Chitosan-polyvinyl alcohol hydrogel / cd s-ni type hybrid material, preparation method thereof and seawater desalination-photocatalytic hydrogen production synergistic application

Abstract

A chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material and its preparation method are disclosed for synergistic application in seawater desalination and photocatalytic hydrogen production, belonging to the field of photothermal and photocatalytic functional materials technology. This material uses a CS-PVA dual-network hydrogel as a three-dimensional porous carrier to grow hexagonal wurtzite CdS nanoparticles (100-200 nm) in situ. Ni is dispersed on the CdS surface in the form of single atoms / clusters, reducing the band gap from 2.40 eV to 2.30 eV. This invention employs a one-step hydrothermal method, which is simple, mild, green, and low-cost. The obtained material can be used in 1 kW·m² applications. ‑2 Under sunlight, the water evaporation rate reaches 2.43 kg·m³. ‑2 ·h ‑1 The solar-to-steam conversion efficiency was 94.7%, and the photocatalytic hydrogen production rate reached 6.28 mmol·g⁻¹. ‑1 ·h ‑1 It possesses excellent resistance to salt crystallization and photocorrosion. This invention can simultaneously achieve seawater desalination and hydrogen production under a single light source, and is suitable for the co-production of freshwater and hydrogen in islands and remote areas. It has the advantages of high efficiency, stability, easy recovery, and scalability.

Description

Technical Field

[0001] This invention belongs to the technical fields of photothermal conversion materials, photocatalytic water splitting for hydrogen production, seawater desalination, and functional materials for the aquatic environment. Specifically, it relates to a hybrid composite material formed by using chitosan-polyvinyl alcohol dual-network hydrogel as a three-dimensional porous carrier, in-situ loading of hexagonal wurtzite cadmium sulfide, and introducing a nickel-based co-catalyst. In particular, it relates to a one-step hydrothermal preparation method of chitosan-polyvinyl alcohol (CS-PVA) hydrogel / CdS-Ni hybrid material, and the integrated synergistic application of this material to simultaneously achieve efficient seawater desalination and stable photocatalytic hydrogen production under simulated sunlight. Background Technology

[0002] Currently, the world faces the dual challenges of extreme freshwater scarcity and dwindling fossil fuel resources. Developing integrated technologies that can simultaneously address water supply and clean energy production has become a core direction for sustainable development strategies worldwide. On the one hand, freshwater resources account for less than 2.5% of the Earth's surface and are extremely unevenly distributed, making seawater desalination a mainstream technological approach to alleviate the water crisis. On the other hand, the overuse of traditional fossil fuels has led to excessive carbon emissions, exacerbated the greenhouse effect, and increased air pollution, making the development of zero-carbon, clean, and storable hydrogen energy a core choice for global energy transition.

[0003] Solar energy, as a renewable energy source with unlimited reserves, wide distribution, and clean, pollution-free characteristics, can simultaneously drive two core technological pathways: solar thermal interface evaporation for seawater desalination and water purification; and semiconductor photocatalytic water splitting for green hydrogen production. If these two functions can be integrated into the same material, the same device, and the same light source, achieving "simultaneous production of fresh water and hydrogen from a single material," it will significantly improve the full-spectrum utilization rate of solar energy, enabling efficient co-production of energy and water resources. This represents the most promising development direction in the current intersection of new energy and water treatment.

[0004] In the field of photocatalytic hydrogen production, cadmium sulfide (CdS) is one of the most representative visible-light-responsive semiconductor photocatalysts. With a band gap of approximately 2.4 eV, it possesses a suitable conduction band potential, strong visible light absorption, and good catalytic activity, making it widely used in photocatalytic water splitting for hydrogen production. However, pure CdS materials face three major bottlenecks that are difficult to overcome:

[0005] 1. The recombination rate of photogenerated electron-hole pairs is extremely fast, the charge separation efficiency is low, and it is difficult to improve the quantum yield;

[0006] 2. Photocorrosion is highly likely to occur under light conditions, and photogenerated holes oxidize lattice sulfur ions, leading to catalyst structural collapse and rapid activity decay;

[0007] 3. Pure powdered CdS is prone to agglomeration, sedimentation, and recycling. It is also prone to deactivation in high-salt environments such as seawater, making it impractical for application.

