Candle soot-modified rPET electrospun nanofibrous membrane for separating on-demand oil-water mixture and emulsions

The CS-rPET electrospun nanofibrous membrane is fabricated from recycled polyethylene terephthalate (rPET) through electrospinning and enhanced with candle soot (CS) to separate oil-water mixtures and emulsions when pre-wetted by oil or water. Using rPET polymers and CS waste reduces the environmental impact of plastic bottle waste and improves its value. The CS-rPET electrospun nanofibrous membrane showed excellent separation performance in oil-water mixtures, achieving over 81.18 % and 71.38 % of separation efficiency through 40 separation cycles after pre-wetting by oil and after washing with ethanol and pre-wetting by water, respectively. The membrane maintained high separation performance after being pre-wetted by oil for water-in-oil emulsions with efficiencies above 99 % and flux exceeding 12,200 L m⁻² h⁻¹. Similarly, the efficiencies remained above 98 % for oil-in-water emulsions after being pre-wetted by water, with a flux over 8000 L m⁻² h⁻¹. Additionally, the CS-rPET electrospun nanofibrous membrane exhibited high separation efficiencies above 97 % and flux over 14,000 L m⁻² h⁻¹ after pre-wetting by oil and 7700 L m⁻² h⁻¹ after pre-wetting by water in harsh environmental conditions. Its adaptability of switchable wettability on-demand after pre-wetting by oil or water highlights its potential for a wide range of challenging oil-water separation applications. However, multiple separation cycles, separation efficiency and flux were reduced, indicating the necessity to improve the membrane's efficiency and reduce the chance of water accumulation in multicycle separation.