A facile nanocomposite strategy to fabricate a rGO–MWCNT photothermal layer for efficient water evaporation

Solar-driven water evaporation assisted by photothermal membranes is considered as one of the sustainable and cost-effective strategies for pure water generation and wastewater treatment. Herein, we report a facile but effective approach to improve the photothermal performance by combining 2D reduced graphene oxide (rGO) and 1D multi-walled carbon nanotubes (MWCNTs), which have different nanomorphologies. The photothermal layer can be easily deposited on different substrate materials via simple vacuum assistance. Such a composite photothermal layer shows a rough surface with a controllable nano-structure, which can thus optimize solar light harvesting. On the other hand, the formation of a loose internal porous structure and suitable wettability ensure water transport inside the photothermal layer during evaporation. The surface temperature reaches as high as 78 °C even under one sun irradiation (1 kW m−2), which is 10 °C higher than the result of pure rGO membranes. When loaded on a PVDF substrate, the rGO–MWCNT based membrane is flexible and shows an obvious improvement in the evaporation rate, about 79.0% and 8.9% higher than those of pure rGO and MWCNT membranes, respectively. The solar thermal conversion efficiency can reach up to 80.4% without any extra accessory for thermal management. Based on our results, the nanocomposite strategy is facile and effective for the development of novel photothermal membranes for high-efficiency evaporation, and contributes to the widespread application in the fields of desalination and wastewater treatment.