Improved Photoresponse of Sunlight-driven Mnn+-ZnO (n=2, 4, 7) Nanostructures: A Study of Oxidative Degradation of Methylene Blue

Sunlight driven Mnn+-ZnO (n = 2, 4 and 7) nanohybrids were prepared via impregnation method using different metal precursors of variable oxidation state. Dynamic light scattering (DLS) spectra showed that the average hydrodynamic size decreased when precursor of higher Mn oxidation state was used. Moreover, the structural analysis revealed that Mn nanoparticles (5-10 nm, d = 0.13 nm) dispersed over ZnO support (20-30 nm, d = 0.39 nm) while KMnO4 was added for impregnation purpose. Interestingly, the co-catalyst (Mn) was loaded in + 2, +4 and + 7 oxidation state when MnSO4.H2O, MnO2 and KMnO4 respectively utilized for loading over ZnO surface, confirmed from X-ray photon spectroscopy. The potential of prepared nanocomposites were investigated for methylene blue (MB) degradation, an organic pollutant and it was observed that oxidation state of the co-catalyst largely influenced the photoactive-response of nanocomposites. Notably, Mn7+-ZnO degraded MB (98%) nearly 3.3 times higher as compared to bare ZnO and also higher than Mn4+-ZnO (91%) and Mn2+-ZnO (83%). The metal nanoparticles played a dual role in the photo-oxidative reaction by sensitizing the nanomaterial in the sunlight and suppressing the recombination rate of electrons-holes to enhance the reaction efficiency.