Cadmium sulfide-nickel hydroxide heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a cadmium sulfide-nickel hydroxide heterojunction photocatalyst which comprises defect-state cadmium sulfide with a cadmium vacancy and nickel hydroxide, and the nickel hydroxide is anchored on the surface of the defect-state cadmium sulfide through the cadmium vacancy to form a heterojunction structure. The preparation method comprises the following steps: dispersing defect-state cadmium sulfide in an alkaline solution, and adding a nickel salt solution for reaction to obtain the cadmium sulfide-nickel hydroxide heterojunction photocatalyst. Compared with traditional PCdS and a non-defective composite system (Ni (OH) 2 / PCdS), the composite material has the advantages that the hydrogen production rate under visible light is obviously improved, and the hydrogen production rates are respectively improved by 197 times and 11.2 times.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a cadmium sulfide-nickel hydroxide heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] With the widespread use of fossil fuels (coal, oil, and natural gas), the emission of large amounts of greenhouse gases such as CO2 has led to rising global temperatures, rising sea levels, and frequent extreme weather events. Meanwhile, my country's rapid economic and social development has resulted in a continuous increase in energy demand, urgently requiring the development of clean and renewable energy sources to balance the dual pressures of energy supply and the ecological environment. Hydrogen, as a high-calorific-value, pollution-free energy carrier, has been widely used in fuel cells, chemical synthesis, and other fields. Photocatalytic hydrogen production technology utilizes solar energy to decompose water into hydrogen, representing a zero-carbon emission energy conversion scheme with significant advantages such as mild reaction conditions, resource sustainability, and environmental friendliness.

[0003] Cadmium sulfide (CdS), a typical narrow bandgap semiconductor (≈2.4 eV), has attracted much attention in the field of photocatalytic hydrogen evolution (HER) due to its excellent visible light absorption and sufficiently negative conduction band potential. Its band structure can satisfy the proton reduction reaction (2H+ + 2e-). - → H2) meets the thermodynamic requirements and has low synthesis cost and flexible morphology control (such as nanorods, quantum dots, etc.). However, the intrinsic defects of CdS severely restrict its practical application: high photogenerated carrier recombination rate and serious photocorrosion problem (sulfur atoms are easily oxidized by holes, leading to structural collapse). To overcome the above bottlenecks, introducing a co-catalyst to optimize the interfacial reaction pathway has become a key strategy. Among them, nickel hydroxide (Ni(OH)2) shows significant advantages due to its unique physicochemical properties: its abundant hydroxyl groups (-OH) on the surface can quickly capture photogenerated holes (h2) of CdS. + It generates ·OH free radicals, inhibiting photocorrosion and promoting oxidation half-reactions; its layered structure provides high-density active sites, reducing H+ ions. + Reduction barrier. Wang et al. achieved an optimal photocatalytic hydrogen production rate of 6.9 times that of pure CdS using a hydrothermal method with Ni(OH)2 / CdS, and the composite catalyst exhibited good stability. However, this strategy had limited improvement on the photogenerated charge separation efficiency, resulting in a less than ideal improvement in hydrogen production performance.

[0004] Furthermore, research shows that cation vacancy CdS (DCdS) constructed through surface defect engineering can significantly optimize the material's band structure, broaden the light absorption range, and enhance carrier separation efficiency; simultaneously, V CdAs atomic-level anchoring sites, crystal defects can stably bind to transition metals to form highly active MS coordination structures, providing abundant active centers for catalytic reactions. Yang et al. improved the photocatalytic activity of CdS with cadmium defects (DCdS) to some extent by constructing it, reporting a 28-fold increase in hydrogen production efficiency compared to pure CdS, revealing the potential of crystal defect engineering in modulating photocatalyst performance. However, repeated experiments verified that although the initial hydrogen production activity of DCdS was significantly higher than that of pure CdS, neither could fundamentally overcome the defect of photochemical instability: after about 3 hours of photocatalytic reaction, DCdS also showed a significant decrease in activity, and the suspension of the reaction system darkened (turned black), which is a typical phenomenon of photocorrosion of CdS-based materials. This indicates that relying solely on the strategy of introducing cadmium defects, although it can improve the initial activity, fails to effectively solve the problem of catalyst durability in long-term reactions.

