Cadmium sulfide cage photocatalysis coupled electroactive biofilm for synergistic promotion of tetracycline degradation and electricity production

Tetracycline (TC) as a common broad-spectrum antibiotic, has been frequently detected in soil and surface water. It becomes a great threat to the ecological environment. Here, a device of photocatalysis assisted microbial fuel cell (photo-MFC) was constructed for TC degradation and energy recovery. In this photo-MFC, cadmium sulfide(CdS) cage photocatalysis can degrade most of TC in a short time. While the Co3O4@C–CC (carbonization and calcination of the ZIF-67 precursor in-situ grown on the carbon cloth (CC)) bioanode degrades the rest of TC as well as the photocatalytic products, thus improving the mineralization. The co-existence of photocatalysis with bioanode changes the microbial community structure of the biofilms. The dominant phylum is Geobacter (60.2%) in normal MFC while that in photo-MFC are Proteobacteria (43.5%) and Geobacter (33.2%). Therefore, the synergistic effect of photocatalytic degradation and biodegradation achieves a chemical oxygen demand (COD) removal of 98.6%, which is higher than that of normal MFC (77.6%) or single CdS cage photocatalysis (23.8%). In addition, the photogenerated electrons can be transferred to the cathode, which reduces their combination with holes and increases the electricity generation of MFC, achieving a maximum power density of 3.37 W/m2. After degradation, the effluent with 200 mg L−1 TC exhibits no visible biotoxity. Furthermore, electrochemical test, finite-difference time-domain (FDTD), density functional theory (DFT) calculation and the free radical trapping experiments verify the possible mechanisms of photocatalytic degradation in this photo-MFC. This strategy paves a new way for low energy consumption removal and energy recovery of organic pollutants.