Cellulose-based mugwort biochar constructs p-n heterojunction micro interfaces to regulate the photocatalytic oxidation of As(III) by ferromanganese ions

•Lignin removal excludes the influence of complex components and enriched ions in the reaction.•The delignified cellulose base exposes more hydroxyl groups to stabilize the metal ions.•Construction of p − n heterojunctions on the micro surface of biochar to increase active sites.•The electron beam disproportionates Mn(III), which in turn generates Fe(III) to oxidize As(III).•FMBC−LR2 − 650 oxidized As(III) 12.31 times more than the original biochar BC. The utilization of a low-cost common waste biomass, mugwort, with a porous structure is important for the treatment of Arsenic (III) pollution in the aquatic environment. In this study, mugwort straw was first delignified to expose more hydroxyl groups, then loaded with MnOOH and α − FeOOH and constructed with p − n heterojunctions on cellulosic biochar microinterfaces. The successful formation of p − n heterojunction effectively enhances the electric field enhancement inside the photocatalyst, promotes charge transfer and suppresses the recombination of photogenerated carriers. Application of high-energy electron beam irradiation of FMBC−LR2 to modulate the generation and dominant mechanism of Fe and Mn in the reaction system. The results showed that Mn3+ underwent disproportionation reaction to form Mn2+ and Mn4+. Among them, Mn2+ led to the formation of MnFe2O4, while Mn4+ exhibited stronger oxidizing properties that could promote the transformation of Fe2+ to Fe3+, thus allowing more Fe3+ to participate in the photocatalytic oxidation of As(III) in a synergistic manner. As(III) oxidation efficiency increased 9.18 times after delignification treatment (FMBC−LR2) and 12.31 times after high-energy electron beam irradiation (FMBC−LR2 − 650) as compared to mugwort straw biochar (BC). In addition, the EPR assay results indicated that ·O2−, ·OH, and 1O2 acted together in the As(III) reaction. This provides new insights into the remediation of composite modified biochar in water bodies and a new environmentally friendly strategy for the comprehensive utilization of straw materials.