Hofmeister Effect-Enhanced Hydration Chemistry of Hydrogel for High-Efficiency Solar-Driven Interfacial Desalination

Solar-driven water evaporation technology holds great potential for mitigating the global water scarcity due to its high energy conversion efficiency. Lowering the vaporization enthalpy of water is key to boost the performance of solar-driven desalination. Herein, a highly hydratable hydrogel (PMH) network, consisting of modified needle coke as photothermal material and polyvinyl alcohol (PVA) as hydratable matrix, is crafted via simple physical cross-linking method. When capitalizing on the PMH as evaporator for 3.5 wt% NaCl solution, a high evaporation rate of 3.18 kg m^-2  h^-1  under one sun illumination is deliver ed, unexpectedly outperforming that in pure water (2.53 kg m^-2  h^-1 ). More importantly, the PMH shows a robust desalination durability, thus enabling a self-cleaning system. Further investigations reveal that the outstanding evaporation performance of PMH in brine roots in its hydrability tuned by chaotropic Cl^- , wherein the Cl^- can mediate the hydration chemistry of PVA in PMH and suppress related crystallinity, thus contributing to the increased content of intermediate water and the lowered vaporization enthalpy of brine. This work first scrutinizes the Hofmeister effect on the evaporation behavior of PMH evaporator in brine and provides insights for high-efficiency solar-driven interfacial desalination.