Selective methane-to-methanol conversion in a biochar-mediated photocatalytic biohybrid system

Biological methane-to-methanol conversion is fundamentally constrained by an intrinsic trade-off between methanol accumulation and intracellular NADH regeneration, often motivating external electron supplementation, which can be inefficient. Herein, a biochar-mediated photocatalytic biohybrid system was constructed by integrating a biochar-TiO₂ composite with Methylosinus trichosporium OB3b for methane-to-methanol conversion. The system achieved a peak methanol yield of 10.89 mmol·L^-1 with a selectivity of 99.4%, combining relatively high methanol accumulation with high selectivity without the addition of sodium formate or methanol dehydrogenase (MDH) inhibitors. Mechanistic investigations support a dual-pathway synergistic electron-transfer model involving Cyt c-associated and quinone-associated electron-transfer processes during pMMO-related methane oxidation. This interfacial reconfiguration reduces the dependence of pMMO electron supply on NADH/Complex I-dependent electron entry, thereby partially decoupling pMMO turnover from endogenous respiratory electron flow. Concurrently, the resulting enhanced interfacial electron delivery contributes to a tri-level reoxidation suppression mechanism: preferential electron delivery may strengthen membrane-bound pMMO catalysis; kinetic modulation may generate a transient local methanol concentration gradient that favors outward methanol transport; and metabolic decoupling substantially reduces the metabolic requirement for downstream methanol oxidation to regenerate NADH. Collectively, this work establishes a light-driven strategy for selective methane valorization and advances the mechanistic understanding of interfacial electron transfer in photocatalytic biohybrid systems.