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

A 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 nanopores (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 nanoelectrode prepared by conventional methods was merely 52.5%. Scanning electron microscopy images indicated that the calcined TNP 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 electrochemical active surface area, the improved electron transfer and suitable surface structure, and not the “anatase-to-rutile” of surface TiO₂ nanotubes. After 90 min of electrolysis, 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.