Decomposition of Nickel(Ⅱ)−Ethylenediaminetetraacetic acid by Fenton−Like reaction over oxygen vacancies-based Cu−Doped Fe3O4@γ−Al2O3 catalyst: A synergy of oxidation and adsorption

Abstract

Nickel (Ⅱ)−ethylenediaminetetraacetic acid (Ni−EDTA) complexes are widely present in electroplating effluents. Owing to its chemical stability, Ni−EDTA is hardly removed in traditional Fenton/Fenton-like processes with conventional iron (Fe)−based catalyst. In this study, oxygen vacancies were introduced into our highly efficient and novel Fe3O4@γ−Al2O3 catalysts using Cu doping for Ni−EDTA decomposition in Fenton−like system. Without noble−metal cocatalyst, the introduction of oxygen vacancies in Cu−doped Fe3O4@γ−Al2O3 catalysts exhibit excellent Fenton−like activity even in neutral or alkaline conditions. Experimental results revealed that, without the aid of extra energy, Ni−EDTA complexes could be effectively decomposed over oxygen vacancies−based catalyst. Electron paramagnetic resonance (EPR), X−ray photoelectron spectroscopy (XPS), oxygen temperature−programmed desorption (O2−TPD), and hydrogen temperature−programmed reduction (H2−TPR) were used to get a deep insight into the decomposition mechanism. Additionally, by employing the Al−containing support, stable layered double−hydroxide phases of NiAl could be formed, indicating that a synergy of oxidation and adsorption could simultaneously take place, which led to the recovery of released Ni2+ ions and also reduction in secondary pollution. To investigate the decomposition process of Ni−EDTA over oxygen vacancies−based catalyst, liquid chromatography−quadrupole/electrostatic field orbitrap high resolution mass spectrometry (LC−MS/MS) was employed to identify the generated intermediates, and thus, a plausible decomposition pathway was successfully conceived.