[0008] To address these issues, researchers typically employ techniques such as morphology control, heterostructure construction, elemental doping, and catalyst loading for modification. Among these, non-precious metal nickel (Ni)-based catalysts are the optimal alternative to precious metal platinum (Pt) due to their low cost, good conductivity, strong electron capture ability, and low hydrogen evolution overpotential. They can significantly improve charge separation efficiency, provide highly efficient hydrogen production active sites, and suppress photocorrosion.

[0009] In the field of seawater desalination, hydrogel-based photothermal interface evaporation systems have emerged as a new generation of high-efficiency solar steam generation technology due to their advantages such as three-dimensional porous networks, high water retention, low thermal conductivity, and reduced enthalpy of evaporation. Chitosan (CS), derived from natural chitin, is non-toxic, biocompatible, highly hydrophilic, and rich in hydroxyl and amino groups; polyvinyl alcohol (PVA) has good water solubility, strong film-forming properties, mechanical stability, and abundant hydrogen bonding. Combining these two materials to form a chitosan-PVA dual-network hydrogel combines the advantages of both natural and synthetic polymers, achieving a balance of high porosity, strong water transport capacity, low thermal diffusion, and excellent mechanical stability. This makes it an ideal carrier for constructing a photothermal-photocatalytic synergistic system.

[0010] Currently, no publicly available patents or literature reports have been found on a technical solution for constructing a dual-functional integrated hybrid material that combines efficient photothermal seawater desalination, highly stable photocatalytic hydrogen production, resistance to salt crystallization and photocorrosion, and easy recycling by in-situ composite of chitosan-polyvinyl alcohol dual-network hydrogel and CdS-Ni photocatalytic components via a one-step hydrothermal method, and achieving simultaneous co-production in a real seawater environment.

[0011] Most existing technologies still have significant shortcomings: they are limited in function, producing only fresh water or only hydrogen; the multi-step preparation process is complex and the interfacial bonding is weak; the catalyst is prone to detachment and agglomeration; salt formation and pore blockage are common in seawater environments; CdS photocorrosion is difficult to suppress; and the powder is difficult to recover. Summary of the Invention

[0012] The technical problems solved by this invention are: 1. Pure CdS suffers from severe recombination of photogenerated carriers, low photocatalytic hydrogen production efficiency, susceptibility to photocorrosion under light, and poor cycle stability; 2. Photocatalysts exist in powder form, which are prone to agglomeration, loss, and difficult separation and recovery, making them unsuitable for direct use in natural seawater systems; 3. Traditional photothermal evaporation materials can only achieve freshwater production, have a single function, and cannot achieve the conversion of solar energy into chemical energy; 4. When multiple components are combined, the interfacial bonding is weak, the structure is prone to collapse, and photothermal and photocatalytic functions interfere with each other; 5. In high-salinity seawater environments, salt ions easily crystallize and block pores, leading to a rapid decline in evaporation efficiency and catalytic activity; 6. The preparation process is complex, involves multiple loading steps, is costly, and is difficult to scale up for production and engineering applications. To address this, the present invention proposes a chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material, which simultaneously completes hydrogel crosslinking, CdS crystal growth and Ni co-catalyst loading through a one-step hydrothermal method, achieving efficient synergy between seawater desalination and photocatalytic hydrogen production under a single light source. It forms a complete technical solution from structural design and preparation process to practical application, solving all the core pain points of the existing technology.

