A Green Method toward Graphene Oxide Reduction by Extracellular Polymeric Substances Assisted with NH 4

Extracellular polymeric substances (EPS) occur naturally and widely on the surface of microbial cells; their reducibility may play a crucial role in graphene oxide reduction. In this work, the conversion of graphene oxide (GO) into reduction graphene oxide (rGO) with EPS (extracted from Bacillus sp.NT 10) as green reductant had been conducted to explore their potential application for graphene preparation. The results showed the GO could be reduced by EPS, especially in the presence of NH4+, and a synergetic effect was found between EPS and NH4+. Further studies hinted the rGO could be also obtained from GO by EPS reduction even under a mild alkaline condition (pH = 8), lightly higher room temperature (40 °C) and a certain amount of time (24 h). The good reduction performance was found to be ascribed to the real deoxygenation of oxygenous functional groups and restoration of electronic conjugation within GO, according to the analysis of XRD, XPS and FT-IR as well as Raman spectra, while the electron-rich tryptophan-like protein and aromatic protein on the surface of EPS as well as the assistance of NH4+ should account for the deoxygenation and restoration in terms of the detection on Zeta potential, AFM and 3D-EEM. These findings revealed the reduction of GO with EPS would be a green, environment-friendly and promising path to obtain rGO, which may open a novel route for the preparing graphene alternatively.