A Three-Dimensional Porous Ag/C/Sodium Alginate@Polyurethane Sponge for Efficient Solar-Driven Seawater Desalination

Carbonized coffee grounds exhibit excellent light absorption properties, while sodium alginate hydrogel is characterized by good biocompatibility, low toxicity, and low cost, rendering it suitable for the fabrication of multi-functional photothermal materials. In this study, polyurethane (PU) sponge and sodium alginate were used as the matrix, onto which coffee ground-derived carbon and silver nanoparticles (AgNPs) were loaded to construct a three-dimensional (3D) porous network. A high-performance, recyclable photothermal-steam conversion composite hydrogel sponge was successfully prepared via a simple drying method. The microstructure, physicochemical stability, mechanical properties, and photothermal performance of the composite sponge were systematically characterized, and the interfacial interaction mechanism between the components was clarified. The results showed that stable interactions were formed between coffee ground-derived carbon and sodium alginate, which regulated the water evaporation rate during the photothermal process. The introduction of AgNPs not only enhanced the mechanical strength of the composite material but also achieved a high photothermal conversion efficiency of up to 92.32%. This study broadens the application prospects of waste coffee ground-derived carbon in the field of photothermal conversion.