[0005] In summary, existing photocatalysts have the following drawbacks:

[0006] (1) CdS photocatalytic hydrogen production has low efficiency, high recombination rate of photogenerated carriers, and photocorrosion problem.

[0007] (2) Although cation defects (cation vacancies CdS) can significantly improve photocatalytic hydrogen production performance, photocorrosion still exists.

[0008] (3) Although the Ni(OH)2 / CdS composite photocatalyst has good stability, its hydrogen production efficiency improvement is relatively limited.

[0009] (4) By constructing sulfur-rich vacancy (V S The defective state CdS was used to induce selective deposition of Ni(OH)2 by utilizing sulfur vacancies as atomic-level anchoring sites, resulting in V S The hydrogen production rate of the CdS / Ni(OH)2 heterojunction is about 45 times higher than that of pure CdS. This work introduces the concept of "defect anchoring" into the CdS / Ni(OH)2 system for the first time, but its defect types are limited to anion vacancies (sulfur vacancies), and it does not involve the anchoring application of cation vacancies (cadmium vacancies), nor does it solve the problem of long-term catalyst stability. Summary of the Invention

[0010] (a) Technical problems to be solved

[0011] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a cadmium sulfide-nickel hydroxide heterojunction photocatalyst. By anchoring Ni(OH)2 on the surface of defect-state cadmium sulfide to form a heterojunction structure, the synergistic effect of cadmium vacancy-induced local electron enrichment and nickel hydroxide heterojunction is significantly enhanced.

[0012] Accordingly, the present invention also provides a method for preparing and applying a cadmium sulfide-nickel hydroxide heterojunction photocatalyst.

[0013] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by this invention include:

[0014] In a first aspect, the present invention provides a cadmium sulfide-nickel hydroxide heterojunction photocatalyst, comprising defective cadmium sulfide having cadmium vacancies and nickel hydroxide, wherein the nickel hydroxide is anchored to the surface of the defective cadmium sulfide through cadmium vacancies to form a heterojunction structure.

[0015] The cadmium vacancy (V) of the present invention Cd The synergistic effect of the localized electron enrichment induced by the nickel hydroxide heterostructure can effectively promote the adsorption and dissociation of water molecules and the proton reduction process, thereby achieving a significant improvement in the efficiency of photocatalytic hydrogen production.

[0016] Cation vacancies can enhance the adsorption and dissociation of water molecules and lower the energy barrier of the Volmer step; nickel hydroxide captures holes and optimizes the proton reduction pathway, significantly improving hydrogen evolution kinetics; cation vacancies and heterojunctions have a synergistic effect to jointly promote photocatalytic hydrogen production.

[0017] This invention constructs a heterojunction composite structure of cadmium sulfide (DCdS) containing cadmium vacancies and nickel hydroxide (Ni(OH)2). It optimizes carrier separation by utilizing lattice distortion induced by cation defects and bandgap modulation, while simultaneously enhancing charge-directed migration through a built-in electric field at the heterojunction interface, significantly improving the reduction efficiency of water molecules by photogenerated electrons. Through the synergistic effect of defect engineering and heterostructure construction, the hydrogen production rate is significantly increased, providing a new pathway for developing efficient non-noble metal photocatalytic hydrogen production systems.

[0018] Specifically, this invention enables nickel hydroxide to form a heterojunction structure on the surface of defective cadmium sulfide through cadmium vacancy anchoring. If nickel hydroxide (Ni(OH)₂) is merely physically mixed with defective cadmium sulfide (DCdS) containing cadmium vacancies or subjected to ordinary loading, without achieving specific chemical anchoring via cadmium vacancies, the constructed catalyst exhibits a hydrogen production rate only 1 / 4 that of this invention. On one hand, Ni(OH)₂ can act as a hole acceptor, partially suppressing photocorrosion and slightly promoting charge separation; on the other hand, the cadmium vacancies in DCdS itself can locally enrich electrons and improve light absorption. However, due to the lack of a strong atomic-level coupling interface, the transinterface transport resistance of photogenerated carriers is high, and recombination is severe, resulting in limited gain in charge separation efficiency. Furthermore, the easy shedding of Ni(OH)₂ leads to incomplete suppression of photocorrosion. In stark contrast, this invention achieves synergistic optimization of ultrafast interfacial charge transport and reaction pathways through a strongly coupled heterojunction constructed by "cadmium vacancy anchoring." This not only fundamentally suppresses photocorrosion, but also results in an unexpected leap of up to 11.2 times in photocatalytic hydrogen production rate compared to the unanchored ordinary composite (Ni(OH)2 / PCdS). This is not something that can be achieved by simple combination, but rather a qualitative change triggered by the deep synergy between "defects" and "interfaces."

