Chemical etching fabrication of uniform mesoporous Bi@Bi₂O₃ nanospheres with enhanced visible light-induced photocatalytic oxidation performance for NO_x

Bulk materials with a microporous structure are adverse to light adsorption, photoelectron and reactant transport in a photocatalytic reaction. Mesoporous photocatalysts have shown many marked advantages in photocatalytic fields. Herein, uniform mesoporous Bi@Bi₂O₃ nanospheres were fabricated by HCl–ethanol chemical etching at low temperature (60 °C). The obtained mesoporous photocatalysis increased the NO removal efficiency (16%) and inhibited toxic NO₂ generation (3%) under visible light irradiation. Further oxidation of Bi and calcination at high temperatures were avoided during template removal. Moreover, the as-prepared sample possessed a remarkably narrower pore size distribution (3.2–3.9 nm) and stronger light and NO adsorption ability than the bulk microporous Bi@Bi₂O₃. Work function and the electron spin resonance test results also indicated that the position of the entire energy bands on Bi₂O₃ was lowered. The amount of reactive oxygen species generated over the uniform mesoporous structure was higher than that over bulk Bi@Bi₂O₃. However, photoelectrochemical measurements indicated that the separation efficiencies of the photo-generated carriers were not improved over the uniform mesoporous Bi@Bi₂O₃. Comprehensive studies have shown that the oxidation ability rather than the enhanced separation efficiency of charge carriers accounted for the enhanced photocatalytic activity. This work elucidates the roles of a uniform mesoporous structure in NO_x photocatalytic oxidation and provides an efficient strategy for structural engineering in preparing highly reactive and practical photocatalysts.