Manganese oxide nanoparticles impregnated graphene oxide aggregates for cadmium and copper remediation

Abstract

Loading metal oxide nanoparticles (NPs) into porous granular materials with excellent hydraulic characteristics offers a promising option to break the technical barriers of direct application of NPs in scaled-up water decontamination. By taking advantage of graphene oxide (GO) mediating the formation of manganese oxide (MO) nanoparticles at the same time aggregating to form macroporous structure under highly alkaline conditions, we fabricated a novel GO-MO composite (D = ∼160 μm). The intraparticle diffusivity of Cd(II) and Cu(II) onto GO-MO was determined to be 3.17 × 10−9 and 4.67 × 10−9 cm2 s−1, respectively, similar to macroporous resin. The GO-MO showed synergistic sorption capacity for Cd(II) and Cu(II) compared to bulky MO and GO due to the high dispersion of MO NPs (<10 nm) in the aggregated GO matrix and Donnan membrane effect. The GO-MO also had strong sorption selectivity in the presence of Ca(II) and humic acid. HADDF-EDS characterization visually showed that Cu(II) and Cd(II) was selectively adsorbed to MO even in the presence of 50 times higher competing Ca(II) ions, which was quantified as ∼93% of the total adsorbed metal for both Cu(II) and Cd(II) by XPS analysis. Moreover, GO-MO was successfully employed in the column operation with effective treatment volume of ∼1650 and ∼1995 BV for simulated Cd(II)- and Cu(II)-contaminated wastewater, respectively. The exhausted GO-MO can be effectively regenerated using acid-salt binary solution with desorption rate >97%. The results from this study may offer insights to rationally design highly efficient engineered nanocomposites for water purification.