Superhydrophobic and superoleophilic cotton fabric membrane with recycled ZnO for oil–water separation: particle size effect micrometric versus nanometric

This study demonstrates the synthesis of superhydrophobic and hydrophobic cotton fabric membranes, used for separating oil–water emulsions, by a simple immersion method with polydimethylsiloxane (PDMS) and zinc oxide (ZnO) from waste alkaline batteries. Scanning electron microscopy (SEM) analysis confirmed the effectiveness of ZnO/PDMS treatment, which increased the surface roughness and enhanced water contact angles (WCAs). The membranes treated with PDMS (5 g PDMS prepolymer, 0.5 g curing agent, 45 mL isopropyl alcohol) exhibited a WCA of 145 ± 1°, whereas those treated with PDMS and 1 g of ZnO (micro or nano) achieved WCAs of 145 ± 1° and 153 ± 1°, respectively. This difference is attributed to the low surface tension of the PDMS layer on the cotton fabric, combined with the surface roughness topography created by the ZnO micro- and nanostructures. Filtration tests showed that the membranes treated with only PDMS achieved >96% oil filtration and 94% water blockage, whereas ZnO/PDMS membranes maintained similar oil filtration efficiency but achieved 100% water blockage. These results highlight the potential of recycled ZnO in cotton fabric membranes for oil–water separation, with micro-ZnO offering a cost-effective and sustainable solution and nano-ZnO providing superhydrophobic behavior, both contributing to improved membrane performance in wastewater treatment applications.