Authors: Maxim K. Rabchinskii, Ryzhkov S.A., Maksim V. Gudkov, Marina V. Baidakova, Savelyev S.D., Sergei I. Pavlov, Vladimir V. Shnitov, Demid A. Kirilenko, Dina Yu. Stolyarova, Sergey V. Pavlov, Vitaliy A. Kislenko, Sergey A. Kislenko, Anna Makarova, Valery P. Melnikov, Pavel N. Brunkov
In this paper, we for the first time demonstrate efficient nitrogen doping of graphene oxide (GO) with nitrogen concentration of up to almost 5 at.% and desired type of the nitrogen species via modified Hummers' method. Using x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and Fourier transform infrared spectroscopy (FTIR) techniques, we have found out graphitic nitrogen to be the dominant type of the implemented nitrogen species. At the same time, the subsequent GO thermal reduction to graphene appears to result in a transformation of the graphitic nitrogen into pyridines and pyrroles. The mechanisms of the observed GO nitrogen doping and conversion of the nitrogen species are proposed, providing an opportunity to control the type and concentration of the implemented nitrogen within the developed approach. A two-time increase of the graphenes' conductivity is observed due to the performed nitrogen doping. Further comprehensive electrical studies combined with the transmission electron microscopy (TEM) and density functional theory (DFT) modeling have allowed us to estimate the conductivity mechanism and the impact of the implemented nitrogen. As a net result, a simple method to synthesize GO and graphene layers doped with specific nitrogen species is developed, which leads to new perspective applications for graphene, i.e. supercapacitors, catalysis, and sensors.