Loose nanofiltration membranes with assembled antifouling surfaces of organophosphonic acid/Fe(III) for managing textile dyeing effluents

Abstract

Loose nanofiltration membranes (LNMs) have attracted increased attention in the field of sustainable management of the highly-saline textile wastewater. Remained challenges include achieving efficient dye/salt fractionation and alleviating high fouling propensity. Herein, functionalized-LNMs (F-LNMs) are developed by the co-deposition of polyethylenimine and tannic acid, followed by the assembly of ferric ions (Fe(III)) and organophosphonic acid (OPa) for antifouling surface construction. Plentiful OPa groups are immobilized onto the membrane surface via the high surface binding affinity and the strong coordination bonding of Fe(III) as ‘bridge’ linkers. The superior hydrophilicity and large steric hindrance of these OPa groups endow the F-LNMs with notably improved antifouling property against organic dye clusters. The optimized F-LNMs show significantly increased membrane permeance (10–30 L m−2 h−1·bar−1) in treating those simulated dye/salt aqueous solutions containing 1.0 g L−1 dye and 80.0 g L−1 Na2SO4. They also exhibit high salt permeation (>94%) and acceptable dye rejection (overall >93%) of Congo red, methyl blue and three hydrolyzed reactive dyes. Furthermore, the direct reuse of Na2SO4 from the actual dyeing effluent is achieved by combining membrane separation and activated carbon adsorption, revealing the promising application prospects of F-LNMs in managing highly-saline textile wastewater.