Preparation And Applications Of Agarose-based Hydrogel Materials For Solar Evaporation

The highly efficient conversion and utilization of solar energy is saving the world from the current energy crisis.As a typical solar energy conversion and utilization method,solar evaporation technology is widely used in seawater desalination,sewage purification and liquid product purification.With the emergence of various novel materials for high-performance photothermal evaporation and innovative designs of photothermal evaporation systems,solar evaporation-separation technology achieved rapid development in recent years.Hydrogel is a porous polymer material with a cross-linked network structure.As a support material for solar evaporation,hydrogel has multiple advantages including reduced evaporation enthalpy,high water transportation rate,highly tunable surface morphology,etc.In this work,a series of novel solar evaporation materials were designed and prepared based on agarose（AG）gel materials,and they were successfully applied in different solar-driven evaporation-separation processes,respectively.To achieve the solar-driven purification of phosphorus-containing wastewater,a novel high-performance solar evaporation device with a double-layer structure was prepared,named as C-AG/AG composite gel.The upper layer containing carbon black particles is responsible for light absorption and solar-steam conversion.The lower layer of pure AG is responsible for the isolation of the upper layer and the bulk water,as well as ensure the sufficient water supply for the upper layer.Since the excellent capability in broadband light absorption and water transportation,as well as the reduced vaporization enthalpy of water in the hydrogel network,the C-AG/AG composite gel material achieved a solar-steam conversion efficiency of 91.6%and a vapor generation rate of 2.03 kg m^-2h^-1 under 1 sun illumination.Furthermore,the C-AG/AG composite gel conducted a solar-driven purification process with ultrahigh evaporation rate for phosphorus-containing wastewater,and the phosphorus content in the recovered condensate completely reached the highest level for phosphorus in the standard for sewage discharge.With the aid of plasma technology,another novel high-efficiency solar evaporation device named as Ag-PSS-AG/AG composite gel is successfully prepared and applicated in the purification of particle suspension systems.With the utilization of the room temperature electron reduction（RTER）technology,The Ag nanoparticles were in situ synthesized and tightly combined with the hydrogel skeleton.The size of the Ag particles was effectively controlled,and the Ag nanoparticles exhibited a discretely spatial distribution with narrow spacing between particles.Thus,the oscillated LSPR effect of the Ag nanoparticles provides a light absorption of 93.14%for the composite gel among the solar spectrum.Together with the effective water transportation capacity and the reduced vaporization enthalpy of water in the hydrogel network,the Ag-PSS-AG/AG composite gel material revealed an excellent solar-steam conversion efficiency of 92.8%,and an ultrahigh solar steam generation rate of 2.10 kg m^-2 h^-1under 1 sun illumination.Besides,this material can be directly used for the purification of sewage and muddy water,providing clean water supply in certain scenarios with the utilization of solar power.To address the issue of oil-water separation,we developed a double-network agarose-based solar evaporation device named as MC-AG composite gel.The hydrophilicity of the carbon powder material was substantially enhanced after surface modification,and it formed a rigid double network with agarose in the gelation procedure.Besides the powerful capabilities in light absorption,water transportation and vaporization enthalpy depression,the MC-AG composite gel material exhibited a water absorption-oil prevention performance in the oil-water mixture owing to the hydrophilic structure of the agarose-based skeleton.Based on the synergistic effect of the above-mentioned excellent characteristics,the MC-AG composite gel material revealed outstanding light-to-heat conversion and solar-driven oil/water separation performances.Under 1 sun illumination,MC-AG composite gel material achieved a98.9%solar-steam conversion efficiency and a 2.22 kg m^-2 h^-1 water evaporation rate.Moreover,with the combination of the selective absorption performance and the solar evaporation capability,the MC-AG composite gel was successfully applied to the oil/water separation process using solar power as the only driving force.The highly efficient solar-driven evaporation-separation system remains a long-term stability and sustainability owing to the solid cross-linked network of the composite gel.