Non-symmetric evaporator by polyvinyl alcohol encapsulated coal tar pitch-based carbon and sponge foam for solar-driven interfacial evaporation

Sponge foam (SF) has attracted much attention in solar-driven interfacial evaporation for its lowcost, abundant sources, hydrophilicity, and accessibility. However, pure foam cannot achieve light and heat conversion and needs to be modified. By integrating a light absorber with the sponge foam matrix, the structural advantage of the sponge foam can be fully exploited, creating an abundant network of water-conducting channels and unique insulating layers that can optimize heat utilization while maximizing water supply. Herein, we employed a simple impregnation method in which SF was immersed in a system of polyvinyl alcohol (PVA)-coal tar pitch-based carbon (NSCTP). The gelatinized PVA can form a coating of NSCTP on the surface of SF, constructing NSCTP@SF evaporators with excellent salt resistance. Under the irradiation of 1 kW·m⁻², the water evaporation rate reaches 1.96 kg·m⁻²·h⁻¹ with a photothermal conversion efficiency of 94.4 %. Most importantly, the evaporator demonstrates superior salt tolerance in low-concentration seawater (3.5 wt% or 10 wt% NaCl) and brackish water during a continuous evaporation process for 12 h. This study presented an eco-friendly, low-cost, and scalable strategy to fabricate a high-performance evaporator with practical applications in solar desalination.