RHA-pva composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion and preparation method and application thereof

Abstract

This invention discloses an RHA-PVA composite solar interfacial evaporator based on carbon-silicon synergistic photothermal conversion, its preparation method, and its application, belonging to the technical field of solar photothermal evaporation and water treatment materials. The method includes rice husk ash pretreatment and silica content control, PVA porous sponge matrix construction, composite impregnation solution preparation, sponge wetting and loading, calcium ion crosslinking and immobilization, and rinsing and drying molding. Sodium alginate and calcium chloride are used to construct an ion crosslinking and immobilization system, and the photothermal conversion efficiency and interfacial evaporation performance are improved by controlling the SiO2 content in the RHA. The resulting evaporator uses PVA sponge as the framework and RHA with SiO2 content controlled by alkali treatment as the photothermal component. It possesses broad-spectrum absorption, excellent hydrophilic water transport, and porous mass transfer characteristics, and has high evaporation efficiency and continuous operation capability. It can be used for seawater desalination and the purification of wastewater containing heavy metal ions, dyes, and antibiotics.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal evaporation and water treatment materials technology, and relates to the construction of biomass-derived photothermal materials and polymer porous matrix composite evaporators. Specifically, it is an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion, its preparation method and application. Background Technology

[0002] With the acceleration of urbanization, industrial wastewater discharge continues to rise. Obtaining freshwater through seawater desalination and wastewater purification technologies has become an effective way to alleviate freshwater shortages and manage the water environment. Currently, traditional desalination and purification technologies such as distillation, membrane separation, and reverse osmosis are widely used. However, these technologies generally rely on fossil fuels and have drawbacks such as high equipment costs, high energy consumption, and potential secondary pollution, making it difficult to meet the needs of low-carbon and sustainable development.

[0003] Solar-driven interfacial evaporation technology converts solar energy into thermal energy using materials with light-absorbing properties, enabling rapid evaporation of water at the water-air interface. Compared to heating the entire water body, this technology effectively confines heat to the surface of the evaporation layer, significantly reducing heat loss and thus increasing the evaporation rate. Simultaneously, during evaporation, soluble pollutants in the water can be trapped in the residual water or adsorbed onto the surface of the photothermal material, making it widely applicable to industrial wastewater treatment. Therefore, designing a high-efficiency solar evaporator and selecting suitable light-absorbing materials with strong solar absorption capacity, high photothermal conversion efficiency, continuous and stable water transport capacity, low heat conduction loss, and suitable steam escape channels are key to improving interfacial water evaporation efficiency and promoting the practical application of this technology.

[0004] Existing solar interfacial evaporation materials mainly include noble metal nanomaterials, semiconductor materials, polymer materials, and biomass-derived carbon materials. However, current research still has the following shortcomings: First, although some materials have strong light absorption capabilities, their thermal localization effect is limited, and interfacial heat loss is relatively significant. Second, some porous matrices have good hydrophilicity, but their stability under the load of photothermal components is insufficient, easily leading to uneven dispersion, poor adhesion, or performance degradation during cycling. Third, their resistance to acids and alkalis, salts, and pollution under complex water quality conditions is still not ideal, easily resulting in surface salt precipitation, pore blockage, or fluctuations in evaporation performance. Fourth, current research still lacks sufficient understanding of the synergistic effects of carbonaceous components and inorganic silicate components in light absorption, thermal regulation, structural stability, and mass transfer behavior, making it difficult to simultaneously achieve high evaporation rates, good stability, and adaptability to multiple purification scenarios.

[0005] In existing technologies, such as Chinese patent CN121627103A, a composite material solar interface evaporation device is disclosed, which uses a PA12 three-dimensional printed support layer and a carbon nanotube-silver particle photothermal layer. However, the material system and preparation process are relatively complex, and PVA is only used as a surface curing film-forming agent, and the control of SiO2 content in RHA is not involved. CN121159932B discloses a self-floating double-layer solar evaporator with Janus characteristics, which constructs a double-layer aerogel through carbonized loofah / PVA-sodium alginate, but focuses on the Janus hydrophobic interface and vertical pore design, without revealing the carbon-silicon synergistic photothermal conversion mechanism.

[0006] In summary, existing solar interfacial evaporators still have shortcomings in terms of photothermal conversion efficiency, interfacial thermal management, continuous water supply, resistance to salt accumulation, and adaptability to complex wastewater. Therefore, how to construct a solar interfacial evaporator that combines high-efficiency interfacial evaporation capacity, stable heat and mass transfer performance, good resistance to salt pollution, and adaptability to complex aquatic environments is an urgent technical problem to be solved. Summary of the Invention

[0007] (a) Purpose of the invention Polyvinyl alcohol (PVA) sponge is a commonly used polymer material. Although it is difficult to degrade in the natural environment and easily leads to waste accumulation, it possesses an ordered macroporous structure and excellent thermal insulation properties, providing ample channels for water flow and effectively reducing heat loss. Based on these characteristics, combining photothermal materials with PVA sponge is considered an ideal solution for constructing high-performance solar evaporators. Furthermore, among various photothermal materials, biomass-derived carbon materials, with their inherent broad-spectrum absorption characteristics, high specific surface area, unique microstructure, and advantages such as low cost and low toxicity, show broad application potential in the field of solar water evaporation. Rice husk ash (RHA) has significant advantages over other biomass raw materials such as corn cobs, bamboo leaves, and straw. Its main components are silicon dioxide and carbon, which not only endow the material with excellent heat resistance and chemical stability, but the presence of silicon dioxide also further enhances the material's light absorption capacity and photothermal conversion efficiency.

[0008] Based on this, the present invention addresses the aforementioned defects and deficiencies of the prior art by providing an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion, its preparation method, and its application. Sodium alginate and calcium chloride are used as crosslinking agents to fix pretreated rice husk ash (RHA) powder into a PVA sponge matrix. By utilizing the ordered macroporous structure and thermal insulation properties of the PVA sponge, a continuous water supply and low heat loss matrix is ​​constructed. Furthermore, the silica (SiO2) content in the rice husk ash (RHA) is pretreated and controlled to leverage the synergistic light absorption and photothermal conversion effects of the carbon and silica components in the RHA. This successfully constructs an RHA-PVA composite evaporator that combines high-efficiency photothermal conversion capability, broad-spectrum absorption characteristics, excellent hydrophilicity, and an ordered porous network structure. This evaporator not only achieves efficient solar-driven water evaporation but also has the ability to remove heavy metal ions, dyes, antibiotics, and other pollutants from water, providing a new technical approach and practical solution for alleviating freshwater resource shortages.

