Preparation Of Composite Aerogel Based On Photothermal Conversion And Its Application In Seawater Desalination

With the continuous increase of the world population and the acceleration of urbanization,the global shortage of freshwater resources is becoming increasingly severe.The rational development and recycling of freshwater resources have become an urgent problem to be solved.Fortunately,solar thermal conversion driven seawater evaporation technology provides an efficient and environmentally friendly solution to address the shortage of freshwater resources.Aerogel has the advantages of light weight and heat insulation,which makes it an excellent base material for evaporators.However,the evaporation rate of seawater desalination evaporators based on aerogel is relatively low at present.In order to prepare an efficient aerogel seawater desalination evaporator,the composite aerogel was prepared by directional freeze-drying,using polyvinyl alcohol and sodium alginate as the matrix materials,adding carbon nanotubes and MXene precipitates as the photothermal conversion materials.The specific research content is as follows:（1）In order to prepare aerogel with excellent mechanical and hydrophilic properties,pure polyvinyl alcohol（PVA）and pure sodium alginate（SA）aerogel with different concentrations were prepared by directional freezing method.PVA aerogel has poor hydrophilicity and high strength;Sodium alginate aerogel has good hydrophilicity and poor strength.Polyvinyl alcohol/sodium alginate composite aerogel with different proportions were further prepared.The composite aerogel have good hydrophilicity and mechanical properties.At the same time,the vertical pores formed by directional freezing aerogel can be used as water transmission channels,and the composite aerogel can be used as a good matrix material for seawater desalination evaporators.（2）Composite aerogel with different aerogel concentrations,different PVA and SA ratios,and different CNT contents were prepared by directional freezing method using carbon nanotubes（CNT）as photothermal conversion materials with polyvinyl alcohol and sodium alginate composite aerogel as the matrix.According to the different concentrations of PVA and SA solution,the internal pores of aerogel evaporators were regulated.The effects of composition of composite aerogel on its microstructure,hydrophilicity and evaporation rate were systematically studied.The influence of two-dimensional and three-dimensional evaporation of CNT composite aerogel on the evaporation rate was further studied.Under the simulated sunlight,the evaporation rate of the evaporator could reach 2.7 kg m^-2h^-1.Finally,the self-cleaning performance of the evaporator was explored by simulating the actual pattern of rising and falling sunlight in the east and west.（3）In order to further improve the evaporation rate of composite aerogel,a new two-dimensional material MXene with 100%internal photothermal conversion efficiency was prepared.Composite gel with different concentrations and contents of MXene precipitates were prepared by directional freeze drying technology.The microstructure,hydrophilicity,thermal management performance,evaporation performance and underwater oil resistance of aerogel were systematically studied,and its practical application in outdoor evaporation and purification effect were further explored.The 4 cm high composite aerogel can achieve an evaporation rate of 4.0 kg m^-2 h^-1,showing excellent water evaporation performance,and has broad application prospects in the field of solar powered seawater desalination.