Explication of hydrophobic silica as effective pore former for membrane fabrication

Abstract

Membrane development is one of the key aspects to enhance the productivity of a filtration process. This study evaluates a hydrophobic silica as pore former for fabrication of polyvinylidene difluoride (PVDF) membrane for liquid based filtration and compare it with a hydrophilic silica. Membranes incorporated with hydrophobic (M-series) and hydrophilic silica (N-series) with loadings of 1, 2 and 3 wt% in the dope solution were fabricated, characterized and subjected to filtration tests using feeds of pure water, raw wastewater, secondary effluent, microalgae solution and activated sludge. Results show that the hydrophobic silica remained within the membrane matrix (7.24% of elemental Si by EDS), almost three-fold higher than the hydrophilic silica (2.48%). It turned the membrane surface to be more hydrophobic ascribed by increasing water contact angle from 87° from the pristine PVDF membrane up to 97° for the membrane with the highest loading of hydrophobic silica. On the other hand, the addition of hydrophilic decreased the contact angle down to 67° for the membrane with the highest loading. Loading hydrophobic silica enhanced the dope solution viscosities up to 1825–2000 cP, upon dropwise addition of nonsolvent (water), whereas the viscosity remained at 880–950cP for the hydrophilic silica. Addition of hydrophobic silica increased the number of surface pore without significantly altering the pore size of about 0.12 µm. On the other hand, an increase in the pore size (up to 0.33 µm) was observed when hydrophilic silica was added. Despite the smaller pore size, the pure water permeance of the hydrophobic silica loaded membranes (450–984 L/m2hbar) outperformed the hydrophilic silica loaded membranes (420–600 L/m2hbar) due to their higher surface porosities thanks to the higher number of surface pores. The filtration results of multiple feeds showed the advantages of loading more hydrophobic silica in improving the hydraulic performance. The findings demonstrate the efficacy of hydrophobic silica as pore former in PVDF membrane fabrication.