  A comprehensive comparison between Bi$_{25}$FeO$_{40}$-reduced graphene
oxide(rGO) nanocomposite and BiFeO$_{3}$-rGO nanocomposite has been performed
to investigate their photocatalytic abilities in degradation of Rhodamine B dye
and generation of hydrogen by water-splitting. The hydrothermal technique
adapted for synthesis of the nanocomposites provides a versatile
temperature-controlled phase selection between perovskite BiFeO$_{3}$ and
sillenite Bi$_{25}$FeO$_{40}$. Both perovskite and sillenite structured
nanocomposites are stable and exhibit considerably higher photocatalytic
ability over pure BiFeO$_{3}$ nanoparticles and commercially available Degussa
P25 titania. Notably, Bi$_{25}$FeO$_{40}$- rGO nanocomposite has demonstrated
superior photocatalytic ability and stability under visible light irradiation
than that of BiFeO$_{3}$-rGO nanocomposite. The possible mechanism behind the
superior photocatalytic performance of Bi$_{25}$FeO$_{40}$-rGO nanocomposite
has been critically discussed.
