Intimate coupling of an N-doped TiO₂ photocatalyst and anode respiring bacteria for enhancing 4-chlorophenol degradation and current generation

Titanium-dioxide (TiO₂) semi-conductors are promising for microbial-fuel-cell anodes, because they can accelerate the biodegradation of refractory organic pollutants while recovering electrical current. To make the coupling of TiO₂ photocatalysis and biodegradation a success, the anode's biofilm must be protected from damage from reactive-oxygen species generated by photocatalysis. In this work, we first realized a photocatalytic bioanode using N-doped TiO₂ coated on macroporous carbon-foam that accumulated biofilm inside. Photocatalysis occurred on the outer surface, while bacteria were protected inside the foam matrix; this is a unique manifestation of intimately coupled photobiocatalysis (ICPB). Experiments focused on degradation of 4-chlorophenol (4-CP) and electrochemical characterization of the ICPB-anode. The illuminated photo-anode, non-photocatalytic bio-anode, and ICPB-anode achieved ∼10%, ∼28%, and ∼41% 4-CP degradation efficiency, respectively; clearly, the ICPB anode achieved the best performance for 4-CP removal. The corresponding mineralization efficiency of the ICPB-anode also was the highest, and current generation by the ICPB-anode was 50% greater than that of a bio-anode. Cyclic voltammetry showed that photocatalyst and biofilm had to be present together to achieve high current density, and it also suggested that the electron-transport activity of c-type cytochromes of anode-respiring bacteria played an essential role in the transport of electrons.