A preparation method of a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen

Abstract

The application relates to a preparation method of a'single atom + cluster' co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen, and relates to the field of hydrogen production.The CdS photocatalyst material co-modified by twin crystal structure in the interior, Fe, Ni and Co single atoms on the surface layer and clusters formed by the transition metals is prepared by using cadmium-containing wastewater and H2S-containing waste gas as raw materials, further introducing inexpensive metals such as Fe, Ni and Co, and adopting a precipitation-photo reduction strategy, and is marked as Z / W-CdS(FeCoNi) SA+C . The crystal structure, band energy level position, morphology and microstructure of the prepared sample are analyzed by using XRD, diffuse reflection, Mott-Schottky, SEM, EDS and HRTEM, and it is confirmed that the Z / W-CdS(FeCoNi) SA+C material is successfully prepared. Hydrogen production test: under the condition of visible light irradiation, the hydrogen production rate of the Z / W-CdS(FeCoNi) SA+C material reaches 3.0253 mmol.h ‑1 .g ‑1 , which is far superior to the performance of various single and binary transition metal modified catalysts, and the hydrogen production performance of the Z / W-CdS catalyst without transition metal modification is improved by 87.9 times.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production catalysts, specifically relating to a method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen. Background Technology

[0002] How to scientifically grasp and seek reliable hydrogen production routes to achieve hydrogen energy supply in an environmentally friendly, economical, safe, and efficient manner has become one of the key scientific issues of concern. This is also the fundamental issue for realizing the "hydrogen energy society" industrial chain. Compared with many gray hydrogen and blue hydrogen production technologies, hydrogen production technology that uses solar energy as a power source to drive catalytic water splitting is considered the ultimate dream of new energy for mankind because it can truly achieve "zero energy consumption" and "zero pollution" hydrogen production. However, the preparation of highly active photocatalysts remains a long-term and arduous challenge. Among many photocatalytic materials, CdS catalysts are considered one of the most promising photocatalytic materials due to their suitable band structure and high visible light response. However, in the application of photocatalytic water splitting for hydrogen production, the defects of easy photocorrosion and rapid recombination of photogenerated carriers have restricted the research and development of CdS catalysts. This is the key and difficult problem for its practical development and application of "solar hydrogen".

[0003] In recent years, the international academic community has conducted a series of beneficial explorations on functional modification strategies such as the construction of protective layers and the matching of co-catalysts. However, it has also been found that protective layer materials are a double-edged sword. While they can alleviate the photocorrosion problem of catalysts, they also increase the difficulty for photogenerated charge carriers to penetrate the protective layer and reach the reaction sites. Considering that CdS is often used as a core material in photocatalytic systems to construct core-shell type catalysts, the designed protective layer material should be thin. If assembled to a thickness of only a few atoms, it is expected to significantly reduce the negative impact of the protective layer material on the water splitting process. In addition, in traditional nanoparticle co-catalyst materials, the surface atomic ratio of the active component is relatively low, which results in fewer active sites and limited addition effect on the catalytic system. Theoretically, if the active component in the co-catalyst material is reduced to a single atom, the utilization rate of the surface active sites on the catalyst can be increased to 100%. In recent years, single-atom catalysts (SACs) have shown great potential and made significant progress in improving the performance of photocatalytic hydrogen production. Compared to traditional nanoparticle-based cocatalysts, the atomically dispersed single-atom active sites on the surface of photocatalysts can effectively enhance carrier separation and provide efficient hydrogen evolution sites. Therefore, the use of noble metal SACs such as Au, P, and Pd to optimize photocatalyst performance has been widely recognized. However, to achieve efficient and stable water splitting for hydrogen production, rate-controlling steps such as water adsorption and dissociation must be considered. Zhang Jiankang's research group used atomic layer deposition (ALD) to implant Pt clusters (C) and Pt single atoms (SA) at a certain distance on the surface of a CdS catalyst. These significantly improved water adsorption and dissociation, as well as hydrogen desorption, respectively. Ultimately, this "SA+C" dual active site synergistically promoted the photocatalytic hydrogen production process. However, the synthesis process of ALD requires highly precise control and strict synthesis conditions, which obviously contradicts the green production concept of energy saving, environmental protection, and ease of operation. Furthermore, considering the limited reserves and high cost of noble metals, preparing inexpensive metal "SA+C" dual active sites using a simple and economical synthesis method is clearly more practical. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and provide a method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen.

