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<p>Groundwater often contains both organic pollutants and heavy metals like Cr(VI). Traditional photocatalysts struggle to handle both at once because their charge carriers compete and recombine. We built a new S‑scheme heterojunction by growing β‑FeOOH nanodomains on nitrogen‑doped defect‑engineered biochar (N‑DEB). This carbon‑mineral structure strongly separates charges and preserves high‑energy electrons and holes. Under visible light, the composite degrades phenol (84.6% TOC removal), carbamazepine (64.3%), and nonylphenol (75.5%) while reducing Cr(VI) efficiently. In mixed solutions, Cr(VI) reduction speeds up by ~ 55% because phenol scavenges holes—a true synergy, not competition. ESR and scavenger tests show simultaneous production of ·OH and ·O₂⁻ radicals. The catalyst remains stable over five cycles (Fe leaching &lt; 0.05&#xa0;mg L<sup>−1</sup>) and works well in simulated groundwater with natural organic matter and competing anions. Finally, a stacked machine learning model (R2≈0.96) predicts reaction kinetics, and SHAP analysis confirms that irradiation time and pollutant concentration control the rate. This work offers a durable, predictive, and truly bidirectional photocatalytic platform for cleaning mixed groundwater contaminants.</p>

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Lignocellulose-derived nitrogen-doped defect-engineered biochar coupled with β-FeOOH for S-scheme bidirectional redox photocatalytic degradation of mixed groundwater pollutants: mechanisms and predictive kinetic modeling

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Vignesh Jagajeevan,
  • Vidhya Lakshmi Sivakumar

摘要

Groundwater often contains both organic pollutants and heavy metals like Cr(VI). Traditional photocatalysts struggle to handle both at once because their charge carriers compete and recombine. We built a new S‑scheme heterojunction by growing β‑FeOOH nanodomains on nitrogen‑doped defect‑engineered biochar (N‑DEB). This carbon‑mineral structure strongly separates charges and preserves high‑energy electrons and holes. Under visible light, the composite degrades phenol (84.6% TOC removal), carbamazepine (64.3%), and nonylphenol (75.5%) while reducing Cr(VI) efficiently. In mixed solutions, Cr(VI) reduction speeds up by ~ 55% because phenol scavenges holes—a true synergy, not competition. ESR and scavenger tests show simultaneous production of ·OH and ·O₂⁻ radicals. The catalyst remains stable over five cycles (Fe leaching < 0.05 mg L−1) and works well in simulated groundwater with natural organic matter and competing anions. Finally, a stacked machine learning model (R2≈0.96) predicts reaction kinetics, and SHAP analysis confirms that irradiation time and pollutant concentration control the rate. This work offers a durable, predictive, and truly bidirectional photocatalytic platform for cleaning mixed groundwater contaminants.