High performance nanocomposite nanofiltration membranes with polydopamine-modified cellulose nanocrystals for efficient dye/salt separation

Cellulose nanocrystals (CNCs), as a class of renewable and sustainable nanomaterials, are attracting increasing attention for membrane-based separation applications. In this study, hierarchical loose thin film nanocomposite (TFN) nanofiltration (NF) membranes are fabricated via the stacking of polydopamine-modified core-shell-structured CNCs on electrospun nanofiber mats (ENMs), followed by the crosslinking with polyethyleneimine (PEI). Prepared by convenient oxidative self-polymerization of dopamine on CNCs, the polydopamine-modified CNCs contain abundant quinonoid active sites for the subsequent crosslinking with PEI. The crosslinking structures are tuned by varying the molecular weight and concentration of PEI for optimum membrane performances. With the loosely constructed crosslinking networks between modified CNCs and PEI, the optimum TFN membrane shows the outstanding performance in the filtration of Congo red (CR)/NaCl solution, with superior dye rejection (99.91%), salt permeation (98.86%), and ultrahigh pure water permeability (PWP, up to 128.4 LMH bar−1). Notably, the optimum TFN membrane also exhibits an impressive selectivity factor of 1098 for the separation of CR/NaCl. The PWP, dye rejection, and dye/salt selectivity are much higher than those of most reported NF membranes. The present work demonstrates the potential of our novel strategy incorporating polydopamine-modified CNCs for the fabrication of high performance NF membranes for various separation applications.