[0005] The present invention discloses a method for preparing a "single-atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen, which is carried out according to the following steps:

[0006] Cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate were added to a reactor and stirred until homogeneous. A 1% hydrogen sulfide / argon gas mixture was then introduced, and the mixture was reacted under light irradiation until a suspension formed. After standing until the solution separated into layers, the lower suspension was collected, washed, centrifuged, and dried to obtain Z / W-CdS(FeCoNi). SA+C catalyst.

[0007] Further, the mass-to-volume ratio of cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate is 0.1~1g: 50~100 mL: 0.016~0.16g: 0.014~0.14g: 0.013~0.13g.

[0008] Furthermore, the mass-to-volume ratio of cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate is 0.5 g: 80 mL: 0.026 g: 0.024 g: 0.033 g.

[0009] Furthermore, the mass concentration of the cadmium acetate solution is 0.00125~0.0125 g / mL.

[0010] Furthermore, the flow rate of the hydrogen sulfide / argon gas mixture is controlled at 0.1~0.5 mL·min. -1 .

[0011] Furthermore, the washing and centrifugation were performed using deionized water, with the washing process repeated twice using deionized water, and a third washing and centrifugation using anhydrous ethanol.

[0012] This invention utilizes cadmium-containing wastewater and H2S-containing waste gas as raw materials, and further introduces inexpensive metals such as Fe, Ni, and Co. Through a precipitation-photoreduction strategy, a cadmium sulfide catalyst material co-modified with catalytic sites including an internal twin structure (Z / W), Fe, Ni, and Co single atoms (SA) on the surface, and clusters (C) formed by the aforementioned transition metals is prepared. This material is labeled Z / W-CdS(FeCoNi). SA+C The crystal structure, band level positions, and microstructure of the prepared samples were analyzed using XRD, diffuse reflectance, Mott-Schottky, SEM, EDS, and HRTEM, confirming that Z / W-CdS(FeCoNi) was the correct crystal structure. SA+C The material was successfully prepared. Compared with Z / W-CdS material, Z / W-CdS(FeCoNi)... SA+C The material exhibits a narrower bandgap of 2.3 eV and a more suitable band structure. CB (vs SHE) = -0.36 V, E VB (vs SHE) = +1.94 V. When photoexcited, Z / W-CdS(FeCoNi) SA+CThe internal electric field formed by the twinned structure within the material provides the thermodynamic driving force for the reaction, while the ternary metal clusters and single-atom catalytic sites on the surface provide active sites for the kinetic processes of "water adsorption-water dissociation-generation of hydrogen and hydrogen peroxide". This dual optimization of thermodynamics and kinetics was further tested in the photocatalytic decomposition of seawater to produce hydrogen, revealing that under visible light irradiation, Z / W-CdS(FeCoNi) exhibits high efficiency. SA+C The material achieves a hydrogen production rate of 3.0253 mmol·h. -1 ·g -1 It outperforms various mono- and binary transition metal modified catalysts, and its hydrogen production performance is 87.9 times higher than that of Z / W-CdS catalysts without transition metal modification. Attached Figure Description

[0013] Figure 1 For Z / W-CdS(A) and Z / W-CdS(FeCoNi) SA+C (B) XRD pattern of the catalyst;

