B-Modified Pd Cathodes for the Efficient Detoxification of Halogenated Antibiotics: Enhancing C-F Bond Breakage beyond Hydrodefluorination.

Abstract

Halogenated antibiotics pose a great threat to aqueous environments because of their persistent biotoxicity from carbon-halogen bonds. Electrochemical reduction (ER) is an efficient technology for dehalogenation, but it still suffers from limited efficiencies in breaking C-F bonds. Herein, we present a strategy to enhance C-F cleavage and promote detoxification by loading benchmark palladium cathodes onto boron-doped carbon. This improves the florfenicol (FLO) degradation rate constant and defluorination efficiency by 1.24 and 1.05 times, respectively, and improves the defluorination of various fluorinated compounds. The cathode with optimal B content shows superior mass activity for FLO degradation (1.11 mmol g^-1 Pd min^-1), which is 5.9 times that of commercial Pd/C and is among the best-reported cathodes. Notably, the exclusive formation of the direct defluorination product (i.e., FLO-F) on Pd/B-C implies a higher intrinsic C-F cleavage ability endowed by B doping. As revealed by experiments and theoretical calculations, boron modification enhances palladium binding and induces stronger strain effects and higher electron density for surface palladium atoms, which boosts H* generation and reduces the energy barrier for C-F cleavage. This study provides an effective cathode design strategy to enhance C-F activation, which may broadly benefit the destruction and detoxification of fluorinated organics that are limited by sluggish C-F cleavage kinetics.