amount of silver doping is 2wt%.

[0055] Table 1

[0056]

[0057] 4. 2% Ag / CIS Catalytic Performance Test

[0058] 4.1 Catalytic performance test of 2% Ag / CIS composite photocatalyst with prolonged illumination time:

[0059] The effect of illumination time on the catalytic performance of the 2% Ag / CIS composite photocatalyst was investigated according to the photocatalytic carbon dioxide reduction performance test. The test results are shown in the figure. Figure 4 ,pass Figure 4 It can be seen that the gaseous products (CO and C2H4) of the 2% Ag / CIS photocatalyst increase linearly with irradiation time, indicating the high selectivity of the photocatalyst for carbon dioxide reduction.

[0060] 4.2 Catalytic performance test of 2% Ag / CIS composite photocatalyst under different catalytic conditions

[0061] Figure 5 The catalytic performance of the 2% Ag / CIS composite photocatalyst under different catalytic conditions was tested. Figure 5 It can be seen that no carbon dioxide reduction products were detected in these reaction systems, indicating that all products originated from the photocatalytic carbon dioxide reduction reaction.

[0062] 4.3 Cyclic test of catalytic performance of 2% Ag / CIS

[0063] The cyclic stability of 2% Ag / CIS was determined according to the photocatalytic carbon dioxide reduction performance test, in which the illumination time was 4 hours and it still had high catalytic activity after 4 cycles. The test results are shown in [Figure number missing]. Figure 6 .

[0064] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. The application of a silver-doped composite photocatalyst in the photocatalytic reduction of carbon dioxide to ethylene, characterized in that, The preparation method of the silver-doped composite photocatalyst includes the following steps: InCl3·4H2O and Cu(CH3COO)2·H2O are added to ethylene glycol. After complete dissolution, precious metal silver is added. After vigorous stirring, thioacetamide is added and vigorous stirring is continued. The resulting mixed solution is heated and cooled to room temperature. After filtration, the precipitate is washed and dried to prepare the silver-doped composite photocatalyst. The mass ratio of InCl3·4H2O to Cu(CH3COO)2·H2O is 7:4; The precious metal silver is AgNO3, and the amount of AgNO3 used accounts for 0.5% to 1.6% of the sum of the mass of InCl3·4H2O and Cu(CH3COO)2·H2O; The heating temperature is 180 ℃; The drying temperature is 60 °C.

2. A method for photocatalytic reduction of carbon dioxide to ethylene using the silver-doped composite photocatalyst described in claim 1, characterized in that, The reactants are carbon dioxide and gaseous water, and the reaction condition is visible light excitation.

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