The max of UV–visible spectra for as synthesized ZnO nanopar-ticles, ZnO nanoparticles (hydrothermal) and ZnO flowers werefound at 369, 375 and 388 nm respectively (Fig. S2, ESI) The calcu-lated band gaps energy for these wavelengths are 3.37 eV, 3.31 eVand 3.20 eV, respectively [29]. The ZnO flowers show a very broadvisible absorption peak. The BET specific surface areas measuredfor ZnO nanoparticles, nanoparticles (hydrothermal) and flowersare found to be 12, 22 and 27 m2g−1, respectively.