Improvement of electron transfer efficiency during denitrification process by Fe-Pd/multi-walled carbon nanotubes: Possessed redox characteristics and secreted endogenous electron mediator

Highlights: • The excellent electron exchange capacity of Pd-Fe/MMWCNTs (ΔEp = 734 mV) contributed to the occurrence of DEET process. • The site of Pd-Fe/MWCNTs (266 mV) were located next to cytochrome C in the DEET pathway. • The secretion of PN induced by Pd-Fe/MWCNTs also promoted the electron transfer during DEET process. Nanomaterials which contacts microbial membranes for extracellular electron transfer, could establish a connection with the internal electron transfer chain of microorganisms. This characteristic could be employed to accelerate the denitrification process. In this study, the effect and mechanism of Pd-Fe/multi-walled carbon nanotubes (MWCNTs) on the extracellular electron transport behavior of Alcaligenes sp.TB was studied using electron transfer inhibitors and electrochemical methods. The main conclusions were as follows: the electron transfer site of Pd-Fe/MWCNTs was 266 mV, which was next to cytochrome c; the excellent electron exchange capacity of Pd-Fe/MMWCNTs (ΔEp = 734 mV) and the secretion of PN (33 mg/L) induced by Pd-Fe/MWCNTs both contributed to the occurrence of DEET process and promoted the electron transfer; the correlation between the electron mediator and the nitrate removal was analyzed were greater than 0.9731.