[0019] Optionally, the nickel hydroxide exists in the form of nanosheets.

[0020] Optionally, the nickel hydroxide in the heterojunction photocatalyst accounts for 5% to 25% by mass.

[0021] Secondly, the present invention also provides a method for preparing the above-mentioned cadmium sulfide-nickel hydroxide heterojunction photocatalyst, which includes the following steps: dispersing defective cadmium sulfide in an alkaline solution, and then adding a nickel salt solution to react and obtain the cadmium sulfide-nickel hydroxide heterojunction photocatalyst.

[0022] This invention uses a chemical precipitation method to load nickel hydroxide onto the surface of DCdS (defective CdS): defective CdS is dispersed in an alkaline solution, and after ultrasonic treatment to break up particle agglomeration, a nickel salt solution is slowly added dropwise. Nickel ions are directionally deposited in an alkaline environment to form nickel hydroxide nanosheets, and a strong interfacial coupling structure is formed by anchoring through cadmium vacancies. Finally, the composite catalyst is obtained by washing and drying.

[0023] Optionally, the method for preparing the defective cadmium sulfide includes the following steps: in the presence of hydrogen peroxide, a cadmium salt is subjected to a hydrothermal reaction with an excess sulfur source to obtain the defective cadmium sulfide. This invention synthesizes cadmium sulfide (DCdS) with cadmium vacancies through a surface defect engineering strategy, induces cadmium vacancy formation under hydrogen peroxide regulation using a hydrothermal method, and utilizes cation-deficient sites to reconstruct the material's band structure and enhance carrier separation efficiency.

[0024] This invention achieves catalyst preparation through a one-step hydrothermal method combined with chemical precipitation. Under normal pressure, low temperature and mild process conditions, it does not require precious metals or complex equipment, exhibits excellent batch stability, and meets the needs of industrial mass production.

[0025] Optionally, the temperature of the hydrothermal reaction is 140~160℃.

[0026] Thirdly, the present invention also provides the application of the cadmium sulfide-nickel hydroxide heterojunction photocatalyst described in any of the above embodiments in photocatalytic water splitting for hydrogen production.

[0027] (III) Beneficial Effects

[0028] The beneficial effects of this invention are:

[0029] The cadmium sulfide-nickel hydroxide heterojunction photocatalyst provided by this invention forms a heterojunction structure by anchoring cadmium vacancies on the surface of defective cadmium sulfide. Compared with traditional PCdS and non-defect composite systems (Ni(OH)2 / PCdS), it significantly improves the hydrogen production rate under visible light by 197 times and 11.2 times, respectively. This is not only achieved by adding nickel hydroxide and introducing cadmium vacancies, but more importantly, by anchoring these vacancies, which fundamentally changes the microscopic processes of charge separation and surface reaction, resulting in a significant increase in the hydrogen production rate. Attached Figure Description

[0030] Figure 1 The XRD patterns of PCdS, DCdS, Ni(OH)2, Ni(OH)2 / PCdS and Ni(OH)2 / DCdS in Example 5;

[0031] Figure 2 The image shows the photocatalytic hydrogen evolution reaction activity of PCdS, DCdS, Ni(OH)2 / PCdS, and Ni(OH)2 / DCdS in Example 6; where (a) is PCdS, (b) is DCdS, (c) is Ni(OH)2 / PCdS, and (d) is Ni(OH)2 / DCdS.

[0032] Figure 3 The UV-Vis diffuse reflectance spectra of the PCdS, DCdS, Ni(OH)2, Ni(OH)2 / PCdS and Ni(OH)2 / DCdS catalysts in Example 7 are shown.

[0033] Figure 4 The photocurrent response diagrams of PCdS, DCdS, Ni(OH)2 / PCdS, and Ni(OH)2 / DCdS under visible light illumination are shown in Example 8. Detailed Implementation

[0034] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0035] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0036] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0037] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0038] Without further limitations, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0039] As understood in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0040] Those skilled in the art to which this application pertains can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0041] Example 1

[0042] This embodiment provides a cadmium sulfide-nickel hydroxide heterojunction photocatalyst, comprising defective cadmium sulfide and nickel hydroxide with cadmium vacancies, wherein the nickel hydroxide is anchored to the surface of the defective cadmium sulfide through the cadmium vacancies to form a heterojunction structure.

