Increase in permeate flux by porosity enhancement of a sorptive UF membrane designed for the removal of mercury(II)

A poly(vinyl alcohol)/poly(4-vinylpyridine) (PVA/P4VP) filtration membrane was modified by two techniques for increasing its porosity, resulting in improved permeate flows. In the impregnation technique, silica particles were added, then removed by dissolution in alkaline medium. The second technique was a phases inversion in acetone that formed an asymmetric membrane. The creation of pores within both membranes was verified by SEM imaging and measurements of water flows. The water flows were 0.5, 18 and 11 cm3 h−1 for the unmodified, silica modified and phases-inversion membrane, respectively. The elimination ratios of Hg(II) ions in frontal filtration (E = 98–100%), show that all membranes had a high efficiency for Hg(II) retention. The sorption capacities were: PVA/P4VP (silica): 656 mg g−1 > PVA/P4VP (unmodified): 460 mg g−1 > PVA/P4VP (phases inversion): 251 mg g−1. By comparison with the theoretical value, 764 mg g−1, the porosity increase due to silica impregnation revealed enhanced accessibility to most of the complexing sites within the membrane. The sorption isotherms followed the Langmuir formalism, indicating that mercury was sorbed by a complexation mechanism. The increase of the filtration flows offers a real possibility of using these membranes for low pressure filtration of polluted water.