Multiphasic bi-component TiO₂–ZnO nanocomposite: synthesis, characterization and investigation of photocatalytic activity under different wavelengths of light irradiation

Nano-composite of biphasic (mixed phase) titania and monophasic (wurtzite) zinc oxide was synthesized by sol–gel method and characterized using, XRD, SEM, EDAX, TEM, UV–DRS PL and FTIR. The structural analysis from XRD reveals the formation of multiphasic TiO₂–ZnO (TARZ) nanocomposite with TiO₂ in anatase–rutile mixed phase (TAR) and ZnO in wurtzite phase (ZW). The nano-composite with an average crystallite size of 15.3 nm shows a red shift in the absorption spectrum with the band-gap of 2.91 eV. The photoactivity of the composite TARZ in the degradation of methylene blue under UV and visible irradiation was found to be higher than the individual components. In UV irradiation nanocomposite shows 1.46 and 1.13 times higher photoactivity than TAR and ZW, respectively. But in visible irradiating it is 2 and 4 times higher than the TAR and ZW, respectively. Further, the study of the photocatalyst, under different near monochromatic light sources, indicates that the sharp increase in visible light activity may be attributed to the synergy of the components and the band-offset at the hetero-junction in addition to small particle size, and elevated and/or extended absorption spectrum.