Formation Of Carbon Nanosheets Research Articles

Biomass Waste Carbonization in Piranha Solution: A Route to Hypergolic Carbons?

In the present work we report for the first time the carbonization of biomass waste, such as stale bread and spent coffee, in piranha solution (H2SO4-H2O2) at ambient conditions. Carbonization is fast and exothermic, resulting in the formation of carbon nanosheets at decent yields of 25–35%, depending on the starting material. The structure and morphology of the nanosheets were verified by X-ray diffraction, Raman, X-ray photoelectron and microscopy techniques. Interestingly, the obtained carbon spontaneously ignites upon contact with fuming nitric acid HNO3 at ambient conditions, thus offering a rare example of hypergolicity involving carbon as the solid fuel (i.e., hypergolic carbon). Based on the relatively large interlayer spacing of the as-produced carbons, a simple structural model is proposed for the observed hypergolicity, wherein HNO3 molecules fit in the gallery space of carbon, thus exposing its basal plane and defect sites to a spontaneous reaction with the strong oxidizing agent. This finding may pave the way towards new type hypergolic propellants based on carbon, the latter exclusively obtained by the carbonization of biomass waste in piranha solution.

Hypergolic Ignition of 1,3-Cyclodienes by Fuming Nitric Acid toward the Fast and Spontaneous Formation of Carbon Nanosheets at Ambient Conditions

A hypergolic system is a combination of organic fuel and oxidizer that ignites spontaneously upon contact without any external ignition source. Although their main usage pertains to rocket bipropellants, it is only recently that hypergolics have been established from our group as a revolutionary preparative method for the synthesis of different types of carbon nanostructures depending on the organic fuel-oxidizer pair. In an effort to further enrich this concept, the present work describes new hypergolic pairs based on 1,3-cyclohexadiene and 1,3-cyclooctadiene as the organic fuels and fuming nitric acid as the strong oxidizer. Both carbon-rich compounds (ca. 90% C) share a similar chemical structure with unsaturated cyclopentadiene that is also known to react hypergolically with fuming nitric acid. The particular pairs ignite spontaneously upon contact of the reagents at ambient conditions to produce carbon nanosheets in suitable yields and useful energy in the process. The nanosheets appear amorphous with an average thickness of ca. 2 nm and containing O and N heteroatoms in the carbon matrix. Worth noting, the carbon yield reaches the value of 25% for 1,3-cyclooctadiene, i.e., the highest reported so far from our group in this context. As far as the production of useful energy is concerned, the hot flame produced from ignition can be used for the direct thermal decomposition of ammonium dichromate into Cr2O3 (pigment and catalyst) or the expansion of expandable graphite into foam (absorbent and insulator), thus demonstrating a mini flame-pyrolysis burner at the spot.

Formation of carbon nanosheets via simultaneous activation and catalytic carbonization of macroporous anion-exchange resin for supercapacitors application.

Two-dimensional mesoporous carbon nanosheets (CNSs) have been prepared via simultaneous activation and catalytic carbonization route using macroporous anion-exchange resin (AER) as carbon precursor and ZnCl2 and FeCl3 as activating agent and catalyst, respectively. The iron catalyst in the skeleton of the AER may lead to carburization to form a sheetlike structure during the carbonization process. The obtained CNSs have a large number of mesopores, a maximum specific surface area of 1764.9 m(2) g(-1), and large pore volume of 1.38 cm(3) g(-1). As an electrode material for supercapacitors application, the CNSs electrode possesses a large specific capacitance of 283 F g(-1) at 0.5 A g(-1) and excellent rate capability (64% retention ratio even at 50 A g(-1)) in 6 mol L(-1) KOH. Furthermore, CNSs symmetric supercapacitor exhibits specific energies of 17.2 W h kg(-1) at a power density of 224 W kg(-1) operated in the voltage range of 0-1.8 V in 0.5 mol L(-1) Na2SO4 aqueous electrolyte, and outstanding cyclability (retains about 96% initial capacitance after 5000 cycles).

Carbon nanorods and graphene-like nanosheets by hot filament CVD: growth mechanisms and electron field emission

Carbon nanorods and graphene-like nanosheets are catalytically synthesized in a hot filament chemical vapor deposition system with and without plasma enhancement, with gold used as a catalyst. The morphological and structural properties of the carbon nanorods and nanosheets are investigated by field-emission scanning electron microscopy, transmission electron microscopy and micro-Raman spectroscopy. It is found that carbon nanorods are formed when a CH4 + H2 + N2 plasma is present while carbon nanosheets are formed in a methane environment without a plasma. The formation of carbon nanorods and carbon nanosheets are analyzed. The results suggest that the formation of carbon nanorods is primarily a precipitation process while the formation of carbon nanosheets is a complex process involving surface-catalysis, surface diffusion and precipitation influenced by the Gibbs–Thomson effect. The electron field emission properties of the carbon nanorods and graphene-like nanosheets are measured under high-vacuum; it is found that the carbon nanosheets have a lower field emission turn-on than the carbon nanorods. These results are important to improve the understanding of formation mechanisms of carbon nanomaterials and contribute to eventual applications of these structures in nanodevices.