This article reports on two novel strontium bismuthate photocatalysts (Sr 6Bi 2O 11 and Sr 3Bi 2O 6) prepared by a solid-state synthesis for which the number of strontium atoms exceeds the number of bismuth atoms in the cation sublattice; for comparison, the bismuthate Sr 2Bi 2O 5 was also re-examined. All three bismuthates were characterized by a variety of spectroscopic techniques (XRD, XPS, EDX, DR, Raman, SEM, and EIS). Direct bandgap energies for the three bismuthates were assessed from diffuse reflectance spectra: 2.61 eV for Sr 6Bi 2O 11; 3.40 eV for Sr 3Bi 2O 6; 3.17 eV for Sr 2Bi 2O 5, while the flatband potentials (versus NHE) of the corresponding valence bands were estimated from XPS spectra: +2.22 eV for Sr 6Bi 2O 11; +1.71 eV for Sr 3Bi 2O 6; +1.61 eV for Sr 2Bi 2O 5. The two novel bismuthates displayed photocatalytic activity toward the photodegradation of acetaldehyde in the gas phase and phenol in aqueous media, with the Sr 6Bi 2O 11 system exhibiting significantly greater photoactivity vis-à-vis the Sr 3Bi 2O 6 bismuthate; by comparison, Sr 2Bi 2O 5 was photocatalytically inactive in this case; their photoactivity was also assessed from the photodegradation of phenol in aqueous media (in all cases using UV-Vis irradiation from a Xe light source). Detailed photocatalytic mechanisms are proposed based on UV-induced coloration studies (carried out using a high-pressure Hg lamp; 365 nm) and on the photodegradation in the presence of radical scavengers to explain how composition and structure of the three bismuthates affect their photocatalytic activity. The role of point defects (oxygen vacancies) in their crystal lattice is described as they affect photocatalytic activity by acting as electron traps and potentially as electron/hole recombination centers.
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