Sol–gel synthesis of iron titanates for the photocatalytic degradation of cyanide

Iron titanate mixed metal oxides were synthesized by the sol–gel method through four different routes. The effect of (i) the solvent of iron precursor, (ii) the addition of the chelating agent to the titanium or iron solution and (iii) the molar ratio between the chelating agent and the titanium or iron precursor over the overall percentage of obtained iron titanates was evaluated. Fourier-transform infrared spectroscopy (FTIR) and UV–Vis spectroscopy (UV–Vis) performed on the reaction medium evidenced the formation of acetate complexes of titanium (IV) or iron (III) during the different routes. X-ray diffraction (XRD) patterns of the obtained materials showed the formation of ilmenite (FeTiO₃), pseudorutile (Fe₂Ti₃O₉) and pseudobrookite (Fe₂TiO₅) in different proportions, as well as hematite (Fe₂O₃), rutile [TiO₂ (R)] and anatase [TiO₂ (A)]. The materials with the highest content of iron titanates obtained in each route were characterized and evaluated in the photocatalytic degradation of cyanide using visible light irradiation. UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS) showed that the samples exhibited energy bandgap values between 2.31 and 2.90 eV, which agrees with the values reported for iron titanates and evidence the possible activation of the materials under visible light. Scanning electron microscopy (SEM) and nitrogen physisorption results showed that the synthesized materials exhibited nanometric particle size and lower surface area (36.7 ± 4.8 m²·g^-1) than TiO₂ Degussa P-25 (72–155 m²·g^-1). The photocatalytic performance of the synthesized materials toward oxidation of CN⁻ exceeded by 56% the activity of pure TiO₂. The content of iron titanates in the synthesized materials was found to be the variable with the greatest influence on the photodegradation of cyanide. In addition, an inversely proportional relationship between the pseudorutile content of the materials and their photocatalytic activity was observed.