Green Reduction of Graphene Oxide into Graphene by Cow Urine

Background: Graphene synthesis via wet chemical route needs chemical reduction of graphene oxide in the presence of reducing agents. To minimize the environmental impacts, natural antioxidants are potential alternatives than the currently used hazardous materials for the reduction of graphene oxide. Cow urine inherently owns excellent anti-oxidant properties by virtue of its high natural nitrogenous content and has researched well for urine therapy throughout the history of mankind. Methods: The reductive ability of cow urine has been used to reduce graphene oxide into graphene nanosheets with ultrasonication followed by heat treatment. Results: Raman analysis reveals that the maximum reduction of graphene oxide is observed at 140 °C by cow urine, with a Raman D to G band intensity ratio of ~ 1.27. XPS analysis validates the Raman signature of maximum removal of oxygen species from graphene oxide, and reveals the attainment of the C/O ratio of ~ 5.25. Conclusion: A simple green and cost effective approach has been demonstrated for the reduction of graphene oxide via cow urine as a natural reducing agent. The reduction degree of graphene oxide is found to be high as processing temperature increases. The maximum reduction of oxygen species from graphene oxide is found at 140 °C. Hence, cow urine offers potential alternative chemicals to avoid the use of hazardous reducing agents for the synthesis of graphene nanosheets at large scale.