Reactive transport and sorption behavior of pollutants in presence of redox-sensitive nano Fe0 impregnated graphene: Advancing towards continuous water filtration

Abstract

Fe⁰ impregnated graphene has shown promising candidature for removing both organic and inorganic contaminants from aqueous solutions. The current study investigates and fills some of the missing gaps in their large-scale environmental applicability, including- contaminants removal from complex water matrices, simultaneous separation of multiple contaminants, and continuous water filtration possibilities. Both metals and dyes were chosen of varying ionic behavior to broaden the scope of the work.

One-step graphene oxide (GO) delamination and iron reduction were performed to prepare Fe⁰ impregnated graphene (GOI) composite. Results have shown growth of smaller spherical Fe⁰ nanoparticles (< 50 nm) on graphene with good dispersion and preserved redox state. XPS analysis of reaction precipitate confirmed that GOI could reduce CrO₄^2- to less toxic Cr(III) through reductive sorption. Removal capacities in batch mode were Ni (30.5 mg/g) < Cr (49.8 mg/g) < Cd (93.7 mg/g) < As (143.6 mg/g) in mono-metallic system. In a multi-metallic system, efficient total metal removal capacity (>340 mg/g) and continuous filtration efficiency (85 mg/g) was observed. GOI composite has also shown efficient removal and continuous separation of cationic methylene blue (81.3 mg/g), anionic methyl orange (79.7 mg/g), and zwitterionic rhodamine-B (31.7 mg/g). Electrostatic attraction on heterogeneous GOI surface, redox transformation, complexation, and co-precipitation with generated iron-oxy-hydroxide were major contaminant removal mechanisms. Results conclude a good potential of GOI composite in the separation of multiple pollutants from environmental matrices and continuous filtration of contaminated waters.