Upcycling Waste Expanded Polystyrene into Fog-Harvesting Nanofiber Membranes for Sustainable Fog Water Collection

The increasing accumulation of non-degradable expanded polystyrene (EPS) waste and the growing demand for alternative freshwater sources highlight the need for sustainable resource recovery technologies. This study demonstrates the conversion of waste EPS into electrospun nanofiber membranes for fog-water harvesting using a biomimetic hydrophilic–hydrophobic design inspired by the Namib Desert beetle (Stenocara gracilipes). Recycled EPS was processed using a greener 1:5 N,N‑dimethylformamide (DMF):d‑limonene solvent system and electrospun into submicron fibers whose surface chemistry was tailored with cetyltrimethylammonium bromide (CTAB) and TiO₂ nanoparticles to enhance surface wettability and water collection performance. The resulting membranes exhibited continuous submicron fibers with reduced bead defects and successful TiO₂ incorporation which confirms the effectiveness of the chosen formulation and processing conditions. Fog-harvesting performance showed significant improvement after surface modification, with the PS + CTAB + TiO₂ membrane achieving a laboratory collection rate of 135.8 mg·cm⁻²·h⁻¹ which represents a 73.4% increase compared with unmodified PS membranes (78.3 mg·cm⁻²·h⁻¹). During outdoor testing under approximately 67% relative humidity, the composite membrane collected 0.44 g of water over 2 h, equivalent to 5.57 L·m⁻²·day⁻¹, while unmodified, pure PS membranes showed negligible collection results. These findings demonstrate a circular, low-energy approach for transforming plastic waste into functional fog-harvesting materials, with potential applications in decentralized water collection and sustainable materials engineering.