pH-Responsive Sponges Fabricated by Ag–S Ligands Possess Smart Double-Transformed Superhydrophilic–Superhydrophobic–Superhydrophilic Wettability for Oil–Water Separation

Advanced applications of surfaces with smart wettability offer great perspectives to design novel materials. pH-responsive smart sponges with double transformation are fabricated via in situ decoration of Ag nanoparticles through an oxidation–reduction reaction and followed by modification with a mixed thiol–ethanol solution containing HS­(CH₂)₁₁CH₃, HS­(CH₂)₁₀COOH, and HS­(CH₂)₁₁OH. The wettability of sponges with optimal thiol proportions can switch reversibly between superhydrophilicity–superhydrophobicity–superhydrophilicity under different pH conditions. In addition, the as-prepared sponges have excellent absorption capacity and high oil–water separation efficiency (99.1%). This report provides a simple approach to prepare smart sponges with switchable wettability which can be further applied to many practical applications, such as marine purification and an oil–water on–off switch.