Biochar is produced by heating biomass under oxygen-limited conditions and is widely studied for agriculture, environmental remediation, and energy storage. Its persistent free radicals can promote reactions that remove pollutants, but they can also generate reactive oxygen species associated with oxidative stress and disruption of soil microorganisms. Understanding their concentration and chemical character is therefore essential for balancing useful reactivity against potential harm. Previous studies have linked radical properties to elemental composition and chemical structure, yet relationships established for limited feedstocks may not transfer to other biochars. Nonlinear relationships and differences among biomass sources have complicated broader prediction.
A study (DOI: 10.48130/bchax-0026-0020) published in Biochar X on 17 August 2026 by Wenmei Tao's team, Kunming University of Science & Technology, shows that elemental descriptors predict radical properties and reveal distinct compositional patterns associated with radical accumulation and oxygen-centered radical formation.
The researchers collected 263 paired records of radical concentration and g-Factor from published studies, removed outliers, standardized concentration units, and used carbon, hydrogen, oxygen, hydrogen-to-carbon ratio, and oxygen-to-carbon ratio as model inputs. The g-Factor, measured by electron paramagnetic resonance spectroscopy, provides an indicator of whether radicals are predominantly carbon-centered or oxygen-centered. Data were randomly divided into 80% for training and 20% for testing. Six approaches were compared: XGBoost, gradient boosting, support vector regression, a shallow neural network, random forest, and an ensemble averaging predictions from four models. SHAP analysis, feature importance, and partial dependence plots were used to explain the predictions. For independent experimental verification, the team prepared biochars from cellulose, lignin, peanut hulls, rice straw, and pine sawdust by heating them at 300–800 °C under nitrogen for one hour. Elemental analysis and electron paramagnetic resonance measurements then linked composition with radical properties. The shallow neural network achieved the highest test R² values, reaching 0.7797 for radical concentration and 0.7647 for g-Factor. Across the models, discrimination between high and low values was also strong, with areas under receiver operating characteristic curves of at least 0.9600 for concentration and above 0.9780 for g-Factor. Model interpretation associated lower hydrogen-to-carbon ratios and lower oxygen contents with greater radical accumulation, whereas higher oxygen contents and oxygen-to-carbon ratios favored higher g-Factors, consistent with more oxygen-centered radicals. Laboratory correlations supported these rankings, with oxygen content and oxygen-to-carbon ratio showing Spearman correlations of 0.905 and 0.882 with g-Factor. At similar oxygen-to-carbon ratios, higher hydrogen content also increased g-Factor. However, experiments indicated that heating above 600 °C could promote carbon condensation and graphitization accompanied by radical disappearance, showing that accumulation does not increase indefinitely as hydrogen-to-carbon ratios decline. These findings suggest that elemental composition captures useful predictive information, while the underlying structural transformations remain important for interpreting trends.
Together, the results connect accessible elemental measurements with biochar’s radical behavior and provide an interpretable framework for further material optimization. The approach could support selection of biochars for environmental applications, although differences in measurement settings among published studies introduce uncertainty, and practical performance and ecological safety require application-specific testing.
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References
DOI
10.48130/bchax-0026-0020
Original Source URL
https://doi.org/10.48130/bchax-0026-0020
Funding information
This research was supported by National Natural Science Foundation of China (Grant Nos 42207286, 42567031), Yunnan Fundamental Research Projects (Grant Nos 202401AT070385, 202201BE070001-041), and Yunnan Key Laboratory of Efficient Utilization and Intelligent Control of Agricultural Water Resources, Yunnan Intelligent Water, Fertilizer and Pesticide Integration Technology and Equipment Innovation Team, Yunnan Seasonal Arid Area, Yunnan Water and Soil Crop System Observation and Research Station.
About Biochar X
Biochar X (e-ISSN 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.