[0014] Figure 2 For Z / W-CdS and Z / W-CdS(FeCoNi) SA+C UV-Vis diffuse reflectance spectrum (A) and corresponding bandgap spectrum (B) of the sample; Z / W-CdS(FeCoNi) SA+C Mott-Schottky curves of the samples (C); Z / W-CdS(FeCoNi) SA+C Energy level and band position distribution diagram (D) inside the sample;

[0015] Figure 3 SEM images (A, B), EDX-Mapping image (CE), and EDS image (F) of the Z / W-CdS sample;

[0016] Figure 4 Z / W-CdS(FeCoNi) SA+C SEM images (A, B), EDX-Mapping image (CH), and EDS image (I) of the samples;

[0017] Figure 5 Z / W-CdS(FeCoNi) SA+C HRTEM images (A, B), HAADF-STEM (C), and EDX-Mapping images (DH) of the samples;

[0018] Figure 6 Figures showing the photocatalytic hydrogen production performance of pure water decomposition for different samples;

[0019] Figure 7 Z / W-CdS(FeCoNi)SA+C Schematic diagram of the photocatalytic decomposition mechanism of pure water to produce hydrogen from the material. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0021] The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0022] Example 1

[0023] Catalyst materials prepared by precipitation-photochemical reduction method

[0024] 1. Preparation of Z / W-CdS catalyst

[0025] In this embodiment, cadmium sulfide catalyst is prepared by chemical precipitation. 0.5 g of cadmium acetate is added to 80 mL of water and placed in a reactor. The reactor is then placed on a magnetic stirrer and stirred until homogeneous. Simultaneously, a 1% hydrogen sulfide / argon mixture is introduced through the reactor inlet (flow rate controlled at 0.2 mL / min). -1 The reaction was carried out at room temperature for one hour, during which the solution gradually changed from a colorless, clear solution to a yellow suspension. After the reaction was complete, the reactor was allowed to stand for one hour. Once the solution showed obvious stratification, the upper clear liquid was poured off, and the lower suspension was poured into a centrifuge tube. The tube was washed with deionized water and centrifuged. The washing was repeated twice with deionized water, and a third washing and centrifugation were performed with anhydrous ethanol. After centrifugation, the centrifuge tube was dried in an oven to obtain the Z / W-CdS powder catalyst.

[0026] 2. Preparation of Z / W-CdS(FeCoNi)SA+C catalyst

[0027] Z / W-CdS(FeCoNi)SA+C catalyst was prepared using a precipitation-photoreduction strategy. 0.5 g cadmium acetate, 80 mL deionized water, 0.026 g nickel sulfate, 0.024 g cobalt nitrate, and 0.033 g ferric nitrate were weighed and added to a reactor. The reactor was placed on a magnetic stirrer and stirred until homogeneous. Simultaneously, a 1% hydrogen sulfide / argon mixture was introduced through the reactor inlet (flow rate controlled at 0.2 mL / min). -1When reacted under light for one hour, the solution gradually changed from a colorless, clear solution to a suspension. After the reaction was complete, the reactor was allowed to stand for one hour. After the solution showed obvious stratification, the upper clear liquid was poured off, and the lower suspension was poured into a centrifuge tube. The tube was washed with deionized water and centrifuged. The washing was repeated twice with deionized water, and a third washing and centrifugation were performed with anhydrous ethanol. After centrifugation, the centrifuge tube was dried in an oven to obtain Z / W-CdS(FeCoNi)SA+C powder catalyst.

