Carbonized coffee-based 3D polymeric xerogels for freshwater recovery by solar steam generation

Interfacial solar steam generation is a promising technology for freshwater recovery from seawater desalination and water purification. Herein, is presented an eco-friendly, three-dimensional (3D) porous composite system, made from materials recovered from waste, able to desalinate and purify water upon solar irradiation. The system that consists of carbonized spent coffee powder embedded in a polyglycerol polymer matrix, is developed upon thermal curing of a water-based solution and presents an interconnected porous network with super-hydrophilic properties. We explore the effect of the 3D shape of the composite on the solar steam generation, by varying the height over the radius (aspect ratio) of the structure, and we prove that biocomposites with higher aspect ratio give rise to a progressively higher solar steam generation rate reaching, under the current conditions, 2.72 kg·m −2 ·h −1 for an aspect ratio of 2.2 under 1 Sun irradiation. This is attributed to the enhancement of the total area of the water–air interface which in turn facilitates the steam escape from the porous structure while, at the same time, permits to the bulk water to be effectively entrapped in the whole porous structure. This, together with the fact that the developed material can be fully biodegradable at the end of its lifespan, opens up new prospective paths for sustainable and effective clean water production. • A biodegradable biocomposite is developed for interfacial photothermal desalination. • The 3D biocomposite is composed of carbonized spent coffee and polyglycerol. • The aspect ratio of the biocomposite affects the solar steam generation performance. • The 3D biocomposite is fully biodegradable at the end of its lifespan.