Preparation Of Fiber Based Photothermal Conversion Material For Solar Interfacial Evaporation

In the context of global clean water scarcity and energy crisis,how to obtain freshwater resources in a low-cost,low-energy way has become a matter of concern.Currently,obtaining fresh water through desalination is considered an effective solution to the global scarcity of fresh water.However,traditional desalination methods such as membrane filtration,reverse osmosis,and thermal distillation still have many limitations,such as high equipment construction and maintenance costs,demanding operating conditions,huge energy consumption,and pollution to the environment.This is contrary to the national sustainable development strategy.Therefore,solar interfacial evaporation desalination has received wide attention because of its low cost,high energy efficiency and small carbon footprint.In order to enhance the solar interface evaporation rate,the design of the interface evaporation device should follow the following three principles:（1）the light absorber material needs to have good photothermal conversion performance to improve energy utilization efficiency;（2）the light absorber should minimize the contact with the volume of water to reduce energy loss;（3）the air-water interface needs to maintain a continuous water supply to enhance the water evaporation rate.Although most of the interfacial evaporation devices are designed according to the above three principles and achieve excellent water evaporation rate,the photothermal conversion materials still have problems such as high cost,poor mechanical properties,easy to fall off and lead to secondary contamination of water bodies,and lack of effective means to remove salt crystals precipitated during long-term application.To address the above problems,this study prepared integrated photothermal conversion fiber materials of different sizes through scalable physical blending and melt spinning technology,and constructed different structures of fiber aggregate solar interface evaporation materials by using the characteristics of high aspect ratio,low stiffness and large specific surface area of fiber materials.Then we studied their solar-driven interface evaporation performance and continuously solved the problems that still exist at each stage of the fiber aggregate interface evaporation materials.This thesis focuses on the following work:（1）An organic/inorganic（PA6/ZrC）integrated micron-scale fiber-based photothermal conversion material was prepared by melt-spinning technology using nylon 6（PA6）and zirconium carbide nanoparticles（ZrC NPs）as raw materials.A bilayer structured fabric was constructed based on the principle of single-phase moisture conduction to achieve good single-phase moisture conduction and excellent photothermal conversion performance.The interfacial evaporation material can achieve 69%solar energy utilization efficiency and 1.3 kg m^-2 h^-1water evaporation rate under one solar（1 KW/m²）irradiation.In addition,thanks to the internal yarn interlock structure,the fabric has excellent mechanical properties,and the salt crystals deposited on the fabric surface during long-term use can be removed by simple scrubbing,providing a simple and efficient salt removal strategy.（2）Organic/inorganic（PVA-co-PE/ZrC）integrated nanofiber-based photothermal conversion materials were prepared from polyvinyl ethylene copolymer（PVA-co-PE）and ZrC NPs by using melt-spinning phase separation technique.Due to its nanoscale size,nanoscale light capture was achieved to further enhance the photothermal conversion performance,and the surface temperature of the nanofibers reached to 135.7°C under one solar irradiation.（3）Using the above nanofiber-based photothermal conversion materials as raw materials,single-layer structured nanofiber membranes,bilayer structured composite nanofiber membranes and three-dimensional structured aerogel interfacial evaporation devices were designed and constructed.The interfacial evaporation performance of different structured interfacial evaporation devices was investigated,and structural optimization was continuously carried out to address their problems.It is demonstrated that the larger specific surface area of the interfacial evaporation device can not only enhance the absorption of light,but also reduce the equivalent evaporation enthalpy of interfacial water,thus accelerating the evaporation of interfacial water;good water transfer rate can replenish the water for the interfacial evaporation system faster and further enhance the interfacial evaporation rate.Through the design and improvement of the structure of the interfacial evaporation device,the floatability,moisture transfer capability and mechanical strength of the interfacial evaporation device were continuously optimized,and finally the three-dimensional aerogel interfacial evaporation material achieved a solar energy utilization efficiency of up to 90.3%and an interfacial evaporation rate of 2.89 kg m^-2 h^-1,and the crystalline salt formed during the long-term use of the interfacial evaporation device was quickly removed in a simple and efficient way to improve its service life.（4）Hydrophilic titanium dioxide nanoparticles（H-Ti O² NPs）were loaded onto the surface of nanofiber-based photothermal conversion materials,and then three-dimensional aerogel materials with photothermal/photocatalytic properties were constructed.This aerogel material achieved a solar energy efficiency of about 90%and a water evaporation rate of 2.38 kg m^-2 h^-1,and reduced the chemical oxygen demand（COD）of textile dyeing wastewater from 5400 mg L^-1 to 170 mg L^-1 only by solar interfacial evaporation,which is significant in broadening the application area of solar interfacial evaporation technology.