A low-cost, easily fabricated sodium alginate-nanoparticle coated paper membrane with superb oil-fouling resistance for efficient oil-in-water emulsion separation

The treatment of kitchen oily wastewater has often been neglected, despite its significant annual discharge and associated environmental risks. This study addresses the issue by developing a novel composite paper membrane, using A4 paper as a substrate coated with a simple and durable hydrogel composite of nanoparticles (SiO 2 or TiO 2 ) and sodium alginate. The optimal membrane preparation conditions were determined to be 0.6 wt% sodium alginate and 0.1 wt% nanoparticles, ensuring a stable and effective coating. Oil-in-water emulsions can be effectively separated by the resultant membrane, which exhibits superhydrophilic and underwater superoleophobic properties, with a water contact angle in air close to 14° and an oil contact angle in water close to 150°. According to experimental findings, adding nanoparticles improved the composite membrane's surface roughness and selective wettability. The membrane demonstrated outstanding oil removal efficiency for five types of oil-water emulsions (>95 %) and exhibited excellent reusability (over 15 cycles), without causing significant environmental concerns after prolonged use. This study introduces an inexpensive and eco-friendly hydrogel composite membrane that is easy to fabricate and demonstrates excellent emulsion separation capabilities, regeneration performance, and practical application potential. It is positioned as a viable material for treating oily wastewater because of these qualities.