Mussel-inspired pH-responsive copper foam with switchable wettability for bidirectional oil-water separation

Abstract Stimuli-responsive materials with switchable wettability for bidirectional oil-water separation show great potential in practical applications. Inspired by mussels, we use dopamine as an anchor molecule to construct a polydopamine (PDA) coating on the surface of copper foam (CF). Silver particles are deposited on the PDA coated surface to construct a multiscale composite structure, and the long-chain alkylthiol with carboxyl and methyl groups at the end is subsequently self-assembled to the modified copper foam surface. The as-modified copper foam has unique pH responsiveness, that is, the water contact angle (WCA) is measured to be about 140° under acidic and neutral conditions, while alkaline conditions radically change the surface property from superhydrophobic to superhydrophilic due to the measured WCA turning to 0°. It can be used efficiently for the bidirectional separation of an oil-water mixture, e.g., the separation efficiency of a 1,2-dichloroethane/water mixture can reach as high as 98.2%. Besides, it maintains 98% separation efficiency and stable wettability for an octane/water mixture, together with excellent mechanical durability; the WCA of the surface maintains at about 130° after ten wear cycles.