Preparation Of Graphene-based Hydrogels And Its Water Evaporation Properties

With the development of society,the shortage of fresh water resources has gradually become a global problem to be solved.At present,seawater desalination technologies put into use,such as thermal distillation,electrodialysis and nanofiltration membrane,have a series of problems such as high cost,low efficiency and harmful by-products to the environment.Therefore,it is urgent to develop new scalable seawater desalination technologies.Solar steam generation technology uses solar energy as renewable and clean energy,and converts solar energy into heat through photothermal conversion materials,which is positioned on the material surface to realize water evaporation and desalination,produce clean fresh water resources and minimize the negative impact on the environment.It is an efficient,sustainable and environment-friendly seawater desalination technology.In recent years,a lot of photothermal conversion materials based on hydrogel have been derived.Hydrogels can produce more weakly bonded intermediate water through the interaction of hydrophilic groups and water molecules through the interaction between their hydrophilic groups and water molecules,resulting in the activation of water and further increase the evaporation rate.Different graphene based composite hydrogels were prepared by combining them with different macromolecules of biomass to prepare photothermal conversion materials:We used ascorbic acid to partially reduce the mixed solution of GO and CNC to obtain RGO/CNC hybrid hydrogel RCH,retaining the hydrophilicity of the system,introducing CNC at the same time,reducing RGO stacking,and reduce the water vaporization enthalpy by increasing the content of intermediate water.Moreover,we increase the height of RCH which makes it absorbs the environmental energy,and produces a solar steam generation with a high evaporation rate and evaporation efficiency exceeding theoretical limit.The 30 mm height RCH-10 can achieve an evaporation rate of 3.61 kg m^-2h^-1and an energy conversion efficiency of 128.8%under one sun illumination.In addition,RCH also has the same performance and lower cost as other methods in practical applications such as seawater desalination and wastewater treatment,and has broad prospects.We prepared RSH by partially reducing the mixed solution of GO/squid ink with ascorbic acid,and then prepared A-RSH with vertically aligned channels by directional freezing for solar-driven steam generation,A-RSH has faster water transport rate.Moreover,RGO nanosheet and squid ink have synergistic photothermal effect,which can improve the light absorption of the system,so as to improve the ability of photothermal conversion and thermal management,RGO and squid ink interact with water molecules to produce weakly bonded water and reduce the water vaporization enthalpy.Finally,under the irradiation of 1 kW m^-2intensity which achieves the evaporation rate of 2.22 kg m^-2h^-1with the photothermal conversion efficiency of 98.2%.This graphene hybrid hydrogel has good salt resistance and 99.9%ion retention when used in desalination and wastewater treatment to produce clean water.