Preparation Of Hyper-crosslinked Porous Ionic Polymer Based Photothermal Conversion Material And Its Photothermal Vapor Conversion Efficiency

With the rapid development of social economy,increasing population,booming industry and serious environmental pollution,people begin to pay attention to a series of problems such as energy shortage,environmental deterioration and drinking water shortage.Among all kinds of energy sources,solar energy is considered as the best way to solve the global energy crisis because of its unique advantages of safety,reliability,unlimited reserves and complete cleanness.It has also become one of the main directions of research and application of new energy and new water sources.In recent years,with the in-depth study of solar thermal evaporation technology and the vigorous development of nano materials in the field of photothermal conversion.Scientific and technological workers have proposed a new solar driven interface solar water evaporation technology.The design is mainly based on the concept of local heating driven evaporation,that is,the process of water vapor generated by solar heating occurs at the thin air-water interface on the surface of solar thermal materials,so as to minimize the heat loss caused by heating the whole water body in the process of solar thermal conversion and the efficiency of solar thermal conversion is greatly improved.After nearly five years of exploration,the research and development of photothermal materials for solar driven evaporation is rapid.The photothermal conversion efficiency of solar driven interface evaporation device mainly depends on the synergy of key factors such as light absorption performance,thermal insulation performance,high porosity and rapid water molecule transport.In terms of the nature of photothermal conversion,the physical and chemical stability,evaporation efficiency,photothermal conversion performance and salt resistance of materials depend largely on the physical and chemical properties of photothermal materials.Therefore,the development of new high-performance photothermal materials with excellent light absorption,high porosity,good thermal insulation and fast water transport performance is still a research hotspot in this field.In addition,the evaporation of solar driven interface evaporation device in high salinity aqueous solution is prone to salt precipitation and aggregation,resulting in the decline of its photothermal conversion efficiency.Therefore,the salt resistance of the interface evaporation device needs to be further improved.In view of the deficiency in the research field of photothermal materials for solar driven interfacial evaporation,this paper focuses on the design,synthesis,photothermal vapor conversion efficiency and salt resistance of bulk porous ionic polymer materials.A series of novel super wetting liquid porous materials were prepared by Friedel crafts alkylation of ionic liquid monomers with different functional groups.The photothermal steam conversion efficiency and salt resistance of the synthesized materials were systematically studied.The main contents and conclusions of this paper are as follows:(1)HCP-MIN1 and HCP-MIN2 were prepared by using 1-benzyl-3-methylimidazole bromide and 1,3-dibenzylimidazole bromide as monomers and methylal as cross-linking agent.The ratio of monomers and cross-linking agent in the reaction system was adjusted to 1:3 by using aromatic monomer assisted cross-linking strategy.The BET specific surface areas of HCP-MIN1 and HCP-MIN2 were 976 m² g^-1 and 926 m² g^-1,respectively,and the porosity was more than 94%.Moreover,the light absorption of HCP-MINs can reach 97%in the wavelength range of 200 nm-2500nm after coated with polydimethylsiloxane treated graphite powder.HCP-MINs are super hydrophilic,while the water contact angle of the graphite layer is 140°,showing super hydrophobic.Based on the large porosity,low thermal conductivity and fast water molecule transport of HCP-MINs,the application of HCP-MINs as a photothermal conversion material in solar photothermal driven steam generation is reported for the first time.Under 1 k W m^-2 solar illumination,the energy conversion efficiency can reach 88.82%and 86.53%respectively,and the HCP-MINs show good salt resistance to different concentrations of brine.(2)HCP-PY1 and HCP-PY2 were prepared by using N-benzyl pyridinium bromide and N-ethyl pyridinium bromide as monomers and methylal as crosslinking agent,respectively.The ratio of monomers to crosslinking agent was adjusted to 1:3 and 1:4,respectively.The BET specific surface areas of HCP-PY1 and HCP-PY2 were 945 m²g^-1 and 967 m² g^-1,respectively,and the porosity was more than 92%.Based on the porous structure,low thermal conductivity and fast water molecular transmission of HCP-PYs,the application of HCP-PYs as a photothermal conversion material in solar photothermal drive steam production is reported for the first time.The surface modified CHCP-PYs were prepared by coating graphite powder with polydimethylsiloxane.The optical absorption of CHCP-PYs was up to 95%in the wavelength range of 200 nm to2500 nm.The energy conversion efficiency of the CHCP-PYs solar evaporator modified by graphite powder was calculated to be 85.74%and 87.86%respectively under 1 k W m^-2 solar illumination,which shows excellent salt resistance to simulated seawater and Na Cl solution of different concentrations.