Dithionite can be used to reduce Fe(II) and produce nanoscale zero-valent iron (nZVI) under conditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfite hydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does not appear to affect their degradation performance under air or N2 gas conditions. The efficiency of trichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured using dithionite (nZVIS2O4), is similar to if not slightly better than that of the more conventional borohydride procedure (nZVIBH4). The other advantages of the dithionite method are that (i) it uses a less expensive and widely available reducing agent, and (ii) there is no production of potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The low oxidant yield based on hydroxybenzoic acid generation is offset by the production of higher concentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH• addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals (
) are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions.
