Enhanced anti-biochemical fouling properties of the polyacrylonitrile membranes assisted by the d-amino acid surface-modified halloysite nanotubes

Abstract

Membrane fouling has always been one of the key problems to be solved in the liquid–liquid separation process of biomacromolecules, proteins, bacteria, etc. Here, halloysite nanotubes (HNTs) surface-modified with D-Amino acid (D-Aa) is synthesized in one step and introduced into the polyacrylonitrile (PAN) ultrafiltration membrane matrix to obtain a PAN mixed matrix membrane (MMM). D-Aas with three different R groups are selected to modify the HNTs. The results show that the carboxyl and amino groups of the D-Aa molecules interact with the surface of HNTs through hydrogen bonds, while the R groups are oriented towards the outside of the tube, thereby becoming the main factor affecting the surface chemical structure of the HNTs. Therefore, due to the low polarity of isobutyl and the good affinity with PAN and DMAc molecules, D-leucine-modified halloysite nanotubes (D-Leu@HNTs) can be evenly dispersed in the PAN membrane matrix and segregate to the membrane top-surface and pore wall during the non-solvent induced phase separation (NIPS) process with the solvent exchange between water and DMAc, thereby significantly improving the pore structure and hydrophilicity of the polyacrylonitrile membrane, and ultimately giving the PAN/D-Leu membrane ultra-high pure water permeability (PWP) of 1334 L·m−2·h−1·bar−1, rejection of 100 %, and excellent anti-biochemical fouling performances. The prepared PAN/D-Leu membrane maintains stable and efficient filtration performances in the 300-hour cross-flow experiment, and the membrane after testing still has excellent anti-biofilm fouling performance, showing a promising industrial application prospect.