[0013] This invention utilizes a chitosan-polyvinyl alcohol (CS-PVA) dual-network hydrogel as a three-dimensional porous carrier, a rapid water molecule transport channel, a photothermal insulation layer, and a catalyst stabilizing framework; hexagonal wurtzite-structured CdS as a visible light-responsive photocatalytic host; and Ni single-atom / nanoclusters as a highly efficient electron trapper, hydrogen production active site, and photocorrosion inhibitor. Through a one-step hydrothermal method, the three processes of "hydrogel cross-linking and molding, in-situ CdS nucleation and growth, and uniform Ni loading" are simultaneously completed, resulting in a high-performance hybrid material integrating photothermal conversion, interfacial evaporation, seawater desalination, photocatalytic hydrogen production, salt crystallization resistance, photocorrosion inhibition, and easy recyclability.

[0014] The present invention discloses a chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material, wherein the hybrid material uses chitosan-polyvinyl alcohol hydrogel as a porous framework, on which CdS nanoparticles with a hexagonal wurtzite structure are grown in situ. Ni element is dispersed in both single-atom and nano-cluster forms on the surface of the long hexagonal wurtzite phase CdS nanoparticles, without independent Ni crystal phase; there is no elemental segregation or particle agglomeration.

[0015] Furthermore, the chitosan-polyvinyl alcohol hydrogel has a pore size of 2~10 μm and a continuous porous structure; the CdS band gap is 2.35~2.55 eV, and the band gap of the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is reduced to 2.15~2.35 eV.

[0016] Furthermore, the Ni loading mass fraction is 3.91%~5 wt%.

[0017] Furthermore, Ni provides electron-capturing sites and hydrogen-producing active centers in the form of a co-catalyst.

[0018] The present invention discloses a method for preparing chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid materials, wherein the method employs a one-step hydrothermal synthesis and includes the following steps:

[0019] Step 1: Dissolve chitosan in glacial acetic acid solution and polyvinyl alcohol in hot water. After mixing, add glutaraldehyde for cross-linking to obtain CS-PVA double network hydrogel precursor solution.

[0020] Step 2: Add cadmium salt, nickel salt and sulfur source to the CS-PVA dual-network hydrogel precursor solution, stir well to obtain a mixture;

[0021] Step 3: Transfer the mixture into the reaction vessel for hydrothermal reaction;

[0022] Step 4: Wash and vacuum dry to obtain CS-PVA / CdS-Ni hybrid material, which is the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material.

[0023] Further, the method for preparing the CS-PVA dual-network hydrogel precursor solution in step 1 is as follows: after mixing chitosan glacial acetic acid solution with a mass concentration of 0.1~1g / mL and polyvinyl alcohol solution with a mass concentration of 0.5~1g / mL, a 25% glutaraldehyde solution is added to obtain the solution; wherein, the volume-mass ratio of the 25% glutaraldehyde solution to chitosan is 1mL:1g.

[0024] Furthermore, in step 2, the mass ratio of cadmium acetate: nickel acetate: thiourea is 2.0~6.0 : 0.1~0.3 : 2.5~6.5, and the stirring time is 10~90 min.

[0025] Furthermore, in step 4, the washing method is to wash with deionized water 1 to 5 times and with anhydrous ethanol 2 to 5 times; the drying conditions are vacuum drying at 50 to 80 ℃ for 6 to 24 h.

[0026] The application of the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material described in this invention is that the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is used for solar-driven seawater desalination and photocatalytic hydrogen production.

[0027] Furthermore, the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is used for solar-driven seawater desalination and photocatalytic hydrogen production. This involves adding the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material to the seawater to be treated, using lactic acid as a sacrificial agent, and purging nitrogen gas to remove oxygen, thereby achieving solar-driven seawater desalination and photocatalytic hydrogen production.

[0028] The present invention has the following beneficial effects:

[0029] 1. Dual-function integrated design, enabling efficient utilization of the entire solar energy spectrum.

[0030] Using the same material, the same light source, and the same system, we can simultaneously achieve efficient seawater desalination and highly stable photocatalytic hydrogen production. Ultraviolet-visible light drives photocatalytic hydrogen production, while infrared and some visible light drive photothermal evaporation, enabling the utilization of a wide spectrum of solar energy. The overall energy utilization rate is far higher than that of single-function materials.

