A sol–gel-derived α-Al2O3 crystal interlayer modified 316L porous stainless steel to support TiO2, SiO2, and TiO2–SiO2 hybrid membranes

Abstract

A homogeneous α-Al2O3 crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al2O3 membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al2O3 membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al2O3 completely transformed into α-Al2O3 and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al2O3 intermediate layer to initially modify its surface. A single α-Al2O3 crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO2, SiO2, and TiO2–SiO2 hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al2O3 crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.