In situ dopamine-driven copper nanoparticle-/thiol-modified superhydrophobic ceramic membranes for oil–water separation and membrane contamination control†

Abstract

To achieve efficient separation of water-in-oil emulsions and to mitigate the issue of easy contamination of conventional ceramic membranes (CMs), modifying CM surface from being hydrophilic to being superhydrophobic is a feasible strategy, thereby improving the separation selectivity and anti-fouling ability of CM. In this study, using dopamine's (DA) self-polymerization and adhesive qualities on various substrate surfaces, a polydopamine (PDA) coating was applied to a ceramic membrane's surface. Using the reducibility of DA, copper ions (Cu²⁺) were reduced to copper nanoparticles (Cu NPs) in situ to construct microstructures on the surface of CM. Finally, the HDT-Cu-PDA-CM superhydrophobic composite film was prepared via the coordination reaction of alkyl mercaptan (HDT) and a metal to realize the grafting of low surface energy substances. Results indicated that the surface roughness of the ceramic membrane increased from 2.7576 μm to 3.4913 μm after introducing Cu NPs. The water contact angle (WCA) of the modified HDT-Cu-PDA-CM composite membrane was 152°, and the separation efficiency of water-in-oil emulsions (n-octane, dichloromethane and toluene) was above 99%. Kinetic analysis of the membrane contamination showed that HDT-Cu-PDA-CM ceramic membrane exhibited strong resistance to contamination. After solvent resistance tests in different organic solvents and acidic and alkaline wastewaters, HDT-Cu-PDA-CM ceramic membrane maintained its superhydrophobicity, emulsion separation efficiency to more than 99%, and excellent solvent resistance. This study offers a novel strategy for the hydrophobic modification of a CM surface using dopamine by in situ reducing the metal nanoparticles on the surface of CM to increase its roughness, followed by grafting alkyl mercaptan.