Geoconductor function of graphitized biochar redirects microbial Fe(III) reduction and stimulates hydroxyl radical production in paddy soil

Abstract Integrating biochar into paddy soil as a hybrid geobattery–geoconductor material offers a transformative approach for sustainable soil decontamination. However, biochar often has an undeveloped graphitized structure and poor geoconductor function, restricting the electron transfer capacity for microbial Fe(III) reduction and subsequent •OH generation. In this study, the flash Joule heating method was used to enhance the graphitized structure of biochar to redirect microbial Fe(III) reduction via a geoconductor function-induced electron self-adaptation pathway. Specifically, a highly conductive framework of graphitized biochar (G-biochar) with a 2.64-fold enhancement in electrical conductivity unchoked the electron transfer obstacle between Fe(III)-reducing bacteria ( Bacillus , Anaeromyxobacter , Citrifermentans , and Flavisolibacter ) and Fe(III), This mechanistic improvement resulted in 18.9% increase in active Fe(II) generation. Accordingly, 54.9% increase in •OH production and 57.2% increase in the sulfamethoxazole degradation rate were evidenced. Finally, G-biochar differentially promoted microbial Fe(III) reduction in various paddy soils, which mainly depended on the activity of the reducing microbial community. These findings redefine the biochar trade-off effect on soil microbial–geochemical processes via the geoconductor function rather than the previously acknowledged geobattery electron reservoir mixing strategy. Graphical Abstract