Counterion-Induced Tailoring of Energy Transfer in Hydrothermally Grown Nanostructured ZnO for Photocatalysis

Morphological tailoring of zinc oxide (ZnO) nanostructures, viz., nanogranules, hexagonal pillars, and nanorods, has been demonstrated using the hydrothermal method by varying the precursor salts of zinc. Counterions of precursor salts, such as zinc chloride, zinc acetate, and zinc nitrate, are found to influence nucleation and growth of the nanostructures. Determination of crystalline and morphological properties of different nanostructures has been carried out by using X-ray diffraction and field emission scanning electron microscopy. The X-ray photoelectron spectroscopy technique is used for the investigation in a comparative surface study of ZnO nanostructures, and possible growth mechanisms of different nanostructures have been described. Bandgap and Urbach energies of the materials are also affected by the counterions of the precursor salts. Fourier transform infrared spectra of ZnO nanostructures show shifting of band positions of the functional group caused by variation of the precursor salt. Features of photoluminescence emission spectra of the ZnO nanostructures are ascribed to the association of different defect states due to the change of counterions. Moreover, the variation of precursor salts also influences the efficiency of Forster resonance energy transfer between the donor (ZnO) and acceptor (MB dye). ZnO with different nanostructures exhibits commendable photocatalysis degradation efficiency toward methylene blue dye (MB dye). Thus, the emission property and photocatalytic property of the ZnO nanostructures can be tuned by the variation of precursor salts. In this work, the role of counterions is established as a tool to control the ZnO nanostructures along with achieving control over the defect state emissions. This work not only establishes a relation between defects and photocatalysis, but also it deals with the variation of oxygen defects induced by the counterions of the zinc precursor salts.