Synthesis of nano-Cu/graphene oxide composites by supercritical CO2-assisted deposition as a novel material for reducing friction and wear

Copper nanoparticle/graphene oxide (Sc-Cu/GO) composites were prepared by an in-situ chemical deposition with assistance of supercritical carbon dioxide (scCO2). The anchored Cu nanoparticles with diameter of 5–10 nm are uniformly distributed on the GO nanosheet surfaces. The tribological properties of the as-prepared Sc-Cu/GO composites as lubricating additive in liquid paraffin oil were evaluated using a four-ball tribometer. The results show that the Sc-Cu/GO nanocomposites as additives in oil have excellent anti-wear and friction-reducing abilities. The base oil mixed with 0.05 wt.% Sc-Cu/GO displays the friction coefficient of 0.065 and the wear scar diameter of 0.26 mm that are respectively reduced by 27.0% and 52.7% compared with the pure oil, 15.6% and 35% compared with the oil with 0.05 wt.% GO, 13.3% and 38.1% compared with oil with 0.05 wt.% nano-Cu. In addition, the lubricating performances of the Sc-Cu/GO composites are much better than that of the Cu/GO nanocomposites produced by the traditional deposition method (without scCO2). The excellent lubrication performances of the Sc-Cu/GO composites derive from the synergistic lubricating action of GO nanosheets and Cu nanoparticles during sliding process. The synergistic lubricating actions are discussed and proposed by analyzing the worn surfaces of the steel balls. This work offers an attractive strategy for fabricating graphene-based nanocomposites as energy efficient lubricant additives.