Heat-treatment effect on the nanosized graphite π-electron system during diamond to graphite conversion

Abstract

Graphite nanoparticles were prepared by the heat treatment of diamond nanoparticles in the range 900-1600°C. X-ray diffraction, transmission electron microscopy ͑TEM͒ and Raman scattering studies indicate that the onset temperature of the diamond-graphite transition is around 1200°C and the complete conversion of diamond to graphite occurs at 1600°C. Based on the structural characteristics the samples are categorized into sp 3 -dominated ͑as-prepared and 900°C͒, sp 2 :sp 3 mixed-phase ͑1200 and 1400°C͒, and sp 2 -dominated systems ͑1600°C͒. The larger c-axis repeat distances and the high-resolution TEM images for the sp 2 :sp 3 mixed-phase systems denote the presence of the remnant buckling feature of the diamond ͑111͒ planes in the graphene sheets. Magnetic susceptibility and ESR studies suggest the development of itinerant--electron system from the 1200°C and higher-temperature heat-treated samples. The completely graphitized sample reveals the important role of edge-inherited nonbonding -electron states in the electronic structure. The Raman G-peak position and the orbital diamagnetism show considerable deviation from the bulk-graphite values, which is explained on the basis of charge transfer from the graphite band to the localized edge states and the resulting shifting of the Fermi level. The enhanced spin-lattice relaxation rates in the case of more graphitized samples heat-treated at 1400 and 1600°C are expected to arise from the involvement of the localized edge-state electrons. In the less-graphitized 1200°C heat-treated sample, however, the corrugated nature of the graphene planes is likely to hinder such fast-relaxation processes.

Comprehensive review on synthesis and adsorption behaviors of graphene-based materials

“…The method of preparing graphene by microwave treatment is just a post-process using chemically synthesized graphene oxide in large quantities in a short time [61][62][63]. Andersson et al [64] and Prasad et al [65] reported that graphene can be synthesized by heating nanodiamonds in an inert or reducing atmosphere. Nanodiamond particles are treated by soaking them in concentrated hydrochloric acid to avoid contamination by magnetic impurities.…”

Influence of the Properties of Macromolecular Carbon on de Novo Synthesis of PCDDs, PCDFs, PCBs, and Chlorobenzenes

“…In general, SO 3 generated from H 2 SO 4 heated to over 290°C had potential of oxidative breakdown. (Prasad et al, 2000;Smith et al, 2009). The gvalue of graphite was determined to be 2.003 and was almost independent of the measured temperatures between 100 K and 300 K (Matsubara et al, 1991).…”

A study of the synthetic methods and properties of graphenes

“…Few-layer graphene can be prepared by heating nanodiamond in an inert or reducing atmosphere (DG) [25,28] and the effect of temperature on the product has been studied by Enoki and co-workers [28,29]. We have examined this procedure in detail.…”