A comprehensive review of salt rejection and mitigation strategies in solar interfacial evaporation systems

Solar interfacial evaporation (SIE), based on thermal localization, is a promising and fast-growing passive desalination pathway due to its high performance as well as flexible size design. Through the development and application of various materials and the thoughtful design of diverse evaporation structures, the performance of SIE systems has improved considerably. With equal importance, the longevity of SIE evaporators is also crucial for practical deployment, which is usually underestimated. The longevity of SIE devices is often compromised by the salting-out phenomena when treating seawater or wastewater, due to the formation of salt crystals. These crystals accelerate the deterioration of evaporation performance and can damage the evaporator, especially under conditions of concentrated brines and high solar irradiation. Addressing the challenge of salt crystallization is essential for maintaining the long-term, efficient, and uninterrupted operation of SIE evaporators. In this review, we summarize the advancements in salt crystallization mitigation strategies in SIE technology, categorizing them into three main approaches: i) mass transfer management (backward diffusion in the dark or during the evaporation process, forward diffusion, and passive convection); ii) mechanical methods (self-rotation cleaning evaporator, mechanical flushing, and localized crystallization) and iii) material engineering (hydrophobic materials, Janus materials, salt rejection materials, and spectrum-controlled absorbing-emitting materials). We detail the diverse material choices, structural designs, and salt mitigation properties for each strategy. Finally, we discuss the existing challenges and future research perspectives in salt mitigation strategies for SIE technology, providing a rational roadmap for its practical application.