Anti-fouling potential evaluation of PVDF membranes modified with ZnO against polysaccharide

In this study, hydrophilic modification of polyvinylidene fluoride (PVDF) membranes with zinc oxide (ZnO) using atomic layer deposition (ALD) was conducted for fouling alleviation of polysaccharide. A uniform and conformal layer of ZnO was formed on both membrane surface and pore walls after modification, leading to slightly reduced pore size but greatly enhanced permeability at only 100 ALD cycles. Besides, the standard blocking model fit well with flux data of the original membrane as well as modified membranes (R2 > 0.99) during sodium alginate (SA, a typical polysaccharide) filtration, indicating that adsorption fouling was the main reason for flux decline. More importantly, both the slower diminishing rate of flux (SA filtration) and decreased adsorption capacity of SA showed better anti-fouling property of modified membranes with ZnO. Further exploration of the anti-fouling mechanism based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory found that the modified membranes exhibited higher energy barriers and lower second minimums compared to the original PVDF membrane. This suggested that larger repulsive energy was needed to be overcome and weaker attractive energy was experienced for the SA adsorption onto the surfaces of modified membranes. Moreover, the analysis of surface topography showed that the PVDF membranes modified with ZnO presented smaller protuberances and lower surface roughness after SA filtration, weakening the attachment of polysaccharide onto the modified membranes.