Lianghao Li,Zhuangpeng Huang,Xiaoxiao Fan,Zhen Zhang,Rongni Dou,Shulong Wen,Yuan Chen,Yuancai Chen,Yongyou Hu
An optimized metal oxide electrode (Ti/SnO 2 -Sb-Pd) was prepared via thermal decomposition and used in the electrochemical degradation of Ni-EDTA. The electrode was characterized by SEM, XRD, XPS, and electrochemical characterizations including linear-sweep voltammetry (LSV), cyclic voltammetry (CV) and chronopotentiometry (CP) techniques. It was found that Pd doping could effectively change the surface morphology and lattice parameters of the metal oxide electrode. Pd can facilitate the entry of more Sb into SnO 2 crystals and promote the reduction of Sb from the +5 to the +3 state. The interaction of these metals raised the oxygen evolution potential (OEP) and electrochemical surface area of the electrode, in addition to reducing the degradation potential and increasing the degradation current of Ni-EDTA. When the molar ratio of Pd:Sn was 2.5%, the electrode could simultaneously degrade 87.5% of Ni-EDTA and recycle 17.9% of elemental Ni on the cathode within 120 min. At the same time, with Pd doping, the lifetime of the electrode was increased more than 40 times, demonstrating good potential for application in industry.
Conventional advanced oxidation processes were used to treat heavy metal complexes. However, a considerable amount of oxidants was required to enable effective oxidative degradation, which led to a significant increase of the treatment costs and subsequent difficulties in the sludge disposal. Based on the abundance of anions in heavy metal wastewater, the effects of anions on the in-situ degradation of Ni-EDTA in an oxidant-free electrochemical system with boron-doped diamond (BDD) as the anode were investigated. The presence of Cl - was found to exert a significant effect on improving the degradation process. Moreover, pH had little effect on the removal of nickel (Ni) and Ni-EDTA within a specific pH range (1 < pH < 9). The removal efficiencies of Ni and TOC reached 100 % and 77.45 %, respectively, at pH 2.16 with 0.4 M NaCl electrolyte, 2 mM Ni-EDTA concentration, and a current density of 50 mA/cm 2 . •OH and Cl• played crucial roles in the removal of Ni-EDTA by disrupting the chelation sites of Ni and EDTA molecules. The released Ni 2+ ions could active the H 2 O 2 in-situ generated at the cathode to produce •OH. The formation of the precipitation products such as NiOOH, Ni(OH) 2 , and NiCO 3 in the Cl - /BDD system were conform based on the XRD and XPS analyses, which suggested the possible pathways for the removal of Ni 2+ and Ni 3+ . Finally, the possible degradation pathways of Ni-EDTA were proposed based on the identification of intermediate products using UPLC-MS.
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