Regulating water flux of loose nanofiltration membrane by dopamine and cellulose nanocrystals for enhanced dye/salt separation

Nanofiltration (NF) membranes are widely used for dye and salt separation, however, a dense NF membrane is generally formed during interfacial polymerization, inducing low permeability of the membrane. Herein, a loose structure of the NF was prepared and regulated by additional other components, such as dopamine (DA) and carboxylated cellulose nanocrystal (C-CNC) through changing the interactions between water and oil phases. The results show that C-CNC not only improves hydrophilicity of the separation layer, but also controls the layer smooth and loose. The obtained membrane with suitable loose structure exhibits high water permeance (37.5 L m-2 h-1 bar -1) and rejection (above 99 %) for dyes including methyl blue (MB), congo red (CR) and direct red 80 (DR80). Additionally, it exhibits low rejection towards NaCl (-10 %) and Na2SO4 (-14 %), but good dye/salt separation factor of 451. The as-fabricated membrane is proved to have long-term stability, chlorine resistance and tolerance towards complex conditions (such as wide pH range, high temperature and composite separation system). The membrane shows good antifouling performance as well. Over all, the prepared membrane is promising for practical applications in textile effluent treatment, resources recycle and molecular separation.