A High-Efficiency and Low-Cost Interfacial Evaporation System Based on Graphene-Loaded Pyramid Polyurethane Sponge for Wastewater and Seawater Treatments

Solar water evaporation is a promising strategy to extract freshwater from seawater or wastewater directly by solar energy. Employing cheap substrates capable of reducing light reflection to prepare photothermal layers helps to develop high-efficiency and lost-cost evaporation systems. Herein, pyramid polyurethane sponge (PPUS), a black sound-absorbing material, was first explored as the substrate for loading graphene (GE) to prepare a novel photothermal layer. The porous microstructure, wettability, and optical property of the obtained GE/PPUS photothermal layer were characterized, measured, and compared with those of the flat polyurethane sponge (FPUS) loaded with GE. It is shown that the modifications of PPUS and FPUS with poly(vinyl alcohol) (PVA) endow the two photothermal layers with good wettability. PPUS exhibits higher optical absorption than FPUS, thereby making the GE/PPUS photothermal layer reaches a solar absorptance of 98.5% in the wavelength range of 200-2500 nm, higher than 97.0% of GE/ FPUS. Consequently, an evaporation efficiency of 85.27% under 1 kW m(-2) is achieved by the system composed of GE/PPUS, 9.23% higher than that of the system based on GE/FPUS. The enhancement in evaporation performance of GE/PPUS as compared with GE/FPUS is attributed to the pyramid-shaped projection units and thus can provide larger evaporation area, reduced light reflection, and induced thermal energy recovery by a spatial temperature distribution. A portable evaporate device employing GE/PPUS as the photothermal layer was fabricated, which can provide an ion rejection rate of 99.9% and excellent cyclic stability and long-term salinity durability.