Tuning the Microstructure of a Zwitterion-Functionalized Polyethylenimine Loose NF Membrane for Dye Desalination

Abstract

Developing a highly efficient and anti-fouling nanofiltration (NF) membrane for the desalination of dye wastewater is one of the hot environmental issues. In this study, loose NF membranes were facially prepared by glutaraldehyde (GA)-diffused crosslinking zwitterion-functionalized polyethylenimine (PEI-SBMA) and subsequent tannic acid (TA) surface modification. The microstructure of the membrane was tuned by optimizing the crosslinking condition to enhance the selectivity of dye/salt. The anti-fouling performance of the membrane was improved by the functionalization of the zwitterion and the adjustment of TA coating. Under optimal preparation conditions, the membrane performed high dye rejection [higher than 99% for fuchsin acid (AF) and methyl blue (MB)] and a high dye/salt selectivity of 93.95 with a water permeance of 118.5 LMH/bar, which were about 7.2 times and 49.5% higher than the membrane without crosslinking, respectively. In addition, the membrane showed enhanced anti-fouling ability and good long-term stability. The way of gradient crosslinking by GA diffusion to tune the microstructure of the loose NF membrane and the combination of zwitterions and TA coating could be useful candidates to enhance the membrane performance for water treatment.