Catalytic debromination of 2, 2′, 4, 4′ – Tetrabromodiphenyl ether by low-cost mechanochemically synthesized graphite-doped oxalated Fe/Ni bimetals: Enhanced generation of adsorbed atomic H and secondary risk control

Abstract

In this work, a cost-effective ball-milling technique was employed to synthesize submicron oxalated zero-valent iron co-doped with graphite and nickel (G@Fe_OX^bm/Ni), aiming to enhance the removal efficiency of the recalcitrant pollutant 2, 2′, 4, 4′ – tetrabromodiphenyl ether (BDE-47) while minimizing secondary risks. The incorporation of graphite significantly improved the debromination efficiency of BDE-47, with a rate constant of 0.26 day⁻¹ in a tetrahydrofuran/water system, which represents a 59.88 % increase over the oxalated zerovalent Fe/Ni without graphite (0.16 day⁻¹). The determination of Ni leaching showed that no nickel ions were detected post-reaction over a broad pH range (3–11). Moreover, the reactivity of G@Fe_OX^bm/Ni was largely unaffected across the pH range (0.26–0.49 day⁻¹), exhibiting excellent resistance to acidic and alkaline conditions. In both ultrapure water and real groundwater matrices, the degradation rate constants for BDE-47 increased to 2.98 day⁻¹ and 0.79 day⁻¹, respectively, achieving debromination yields of 97.86 % and 50.18 % for the final product, diphenyl ether. Based on the established degradation pathway and electrochemical analysis, the debromination of BDE-47 follows a catalytic debromination and hydrogenation process by adsorbed atomic hydrogen (H*_ADS). The graphite doping enhanced the debromination of BDE-47 by increasing the production of H*_ADS. The adsorption effect of graphite on metal ions effectively controlled secondary pollution and improved the material’s tolerance to acidic and alkaline environments. This work offers an efficient method for the degradation of low brominated diphenyl ether pollutants at a low cost and without secondary risks.