Electro-enhanced metal-free boron/peroxymonosulfate (B/PMS) system has demonstrated potential for efficient metal-organic complexes degradation in an eco-friendly way. However, the efficiency and durability of the boron activator are limited by associated passivation effect. Additionally, the lack of suitable methods utilizing in-situ recovery of metal ions liberated from decomplexation causes huge resource waste. In this study, B/PMS coupled with a customized flow electrolysis membrane (FEM) system is proposed to address above challenges with Ni-EDTA used as the model contaminant. Electrolysis is confirmed to remarkably promote the activation performance of boron towards PMS to efficiently generate • OH which dominated Ni-EDTA decomplexation in the anode chamber. It is revealed that the acidification near the anode electrode improves the stability of boron by inhibiting passivation layer growth. Under optimal parameters (10 mM PMS, 0.5 g/L boron, initial pH = 2.3, current density = 68.87 A/m 2 ), 91.8% of Ni-EDTA could be degraded in 40 min, with a k obs of 6.25 × 10 −2 min −1 . As the decomplexation proceeds, nickel ions are recovered in the cathode chamber with little interference from the concentration of co-existing cations. These findings provide a promising and sustainable strategy for simultaneous metal-organic complexes removal and metal resources recovery.
Wuming Xie,Fengping Zhou,Xiaolin Bi,Dongdong Chen,Zijun Huang,Yuhui Li,Shuiyu Sun,Jingyong Liu
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 Fe 3 O 4 @γ−Al 2 O 3 catalysts using Cu doping for Ni−EDTA decomposition in Fenton−like system. Without noble−metal cocatalyst, the introduction of oxygen vacancies in Cu−doped Fe 3 O 4 @γ−Al 2 O 3 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 (O 2 −TPD), and hydrogen temperature−programmed reduction (H 2 −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 Ni Al could be formed, indicating that a synergy of oxidation and adsorption could simultaneously take place, which led to the recovery of released Ni 2+ 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.
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