[0009] (II) Technical Solution To achieve the objective of this invention and solve its technical problems, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for preparing an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion. This method is used to prepare a composite solar interface evaporator with polyvinyl alcohol (PVA) sponge as the matrix and rice husk ash (RHA) with controlled silica content as the photothermal component. The method includes at least the following steps: SS1. RHA pretreatment and carbon-silicon composition control: After washing and drying the rice husk raw material, calcination was carried out. The calcined product was crushed and sieved to obtain RHA powder with uniform particle size distribution. The RHA powder was soaked and stirred with alkaline solution, and the SiO2 content in RHA was controlled by controlling the reaction time. Then the treated RHA powder was washed with water and dried. SS2. Construction of PVA porous matrix: PVA precursor solution was prepared with polyvinyl alcohol, and after being heated and dissolved to form a homogeneous system, a PVA porous sponge matrix with interconnected pore structure was prepared by a combination of freeze molding and thawing treatment. The PVA porous sponge matrix was then washed and cut into shape. SS3. Construction of composite impregnation solution: Sodium alginate was dissolved in hot deionized water to form a sodium alginate solution. Pretreated RHA was added to deionized water and dispersed evenly. The dispersed RHA suspension was added to the sodium alginate solution and mixed to obtain a composite impregnation solution containing pretreated RHA. SS4. PVA sponge loading composite: The pre-formed PVA porous sponge matrix is ​​placed in the composite impregnation liquid. By squeezing and wetting, the composite impregnation liquid enters the internal channels of the PVA porous sponge matrix and adheres to the surface of the skeleton, so that the pretreated RHA is distributed inside and outside the PVA porous sponge matrix. SS5. Ionic crosslinking and photothermal component immobilization: The PVA porous matrix with the completed composite impregnation solution is immersed in a crosslinking solution containing calcium ions to allow sodium alginate to undergo ionic crosslinking with calcium ions, and the pretreated RHA is immobilized on the inner and outer surfaces and internal pore structure of the PVA porous sponge matrix. SS6. Washing, Drying and Evaporator Forming: The composite matrix after ion crosslinking is washed with deionized water to remove unfixed components and residual crosslinking liquid. After drying, an RHA-PVA composite solar interface evaporator with carbon-silicon synergistic photothermal conversion capability and hydrophilic water transport performance is obtained.

[0010] The second objective of this invention is to provide an RHA-PVA composite solar interface evaporator, which is prepared using a method based on carbon-silicon synergistic photothermal conversion. This method combines broad-spectrum absorption, continuous water delivery, stable porous mass transfer, and interfacial thermal localization characteristics, and also has high evaporation efficiency and pollutant removal capabilities.

[0011] The third objective of this invention is to provide an application of the above-mentioned RHA-PVA composite solar interface evaporator in seawater desalination and / or wastewater treatment.

[0012] (III) Technical Effects Compared with the prior art, the RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion, its preparation method, and its application, as described in this invention, have the following beneficial and significant technical effects: (1) This invention regulates the SiO2 content by treating RHA with alkali, utilizes the synergistic light absorption and photothermal conversion of carbon components and SiO2 components, and combines it with the three-dimensional porous network of PVA sponge to improve the full spectrum absorption capacity and interface temperature rise response under light, and enables the evaporation rate to reach a high level under suitable composition conditions, thereby enhancing the solar interface evaporation efficiency from the material composition level.

[0013] (2) In this invention, PVA sponge is used as a porous matrix, and RHA is stably immobilized on the surface and internal pores of PVA sponge skeleton by crosslinking sodium alginate and calcium chloride. While maintaining three-dimensional interconnected pores and excellent hydrophilic permeability, heat diffusion to bulk water is effectively suppressed, thereby taking into account continuous water delivery, steam escape and interfacial heat localization, and improving the stability and continuity of the evaporation process.

[0014] (3) The RHA-PVA composite solar interface evaporator prepared by the present invention has both efficient seawater desalination and purification functions for multiple types of polluted water. It exhibits good separation and removal effects on salt ions, organic dyes, heavy metal ions and antibiotic pollutants. At the same time, the evaporator has strong acid and alkali resistance, salt crystallization resistance and self-cleaning ability. Therefore, it has good application prospects in seawater desalination and resource utilization of high-salt and high-pollution wastewater. Attached Figure Description

[0015] Figure 1 The diagram shows the implementation flow chart of the RHA-PVA composite solar interface evaporator preparation method based on carbon-silicon synergistic photothermal conversion provided by the present invention.

[0016] Figure 2 The diagram shows the preparation process and structural characterization of the RHA-PVA composite solar interface evaporator, where: (a) is the preparation process of the RHA-PVA sponge; (b) and (c) are scanning electron microscope images of the PVA sponge and RHA-PVA sponge, respectively; (d) to (f) are contact state diagrams of water droplets and RHA-PVA sponge at 0 ms, 33 ms, and 66 ms, respectively; (g) is the ultraviolet-visible-near-infrared absorption spectrum of the PVA sponge and RHA-PVA sponge; and (h) is the thermal conductivity of the PVA sponge and RHA-PVA sponge.

[0017] Figure 3 The diagram shows the photothermal response and evaporation performance verification of the RHA-PVA composite solar interface evaporator, where: (a) is the surface temperature change curve of pure water, PVA sponge and RHA-PVA sponge over time under the same solar irradiation conditions; (b) is the mass change curve of pure water, PVA sponge and RHA-PVA sponge under the same solar irradiation conditions; (c) is the cyclic evaporation rate diagram of RHA-PVA sponge under the same solar irradiation conditions; (d) is the infrared thermal image of RHA-PVA sponge at different times under 0.5 solar, 1 solar and 2 solar irradiation conditions; and (e) is the comparison diagram of the evaporation rate of RHA-PVA sponge under different solar flux conditions.

