Electrochemically mediated nitrate reduction on nanoconfined zerovalent iron: Properties and mechanism

• Published in: Water research (Oxford) 2020-04, Vol.173, p.115596-115596, Article 115596
• Main Authors: Liu, Zhenwei, Dong, Shangshang, Zou, Di, Ding, Jie, Yu, Anqing, Zhang, Jing, Shan, Chao, Gao, Guandao, Pan, Bingcai
• Format: Article
• Language: English
• Subjects: Electrochemical regulation; Flow-through reactor; Iron; Nitrate reduction; Nitrates; Nitrogen Oxides; nZVI@D201; Oxidation-Reduction; Water Pollutants, Chemical; Water Purification
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2020.115596

Selective reduction of nitrate to N2 is attractive but still a difficult challenge in the water treatment field. Herein, we established a flow-through electrochemical system packed with polymeric beads supported nZVI (nZVI@D201) for selective nitrate reduction. Consequently, efficient nitrate reduction in the flow mode was achieved on nZVI@D201 under electrochemical regulation with N2 selectivity of up to 95% for at least 60 h. Otherwise, nZVI was gradually exhausted after 20 h, and the product was mainly the undesired NH4+. Through a series of comparative experiments, we clarified that the enhanced nitrate reduction on nZVI under electrochemical regulation was mainly attributed to electrons (from cathode) and active hydrogen ([H]) rather than the previously speculated H2. Combining the characterizations of nZVI during nitrate reduction by X-ray diffraction and X-ray photoelectron spectrometry, we found that nitrate reduction under electrochemical regulation was mediated by nZVI along with the resultant Fe0@FexOy-Fe(II) structure and was sustained by electrons (from cathode) and [H] via the in situ reduction of Fe(III) back to Fe(II). Meanwhile, the undesirable product NH4+ was efficiently oxidized to N2 by the active chlorine generated on the anode. This study not only clarifies the mechanism of enhanced nitrate reduction on nZVI via electrochemical regulation but also advances the technological coupling of nZVI reduction with electrochemistry. [Display omitted] •Selective nitrate reduction was achieved in a flow-through electrochemical system.•Nitrate was reduced with N2 selectivity up to 95% via electrochemical regulation.•Enhanced nitrate reduction was attributed to electrons (from cathode) and [H].•The study advances technological coupling of nZVI reduction with electrochemistry.