[0043] Nickel hydroxide exists in the form of nanosheets.

[0044] Nickel hydroxide accounts for 5% to 25% of the mass of the heterojunction photocatalyst.

[0045] In some other specific embodiments, nickel hydroxide accounts for 10% or 15% of the mass of the heterojunction photocatalyst.

[0046] Example 2

[0047] This embodiment provides a method for preparing defective cadmium sulfide, the steps of which are: in the presence of hydrogen peroxide, cadmium salt and sulfur source are subjected to a hydrothermal reaction to obtain defective cadmium sulfide.

[0048] In other specific embodiments, the preparation method is as follows: 3.5 mmol of cadmium acetate and 0.4 ml of 10% H₂O₂ are dissolved in an acidic aqueous solution with pH=1 to obtain a cadmium salt mixture; separately, 8 mmol of Na₂S·9H₂O is dissolved in deionized water to obtain a sulfur source solution. The cadmium salt mixture is slowly added dropwise to the sulfur source solution under rapid stirring, and after forming a suspension, it is transferred to a polytetrafluoroethylene autoclave and reacted at 160°C for 1080 minutes. After cooling to room temperature, the mixture is collected by centrifugation, washed with deionized water, and vacuum dried to obtain defective cadmium sulfide (DCdS).

[0049] The defective cadmium sulfide obtained in this embodiment was used to prepare the catalyst in Example 1. In this embodiment, a hydrothermal method was used to induce the formation of cadmium vacancies under the control of hydrogen peroxide. The band structure of the material was reconstructed by utilizing the cation-deficient sites, thereby enhancing the carrier separation efficiency. The obtained cadmium vacancies have high chemical activity, and their unsaturated coordination sites can provide atomically precise and robust active sites for the chemical anchoring of nickel hydroxide (Ni(OH)2).

[0050] Example 3

[0051] This embodiment provides a method for preparing a cadmium sulfide-nickel hydroxide heterojunction photocatalyst, which includes the following steps: dispersing defective cadmium sulfide in an alkaline solution, then adding a nickel salt solution to react and obtain the cadmium sulfide-nickel hydroxide heterojunction photocatalyst.

[0052] In some other specific embodiments,

[0053] DCdS was dispersed in NaOH solution, sonicated, and stirred. Nickel nitrate aqueous solution was slowly added dropwise, controlling the dropping rate to ensure complete reaction of nickel ions. Stirring continued for 4 hours, followed by filtration, washing several times with deionized water, and vacuum drying at 60℃ for 12 hours to obtain a cadmium sulfide-nickel hydroxide heterojunction photocatalyst, namely: Ni(OH)2 / DCdS composite catalyst. By precisely adjusting the amount of nickel nitrate aqueous solution added, composite materials with different Ni(OH)2 loadings can be prepared. The loading is expressed as the theoretical mass ratio of Ni(OH)2 to DCdS. Taking 5% Ni(OH)2 / DCdS as an example, the theoretical mass ratio of Ni(OH)2 to DCdS is 0.02:0.4; similarly, the corresponding mass ratios for 10% Ni(OH)2 / DCdS and 15% Ni(OH)2 / DCdS are 0.04:0.4 and 0.06:0.4, respectively.

[0054] In some other, more specific embodiments

[0055] 0.4 g of DCdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes. 4.31 mL of 0.05 mol / L nickel nitrate aqueous solution was slowly added dropwise, and the dropping rate was controlled to ensure that the nickel ions reacted completely. The mixture was stirred continuously for 4 hours, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 hours to obtain a 5% Ni(OH)2 / DCdS composite catalyst.

[0056] In some other, more specific embodiments

[0057] 0.4 g of DCdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes. 8.63 mL of 0.05 mol / L nickel nitrate aqueous solution was slowly added dropwise, controlling the dropping rate to ensure sufficient reaction of nickel ions. The mixture was stirred continuously for 4 hours, filtered, washed three times with deionized water, and vacuum dried at 60 °C for 12 hours to obtain a 10% Ni(OH)2 / DCdS composite catalyst.

