Heterolamellar Bi2Se3/Bi2WO6and Bi2Se3/N-Doped Bi2WO6Nanosheet Composites as Potential Antifriction and Antiwear Agents

Hydrothermally synthesized bismuth selenide (Bi2Se3) nanosheets were reinforced by introducing lamellar bismuth tungstate (Bi2WO6) to obtain a heterolamellar structure anticipating higher tribological efficiency. For the furtherance of efficiency, the bismuth tungstate was nitrogen-doped (N-Bi2WO6) and was used to reinforce Bi2Se3nanosheets. The propensity toward two-dimensional (2D) materials for the fabrication of composites was based on the presence of weak van der Waals forces between the adjacent layers, which eventually promotes lubricious behavior together with enhanced dispersibility. Examination of the hybrid nanosheets Bi2Se3/Bi2WO6and Bi2Se3/N-Bi2WO6by high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM) demonstrated that Bi2WO6and N-Bi2WO6nanosheets were distributed uniformly onto Bi2Se3nanosheets. The tribological attributes of well-identified nanoadditives Bi2Se3, Bi2WO6, N-Bi2WO6, Bi2Se3/Bi2WO6, and Bi2Se3/N-Bi2WO6were evaluated in paraffin oil (PO) on a four-ball tester at an optimized concentration of 0.050% w/v operating ASTM D4172 and ASTM D5183 tests. The tribological data, mean wear scar diameter (MWD), friction coefficient (COF), and seizure load divulged that N-Bi2WO6nanosheets behaved significantly better than Bi2WO6nanosheets, which, in turn, surpassed the Bi2Se3nanosheets. However, substantial upgradation of tribological activity was noted for the hybrid Bi2Se3/Bi2WO6due to a heterolamellar structure with reduced interlaminar shear strength that effectively prevents restacking and agglomeration of nanosheets. For the advancement of tribological activity, the hybrid Bi2Se3/N-Bi2WO6was prepared, which performed more efficiently than Bi2Se3/Bi2WO6. According to energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses of the worn pathway, the generated tribo-film comprised metal oxides, Bi2O3, SeO2, WO3, and tungsten nitride, which synergetically improved the lubricity. The wear scar surface analysis by atomic force microscopy (AFM) and SEM validated the observed tribological results.