[0031] 2. Top-notch photothermal evaporation performance, resistant to salt crystallization and does not clog pores.

[0032] Under one times the sunlight intensity, the water evaporation rate reaches as high as 2.43 kg·m³. -2 ·h -1 The solar-to-steam conversion efficiency reaches 94.7%; the three-dimensional interconnected channels of the hydrogel enable high-speed transport of water molecules and reverse diffusion of salt ions, preventing salt formation, pore blockage, and efficiency reduction in high-salt seawater.

[0033] 3. Significantly enhanced hydrogen production activity and extended lifespan against photocorrosion.

[0034] The optimal hydrogen production rate reached 6.28 mmol·g. -1 ·h -1 It is more than 15 times that of pure CdS; Ni co-catalyst rapidly extracts photogenerated electrons, significantly reducing the electron-hole recombination rate; hydrogel network physically encapsulates and inhibits CdS particle aggregation, and works synergistically with lactic acid sacrificial agent to fundamentally inhibit photocorrosion, with no activity decay after 4 hours of continuous operation.

[0035] 4. Three-dimensional porous structure enhances the solid-liquid-gas interfacial reaction.

[0036] The continuous interconnected network with pore sizes of 2~10 μm provides high-speed channels for water transport, steam overflow, ion diffusion, and gas release; the catalyst is highly dispersed and the active sites are fully exposed, which greatly improves reaction kinetics and significantly reduces mass transfer resistance.

[0037] 5. One-step hydrothermal synthesis, simple process, mild conditions, and scalable.

[0038] Hydrothermal processes are completed simultaneously in one step: hydrogel crosslinking, CdS growth, and Ni loading. No high-temperature calcination, multi-step impregnation, or complex equipment are required. The preparation process is short, energy-efficient, reproducible, and environmentally friendly, making it suitable for industrial scale-up.

[0039] 6. Self-supporting block structure, easy to recycle, and no secondary pollution.

[0040] The monolithic block hydrogel material can be used directly by floating and can be taken out and recycled as a whole. It does not require centrifugation or filtration and will not be lost with water, completely solving the industry pain points of powder catalysts being difficult to recycle and easily causing water pollution.

[0041] 7. Can be used directly in natural seawater; resistant to salt and impurities; highly practical.

[0042] It can operate stably directly in natural seawater, brackish water, and high-salt wastewater without pretreatment, impurity removal, or ion concentration adjustment. It is suitable for simultaneous freshwater and hydrogen energy supply in islands, ocean-going vessels, field operations, and remote areas.

[0043] 8. Green and environmentally friendly, with inexpensive raw materials and good biocompatibility.

[0044] Chitosan and polyvinyl alcohol are both non-toxic, biodegradable, and biocompatible green polymers; using non-precious metal Ni eliminates the need for precious metals, resulting in extremely low raw material costs; the entire system contains no toxic reagents and causes no secondary pollution, conforming to the concepts of carbon neutrality and green chemistry. Attached Figure Description

[0045] Figure 1. XRD diffraction patterns of pure CdS, CS-PVA hydrogel, CS-PVA / CdS, and CS-PVA / CdS-Ni;

[0046] Figure 2. SEM microstructure and EDS elemental distribution (C, O, Cd, S, Ni) of CS-PVA / CdS-Ni hybrid material at different magnifications.

[0047] Figure 3. UV-Vis diffuse reflectance absorption spectra of each sample and calculation of Kubelka-Munk bandgap;

[0048] Figure 4. Comparison of mass loss and rate of photothermal evaporation of pure water, pure hydrogel, and CS-PVA / CdS-Ni;

[0049] Figure 5. Comparison of surface temperature change curves of each sample under illumination and infrared thermal imaging;

[0050] Figure 6. Stability curves of CS-PVA / CdS-Ni in simulated seawater after 10 consecutive evaporation cycles;

[0051] Figure 7. Comparison of photocatalytic hydrogen production capacity and rate between pure CdS, CS-PVA / CdS, and CS-PVA / CdS-Ni;

[0052] Figure 8. Schematic diagram of the synergistic mechanism of CS-PVA / CdS-Ni seawater desalination-photocatalytic hydrogen production dual pathway. Detailed Implementation

[0053] The present invention will be further described in detail with reference to specific embodiments. The following embodiments are preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto.

