Biogenic gold nanoparticles-reduced graphene oxide nanohybrid: synthesis, characterization and application in chemical and biological reduction of nitroaromatics

The environment-friendly biosynthesis of gold nanoparticles and reduced graphene oxide nanohybrid (bio-AuNPs/ rGO) was achieved with Shewanella oneidensis MR-1 under ambient and growing conditions. Both MR-1 cells and its metabolites were vital for the synthesis of bio-AuNPs/rGO, which showed comparable structural features to the chemically synthesized counterpart (chem-AuNPs/rGO). Compared to chem-AuNPs/rGO, bio-AuNPs, bio-rGO and their mixture, bio-AuNPs/rGO not only exhibited better catalytic activity and reusability towards the chemical reduction of 4-nitrophenol, but also showed higher stimulating effect on microbial reduction of nitrobenzene. These might be due to the good morphology/structure properties, introduction of N-doping and synergistic effects between AuNPs and rGO. The MR1 cells could attach themselves closely to bio-AuNPs/rGO, which might facilitate the transfer of electrons from cells to nitrobenzene during reduction. Moreover, bio-AuNPs/rGO could also enhance the nitrobenzene bioreduction by some MR-1 mutant strains lacking components of the Mtr pathway (Delta cymA, Delta mtrA and Delta mtrB), whereas no stimulating effect on nitrobenzene reduction by Delta omcA/Delta mtrC mutant strain was observed. This study provided a simple and eco-friendly method to synthesize graphene-based nanohybrid capable of stimulating reductive transformation of environmental pollutants.