Enhancement of nitrobenzene degradation by co-pyrolysis biochars in sulfide-mediated aqueous environment:adsorption and reduction contribution

In-situ reductive remediation is promising for groundwater treatment due to the natural abundance and stability of sulfides. This study developed co-pyrolysis biochars from wormwood (W) and lobster shells (L) to enhance sulfide-driven nitrobenzene (NB) reduction. The biochars were produced at varying W:L ratios (1:0, 3:1, 1:1, 1:3 and 0:1) and pyrolyzed under 700°C. The co-pyrolyzed W1L1 (W: L ratio = 1:1) significantly enhanced the reduction removal capacity of NB compared to biochar from single biomass, achieving 99.2% NB removal (sulfide: 2 mM, pH: 9) with the pseudo-first-order kinetic constant (k obs = 0.021 h -1 ) for the reduction reaction stage. The enhancement mechanism involves: (i) NB pre-adsorption via microporosity and π–π interactions, (ii) The synergistic contributions—wormwood provided adsorption sites, while lobster shells introduced graphitic nitrogen (facilitating electron transfer) and oxygen-containing groups (promoting sulfide activation). (iii) The enhancement in electron transfer ability due to the high electrochemical surface area (0.123 cm 2 ) and low charge transfer resistance (R ct = 150.8 Ω). Furthermore, the applicability of co-pyrolysis biochar in NB removal was demonstrated across varied reaction conditions and groundwater environmental factors. The reduction pathway of NB proceeded via a three-step, two-electron transfer process, ultimately yielding aniline, with nitrosobenzene detected as an intermediate. These findings establish co-pyrolysis biochars as sustainable materials for in-situ NB remediation.