Photocatalytic degradation of formic acid using Fe/TiO2 catalysts: the role of Fe3+/Fe2+ ions in the degradation mechanism

The photocatalytic degradation of formic acid by Fe-doped (0.5, 2 and 5% w/ w in Fe) and calcined (773 and 1073 K) TiO2 has been studied. For 773 K cal cined catalyst, results suggest that Fe is extracted through the formation of a [Fe-OOCH](2+) complex by which formic acid degrades. Fe2+ ions that re main in solution after formic acid degradation go back to the catalyst surf ace and are oxidized by photogenerated holes. In this way the catalyst is r eactivated becoming ready for a new degradation process. The formation of h ydrogen-carbonates on the TiO2 catalyst through OH radicals insertion has b een detected by FTIR. This way the formic acid degradation by OH insertion is inhibited and the formation of [Fe-OOCH](2+) complex is favored. On the other hand, a markedly lower capacity for the formic acid degradation has b een determined fur the 1073 K calcined catalysts. This behavior can be attr ibuted to the lower surface area and the major presence of lower active pha ses such as rutile and Fe2TiO5. (C) 2001 Elsevier Science B.V. All rights r eserved.