Sodium Alginate/TiO₂ Bilayer Material Multiphase Photocatalytic Degradation of Seawater Pollutants and Synergistic Seawater Evaporation

Solar Interfacial Evaporation (SIE), which relies solely on solar energy, reduces heat loss by concentrating heat at the water–air interface, making it an ideal approach for solar-driven seawater desalination and wastewater purification. Recently, biomass-based carbon materials have become prominent SIE materials for seawater desalination due to their abundant sources, excellent thermal stability, high specific surface area, and rich internal pore structures. In this work, a porous composite material was developed by cross-linking alginate and cellulose with calcium chloride, followed by loading TiO2 onto the material’s surface to create a composite with a hydrophilic transport layer and a hydrophobic evaporation layer (SAC/CTi). This material enables efficient water recovery via solar evaporation of seawater and wastewater purification through a three-phase photocatalysis. Under 0.25 W/cm2 illumination, the surface temperature of the sample can reach 192 °C within 3 min. During light-induced evaporation, the layered structure retains water between the hydrophilic transport and hydrophobic layers, balancing the water supply and evaporation. The spherical design of the evaporator maintains a high photothermal conversion efficiency from different angles. When light is incident vertically, the evaporator achieves a peak seawater evaporation rate of 1.7 kg/(m2·h). Additionally, the double-layer evaporator demonstrates a strong photocatalytic performance, acid–base resistance, and effective pollutant purification while evaporating seawater. SAC/CTi holds significant potential for applications in seawater desalination, water pollution treatment, and broader environmental remediation processes.