Research on the influence of light on persistent free radicals in coal

In this study, the effect of light on the persistent free radicals and functional groups in coal samples with different degrees of deterioration was investigated by the equilibrium light experiment. Spectral characteristics, concentration, g-value and linewidth changes of persistent free radicals in coal samples before and after illumination were analyzed by electron paramagnetic resonance technique; Changes in the content of major functional groups were determined using diffuse reflectance Fourier transform infrared spectroscopy. The results show that the mechanism of photo-oxidation on the properties of persistent free radicals in coal depends mainly on the chemical structure characteristics of coal. Among them, the spectral characteristics, persistent free radicals concentration and line width variation of anthracite were significantly lower than those of other coal types. The g values of all coal samples showed a decreasing trend as the heteroatomic structure decreased and the proportion of aromatic structure increased in the coal. Post-illumination, coal functional group compositions vary markedly with metamorphic degrees, especially for aromatic, aliphatic and oxygen-containing groups. Low-metamorphism coal is rich in oxygen-containing groups and aliphatic side chains, while high-metamorphism coal has elevated aromatic content, verifying its chemical stability.