[0018] Figure 4 The figure shows the performance characterization of the RHA-PVA composite solar interface evaporator in wastewater purification, where: (a)~(b) are the UV-Vis absorption spectra of methylene blue (MB) and rhodamine B (RhB) solutions before and after evaporation, respectively; (c) is the evaporation rate of RHA-PVA sponge in MB and RhB; (d) is the ion concentration and ion repulsion rate of heavy metal ion solutions before and after evaporation; (e) is the UV-Vis absorption spectrum of ciprofloxacin (CPFX) solution before and after evaporation; and (f) is the UV-Vis absorption spectrum of tetracycline (TCH) solution before and after evaporation.

[0019] Figure 5 The figure shows the performance characterization of the RHA-PVA composite solar interface evaporator in seawater desalination, where: (a) is the evaporation rate of RHA-PVA sponge in pure water and seawater; (b) is the concentration of four major salt ions and the percentage of ion repulsion before and after simulated seawater evaporation; (c) is the evaporation rate of RHA-PVA sponge in sodium chloride solutions of different salinities on the first and second days; and (d) is a digital photograph of the surface state of RHA-PVA sponge under different salinity sodium chloride solutions and different evaporation time conditions. Figure 6 The diagram shows the self-cleaning process of salt on the surface of the RHA-PVA composite solar interface evaporator under off-light conditions. The digital photos of the dissolution state of NaCl particles on the evaporator surface at different time points are shown at 0 min, 10 min, 20 min, 30 min, 40 min, 50 min and 60 min. Detailed Implementation

[0020] This invention aims to provide an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion, its preparation method, and its application. To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in more detail below with reference to the accompanying drawings of the embodiments. The described embodiments are some, but not all, embodiments of this invention, and are exemplary, intended to explain the invention, and should not be construed as limiting the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Example 1: Method for preparing a solar interface evaporator As a specific example, the method for preparing an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion provided in this invention is used to prepare a composite solar interface evaporator with polyvinyl alcohol (PVA) sponge as the matrix and rice husk ash (RHA) with silica content regulated as the photothermal component. This method achieves comprehensive improvements in light absorption, heat localization, continuous water delivery, and adaptability to complex aquatic environments through the synergistic coordination of RHA carbon-silicon component regulation, PVA porous matrix construction, composite impregnation liquid loading, ion crosslinking immobilization, and post-treatment molding. Specifically, as... Figure 1 As shown, the method mainly includes the following steps when implemented: SS1. RHA pretreatment and carbon-silicon composition regulation: After washing, removing impurities, and drying the rice husk raw material, calcination is carried out. The calcined product is crushed and sieved to obtain RHA powder with uniform particle size distribution. The RHA powder is soaked and stirred with alkaline solution, and the SiO2 component content in RHA is adjusted by controlling the reaction time. Subsequently, the treated RHA powder is washed with water and dried.

[0022] Preferably, the calcination treatment of the washed, cleaned, and dried rice husk raw material includes: placing the washed and dried rice husk raw material in a muffle furnace or tube furnace, heating it to 500-800 ℃ at a heating rate of 5-15 ℃ / min under nitrogen protection or oxygen-limited atmosphere, calcining at a constant temperature for 2-6 h, and then cooling it with the furnace or under a protective atmosphere to room temperature to obtain a calcined product containing carbon components and a SiO2 framework structure; the crushing and sieving process includes: grinding the calcined product in a ball mill and then performing standard sieving with a sieve mesh size of 700-2500 mesh to obtain RHA powder with a median particle size of 5-20 μm; the coarse particles that do not meet the particle size requirements after sieving are returned to the ball milling process for further grinding to improve the uniformity of the particle size distribution of the obtained RHA powder and the consistency of subsequent alkaline treatment.

[0023] Furthermore, when performing alkaline soaking and stirring treatment on RHA powder, the alkaline solution is a NaOH or KOH solution with a concentration of 0.5~3.0 mol / L, the liquid-solid ratio of RHA powder to alkaline solution is 10:1~30:1 mL / g, the treatment temperature is 20~80 ℃, the stirring speed is 200~800 rpm, and the treatment time is 6~168 h. After the alkaline soaking and stirring treatment, the RHA powder is washed with deionized water until the washing solution is neutral or weakly alkaline, and then dried at 60~120 ℃ to obtain pretreated RHA powder with controlled silica content, increased specific surface area, and suitable for subsequent composite impregnation and ion crosslinking immobilization.

[0024] Furthermore, this invention preferably uses a gradient of alkaline soaking and stirring treatment time to grade and control the SiO2 content in RHA, so that different treatment times correspond to RHAs with different carbon and silicon compositions. The SiO2 content of the RHA after alkaline treatment is controlled to a range that can take into account broad-spectrum absorption performance, particle dispersion, and interfacial evaporation efficiency. The pretreated RHA with the target SiO2 content is selected according to the requirements of evaporator preparation. After alkaline treatment of RHA powder, it is also preferred to use a silane coupling agent to functionalize the RHA surface: the washed and dried RHA powder is dispersed in an ethanol aqueous solution, 1-3% by mass of amino or carboxyl silane coupling agent is added, and the mixture is refluxed at 60-80 °C for 4-8 h to introduce active functional groups on the RHA surface, enhance the bonding force between it and the PVA porous sponge matrix and sodium alginate crosslinking network, and improve the structural stability of the composite evaporator under extreme acid and alkaline environments.

[0025] It should be noted that step SS1 is the core pretreatment step for achieving carbon-silicon synergistic photothermal conversion in this invention. Its key is not simply obtaining rice husk ash powder, but rather establishing a foundation for the synergistic regulation of carbon and SiO2 components in RHA through continuous processing including raw material cleaning, temperature-controlled calcination, particle size shaping, and selective alkaline etching. RHA naturally possesses a unique biomass silicon-carbon symbiotic structure, in which the amorphous SiO2 framework not only acts as the physical support for carbon particles, preventing the aggregation of photothermal carbon components under high loading, but also generates a strong multi-level light scattering effect through its naturally porous microcavities, significantly extending the propagation path of incident light within the material. By dynamically controlling the alkaline treatment time, some SiO2 can be selectively removed, exposing more active carbon absorption sites while constructing core-shell or network micro / nano structures with higher specific surface area. This carbon-silicon synergistic effect not only optimizes the material's broad-spectrum absorption rate from ultraviolet to near-infrared, but also enhances the dispersion stability of photothermal components in the aqueous system by improving the density of hydrophilic functional groups on the RHA surface, laying a structural foundation for the subsequent construction of high-performance composite evaporators.

