Preparation of superhydrophobic-superoleophilic ZnO nanoflower@SiC composite ceramic membranes for water-in-oil emulsion separation

Superhydrophobic-superoleophilic (SHB-SOL) wettability has proved its superiority in simultaneously enhancing the permeability and selectivity of porous interfacial materials for water-in-oil (w/o) emulsion separation. Here, ZnO nanoflower (NF) modified SiC (ZnO NF@SiC) composite ceramic membranes are reported through a chemical bath deposition method. ZnO NFs with different sizes were grown onto SiC grains forming tunable micro-nano hierarchical structures on the membrane surfaces. After n-octyltriethoxysilane grafting, all the composite ceramic membranes exhibit outstanding SHB-SOL wettability (water contact angle > 150 degrees and sliding angle SA < 10 degrees). The ZnO NF@SiC membrane owning a middle-sized ZnO NF displays the highest SHB-SOL property. When used for w/o emulsion separation, the SHB-SOL ZnO NF@SiC membranes show significantly improved oil flux and water rejection compared with the pristine and the sole silane grafted SiC membranes. The water rejection of the optimal membrane for 1000 ppm water-in-hexane emulsion is -99% and the initial state oil flux is -1300 L.m(-2).h(-1) under a transmembrane pressure of 1 bar, which is relatively competitive among the reported hydrophobic ceramic membranes. The mechanisms of surface hierarchical structures, wetting behavior and separation performance are further revealed. This work may offer new insights into preparing SHB-SOL ceramic membranes for practical w/o emulsion separation.