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Zero-valent iron nanoparticles embedded into reduced graphene oxide-alginate beads for efficient chromium (VI) removal

Lv, Xiaoshu, Zhang, Yuling, Fu, Wenyang, Cao, Jiazhen, Zhang, Jiao, Ma, Hanbo, Jiang, Guangming
Journal of colloid and interface science 2017 v.506 pp. 633-643
adsorption, alginates, chromium, dispersibility, graphene, graphene oxide, ionic strength, iron, models, nanoparticles, oxidation, pH, pollutants, sorption isotherms, strength (mechanics), surface water, synergism, temperature
Zero-valent iron nanoparticles (Fe⁰ NPs) technologies are often challenged by poor dispersibility, chemical instability to oxidation, and mobility during processing, storage and use. This work reports a facile approach to synthesize Fe⁰ NPs embedded reduced graphene oxide-alginate beads (Fe@GA beads) via the immobilization of pre-synthesized Fe⁰ NPs into graphene oxide modified alginate gel followed by a modelling and in-situ reduction process. The structure/composition characterization of the beads finds that the graphene sheets and the Fe⁰ NPs (a shape of ellipsoid and a size of <100nm) are uniformly dispersed within the alginate beads. We demonstrate that these Fe@GA beads show a robust performance in aqueous Cr(VI) removal. With a optimized Fe and alginate content, Fe@GA bead can achieve a high Cr(VI) removal efficiency and an excellent mechanical strength. The initial Cr(VI) concentration, ionic strength, temperature and especially solution pH are all critical factors to control the Fe@GA beads performance in Cr(VI) removal. Fitness of the pseudo second-order adsorption model with data suggests adsorption is the rate-controlling step, and both Langmuir and Freundlich adsorption isotherm are suitable to describe the removal behavior. The possible Cr(VI) removal path by Fe@GA beads is put forward, and the synergistic effect in this ternary system implies the potentials of Fe@GA beads in pollutant removal from water body.