Simple surface modification of PVDF membrane via a quaternization of NM88B for efficient oil/water separation

Developing a stable MOF-modified membrane for efficient treatment of oily wastewater remains a challenge. In this study, NH2-MIL-88B(Fe) (NM88B) was deposited on the commercial polyvinylidene fluoride (PVDF) membranes, and grafted with perfluorohexane-1-sulfonic acid potassium salt (PFHx) to achieve quaternization modification. This reaction proceeds in an environmentally friendly manner due to the absence of any catalyst. The introduction of fluorine atoms through grafting PFHx resulted in the modified PVDF membrane (NPF) demonstrating remarkable underwater superoleophobic property with an underwater oil contact angle at ∼180°. In separation of various oil-water emulsions, the NPF membrane afforded a high permeation flux (up to 2043 L·m−2·h−1) and rejection rate (∼99 %). The oil rejection of NPF membrane was >99 % after 10 filtration cycles of n-hexadecane-water emulsion, and the pure water flux of the recovered membrane was kept at 82.65 % of the original flux, indicating a very good reusability and stability. Filtration of mixed dye/oil-water emulsions showed that the NPF membrane remove 99 % of both oil and dye from the mixture. This work provides a simple and stable modification of PVDF membrane, exhibiting remarkable underwater superoleophobicity and hydrophilicity, thereby harboring substantial prospects in the treatment of oily wastewater.