Photocatalytic degradation of methylene blue on Bi 2MNbO 7 (M = Al, Fe, In, Sm) sol–gel catalysts

Abstract

Photocatalysts with general formula Bi 2MNbO 7 (M = In, Al, Fe, Sm) have been prepared following the sol–gel method by gelling niobium ethoxide with bismuth acetate and In, Al, Fe and Sm precursors. XRD, TGA/DTA, FT-IR, UV–vis, SEM and nitrogen adsorption techniques were used to characterize the solids. The evolution of the crystalline phases of the sol–gel samples with the annealing temperature was followed by XRD. At annealing temperatures lower than 400 °C crystalline Bi 2MNbO 7 phases were not detected, while at 800 °C only pyrochlore phase was observed. The energy band gap values were found from the UV–vis spectra of the samples calcined at 400 °C between 1.43 and 2.24 eV. Kinetic t 1/2 (half life) parameters for the photodegradation of methylene blue shown that Bi 2FeNbO 7 sol–gel catalysts were more active ( t 1/2 = 13 min) than TiO 2 P-25 ( t 1/2 = 45 min) reference photocatalyst. For comparative purposes solid state preparations of Bi 2MNbO 7 were also studied, showing a lower photocatalytic activity than the sol–gel preparations but it was in the same order of TiO 2 P-25 catalyst.