| Autor: |
Krasnov AG; Institute of Chemistry, Federal Research Center Komi Science Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Russia., Napalkov MS; Institute of Chemistry, Federal Research Center Komi Science Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Russia.; Syktyvkar State University, Syktyvkar, Russia., Vlasov MI; Ural Federal University, NANOTECH Center, Ekaterinburg, Russia.; Institute of High Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences, Ekaterinburg, Russia., Koroleva MS; Institute of Chemistry, Federal Research Center Komi Science Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Russia., Shein IR; Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences, Ekaterinburg, Russia., Piir IV; Institute of Chemistry, Federal Research Center Komi Science Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Russia. |
| Abstrakt: |
The photocatalytic properties of Bi 2- x Ti 2 O 7-1.5 x ( x = 0, 0.5) pyrochlores are examined via ab initio calculations and experiments. A coprecipitation method is applied for the synthesis of nanopowder pyrochlores. The pyrochlore phase formation starts at 500 °C (Bi 2 Ti 2 O 7 ) and 550 °C (Bi 1.5 Ti 2 O 6.25 ). Nanopowders are found to be a metastable character of pyrochlore phases. The presence of bismuth and oxygen vacancies enhances the thermal stability of the Bi 1.5 Ti 2 O 6.25 phase in comparison with the Bi 2 Ti 2 O 7 phase. The estimated crystallite size is 30-40 nm with noticeable agglomerates of about 100-300 nm according to scanning electron microscopy (SEM) and with the formation of particles (510-580 nm) in the aqueous medium. The isoelectric points of the nanopowders seem to be shifted to the strongly acidic region, resulting in the formation of negative surface particle charges of -33 mV (Bi 2 Ti 2 O 7 ) and -27 mV (Bi 1.5 Ti 2 O 6.25 ) at pH 5.88 in distilled water. The specific surface area is 11.5 m 2 /g (Bi 2 Ti 2 O 7 ) and 12.00 m 2 /g (Bi 1.5 Ti 2 O 6.25 ). The use of the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional allows achieving an excellent agreement between theoretical and experimental structural parameters. The screened Coulomb hybrid HSE03 functional is the most appropriate for describing the optoelectronic properties. Bismuth titanate pyrochlores are wide-gap semiconductors with strong abilities to be active photocatalysts under visible irradiation. The optical E g values for direct/indirect transition according to the experiment, 3.19/2.94 eV ( x = 0) and 3.24/3.03 eV ( x = 0.5), and the DFT/HSE03 calculations, 2.92/2.87 ( x = 0) and 3.42/- eV ( x = 0.5), are in the visible light region and are close. The calculated low effective masses of the charge carriers and suitable band edge positions confirm the ability of the pyrochlores to act as photocatalysts. The photocatalytic activity has been evaluated through the decomposition of rhodamine B under visible irradiation. Bi 2 Ti 2 O 7 shows the highest activity in comparison with Bi 1.5 Ti 2 O 6.25 , which is in good agreement with theoretically predicted and experimentally revealed characteristics. |
