Ternary Composite of Methionine-Functionalized Graphene Oxide, Lanthanum-Doped Yttria Nanoparticles, and Molybdenum Disulfide Nanosheets for Thin-Film Lubrication

Abstract

For enhancement of the tribological activity of nanolamellar graphene oxide (GO), its nucleophilic substitution was performed by methionine to yield methionine-functionalized reduced graphene oxide (M-rGO). Further, noncovalent functionalization of another tribo active material, nanolamellar MoS2, was accomplished by lanthanum (7%)-doped yttria nanoparticles (NPs), resulting in the formation of a nanocomposite, (La-Y2O3)-MoS2. The doped NPs were deliberately chosen for this purpose because there was a clear increase in the wear/friction-reducing tendencies of yttria after doping with lanthanum. For further advancement of the tribological activity, a ternary nanocomposite (La-Y2O3)-MoS2-(M-rGO) was synthesized containing lanthanum-doped yttria NPs, M-rGO, and MoS2 nanosheets. The NPs, nanosheets, and composites have been characterized by powder X-ray diffraction, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy, and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical states of different elements in (La-Y2O3)-MoS2-(M-rGO). The tribological properties of well-characterized composites were evaluated in paraffin oil (PO) using a four-ball tester according to ASTM D4172 and ASTM D5183 standards at the optimized concentration, 0.20% (w/v). There was incremental evolution in the tribological properties from plain PO through Y2O3, MoS2, M-rGO, La-Y2O3, and (La-Y2O3)-MoS2 and finally to (La-Y2O3)-MoS2-(M-rGO). Here functionalization of GO has invigorated its structure. Both nanosheets coordinated to control agglomeration of the NPs. The NPs prevented the nanosheets from restacking. SEM and atomic force microscopy images of the wear scar validated the results of tribological tests. The presence of yttrium, lanthanum, sulfur, and molybdenum besides carbon, nitrogen, and oxygen in the energy-dispersive X-ray spectrum of the worn surface in the presence of PO blended with (La-Y2O3)-MoS2-(M-rGO) is indicative of its strong adsorption on the surface. On the basis of XPS studies of the wear track, the constituents of the tribofilm could be identified as adsorbed rGO, yttria, lanthanum oxide, and MoS2 in addition to tribochemically produced Fe2O3, MoO3, and SO4 2–. The mutualistic approach of the constituents has yielded splendid results.

Reinforcement of nanoporous lanthanum-doped zinc borate by vanadium selenide nanosheets for improved tribological activity

“…4a. 5 The presence of a peak at binding energy spectrum, Fig. 4d, exhibits peaks at 530.2 and 531.6 eV for metal oxides bonds [La-O and Zn-O] and absorbed water, respectively.…”

“…Moreover, the peaks that appear in the Fe 2p XPS spectrum at 710.5 eV (Fe 2p 3/2 ) and 724.2 eV (Fe 2p 1/2 ), [12][13][14][15][16][17] indicate the formation of Fe 2 O 3 through the oxidation of Fe of the steel. 2,3,5,6 Thus, the presence of various oxides, particularly ZnO, 3 La 2 O 3 , 5 B 2 O 3 , 29 and V 2 O 5 , 52 usually facilitate lubrication and promote the tribological properties of LZB/VSe 2 .…”

“…3 Undoubtedly, the layered structure of VSe 2 has facilitated the sliding motion due to weak van der Waals forces. 3,5,6 Under thermo-mechanical effects 40 of the tribological test, the nanosheets were squeezed and smeared on the worn surface of the porous LZB matrix due to high contact pressure. The drastic friction at the interface is therefore weakened.…”

“…43,44 The enhancement in tribological properties of doped nanomaterials, like magnesium doped zinc oxide, ceria doped zirconia, lanthanum-doped yttria, has been reported from our laboratory. 1,5,45 Furthermore, the composites of the doped nanomaterials with layered materials like graphene, graphitic carbon nitride, molybdenum disulde, and copper phthalocyanine have been proclaimed from our group to manifest exemplary tribological behavior. 1,3,5,6 Considering the above, it engrossed us to synthesize nanoporous zinc borate(ZB), lanthanum doped zinc borate(LZB), lamellar vanadium selenide(VSe 2 ), and use the synthesized VSe 2 to reinforce LZB (LZB/VSe 2 ) for upgrading its tribological behavior.…”

Enhancement of Triboactivity of Nanolamellar Graphitic-C3N4 by N-Doped ZnO Nanorods

“…Employing lubricants with additional friction modifiers produces encouraging results. An extensive overview of literature proclaims that several types of nanomaterials such as nanoparticles, nanosheets, or nanocomposites have been used for the purpose owing to their fast tribo-action. − Nowadays, carbon-based materials such as graphene, fullerene, and carbon nanotubes are the center of attention in this innovative research area. − From our laboratory, too, carbon microspheres, , reduced graphene oxide, and their composites with nanoparticles, doped nanoparticles, or nanosheets have been recently documented as tribologically active materials. − A carbon nitride polymer of high thermal stability possessing graphitic structure g-C 3 N 4 with weak van der Waals forces amid the 2D-nanosheets appears to be very influential in the field. Still, it has been seldom studied. , Zhu et al have described the antiwear performance of bulk g-C 3 N 4 with polyvinylidene difluoride (PVDF) .…”