[0054] Example 1 Material Preparation

[0055] This case study details the complete preparation process, reagents, and instruments used for CS-PVA pure hydrogel, pure CdS powder, CS-PVA / CdS composite hydrogel, and CS-PVA / CdS-Ni hybrid materials. It also clarifies the testing methods for two key performance indicators: photothermal seawater desalination and photocatalytic hydrogen production. All reagents used were analytical grade, including chitosan, polyvinyl alcohol, cadmium acetate dihydrate, nickel acetate tetrahydrate, thiourea, glacial acetic acid, glutaraldehyde, anhydrous ethanol, and deionized water. The experimental equipment included a standard analytical and testing instrument such as an electronic analytical balance, magnetic stirrer, hydrothermal synthesis reactor, high-speed centrifuge, vacuum drying oven, X-ray diffractometer, scanning electron microscope, UV-Vis spectrophotometer, xenon lamp light source, gas chromatograph, and infrared thermal imager. First, a CS-PVA dual-network hydrogel precursor solution was prepared. Chitosan was dissolved in glacial acetic acid aqueous solution, and polyvinyl alcohol was dissolved in a 90℃ water bath. After the two solutions were mixed evenly, glutaraldehyde was added as a crosslinking agent to obtain a stable precursor solution. Subsequently, a series of samples were prepared using a one-step hydrothermal method. The precursor solution was directly hydrothermally reacted to obtain pure CS-PVA hydrogel. Cadmium acetate and thiourea were added to the precursor solution in sequence, and CS-PVA / CdS composite material was hydrothermally synthesized. Cadmium acetate, nickel acetate, and thiourea were compounded in the precursor solution to generate CS-PVA / CdS-Ni hybrid material in situ under hydrothermal conditions of 200℃ and 24 h. At the same time, pure Cd powder was prepared as a control sample under the same reaction conditions. After all products were reacted, they were naturally cooled, centrifuged, washed multiple times with deionized water and anhydrous ethanol, and vacuum dried at 60℃ before the finished product was collected. For performance testing, the photothermal seawater desalination experiment was conducted by floating the sample on the surface of simulated seawater and using a xenon lamp to simulate 1 kW·m -2 Standard sunlight was used to record mass changes via an electronic balance and monitor surface temperature using an infrared thermal imager to calculate evaporation rate and photothermal conversion efficiency. In the photocatalytic hydrogen production experiment, samples were dispersed in an aqueous solution with added lactic acid as a sacrificial agent. After purging the system with nitrogen, light was applied, and hydrogen production was periodically detected using gas chromatography to calculate the hydrogen production rate. This one-step hydrothermal process can simultaneously complete hydrogel crosslinking and in-situ growth of photocatalytic components, resulting in tight interfacial bonding between components. The operation is simple and allows for the batch preparation of comparative samples with different components.

