perovskites of Sm2Ti2S2O5(Eg2.0 eV)

perovskites of Sm2Ti2S2O5(Eg2.0 eV) is known for water oxidation and reduction reaction for oxygen
and hydrogen evolution, respectively in presence of sacrificial agents under low photon energy
wavelengths of 650 nm. The band structure of this phase reveals that the presence of sulphur narrows
the band gap and enables visible light absorption [130].
Oxynitride compounds such as CaNbO2N, SrNbO2N, BaNbO2N, and LaNbON2belong to the
perovskite type crystal structures [131]. Photocatalytic hydrogen evolution has been reported under
visible light from methanol solution. SrNbO2N (Eg1.8 eV) has been investigated in detail, where the
photoelectrode of SrNbO2N on a transparent conducting surface shows water oxidation reaction under
no external bias [132]. Tantalum counterparts of these compounds weredeveloped and utilized in the
Z scheme photocatalysis. Compounds such as CaTaO2N and BaTaO2N were loaded with Pt
co-catalyst and coupled with pt/WO3for Z scheme water splitting [133]. A solid solution of BaTaO2N
and BaZrO3was formulated for hydrogen and oxygen evolution, which showed improved performance
compared with the individual photocatalysts under visible light [134]. LaTiOxNy is another perovskite
type compound which shows high photocurrentdensity under visible light [135].
Apart from the double perovskites belonging to the general formula AA'BB'O6, there are a several
other compounds that show crystal structures close to the perovskitetype structure, however such
compounds are not included in the current review. Theoretically, double perovskites offer a wider
scope to design photocatalysts by selecting suitable cations and AA' and BB' sites in the lattice. Work
on design and development of double perovskite is currentlylimited and synthesis and characterization
of new materials in thiscategory are needed.