Hollow mesoporous SiO₂-BiOBr nanophotocatalyst: Synthesis, characterization and application in photodegradation of organic dyes under visible-light irradiation

In this paper, a novel visible-light-driven hollow mSiO₂-BiOBr (H-mSiO₂-BiOBr) nanophotocatalyst was successfully synthesized by a facile three-step method. First, the hollow mesoporous silica submicrospheres with orderly mesoporous opening structure and an independent internal cavity were synthesized by combining Stöber hydrolysis and chemical etching. Second, the hollow mesoporous silica submicrospheres were functionalized by 3-triethoxysilylpropylamine (APTES), then the amino-groups were successfully introduced into the surface of this material. Third, the BiOBr nanophotocatalyst with size of about 8-15 nm was successfully synthesized on the surface of the aforementioned amino-functionalized hollow mesoporous silica submicrospheres by solvothermal synthesis with the aid of the oriented function of the surface amino-groups. After several characterizations of the materials, the photocatalytic degradation of RhB by this H-mSiO₂-BiOBr nanophotocatalyst under visible-light irradiation was investigated. The experimental results revealed that the photocatalytic activity of the H-mSiO₂-BiOBr nanophotocatalyst was higher than that of the core-shell SiO₂@mSiO₂-BiOBr nanophotocatalyst under visible-light irradiation. More importantly, the nanoscale BiOBr photocatalyst, which was synthesized by controlling the addition amounts of the bismuth source, would lead to an increased band gap (1.47 eV), and it would further lead to the effective restraint for the recombination of the photoexcited electron-hole pairs. However, the rapid migration of the interface charges would enhance the photoactivity of this novel supported nanophotocatalyst significantly. Furthermore, the existence of the internal cavities of this novel nanophotocatalyst would lead to the multiple reflections of the irradiated light and effectively prolong its action time, which is also very conducive to the enhancement of the photoactivity of this supported nanophotocatalyst. Beyond that, the orderly mesoporous opening structure and the independent internal cavities can effectively facilitate the transfer of reactant molecules. This would lead to the enhanced photocatalytic performance of this novel supported BiOBr nanophotocatalyst.