The reactivity of well-dispersed zerovalent iron nanoparticles toward pentachlorophenol in water.

In order to prevent the aggregation of nanoparticles (NPs), surface modification or the addition of a stabilizer are used for stabilization. However, the real reactivity of NPs is still unclear because of the surface coating. For different physical dispersion methods, the particle stabilization for nanoscale zerovalent iron (NZVI) particles and their reactivity are studied. The particle properties of different preparations and their reactivity toward one polychlorinated aromatic compound, pentachlorophenol (PCP), with different electrolytes are also evaluated. Ultrasonication (US) with magnetic stirring disperses NZVI and Pd/Fe NPs well in water and does not affect the surface redox property a lot under the operating conditions in this study. The well-suspended NZVI cannot dechlorinate PCP but adsorption removal is observed. Compared to shaking, which gives limited removal of PCP (about 43%), Pd/Fe NPs remove 81% and 93% of PCP from water in the US and the US/stirring systems, respectively, which demonstrates that a greater surface area is exposed because of effective dispersion of Pd/Fe NPs. As the Pd doping increases, the dechlorination kinetics of PCP is improved, which shows that a catalyst is needed. With US/stirring, chloride ions do not significantly affect the removal kinetics of PCP, but the removal efficiency increases in the presence of nitrate ions because PCP anions were adsorbed and coagulated by the greater amount of iron (hydro)oxides that are generated from the reduction of nitrate on Pd/Fe. However, bicarbonate ions significantly block the adsorption and reaction sites on the Pd/Fe NP surface with US/stirring. The US/stirring method can be used to evaluate the actual activity of NPs near the nanoscale. The use of Pd/Fe NPs with US/stirring removes PCP from water effectively, even in the presence of common anions expect a high concentration of bicarbonate.