[0026] SS2. Construction of PVA porous matrix: A PVA precursor solution was prepared using polyvinyl alcohol. After being heated and dissolved to form a homogeneous system, a PVA porous sponge matrix with interconnected pore structures was obtained by combining freeze molding and thawing. The PVA porous sponge matrix was then washed and cut into shape.

[0027] In this embodiment, the PVA porous sponge matrix not only serves as the supporting framework for photothermal components but also undertakes the structural functions of continuous water supply, steam escape, and heat diffusion suppression. The preferred mass percentage concentration of the PVA precursor solution is 8-15%. After stirring and dissolving at 80-95 °C for 1-4 h to form a homogeneous system, it is injected into a predetermined mold and frozen at -30 °C to -10 °C for 4-24 h, then thawed at 10-30 °C for 2-12 h. This freeze-thaw cycle is repeated 3-5 times to induce the PVA molecular chains to form a stable crystalline network through physical cross-linking, thus constructing a PVA porous sponge matrix with a three-dimensional interconnected pore structure with a pore size between 50-200 μm.

[0028] Furthermore, when constructing the PVA porous sponge matrix, it is preferable to add a porogen with a mass fraction of 1-5% to the PVA precursor solution. The porogen is polyethylene glycol, sodium chloride microcrystals, and / or ammonium bicarbonate particles. After freeze-forming, the porogen is removed by solvent extraction or thermal decomposition to introduce micropores and mesopores on the walls of the interconnecting pores of the PVA porous sponge matrix, constructing a water transport channel with hierarchical pore characteristics and increasing the effective surface area of ​​the evaporation interface.

[0029] It is important to note that the core of this step lies in inducing a stable physical cross-linking network through freeze-thaw cycles, enabling the PVA matrix to simultaneously possess macroscopically interconnected pores and locally rough pore walls. During repeated freeze-thaw cycles, the growth of ice crystals displaces the PVA polymer chains, causing them to highly aggregate in the ice crystal gaps and form stable physically cross-linked crystalline regions through hydrogen bonding. When the ice crystals melt, the space left in situ transforms into highly interconnected three-dimensional open channels. The resulting porous PVA sponge not only serves as the supporting framework for the RHA photothermal components but also simultaneously undertakes the functions of interfacial water replenishment, vapor escape, and heat barrier. The optimized pore size range and hierarchical pore structure achieve a balance between capillary water transport capacity and vapor diffusion resistance, avoiding insufficient water supply due to excessively narrow pores or excessive heat transfer to the bulk water due to excessively large pores, thereby improving the steady-state operating efficiency of the evaporation interface. The hierarchical pores introduced by the porogen further reduce the resistance to water transport and increase the free surface area of ​​the evaporation front, achieving a balance between efficient water transport and rapid evaporation.

[0030] SS3. Construction of composite impregnation solution: Sodium alginate was dissolved in hot deionized water to form a sodium alginate solution. Pretreated RHA was added to deionized water and dispersed evenly. The dispersed RHA suspension was added to the sodium alginate solution and mixed to obtain a composite impregnation solution containing pretreated RHA.

[0031] Preferably, sodium alginate is dissolved in deionized water at 80-90 °C in portions, and stirred at 300-800 rpm for 0.5-2 h to form a sodium alginate solution with a mass-volume concentration of 1.5-3.0 g / mL. After complete dissolution, the sodium alginate solution is cooled to 20-40 °C and allowed to stand for 0.5-4 h to reduce the bubble content and improve the solution homogeneity and flow stability, thus serving as a precursor medium for subsequent pretreated RHA dispersion loading and calcium ion crosslinking immobilization. The construction process of the composite impregnation solution is as follows: pretreated RHA is added to deionized water at a mass-volume ratio of 0.02-0.20 g / mL, dispersed under ultrasonic power of 100-400 W for 10-40 min to form an RHA suspension, and then the RHA suspension is added to the sodium alginate solution at a volume ratio of 1:3-1:15, and stirred at 20-40 °C and 200-800 rpm for 0.5-2 h. h, a uniformly dispersed composite impregnation solution is obtained to improve the load uniformity and solidification stability of pretreated RHA in subsequent PVA porous sponge matrix.

[0032] In addition, the composite impregnation solution preferably contains photocatalytically active nano-titanium dioxide or zinc oxide particles, with an addition amount of 5-15% of the RHA mass. By simultaneously immobilizing the photocatalytic component with RHA in the SS5 step, the final RHA-PVA composite solar interface evaporator is endowed with a self-cleaning function, enabling it to degrade antibiotics and organic pollutants attached to the evaporator surface in situ under sunlight, effectively preventing biofilm growth and extending the service life of the evaporator.

[0033] It should be noted that the key to this step lies in constructing a composite impregnation system that combines dispersion stability, wettability, and crosslinking capability to achieve stable dispersion and uniform suspension of RHA particles in the polymer precursor system. Sodium alginate in this invention serves not only as a particle dispersion and adhesion medium but also as a reaction precursor for subsequent ionic crosslinking, used to generate a stable coating network in situ on the PVA framework surface. By first ultrasonically pre-dispersing the RHA and then compounding it with a sodium alginate solution, particle aggregation and rapid sedimentation can be significantly inhibited, resulting in a uniform distribution of photothermal components at both the macroscopic and microscopic scales. This lays the foundation for subsequent simultaneous loading inside and outside the pores, avoiding local blockage, and improving the consistency of interfacial evaporation.

[0034] SS4. PVA sponge load-bearing composite: The pre-formed PVA porous sponge matrix is ​​placed in a composite impregnation solution. By squeezing and wetting, the composite impregnation solution enters the internal channels of the PVA porous sponge matrix and adheres to the surface of the skeleton, so that the pretreated RHA is distributed inside and outside the PVA porous sponge matrix.

