Hybrid-valence carbon-coated iron as an electron pump to stimulate microbial reductive dechlorination of chlorophenols.

Microbial reductive dechlorination is a prospective strategy for remediating chlorophenol-contaminated groundwater, yet its practical application is frequently constrained by inefficient electron transfer and the accumulation of toxic intermediates, particularly 4-chlorophenol (4-CP). Although iron-based materials have been widely employed to stimulate microbial dechlorination, uncontrolled electron release and limited biocompatibility often compromise their long-term performance. Here, we developed carbon-coated iron materials with tunable iron valence states and investigated their ability to promote the microbial reductive dechlorination of 2,4-dichlorophenol (2,4-DCP). Among the tested materials, hybrid-valence Fe(0&II)@C exhibited the highest dechlorination efficiency and reduced residual 4-CP by 94.6% compared with microbial dechlorination alone, effectively overcoming the major bottleneck of chlorophenol bioremediation. Integrated electrochemical characterization and X-ray photoelectron spectroscopy revealed that the hybrid Fe(0)/Fe(II) structure sustained continuous electron donation through Fe(II)/Fe(III) redox cycling, while the conductive carbon shell facilitated efficient electron delivery to dechlorinating microorganisms. This hybrid-valence architecture therefore functioned as an electron pump, enabling controlled and sustained electron transfer rather than rapid electron depletion. Meta-omics analyses identified key reductive dehalogenase genes, including DBB.rdh and cprA3, with WCHB1-27 identified as an active host. Enhanced cytochrome c and type TV pili-associated genes suggested potential contribution of Geobacter in interfacial electron transfer and Fe(III) cycling. These microbial and functional shifts were accompanied by the formation of electroactive biofilms on the material surface, collectively promoting efficient reductive dechlorination and suppressing 4-CP accumulation. This study establishes a mechanistic framework for integrating conductive iron-carbon materials with dechlorinating microbiomes and provides an electron-pump strategy for enhancing the bioremediation of chlorophenol-contaminated groundwater.