Abstract
Sulfur-doped graphene oxide (SA-GO) prepared by sulfuration and alkylation of graphene oxide is applied as an efficient green anti-wear additive for harsh operation conditions of engines. X-ray photoelectron spectroscopy analysis reveals the sulfur content of octadecylamine-modified SA-GO (sulfuration follows alkylation) is increased by 79 times compared with the reverse process that alkylation follows sulfuration, suggesting the preparation route is a key factor of the sulfuration process. The higher sulfur content and –C–S–C– sulfur bonding constitution result better lubrication effect, while the investigation of chain length of alkylation modification and concentration of the alkylated sulfur-doped graphene oxide indicates the octylamine-modified SA-GO shows smaller diameter of wear scar within the concentration range between 1 × 10−4 and 2.5 × 10−4 wt%. The decrement percent of wear scar diameter is 43.2% in 928 lubrication oil and 17.2% in PAO4 oil while the SA-GO modified by octylamine is applied with the concentrations 2.5 × 10−4 wt% in PAO4 and 1 × 10−4 wt% in 928 oil, respectively. The sulfur content in oil samples is only 0.006~0.001 wt%, which is much lower than the sulfur content standard recommended by ILSAC that is 0.5 wt%. The research work indicates the SA-GO additive is more feasible for the pollution treatment which focuses the substantial reduction of sulfur content in lubrication oil on the premise of improving lubrication capability.
Highlights
Sulfur-based organic anti-wear additives are widely used in the application of lubrication oils to promote the antiwear ability of friction pairs under extreme pressure in which oil membrane failed to separate the moving parts, such as sulfur-containing gear oil [1]and poly-α-olefin [2]
Since the excessive active sulfur in organic compounds could poison the ternary catalyst of emission reduction system while serving on the piston ring and cylinder wall, which has been resulting to serious environment pollution, the coming mandatory standard from the International Lubricant Standardization and Approval Committee (ILSAC) [3] requires the sulfur content of lubrication oil should be less than 0.5 wt%, for the reason that the higher sulfur content in lubricant
The results indicate that the alkylation before sulfuration would dramatically reduce the active points on the graphene oxide, which results significant efficiency decrement of the followed sulfuration of AS-Graphene oxide (GO)
Summary
Sulfur-based organic anti-wear additives are widely used in the application of lubrication oils to promote the antiwear ability of friction pairs under extreme pressure in which oil membrane failed to separate the moving parts, such as sulfur-containing gear oil [1]and poly-α-olefin [2]. This paper focuses to prepare the sulfur-doped graphene oxide to act as an efficient low-sulfur content anti-wear additive for harsh operation conditions at high temperature. Based on the preparation researches of sulfur-doped graphene, the unique nanomaterials could be obtained by the reactions of thiourea [11], NaHSO3 [12], K2S2O8 [13], phenyl disulfide [14, 15], sulfur [16], Na2S [17], CS2 [18], P4S10 [19], H2S [20], SO2 [21], CS2. After the sulfur doping process, sulfur-doped graphene oxide could significantly improve the anti-wear properties of the based oil. The most important feature of the unique anti-wear additive is the sulfur element that was anchored in the molecular structure of sulfur-doped graphene oxide. Adding the sulfur-doped graphene oxide in lubrication oil would simultaneously keep the advantages of sulfur-containing anti-wear additives and reduce the sulfur content to ~ 1/1000 compared with organic sulfur additives
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