Biochar derived from nitrogen-rich pyrolysis of biomass can be used as a soil conditioner, but it contains a large amount of environmental persistent free radicals (EPFRs). EPFRs are a newly identified environmentally harmful substance, and the detection and research on EPFRs in nitrogen-rich pyrolyzed char is lacking. Biochars prepared from cellulose-urea mixtures at different temperatures, residence times, and urea ratios were analyzed in this study. EPFRs in biochar prepared at 500 °C had the highest spin concentrations. Substituted aromatic compounds were the precursors to the EPFRs. The types of EPFRs in biochars shifted from oxygen-centered at 400 °C to carbon- and oxygen-centered in the 450–600 °C range due to a reduction in oxygen-containing functional groups. Residence time experiments showed that most EPFRs formed in the first 5 min of pyrolysis. C was the main element used for the formation of EPFRs, while N content was negatively correlated with the concentration of EPFRs. Pyrolysis temperature was the key factor determining the types of EPFRs produced, while proportion of urea only affected the concentrations of EPFRs and not type. The results of this study are of great significance for understanding the environmental behavior of common EPFRs in nitrogen-rich biochar.

生物质富氮热解得到的生物炭可用作土壤调节剂，但它含有大量的环境持久性自由基（EPFR）。EPFRs是一种新发现的对环境有害的物质，对富氮热解焦炭中EPFRs的检测和研究尚缺乏。本研究分析了在不同温度、停留时间和尿素比例下由纤维素-尿素混合物制备的生物炭。在 500 °C 下制备的生物炭中的 EPFR 具有最高的自旋浓度。取代的芳香族化合物是 EPFR 的前体。由于含氧官能团的减少，生物炭中 EPFR 的类型从 400°C 的氧中心转变为 450-600°C 范围内的碳和氧中心。停留时间实验表明，大多数 EPFR 在热解的前 5 分钟内形成。C是形成EPFRs的主要元素，而N含量与EPFRs的浓度呈负相关。热解温度是决定所产生EPFRs种类的关键因素，而尿素的比例只影响EPFRs的浓度而不影响其种类。本研究结果对了解富氮生物炭中常见EPFRs的环境行为具有重要意义。