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Matrix hybrid membranes, based on polyvinylidene fluoride (PVDF), poly (N-vinylpyrrolidone) (PVP), silica gel (SG) and zinc oxide (ZnO) were synthesized by phase inversion via immersion precipitation method. The characterization of membrane samples was performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), optical microscopy, contact angle, porosity, mean pore size and water permeability measurements. The FTIR analysis showed the appearance of new bands attributed to the functional groups of SG and ZnO. The XRD analysis confirmed a modification in the structure of membranes. The prepared membranes were used for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. Membrane filtration experiments show that the water permeability and Cr(VI) rejection ratios increase with increasing the weight ratio ZnO (%)/SG (%). The maximum values of the Cr(VI) rejection rate and water permeability were respectively 85% and 685 L/m2hbar for weight ratios (0.75% of ZnO/0.25% of SG).

The removal and transport of ionized and non-ionized selenium's were systemically investigated in this study. The charge repulsion between the membrane surface and selenium ions was an important mechanism for the rejection of ions by a charged membrane. In addition, selenium removal was significantly affected by the J 0 /k ratio, but was not affected by the cross-flow velocity. Both diffusion and convection are proven to affect the transport of selenium ions transports. The reflection coefficients of both UF and NF membranes increased with increasing the pH, and with the reflection coefficients of selenate are being higher than those of selenite at under the same operating conditions. The spiral-wound type module exhibited slightly higher selenate removal compared to than the flat-sheet type module at under the same operation conditions.

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