Complete dehalogenation of chloramphenicol by bimetallic alloy Pd-Au nanoparticles in a H2-Based membrane Catalyst-Film reactor

An effective treatment method to achieve complete dehalogenation of halogenated antibiotics is an urgent affair, because partially dehalogenated products remain persistent pollutants and sometimes having higher toxicity than the original antibiotics. This study is the first to achieve complete reductive dechlorination of chloramphenicol (CAP) using bimetallic alloy Pd-Au nanoparticles (Pd-AuNPs) in a hydrogen (H2)-based membrane catalyst-film reactor (H2-MCfR). Compared to mono-Pd nanoparticles (PdNPs), bimetallic alloy Pd-AuNPs gave faster removal and more complete dechlorination of CAP in batch and continuous-flow experiments. Notably, complete CAP dechlorination was achieved with a catalyst film of Pd-AuNPs (mole ratio 1:1) that had negligible catalyst loss in a 20-day continuous operation. LC-MS identified the products of reductive dechlorination, and the dominant pathways differed significantly between PdNPs and Pd-AuNPs. In particular, Pd-AuNPs favored reductive dechlorination, while PdNPs favored reduction of the -NO2 group, which led to partially dechlorinated products that were stable. Density functional theory (DFT) calculations showed how the Au atoms reduced the adsorption energy of reactants, which affected reaction selectivity. Toxicity prediction model confirmed that reducing dechlorination significantly decreased acute toxicity to fish, daphnia and green algae. Thus, the MCfR with Pd-AuNP catalysts offers promise for achieving complete dechlorination of CAP and inspires further studies for other halogenated antibiotics.