Porous Al2O3 ceramics with directional gradient pore structure modified by cobweb-bridged WO3 nanowires for oil/water emulsions separation

A novel Al₂O₃ ceramic membrane modified by cobweb-bridged WO₃ nanowires was successfully fabricated for oil/water emulsions separation. Freeze-casting was employed to obtain directional gradient Al₂O₃ porous ceramics at first. Then, the cobweb-bridged WO₃ nanowires were successfully introduced into the separation layer by in-situ hydrothermal synthesis to construct the WO₃ nanowires/Al₂O₃ membrane. Results showed that WO₃ nanowires increased the surface roughness from 45.9 nm to 54.8 nm, the instantaneous water contact angle (WCA) and underwater oil contact angle (UOCA) reached the optimum values of 8.5° and 157.8°, respectively. Construction of cobweb-bridged WO₃ nanowires not only achieved a high separating efficiency of oil/water emulsions up to 92.35%, but also maintained high permeation fluxes at around 1600 L/m²·h·bar. After 10 cycles, the separation efficiency of the membrane remained above 90%. Moreover, the WO₃ nanowires/Al₂O₃ membrane still maintained underwater superoleophobicity after being immersed in strongly acidic, alkaline, and saline solutions, showing a high UOCA above 150° for all tested oil. The WO₃ nanowires/Al₂O₃ membrane is promising in oil/water emulsions separation application for its high separation efficiency, durability, and excellent chemical stability.