The Tribological Properties of Reduced Graphene Oxide Doped by N and B Species with Different Configurations

Reduced graphene oxide (rGO) was doped by nitrogen (N) and/or boron (B), leading to four different configurations: N-rGO (N-doped rGO), B-rGO (B-doped rGO), N–B-rGO (N and B codoped rGO with formation of B–N bond), and N,B-rGO (N and B isolate-doped rGO without formation of B–N bond). The preparations of different configurations were controlled by the chemical vapor deposition procedure, and their structures were further confirmed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD). The tribological performance of these was tested via a ball-on-flat tribometer under 5 N load. N,B-rGO displayed better friction-reducing and antiwear performance than N-rGO and B-rGO, while N–B-rGO presented poorer tribological properties. The morphology and components of the wear track after friction were further explored, revealing that N,B-rGO can be adsorbed on the rubbing surface to form a graphene-based protective layer, while N–B-rGO cannot. In addition, first-principles calculations based on density functional theory further confirmed a stronger interfacial energy of N,B-rGO on steel surface than that of N–B-rGO on the steel surface, which was in accordance with the experimental results.