[0058] In some other, more specific embodiments

[0059] 0.4 g of DCdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes. 12.94 mL of 0.05 mol / L nickel nitrate aqueous solution was slowly added dropwise, and the dropping rate was controlled to ensure that the nickel ions reacted completely. The mixture was stirred continuously for 4 hours, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 hours to obtain a 15% Ni(OH)2 / DCdS composite catalyst.

[0060] In some other, more specific embodiments

[0061] 0.4 g of DCdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes. 17.26 mL of 0.05 mol / L nickel nitrate aqueous solution was slowly added dropwise, and the dropping rate was controlled to ensure that the nickel ions reacted completely. The mixture was stirred continuously for 4 hours, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 hours to obtain a 20% Ni(OH)2 / DCdS composite catalyst.

[0062] In some other, more specific embodiments

[0063] 0.4 g of DCdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes. 21.57 mL of 0.05 mol / L nickel nitrate aqueous solution was slowly added dropwise, and the dropping rate was controlled to ensure that the nickel ions reacted fully. The mixture was stirred continuously for 4 hours, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 hours to obtain a 25% Ni(OH)2 / DCdS composite catalyst.

[0064] Example 4

[0065] This embodiment provides the application of the Ni(OH)2 / DCdS composite catalyst obtained in the above embodiment in the determination of photocatalytic hydrogen evolution reaction.

[0066] Take 50 mg of the Ni(OH)₂ / DCdS composite catalyst obtained in the above examples and add it to 100 mL of 10% lactic acid solution. Disperse the solution ultrasonically for 5 minutes to form a uniform suspension. Transfer the suspension to a sealed quartz reactor and continuously purge it with high-purity argon (Ar) gas for 30 minutes to fully replace the air in the system. Irradiate the reaction system vertically with a 300W xenon lamp source (λ≥420 nm) and maintain a constant temperature of 10°C. Take 1 mL of headspace gas sample every hour using a gas-tight needle.

[0067] In this embodiment, H2 production can be quantitatively analyzed using gas chromatography (GC1949 type).

[0068] Example 5

[0069] (1) Preparation of DCdS: 3.5 mmol of (CH3CO2)2Cd·2H2O and 0.4 mL of 10% H2O2 were dissolved in 20 mL of acidic aqueous solution with pH=1 to form a cadmium salt mixture; 8 mmol of Na2S·9H2O was dissolved in 20 mL of deionized water to form a sulfur source solution. The cadmium salt mixture was slowly added dropwise to the sulfur source solution under rapid stirring to generate a CdS precursor suspension. The suspension was transferred to a polytetrafluoroethylene autoclave and reacted at 160 °C for 1080 minutes. After cooling, the suspension was centrifuged and washed three times to remove impurities, and then vacuum dried at 60 °C for 720 minutes to obtain DCdS.

[0070] (2) Preparation of ordinary cadmium sulfide (PCdS): Compared with (1), no H2O2 was added and the amount of Na2S·9H2O added was different. The specific method is as follows: 3.5 mmol of (CH3CO2)2Cd·2H2O was dissolved in 20 mL of deionized water to form a cadmium salt mixture; Na2S·9H2O was dissolved in 20 mL of deionized water according to the cadmium-sulfur equimolar ratio to form a sulfur source solution. The cadmium salt mixture was slowly added dropwise to the sulfur source solution under rapid stirring to generate a CdS precursor suspension. It was transferred to a polytetrafluoroethylene autoclave and reacted at 160 °C for 1080 minutes. After cooling, it was centrifuged and washed 3 times to remove impurities, and then vacuum dried at 60 °C for 720 minutes to obtain PCdS.

[0071] (3) Preparation of Ni(OH)2 / DCdS composite catalyst: 0.4g of DCdS obtained in (1) was dispersed in 20mL of 0.25M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes; 12.94mL of 0.05mol / L nickel nitrate aqueous solution was slowly added dropwise, and the dropping rate was controlled to ensure that the nickel ions reacted fully; stirring was continued for 4 hours, and after filtration, the solution was washed three times with deionized water and dried under vacuum at 60℃ for 12 hours to obtain cadmium sulfide-nickel hydroxide heterojunction photocatalyst, namely: 15%Ni(OH)2 / DCdS composite catalyst. Among them, 15% in 15%Ni(OH)2 / DCdS is the theoretical mass ratio of Ni(OH)2 to DCdS.

