A new study reveals that a small but powerful component of biochar, known as dissolved organic matter, plays a surprisingly large role in capturing toxic lead from contaminated water. The research, published in Biochar, uncovers how this dissolved material enhances the metal-binding power of biochar and offers molecular-level insights that could guide safer and more effective cleanup strategies.
Biochar, a carbon-rich substance produced by heating crop residues or other organic waste in limited oxygen, has been widely used to immobilize heavy metals in soils and water. However, scientists have long puzzled over why biochar made at lower temperatures often shows higher metal removal efficiency. The new study provides an answer.
Researchers from Northeast Agricultural University and collaborating institutions compared the ability of regular and water-washed biochar to capture lead ions. When the biochar's dissolved organic matter was removed by washing, its lead adsorption capacity dropped by nearly two-thirds, from 96 to 35 milligrams per gram. This dramatic decline pointed to a hidden but essential role of the dissolved organic fraction.
Using a suite of advanced spectroscopic tools, including infrared spectroscopy, X-ray photoelectron spectroscopy, and multidimensional fluorescence analyses, the team mapped how lead interacts with the functional groups present in biochar and its dissolved components. They found that oxygen-containing groups such as hydroxyl, carboxyl, carbonyl, and ether groups form strong chemical complexes with lead, rather than relying solely on physical trapping. Most of the bound lead was identified as stable compounds such as basic lead carbonate, indicating that chemical complexation is the dominant mechanism of immobilization.
Fluorescence and ultraviolet analyses further revealed that the dissolved organic matter in biochar is far from uniform. It contains multiple humic-like components, each showing different reactivity toward lead. Among them, one component rich in humic and tyrosine-like substances showed the strongest binding affinity. Additional two-dimensional correlation analyses demonstrated that carboxyl groups in humic substances respond most rapidly and strongly to lead exposure, confirming that these groups serve as key binding sites.
"By combining several complementary spectroscopic methods, we could visualize how different molecular sites within dissolved organic matter interact with lead," said corresponding author Professor Song Cui of Northeast Agricultural University. "These insights help explain why certain types of biochar perform better in removing heavy metals and how we can design them more effectively."
The findings provide not only a mechanistic understanding of biochar's interaction with lead but also a scientific foundation for developing next-generation biochar materials enriched with reactive carboxyl and humic-like structures. Such materials could significantly improve the stability and efficiency of heavy-metal remediation in real environmental conditions.
The authors emphasize that future work should examine how biochar interacts with mixtures of metals and under varying pH levels that mimic natural soils and waters. Understanding these complex interactions will be critical for scaling up biochar-based technologies to protect ecosystems and human health from heavy-metal pollution.
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Journal Reference: Zhang, F., Zhou, B., Fu, Q. et al. Binding mechanisms of Pb(II) adsorption by biochar-derived dissolved organic matter: unraveling site heterogeneity and kinetics through advanced spectral analysis. Biochar 7, 116 (2025). https://doi.org/10.1007/s42773-025-00522-7
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About Biochar
Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
