Cross-linked iron nanoparticle-doped reduced graphene oxide membranes for micropollutant removal from water

Emerging contaminants in potable waters and wastewaters are a global concern exacerbated by industrial growth. Graphene-based nanomaterials (e.g., rGO) incorporated at a membrane’s surface have been shown to enhance separation performance by increasing adsorption and altering membrane pore size. However, rGO surface-deposited membranes demonstrate low water fluxes and poor stability due to high rGO interlayer packing density and nanosheet swelling. Herein, a cationic polyelectrolyte cross-linked rGO nanocomposite membrane was developed to address these issues. These membranes were formed by a layer of iron doped rGO (rGO–Fe) cross-linked with hyperbranched polyethylenimine (HPEI) vacuum-deposited onto a polydopamine (PDA) coated polyethersulfone (PES) ultrafiltration membrane. The HPEI cross-linking of iron-doped rGO was accomplished by 1) activating the carbonyl groups of the iron nanoparticle-decorated graphene oxide (GO–Fe) by N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC hydrochloride) and N-Hydroxysuccinimide (NHS), 2) cross-linking GO–Fe through the primary amines of HPEI, and 3) chemical reduction of cross-linked GO–Fe by NaBH4. The resulting rGO nanocomposite membrane was moderately stable in aqueous solution for over 20 days. The optimized membrane achieved a water permeance of 39.8 L·m−2·hr−1·bar−1, which was comparable or higher than most reported graphene-based membranes. In addition to adsorption and size exclusion, pH-dependent electrostatic interactions were identified to control charged solute separation, resulting in removals >75.8%, 81.6% and 95.7% respectively for p-nitrophenol (PNP, 6.5 mg/L), methylene blue (MB, 20 mg/L) and methyl orange (MO, 20 mg/L) during dead-end ultrafiltration. This study provides a promising material framework for rGO nanocomposite membranes useful for low-pressure micropollutant removal.