UV/V-LED-driven reverse electrodialysis system with TiO2 nanotubes photoanode and air cathode for energy-efficient degradation of tetracycline hydrochloride

Abstract

A novel photonic salinity-gradient energy (PSE) system was developed by integrating an ultraviolet light-emitting diodes (UV-LEDs) and a salinity-gradient energy source to achieve effective and energy-efficient pollutant degradation. The UV-LED PSE system exhibited a strategically designed reverse electrodialysis (RED) stack positioned between a TiO<inf>2</inf> nanotube (Ti (Anodized)) photoanode and an air cathode. A novel flow design of 5 to 15 pairs of low and high concentration NaCl solutions is serially directed into each RED stack cell. The system efficiently oxidized tetracycline hydrochloride (TTH) in wastewater near a photoanode surface with an external electrical field, thereby enhancing charge-carrier separation. This unique integration effectively resulted in thermodynamic advantages, optimizing energy utilization and enhancing •OH production. As a result, 71.3 % TTH removal and a maximum power density of 288 mW/m2 were achieved. Furthermore, the system demonstrated an energy efficiency of 24.3 % under an ultra-low energy input of only 1.26 W for UV-LED irradiation, corresponding to an energy consumption of only 7.56 kWh/m3 for treated wastewater. These values significantly surpass the energy efficiencies and consumption of previously reported UV-based pollutant treatment systems. In addition, the simultaneous use of the V-LED PSE system resulted in superior electricity production compared to that achieved using the UV-LED PSE system. These findings highlight the synergistic effects of photocatalysis and external electrical fields in optimizing pollutant degradation and energy recovery.