Thermal stability of hydrophilic PEO-silane modified ceramic membranes

Abstract

Industrial oily wastewaters often contain many recalcitrant species, such as dissolved metal ions, salts, bitumen, clays and humics. These species possess surface charges due to acidic, basic and amphoteric groups, thus leading to severe ceramic membrane fouling. To address this problem, ceramic membrane surfaces were chemically modified with highly hydrophilic PEO-based organosilanes. Three different membrane surface layers (ZrO2-TiO2, ZrO2 and TiO2) were modified at varying silane concentrations and reaction times to test their reactivity and stability. All modified membranes maintained hydrophilic behavior, as shown by water contact angles of <25° and pure water fluxes of 500–600 Lmh. Modified TiO2 membranes exhibited superhydrophilicity with contact angles <10°. It was found that TiO2 membranes were the most reactive, achieving maximal silane surface coverage at lower concentrations and reaction times, followed by ZrO2 and ZrO2-TiO2 membranes. The silylated TiO2 membrane was also the most thermally stable surface at 130 °C and 160 °C. Increasing the length of the PEO chain in the silane was also found to increase the thermal stability of the silane surface. TiO2 membranes modified with the higher molecular weight silane maintained 97% of the silane at the membrane surface when exposed to heat at 130 °C. In enhancing the suitability of ceramic membranes in challenging applications; titania membranes over zirconia and zirconia-titania should be used and modified with PEO-silanes containing 9–12 repeat units to ensure maximal surface coverage and enhanced thermal stability.