Efficient electrochemical-catalytic reduction of nitrate using Co/AC0.9-AB0.1 particle electrode.

In this work, a composite particle electrode (Co/ACx-ABy) was proposed using cobalt as the catalyst, active carbon (AC) as the carrier, and acetylene black (AB) as the conductor. The proposed particle electrodes were applied in a continuous three-dimensional (3D) electrochemical reactor. Based upon the removal efficiency of total nitrogen (TN) and the corresponding energy consumption, the optimum mass ratio of AC to AB was determined to be 0.9:0.1. Scanning electron microscopy (SEM) and energy dispersive system (EDS)-mapping revealed the presence of metal particles on the surface of Co/AC0.9-AB0.1 electrode. Furthermore, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that Co/AC0.9-AB0.1 contained three valence states of Co, namely Co0, Co2+, and Co3+. Additionally, batch experiments showed that 95% of TN removal was achieved under the current of 0.4 A, pH of 7, hydraulic retention time (HRT) of 60 min and the initial TN of 20 mg/L. The addition of Cl- was obviously beneficial to the removal of TN, whereas HCO3-, PO43-, CO32-, and dissolved organic matter (DOM) inhibited the removal of TN. The cyclic voltammetry (CV) curve and the atomic H detected by electron spin resonance (ESR) demonstrated that nitrate was directly reduced by Co0 ions and indirectly reduced by H radicals.