Recycling of Particulate Photoabsorbers for Highly Stable Solar Desalination Operation

Porous graphitic carbon produced from waste coffee grounds (WCG), enormous amounts of which are generated and thrown away worldwide every year, is demonstrated as an effective broadband solar photoabsorber with a large surface area for water evaporation via an environmentally friendly and cost-efficient way. A WCG-based solar desalination device on a wood substrate exhibited an average evaporation rate of ∼1.45 kg/m2 h and a solar-to-vapor conversion efficiency of ∼82.7% under 1 sun illumination. The combination of particulate photoabsorbers with a polyvinylidene fluoride binder resulted in much higher stability and produced a hydrophobic surface with antifouling effects and strong adhesive properties, which make particulate photoabsorbers washable. As a result, there was no noticeable decline in performance after 40 repeated cycles, and the devices retained 94% of initial performance after 6 h of operation in long-term tests. Ultimately, the WCG and binder material-based device suggest a straightforward approach to highly stable and efficient solar desalination at low cost.