Nature and kinetics of paramagnetic defects induced by beta-irradiation of chitosan

A set of chitosan samples irradiated by electrons with various doses were studied using the EPR method. Two kinds of paramagnetic defects PC1 and PC2 initiated by this irradiation due to the breakage of bonds in positions C5 and C1 of the chitosan structure are revealed in the “amorphous” and “crystalline” samples of chitosan. The structure of defects, their spectroscopic parameters, and kinetics of accumulation/decay have been established for the first time. It is found that EPR spectrum of the “crystalline” samples consists of 10 almost equidistant lines of the super-hyperfine (SHF) structure with the splitting between them A = 7.4 G for PC1 center, and a single wide line with the markedly different g-value, attributed to the PC2 one. Both these lines are also present in powder “amorphous” samples, but the SHF structure of the PC1 centers in them is not registered because of broadening the individual SHF components. Kinetics of defect accumulation with increasing dose D of the irradiation, and their gradual disappearance during prolonged storage of samples in air was discovered and studied. Kinetic equations were solved, and the D-dependence and decay times were found from the comparison of theoretical results with the experimental ones. It has been shown that the concentration of shallow and deep traps for electrons affect the rate of the decay process. The recovery process is much slower in the samples having a more perfect crystalline structure

Spectroscopical study of natural nanostructured carbonaceous material shungite

The correlation between morphology, local structure and magnetic properties of the different origin shungite material with nanocarbon content 25-40 wt. % was studied by SEM, EPR, and Raman scattering methods. It was established that structure of the shungite samples is formed by micron size agglomerations of carbon and silicon dioxide clusters with impregnations of pyrite (FeS₂), iron oxide and aluminium oxide particles. It was found from the Raman data that nanocarbon fraction is formed from sp²-hybridized well ordered carbon clusters, size of which increases from 9 nm up to 12 nm after annealing of the samples. It was found for the first time that origin of L3 and L4 EPR lines is due to oxy-deficiency centers in the silicon dioxide clusters