Polymer-derived porous SiOC ceramic membranes for efficient oil-water separation and membrane distillation

Abstract

Porous SiOC ceramic membranes (PSCM), with a narrow pore size distribution, were prepared by a casting method, using a polymer liquid (polydimethylsiloxane, PDMS), as a pore-forming agent, and a pre-ceramic liquid (polysiloxane, PSO), followed by pyrolysis at 1200 °C in flowing Ar gas. Pore size, porosity, and N2 and water permeation increased with increasing PDMS content in the mixture of the precursors. An oil-in-water emulsion, with an average oil diameter of 0.83 μm, was effectively separated (95% rejection rate) with membranes which had an average pore size of 0.59 μm. PDMS was also used for membrane surface modification and the surfaces became super-hydrophobic. After modification, membranes with an average pore size of 0.95 μm were tested in sweeping gas membrane distillation. High salt rejection of 99.9% was achieved with NaCl solution (at various concentrations, 4–16 wt%) at several temperatures (55–85 °C). A stable performance was recorded for over 100 h, using 4 wt% NaCl in the feed at 75 °C. The produced membranes displayed clear separation and high efficiency in separation rates, which was reflected in the high permeation flux in both oil-in-water emulsion filtration and membrane distillation, attributed to the narrow pore size distribution.