[0072] (4) Preparation of Ni(OH)2 / PCdS composite catalyst: This embodiment uses the method of (3), but replaces the DCdS in (3) with an equimolar amount of PCdS obtained in (2) to obtain Ni(OH)2 / PCdS composite catalyst.

[0073] In this embodiment, XRD patterns were obtained for DCdS, Ni(OH)2 / DCdS composite catalyst, Ni(OH)2 / PCdS composite catalyst, ordinary cadmium sulfide (PCdS), and Ni(OH)2. The instrument used a copper target (Cu Kα, (λ=1.5418 Å),) with a voltage of 40 kV and a current of 40 mA. The diffraction angle (2θ) scanning range of the samples was 10–80°, and the scanning speed was 10° / min. The test results are as follows: Figure 1 As shown.

[0074] like Figure 1 The XRD phase analysis shown indicates that all materials have a well-defined crystal structure. The diffraction pattern of ordinary cadmium sulfide (PCdS) is in high agreement with the standard card of cubic zincblende structure (JCPDS#75-1546), with characteristic peaks at 26.50° (111), 30.70° (200), 43.97° (220), 52.08° (311), 54.58° (222), 63.93° (400), 70.47° (331), and 72.58° (420), indicating good crystallinity. In contrast, the diffraction peaks of cadmium-defective cadmium sulfide (DCdS) show a systematic shift (e.g., the (111) face shifts to a lower angle of about 0.1°-0.2°), but the peak shape does not change significantly, indicating that the introduction of Cd vacancies leads to lattice expansion and an increase in cell parameters, but does not change its wurtzite phase structure. The diffraction peaks of nickel hydroxide (Ni(OH)2) correspond perfectly to the standard card of α-Ni(OH)2 (JCPDS#14-0117), exhibiting typical layered diffraction characteristics at 19.25°(001), 33.07°(100), 38.54°(101), 52.10°(102), 59.05°(110), 62.73°(111), 70.48°(103) and 72.74°(201). In the spectra of Ni(OH)2 / PCdS and Ni(OH)2 / DCdS composite catalysts, characteristic diffraction peaks from CdS (e.g., 26.50° and 43.97°) and Ni(OH)2 (e.g., 33.07° and 38.54°) can be observed simultaneously. The peak positions of the two phases are clear and no impurity peaks are generated, confirming that a heterojunction composite structure has been successfully constructed without the formation of a new phase. It is worth noting that Ni(OH)2 / DCdS still retains the lattice shift characteristics unique to DCdS, indicating that defect engineering and heterostructure construction strategies can work synergistically in the design of photocatalytic materials.

[0075] Example 6

[0076] The photocatalytic hydrogen production activities of the Ni(OH)2 / DCdS composite catalyst, Ni(OH)2 / PCdS composite catalyst, ordinary cadmium sulfide (PCdS), and DCdS obtained in Example 5 were measured.

[0077] In Example 5, the preparation method of Ni(OH)2 / DCdS composite catalyst (3) was obtained by adjusting the amount of nickel nitrate aqueous solution added to obtain Ni(OH)2 / DCdS composite catalysts with different loadings of Ni(OH)2. The loading was expressed as the theoretical mass ratio of Ni(OH)2 to DCdS.

[0078] When the amount of nickel nitrate aqueous solution added was 4.31 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 5% was obtained, which is expressed as 5%Ni(OH)2 / DCdS;

[0079] When the amount of nickel nitrate aqueous solution added was 8.63 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 10% was obtained, which is represented as 10%Ni(OH)2 / DCdS.

[0080] When the amount of nickel nitrate aqueous solution added was 12.94 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 15% was obtained, which is represented as 15%Ni(OH)2 / DCdS.

[0081] When the amount of nickel nitrate aqueous solution added was 17.26 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 20% was obtained, which is represented as 20%Ni(OH)2 / DCdS.

[0082] When the amount of nickel nitrate aqueous solution added was 21.57 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 25% was obtained, which is expressed as 25%Ni(OH)2 / DCdS.

[0083] When the amount of nickel nitrate aqueous solution added was 26.89 ml, a Ni(OH)2 / DCdS composite catalyst with a Ni(OH)2 loading of 30% was obtained, which is represented as 30%Ni(OH)2 / DCdS.

