Superhydrophilic and underwater superoleophobic ceramic membranes grafted by layered polydopamine and polydopamine encapsulated silica particles for efficient separation of oil-in-water emulsions

Abstract

Owing to frequent oil spills and the increasing discharge of oily wastewater, oil pollution has threatened the sustainability of the ecosystem. Ceramic membranes (CM) have been employed for oily wastewater treatment because of their mechanical and chemical stability, but a suitable separating layer is required to treat surfactant-stabilized oil-in-water emulsions effectively. Herein, a separating layer was rationally designed on the CM surface by combining cross-linked layered polydopamine (CL-LPDA) and polydopamine-encapsulated silica particles (SiO2@PDA) with appropriate permeation flux and antifouling characteristics. The resulting CL-LPDA-SiO2@PDA-CM demonstrated superhydrophilicity with a water contact angle of 0° and underwater superoleophobicity with an underwater oil contact angle of 157°, making it an ideal membrane for separating oil-in-water emulsions. The designed membrane could treat a surfactant-stabilized oil-in-water emulsion with a maximum separation efficiency of 97 % and a permeation flux of 109.76 L m−2h−1. The CL-LPDA-SiO2@PDA-CM has also shown significant resistance to fouling under 20 cycles of observation, and the flux recovery ratio (FRR) was higher than 90 %, indicating that pore-clogging could be effectively prevented in the separating layer.