| Solar desalination is a green and sustainable technology that can simultaneously solve the two major problems of"energy crisis"and"freshwater crisis".In recent years,exploit high-efficiency photothermal conversion materials and high-energy utilization structural devices are both useful to improve the solar-water evaporation rate.The main factors affecting the water evaporation rate are temperature,water-air interface area,and the steam pressure in the environment(i.e.,relative humidity).Regardless of ambient conditions,the temperature of bulk water mainly depends on the photothermal conversion efficiency and heat energy utilization of the materials during the static evaporation process,and the water-air interface area is affected by the device structure.However,the current researches mostly focus on the former rather than water-air interface.Therefore,turning the water-air interface area of device through structural optimization is an effective strategy to improve the solar-water evaporation rate.This thesis takes the construction of high-efficiency photothermal conversion device as the research goal,realizes hierarchical water management by designing and optimizing the device structure.Then hydrogel was selected to construct a 3D porous device structure and committed to solving the two major scientific problems of‘the small water-air interface area'and‘low thermal energy utilization'.It has promoted the development of high-efficiency photothermal conversion device design.The specific work content is as follows:(1)The term of‘Water Mass per Unit Surface Area(WMUA)'was introduced to reveal that hierarchical water management is efficient for improving the solar water evaporation rate.Several materials with different WMUA were selected to construct the‘multi-layer structure device',which was consisted of‘water storage layer(STOR)',‘water restriction layer(RES)'and‘photothermal layer(PTM)'.Taking advantage of the hierarchical water management function from STOR and RES,the water evaporation rate of this multi-layer structure device can reach 1.6-1.8 kg·m-2·h-1 under1 sun intensity,while achieving a solar-to-steam conversion efficiency of 86.1%-92.0%.(2)Polyvinyl alcohol(PVA)hydrogel with 3D network structure was used as the RES and to simplify the hierarchical water management process and improve the heat energy utilization of solar-water evaporation device,result in higher evaporation rate.In addition,carbon nanospheres(CNS)with broader light absorption range and higher photothermal conversion efficiency was selected as the PTM material.Subsequently,combine the above materials with suedette sponge to construct a‘bilayer structure composite solar-water evaporation device'.We embed the CNS to the 3D framework of PVA hydrogel by the sol-gel method and successfully achieve the balance between water content and heat energy in solar-water evaporation device.As a result,the‘bilayer structure solar-water evaporation device can reach steam generation rate of 2.15 kg·m-2·h-1 and a solar energy conversion efficiency of 93.7%under 1 sun intensity(1 k W·m-2).Moreover,the effective seawater desalination performance and stable recycling performance of this device make it have potential to be promoted to the practical application in the future,and it has some enlightening significance for broadening the raw materials selection range of solar desalination device. |
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