Bismuth–titanium oxide nanopowders prepared by sol–gel method for photocatalytic applications

• Bismuth–Titanium oxide nanopowders were synthesized by the sol–gel technique.
• The evolution of the different crystalline phases was determined.
• Materials with band gap as low as 1.4 eV were obtained.
• Good photocatalytic activity using visible light was observed.

TiO2 has been widely studied for photocatalytic applications; however, its band gap is so large (Eg = 3.2 eV for anatase) that it can only be excited by ultraviolet light which accounts for only 5% of the incoming solar energy. Thus, it is important to develop a visible light driven photocatalyst with a lower band gap value. For this purpose, different TiO2–Bi2O3 binary compounds were prepared by the sol–gel technique. The obtained materials were characterized by Energy Dispersed Spectroscopy, X Ray Diffraction, Transmission Electron Microscopy, Raman Spectroscopy and Diffuse Reflectance Spectroscopy, in order to obtain information on their chemical composition, crystalline structure, vibrational features and optical properties. Compositional characterization reveal that the Bi content can be varied from 0.3 to 43.6 at.% in an easy way in the binary compounds. Structural characterization shows that the starting material corresponds to the crystalline anatase phase of TiO2 and upon Bi addition a phase transition to bismuth titanates and finally to bismuth oxide occurs. Raman results suggest the formation of titanates for compounds with a low content of Bi whilst for higher metal contents a mixture of oxides is obtained. HRTEM results demonstrated that the prepared nanopowders are quite crystalline. Optical measurements reveal that the band gap narrows from 3.2 eV to values as low as 1.4 eV. The photocatalytic activity was tested in the degradation of Malachite Green dye under illumination using a solar simulator with good results.

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