Integrated Conical Hydrogel Evaporator for High Salinity Brine Solar Evaporation and Zero Liquid Discharge

During the process of seawater evaporation for freshwater production, the gradual increase of brine salinity results in the crystallization and accumulation of salts at the evaporation interface to severely restrict long-term operation stability. Herein, the conical double network hydrogel interface evaporator (PACC, composed of poly(vinyl alcohol), acrylamide, and Chinese ink) with solid structural stability was developed, which achieves efficient solar-driven interfacial steam production performance with exceptional salt recovery capability. The rationally designed conical geometry induces both radial and axial temperature gradients, where the periphery experiences greater convective heat loss and results in a lower local temperature. This thermal differential drives the surface tension discrepancy and strong Marangoni convection, thus accelerating salt directional transport toward the edges and enabling preferential salt crystallization at the periphery. Therefore, the conical hydrogel evaporator achieves a high evaporation rate of 2.797 kg·m –2 ·h –1 and 94.58% photothermal conversion efficiency, with sustained performance by directing salt crystallization away from critical surfaces. Meanwhile, the evaporation rates remain stable under high brine concentrations, while a remarkable salt recovery rate of 95.69% under saturated brine can be achieved. This strategy provides a promising approach toward efficient freshwater production and sustainable salt recovery with zero liquid discharge from high salinity brines or seawater.