Natural Carbon Nanostructuring Materials

Abstract

Synthesizing and isolating new forms of carbon allotropes (fullerenes, nanotubes, graphene) has been the focus of much research during the last two decades in different countries. In magmatic and metamorphic rocks the main form of carbon allotropes is graphite that is usually observed in the form of lamellar crystals of hexagonal syngony. However, the study of graphite mineralization in leikogabbro of Verhnetalnahskaya intrusion [1] have established submicroscopic carbon of different morphologies in the forms of singlewalled and multiwalled micro-and nanotubes, foam-like, and wool-like spongy aggregates, and onion-like carbon particles. The analytical procedure involved the following stages: (1) chemical decomposition; (2) handle rejection of carbon formations under a microscope; (3) study of multiple scan frames and isotope composition in order to distinguish different forms of nanostructuring carbon materials. One sample contains the following morphological types of carbon nanostructuring materials: (1) Quasi-cylindrical tubes consist of three complex zones: (a) the inner hollow tubes with a diameter of up to 100 microns ($μ$m); (b) intermediate foam-like layer (10--20 $μ$m); (c) outer zone consisting of a ``forest'' of microtubes (length---0.2--0.3 mm, diameter---1--5 $μ$m) and nanotubes (diameter---100 nm). (2) Planar carbon structures, that is characterized by zonal morphologies. In cross-sectional view of a planar structure are defined: (a) plane of nanometer thicknes; (b) intermediate foam and wool-like layer (20 $μ$m); (c) microtubes and nanotubes emerged from the intermediate layer (diameter---5 $μ$m, length---100--150 $μ$m). (3) Large onion-like fullerens (diameter---5 $μ$m). An important question is the origin of nanostructuring materials. Carbon isotopic data had shown closeness of isotopic values for the various components of nanostructuring materials: for nano- and microtubes $δ$13C: −13.2 to −13.5% (VPDB), for honeycomb material $δ$13C: −13.8 to −14.2 %. These isotopic data and morphological features lead to the conclusion: honeycomb carbon material is a ``breeding ground'' for the cultivation of microtubes and nanotubes in natural geological conditions. Carbon source for all of the investigated nanostructured materials is CO2, with the carbon isotope composition characterized by an interval---17.4--18.7%. Taking into account the fractionation of carbon isotope composition during the graphite precipitation in the system CO2---graphite, temperature calculated by obtained isotopic data is approximately 800 {\textdegree}C.