Enhanced arsenic removal by reusable hexagonal CeO₂/Fe₂O₃ nanosheets with exposed (0001) facet

Arsenite in wastewater has caused increasing concern because of high toxicity and mobility. Iron oxides are widely available and regarded as effective adsorbents for arsenic. However, conventional iron oxides usually are only effective for arsenate (As(V)) adsorption by complexation, but not for As(III) adsorption because of their poor catalytic oxidation activities, which greatly limits arsenic removal efficiency. In this study, a uniform hexagonal FeCe bimetal oxide nanosheets (Fe_0.21Ce_0.29O) enclosed by high active (0001) planes was synthesized by a solvothermal method to improve the catalytic activity of Fe₂O₃. The experimental results showed that adsorption capacity of Fe_0.21Ce_0.29O reached 61.1 mg/g for arsenic and 70 % of that at equilibrium was achieved in <10 min. Based on characterization analyses and density functional theory simulation, the new insight in oxidation and complexation mechanism of arsenic was proposed. Firstly, As(III) was adsorbed to adsorbent surface by forming stable structure of Ce-O-As or Fe-O-As, and then converted into As(V) by dissolved oxygen under the catalysis of (0001) planes densely distributed on Fe₂O₃ and CeO₂ surfaces. The formed As(V) species were bound on Fe_0.21Ce_0.29O surface by forming bidentate and monodentate surface complexes. Finally, the safety of As-containing solution treated with Fe_0.21Ce_0.29O was well proved by the zebrafish embryo developmental toxicity tests.