Cotton-Based Janus fabrics with asymmetric superwettability for efficient emulsion separation

Efficient and sustainable oil–water separation technologies are vital for crude oil recovery, wastewater treatment, and environmental protection. Selective superwettable surfaces have gained attention for their ability to differentiate oil and water via surface energy contrast and structural design. However, their application to emulsion separation remains limited due to trade-offs between pore size, selectivity, and permeability. In this study, bilaterally asymmetric Janus fabrics were fabricated using low-cost dip-coating combined with spray deposition or ultraviolet irradiation. Two configurations were developed: superoleophilic/superhydrophobic paired with superoleophobic/superhydrophilic, enabling directional liquid transport and selective separation. The Janus fabrics achieved separation efficiencies above 99.7 % for both water-in-oil and oil-in-water emulsions. A maximum flux of 70 L·m⁻²·h⁻¹ was obtained under gravity-driven conditions, without external pressure or vacuum, demonstrating a passive, energy-efficient approach. This environmentally friendly and scalable fabrication method offers strong potential for industrial wastewater treatment, oil spill cleanup, and broader applications in fog harvesting, directional fluid transport, and antifouling surfaces.