[0028] Figure 1 A shows the XRD images of the Z / W-CdS catalyst synthesized by precipitation-photoreduction method. By comparing with cubic zincblende cards (PDF#10-0454) and hexagonal wurtzite cards (PDF#41-1049), it can be seen that the Z / W-CdS catalyst has characteristic peaks of both cubic and hexagonal phases. 2θ is 24.8°, 28.5°, 36.5°, 43.7°, 47.8°, 51.8°, and 66.9°, which correspond to the (100), (101), (102), (110), (103), (102), and (203) crystal planes of hexagonal cadmium sulfide, respectively. At the same time, we noticed that the peak intensity at 26.5° is significantly greater than that at 24.8° and 28.5°. This is because the peaks of the cubic (111) crystal plane and the hexagonal (002) crystal plane in Z / W-CdS are superimposed. Calculations using the Bragg equation show that the interplanar spacing of the dominant growth crystal planes (111) or (002) is 0.336 nm. Furthermore, observations... Figure 1 B found that after loading Fe, Co, Ni single atoms and clusters as active sites, the peak intensities of the (111) crystal plane of the cubic phase and the (002) crystal plane of the hexagonal phase in Z / W-CdS were further enhanced, indicating that the modification of transition metal elements induced further growth of these crystal planes. Due to the low content of the two active species, single atoms and clusters, their characteristic peaks were not detected.

[0029] Figure 2 A shows that compared to Z / W-CdS, Z / W-CdS(FeCoNi) SA+C The catalyst exhibits a significant redshift at the absorption edge, indicating that the absorption range of the modified cadmium sulfide catalyst is significantly larger than that of the pure cadmium sulfide catalyst. The band structure transformation spectrum of the sample was calculated using the Tauc plot method. Figure 2 B), it can be seen that the band gap of the pure CdS catalyst sample is 2.34 eV, Z / W-CdS(FeCoNi) SA+C The catalyst has a band gap of 2.30 eV. Literature review indicates that a narrower band gap facilitates the absorption of visible light. Therefore, the Z / W-CdS(FeCoNi) prepared in this embodiment... SA+CCatalysts have better efficiency in utilizing sunlight.

[0030] To further understand the energy level band positions of the catalyst, Mott-Schottky tests were performed. Figure 2 As shown in Figure C, the slope of the test curve is positive, indicating that Z / W-CdS(FeCoNi) SA+C The catalyst is an n-type semiconductor. Based on the band edge of the test curve, the conduction band position of the catalyst is deduced to be: E CB (vs SHE) = -0.36 V, and the valence band position can be deduced from the band gap width as: E VB (vs SHE) = +1.94 V. Since Z / W-CdS materials contain two crystalline phases, this band position should be attributed to the average conversion values ​​of the conduction and valence bands of cubic and hexagonal CdS, respectively. According to literature review, H... + The reduction potential of H₂O / H₂O₂ and the oxidation potential of H₂O / H₂O₂ are 0 V (vs SHE) and 1.80 V (vs SHE), respectively. Therefore, Z / W-CdS(FeCoNi) SA+C The catalyst has sufficient reducing and oxidizing capabilities. Figure 2 D), which can decompose pure water into H2 and H2O2.

[0031] Figure 3 The SEM images (A, B), EDX-Mapping images (CE), and EDS images of the Z / W-CdS samples are shown. Figure 3 As can be seen from A, the morphology of the Z / W-CdS catalyst is mainly agglomerated. Further analysis... Figure 3 The magnified portion circled in red in section A shows that the particle size of the agglomerated material is relatively large, approximately between 150 and 300 nm. Figure 3 B). Figure 3 CE shows the distribution of Cd and S elements in the Z / W-CdS sample. Observation shows that both elements are uniformly and orderly distributed within the sample, proving the successful preparation of the Z / W-CdS sample. EDS test results ( Figure 3 F) further confirms this point.

