Enhanced visible-light photocatalytic activity of Bi2MoO6 nanoplates with heterogeneous Bi2MoO6-x@Bi2MoO6 core-shell structure

A series of Bi2MoO6 (BMO) nanoplates with a heterogeneous Bi2MoO6-x@Bi2MoO6 core/shell structure were successfully obtained by reduction with CaH2 at 140 degrees C and subsequent reoxidation in air under low temperatures (<= 250 degrees C). It is found that the oxygen vacancies mainly exist in the core, while the shell is formed by surface disorder layer with few oxygen vacancies, which is almost stoichiometric. The controllable growth of the surface disorder layer can be realized by the reduction and/or reoxidation temperatures. The reoxidized BMO with the surface disorder layer exhibits about five times higher visible-light photocatalytic activity toward phenol degradation and an order of magnitude higher activity toward methylene blue (MB) degradation than those of the unmodified sample. The visible-light absorption is mainly dominated by the oxygen vacancies through the modulation of the band gap structure, which promote the solar light utilization and photogenerated charge carriers. Density functional theory calculation shows that BMO is a direct band gap semiconductor. It is suggested that the surface disorder layer could suppress the direct recombination of photogenerated carriers and improve surface reactivity, and results in the enhancement of the photocatalytic activity. In addition, the existence of the stoichiometric surface disorder can promote the catalyst stability. It is demonstrated that the reduction- reoxidation method applied here is simple, easily control, and beneficial for the design and realization of heterogeneous core-shell nanostructured photocatalysts to improve visible and infrared optical absorption by engineering the surface disorder and the oxygen vacancies inside core of Bi2MoO6 nanoplates and the related nanostructured photocatalysts.