[0035] Preferably, the PVA porous sponge matrix is ​​a pre-cut sponge matrix. After being placed in the composite impregnation liquid, it is impregnated by repeated squeezing and depressurization to allow the composite impregnation liquid containing pretreated RHA and sodium alginate to fully penetrate the internal interconnecting channels of the sponge and wet its skeleton surface, forming a coating layer with a thickness of 5~20 μm. This process continues until the PVA porous sponge matrix reaches a state of simultaneous internal and external liquid absorption, thereby achieving a full composite distribution of pretreated RHA inside and outside the sponge.

[0036] It should be noted that this step establishes a pressure difference between the inside and outside of the pores through alternating compression and decompression, prompting the composite impregnating liquid to rapidly penetrate the deep regions of the sponge and form a continuous adhesion layer along the skeleton surface. This method utilizes the pressure difference within the PVA sponge pores to drive the composite impregnating liquid to quickly enter the internal interconnected structure, significantly improving the wetting depth and load uniformity, and avoiding the problems of outer layer enrichment, internal load depletion, and pore blockage that are prone to occur in traditional surface coating processes. By controlling the compression frequency, wetting time, and coating layer thickness, it is possible to ensure sufficient distribution of photothermal components on the evaporation surface while maintaining continuous pore openness, thus achieving efficient light absorption, continuous water replenishment, and low-resistance vapor escape.

[0037] SS5. Ionic crosslinking and photothermal component immobilization: The PVA porous matrix loaded with the composite impregnation solution is immersed in a crosslinking solution containing calcium ions for treatment, allowing sodium alginate to undergo ionic crosslinking with calcium ions. Pretreated RHA is then immobilized on the inner and outer surfaces and internal pore structures of the PVA porous sponge matrix. The crosslinking solution containing calcium ions is preferably a CaCl2 solution with a concentration of 0.1–0.5 mol / L. The PVA porous sponge matrix loaded with the composite impregnation solution is immersed in the crosslinking solution at a liquid-to-solid ratio of 10–30 mL / g, and soaked at 20–40 °C under static or slow agitation conditions for 12–36 h. This allows sodium alginate to form an ionic crosslinking network with calcium ions, and the pretreated RHA to be immobilized on the inner and outer surfaces and internal pore walls of the PVA porous sponge matrix, thereby improving the stability of the photothermal component loading and the integrity of the composite structure.

[0038] It should be noted that this step utilizes the ionic cross-linking between calcium ions and sodium alginate to construct an integrated coating-fixation network on the surface and within the pores of the PVA framework, transforming the RHA particles from a physically attached state to a stable, fixed state constrained by the cross-linked network. This treatment not only improves the structural integrity of the evaporator under long-term immersion and repeated heating conditions but also helps reduce the risk of photothermal component detachment, thereby enhancing the evaporator's operational stability in complex brine and wastewater systems.

[0039] SS6. Washing, drying, and evaporator forming: The composite matrix after ion crosslinking is rinsed with deionized water to remove unfixed components and residual crosslinking liquid, and then dried to obtain an RHA-PVA composite solar interface evaporator that has both carbon-silicon synergistic photothermal conversion capability and hydrophilic water transport performance.

[0040] As a preferred method, the composite matrix after ion crosslinking is rinsed 2 to 6 times with deionized water at a liquid-to-solid ratio of 15 to 40 mL / g, with each rinsing time being 2 to 15 min, to remove unsupported components and residual crosslinking liquid. After rinsing, it is dried at 40 to 80 °C for 4 to 24 h, or pre-frozen at a freezing temperature of -40 to -10 °C for 2 to 12 h and then freeze-dried for 12 to 48 h to obtain an RHA-PVA composite solar interface evaporator that maintains a porous framework structure and has continuous water delivery capability.

[0041] In summary, Example 1 successfully prepared an RHA-PVA composite solar interfacial evaporator through a synergistic design involving controllable adjustment of the RHA carbon-silicon composition, construction of a porous PVA framework, sodium alginate composite impregnation, and in-situ calcium ion crosslinking. This method utilizes readily available raw materials, employs mild process conditions, features tightly integrated steps, and is easily scalable. It offers a low-cost, high-performance interfacial evaporation material preparation scheme with promising engineering applications in seawater desalination and complex wastewater purification.

[0042] Example 2: Performance Verification and Application Case Based on the RHA-PVA composite solar interface evaporator preparation method shown in Example 1 above, Example 2 further provides the structural characterization of the evaporator, the verification of its pure water evaporation performance, and application examples in wastewater purification and seawater desalination, to illustrate the comprehensive technical effects of the evaporator obtained in Example 1 in terms of material composition control, interfacial thermal management, and adaptability to complex aquatic environments. The evaporator used in Example 2 was prepared according to steps SS1-SS6 of Example 1. In step SS1, pretreated RHA with treatment times of 6h, 12h, 24h, 48h, and 168h were obtained by adjusting the alkaline soaking and stirring time. The corresponding RHA-PVA composite solar interface evaporators were prepared under the premise that other conditions remained consistent, to compare the influence of different carbon-silicon compositions on evaporation performance. After screening, the pretreated RHA obtained after 48h of reaction was used as a representative sample for subsequent performance evaluation.

[0043] In the preparation of the RHA-PVA composite evaporator, 2 g of sodium alginate was weighed and added in portions to 90 mL of deionized water at 85 °C. The solution was stirred until fully dissolved, forming a homogeneous sodium alginate solution. Pretreated RHA powder was added to 10 mL of deionized water and dispersed evenly by ultrasonic vibration. This dispersion was then transferred to the aforementioned sodium alginate solution and stirred for 1 hour to obtain a composite impregnation solution containing RHA. Subsequently, pre-cut PVA sponges were placed into the above mixed solution and repeatedly squeezed to fully impregnate the internal pores of the sponges. After the sponges were fully saturated, they were removed and then transferred to 100 mL of 0.2 mol / L CaCl2 solution for 24 hours to achieve in-situ ionic cross-linking of sodium alginate and calcium ions. This stabilized RHA on the surface and internal pores of the PVA sponge, ultimately yielding the RHA-PVA composite solar interface evaporator. The preparation process is as follows: Figure 2 As shown in (a).