[0032] Figure 4 Z / W-CdS(FeCoNi) was demonstrated. SA+C SEM images (A, B), EDX-Mapping image (CE), and EDS image of the sample. (From...) Figure 4 A shows that Z / W-CdS(FeCoNi) SA+C The sample exhibits a nanoparticle morphology. To further observe the particle size, we... Figure 4Magnified observation of the portion circled in red in Figure A reveals that: Z / W-CdS(FeCoNi) SA+C The sample particle size distribution is between 20 and 40 nm. Figure 4 B), with a particle size significantly smaller than that of the Z / W-CdS sample. This indicates that the Z / W-CdS (FeCoNi) sample... SA+C The sample has a larger specific surface area and exhibits more active sites, which will be more conducive to the photocatalytic decomposition of pure water. Figure 4 CH showed Z / W-CdS(FeCoNi) SA+C The distribution of various elements in the sample shows that Cd and S are uniformly and orderly distributed inside the sample, while Fe, Co, and Ni are partially uniformly distributed on the sample surface, and partially slightly aggregated on the sample surface. This may be because Fe, Co, and Ni elements form single-atom and cluster active sites on the surface of CdS, respectively, further confirming Z / W-CdS(FeCoNi). SA+C The sample was successfully prepared.

[0033] Figure 5 Z / W-CdS(FeCoNi) was demonstrated. SA+C HRTEM images (A, B), HAADF-STEM (C), and EDX-Mapping (DH) of the samples. This was achieved through analysis of Z / W-CdS(FeCoNi). SA+C Observation of the internal crystal structure of the sample Figure 5 A) It can be seen that the sample contains a twinned structure (a clear twinned interface and a SAED pattern with twinning characteristics in the upper right corner are visible), and the interplanar spacing is 0.336 nm, which corresponds to the (111) crystal plane of the cubic phase or the (002) crystal plane of the hexagonal phase, respectively. This is consistent with the XRD observation results, indicating that CdS grows preferentially along the

[111] or

[002] direction, and once again confirms that Z / W-CdS(FeCoNi) SA+C Sample preparation was successful. Further observation of Z / W-CdS(FeCoNi) was conducted using aberration-corrected high-resolution electron microscopy. SA+C The sample revealed that the particles of the species marked by the red circles in the sample were slightly larger than the size of a Cd atom. Figure 5 B) indicates that this species may be a FeCoNi ternary metal cluster adsorbed on the surface of the CdS material. Furthermore, the atomic contrast is low in the area marked by the blue circle ( Figure 5 B) may be caused by cadmium vacancies forming on the surface of the CdS material. To further verify whether there are single-atom sites filling the cadmium vacancies, we further observed EDX-mapping (B). Figure 5 CH), research found that the large-particle-size material marked with a red circle is indeed composed of three elements: Fe, Co, and Ni. Figure 5 C, FH), confirming the existence of the ternary cluster structure; in the region marked by the blue circle, Fe, Co, and Ni are evenly distributed, confirming that the cadmium vacancies in this region are indeed filled with single atoms of Fe, Co, and Ni. Figure 5 C, FH). This finding further confirms the presence of Z / W-CdS(FeCoNi). SA+C The material was successfully prepared.

[0034] Figure 6 The photocatalytic hydrolysis of pure water to produce hydrogen was demonstrated. Calculations showed that the hydrogen production rate of the Z / W-CdS sample was only 0.0344 mmol·h⁻¹. -1 ·g -1 Z / W-CdS(Fe) modified with ferric nitrate SA+C The hydrogen production rate of the sample was 0.5695 mmol·h. -1 ·g -1 Z / W-CdS(Co) modified with cobalt nitrate SA+C The hydrogen production rate of the sample was 0.7961 mmol·h. -1 ·g -1 Z / W-CdS(Ni) modified with nickel sulfate SA+C The hydrogen production rate of the sample was 0.9399 mmol·h. -1 ·g -1 Z / W-CdS(FeCo) modified with ferric nitrate and cobalt nitrate SA+C The hydrogen production rate of the sample was 0.823 mmol·h. -1 ·g -1 Z / W-CdS(FeNi) modified with ferric nitrate and nickel sulfate. SA+C The hydrogen production rate of the sample was 1.0329 mmol·h. -1 ·g -1 Z / W-CdS(CoNi) modified with cobalt nitrate and nickel sulfate. SA+C The hydrogen production rate of the sample was 1.1412 mmol·h. -1 ·g -1 Z / W-CdS(FeCoNi) modified with ternary metals of Fe, Co, and Ni. SA+C The hydrogen production rate of the sample was 3.0253 mmol·h. -1 ·g -1 Compared to the sample modified with a monometallic metal, Z / W-CdS(FeCoNi) SA+C The hydrogen production performance of all samples was improved by more than 4 times; compared with the binary metal modified sample, Z / W-CdS(FeCoNi) showed a significant improvement. SA+CThe hydrogen production performance of all samples was improved by more than 3 times; it was even 87.9 times higher than that of the unmodified Z / W-CdS sample. Literature review indicates that metal clusters can efficiently adsorb and dissociate water molecules, and single-atom active sites can accelerate the hydrogen production reaction. The results of this test suggest that ternary metal clusters may exhibit higher water adsorption energy and lower water dissociation energy than unary and binary metal clusters. Whether the three types of mixed single-atom sites exhibit a lower Gibbs free energy for hydrogen production than unary and binary single-atom sites requires further experimental and theoretical calculations for confirmation.

