Simultaneous N doping and reduction of GO: Compositional, structural characterization and its effects in negative electrostatic charges repulsion

Abstract

The present work is focused on the modification of reduced graphene oxide with nitrogen doping to achieve electrostatic charges repulsion as well as, the extensive characterization of generated material. Graphene related materials, such as graphene oxide (GO) and reduced graphene oxide (rGO) have a wide field of applications and can be easily modified to obtain specific characteristics such as the high repulsion capacity to negative electrostatic charges promoted by nitrogen doping and which may be useful in biomedical applications, for example, to repel negatively charged cholesterol particles, which are deposited in arterial walls and catalyze atherosclerosis disease. In this work we present detailed characterization graphene oxide (GO) and nitrogen doped reduced graphene oxide (N-rGO) obtained in a low temperature process. Stacked sheets of GO with wrinkles were found, by TEM a hexagonal atomic arrangement with a thickness of 2.2 nm was observed. A distortion of the network after doping was also found and was attributed to an increase in defects due to GO reduction and nitrogen presence. The interplanar spaces were corroborate by DRX being 3.51 Å for N-rGO and 8.37 Å for GO. The corresponding bonds for nitrogen doping were found by XPS and FTIR, the total content of N was 9.57% with predominance of pyrrolic nitrogen. By means of contact angle measurements, resultant angles for N-rGO samples were >100° with different biological materials negative charged, demonstrating the repulsion capacity of the N-rGO. From measurements by Electrostatic Force Microscopy (EFM) it was verified that the repulsive behavior is due to the electrical charge in the surface of N-rGO and the negative surface potential of the material was verified by Scanning Kelvin Probe Microscopy (SKPM). Finally, cell viability tests were carried out on endothelial cells, obtaining a favorable behavior in contact with N-rGO. The characterization results confirmed the reduction of graphene oxide doped with nitrogen and the increase of negative charge in the surface was attributed to the free electrons that have the pyrrolic nitrogen, which allows the repulsion of negative electric charges, making N-rGO an ideal candidate for different applications.