Antibiotic pollution in water is a growing global concern, as residues from human medicine, livestock production, and aquaculture can persist in the environment and contribute to the spread of antibiotic resistance. A new study shows that the molecular structure of antibiotics plays a decisive role in how effectively they can be removed from water using biochar, a carbon-rich material produced from agricultural waste.
Researchers investigated five widely used tetracycline antibiotics and examined how their structural differences influence adsorption onto rice straw biochar produced at high temperature. Their findings provide new insight into how pollutant chemistry governs removal efficiency and offer guidance for designing better biochar-based water treatment materials.
"Our work shows that not all antibiotics behave the same in water treatment systems," said the study's corresponding author. "Even subtle structural differences can change how strongly a molecule interacts with biochar surfaces, which ultimately determines how fast and how effectively it can be removed."
Tetracyclines are commonly detected in wastewater and surface waters because large fractions of administered antibiotics are excreted unmetabolized. Conventional treatment methods often fail to fully eliminate them, allowing residues to enter natural ecosystems where they can disrupt microbial communities and promote resistance genes.
To understand how molecular structure affects removal, the research team combined advanced spectroscopy, adsorption experiments, and quantum chemical modeling. Their results revealed that hydrogen bonding between amino groups on tetracycline molecules and carbonyl groups on biochar surfaces is the dominant interaction across different environmental conditions.
However, the strength of this interaction depends strongly on substituent groups attached to the antibiotic molecules. Compounds containing electron-donating functional groups showed enhanced adsorption, while electron-withdrawing substituents slowed the process. As a result, the five antibiotics displayed markedly different removal rates, with doxycycline and minocycline binding most rapidly and oxytetracycline showing the slowest adsorption.
The study also demonstrated that adsorption occurs in two stages: a rapid initial binding phase followed by a slower diffusion-controlled stage. By linking molecular descriptors to kinetic parameters, the researchers developed predictive models capable of estimating adsorption behavior based solely on chemical structure.
"This predictive capability is important," the lead author explained. "It means we can begin designing biochar materials tailored for specific pollutants instead of relying on trial and error."
Beyond improving water treatment, the findings highlight the potential for agricultural residues such as rice straw to be transformed into high-value environmental remediation materials. By optimizing pyrolysis conditions and surface chemistry, biochar could be engineered to selectively target classes of emerging contaminants.
The researchers emphasize that understanding pollutant structure is essential for improving remediation strategies in a world facing increasing chemical contamination.
"As new pharmaceuticals enter the environment, we need smarter materials and smarter models to remove them," the author said. "This study provides a framework for linking molecular chemistry with environmental cleanup performance."
The team hopes their work will guide future efforts to develop low-cost, sustainable adsorbents capable of removing antibiotics and other emerging pollutants from water systems worldwide.
===
Journal reference: Yao J, Ji J, Zhang J, Fang J. 2026. Molecular structure-dependent adsorption mechanisms of tetracycline antibiotics congeners on biochar. Biochar X 2: e008 doi: 10.48130/bchax-0026-0007
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0007
===
About the Journal:
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.
