Surfactant free, simple, morphological and defect engineered ZnO nanocatalyst: Effective study on sunlight driven and reusable photocatalytic properties

• Surface area and defect states engineering of ZnO photocatalysts with naught shape directing agents.
• Dependence investigation of defect states, reactive oxygen species (ROS) production and photocatalytic (PC) properties of the ZnO photocatalyst.
• Efficient charge separation and high ROS production resulting in higher PC properties.
• Reusable PC studies revealed decrease in PC activity of the nanocatalyts due to catalyst poisoning.

We demonstrate the facile synthesis of solution grown ZnO structures (rods, buds, brooms, spindles, stars, flowers, multipods) without using any surfactant and capping agents. Morphology of the nanostructures was simply controlled by varying the Zn supersaturation in the growth solution which transforms the growth mode from anisotropic to isotropic and then to hierarchical nature. All photocatalysts were characterized by X-ray diffraction, UV–vis absorption, photoluminescence, scanning electron microscopy, high resolution transmission electron microscopy analysis. ZnO nanoflowers show excellent photocatalytic (PC) degradation efficiency above 95% against Methyl orange, Rodamine B and Methylene blue dyes in 120 min under natural solar irradiation compared to the other nanostructures. It is noteworthy that the PC performance of the ZnO nanostructures correlates well with the defect states and the production of photo induced reactive oxide species (ROS). Investigations show that the enhanced PC performance of ZnO nanoflowers was due to the synergy of larger surface area and oxygen related defects assisted ROS production. The photocatalytic recycling ability of ZnO nanoflowers was investigated. ZnO flowers showed excellent recyclability with a slight decrease in photocatalytic efficiency after being subjected to ten consecutive cycles.

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