Functional Design And Application Of Interfacial Solar Evaporator With Janus Structure

Water and energy are indispensable and essential resources for the sustainable development of human society.The water and energy resources shortage has gradually become an increasingly severe global problem.Solar distillation technology is a green,clean,and sustainable water purification technology that can use abundant solar energy to obtain clean water from various water sources（such as seawater,high-salinity wastewater,oily wastewater,etc.）,which is potential for application.Limited by way of volume heating,traditional solar distillation technology suffers from low evaporation efficiency,limiting its large-scale practical application.In recent years,due to the rapid development of photothermal materials,solar-driven interfacial water evaporation technology has made significant progress,which can convert solar energy into thermal energy and locate the heat at the interface of water and air,thereby significantly improving evaporation efficiency.Recent researches mainly focus on improving the evaporation rate of solar-driven interfacial evaporators by enhancing light absorption and reducing heat loss through the design of absorber materials.However,less attention was paid to treating high-salinity or oily wastewater.The salt scale and oil pollution are the main bottlenecks hindering the large-scale commercial application of solar-driven interfacial evaporators.Achieving stable zero liquid discharge and effective anti-pollution while realizing high-efficiency water evaporation is an urgent problem to be solved in solar-driven interfacial water evaporation technology.Based on the above problems,through evaporator structure innovation,material innovation,and operation mode innovation,this paper designed a PPy-based wood sponge with Janus structure for solar desalination,a 2D Janus-based evaporator with directional flow structure for high-salinity treatment,a 3D Janus-based evaporator for high-efficient zero-liquid discharge,and a hierarchic double-Janus solar evaporator for oil-water separation,aiming to propose new strategies to endow the evaporator with stable desalination and high-efficiency oily wastewater purification ability.The specific works are as follows:（1）A PPy-based wood sponge with Janus structure（Janus-WS）was constructed and used for solar desalination of seawater.The top of the Janus-wood sponge was a hydrophobic Si/PPy layer for light absorption and salt-blocking,and the bottom was the water transport layer with rich micropores for salt diffusion.Under 3 sun,the Janus-WS showed a stable evaporation performance in 3.5 wt%Na Cl solution for 70 h,with an average evaporation rate of 3.51 kg m^-2h^-1.Other PPy-based sponges with a Janus structure also exhibited excellent desalination performance in 20 wt%Na Cl solution under 3 sun,proving that the Janus structure is reliable in solving the problem of salt scale on the absorber.（2）A two-dimensional Janus-based evaporator（JSE）with a directional salt transfer structure was constructed to simultaneously realize salt recovery and stable desalination.JSE realized stable evaporation for 5 days in 10 wt%Na Cl solution under 1 sun,with an average evaporation rate of 1.21 kg m^-2 h^-1 and a corresponding salt production rate of 876.3 g m^-2 d^-1.In addition,JSE achieved stable desalination and salt recovery from the concentrated seawater with Ca²⁺and Mg²⁺being removed and simulated dyeing wastewater,which laid the foundation for zero liquid discharge of the solar interface evaporator in high-salinity wastewater.（3）To further improve the durability of the hydrophobic coating,optimize the water evaporation performance and realize stable crystallization in the concentrated seawater,a 3D Janus-based evaporator（3D-JSE）was constructed using PVDF as the hydrophobic coating.The intermittent operation mode and the addition of antiscalant enabled JSE to achieve stable crystallization in the concentrated seawater.Since the antiscalant NTA can inhibit the formation of salt scale through chelation and promote the formation of the porous structure of Na Cl crystals through lattice distortion,JSE achieved stable salt crystallization in the 20 wt%simulated concentrated seawater with an average evaporation rate of 2.26 kg m^-2 h^-1（under 1.5sun）.In the outdoor experiment,owing to the combined effect of intermittent operation mode,Janus structure,and NTA,the evaporator achieved a stable zero liquid discharge of 20 wt%concentrated seawater,with an average evaporation rate of 18.63 kg m^-2 d^-1 and an average salt production rate of 11.27 kg m^-2 d^-1,which provides the possibility for solar evaporators to be used in large-scale seawater zero liquid discharge.（4）To solve the oil pollution problem of the evaporator for oily wastewater purification,a CF-PVA hydrogel with super hydrophilicity and oleophobicity was prepared by a one-step in situ synthesis method.Based on the CF-PVA hydrogel,a hierarchic double-Janus solar evaporator（HDJE）with both a hydrophobic photothermal upper surface and a superhydrophilic/oil-water-resistant transport channel was constructed for the first time.HDJE realized an evaporation rate of 1.82 kg m^-2 h^-1 in a 1 vt%silicone oil emulsion under 1 sun.In addition,due to the excellent oleophobic properties of CF-PVA hydrogel,the evaporator achieved efficient oil-water separation in silicone oil emulsions with different concentrations（1vt%,5 vt%,10 vt%and 20 vt%）and 1 vt%emulsions of different types（soybean oil,soybean oil,decane,cetane and kerosene）.When dealing with salt-containing emulsion,HDJE showed good evaporation performance and self-cleaning ability within 7 cycles,with an average evaporation rate of 1.73 kg m^-2 h^-1,and no salt crystallization appeared on the surface of the absorber.In the outdoor experiment,HDJE realized efficient purification of natural seawater containing 1 vt%silicone oil emulsion.The average evaporation rate of the evaporator was 1.24kg m^-2 h^-1,and the average daily water production was 3.59 kg m^-2.The purification efficiency of silicone oil and salt was as high as 99.8%and 99.9%,respectively,which provides a new idea for solar interface water evaporation to produce fresh water from emulsion with salt.