Enhanced electrochemical nitrate removal from groundwater by simply calcined Ti nanopores with modified surface characters

Abstract

Simple and convenient preparation method with high catalytic reduction activity is crucial for the remediation of nitrate contamination. In this study, the innovation for fabricating a nanoelectrode was developed by calcinating the anodized plate to alter the surface crystalline phase of the material. The prepared calcined Ti nano-pores (TNPs) electrode could effectively remove up to 95.1% nitrate from simulated groundwater at 30 mA·cm–2 electrolysis for 90 min, while under the same conditions, the removal efficiency of nano electrode prepared by conventional methods was merely 52.5%. SEM images indicated that the calcined-TNPs nanoelectrode was porous with different pore sizes. The higher nitrate removal efficiency of TNPs-500 (95.1%) than TNPs-400 (77.5%) and TNPs-550 (93.4%) may resulted from the positive nonlinear response of the larger ECSA, the improved electron transfer and suitable surface structure, and not the “anatase-to-rutile” of surface TiO2 nanotubes. After 90 min of electrolysis, by using RuO2 as an anode and adding 0.3 g·L–1 NaCl solution, 87.5% nitrate was removed, and the by-products (ammonia and nitrite) were negligible. Increased temperature and alkaline conditions can enhance the nitrate removal, while higher initial nitrate concentration only improved the nitrate removal slightly. Moreover, The TNPs-500 electrode also exhibited excellent nitrate removal performance in real groundwater with the efficiency at 82.9% and 92.1% after 90 and 120 min, which were 0.87 (removal efficiency=95.1%), 0.92 (removal efficiency=100%) of the efficiency for simulated groundwater, indicating the widely applicable conditions of the TNPs-500 electrode. This approach of surface bonded elements and structure modification through calcination significantly improves catalytic activity, and will guide the simple designing of functional nanostructured electrodes with wide application conditions.