Marangoni-driven biomimetic salt secretion evaporator

Abstract

Solar-driven steam generation is regarded as a sustainable strategy for high salinity wastewater treatment. However, the salt accumulation problems associated with vigorous water evaporation limit the practicality of solar evaporators. Herein, inspired by the salt secretion mechanism of natural mangrove leaves, a biomimetic salt secretion evaporator (BSSE) composed of a wood shell and photothermal hydrogel was designed to induce salt crystallization outside the steam generation interface during brine evaporation. Directional salt migration, secretion, and crystallization was driven through region-dependent inhomogeneous thermal and water evaporation management. This exceptional function endows BSSE with superior high-salinity brine evaporation (2.08 kg m−2 h−1, 20 wt% NaCl) and long-term salt rejecting (continuous operation 100 h without any post-cleaning treatment). Experiments characterization and numerical simulations provide a consistent result in which Marangoni convection induced by the thermocapillary and solute capillary effect formed in evaporation interface is the origin of dynamic salt secretion. Moreover, due to the salt secretion characteristics of biomimetic structure design, BSSE can effectively extract the salt from salinized soil and permanently reduce its internal salinity, which provides a logical solution for simultaneously solve global water and food problems.