Nanomaterials for facilitating microbial extracellular electron transfer: Recent progress and challenges

Nanomaterials for facilitating the microbial extracellular electron transfer (EET) process have drawn increasing attention due to their specific physical, chemical and electrical properties. This review summarizes the research advances of nanomaterials for accelerating the EET process. Nanostructured materials, including oligomer, carbon nanotube (CNT), graphene, metal, metal oxides, and polymer, exhibit numerous admirable properties such as large surface area, high electrical conductivity, and excellent catalytic activity. In this review, depending on the exact site where the nanomaterials work, the nanomaterials are classified into four groups: inside-membrane, interface, inside-biofilm and interspecies. Synthesis of the nanomaterials, EET enhancement performance, and corresponding enhancement mechanisms are also discussed. In spite of the challenges, nanomaterials will be extremely promising for promoting the EET process application in the future.