Facile Synthesis of Face Oriented ZnO Crystals: Tunable Polar Facets and Shape Induced Enhanced Photocatalytic Performance

This study reports on the formation of unique oriented ZnO structures (face oriented hexagonal discs, 3D trapezoids, rings, doughnuts, and hemispheres) with tunable percentage of exposed polar facets synthesized via a simple hydrothermal route in aqueous base environment The significance of the synthetic strategy is the generation of exotic structures without using any templates/structure directing agents and successful realization of morphologies with increased polar to nonpolar facet ratio. Detailed investigation reveals that the size and shape of ZnO microstructures can be conveniently tailored by systematically exercising control on the choice of precursor (zinc source), concentration of reactants, use of Trizma as a base (pH control) which is also seen as structure directing agent. The Trizma base with an appreciably short pH range effectively controls the rate of hydrolysis, regulates nucleation, and restrains rapid growth leading to these well-defined ZnO structures. Photocatalytic degradation of methylene blue as a model system was used to showcase the morphology-dependent enhanced photoactivity under UV-light. The enhanced photocatalytic performance could be attributed to the higher fraction of exposed (0001) and (0001) ZnO polar facets present.