Decomposition of complexed Pb(II) and subsequent adsorption of Pb(II) with yolk-shell Fe3O4@ hydrous zirconium oxide sphere

Abstract

Purification of water containing heavy metals that are complexed by organic chelating agents remains a challenging task. In this study, a yolk-shell Fe3O4@hydrous zirconium oxide (Zr(OH)x) sphere sphere (YHZOs) nanomaterial was evaluated for its ability to remove ethylene diamine tetraacetic acid complexed Pb2+ (Pb-EDTA) from aqueous solution. Specifically, it is hypothesized that upon addition of H2O2, the Fe3O4 core of YHZOs served as a Fenton-type catalyst that results in oxidation of the Pb-complexed EDTA, and the Zr(OH)x shell acted as an adsorbent, removing the released Pb2+ from solution. From an aqueous solution containing 0.1 mM Pb-EDTA at pH 5, 0.5 g/L YHZOs, and 20 mM H2O2, TOC reduction and Pb removal were determined to be 65.3% and 89.8%, respectively. HPLC-MS, IC and continuous flow analyzer results identified major intermediates of EDTA decay to be ethylenediaminetriacetate, (ED3A), ethylenediamine-N,N’-diacetate (ED2A), nitrilotriacetate (NTA), iminodiacetate (IDA), ethylenediamine (EDA), acetic acid, formic acid, oxalic acid, ammonia, and nitrate, with the first 5 species having some affinity to remain complexed to Pb2+. The adsorption of Pb2+ onto the Zr(OH)x shells was confirmed by scanning transmission electron microscopy (STEM) with mapping and X-ray photoelectron spectra (XPS). Moreover, the Pb2+-adsorbed YHZOs could be easily recovered due to their magnetic properties, with the Pb2+ rinsed from them at low pH. Indeed, reused for five cycles showed only minor capacity loss. These findings suggest that the removal of chelated Pb2+ from water, and presumably other heavy metals, by yolk-shell Fe3O4@Zr(OH)x may prove to be a useful technology for some contaminated waters.