Efficient Solar Steam Generation System Based On Bionic Structure And Biomass Material

Water resources are the basic guarantee for the rapid development of society and human life,and nowadays the shortage of freshwater resources seriously affects the development of society.Solar steam generator（SSG）is considered as one of the effective solutions to the contemporary problems such as water shortage.SSG is a process of evaporating seawater to obtain fresh water by converting sunlight into thermal energy through photothermal materials using sunlight as the driving force.In recent years,metal nanoparticles,polymer materials,semiconductor materials and carbon-based materials have been reported as photothermal materials for SSG applications and have made great progress.However,most of the photothermal materials have high cost,complicated preparation methods,low photothermal efficiency,complex structure of water evaporator,and poor stability,which limit their practical applications in seawater desalination.Therefore,it is particularly important to research and develop water evaporators with low cost,simple structure and high photothermal conversion efficiency.In this paper,based on biomass materials,different types of solar water evaporators with bionic structures and biomass materials are designed and prepared,and the light absorption performance and thermal management of the water evaporators are optimized to effectively improve their water evaporation rate and energy conversion efficiency in the water evaporation process.The details are as follows:（1）A self-floating and integrated bionic mushroom solar steam generator（BMSSG）is prepared using reduced graphene oxide（RGO）,polyvinyl alcohol（PVA）and wood strips as raw materials.RGO and PVA are treated by freeze-drying and photoreduction to obtain porous structured graphene aerogel（PVA-GA）,which is used as a photothermal material to simulate the pileus of the mushroom.The introduction of PVA increases the physical properties and hydrophilicity of the graphene aerogel,ensuring its long-term stability without damage,and the wooden strip is inserted in the GA as a water transport channel while simulating the stipe of the mushroom.Compared to conventional interfacial evaporation devices,BMSSG is an integrated structure without insulation and an absorbent wick,which not only increases compactness and facilitates stability and reliability,but also reduces fabrication costs.The final water evaporation rate of the BMSSG is 1.67 kg m^-2 h^-1 at the irradiation intensity of one sun,and the salinity in the desalinated seawater is well below the WHO drinking water standard.（2）An all-in-one high-efficiency self-floating jellyfish-like SSG（SFJ-SSG）based on partially carbonized marshmallow（EA）aerogel（PCEAA）is developed.The waste biomass is converted into a photothermal material with excellent photothermal performance by simple freeze-drying and surface carbonization.The uncarbonized EA retains hydrophilicity and excellent water transport capacity due to the nature of tubular marshmallow cellulose,and the uncarbonized EA also has an insulating effect that impedes heat transfer from the water evaporation surface,which is very beneficial for interfacial water evaporation.After optimizing the carbonization time and height of SFJ-SSG,a high evaporation rate of 1.87 kg m^-2 h^-1 is obtained under 1solar irradiation,which exceeded most SSGs based on carbonized biomass.The EA-based SFJ-SSG not only has a simple structure,low cost and recyclability,but also solves EA contamination,ensuring its promising future in practical applications.（3）A double-layer SSG based entirely on biomass material is prepared using waste biomass Enteromorpha and wood strips as raw materials.The Enteromorpha is carbonized at high temperature,ground,and evenly coated on the surface of the wood strip as a photothermal material for photothermal conversion,where the high temperature carbonization enhanced the light absorption capacity of the Enteromorpha.Wooden strips have both water transport function and thermal insulation function in water evaporation structure due to their porous structure at the top,cellulose in vertical direction and hydrophilic and low thermal conductivity.By optimizing the carbonization temperature of the marshmallow and the size of the wood strips,the photothermal performance of the water evaporator is studied,and the water evaporation performance could achieve stable evaporation under the light,and the water evaporation rate is 2.56 kg m^-2 h^-1 under the light intensity of 1 sun.By optimizing the carbonization temperature of the Enteromorpha and the size of the wood strips,we studied the photothermal performance of the water evaporator and the water evaporation performance.The water evaporator achieves stable evaporation under light,with a water evaporation rate of 2.56 kg m^-2 h^-1 under 1 sun.