Degradation of Trichloroethylene and Methylene Blue by a Mixture of Fe0 and γ-Fe2O3 A Review

In this chapter, relationships between local structure and organic compounds decomposing ability of Fe-0 + y-Fe2O3 mixture were introduced by applying gas chromatography (GC), ultraviolet-visible light absorption spectroscopy (UV-VIS), electrospray-ionized mass spectroscopy (ESI-MS), X-ray diffractometry (XRD) and Fe-57-Mossbauer spectroscopy. Decrease in concentration of trichloroethylene (TCE) aqueous solution from 10.0 to 0.09 mg L-1 was observed from 10-day decomposition test using mixture of industrially produced Fe-0 (zero valent iron) and iron oxide mainly composed by gamma-Fe2O3 with the total amount and the mass ratio of 5.0 g and 3:7, respectively. 57Fe-Mossbauer spectra of iron+iron oxide mixture during the decomposition test showed decrease in the absorption area (A) of iron from 40.6 to 1.0 %, and increase in 'A' attributed to Fe25+O6 octahedra (O-h) from 15.4 to 49.2 %, indicating that iron+iron oxide mixture is converted to Fe3O4 caused by an oxidation of Fe. A consistent first order rate constant (k) of 0.30(+/- 0.01) day(-1) for oxidation of iron in the iron+iron oxide mixture and decomposition of TCE was estimated, indicating that TCE was decomposed by the oxidation from Fe to Fe25+(O-h)O-6 in Fe3O4. A precipitation of Fe3O4 due to oxidation from Fe-0 to Fe2.5+(O-h)O-6 was also observed from the decomposition test using Fe-0+gamma-Fe2O3 (3:7) bulk mixture and 10 mu mol L-1 methylene blue (MB) aqueous solution. The k value of MB decomposition determined to be 6.5(+/- 09) x 10(-3) h(-1) becomes larger when using nanoparticles (NPs) of gamma-Fe2O3 (k = 1.2(+/- 0.1) x 10(-1) h(-1)), suggesting that the increase in surface area of gamma-Fe2O3 NPs affects the effectiveness of MB decomposing ability. It is concluded that Fe-0+gamma-Fe2O3 mixture can be utilized for environmental purification, and organic compounds decomposing ability can be enhanced by using iron or iron oxide nanoparticles.