Synthesis, Characterization And Application Of Functionalized Graphene Nanoplatelets

Since the first experimental isolation of a single graphene sheet in 2004, graphene nanoplatelets(GNs) have attracted enormous attention. In this work, we report on a novel and facile magnetic grinding method to prepare functionalized graphene nanoplatelets(FGNPs). The chemical and structural properties of the FGNPs were tested by various methods. The resultant FGNPs were further modified chemically by N-dodecyltriethoxysilane(DTES). The modified FGNPs show strong synergistic effects if used as lubricant additive, as confirmed by standard four-ball friction tests. The thesis deals with the following issues respectively:Preparation of FGNPs: With the friction, collision, and shear forces created by the needles rotating at high speed, natural flake graphite could be exfoliated into nano scale with extremely high efficiency through magnetic grinding method. The sample were tested by Nitrogen-sorption measurements, SEM, TEM, FTIR, TGA and XRD. The results show that graphene nanoplatelets with a BET surface area of 738.1 m2 g-1 could be reached after ground for only 4h, about 434 times larger than that of pristine graphite(1.7 m2 g-1). FTIR test shows that the as-prepared GNPs is full of oxygen-containing functional groups like carboxylic acids(-COOH) and hydroxylic(-OH). XRD and SAED results reveal that the sample has good crystallinity.Modification of FGNPs: The oxygen-containing functional groups in the as-prepared FGNPs make it possible to modify the sample with different modifiers like dodecyltriethoxysilane, stearic acid and oleic acid. The long chain alkyl could be attached to the edge of the FGNPs to improve its suspension stability in lubricant oil. New peaks emerge in the FTIR spectra of the FGNPs after modified indicated that the sample has asymmetric methyl(-CH3), asymmetric and symmetric vibrations of methylene(-CH2-).After centrifuged under the same speed and time, modified FGNPs performed better suspension stability.Tribological properties of modified: Based on their nano-sized, ultra-thin morphology combined with high strength, the MFGNPs can efficiently improve the tribological properties of lubricant oil. The four ball tribo testers results show that the average friction coefficient(AFC) and wear scar diameter(WSD) of the steel ball tested in base oil without is 0.1170 and 482 μm, respectively. If 1 wt‰ of MFGNPs was added, the AFC and WSDof the base oil is reduced to 0.0642 and 353 μm, corresponding to a decrease by 45.1 %and 26.8 %. When the adding amount reached 1.5 wt‰, the AFC and WSD was 0.0282 and 284 μm, decreased by about 75.9 % 41.1 %.The new way of preparing FGNPs is a high efficient, eco-friendly and low cost, and can realize it’s large-scale production. In addition, the efficiency of the exfoliation on pristine graphite is also studied.