Amino Borate-Functionalized Reduced Graphene Oxide Further Functionalized with Copper Phthalocyanine Nanotubes for Reducing Friction and Wear

Abstract

Covalent functionalization of graphene oxide (GO) was performed by 2-aminoethyl diphenyl borate (ADB) to overcome the demerits of plain GO/reduced GO (rGO) during lubrication such as the agglomeration and restacking of nanosheets, poor dispersibility in the base lube, poor adhesion to the steel surface, inadequate friction and wear-reducing characteristics, and last abysmal load-carrying ability. ADB was deliberately chosen to outreach the benefits of the enhanced lubrication by in situ formed boron nitride during tribological testing due to boron–nitrogen synergy. Nucleophilic attack of the −NH2 group of ADB opened epoxide rings of GO, forming −NH–C–C–OH and simultaneously reducing GO to rGO. The product, therefore, is represented as ADB–rGO. For the betterment of lubricity, further noncovalent functionalization was also considered using triboactive phthalocyanine (Pc) or copper­(II) phthalocyanine (CuPc). Based on the results of molecular dynamics and tribological tests in paraffin oil (PO), CuPc was preferred over Pc. Configurations of the adsorbate CuPc on the surface reveal that CuPc tends to fold/unfold upon adsorption. Thus, the CuPc nanotubes (NTs) were used for the noncovalent functionalization of ADB–rGO. The techniques FTIR, p-XRD, SEM/HR-SEM, TEM/HR-TEM, EDX, and XPS were applied to characterize the additives. The tribological activity of different additives evaluated on a four-ball tester based on ASTM D4172 and ASTM D5183 tests reveals the order for antiwear/antifriction efficiencies and reduction in wear rates as CuPc–(ADB–rGO) > CuPc NTs > Pc > ADB–rGO > GO > PO. Thus, CuPc–(ADB–rGO) overpowered the demerits of GO. The morphology of the surface lubricated with GO, ADB–rGO, was studied using SEM and AFM (contact mode). EDX analysis of the steel surface in the presence of CuPc–(ADB–rGO) divulges the additional elements boron, nitrogen, and copper in the in situ formed tribofilm, highlighting their active role in improving the tribological activity. XPS studies of the tribofilm show boron nitride, boron oxide, iron oxides, cupric oxide, and graphitic compounds. The synergic performance of layered structures rGO, CuPc, and in situ formed boron nitride validated the spectacular tribological performance of CuPc–(ADB–rGO).

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

“…A little shift in the peaks indicates that the zinc oxide nanorod might have tribosinterized at the tribosurfaces. Besides, the iron of the steel surface is oxidized to ferric oxide, as revealed by the presence of peaks in the Fe 2p spectrum for Fe 2p 3/2 (710.5 eV) and Fe 2p 1/2 (724.2 eV). − Thus, based on the characterization of tribofilm by XPS spectra, it may be inferred that tribofilm is made up of the adsorbed organic contents of g-C 3 N 4 , N–ZnO, and tribochemically oxidized Fe 2 O 3.…”

“…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) .…”

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

“…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.…”

“…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. Accordingly, VSe 2 nano-sheets, ZB, LZB, and LZB/VSe 2 were synthesized, and their tribological activity was appraised in paraffin oil (PO) on a four-ball tester machine under ASTM D4172 and ASTM D5183 conditions.…”