Advancement of\nTriboactivity of Nanolamellar Ni–Mn-Based\nBimetallic-Organic Frameworks by Molybdenum-Doped Bismuth Vanadate\nNanorods

To pave the way for highly tribologically efficient 2D\nmaterials,\na Ni–Mn-based bimetallic-organic framework (NMF) was synthesized\nultrasonically. Considering further advancement of its activity, hydrothermally\nsynthesized BiVO<sub>4</sub> (BV)/Mo-doped bismuth vanadate (MBV)\nnanorods were introduced to obtain nanohybrids, MBV/NMF. The TEM,\nHR-SEM, and HR-TEM investigations of the hybrid (MBV/NMF) divulge\nthat Mo-doped BiVO<sub>4</sub> nanorods were spread over NMF nanosheets\nand strengthened them. Using ASTM D4172 and ASTM D5183 standard tests,\nthe tribological performances of well-characterized nanomaterials,\nBV, MBV, NMF, and MBV/NMF, were assessed in paraffin oil (PO) at the\noptimal concentration, 0.1% w/v on a four-ball tester. The mean wear\nscar diameter (MWD) value for base oil PO shows a % reduction: BV\n(22%), MBV (27%), NMF (33%), and MBV/NMF (42%). The % reduction in\naverage coefficient of friction (COF) value of base lube follows a\nsimilar trend to that of MWD: BV (20%), MBV (25%), NMF (33%), and\nMBV/NMF(60%). The tribological data such as MWD, COF, and seizure\nload revealed significantly better activity of NMF nanosheets than\nthe nanorods, possibly owing to weak van der Waals forces existing\namid the lamellae. Certainly, the molybdenum doping has increased\nthe activity of BiVO<sub>4</sub> nanorods. The hybrid MBV/NMF exhibited\nhighly advanced activity because of noncovalent synergistic interactions\nbetween nanosheets and nanorods. Investigations of the wear track\nvia EDX and XPS studies indicate that the generated tribofilm comprises\nlubricious metal oxides: MoO<sub>3</sub>, Bi<sub>2</sub>O<sub>3</sub>, V<sub>2</sub>O<sub>5</sub>, MnO<sub>2</sub>, Mn<sub>2</sub>O<sub>3</sub>, NiO, Ni<sub>2</sub>O<sub>3</sub>, and metallic alloy (Ni–Fe),\nwhich prevented metal–metal contact between sliding surfaces\nand thus synergetically improved the lubricity. Tribological findings\nof the wear track were validated by SEM and AFM. A plausible lubrication\nmechanism has been demonstrated.