Effect of MWCNT-modified graphite felts on hexavalent chromium removal in biocathode microbial fuel cells

Multi-walled carbon nanotubes (MWCNTs) and oxidative acid pretreated MWCNTs (oxidized MWCNTs, O-MWCNTs) were used to modify graphite felts as biocathode electrodes in Cr(vi)-reducing microbial fuel cells (MFCs). The results showed that both MWCNT modifications improved the efficiency of the Cr(vi)-reducing biocathode. In particular, the O-MWCNT modification led to a better performance due to the induced oxygen-containing functional groups on the O-MWCNTs. The O-MWCNT-modified graphite felt significantly promoted the Cr(vi) removal and electricity generation of the MFC. The Cr(vi) removal rate increased to 2.00 ± 0.10 mg L^-1 h^-1, which was 2.05 times higher than that of the unmodified control. The improvement was ascribed to the strong affinity and capacity of the O-MWCNTs towards microorganisms and Cr(vi) ions. In addition, this study further confirmed that the ex situ biocathode acclimatization method could be an efficient way to screen potential biocathode materials for Cr(vi)-reducing MFCs.