Local structure and paramagnetic properties of the nanostructured carbonaceous material shungite

Abstract

Using a scanning electron microscopy, elemental analysis, electron paramagnetic resonance, and Raman scattering methods, two types of the shungite materials (Sh-II from Zazhogino deposit and shungite from a commercial filter (ShF)), with different carbon content and porosity, are studied in this work. It was established by scanning electron microscopy data that the structure of the shungite samples is formed by a micron-size agglomeration of carbon and silicon dioxide clusters. It is found from the Raman data that carbon fraction is formed from sp2-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples. High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes. Big clusters give the conduction electron spin resonance signal with a Dysonian line shape with variable g-factor and line width.The careful search of the nature of two other narrow electron paramagnetic resonance signals in shungite, which used to be prescribed to fullerene-like molecules, is fulfilled. Here, it is shown that the oxygen-deficient E'γ centers are responsible for these signals. A strong correlation is revealed between the concentration of Е'γ centers and the line width of conduction electron spin resonance signal, which occurs under annealing process of the samples at T = 570 K. The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

EPR Study of Porous Si:C and SiO2:C Layers

“…A small decrease in the CRD g ‐value in por‐SiO 2 :C layers from 2.0035 to 2.0030 and an increase of the EPR linewidth can be possibly explained by the appearance of the sp 2 ‐coordinated C clusters formed in por‐SiO 2 :C layers after oxidation. The STEM image of the pores shown in Figure suggests the existence of the carbon nanoprecipitates in por‐SiO 2 :C. The EPR signal of small C clusters with a similar g ‐value was observed previously in nanostructured carbonaceous shungite . This conclusion correlates with COC bonds found in EEL spectra of the C K‐edge region in por‐SiO 2 :C layers.…”

sp2 Carbon Stable Radicals

“…Nevertheless, in fact, by now there have not been communications joining radical terminology and the vast available data concerning sp 2 amorphous carbons. At the same time, specific peculiarities concerning metal free carbocatalysis [95][96][97][98][99][100][101][102][103][104][105][106] (see a brief review of the latter state of art [107]) and electron-spin resonance [108][109][110][111][112][113][114][115] have been really observed. However, until now, they have not been connected with specific radical properties of sp 2 carbons as well.…”

Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite

“…The electrical conductivity was found to be similar to the conductivity of graphite in the direction perpendicular to graphite layers . Other reported studies dealt with the globular structure, paramagnetic properties, thermal conductivity, and acoustical properties . In this case all edges were much longer than the skin depth δ, thereby the placening in the resonator wasn't crucial.…”