[0056] Example 2 XRD Crystal Phase Structure Analysis

[0057] This case study utilizes a D8 Advance X-ray diffractometer to perform crystal and phase analysis on four samples: pure CdS, CS-PVA hydrogel, CS-PVA / CdS, and CS-PVA / CdS-Ni, within a scanning range of 10°–80° and under Cu Kα radiation conditions. The analysis was compared with the hexagonal wurtzite CdS standard card (PDF#00-006-0314). Figure 1 As shown, pure CdS powder exhibits sharp characteristic diffraction peaks at multiple locations with 2θ values ​​of 24.8°, 26.5°, and 28.2°, corresponding to various crystal planes of hexagonal wurtzite CdS, demonstrating the good crystallinity of the prepared CdS. The CS-PVA hydrogel only shows a broad, diffuse peak around 20°, consistent with the amorphous characteristics of amorphous polymers. The CS-PVA / CdS sample simultaneously shows both hydrogel diffuse peaks and CdS characteristic peaks. The CdS diffraction peak intensity is slightly reduced and the peak shape is slightly broadened, which is due to the spatial confinement effect of the hydrogel network reducing the CdS grain size, but the crystal phase remains unchanged. The diffraction pattern of the CS-PVA / CdS-Ni sample is basically consistent with that of CS-PVA / CdS, without the characteristic peaks of nickel-based materials such as NiO and NiS, indicating a low Ni doping level. The Ni element is highly dispersed on the CdS surface and in the lattice in the form of single atoms or ultrafine clusters, without forming an independent crystal phase. Overall test results confirm that the introduction of hydrogel carrier and Ni additive does not damage the original hexagonal wurtzite crystal structure of CdS, and the material has excellent crystal phase stability.

[0058] Example 3 Microscopic Morphology Analysis

[0059] This case study utilizes a Hitachi SU8010 scanning electron microscope combined with EDS elemental analysis and EDX elemental mapping techniques to observe the microstructure, pore structure, particle distribution, and elemental composition of CS-PVA / CdS-Ni hybrid materials. Figure 2As shown, the material forms a three-dimensional interconnected porous network structure with pore sizes ranging from 2 to 10 μm. The interconnected pores provide unobstructed mass transfer channels for seawater transport and water vapor escape. Under high magnification, it can be clearly observed that CdS-Ni nanoparticles with diameters of 100–200 nm are uniformly attached to the surface of the hydrogel framework. The particles and gel are firmly bonded, with only a small amount of slight agglomeration, proving that the one-step hydrothermal method achieves uniform loading of catalytic components. EDX elemental mapping results show that C and O elements are uniformly distributed throughout the material region, corresponding to the CS-PVA hydrogel matrix; the distribution areas of Cd and S elements highly overlap, corresponding one-to-one with the particle positions; Ni elements show no local enrichment and are uniformly dispersed on the surface of CdS particles. EDS quantitative analysis shows that the atomic ratio of Cd to S is close to 1:1, and the actual Ni loading is basically consistent with the theoretical feed. Comprehensive characterization results indicate that the material has a reasonable microstructure design, the porous structure ensures mass transfer efficiency, and the active components are uniformly dispersed, providing a good structural basis for photothermal evaporation and photocatalytic reactions.

[0060] Example 4: Ultraviolet-Visible Absorption Spectroscopy and Band Gap Calculation

[0061] This case study uses a UV-3600 UV-Vis spectrophotometer with BaSO4 as a reference to measure the diffuse reflectance spectra of each sample in the wavelength range of 200–800 nm. The optical band gap is calculated using the Kubelka-Munk function and the Tauc formula to analyze the impact of component modification on the material's light absorption capacity and band structure. Figure 3 As shown, pure CS-PVA hydrogel exhibits extremely low absorbance across the entire wavelength range, essentially absorbing no sunlight and serving only as an inert support. Pure CdS has its absorption edge concentrated around 500 nm, utilizing only ultraviolet and short-wavelength visible light. After CdS is loaded onto the hydrogel, the absorption range of the CS-PVA / CdS sample slightly widens, while the absorption edge of the CS-PVA / CdS-Ni sample, after the introduction of Ni, further redshifts, significantly increasing absorbance in the longer wavelength region. This indicates that Ni doping effectively expands the spectral response range of the material. Bandgap calculations show that the optical bandgap of pure CdS is 2.40 eV, the bandgap of CS-PVA / CdS decreases to 2.35 eV, and the bandgap of CS-PVA / CdS-Ni further decreases to 2.30 eV. This is because Ni introduces impurity energy levels into the CdS bandgap, lowering the electronic transition energy barrier. Optical performance tests demonstrate that Ni modification and hydrogel loading synergistically improve the material's utilization efficiency of visible light, enabling the excitation of more photogenerated carriers and providing favorable conditions for photocatalytic reactions.

