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 Bi2Se3 nanosheets. 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/Bi2WO6 and Bi2Se3/N-Bi2WO6 by high-resolution scanning electron microscopy (HR-SEM),
transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM)
demonstrated that Bi2WO6 and N-Bi2WO6 nanosheets were distributed uniformly onto Bi2Se3 nanosheets. The tribological attributes of
well-identified nanoadditives Bi2Se3, Bi2WO6, N-Bi2WO6, Bi2Se3/Bi2WO6, and Bi2Se3/N-Bi2WO6 were 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-Bi2WO6 nanosheets behaved
significantly better than Bi2WO6 nanosheets,
which, in turn, surpassed the Bi2Se3 nanosheets.
However, substantial upgradation of tribological activity was noted
for the hybrid Bi2Se3/Bi2WO6 due 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-Bi2WO6 was 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.