[0084] The determination method is as follows:

[0085] Take 50 mg of any of the above samples and add it to 100 mL of 10% lactic acid solution. Disperse the solution ultrasonically for 5 minutes to form a homogeneous suspension. Transfer the suspension to a sealed quartz reactor and continuously purge with high-purity argon (Ar) gas for 30 minutes to fully replace the air in the system. Irradiate the reaction system vertically with a 300W xenon lamp (λ≥420 nm) and maintain a constant temperature of 10℃. Take 1 mL of headspace gas sample every hour using a gas-tight needle. The H2 yield can be quantitatively analyzed by gas chromatography (GC1949 type).

[0086] The measurement results are as follows Figure 2 The image shows the photocatalytic hydrogen evolution reaction activity of PCdS, DCdS, Ni(OH)2 / PCdS, and Ni(OH)2 / DCdS catalysts. All materials exhibit photocatalytic hydrogen evolution activity, but their performance varies significantly. PCdS alone exhibits the lowest activity, which is related to its severe photogenerated electron-hole recombination. Introducing Ni(OH)2 and recombinating it significantly improves hydrogen production, demonstrating that the construction of the heterojunction effectively promotes charge separation. More importantly, DCdS containing Cd defects exhibits significantly higher intrinsic activity than PCdS, directly confirming the success of defect engineering. Cd vacancies serve as effective active sites, optimizing the charge separation efficiency or reaction kinetics of the materials.

[0087] Combining these two strategies resulted in synergistic performance enhancement. As shown in the figure, the hydrogen production performance of the Ni(OH)₂ / DCdS composite was significantly better than that of the Ni(OH)₂ / PCdS composite and DCdS alone. Among them, the 15% Ni(OH)₂ / DCdS composite catalyst exhibited the best performance, with a hydrogen production rate as high as 9385.19 μmol·h⁻¹. -1 Compared with PCdS and Ni(OH)2 / PCdS, it is 197 times and 11.2 times higher, respectively, while nickel hydroxide has no hydrogen production activity at all.

[0088] Example 7

[0089] The Ni(OH)₂ / DCdS composite catalyst, Ni(OH)₂ / PCdS composite catalyst, ordinary cadmium sulfide (PCdS), and DCdS obtained in Example 5 were subjected to UV-Vis diffuse reflectance spectra measurement using a Shimadzu UV-2700 spectrophotometer. Spectral data were collected in the wavelength range of 200-800 nm, with BaSO₄ used as a background reference. Finally, the measured diffuse reflectance data were converted into absorbance according to the Kubelka-Munk equation to analyze the light absorption characteristics of the materials. The measurement results are as follows: Figure 3 As shown.

[0090] like Figure 3As shown, all samples exhibit an intrinsic absorption edge of hexagonal wurtzite CdS near 520 nm. Among them, cadmium-defective cadmium sulfide (DCdS) shows a slight blue shift in its absorption edge compared to ordinary cadmium sulfide (PCdS), indicating that the introduction of Cd vacancies effectively alters the material's bandgap. Notably, the composite of Ni(OH)₂ and CdS significantly enhances the light absorption intensity in the long-wavelength region (550-800 nm), and the Ni(OH)₂ / DCdS composite catalyst exhibits the strongest light absorption performance across the entire spectral range. This synergistic enhancement of optical performance—originating from bandgap optimization through defect engineering and improved light-harvesting ability due to heterojunction composite—achieved the highest photocatalytic hydrogen production rate (9385.19 μmol·g⁻¹) for the Ni(OH)₂ / DCdS sample. -1 ·h -1 It provides a key foundation for photophysics.

[0091] Example 8

[0092] The photocurrent response of the 15% Ni(OH)₂ / DCdS composite catalyst, Ni(OH)₂ / PCdS composite catalyst, ordinary cadmium sulfide (PCdS), and DCdS obtained in Example 5 was measured. The measurement method was as follows: a standard three-electrode system was used, in which an electrode made of catalyst slurry (usually composed of catalyst powder, Nafion solution, and ethanol dispersant) coated on FTO conductive glass was used as the working electrode, an Ag / AgCl electrode (filled with saturated KCl solution) was used as the reference electrode, and a platinum sheet or graphite electrode was used as the counter electrode. The test was usually carried out in a 0.5 mol / L Na₂SO₄ aqueous electrolyte to ensure a stable ionic conductivity environment. During testing, under open-circuit potential, a xenon lamp with a cutoff filter of λ ≥ 420 nm was used to simulate visible light irradiation. By periodically switching the light source, the voltage signal across the sampling resistor was collected using a CHI760E electrochemical workstation (which was then converted into a current signal using Ohm's law). The transient photocurrent response curve (it curve) of the working electrode under alternating light and dark conditions was recorded to evaluate the photogenerated carrier separation and transport efficiency of the material.