[0062] Example 5: Study on the synergistic performance of seawater desalination and photocatalytic hydrogen production

[0063] This case study conducts two performance tests: photothermal seawater desalination and photocatalytic hydrogen production. It systematically analyzes the effects of crosslinking time and component ratio on material properties and evaluates the sample's cycling stability and application feasibility. Figure 4 and Figure 5 As shown, at 1 kW·m -2 Seawater desalination tests under simulated sunlight conditions: Pure water evaporation rate is only 0.37 kg·m³. -2 ·h -1 The interface temperature rises slowly, with the surface temperature only reaching 30℃ after 60 min; the properties of pure CS-PVA hydrogels with different crosslinking times vary significantly, with the evaporation rate of the sample after 1 h of crosslinking reaching 1.55 kg·m³. -2 ·h -1 When the surface temperature rises to 44.2℃, the evaporation efficiency reaches 75%. With prolonged cross-linking time, the pores gradually shrink, and the evaporation rate decreases synchronously with the surface temperature. The evaporation rate of the CS-PVA / CdS-Ni hybrid material is 1.45 kg·m³. -2 ·h -1 The photothermal conversion efficiency is 70%, and the surface temperature is 41.0℃. CdS-Ni can help improve the photothermal capacity, but some light energy is used for photocatalytic reactions, so the evaporation performance is slightly lower than that of the optimal pure hydrogel. Infrared thermal imaging results directly confirm the interfacial thermal localization advantage of the hydrogel, and the CS-PVA / CdS-Ni exhibits excellent thermal aggregation effect. Figure 6 As shown, the material exhibits an 89% evaporation rate retention rate after 10 consecutive evaporations, with no salt crystal precipitation on the surface. Only slight performance degradation occurs due to minor gel shrinkage and a small amount of particle shedding, demonstrating good short-term cycling stability. Figure 7 As shown, the hydrogen production rate of pure CdS is only 0.399 mmol·h. -1 ·g -1 The activity improvement of CS-PVA / CdS was slight; Ni modification significantly improved hydrogen production activity. Powdered CdS-Ni with a ratio of 5 wt% showed the best performance, while the hydrogen production rate of CS-PVA / CdS-Ni with 5 wt% Ni doping reached 2.776 mmol·h. -1 ·g -1 The hydrogen production rate is approximately seven times that of pure CdS, and the hydrogen production steadily increases during 4 hours of continuous testing. Ni acts as an active site to capture photogenerated electrons and suppress carrier recombination and CdS photocorrosion. The confinement effect of the hydrogel further prevents particle aggregation and loss, achieving a good balance between hydrogen production activity and stability. In summary, this material can simultaneously achieve photothermal evaporation and photocatalytic reaction, making it suitable for applications involving the co-production of freshwater and green hydrogen.

[0064] Example 6: Analysis of the Synergistic Mechanism between Seawater Desalination and Hydrogen Production

[0065] This case study analyzes the synergistic mechanism of photothermal seawater desalination and photocatalytic hydrogen production using CS-PVA / CdS-Ni hybrid materials under a single light source, combining material structure, optical properties, and various performance data. Figure 8 As shown, the CS-PVA dual-network hydrogel serves as the core carrier. Its three-dimensional interconnected porous structure allows for the continuous transport of seawater and rapid extraction of water vapor, while simultaneously reducing the enthalpy of water evaporation and enhancing the interfacial thermal localization effect. The confinement effect of the hydrogel also inhibits the aggregation and loss of CdS-Ni particles, mitigating CdS photocorrosion. Under illumination, solar energy undergoes two conversion pathways: some high-energy photons are absorbed by CdS, generating photogenerated electron-hole pairs. The Ni active sites distributed on the CdS surface can quickly capture these photogenerated electrons, effectively suppressing carrier recombination. Electrons at the Ni sites reduce water protons to hydrogen, while the photogenerated holes are promptly consumed by the lactic acid sacrificial agent in the system, ensuring stable operation of the catalytic cycle. The other pathway involves the conversion of low-energy photons and some light energy into heat energy, creating localized high temperatures at the material interface, driving rapid seawater evaporation and achieving seawater desalination. The two functions occur simultaneously and synergistically, with only a small amount of light energy competition and no mutual interference. This system leverages the structural advantages of hydrogels and the electronic regulation effect of Ni additives to achieve efficient and graded utilization of solar energy, enabling the co-production of freshwater and green hydrogen. The overall mechanism is clear, and the materials exhibit strong stability and practicality. It can be applied to integrated equipment for comprehensive solar energy utilization, seawater desalination, and hydrogen production in island and coastal areas.

