Influence of membrane support structure on the efficiency of an iron-modified silica nanofiltration membrane

Abstract

Inorganic membranes are generally created by depositing a thin film separation (membrane) layer atop a supporting structure in order to provide for the physical durability of the membrane. The separation layer thickness and morphology are normally evaluated to determine their contribution to fluid flow resistance across the membrane. The supporting structure is often ignored, yet can affect the quality of the membrane formed and significantly influence the global efficiency of the membrane module. In this paper, three different support structures are compared and evaluated with respect to the efficiency (rejection and flux) of an iron-modified silica separation layer. The main difference in the supports was the nominal pore size of the surface responsible for facilitating the membrane layer. The pore sizes of the supports investigated were 5, 10, and 20 nm in diameter. It was hypothesized that the largest pore size support would produce a higher water flux. However, this support did not provide an adequate surface for the deposition of a high quality membrane layer. The formation of an intact membrane layer was successfully achieved using the other two support structures. From the results obtained from salt rejection and flux data of these two functional membrane modules, the influence of the support structure on the overall efficiency of the membrane module was assessed. The 10 nm support structure produced a water flux that was 1.6 times greater than that of the 5 nm pore size support, without sacrificing the rejection of the electrolytes studied.