Preparation Of High Performance Photothermal Materials For Brine Water Treatment

With the development of industrialization and the expansion of the population,the shortage of freshwater has gradually become a worldwide problem.Salt water desalination is a promising pathway to obtain freshwater.Traditional desalination methods have high requirements for the water pretreatment,fossil energy needed,and cannot build large-scale plants in remote and developing areas.Solar energy as a kind of green and sustainable energy,has received extensive attention in the saline desalination.The photothermal conversion is realized by constructing photothermal materials.The solar photothermal evaporator is designed to realize the treatment of salt water and obtain fresh water.At present,solar desalination devices generally have the problem of low evaporation rate and device failure due to salt precipitation.Therefore,the development of high-performance photothermal conversion materials which can prevent salt precipitation played a key role in the development of solar desalination devices.Based on the above issues,we focused on the following issues:（1）Natural wood has a hydrophilic three-dimensional porous structure,which can benefit water transmission.We in situ modified polypyrrole on the surface of balsa wood to prepare Ppy/wood photothermal material.The Ppy/wood can float on the water surface and has low thermal conductive which can localize heat on the top surface.The evaporation rate of Ppy/wood is 1.08 kg·m^-2·h^-1,and the efficiency reached 77.0%under 1 sun illumination.The diameter of the vessels in the balsa wood exceeds 300μm,which can form a hierarchical pore structure with ordinary cells,this structure can avoid the salt precipitate on the upper surface of the material effectively.After 48h desalination process by using the South China Sea water and the laboratory-prepared brackish water,there is no salt precipitation on the upper surface of the Ppy/wood,and the ion concentration in the freshwater is significantly reduced after desalination.Therefore,Ppy-wood has the advantages of good stability,good scalability,and low cost in solar desalination.（2）3D printing can enhance the design freedom in material preparation.We used3D printing technology to prepare a hydrophilic reduced graphene oxide aerogel（3D rGA）with a corrugated top and an array of vessles inside.The corrugated top surface can increase the light absorption area of the material under the fixed condition of the projected area,which can increase the water evaporation rate.The array of vessles ensures that water transported to the top surface while forming a hierarchical pore structure with the small pores inside the aerogel,which prevented salt precipitation effectively.The evaporation rate of 3D rGA reached 1.43 kg·m^-2·h^-1,and the efficiency of 3D rGA is 94.5%under one sun illumination.No salt is precipitated on the top surface of the material in the continuous 48 h desalination experiment,and the ion concentration of the water sample is significantly reduced after desalination.Our material has the ability of high efficiency,and can be enlarge eaily.（3）In the previous work,the seawater desalination material usually floated on the water surface as a block,and loss massive of heat to the bulk water,and the salt was dissolved back into the bulk water thus could not be recovered.Fe³⁺can catalyze wood pyrolysis process,which can significantly reduce the temperature and the time required for wood carbonization.We used Fe-catalyzed pyrolysis longitudinal wood chips（C-L-wood）as the photothermal material and connect it to another natural wood chip to form a T-shaped structure.This material has a linear water transportation center,the salt concentrated and precipitated at the double edge of the photothermal material as the water evaporate.The material has an obvious heat localization effect,and has large surface area where the temperature is lower than the ambient temperature,which can absorb energy from the surrounding environment to increase the water evaporation rate.The evaporation rate of the T-shaped C-L-wood reached 2.43 kg·m^-2·h^-1,and the salt recovery rate of the T-shaped C-L-wood in 3.5%NaCl solution reached 56.6 g·m^-2·h^-1.The solar desalination device was successfully assembled and used for the desalination of the brackish water.The T-shaped C-L-wood can recover salt while collecting freshwater,which realized zero liquid discharge desalination.This material has the advantages of high efficiency,preparation easily,green and sustainable.