Modification of Pd-Fe nanoparticles for catalytic dechlorination of 2,4-dichlorophenol.

To reveal how different dispersants influence the dispersity and physicochemical properties of palladium/iron nanoparticles (Pd/Fe NPs), we modified Pd/Fe NPs with poly(methylmethacrylate) (PMMA), polyacrylic acid (PAA) and cetyltrimethylammonium bromide (CTAB) respectively and obtained three hybrid NPs denoted M-Pd/Fe NPs, A-Pd/Fe NPs and C-Pd/Fe NPs. The physical properties of the three hybrid Pd/Fe NPs were studied, together with their behaviors in the room-temperature dechlorination in aqueous solution of 2,4-dichlorophenol (2,4-DCP). Dispersant effects of the three dispersants were observed, as well as changes in the properties of resulted Pd/Fe NPs. The pristine Pd/Fe NPs experienced more severe oxidation than A-Pd/Fe NPs, while there was no evidence for the presence of oxidation phase of M-Pd/Fe NPs and C-Pd/Fe NPs. Degradation results showed that compared with pristine Pd/Fe NPs, the catalytic dechlorination efficiency of 2,4-DCP with modified Pd/Fe NPs increased by 23%-58% within a given reaction period of 20 min. The role of dispersants themselves in dechlorination properties of Pd/Fe NPs is more significant than that of volume ratio of PAA to water, weight ratio of PMMA to anisole and volume ratio of water to ethanol in determining the properties of A-Pd/Fe, M-Pd/Fe and C-Pd/Fe NPs, respectively. Studies on the kinetics of 2,4-DCP reacted with Pd/Fe NPs in our cases implied that their behaviors didn't match the first- or pseudo-first-order kinetics: because the presence of oxidation phases on the surface of pristine Pd/Fe NPs and the dispersants on the surface of NPs could influence the diffusion of 2,4-DCP onto reactive sites, thus affecting the whole degradation process. So, an innovatively revised kinetics was proposed in the study for considering the effects of oxidation phases and the dispersants.