ИСТИНА

Graphene oxide (GO) attracts the attention of researchers since it is a precursor of various graphene-based materials, in particular, graphene oxide membranes. Many details of the internal structure of the material are still unclear. Electron paramagnetic resonance (EPR) is a powerful toolto study the molecular organization of different media, which could provide new insights into the properties of GO. The present report is devoted to the study of GO by a site-specific spin probe. Nitroxide radical 4-aminoTEMPO was chosen as a spin probe capable of localizing acidic groups of GO. The spin probe was introduced into GO powder and GO membrane from acetonitrile according to the procedure described in [1]. It was found that the nitroxide cannot be further removed by washing with acetonitrile or water as opposed to TEMPO and TEMPOL radicals. We believe that this is due to the ion-pair binding between carboxylic groups of GO and amino groups of 4-aminoTEMPO.Temperature dependence and angular dependence of EPR spectra were used for the determination of rotational mobility and orientational alignment of the paramagnetic molecules in the GO powder and GO membrane, correspondingly. The orientation distribution function of the radicals has been determined through numerical simulation of the EPR spectra angular dependence, according to the method [2]. The value of the order parameter P20 was found to be 30% lower than the value of P20 for TEMPOL in the same graphite oxide membrane. As 4-aminoTEMPO reflects mostly the orientational distribution of the carboxylic groups contrary to TEMPOL, which characterizes the average orientation of the graphene planes, the data obtained experimentally confirm the assumption that the carboxylic groups are located on the edges of GO flakes.