Improvement of the chlorine resistance of graphene oxide membranes through siloxane cross-linking

Nanofiltration membranes exhibit performance deterioration when exposed to highly concentrated chlorinated environments. This is a major challenge of nanofiltration process as chlorine-based chemicals are prevalent within industry for the treatment of organic fouling; thus, making membrane chlorine sensitivity detrimental to sustainable operation. Graphene oxide has an inherent chlorine sensitivity and degrades under exposure to high concentration of chlorine. This work describes a novel nanofiltration membrane fabrication strategy in which Polyethyleneimine and siloxane crosslinking chemistries were used to protect the carboxylic, hydroxyl, and epoxy functional groups of GO nanosheets from the attack of free chlorine. These chemistries were used to improve the chlorine-stability of the GO nanosheets. Polyethyleneimine (PEI) reduces GO and cross-links with oxygenated functional groups preventing their further reaction with chlorine. This chemistry was compared to the chlorine-tolerant siloxane cross-linkers which react with GO’s functional groups to decrease reaction sites. The use of (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GLYMO) cross-linkers resulted in stable retentions that varied by less than 0.5% following 1,000 ppm chlorine exposure for 1 h. Additionally, GLYMO functionalisation of the GO membrane exhibited exceptional chlorine resistance maintaining a methyl blue retention of 98.0 ± 2.15% following 1 h of exposure 30,000 ppm of chlorine.