Catalytic generation of adsorbed atomic H for degradation of 2,2',4,4'-tetrabromodiphenyl ether by mechanochemically prepared Ni-doped oxalated zero-valent iron

Abstract

In the homologous series of polybrominated diphenyl ethers (PBDEs), the debromination of low-brominated diphenyl ethers with higher toxicity remains a challenge. Nano zero-valent iron (nZVI) has been extensively studied for the debromination of PBDEs, but its inherent direct electron transfer mechanism is less efficient for low-brominated diphenyl ethers, and there are issues with high preparation costs. In this work, we synthesize Ni-doped oxalated submicron ZVI (Fe_OX^bm/Ni) using a low-cost ball-milling method. Fe_OX^bm/Ni exhibits a debromination rate constant of 0.48 day^-1 for 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47) in tetrahydrofuran (THF)/water. The debromination rate of Fe_OX^bm/Ni for BDE-47 in water is even faster (0.98 day^-1), with the yield of the complete debromination product, diphenyl ether, reaching 76.71%. In real groundwater, Fe_OX^bm/Ni also shows high reactivity toward BDE-47, with a rate constant of 0.33 day^-1. Kinetic experiments, quenching experiments, and degradation pathway indicate that the attack of atomic hydrogen on C-Br bonds is the primary degradation mechanism. Electrochemical analysis further show that Ni⁰ sites could cleave hydrogen into absorbed atomic hydrogen (H*_ABS) and adsorbed atomic hydrogen (H*_ADS), with H*_ADS playing the main role. These findings contribute valuable insights into advancing the large-scale application of ZVI and offer promising strategies for thorough remediation of PBDEs pollution.