Band-gap engineering in novel delafossite-type multicomponent oxides for photocatalytic degradation of methylene blue

A series of novel mixed oxides with honeycomb layered structure viz. delafossite-type Na3M2SbO6 (where M = Cu; Ni; Cu, Ni; Cu, Ni, Co; Cu, Ni Co, Fe; Cu, Ni Co, Fe, Mn) were synthesized by a facile method. The synthesis involved heating of the metal precursors at 1100 °C followed by air quenching. The structure was analogous to that of Na3Ni2SbO6 (space group: C2/m). The effect of increased entropy on the Jahn-Teller distortion effect, as previously reported in M = Cu system, was evident from the X-ray diffraction (XRD)/Rietveld structural analysis. The as-synthesized oxides showed photocatalytic activity as confirmed by the degradation of methylene blue. This was correlated to a drop in the optical band-gap from 2.41 to 1.96 eV on increasing the number of elements as well as its effect on the band energies are proposed here.