Evaluating of the performance of natural mineral vermiculite modified PVDF membrane for oil/water separation by membrane fouling model and XDLVO theory

A novel vermiculite nanoparticles (Verm NPs) modified poly(vinylidene fluoride) (PVDF) ultrafiltration membrane was firstly fabricated via surface coating at pH 7.2–7.3. The dense but porous modified surface formed by controlling the self-polymerization rate of dopamine at relatively weak alkalinity provided both high water flux and rejection rate of BSA, which broke the trade-off between permeability and rejection rate. The contact angle of optimal modified membrane decreased from 69.6° to 45.0°, showing the effectively enhancement of hydrophilicity. By filtrating two kinds of real oil-in-water emulsions, the stable flux of modified membrane was approximately 2 times higher than that of pristine membrane for both low and high concentration oil-in-water emulsions. In addition, the Verm-PVDF membrane also showed a higher removal efficiency of oil and total organic carbon. According to membrane fouling model analysis, the fouling behavior including adsorption, deposition, blockage of membrane pores and formation of cake layer had obviously alleviated after Verm modification for the two kinds of oil-in-water emulsions due to the formation of water layer by isomorphism substitution and surface hydroxylation of Verm NPs. Assessed by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, Verm-PVDF membrane exhibited a higher energy barrier and an extremely strong repulsive force for foulants to overcome in low and high concentration emulsions during fouling. Overall, the improved antifouling ability and separation performance of modified membrane indicated that the inartificial Verm NPs was a robust material for pH-control membrane modification with potential application value in oil/water separation.