Claims

1. A chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material, characterized in that: The hybrid material uses chitosan-polyvinyl alcohol hydrogel as a porous framework, on which CdS nanoparticles with a hexagonal wurtzite structure are grown in situ. Ni element is dispersed in the surface of the long hexagonal wurtzite phase CdS nanoparticles in both single-atom and nano-cluster forms; there is no element segregation or particle agglomeration.

2. The chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material according to claim 1, characterized in that: The chitosan-polyvinyl alcohol hydrogel has a pore size of 2~10 μm and a continuous porous structure; the CdS band gap is 2.35~2.55 eV, and the band gap of the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is reduced to 2.15~2.35 eV.

3. The chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material according to claim 1, characterized in that: The Ni loading mass fraction is 3.91%~5 wt%.

4. A chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material according to claim 1 or 3, characterized in that: Ni provides electron-capturing sites and hydrogen-producing active centers in the form of a co-catalyst.

5. A method for preparing the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material according to any one of claims 1 to 4, characterized in that, The chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material was synthesized using a one-step hydrothermal method, including the following steps: Step 1: Dissolve chitosan in glacial acetic acid solution and polyvinyl alcohol in hot water. After mixing, add glutaraldehyde for cross-linking to obtain CS-PVA double network hydrogel precursor solution. Step 2: Add cadmium salt, nickel salt and sulfur source to the CS-PVA dual-network hydrogel precursor solution, stir well to obtain a mixture; Step 3: Transfer the mixture into the reaction vessel for hydrothermal reaction; Step 4: Wash and vacuum dry to obtain CS-PVA / CdS-Ni hybrid material, which is the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material.

6. The preparation method according to claim 5, characterized in that: The method for preparing the CS-PVA dual-network hydrogel precursor solution in step 1 is as follows: mix chitosan glacial acetic acid solution with a mass concentration of 0.1~1g / mL with polyvinyl alcohol solution with a mass concentration of 0.5~1g / mL, and then add glutaraldehyde solution with a volume percentage of 25%; wherein, the volume-mass ratio of 25% glutaraldehyde solution to chitosan is 1mL:1g.

7. The preparation method according to claim 5, characterized in that: In step 2, the mass ratio of cadmium acetate: nickel acetate: thiourea is 2.0~6.0 : 0.1~0.3 : 2.5~6.5, and the stirring time is 10~90 min.

8. The preparation method according to claim 5, characterized in that: In step 4, the washing method is to wash with deionized water 1 to 5 times and with anhydrous ethanol 2 to 5 times; the drying conditions are vacuum drying at 50 to 80 ℃ for 6 to 24 h.

9. The application of the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material according to any one of claims 1 to 4, characterized in that: The chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is used for solar-driven seawater desalination and photocatalytic hydrogen production.

10. The application according to claim 9, characterized in that: The chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material is used for solar-driven seawater desalination and photocatalytic hydrogen production. It involves adding the chitosan-polyvinyl alcohol hydrogel / CdS-Ni hybrid material to the seawater to be treated, using lactic acid as a sacrificial agent, and purging nitrogen gas to remove oxygen, thereby achieving solar-driven seawater desalination and photocatalytic hydrogen production.

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