New approach for biological synthesis of reduced graphene oxide

Graphene synthesis has created great interest because of the potential applications in various fields. Many works of graphene synthesis from chemical reduction of graphene oxide involving harmful reactants have been published. A battery of both aerobic and anaerobic gram-negative and gram-positive strains as well as an extremophile microbial consortium from natural environment (Rio Tinto, Spain) were tested in graphene oxide reduction at simplest operating conditions. Results showed biological reduction of GO by all microorganisms, under aerobic conditions without any nutrient and carbon source addition and at room temperature (20-25 degrees C). UV-vis spectra of RGO showed the adsorption maximum gradually shifted from 230 nm to 270 nm, indicating an increase in the electronic conjugation. Moreover, G band in Raman spectra of RGO shifted from the original value of 1589 +/- 1 cm(-1) in GO. TGA analyses indicated that only weak weight losses of 2.5% both at 200 degrees C and above 300 degrees C, were achieved for Shewanella baltica strain and extremophile microbial consortium related to the presence of oxygen functional groups, indicating the GO reduction. The main novelty of the present work suggests that RGO biosynthesis was mediated by chemical oxidation independently of the bacterial respiration. The method described in the present work is comparable to other biological as well as physicochemical processes and environmentally friendly taking advantage of natural resources for graphene synthesis.