[0044] Subsequently, the microstructure and phase composition of the prepared RHA-PVA composite solar interface evaporator were characterized. Scanning electron microscopy (SEM) analysis of the morphology of the RHA / PVA composite solar interface evaporator revealed that the PVA sponge forms a porous framework, such as... Figure 2 As shown in (b), its interior has abundant three-dimensional interconnected channels, providing a stable pathway for the upward transport of liquid water and the escape of steam; RHA is stably attached to the inner and outer surfaces of the sponge and the walls of the internal channels through the cross-linking of sodium alginate and calcium chloride ions, as shown in (b). Figure 2 As shown in (c), an integrated RHA-PVA composite interface structure is formed. Wetting performance test results show that the original PVA sponge has a contact angle with water close to 0°, indicating strong hydrophilicity; after introducing RHA, the evaporator still maintains good wetting and water transport capabilities, such as... Figure 2 As shown in (d) to 2(f), water droplets spread rapidly and completely penetrated into the material within 0 ms, 33 ms and 66 ms, indicating that the RHA load did not disrupt the continuous hydrophilic channels of the PVA sponge.

[0045] Furthermore, the optical and thermal properties of the evaporator were tested. Figure 2 (g) It can be seen that, compared with PVA sponge, the RHA-PVA composite evaporator exhibits higher absorption rates in the ultraviolet, visible, and near-infrared bands, indicating that RHA significantly improves the full-spectrum absorption capacity of the interface material. Combined with Raman spectroscopy, it can be confirmed that there is a carbon structure in RHA, while X-ray diffraction analysis shows that there are characteristic diffraction peaks corresponding to the SiO2 crystal plane at approximately 2θ 21.9°, 28.4°, and 36.0°, which correspond to the (101), (111), and (200) crystal planes of (PDF: 39-1425), respectively, indicating that the pretreated RHA retains both the carbon component and the SiO2 framework structure. Figure 2 (h) shows that the thermal conductivity of the PVA and RHA-PVA composite evaporators is approximately 0.34 W·m. -1 ·K -1 and 0.67 W·m -1 ·K -1 Although the thermal conductivity of the material is improved after loading with RHA, it is still at a low level overall, which is conducive to concentrating the photothermal effect on the evaporation surface and reducing the diffusion of heat into the bulk water.

[0046] Regarding the verification of component regulation, a comparison of RHA obtained with different alkali treatment times revealed that as the soaking time increased, the SiO2 content in the RHA gradually decreased, the particle size decreased accordingly, and the specific surface area decreased from 57.11 m² / s². 2 / g increased to 117.83m 2 / g. Interfacial evaporation evaluation was conducted after preparing RHA with different pretreatment times as evaporators. It was found that when the SiO2 content in the RHA was adjusted to 54.9%, the evaporation performance reached a superior level, with an evaporation rate of 2.57 kg·m³. -2 ·h -1 Therefore, in this embodiment, the RHA obtained after 48 hours of alkali treatment was used as the representative sample for subsequent performance tests.

[0047] In verifying the performance of pure water evaporation, pure water, PVA sponge, and RHA-PVA composite evaporator were respectively placed under one solar irradiation condition for comparative testing. Figure 3 (a) As can be seen, the surface temperature of pure water and PVA sponge mainly remained in the range of 30~33 ℃, while the RHA-PVA composite evaporator could rise to about 41 ℃ within 10 min and remain stable, indicating that the evaporator has a faster photothermal response and better interfacial thermal localization performance. Figure 3 (b) It is evident that, within the same test time, the mass loss of the RHA-PVA composite evaporator is significantly higher than that of pure water and PVA sponge, corresponding to evaporation rates of 0.62 kg·m⁻². -2 ·h -1 1.26 kg·m -2 ·h -1 and 2.56 kg·m -2 ·h -1 .Depend on Figure 3 (c) It can be seen that after 10 consecutive cycles of testing, the evaporation rate of the RHA-PVA composite evaporator did not decrease significantly, indicating that the constructed ion-crosslinked immobilized structure has good cycle stability.

[0048] Further investigation was conducted into the evaporation performance under different solar fluxes. For example... Figure 3 As shown in (d), under conditions of 0.5 solar flares, 1 solar flare, and 2 solar flares, the RHA-PVA composite evaporator can reach a stable temperature within approximately 10 minutes, with stable temperatures of approximately 39℃, 41℃, and 44℃, respectively. Figure 3 As shown in (e), as the solar flux increases from 0.5 to 2 solar masses, the evaporation rate increases from 2.00 kg·m³. -2 ·h -1 Increased to 2.87 kg·m -2 ·h -1 This indicates that the evaporator has good light adaptability and evaporation response capability. Further verification was conducted using PVA sponge after actual use as a substrate, and the resulting RHA-PVA composite evaporator still achieved approximately 2.57 kg·m³. -2 ·h -1 The evaporation rate indicates that the preparation method has good compatibility with PVA matrix.

[0049] In wastewater purification applications, methylene blue (MB) and rhodamine B (RhB) were selected as organic dye model pollutants, Cd, Co, Cu, and Ni ions were selected as heavy metal model pollutants, and levofloxacin, ciprofloxacin, and tetracycline were selected as antibiotic model pollutants to verify the purification capacity of the evaporator. Figure 4 (a) and Figure 4 (b) It can be seen that the original dye solution has a significant absorption peak in the visible light region, while the condensate obtained by evaporation has almost no obvious absorption peak and appears colorless and transparent, indicating that the RHA-PVA composite evaporator can effectively block organic dyes from entering the product water side. Figure 4 (c) indicates that the evaporation rate in both the methylene blue and rhodamine B systems remained at approximately 2.54 kg·m³. -2 ·h -1 The level is close to that under pure water evaporation conditions, indicating that the presence of dye did not significantly weaken its evaporation capacity.

