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.

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.