  We demonstrated crystal structures, magnetic, optical, and photocatalytic
properties of the B-site substituted double perovskite
Ba$_{2}$Pr(Bi$_{1-x}$Sb$_{x}$)O$_{6}$ ($x$=0, 0.1, 0.2, 0.5 and 1.0)
synthesized by the citrate pyrolysis method. The single-phase polycrystalline
samples with the light Sb substitution crystallized in a monoclinic structure
($I2/m$). Magnetization measurements on all the samples showed that the
effective magnetic moments are located around 3 $\mu_{B}$ , indicating the
valence mixing states between Pr$^{3+}$ and Pr$^{4+}$.The magnitudes of band
gap energy for the two end member samples were estimated from the optical
measurements to be $E_{g}$ =1.06 eV at $x$=0 and 2.71 eV at $x$=1.0. The
Ba$_{2}$Pr(Bi$_{1-x}$Sb$_{x}$)O$_{6}$ ($x$=0, and 0.1) powders obtained by the
present technique exhibited enhanced photocatalytic activities when compared to
the same compounds prepared by the conventional solid state method. Our
findings suggest that the higher photocatalytic activities strongly depend on
powder preparation method as well as the band gaps and charge separation.
