Preparation Of Functional Photothermal Conversion Material And Its Solar Interfacial Water Evaporation Performance

As an emerging desalination method,solar interfacial evaporation has attracted great attention from researchers due to its advantages of low energy consumption,low cost and no-secondary pollution.As the core part of solar interfacial evaporation,photothermal conversion materials have been designed by a large number of studies and have achieved some results.However,the existing photothermal conversion materials are still plagued by the complex preparation process,low photothermal conversion efficiency and inability to continuously operate under intermittent solar irradiation.Based on the above research background,three composite photothermal conversion materials were designed and prepared from the perspective of preparation process,photothermal conversion and thermal energy storage,and then the solar interfacial water evaporation performance was studied in depth.The main contents of this thesis are concluded as follows:（1）Graphene oxide（GO）and silver nanoparticles（Ag NPs）were selected as photothermal conversion media to enhance photothermal conversion and solar energy utilization.At the same time,in order to solve the problems of long production cycle,high requirements for equipment and high energy consumption in the preparation of aerogels,a low-temperature-crosslinking method was proposed to prepare aerogels in a short time under normal pressure,which can avoid long-time freeze-drying.Bacterial cellulose/graphene oxide-nano silver（BC/GO-Ag）composite aerogels were prepared by this method and in-situ reduction method.Thanks to the synergistic photothermal effect and open porous structure of aerogel,84.1%light absorption is achieved in the full spectral range.Under the illumination of 1 k W·m^-2,the evaporation rate of aerogels can reach 2.36 kg·m^-2·h^-1,and the photothermal conversion efficiency can reach 94.5%.In the 10 cycle evaporation tests,the evaporation rate of aerogels remains stable,showing good reusability.In addition,the aerogel not only shows good desalination ability for simulated seawater and saline-alkaline water,but also shows excellent purification effect for acidic solution,alkaline solution and dye wastewater.（2）A simple,rapid,low-cost and environment-friendly preparation method of polymer foam,namely surfactant foaming method,was developed,which solved the problems of complex high-pressure equipment and potential safety hazards in polymer foam preparation.Agar/SA/GO-Ag composite foam with three-dimensional porous structure was prepared by surfactant foaming method and in-situ reduction method with GO and Ag NPs as photothermal conversion medium and agar（Agar）and sodium alginate（SA）as basic skeleton.The foam has good wettability,and 96.7%light absorption is achieved in the full spectral range.Under the illumination of 1 k W·m^-2,the evaporation rate is as high as 2.55 kg·m^-2·h^-1,and the photothermal conversion efficiency is as high as 97.3%,showing excellent evaporation performance.At the same time,the evaporation performance of the foam was not attenuated in 10 consecutive cycle evaporation tests,showing good reusability.The foam was used for desalination of salt water and purification of wastewater,and the related indexes of treated water samples met the drinking water standards stipulated by the World Health Organization（WHO）and the US Environmental Protection Agency（EPA）.（3）In order to solve the problem that photothermal conversion materials cannot run continuously under intermittent solar irradiation,phase change energy storage is skillfully introduced into interfacial evaporation.Polyethylene glycol（PEG）is selected as phase change energy storage material,polyacrylic acid（PAA）hydrogel is used as leak-proof support material to stabilize PEG morphology,and GO and Ag NPs are used as photothermal conversion media.PEG/PAA/GO-Ag composite phase change materials with photothermal conversion and phase change energy storage are constructed by sol-gel method and in-situ reduction method.In the full spectral range,95.4%light absorption is achieved.Under the illumination of 1 k W·m^-2,the evaporation rate of 2.14 kg·m^-2·h^-1 and the photothermal conversion efficiency of 91.2%were obtained.When there is no light,the stored heat energy released by the phase-change process continues to evaporate,and the evaporation rate of 0.73 kg·m^-2·h^-1 and the photothermal conversion efficiency of 35.0%are obtained.In addition,the material not only shows excellent performance stability in 10 consecutive heating-cooling cycle evaporation tests,but also can be used for desalination of salt water and purification of dye wastewater.