[0093] The measurement results are as follows Figure 4 As shown, from Figure 4As can be seen, PCdS exhibits the weakest photocurrent response, indicating severe recombination of photogenerated carriers. DCdS shows an improved photocurrent compared to PCdS, confirming that the introduction of Cd vacancy defects effectively suppresses some electron-hole pair recombination. Notably, the photocurrent of Ni(OH)2 / PCdS after recombination with CdS is significantly enhanced, demonstrating that the heterojunction interface effectively promotes charge separation. Furthermore, the Ni(OH)2 / DCdS sample, constructed by combining defect engineering and the heterostructure, exhibits a synergistic enhancement effect, demonstrating the best photoelectrochemical performance, with its photocurrent density reaching the highest value, significantly higher than other samples. This result is completely consistent with previous XRD, DRS, and photocatalytic hydrogen production performance data, jointly proving that the synergistic effect of defect engineering and the heterostructure can significantly improve the photogenerated charge separation efficiency, thereby endowing the material with excellent photocatalytic hydrogen production activity.

[0094] Example 9

[0095] This embodiment provides a Ni(OH)2 / V S The preparation method of the -CdS composite catalyst includes the following steps:

[0096] 3.5 mmol of cadmium acetate was dissolved in 20 mL of deionized water, and 3.5 mmol of Na₂S·9H₂O was dissolved in 20 mL of deionized water. The cadmium salt solution was added dropwise to the sulfur source solution while stirring. The resulting suspension was transferred to an autoclave and reacted at 160 °C for 1080 min. After cooling, the mixture was centrifuged and washed three times to remove impurities, and then dried under vacuum at 60 °C for 720 min to obtain PCdS. 0.5 g of PCdS was reduced at 200 °C under a H₂ / Ar mixed atmosphere for 2 hours, followed by centrifugation, washing, and drying to obtain V₂S rich in sulfur vacancies. S -CdS.

[0097] Take 0.4gV S -CdS was dispersed in 20 mL of 0.25 M NaOH solution, sonicated for 30 minutes, and mechanically stirred for 30 minutes; 12.94 mL of 0.05 M nickel nitrate solution was slowly added dropwise, and stirring was continued for 4 hours. After filtration and washing, the solution was dried under vacuum at 60 °C for 12 hours to obtain 15% Ni(OH)2 / V S -CdS composite catalyst (theoretical loading 15%).

[0098] After measurement, Ni(OH)2 / V S The hydrogen production rate of the -CdS composite catalyst was significantly lower than that of the 15%Ni(OH)2 / DCdS in Example 6.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cadmium sulfide-nickel hydroxide heterojunction photocatalyst, characterized by, It includes: It includes defective cadmium sulfide with cadmium vacancies and nickel hydroxide, wherein the nickel hydroxide is anchored to the surface of the defective cadmium sulfide through cadmium vacancies to form a heterojunction structure.

2. The cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in claim 1, characterized in that: The nickel hydroxide exists in the form of nanosheets.

3. The cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in claim 1, characterized in that: The nickel hydroxide in the heterojunction photocatalyst accounts for 5% to 25% by mass.

4. A method for preparing a cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in claim 1 or 2, characterized in that, It includes the following steps: After dispersing defective cadmium sulfide in an alkaline solution, a nickel salt solution is added to react and obtain the cadmium sulfide-nickel hydroxide heterojunction photocatalyst.

5. The preparation method of the cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in claim 4, characterized in that, The method for preparing the defective cadmium sulfide includes the following steps: in the presence of hydrogen peroxide, cadmium salt and sulfur source are subjected to a hydrothermal reaction to obtain the defective cadmium sulfide.

6. The preparation method of the cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in claim 5, characterized in that: The temperature of the hydrothermal reaction is 140~160℃.

7. The application of a cadmium sulfide-nickel hydroxide heterojunction photocatalyst as described in any one of claims 1-3 in photocatalytic water splitting for hydrogen production.

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