[0050] For heavy metal ion wastewater Figure 4 (d) shows that after evaporation, the concentrations of Cd, Co, Cu, and Ni ions in the resulting condensate decreased to 0.0043 mg / L, 0.0042 mg / L, 0.0067 mg / L, and 0.023 mg / L, respectively, with ion rejection rates all above 99%. This indicates that the evaporator can achieve highly efficient blocking of various heavy metal ions while maintaining high water production efficiency. For antibiotic systems, Figure 4 (e) and Figure 4 (f) shows that the characteristic absorption in the condensate decreased significantly after evaporation, indicating that the evaporator also has good purification capabilities for antibiotics such as levofloxacin, ciprofloxacin, and tetracycline. Furthermore, after immersing the evaporator in 0.1 mol / L hydrochloric acid solution and 0.1 mol / L sodium hydroxide solution for 10 h, respectively, no obvious structural damage or morphological changes were observed in the samples, and the pH of the resulting distilled water remained neutral, indicating that the solid support structure constructed from sodium alginate and CaCl2 gives the evaporator good resistance to acid and alkali corrosion.

[0051] In seawater desalination applications, the RHA-PVA composite evaporator is used to simulate the interfacial evaporation of seawater and NaCl solutions with different salinities. Figure 5 (a) It can be seen that the evaporation rate of this evaporator in pure water and seawater is approximately 2.56 kg·m³, respectively. -2 ·h -1 and 2.34 kg·m -2 ·h -1 This indicates that it can still maintain high evaporation activity in salt-containing systems. Figure 5 (b) It can be seen that the Na in the condensate obtained by evaporation + Mg 2+ K+ and Ca 2+ The concentrations were 72.47 mg / L, 6.54 mg / L, 7.29 mg / L and 33.64 mg / L, respectively, all of which were lower than the corresponding drinking water reference limits, indicating that the evaporator has a high ion barrier capacity and desalination effect.

[0052] Furthermore, continuous evaporation tests were conducted on 3.5 wt%, 7.0 wt%, and 10.0 wt% NaCl solutions. Figure 5 (c) It can be seen that, under the condition of 3.5 wt%, the evaporator exhibited relatively stable evaporation capacity during the two-day test period, with an average evaporation rate of approximately 2.11 kg·m³. -2 ·h -1 Under 7.0 wt% conditions, the evaporation rate decreased to approximately 1.82 kg·m³. -2 ·h -1 A small amount of salt precipitation occurred around 10 hours later on the second day; under 10.0 wt% conditions, the evaporation rate increased from approximately 1.71 kg·m³ on the first day. -2 ·h -1 It dropped to approximately 1.61 kg·m on the second day. -2 ·h -1 Meanwhile, surface salting out is more pronounced. Figure 5 The photograph shown in (d) further confirms the trend of increasing salt crystals on the evaporation surface with increasing salinity. These results indicate that as salinity increases, the evaporation driving force decreases and salt accumulation intensifies, but the evaporator can still maintain continuous operation.

[0053] To further investigate its self-cleaning ability, 0.25g of NaCl particles were placed on the surface of the RHA-PVA composite solar interface evaporator, and the change in surface salinity was observed under conditions of no light. Figure 6 It is evident that significant salt particle accumulation exists on the evaporator surface at 0 min. With increasing time, the number and size of salt particles gradually decrease at 10, 20, and 30 min; by 40 and 50 min, only a small amount of salt crystals remain on the surface; and by 60 min, the surface salt has essentially dissolved and disappeared. This result indicates that under light-free conditions, salt particles gradually dissolve and essentially disappear over time, suggesting that in the dark or at night, the continuous water transport channels inside the evaporator can promote the redissolution and return of surface salt crystals formed during evaporation to the main brine. This demonstrates that the thermal effect of RHA and the porous structure of PVA jointly promote brine transport and surface salt dissipation, thereby enabling the evaporator to possess self-recovery and self-cleaning capabilities, which is beneficial for extending its continuous service life under actual seawater desalination conditions.

[0054] In summary, this embodiment 2 combines Figures 2-6The results shown validate the comprehensive performance of the RHA-PVA composite solar interface evaporator obtained in Example 1 from multiple perspectives, including structural characterization, pure water evaporation, wastewater purification, seawater desalination, and self-cleaning. The results indicate that the RHA-PVA composite evaporator enhances full-spectrum absorption and photothermal conversion capabilities through the synergistic effect of the carbon and SiO2 components in the RHA, maintains rapid wetting, continuous water delivery, and steam escape channels via the porous PVA sponge framework, and achieves stable immobilization of the photothermal components through the crosslinking of sodium alginate with CaCl2 ions. Therefore, it exhibits good technical performance in pure water evaporation, wastewater purification, and seawater desalination scenarios.

[0055] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for preparing an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion, characterized in that, It should include at least the following steps: SS1. After washing and drying the rice husk raw material, calcination is carried out. The calcined product is crushed and sieved to obtain RHA powder. The RHA powder is soaked and stirred with alkaline solution, and the SiO2 component content in RHA is controlled by controlling the reaction time. Then the RHA powder is washed with water and dried. SS2. A PVA precursor solution was prepared with polyvinyl alcohol, and after being heated and dissolved to form a homogeneous system, a PVA porous sponge matrix with a connected pore structure was prepared by a combination of freeze molding and thawing treatment. The PVA porous sponge matrix was then washed and cut into shape. SS3. Sodium alginate is dissolved in hot deionized water to form a sodium alginate solution. Pretreated RHA is added to deionized water and dispersed evenly. The dispersed RHA suspension is added to the sodium alginate solution and mixed to obtain a composite impregnation solution containing pretreated RHA. SS4. The pre-formed PVA porous sponge matrix is ​​placed in the composite impregnation liquid. By squeezing and wetting, the composite impregnation liquid enters the internal channels of the PVA porous sponge matrix and adheres to the surface of the skeleton, so that the pretreated RHA is distributed inside and outside the PVA porous sponge matrix. SS5. The PVA porous matrix that has been loaded with composite impregnation solution is immersed in a crosslinking solution containing calcium ions to treat it, so that sodium alginate and calcium ions undergo ionic crosslinking, and the pretreated RHA is immobilized on the inner and outer surfaces and internal pore structure of the PVA porous sponge matrix. SS6. The composite matrix after ion crosslinking is rinsed with deionized water to remove unfixed components and residual crosslinking liquid, and then dried to obtain the RHA-PVA composite solar interface evaporator.

