Insight into enhanced tetracycline photodegradation by hematite/biochar composites: Roles of charge transfer, biochar-derived dissolved organic matter and persistent free radicals

Qian Liu; Zhuoyue Wang; Ting Chang; Tingxin Wang; Yafeng Wang; Zhilei Zhao; Meifeng Li; Jue Liu

doi:10.1016/j.biortech.2025.132118

Insight into enhanced tetracycline photodegradation by hematite/biochar composites: Roles of charge transfer, biochar-derived dissolved organic matter and persistent free radicals

Bioresour Technol. 2025 Jan 25:420:132118. doi: 10.1016/j.biortech.2025.132118. Online ahead of print.

Authors

Qian Liu¹, Zhuoyue Wang¹, Ting Chang¹, Tingxin Wang², Yafeng Wang³, Zhilei Zhao¹, Meifeng Li⁴, Jue Liu⁵

Affiliations

¹ National&Local Joint Engineering Research Center of Metrology Instrument and System, College of Quality and Technical Supervision, Hebei University, Baoding 071002, China.
² National&Local Joint Engineering Research Center of Metrology Instrument and System, College of Quality and Technical Supervision, Hebei University, Baoding 071002, China. Electronic address: tingxinwang@126.com.
³ Yunnan Provincial Key Laboratory of Soil Carbon Sequestration and Pollution Control, Faculty of Environmental Science & Engineering, Kunming University of Science &Technology, Kunming, 650500, China.
⁴ Department of Chemical and Materials Engineering, University of Alberta, Edmonton T6G2R3, Canada.
⁵ National&Local Joint Engineering Research Center of Metrology Instrument and System, College of Quality and Technical Supervision, Hebei University, Baoding 071002, China. Electronic address: jueliu@buaa.edu.cn.

PMID: 39870140
DOI: 10.1016/j.biortech.2025.132118

Abstract

The combination of hematite and biochar significantly accelerated tetracycline (TC) removal under visible light irradiation. The k_init of TC removal with Hem/BC-5 reached 0.103 min^-1, 3.8 and 6.1 times faster than those with hematite and biochar, attributed to boosting free radicals. The enhanced light absorption and charge transfer helped generate more H₂O₂ and •OH through 2e^- oxygen reduction and direct valence band (VB) oxidation. Persistent free radicals (PFRs) on biochar helped generate H₂O₂. Biochar as electron shutter facilitated Fe³⁺/Fe²⁺ redox cycling and triggered more efficient photo-Fenton reaction. Biochar-derived dissolved organic matter (DOM) helped generate ³DOM*, a reactive intermediate to produce H₂O₂, •OH, and ¹O₂. Hem/BC composites have excellent photoactivity for the degradation of TC in different water matrixes under visible light irradiation. The degradation pathway was proposed based on theoretical calculation and detected degradation intermediates. These findings contribute to the development of biochar-based catalysts for organic pollutants removal.

Keywords: Biochar; Free radicals; Hematite; Photoactivity; Redox cycling.