Enhanced bioelectricity generation and Cr(VI) removal with polydopamine-functionalized carboxylated carbon nanotubes...

Cr(VI) with high redox potential, can be effectively reduced using microbial fuel cell (MFC). High-performance bioanodes play a crucial role in enhancing both power generation and Cr(VI) removal. In this study, carbon nanotubes were modified via a sequential two-step strategy combining covalent acid oxidation and polydopamine (PDA) non-covalent coating. Systematic evaluation verified that polydopamine-functionalized carboxylated carbon nanotube (POC) was a highly efficient anode modification material for MFCs. The POC modified carbon brush (POC/CB) improved the surface morphology of carbon fibers and introduced abundant functional groups and catalytically active sites, thereby significantly enhancing the hydrophilicity, biocompatibility, and electrochemical activity of carbon brushes. MFCs with POC/CB anodes (POC/CB-MFCs) achieved a maximum power density of 23.5 ± 0.16 W m^-3, outperforming those with commercial carbon brushes (10.6 ± 1.22 W m^-3), and demonstrated stable electricity generation over six months. For 150 mg L^-1 Cr(VI) catholyte, 100% removal was achieved in 46 h by POC/CB-MFCs (3.26 g m^-3 h^-1), compared to 60% removal at 1.96 g m^-3 h^-1 in CB-MFCs. Mechanism analysis confirmed that the modified bioanode enhanced extracellular electron transfer efficiency and enriched functional microbes. This work offers valuable insights into designing advanced bioelectrochemical systems for sustainable chromium wastewater treatment and resource recovery.