Photodegradation of thiacloprid using Fe/TiO2 as a heterogeneous photo-Fenton catalyst

Three Fe/TiO2 photocatalysts with different content of Fe (1.9, 7.2 and 13.9%, w/w) were synthesized by a simple deposition-precipitation method and characterized by XRD, SEM, N-2 physisorption at 77K and Mossbauer spectroscopy. The characterization showed the presence of nano-sized Fe2O3 particles (less than 4 nm) on the TiO2 support. The photocatalytic efficiency of the catalysts was examined on the example of thiacloprid (TCL) degradation under UV light irradiation in aqueous suspension in the presence/absence of H2O2. Since the efficiency of TCL degradation in the presence of H2O2 (heterogeneous photo-Fenton process) was more than two times higher, all other investigations were conducted in the presence of H2O2. The photocatalyst with 7.2%, w/w Fe (denoted as 7.2Fe/TiO2) appeared to be most efficient. The photocatalytic degradation studied under different operating conditions indicated that 0.5 g L-1 of 7.2Fe/TiO2 was an optimal catalyst loading, and the optimal pH was 2.8. In the investigated range of initial concentrations of TCL (0.06-0.32 mM) the photocatalytic degradation in the first stage of the reaction followed approximately a pseudo-first order kinetics. The suspended Fe/TiO2 spontaneously precipitated once the stirring of the reaction mixture was terminated (>90% after 15 min). The results clearly demonstrated that 7.2Fe/TiO2 was stable and resistant to photocorrosion during the photocatalytic degradation of TCL The higher efficiency of 7.2Fe/TiO2 compared to Degussa P25 under the optimal experimental conditions of TCL photodegradation, spontaneous precipitation of the suspension, possibility of reusing the catalyst, as well as an insignificant increase in the iron concentration in water solution, all this indicates the possibility of the practical application of this photocatalyst for water treatment. (C) 2011 Elsevier B.V. All rights reserved.