Environmental application of millimetre-scale sponge iron (s-Fe0) particles (III): The effect of surface silver

Abstract

To enhance the dechlorination reactivity of millimetric sponge iron (s-Fe0), a facile one-pot method was used to decorate s-Fe0 with Ag+ ions under ambient conditions. The results recorded by X-ray diffraction patterns, X-ray photoelectron spectra and high-resolution transmission electron microscopy demonstrated that the growth of Ag0 was dominated primarily by (111) plane with a mean length of ∼20nm. The roles of Ag0 loading, catalyst dosage, particle size, initial pH and contaminant concentration were assessed during the removal of pentachlorophenol (PCP). Catalyst recyclability was also studied. The results revealed that 3–5mm s-Fe0 particles with 5wt% Ag0 loading exhibited the best performance with a dose of 3.0g per 60mL PCP solution. In addition, the dechlorination of PCP followed two-step, pseudo-first-order reaction kinetics, and Ag0-s-Fe0 was advantageous compared with bimetals of nanoscale zero-valent iron, iron power and iron flakes. The dechlorination mechanism of PCP over Ag0-s-Fe0 was attributed to the surface Ag0 decoration, which catalyzed the formation of reactive hydrogen atoms for indirect reaction, and the direct electron transfer via Fe–Ag0 galvanic cells for direct reaction. This suggests that Ag-based bimetals of s-Fe0 have great potential in the pretreatment of organic halogen compounds in aqueous solution.