Smart filter paper with pH-responsive wettability for effective separation of oil/water mixtures and emulsions

Abstract

Materials with stimulus-responsive wettability are attracting increasing attention because of their potential applications in oil/water separation and oil spill remediation. Herein, a pH-responsive filter paper was rapidly fabricated by initially forming a complex between TiO₂ and octadecylamine, followed by immersion in an ethanolic solution of SiO₂ nanoparticles. The resultant filter paper exhibited superhydrophobicity and superoleophilicity in air when the solution pH was greater than 6.0, whereas it became superhydrophilic and superoleophobic when the solution pH was less than 2.0. The treated filter paper was used for the controllable separation of complex oil/water/oil ternary mixtures, demonstrating its strong response to pH changes. The pH-responsive filter paper effectively separated both immiscible oil/water mixtures and different kinds of oil-in-water emulsions with separation efficiencies exceeding 99%. The durability of the pH-responsive filter paper was demonstrated by its ability to maintain a separation efficiency of around 99%, even after 25 cycles of separating a typical emulsion of tetrachloromethane in water. The developed approach has the potential to provide innovative smart materials for the treatment of oil-contaminated wastewater.

Graphical abstract