Insight into the removal of graphene oxide by nanoscale zero-valent iron

Graphene oxide (GO) and nanoscale zero-valent iron (nZVI), two of the most widely used nanomaterials, may come into contact with each other after their application in environmental remediation. To assess the role of nZVI in the environmental behavior of GO, the removal of GO by nZVI as a function of physicochemical properties of nZVI (i.e., initial concentration of nZVI, nZVI nanoparticle size and Fe dissolution) and solution chemistry (i.e., pH, ionic strength and cation type) is conducted by using batch experiments. The results indicate that nZVI can promote the aggregation of GO depending on the partide size and concentration of nZVI at pH < 5.0 and on ionic strength and the cation type in the whole tested pH values. The pH- and cation-induced homoaggregation of GO and the heteroaggregation of GO with nZVI induced by electrostatic attraction contribute to the removal of GO in the acidic solution; while the removal of GO in the alkaline solution is attributed to the attachment of GO with small size on nZVI, which is independent of pH, nZVI size, and nZVI concentration. These findings to some extent can reveal information not only for the preparation of GO-supported nZVI composites but also for the assessment of the application of nZVI as adsorbent for GO removal and the environmental fate of GO after it comes into contact with nZVI. (C) 2020 Elsevier B.V. All rights reserved.