Efficient reductive debromination of 2,2′,4,4′-tetrabromodiphenyl ether on nano-Pd-decorated ZnIn₂S₄ photocatalyst

Polybrominated diphenyl ethers (PBDEs) represent a significant category of persistent organic pollutants (POPs) that are garnering increasing attention due to their environmental impact. This investigation details the efficient degradation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) facilitated by nano-Pd-modified ZnIn₂S₄ microspheres. At an optimal palladium loading of 0.1 %, BDE-47 exhibited an outstanding degradation efficiency of 99 % and the fastest reaction rate of 2.252 h⁻¹ within 3 h under visible light irradiation (λ > 420 nm) using methanol as the solvent and N,N-diisopropylethylamine as the hole-sacrificing agent. The nano-Pd modification significantly enhanced the migration of photogenerated carriers in ZnIn₂S₄, thereby improving the removal efficiency of BDE-47. The degradation pathway of BDE-47 involved stepwise debromination, with photo-generated electrons serving as the primary active species responsible for initiating the reductive debromination process. The BDE-47 reduction predominantly yielded 2,4,4′-tribromodiphenyl ether (BDE-28). Density functional theory calculation indicates that nano Pd interacts with the CBr bond in BDE-47, particularly the ortho-C-Br bond, which exhibits a stronger affinity for nano Pd compared to the CBr bond in the para-position. This is a key factor contributing to the efficient and priority removal of bromine atoms in the ortho-position. This study underscores the promising potential of Pd/ZnIn₂S₄ composites in the photocatalytic removal of halogenated environmental contaminants.