Evolution and prediction model of environmentally-persistent free radicals in biomass three-component pyrolytic carbon with pyrolysis temperature

To clarify the evolution mechanism of environmentally-persistent free radicals (EPFRs) in biochar as a function of pyrolysis temperature, three-component pyrolytic carbon was characterized by electron paramagnetic resonance (EPR) spectroscopy. Four types of EPFRs were distinguished by using the peak splitting method. The EPFRs in three-component pyrolytic carbon obtained at a pyrolysis temperature of 300 degrees C were mainly oxygen-containing free radicals (57.31-83.63 %). Upon increasing the pyrolysis temperature, simple aromatic ring radicals were formed by the dehydrogenation of biomass, and then the polymeric aromatic radicals formed, accompanied by pi-electron delocalization to form phenyl-pi radicals. Biomass pyrolysis was simulated by mechanically mixing the three components in different proportions. A comparison of the experimental and theoretical values indicated that interactions between the three components did not obviously affect the EPFR concentration in the range of 450-550 degrees C, with a maximum relative error of 12.78 %. A prediction model for the EPFRs concentration in multi-component pyrolytic carbon was proposed. This study also clarified the generation and transformation mechanisms of EPFRs in three-component pyrolytic carbon, thus providing guidance for generating and regulating biochar EPFRs.

Automated summary

The evolution mechanism of EPFRs in three-component pyrolytic carbon was characterized using EPR spectroscopy. The types of EPFRs changed with increasing pyrolysis temperature, shifting from oxygen-containing free radicals to aromatic ring and polymeric aromatic radicals. The interaction between the three components did not significantly affect the concentration of EPFRs. This study provides guidance for the generation and regulation of EPFRs in biochar.