In order to develop original and efficient visible light response photocatalysts for degrading organic pollutants in wastewater, new photocatalysts Bi₂GaSbO₇ and Bi₂InSbO₇ were firstly synthesized by a solid-state reaction method and their chemical, physical and structural properties were characterized. Bi₂GaSbO₇ and Bi₂InSbO₇ were crystallized with a pyrochlore-type structure and the lattice parameter of Bi₂GaSbO₇ or Bi₂InSbO₇ was 10.356497 Å or 10.666031 Å. The band gap of Bi₂GaSbO₇ or Bi₂InSbO₇ was estimated to be 2.59 eV or 2.54 eV. Compared with nitrogen doped TiO₂, Bi₂GaSbO₇ and Bi₂InSbO₇, both showed excellent photocatalytic activities for degrading methylene blue during visible light irradiation due to their narrower band gaps and higher crystallization perfection. Bi₂GaSbO₇ showed higher catalytic activity compared with Bi₂InSbO₇. The photocatalytic degradation of methylene blue followed by the first-order reaction kinetics and the first-order rate constant was 0.01470 min-1, 0.00967 min-1 or 0.00259 min-1 with Bi₂GaSbO₇, Bi₂InSbO₇ or nitrogen doped TiO₂ as a catalyst. The evolution of CO₂ and the removal of total organic carbon were successfully measured and these results indicated continuous mineralization of methylene blue during the photocatalytic process. The possible degradation scheme and pathway of methylene blue was also analyzed. Bi₂GaSbO₇ and Bi₂InSbO₇ photocatalysts both had great potential to purify textile industry wastewater.
Keywords: Bi2GaSbO7; Bi2InSbO7; methylene blue; photocatalysts; photocatalytic degradation; visible light irradiation.