Positively Charged Membranes for Dye/Salt Separation Based on a Crossover Combination of Mannich Reaction and Prebiotic Chemistry

Abstract

With the advent of increasingly loose nanofiltration membranes for dye desalination, synthesis methods based on interfacial polymerization and bio-inspired materials such as polydopamine (pDA) have been investigated. However, the long polymerization time of pDA greatly limits the synthesis and application of fast dye/salt separation membranes. In this work, prebiotic chemistry-inspired aminomalononitrile (AMN) was used as a binder to co-deposit the Mannich reaction of tetrakis(hydroxymethyl)phosphonium chloride (THPC) and polyethyleneimine (PEI) to form the positively charged selective layer rapidly. The optimum membrane had a water permeance of 30.7 LMH bar -1 and a rejection of positively charged Victoria blue B (VBB, 200 ppm) and Na 2 SO 4 (1g/L) of 99.5% and 9.9%. Moreover, the results of a practical application test showed that it had excellent separation performance towards various positively charged dyes and salts, as well as an outstanding long-term stability. The dye/salt separation membrane has a good antifouling performance due to the dense and hydrophilic selective layer obtained via the Mannich reaction. Further antibacterial tests were carried out, and the inactivation effect of the membrane on E. coli was also confirmed. The preparation method proposed in this work provides technical support for developing new dye/salt separation membranes.

Keywords: Mannich reaction, prebiotic chemistry, positively charged dye desalination, textile wastewater, aminomalononitrile