[0035] Figure 7 Z / W-CdS(FeCoNi) was demonstrated. SA+C The mechanism of photocatalytic decomposition of pure water to produce hydrogen in the sample is illustrated as follows: (1) When the catalyst is excited by light, electrons inside the CdS material jump from the valence band to the conduction band, forming electron-hole pairs with the holes existing in the valence band. Driven by the electric field of the type II homojunction formed by the internal twin structure, the photogenerated electrons and holes are efficiently separated and transported to the surface of the material; (2) The photogenerated holes are further transferred to the ternary metal clusters. Since the adsorption energy and dissociation energy of the ternary metal clusters for water are lower, Z / W-CdS(FeCoNi) SA+C The ternary metal clusters on the surface of the material preferentially adsorb water molecules and dissociate them. The hydroxide ions generated by dissociation react with photogenerated holes in situ to generate hydrogen peroxide. (3) The hydrogen ions generated by the dissociation of water from the ternary metal clusters diffuse to the single-atom catalytic sites (Fe, Co, Ni). (4) At the same time, photogenerated electrons are transferred to the single-atom catalytic sites and react with the diffused hydrogen ions to generate hydrogen gas.

[0036] In summary, the internal electric field formed by the twinned structure provides the thermodynamic driving force for the reaction; the ternary metal clusters and single-atom catalytic sites provide active sites for the kinetic processes such as water adsorption-water dissociation-generation of hydrogen and hydrogen peroxide. This dual optimization of thermodynamics and kinetics ensures the success of Z / W-CdS(FeCoNi) reaction. SA+C The material can efficiently and stably perform photocatalytic decomposition of pure water.

Claims

1. A method for preparing a "single-atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen, characterized in that, It is done in the following steps: Cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate were added to a reactor and stirred until homogeneous. A 1% hydrogen sulfide / argon gas mixture was then introduced, and the mixture was reacted under light irradiation until a suspension formed. After standing until the solution separated into layers, the lower suspension was collected, washed, centrifuged, and dried to obtain Z / W-CdS(FeCoNi). SA+C The catalyst; the mass-to-volume ratio of cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate is 0.5 g: 80 mL: 0.026 g: 0.024 g: 0.033 g.

2. The preparation method of a "single-atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen gas according to claim 1, characterized in that, The mass concentration of the cadmium acetate solution is 0.00125~0.0125 g / mL.

3. The preparation method of a "single-atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen gas according to claim 1, characterized in that, The flow rate of the hydrogen sulfide / argon mixture was controlled to be 0.1~0.5 mL·min. -1 .

4. The preparation method of a "single-atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen gas according to claim 1, characterized in that, The washing and centrifugation process involves washing and centrifuging twice with deionized water, followed by a third washing and centrifugation with anhydrous ethanol.

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