| In this study, stainless steel mesh was loaded with photocatalyst BiVO4 and/or polyaniline (PANI) composited PANI/BiVO4 and tested as cathode in coupled microbial fuel cells (MFC) reactor for electro-catalytic and/or photo-electro-catalytic removal of RhB and ammonium nitrogen. Characterizations by XRD, SEM, UV-diffuse reflectance spectra and cyclic voltammograms were used to analyze the as-prepared catalysts. RhB and NH4+-N were used as the targeted model pollutants, and the removal efficiency were determined in photocatalytic system (PC), photo-electrochemical (PEC) coupled microbial fuel cell (MFC) system (PEC-MFC) and electrochemical (EC) coupled microbial fuel cell (MFC) system (EC-MFC). The electrical energy per order (EEO), output voltage and power density were calculated to evaluated the energy consumption and electric energy output of PEC-MFC. Further more, the reaction mechanism and the main reactive oxygen species in different systems were in-depth study as well. The results and conclusions are shown as follows:(1) The as-prepared BiVO4 photocatalysts were of monoclinic type which had the highest photocatalytic activity among all the crystal structures of BiVO4. The BiVO4 and PANI/BiVO4 powders had rodlike and cluster aggregate structures with monoclinic crystal BiVO4 nano-particles (70 nm). The compositing with PANI narrowed the band gap of BiVO4 to 2.14 eV, with red shift in absorbency spectrum. The CV curves for PANI/BiVO4 (5%) electrodes showed higher current density than BiVO4 electrode and suggested higher electron transfer reaction activity.(2) PANI/BiVO4 exhibited higher catalytic activity than BiVO4 both in purely photocatalytic reactor and in the coupled reactor. In the coupled system, removal of 93% RhB in 2h, and removal 91%RhB in 30 min (adjusting the pH to 3) can be achieve in PEC-MFC system under visible light illumination. And even in the EC-MFC system using pure BiVO4 as cathode catalyst, the removal efficiency can reach 62%.(3) The electrical energy per order (EEO) of PEC-MFC and EC-MFC system were 0.895 and 0 kWh·m-3. respectively, However, the EEO of photocatalytic system was 2.687 kWh·m-1 which was 3-fold higher than that of PEC-MFC system. As to electric energy output, the maximal cell voltage 0.527 V and power density 926 mW·m-2 related with contaminants concentration and cathode catalyst, can be achieved in the coupled bio-electrochemical and photo-electro-catalytic reactor.(4) As bias was applied and electrons were supplied from bio-anode, they disturb the bending of surface potential at the liquid interface, change the electrostatic layer, thus activating and forming reactive species (highly active OH?·O2-) for oxidation reaction.(5) Removing 75%?and 67%?of NR4+-N in 120 min without producing NO2--N and NO3-N in PEC-MFC and EC-MFC system, can be achieved in the cathode chamber under visible light illumination.The catalytic cathode integrated in the coupled PEC-MFC system had higher activity in removing contaminants than in uncoupled purely photocatalysis reactor. This study demonstrated that the PANI/BiVO4 catalytic cathode coupled in MFC system has high efficiency in removing pollutants in cathode chamber, with power generation and possible energy-saving. |
PDF Full Text Request