Marine biomass-derived bilayer hydrogel for efficient solar desalination

The growing global demand for freshwater has intensified the need for sustainable and cost-effective desalination technologies. Here, we report a marine-biomass-bilayer-hydrogel (MBBH) evaporator composed of chitosan, sodium alginate, and squid-ink pigment for efficient solar-driven water purification. The bilayer design integrates a photothermal black layer for broadband solar absorption with a white supporting layer that provides water transport and thermal insulation. A double-lyophilization process produces a hierarchical porous network that ensures rapid capillary water supply, high light-to-heat conversion efficiency, and excellent structural stability. Under 1 Sun illumination, the MBBH achieves an evaporation rate of 2.9 kg/(m 2 ·h), while concentrated 5 Suns exposure yields up to 16.3 kg/(m 2 ·h) without structural degradation. The device exhibits strong salt resistance, maintaining stable performance even at 10 wt% sodium chloride. Comparative studies of water-supply and insulation strategies reveal that indirect water feeding, and side-foam insulation effectively suppress heat loss and enhance efficiency. This work demonstrates a scalable, low-cost, and environmentally benign approach to solar desalination using fully marine-sourced biopolymers.