Preparation Of High Efficiency Photothermal Coating And Its Interfacial Light-vapor Conversion Performance

Freshwater is the basis for the survival of human beings and other creatures on the earth.Since the 21st century,the shortage of freshwater resources has become more and more serious which has aroused widespread concern.Scientists are seeking portable technologies for obtaining freshwater resources in an efficient pathway.In recent years,the interfacial solar steam generation technology which uses solar energy to obtain freshwater out of seawater desalination directly has been developed.The advantages of interfacial solar steam generation technology include high efficiency,portability,independent of fossil energy,and no need for large-scale investment.At present,this field is rapid developing,and the types of the materials used in this field are gradually increasing,but there are some limitations such as complicated preparation process,difficulty in mass production,and high production cost.Based on these current limitations,this thesis reports three kinds of photothermal coatings for interfacial evaporation and research on their preparation method and performance.The research content is as follows:（1）An efficient photothermal coating was prepared by radical polymerization,in which polypyrrole（PPy）was used as the light-to-heat conversion material,2-acrylamide-2-methylpropanesulfonic acid（AMPS）was used as the hydrophilic component,polyvinyl alcohol（PVA）was used as a film-forming component,persulfuric acid ammonium（APS）was used as the initiator.The interfacial evaporation performance was investigated with the filter paper or cotton cloth coated with the photothermal coating.The test device is composed of a cotton fabric or filter paper coated with a photothermal coating,a polyurethane foam with excellent thermal insulation performance,and a water-absorbing cotton sliver.The research results show that the photothermal coating has excellent photothermal conversion performance which can absorb most of the light and convert it into heat,the material is floated on the surface of water which can confine the heat to the gas-liquid interface.Under 1kw·m^-2illumination intensity,the solar energy utilization rate of this photothermal coating can reach 87.98%,and the evaporation rate can reach1.61Kg·m^-2·h^-1,showing excellent energy efficiency and evaporation rate.In addition,the coating has excellent stability,seawater desalination and sewage treatment performance.（2）A high-efficiency photothermal mud without any complicated chemical synthesis was prepared with Fe₃O₄,chitosan solution,sodium alginate and water as the main components.The photothermal mud was coated on the surface of the filter paper for the further test.The Fe₃O₄acts as a light-to-heat conversion material and form cordinates with the carboxyl anion in sodium alginate to cross-link the liner polymer chains to fix the shape,and sodium alginate is used as a hydrophilic substance to regulate the performance of the material.The research results show that the photothermal mud has excellent light absorption capacity,with an average light absorption rate of more than 95%in the spectral range of 200-2500nm.Under the illumination intensity of 1kw·m^-2,the evaporation rate can reach 1.69 Kg·m^-2·h^-1,showing excellent water evaporation performance.The raw materials of the photothermal mud are environmentally friendly,non-toxic and harmless,and do not require any chemical synthesis,which greatly reduces the preparation cost and the burden on the environment in the preparation process of traditional materials.（3）A photothermal coating was prepared with Polypyrrole（PPy）as the light-to-heat conversion material,n-butyl acrylate（BA）,acrylamide（AM）,2-acrylamide-2-methylpropanesulfonic acid（AMPS）as the polymerization monomers methyl sulfoxide（DMSO）as the solvent and ammonium persulfate（APS）as the initiator.The DMSO is a good solvent which makes the three monomers polymerize in a uniform way to form a uniformly dispersed polymer coating.After DMSO exchange with water,the hydrophobic poly（n-butyl acrylate）block will form the hydrophobic aggregation to form crosslink points.The stable crosslinking points gives the coating excellent stability,and polyacrylamide and PAMPS and PAAm polymer block provide good hydrophilicity of the material.The research results show that the average light absorption rate of this photothermal coating in the 200-2500nm spectral range is about 95%.Under the illumination intensity of 1kw·m^-2,the solar energy utilization rate can reach 93.3%,and the evaporation rate can reach1.81kg·m^-2·h^-1,in addition,the material also shows excellent stability,seawater desalination and sewage treatment performance.