Co-Deposition of Pyrogallol/Polyethyleneimine on Polymer Membranes for Highly Efficient Treatment of Oil-in-Water Emulsion

Abstract Poly(vinylidene fluoride) (PVDF) has been widely used in the field of water treatment due to its outstanding chemical tolerance and excellent mechanical strength. However, PVDF membrane often suffers from oil fouling and low flux for separating oil/water emulsions because of low surface energy and strong hydrophobicity. In this work, we propose a bio-inspired biomimetic hydrophilic coating design strategy, in which pyrogallol (PG) and polyethyleneimine (PEI) are used as reactants, and NaIO4 (SP) is used as an oxidant to modify PVDF microfiltration membrane. This strategy realized the conversion of PVDF membrane surface wettability from hydrophobic to superhydrophilic. The membrane structures and performances were investigated by SEM, FT-IR/ATR, XPS, PMI, water contact angle, pure water permeability and oil rejection for toluene-in-water emulsion. The experimental results showed that the membranes deposited with a PG/PEI mass ratio of 1:1 exhibited the best hydrophilicity and water permeation flux. PVDF-PG/PEI-0.2/0.2 was used to treat surfactant-stabilized toluene-in-water emulsion with the highest flux of 1053 L·m−2·h−1 at 0.1 bar and the oil rejection of 98.3%. Moreover, the flux could be wholly restored after simple washing, indicating that the modified PVDF membrane possessed good reusability. Due to the robust adhesion of PG/PEI composite coatings, the proposed strategy for preparing hydrophilic coatings holds significant potentials in the hydrophilic modification of polymer membranes.