Paddy soils are living chemical reactors. Under flooded and drained conditions, microbes, minerals, oxygen, and organic matter constantly exchange electrons, shaping how pollutants move, transform, or disappear. A new study published in Biochar reports that a specially engineered form of biochar can redirect these electron flows, helping paddy soils generate more hydroxyl radicals, one of nature's most powerful oxidants, and break down the antibiotic sulfamethoxazole more efficiently.
The research team prepared graphitized biochar, or G-biochar, using flash Joule heating, a rapid electrical heating method that reorganizes the carbon structure of conventional biochar. Unlike ordinary biochar, which often acts mainly as an electron storage material, G-biochar behaved more like an electrical conductor in soil. Its enhanced graphitized framework increased electrical conductivity by 2.64 times, allowing electrons to move more easily between Fe(III)-reducing bacteria and iron minerals.
"We found that graphitized biochar does not simply store electrons. It helps guide them to where they are needed in the soil system," said corresponding author Xiangdong Zhu. "This geoconductor function creates a more efficient electron transfer pathway between microorganisms and iron minerals, which then supports the production of reactive oxidants."
In paddy soils, microbial Fe(III) reduction plays a central role in producing active Fe(II) species. These Fe(II) species can react with oxygen during redox fluctuations and promote the formation of hydroxyl radicals. Hydroxyl radicals are highly reactive molecules that can oxidize many organic pollutants, including antibiotics that enter agricultural soils through manure, wastewater, and irrigation.
The study found that G-biochar increased active Fe(II) generation by 18.9% compared with untreated soil. This improvement was linked to the enrichment of Fe(III)-reducing bacteria, including Bacillus, Anaeromyxobacter, Citrifermentans, and Flavisolibacter. The conductive G-biochar appeared to support these microbial communities by easing electron transfer, creating a self-reinforcing cycle in which more active bacteria supplied more electrons for iron reduction.
This microbial and geochemical shift had a clear environmental effect. G-biochar boosted hydroxyl radical production by 54.9% and increased the degradation rate of sulfamethoxazole by 57.2%. In the experimental system, sulfamethoxazole degradation reached 100% after 120 hours with G-biochar, compared with 79.8% using conventional biochar and 46.3% in the blank treatment.
"The key message is that biochar's environmental function can be redesigned by tuning its carbon structure," said first author Hua Shang. "By strengthening the graphitized network, we transformed biochar from a passive amendment into an active electron-transfer bridge for soil remediation."
The team also tested G-biochar in different paddy soils, including red soil, cinnamon soil, and black soil. G-biochar enhanced hydroxyl radical production in all three, although the strongest effect occurred in black soil, where microbial reducing activity was highest. This suggests that soil type and microbial community structure will influence how well G-biochar performs in real-world remediation.
The findings challenge the traditional view that biochar improves soil redox processes mainly through a "geobattery" role, where oxygen-containing functional groups store and release electrons. Instead, the study highlights the importance of the geoconductor function, in which graphitized carbon structures provide a direct and stable pathway for electron movement.
By revealing how electrically conductive biochar can stimulate microbial iron cycling and pollutant degradation, the study offers a new strategy for sustainable soil decontamination in rice-growing regions. Future work may explore how G-biochar performs under field conditions and how its structure can be optimized for different soils and pollutants.
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Journal Reference: Shang, H., Jia, C., Wu, S. et al. Geoconductor function of graphitized biochar redirects microbial Fe(III) reduction and stimulates hydroxyl radical production in paddy soil. Biochar 8, 92 (2026).
https://doi.org/10.1007/s42773-026-00597-w
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About Biochar
Biochar (e-ISSN: 2524-7867) 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.
