Photocatalytic degradation of methylene blue on Bi2MNbO7 (M = Al, Fe, In, Sm) sol–gel catalysts

Photocatalysts with general formula Bi2MNbO7 (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 Bi2MNbO7 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 t1/2 (half life) parameters for the photodegradation of methylene blue shown that Bi2FeNbO7 sol–gel catalysts were more active (t1/2 = 13 min) than TiO2 P-25 (t1/2 = 45 min) reference photocatalyst. For comparative purposes solid state preparations of Bi2MNbO7 were also studied, showing a lower photocatalytic activity than the sol–gel preparations but it was in the same order of TiO2 P-25 catalyst.

Graphical abstractSol–gel Bi2FeNbO7 compound treated at 400 °C presents in the methylene blue decomposition the higher photocatalytic activity (t1/2 = 13 min) compared with similar composition prepared by solid state reaction (t1/2 = 37 min). Moreover, sol–gel preparations are most active than the well-know TiO2 (Degussa P-25) photocatalyst (t1/2 = 45 min). Figure optionsDownload full-size imageDownload as PowerPoint slide