Comparison of reactivity of persistent free radicals on tobacco stem biochar
QIU Shu-yue1,2, ZHAO Ze-ying1,2, CHEN Fang-yuan1,2, LI Fang-fang1,2, DUAN Wen-yan1,2
1. Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, China; 2. Yunnan Provincial Key Laboratory of Carbon Sequestration and Pollution Control in Soils, Kunming 650500, China
Abstract：In this study, tobacco stem biochar prepared at different pyrolysis temperatures (300℃, 500℃ and 700℃) was used for the adsorption and degradation of organic pollutants p-nitrophenol (PNP). The aim of this research was to explore the relationship between the intensity of environmental persistent free radicals (EPFRs) on tobacco stem biochar and its reactivity towards organic pollutants degradation. The results showed that the intensity of EPFRs in the tobacco stem biochar increased from 6.155×104 to 1.343×105 at first and then declined to 5.458×104 with the increase of pyrolysis temperature, while the degradation rate of PNP remained unchanged at around 31% and then declined to 14.64% with the increase of pyrolysis temperature. These phenomena indicated that the intensity of EPFRs in biochar was not directly correlated to its reactivity. The oxygen-centered EPFRs in biochar pyrolyzed at 300℃ could transfer electrons to oxygen molecules in the water and generate reactive oxygen species (ROS), thus promote the degradation of PNP. The carbon-centered EPFRs in biochar pyrolyzed at 500℃ and 700℃ could be consumed after reacting with water or pollutants, and the newly generated free radicals were stabilized on the surface of biochar, which led to a significant increase in their intensity but their degradation activity declined dramatically.
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