Optical properties of a new Bi38Mo7O78 semiconductor with fluorite-type δ-Bi2O3 structure

Abstract Bi 3+ -containing inorganic materials usually show rich optical and electronic properties due to the hybridization between 6s and 6p electronic components together with the lone pair in Bi 3+ ions. In this work, a new semiconductor of bismuth molybdate Bi 38 Mo 7 O 78 (19Bi 2 O 3 ·7MoO 3 ) was synthesized by the sol-gel film coating and the following heat process. The samples developed into nanoparticles with average size of 40 nm. The phase formation was verified via the XRD Rietveld structural refinement. Orthorhombic Bi 38 Mo 7 O 78 can be regarded to be derived from the cubic δ-phase Bi 2 O 3 structure. The microstructure was investigated by SEM, EDX, TEM, BET and XPS measurements. The UV-vis absorption spectra showed that the band gap of Bi 38 Mo 7 O 78 (2.38 eV) was greatly narrowed in comparison with Bi 2 O 3 (2.6 eV). This enhances the efficient absorption of visible light. Meanwhile, the conduction band of is wider and shows more dispersion, which greatly benefits the mobility of the light-induced charges taking part in the photocatalytic reactions. Bi 38 Mo 7 O 78 nanoparticles possess efficient activities on the photodegradation of methylene blue (MB) solutions under the excitation of visible-light. The photocatalysis activities and mechanisms were discussed on the crystal structure characteristics and the measurements such as photoluminescence, exciton lifetime and XPS results.