Fabrication of Chitosan Nanofiltration Membranes by the Film Casting Strategy for Effective Removal of Dyes/Salts in Textile Wastewater

The development of facile strategies and techniques to fabricate nanofiltration (NF) membranes with ideal molecular sieving ability has received growing attention in both academia and industry. Chitosan (CS) is deemed to be a promising renewable membrane material. However, the scalable and low-cost fabrication of pure CS membranes is severely limited by their poor solubility in organic solvents. Herein, a simple and effective film casting strategy is presented to prepare a positively charged CS-based NF membrane for effective rejection of dye and salt in textile wastewater. The penetration performance of CS membranes can be elaborately tuned by regulating the casting parameters during the fabrication process. The as-synthesized CS membranes with suitable thickness and tensile strength exhibit considerable water permeance and high rejection rates of up to 94.8% for CaCl2 and 87.8% for MgSO4. Especially, the CS membrane with a molecular size cutoff of 5.015 Å (hydrated radius) shows an ultrahigh rejection rate of >99% to six kinds of conventional dyes in textile wastewater. The long-time evaluation of dye and salt separation demonstrates the superior stability of the CS membrane. This work aims to develop a facile and cost-effective solution to construct CS NF membranes with superhigh filtration capacity for dye and salt removal from actual textile wastewater.