Visible-light photoactivity of Bi-pyrochlores with high Fe contents.

Three Bi-pyrochlores with different Fe contents (Bi(2)Ti(2)O(7), Bi(1.65)Nb(1.12)Fe(1.16)O(7) and Bi(1.9)Te(0.58)Fe(1.52)O(6.87)) were synthesized in the form of nanopowders with similar morphological characteristics. All three nanopowders show an intensive visible-light photocatalytic activity. The analysis of their band gap and absorption characteristics has shown a strong correlation with the Fe-content indicating that a significant band gap reduction can be obtained by Fe incorporation. The photocatalytic activity has not followed this trend. The initial increase in the Fe-content has resulted in a significant enhancement of the photoactivity while with the further increase the photoactivity has slowly decreased. The reason for this behaviour has been proposed to be in an opposing influence of the increased exciton density and recombination rate.