Influences of Amphiphiles on Dechlorination of a Trichlorobenzene by Nanoscale Pd/Fe: Adsorption, Reaction Kinetics, and Interfacial Interactions

Abstract

The influences of amphiphiles on the catalytic dechlorination of 1,2,4-trichlorobenzene (124TCB) bythe nanoscale Pd/Fe particles were comprehensively examined. The fresh and reacted Pd/ Fe particles were characterized with XRD, TEM, SEM, FTIR spectrometry, and goniometry. Adsorption of amphiphiles on the Pd/Fe particles, iron dissolution, and H2 evolution in the Pd/Fe-water system were quantified to expound the influences of the various amphiphiles on the dechlorination process. The Langmuir-Hinshelwood model is used to elucidate the dechlorination kinetics, and it provides insight into the influence of amphiphiles on 124TCB partitioning to the interfacial layer and the resulting dechlorination rates. The rate constants increased by a factor of 1.5--2.5 with the presence of cationic cetyltrimethylammonium bromide (CTAB). In the anionic sodium deodecyl sulfate(SDS) or nonionic nonylphenol ethoxylate (NPE) and octylphenolpoly (ethylene glycol ether)x (TX-100) surfactant solutions, the 124TCB dechlorination rates were slightly increased over those observed in ultrapure water. However, when concentrations of the surfactants were above their CMCs, the dechlorination rates decreased. The findings also showed that DPC (dodecylpyridinium chloride) and NOM (natural organic matter) might be the competitive H2 acceptors to 124TCB, and they significantly retarded its catalytic dechlorination by the Pd/Fe particles. CTAB at a concentration below the CMC appeared to be the most benign to the 124TCB dechlorination.