Novel dual-photoelectrode photoelectrocatalytic system based on TiO2 nanoneedle arrays photoanode and nitrogen-doped carbon dots/Co3O4 photocathode for efficient water purification at low/no applied voltage

A novel tandem photoelectrocatalysis (PEC) cell consisting of TiO2 nanoneedle arrays (TiO2 NNs/Ti mesh) photoanode and nitrogen-doped carbon dots (NCDs) modified Co3O4 photocathode (NCDs/Co3O4/Ti mesh) is designed to work at low/no applied voltage. Electrochemical impedance spectroscopy, incident photo-to-current conversion efficiency, and open-circuit voltage confirmed enhancement in the photogenerated charge transfer efficiency and internal photovoltage, which is due to synergistic effect in combination of two photoelectrodes. Under light-emitting diode (LED) light irradiation and cell voltage of 0.4 V, the system represented high activity and stability (0.0527 min−1 after 20 cycles) and energy efficiency (2.09 kWh m−3 order−1) for sulfadiazine removal. Based on the main •OH-induced reaction, the cooperative operation mechanism of TiO2 NNs/Ti mesh and NCDs/Co3O4/Ti mesh for sulfadiazine degradation was elaborated. Finally, the high performance under real water matrices or real sunlight irradiation without external voltage confirmed the feasibility of this PEC system in practical application for efficient water purification.