Modification of PVDF membrane by post-modified NH2-MIL-88B(Fe) showing improved permeability and oil/water separation performance

Abstract

Metal organic frameworks (MOFs) possess excellent post-modification characteristics, high specific surface area, diversity of skeleton composition and pore tunability, have been increasingly applied in membrane modifications. In this work, NH2-MIL-88B(Fe) (NM88B) was first fixed onto polyvinylidene fluoride (PVDF) membrane by polyethyleneimine (PEI) through a vacuum-assisted self-assembly process, and the deposited NM88B was subsequently grafted with perfluoroalkyl polyethoxyacetic acid (FPEOAA) via a condensation reaction to realize the surface modifications. The modified membranes (named as N1Fx) showed improved hydrophilicity and underwater-oleophobicity. In addition, very high pure water flux (up to 9403 L‧m−2‧h−1) was obtained for the N1Fx membranes due to the high porosity of introduced NM88B. In the dead-end filtration experiments of n-hexadecane-water emulsion, the optimum membrane N1F20 showed a good oil rejection rate (98.3%) and high permeation flux (667 L‧m−2‧h−1) which is approximately seven times of the pure PVDF membrane, indicating that the surface-modified membranes had excellent permeability and good separation performance. Even after four filtration cycles of oil-water emulsion, the rejection rate maintained higher than 97%, showing good reusability. Furthermore, the study found that N1F20 had certain acid and alkaline resistance and great potential for engineering applications.