The role of carbon nanostructures in the ozonization of different carbon black grades, together with graphite and rubber crumb in an IR gas cell

摘要

Four carbon black grades (namely N234, N375, N660, and N991) having surface area of 120, 90, 36, and 8 m(2)/g have been studied together with a micronized synthetic graphite and a rubber crumb in their reaction with ozone. The study was conducted at room temperature in heterogeneous and static conditions inside an infrared gas cell. Using gas-phase infrared spectroscopy it has been followed the evolution Of CO2 formed by the O-3 attack directed toward the carbon surface and the consumption of ozone admitted into the cell using the ozone absorption band at 1056 cm(-1). The pseudofirst kinetic rate constant k derived from the ozone consumption in presence of carbon materials was determined for all the carbon materials studied. The reaction between ozone and carbon blacks essentially involves two stages: the gasification of the surface to CO2 and its functionalization with oxygenated chemical groups, mainly under the form of COOH but also many other groups. The pseudorfirst order kinetics appears adequate to describe the heterogeneous reaction between ozone and the selected carbon materials. Graphite reacts with O-3 in the conditions selected in this work with evolution of CO2. Graphite is less reactive with ozone than carbon blacks but its reactivity is comparable to that shown by powdered solid C-60 and C-70 fullerenes. Rubber crumb can be considered a carbon material in fact it reacts with ozone releasing CO2 at least at the early stages of exposure. This fact is really surprising and a mechanism involving free carbon black on the crumb surface has been advocated to justify this result. The discussion of the results has been focused on the role played by carbon nanostructures, in particular by the fullerene-like structures present in the graphene sheets to explain the phenomena of gasification and surface functionalization.