Synthesis of N-doped carbon quantum dots as lubricant additive to enhance the tribological behavior of MoS2 nanofluid

Abstract

In this study, a novel lubricant additive nitrogen-doped carbon quantum dot (N-CQD) nanoparticle was prepared by the solvothermal method. The synthesized spherical N-CQD nanoparticles in the diameter of about 10 nm had a graphene oxide (GO)-like structure with various oxygen (O)- and nitrogen (N)-containing functional groups. Then N-CQDs were added to MoS2 nanofluid, and the tribological properties for steel/steel friction pairs were evaluated using a pin-on-disk tribometer. Non-equilibrium molecular dynamics (NEMD) simulations for the friction system with MoS2 or MoS2 + N-CQD nanoparticles were also conducted. The results showed that friction processes with MoS2 + N-CQD nanofluids were under the mixed lubrication regime. And MoS2 nanofluid containing 0.4 wt% N-CQDs could achieve 30.4% and 31.0% reduction in the friction coefficient and wear rate, respectively, compared to those without N-CQDs. By analyzing the worn surface topography and chemical compositions, the excellent lubrication performance resulted from the formation of tribochemistry-induced tribofilm. The average thickness of tribofilm was about 13.9 nm, and it was composed of amorphous substances, ultrafine crystalline nanoparticles, and self-lubricating FeSO4/Fe2(SO4)3. NEMD simulation results indicated the interaction between S atoms in MoS2 as well as these O- and N-containing functional groups in N-CQDs with steel surfaces enhanced the stability and strength of tribofilm. Thereby the metal surface was further protected from friction and wear.

Compaction of Hydrophobic Molybdenum Disulfide Coatings for Promoting Tribological Behaviors on Engineering Steel

“…As shown in Figure c, the Fe 2p 3/2 peaks at the bands of 710.5 (Fe 2+ ), 712.1 eV (Fe 3+ ), and Fe 2p 1/2 peaks at the bands of 724.1 (Fe 2+ ) and 725.5 eV (Fe 3+ ) were attributed to the iron oxides, including Fe 2 O 3 and Fe 3 O 4 . Meanwhile, the Fe 2p peak at 713.9 eV proved the generation of FeSO 4 and Fe 2 (SO 4 ) 3 . − The reason is that iron-containing debris is produced on the friction surface, which reacts with MoS 2 in the effect of friction heat to generate sulfate and iron oxide particles. After further oxidation, sintering, and compaction, these substances remain on the worn surface and finally form a friction layer, which provides some protection to the worn surface and prevents further wear of the coating.…”

In Situ Graphene Formation Induced by Tribochemical Reaction for Sustainable Lubrication

“…Thereinto, carbon materials acquire more attention in virtue of their excellent mechanical properties, superior thermal and chemical stability, environmentally friendly property, and peculiar self-lubricating property . However, the commonly carbon lubricating materials, such as grapheme, fullerenes, carbon quantum dots, and carbon nanotubes, demand a complex synthesis process and massive energy inputs, which causes environmental pollution and increases production cost.…”

Nitrogen-Doped Carbon Dot as a Lubricant Additive in Polar and Non-polar Oils for Superior Tribological Properties via Condensation Reaction

“…The abundant oxygen-containing and nitrogen-containing functional groups on the CQD-N surface lets it adsorb on the metal surface conveniently and quickly and play the role of a rolling and protective film of CQD-N. Cui et al synthesized nitrogen-doped CDs (NCDs) using p -phenylenediamine and o -phenylenediamine as nitrogen sources during hydrothermal process and used the nitride protective film formed by nitrogen on the metal surface to reduce metal corrosion. He et al prepared NCDs by the solvothermal method and studied their tribological properties in MoS 2 nanofluids. The interaction between nitrogen atom functional groups and metal surface provides preconditions for the formation of a friction protective film and protects the friction interface from severe wear.…”