Heterolamellar Bi₂Se₃/Bi₂WO₆ and Bi₂Se₃/N-Doped Bi₂WO₆ Nanosheet Composites\nas Potential Antifriction\nand Antiwear Agents

Abstract

Hydrothermally synthesized bismuth\nselenide (Bi₂Se₃) nanosheets were reinforced\nby introducing lamellar\nbismuth\ntungstate (Bi₂WO₆) to obtain a heterolamellar\nstructure anticipating higher tribological efficiency. For the furtherance\nof efficiency, the bismuth tungstate was nitrogen-doped (N-Bi₂WO₆) and was used to reinforce Bi₂Se₃ nanosheets. The propensity toward two-dimensional (2D) materials\nfor the fabrication of composites was based on the presence of weak\nvan der Waals forces between the adjacent layers, which eventually\npromotes lubricious behavior together with enhanced dispersibility.\nExamination of the hybrid nanosheets Bi₂Se₃/Bi₂WO₆ and Bi₂Se₃/N-Bi₂WO₆ by high-resolution scanning electron microscopy (HR-SEM),\ntransmission electron microscopy (TEM), and high-resolution TEM (HR-TEM)\ndemonstrated that Bi₂WO₆ and N-Bi₂WO₆ nanosheets were distributed uniformly onto Bi₂Se₃ nanosheets. The tribological attributes of\nwell-identified nanoadditives Bi₂Se₃, Bi₂WO₆, N-Bi₂WO₆, Bi₂Se₃/Bi₂WO₆, and Bi₂Se₃/N-Bi₂WO₆ were evaluated in paraffin\noil (PO) on a four-ball tester at an optimized concentration of 0.050%\nw/v operating ASTM D4172 and ASTM D5183 tests. The tribological data,\nmean wear scar diameter (MWD), friction coefficient (COF), and seizure\nload divulged that N-Bi₂WO₆ nanosheets behaved\nsignificantly better than Bi₂WO₆ nanosheets,\nwhich, in turn, surpassed the Bi₂Se₃ nanosheets.\nHowever, substantial upgradation of tribological activity was noted\nfor the hybrid Bi₂Se₃/Bi₂WO₆ due to a heterolamellar structure with reduced interlaminar shear\nstrength that effectively prevents restacking and agglomeration of\nnanosheets. For the advancement of tribological activity, the hybrid\nBi₂Se₃/N-Bi₂WO₆ was prepared,\nwhich performed more efficiently than Bi₂Se₃/Bi₂WO₆. According to energy-dispersive X-ray\n(EDX) and X-ray photoelectron spectroscopy (XPS) analyses of the worn\npathway, the generated tribo-film comprised metal oxides, Bi₂O₃, SeO₂, WO₃, and tungsten nitride,\nwhich synergetically improved the lubricity. The wear scar surface\nanalysis by atomic force microscopy (AFM) and SEM validated the observed\ntribological results.