Interfacial Solar-to-vapor Conversion: Fabrication Of Multifunctional Hydrogel And Its Long-term Application In Seawater Desalination

Recently,solar-powered desalination technology has proven to be an effective solution to water crisis because its advantages of sustainable energy source,low cost and applicability to remote areas.However,for practical application in marine environment,the accumulation of salt and growth of microorganisms such as bacteria will cause scarring and fouling of the evaporators,depressing the potential for long-term sustainable use.Therefore,fabricating a self-cleaning evaporator with functions including salt resistance and antibacterial property as a significant influence in desalination.In order to solve the problems of salt accumulation and bacterial growth on the device and maintain high evaporation efficiency at the same time,a kind of solar-driven interfacial water evaporation hydrogel was prepared by UV polymerization from two aspects of raw material selection and structure design.The hydrogel uses pyrrole,chitosan and acrylamide as raw materials.While selecting the raw materials for the hydrogel,the microporous structure in the hydrogel,the distribution of the light-to-heat conversion material polypyrrole on the hydrogel skeleton,and the floatability of the hydrogel are adjusted to obtain an integrated three-layer gradient structure.This structure can achieve stable and excellent evaporation performance and self-cleaning performance in seawater,salty and bacterial seawater,and high-concentration saltwater.The main results are summarized as followings:(1)Our study adjusts the polymer ratio and the distribution of the photothermal conversion material to obtain optimized production conditions,that is,the weight ratio of chitosan,water and pyrrole monomer is 1:13:0.25,and the photothermal conversion material shows a gradient distribution in the longitudinal direction of the hydrogel and thermal-treat the bottom layer of the hydrogel.The pores distribution,color,hydrophilicity and hydrophobicity of the adjusted device are longitudinally anisotropic.The different properties enable the top layer of the hydrogel to localize light energy at the gas-liquid interface.As for the upper conveying,the bottom insulation layer design helps the device to float on the water surface.The hydrogel device has a light absorption rate of 97.6%at the range of 250 nm to 2500 nm,and reaches a high water evaporation rate of 2.41 kg m^-2 h^-1 under 1 kw m^-2 illumination.(2)The device retains the antimicrobial amino group of chitosan in the hydrogel by physical cross-linking,so that the hydrogel has outstanding antimicrobial corrosion resistance in actual seawater applications.Under 1 kw m^-2 illumination,the device evaporates continuously for 14 days in simulated seawater containing a mixture of bacteria with a stable evaporation rate at 2.30 kg m^-2 h^-1.(3)The dual-channel structure design of the interfacial water evaporation system makes it exhibit good evaporation performance in seawater with different salinities(3.5 wt%,15 wt%),bubbles(200?400?m)and micron-sized pores(10?40?m)in the hydrogel framework form a rapid salt exchange channel,which has excellent self-cleaning performance for salt accumulation,and has good application value in actual seawater.The evaporator has excellent resistance to salt accumulation in high salt water(15 wt%).After five days of evaporation test,the evaporation rate exceeds 2 kg m^-2 h^-1.