COMPARISON OF THE REACTIVITY OFNANOSIZED ZERO-VALENT IRON (nZVI) PARTICLESPRODUCED BY BOROHYDRIDE ANDDITHIONITE REDUCTION OF IRON SALTS

摘要

Dithionite can be used to reduce Fe(II) and produce nanoscale zero-valent iron (nZVI) underconditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfitehydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does notappear to affect their degradation performance under air or N_2gas conditions. The efficiency oftrichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured usingdithionite (nZVIs_2O_4), is similar to if not slightly better than that of the more conventionalborohydride procedure (nZVI_(BH)_4). 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 productionof potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVIs_2O_4particlesresults in different byproducts than those produced when nZVI_(BH_4)particles are used. The lowoxidant yield based on hydroxybenzoic acid generation is offset by the production of higherconcentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acidssuggests that OH~ addition is not the primary oxidation pathway when one is using the nZVIs204particles. It is proposed that sulfate radicals (SO_4~(-) ) are produced as a result of hydroxyl radicalattack on the sulfite matrix surrounding the nZVIs_2O_4particles, with these radicals oxidizingbenzoic acid via electron transfer reactions rather than addition reactions.