Hierarchically porous interlayer for highly permeable and fouling-resistant ceramic membranes in water treatment

Abstract

Ceramic membranes are being increasingly adopted in water and wastewater treatment owing to their performance and long-term benefits. In addition to the attempts to reduce the fabrication cost, rationalizing the microstructure of ceramic membranes also draws increasing attention. In this work, titania (TiO2) nanoparticle suspensions with and without polystyrene beads (PS beads) were successively coated on the macroporous Al2O3 support. Followed by co-sintering the two layers at 850 °C, the PS beads in the interlayer were removed, and a dual-layer membrane structure with the hierarchically porous interlayer being covered by a well-integrated top filtration layer was successfully produced. The open porosity and thickness of the interlayer and top layer was optimized by the content of PS beads and TiO2 particles, respectively. The interlayer with a thickness of ∼ 19 μm was rationalized with 40 vol% of PS to achieve a balance between the high open porosity (∼58%) and well structural stability. Significantly, the ceramic membranes with the hierarchically porous interlayer showed largely increased water flux (1000 ∼ 2000 LMH) yet insignificant reduction in removal efficiency (up to 86%) to 90 nm PS beads (2 ppm) compared to the control (<500 LMH and ∼ 89%). The membrane fouling mechanism in sodium alginate solution (50 mg/L) was revealed to be intermediate pore blocking in the entire filtration process, while that of the conventional ceramic membrane rapidly developed to the cake layer. This suggests that the ceramic membranes with a hierarchically porous interlayer are of high efficiency in water treatment due to the enhanced permeate flux and retarded membrane fouling process.