Clean water is essential for good health and public sanitation. In addition to conventional solar desalination strategies, the emergence of solar interfacial evaporation has been described as a game-changer in clean water harvesting owing to its high water evaporation rate and solar-to-vapor efficiency. Different solar evaporators such as polymers and plasmonic nanoparticles are often used to achieve high solar-to-vapor efficiency. Although solar evaporators are potential candidates for increasing clean water harvesting, they suffer from salt-fouling that significantly limits their practical applications. During solar interfacial evaporation, the precipitated salts not only reduce the evaporation rate and solar-to-vapor efficiency but also degrades the lifespan of the solar evaporators. Existing approaches for solving the salt-fouling problem, such as using sufficient water supply and electrifying seawater to transform salt to an ionic state, have several drawbacks that hinder their large-scale application. Thus, more effective and feasible strategies for solving salt-fouling issues are highly desirable.
Significant research efforts have been devoted to enhancing evaporation performance and salt tolerance of solar evaporators. Unfortunately, most existing studies have been carried out in open systems, while solar interfacial evaporation used in clean water collection must be conducted in closed systems. However, closed systems are characterized by significantly lower evaporation performance (above 30%) due to high temperature and relative humidity and lower light intensity. In addition, the differences between evaporation rates and salt tolerances between open and closed systems are poorly understood. To this end, a thorough understanding of the performance differences between open and closed systems is of great importance in designing solar evaporators for application in closed systems.
In a new study, Tao Hu (PhD student), Kai Chen (PhD student), Dr. Lingxiao Li and led by Professor Junping Zhang from Lanzhou Institute of Chemical Physics, the Chinese Academy of Sciences proposed to design of carbon [email protected] solar evaporators with controllable salt-tolerance for efficient water evaporation in closed systems. The newly designed evaporators consisted of a superhydrophilic shell with a controllable thickness (Tsuperhydrophilic) and a superhydrophobic core. The effects of the Tsuperhydrophilic on the salt tolerance and evaporation performance of the closed system were thoroughly investigated. Also, the authors studied the differences between the evaporation rates and salt-tolerance of the solar evaporators in the closed and open systems to provide a better understanding of the same. Their research work is currently published in the Journal of Material Chemistry A.
The authors findings showed that the evaporation rate and salt-tolerance of the closed system were accurately controlled by Tsuperhydrophilic, i.e., time taken to activate the evaporator by O2-plasma (tplasma) of the proposed solar evaporators. During short-term seawater evaporation, an increase in Tsuperhydrophilic enhanced the salt-tolerance but degraded the evaporation rates. A higher water evaporation rates up to 1.34 kg m-2h-1 under 1 sun was reported in a closed system. The salt-tolerance of a particular evaporator in a closed system was significantly higher than that of an open system attributed to the effects of higher relative humidity, lower light intensity and higher temperature. Moreover, the evaporation rates and salt-tolerance in the open and closed systems exhibited different tendencies, which were highly influenced by the Tsuperhydrophilic.
In summary, the research team reported the design of carbon [email protected] solar evaporators and successfully demonstrated their feasibility in controlling salt-tolerance and enhancing seawater evaporation rates in closed systems. Based on the differences between the open and closed systems in terms of salt-tolerance and evaporation rates, the authors concluded that efficient water collection could only be achieved if the solar evaporators were designed and optimized based on salt-tolerance and evaporation performance of closed systems and not open systems. In a statement to Advances in Engineering, Professor Junping Zhang, the lead and corresponding author explained the study contribute to design of novel solar evaporators with high evaporation performance in closed systems for efficient clean water collection.
Hu, T., Chen, K., Li, L., & Zhang, J. (2021). Carbon [email protected] solar evaporators with controllable salt-tolerance for efficient water evaporation in a closed system. Journal of Materials Chemistry A, 9(32), 17502-17511.