Ultrasonication-Enhanced Reduction of Tetrabromobisphenol A by Activating Nascent H2 on Raney Ni Catalyst: Kinetics, Mechanisms, and Hydrogenation Pathways

The deep dehalogenation of polyhalogenated organic pollutants is receiving widespread attention. In this work, Raney Ni (R-Ni) catalyst with a sponge porous structure was selected, and nascent hydrogen (Nas-H₂) bubbles generated in situ from the cathode were used as a hydrogen source for tetrabromobisphenol A (TBBPA) hydrodebromination. The reaction conditions were first optimized by adjusting R-Ni dosage and Nas-H₂ production. On this basis, the investigation showed that the hydrogen utilization in the R-Ni/Nas-H₂ system was hundreds of times higher than that in the control group injected with regular hydrogen gas due to the refinement of hydrogen bubble size. Furthermore, the ultrasonication-enhanced R-Ni/Nas-H₂ system was constructed. The experimental results showed that the hot spots and microjets generated by cavitation promoted the dispersion of the R-Ni catalyst, the nanonization of Nas-H₂ bubbles, and the mass transfer. TBBPA degradation and the debromination ratio reached 94.6% and 68.2% in 2.0 h, respectively, in which the hydrogen adatoms (H_ads*) produced by the dissociative adsorption of hydrogen molecules are the active species. TBBPA debromination follows pseudo-first-order kinetics with a rate constant of 1.50 h^–1, which is 2.1 times higher than that without ultrasonication. In addition, TBBPA follows the gradual hydrodebromination, and the toxicity of the hydrogenated product decreases with the reduction of bromine atoms. The coupled ultrasonication and R-Ni/Nas-H₂ system may hold great potential for the efficient removal of TBBPA from contaminated water.