ZnO and Co-ZnO nanorods—Complementary role of oxygen vacancy in photocatalytic activity of under UV and visible radiation flux

Enhancement in photoactivity of zinc oxide, a UV active photocatalyst, can be achieved through nanostructuration in addition to doping induced red-shift in absorption spectrum. For this, nanorods of cobalt-doped-ZnO (Co-ZnO) were synthesized by hydrothermal method. As expected, Co-ZnO nano-rods showed high photocatalytic activity in degradation of methylene blue dye (MB) and phenol under visible radiation flux compared to pristine ZnO nano-rods, synthesized identically. XRD, SEM, TEM, EDX, UV-DRS, PL and FTIR studies were used to characterize the photocatalysts. ZnO and Co-ZnO, both had wurtzite phase of ZnO with nano-rod morphology having length:diameter of 440 nm:120 nm and 1460 nm:162 nm, respectively. Surprisingly, under UV light the ZnO-nanorods showed more activity than Co-ZnO. These contrasting results, when correlated with dopant-induced quenching of oxygen vacancies, indicated toward complementary role of oxygen vacancy in the photoactivity of the materials with the dominant role of band gap-assisted red-shift in the absorption spectrum.