Superhydrophobic alumina membrane by steam impingement: Minimum resistance in microfiltration

Fluoroalkylsilane (FAS) grafting allows the conversion of hydrophilic ceramic membranes into superhydrophobic thin layer, unfortunately with a great increment of mass transfer resistance. In this study, superhydrophobic alumina membranes were synthesized by direct grafting of (heptadecafluoro-1,1,2,2-tetra hydrodecyl) triethoxysilane on alumina support with varied concentration. In order to reduce transport resistance generated from FAS grafting, the calcinated (450 °C) or steam impinged sol–gel layers were coated on alumina support before grafting. The prepared membranes were characterized and tested in microfiltration. In general, the sol–gel coated membranes and the direct grafted membranes with high FAS concentration exhibited reduced pore size due to the formation of small pore in sol–gel layer and/or pore blockage by FAS chains. The direct grafted membrane and sol–gel coated membrane after calcination showed great resistance in N2 permeance measurement due to the penetration of FAS into membrane support. Superhydrophobic alumina membranes (SS) with contact angle of 158.4° can only be achieved by FAS grafting on sol–gel coated membranes after steam impingement. This is because of the formation of rough nanostructure on sol–gel layer and additional roughness introduced by steam treatment. In addition, less FAS penetration and more valleys created by steam treatment resulted minimum transport resistance in SS sample. With minimum membrane resistance of Rm, 1.03 × 1011 m−1, SS sample showed a water rejection up to 99.99% and the highest kerosene flux (117.1600 ml/min) in the filtration of kerosene–water mixture.

► Superhydrophobic alumina membrane prepared by FAS grafting on steam impinged sol–gel layer.
► Low membrane resistance.
► Great kerosene flux and 99.9% rejection of water achieved in microfiltration.