Maleic acid photocatalytic degradation using Fe-TiO2 catalysts: Dependence of the degradation mechanism on the Fe catalysts content

The photocatalytic degradation of maleic acid by using Fe-doped (0.15, 0.5, 2 and 5% w/w in Fe) TiO2 catalysts has been studied. Catalysts with the lowest Fe content (0.15 and 0.5%) show a considerably better catalytic behavior than non-doped TiO2 and catalysts with higher Fe contents. Maleic acid molecules interact with the surface of the lowest Fe-containing catalysts and as a consequence, iron atoms are extracted from the catalyst surface as photoactive Fe3+–maleic acid complexes. When this complex is degraded, the resulting Fe2+ ions react with TiO2 holes (h+) and the iron return to the catalyst surface as Fe2O3. In catalysts with low Fe content (0.15 and 0.5% w/w in Fe) the quite and return of the metal to the surface occurs in a fast way. On the contrary, in catalysts with high Fe content (2 and 5% w/w in Fe) the formation of less photoactive complexes seems to predominate. FTIR studies have proven the formation of such complexes in the doped catalysts.