2. The method according to claim 1, characterized in that, In step SS1, the calcination process includes: placing the washed and dried rice husk raw material in a muffle furnace or tube furnace, heating it to 500-800 ℃ at a heating rate of 5-15 ℃ / min under nitrogen protection or oxygen-limited atmosphere, calcining it at a constant temperature for 2-6 h, and then cooling it with the furnace or cooling it to room temperature under a protective atmosphere to obtain a calcined product containing carbon components and a SiO2 framework structure; the crushing and sieving process includes: grinding the calcined product in a ball mill and then performing standard sieving with a sieve mesh size of 700-2500 mesh to obtain RHA powder with a median particle size of 5-20 μm; coarse particles that do not meet the particle size requirements after sieving are returned to the ball milling process for further grinding.

3. The method according to claim 1 or 2, characterized in that, In step SS1, when the RHA powder is subjected to alkaline soaking and stirring treatment, the alkaline solution is a NaOH or KOH solution with a concentration of 0.5~3.0 mol / L, the liquid-solid ratio of RHA powder to alkaline solution is 10:1~30:1 mL / g, the treatment temperature is 20~80 ℃, the stirring speed is 200~800 rpm, and the treatment time is 6~168 h. After the alkaline soaking and stirring treatment is completed, the RHA powder is washed with deionized water until the washing solution is neutral or weakly alkaline, and then dried at 60~120 ℃ to obtain pretreated RHA powder.

4. The method according to claim 3, characterized in that, In step SS1, the SiO2 content in RHA is graded and controlled by setting an alkaline soaking and stirring time gradient, so that different treatment times correspond to different carbon and silicon compositions of pretreated RHA. The SiO2 content of RHA after alkaline treatment is controlled to a range that can take into account broad spectrum absorption performance, particle dispersion and interfacial evaporation efficiency. The target SiO2 content of pretreated RHA is selected according to the requirements of evaporator preparation. After alkaline treatment of RHA powder, the surface of RHA is functionalized by using a silane coupling agent: the water-washed and dried RHA powder is dispersed in an ethanol aqueous solution, 1-3% by mass of amino or carboxyl silane coupling agent is added and refluxed at 60-80℃ for 4-8 h.

5. The method according to claim 1, characterized in that, In step SS2, the mass percentage concentration of the PVA precursor liquid is 8-15%. After stirring and dissolving at 80-95 ℃ for 1-4 h to form a homogeneous system, it is injected into a predetermined mold and frozen at -30℃ to -10℃ for 4-24 h, then thawed at 10-30℃ for 2-12 h. The freeze-thaw cycle is repeated 3-5 times to construct a PVA porous sponge matrix with a three-dimensional interconnected pore structure with a pore size between 50-200 μm.

6. The method according to claim 5, characterized in that, In step SS2, when constructing the PVA porous sponge matrix, a porogen with a mass fraction of 1-5% is added to the PVA precursor solution. The porogen is polyethylene glycol, sodium chloride microcrystals, and / or ammonium bicarbonate particles. After freeze-forming, the porogen is removed by solvent extraction or thermal decomposition to introduce micropores and mesopores into the walls of the interconnected pores of the PVA porous sponge matrix, thereby constructing a water transport channel with hierarchical pore characteristics.

7. The method according to claim 1, characterized in that, In step SS3, sodium alginate is dissolved in deionized water at 80-90 ℃ by adding it in portions, and stirred at 300-800 rpm for 0.5-2 h to form a sodium alginate solution with a mass-to-volume ratio of 1.5-3.0 g / mL. After the sodium alginate solution is completely dissolved, it is cooled to 20-40 ℃ and allowed to stand for 0.5-4 h. The construction process of the composite impregnation solution is as follows: pretreated RHA is added to deionized water at a mass-to-volume ratio of 0.02-0.20 g / mL, and dispersed at an ultrasonic power of 100-400 W for 10-40 min to form an RHA suspension. The RHA suspension is then added to the sodium alginate solution at a volume ratio of 1:3-1:15, and stirred at 20-40 ℃ and 200-800 rpm for 0.5-2 h to obtain a uniformly dispersed composite impregnation solution.

8. The method according to claim 1, characterized in that, In step SS4, the PVA porous sponge matrix is ​​a pre-cut sponge matrix. After being placed in the composite impregnation liquid, it is impregnated by repeated squeezing and depressurization to allow the composite impregnation liquid containing pretreated RHA and sodium alginate to fully penetrate the internal interconnecting channels of the sponge and wet its skeleton surface, forming a coating layer with a thickness of 5~20 μm, until the PVA porous sponge matrix reaches a state of synchronous internal and external liquid absorption.

9. The method according to claim 1, characterized in that, In step SS5, the calcium ion-containing crosslinking solution is a CaCl2 solution with a concentration of 0.1~0.5 mol / L. The PVA porous sponge matrix loaded with the composite impregnation solution is immersed in the crosslinking solution at a liquid-to-solid ratio of 10~30 mL / g. It is then left to stand or slowly shake and soaked at 20~40 ℃ for 12~36 h to allow sodium alginate and calcium ions to form an ionic crosslinking network, and to immobilize the pretreated RHA on the inner and outer surfaces and internal pore walls of the PVA porous sponge matrix.

10. The method according to claim 1, characterized in that, In step SS6, the ion-crosslinked composite matrix is ​​rinsed 2 to 6 times with deionized water at a liquid-to-solid ratio of 15 to 40 mL / g, with each rinsing time being 2 to 15 min. After rinsing, it is dried at 40 to 80 ℃ for 4 to 24 h, or pre-frozen at a freezing temperature of -40 to -10 ℃ for 2 to 12 h and then freeze-dried for 12 to 48 h to obtain an RHA-PVA composite solar interface evaporator that maintains a porous framework structure and has continuous water delivery capability.

11. An RHA-PVA composite solar interface evaporator, characterized in that, The evaporator is prepared using the method for preparing an RHA-PVA composite solar interface evaporator based on carbon-silicon synergistic photothermal conversion as described in any one of claims 1 to 10.

12. The application of the RHA-PVA composite solar interface evaporator as described in claim 11 in seawater desalination and / or wastewater treatment.

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