Preparation Of Photothermal Conversion Materials Based Hypercrosslinked Polymers And The Solar Interfacial Evaporation Properties

With the rapid development of modern industry,freshwater scarcity and energy crisis have become the global issues threatening human’s survival and development.Under the dual pressure of energy shortage and environmental protection,using solar interfacial evaporation technology for seawater desalination is of great practical significance for alleviating the shortage of freshwater.As the core of solar interfacial evaporation system,the performance of photothermal conversion material directly determines the evaporation efficiency.Researchers have designed and prepared various photothermal conversion materials to improve the solar interfacial evaporation performance.However,the existing photothermal conversion materials still have some problems,such as high preparation cost,cumbersome preparation procedure and poor salt resistance.Therefore,the development of photothermal conversion materials with easy preparation,inexpensive,stable evaporation performance and excellent salt resistance is the research focus in the field of solar interfacial evaporation.Hypercrosslinked polymer（HCPs）is a kind of porous organic polymer materials with high specific surface area and excellent physical and chemical stability.HCPs can be prepared by Friedel-Crafts reaction without expensive raw materials and catalysts.In addition,HCPs show the advantages of adjustable porous structure,good thermal insulation and easy modification in many applications,which provides a new idea for the preparation of high performance photothermal conversion materials.Based on this,in this paper,a series of HCPs based photothermal conversion materials with superhydrophilicity,low thermal conductivity and excellent light absorption property were prepared by mild synthesis and modification method and bulk chemical as monomer.And their solar interfacial evaporation performance,stability and salt resistance were systematically studied.The main contents and conclusions of this paper are as follows:（1）A polymer precursor Poly HIPE with macroporous network structure was synthesized by polymerization of high internal phase emulsion with styrene as monomer and divinylbenzene as crosslinker.Then,it was swollen in 1,2-dichloroethane,and Friedel-Crafts alkylation reaction took place under the action of crosslinker and catalyst to obtain the hypercrosslinking polymer HCP-Poly HIPE.HCP-Poly HIPE possesses abundant pore structure,excellent thermal stability and low thermal conductivity.The photothermal conversion material C-M-HCP-Poly HIPE was obtained by hydrophilic modification and carbon black layer modification.The upper layer of C-M-HCP-Poly HIPE show high light absorption capacity,with an average light absorption rate of 98%in the range of 200 to 2500nm,and the lower layer show excellent hydrophilic ability.As a solar interfacial evaporator,the energy conversion efficiency of C-M-HCP-Poly HIPE can reach88.04%under 1 k W m^-2 illumination.Based on the superhydrophilicity and porous property of M-HCP-Poly HIPE,the energy conversion efficiency of C-M-HCP-Poly HIPE in 20 wt%Na Cl solution was tested to be 83.37%under 1 k W m^-2illumination.（2）Two kinds of hypercrosslinked polymers HCP-Cl and HCP-Br were synthesized by self-polycondensation reaction promoted by anhydrous Fe Cl₃ withα,α’-dichloro-p-xylene andα,α’-dibromo-p-xylene as monomers,1,2-dichloroethane as solvent.The HCP-Cl and HCP-Br have abundant porosity and high specific surface area.After modification with polyvinyl alcohol,the obtained PVA-HCP-Cl and PVA-HCP-Br show superhydrophilicity and excellent insulation performance.Then the surface of the PVA-HCPs was sprayed with polypyrrole and silver particles as sunlight absorption layer,the photothermal conversion materials Ag/PPy-PVA-HCP-Cl and Ag/PPy-PVA-HCP-Br were prepared,and the average light absorption rate of Ag/PPy-PVA-HCPs is 91%over the range of 200-2500 nm.The energy conversion efficiencies of 86.66%for Ag/PPy-PVA-HCP-Cl and 87.39%for Ag/PPy-PVA-HCP-Br were achieved under 1 k W m^-2 illumination.In addition,due to the superhydrophilicity and porous structure of Ag/PPy-PVA-HCP-Br,the energy conversion efficiency of Ag/PPy-PVA-HCP-Br was found to be 83.25%in 20 wt%Na Cl solution.（3）Two kinds of hypercrosslinked polymers HCP-1 and HCP-2 were synthesized by Friedel-Crafts alkylation reaction using benzene and methylbenzene as monomers,formaldehyde dimethyl acetal as external cross-linker.The prepared HCPs possess large specific surface area,low apparent density and excellent thermal stability.After modification with sodium alginate and polypyrrole,the resulting samples PPy-M-HCPs show superhydrophilicity and outstanding light absorption performance,the average light absorption rate can reach 95%over the range of 200-2500 nm.Under 1 k W m^-2 illumination,the energy conversion efficiencies of PPy-M-HCP-1 and PPy-M-HCP-2 were tested to be 87.46%and 87.58%,respectively.Due to the porous structure and superhydrophilic surface of both PPy-M-HCP-1 and PPy-M-HCP-2,the energy conversion efficiency of these two materials can reach more than 85%in 20 wt%Na Cl solution.（4）Phenolic aldehyde hypercrosslinked polymers PAHCP-1 and PAHCP-2 were prepared by solvothermal reaction of hydroquinone and phenol with formaldehyde under the catalysis of hydrochloric acid.Both PAHCP-1 and PAHCP-2 have superhydrophilicity and excellent thermal insulation property.After deposition the layer of carbon soot on PAHCPs,the photothermal conversion materials C-PAHCP-1and C-PAHCP-2 were obtained,the average light absorption rate of C-PAHCPs can reach 90%in the range of 200-2500 nm.The energy conversion efficiencies of C-PAHCP-1 and C-PAHCP-2 under 1 k W m^-2 illumination were tested to be 87.29%and 87.86%,respectively,and the energy conversion efficiencies in 20 wt%Na Cl solution were found to be 81.24%and 82.83%.In addition,the outdoor evaporation experiment was conducted under natural sunlight,C-PAHCP-1 and C-PAHCP-2 still possess favorable evaporation performance,shows a great potential for practical application.