Superhydrophobic-superoleophilic SiC membranes with micro-nano hierarchical structures for high-efficient water-in-oil emulsion separation

Superhydrophobic-superoleophilic ceramic membranes with chemical, thermal and mechanical robustness are promising for efficient water-in-oil emulsion separation. Here, we report a facile approach to fabricate superhydrophobic-superoleophilic SiC membranes via ZnO nanosphere (NS) deposition and n-octyltriethoxysilane surface grafting. ZnO NSs were grown onto SiC grains by chemical solution deposition method to form micro-nano hierarchical structures for the membrane surfaces. By tuning the precursor concentration, the surface structures of SiC-25, SiC-50 and SiC-75 membranes (C(Zn²⁺) = 25, 50 and 75 mM) were tailored with the increasing density of ZnO NSs. We found that the surfaces of SiC-50 and SiC-75 membrane were superhydrophobic-superoleophilic. Compared with pristine and simply grafted SiC membranes, the three SiC membranes with ZnO NS and grafting modification displayed excellent water rejection (>99.0%) and superior oil flux. The SiC-50 membrane displayed the optimal performance with steady-state flux was up to ~1000 L m^-2 h^-1 under 1 bar for 500 ppm water-in-hexane emulsion. The effects of surface structure and wettability on water-in-oil emulsion separation performance is revealed. We also confirmed the stability of the superhydrophobicity for the SiC-75 membrane. This work offers new insights into constructing robust superhydrophobic-superoleophilic ceramic membranes for high-performance water removal from oil products.