SummaryHydrothermally grown ZnO nanorods have inherent crystalline defects primarily due to oxygen vacancies that enhance optical absorption in the visible spectrum, opening up possibilities for visible light photocatalysis. Comparison of photocatalytic activity of ZnO nanorods and nanoparticle films on a test contaminant methylene blue with visible light irradiation at 72 kilolux (klx) showed that ZnO nanorods are 12–24% more active than ZnO nanoparticulate films. This can be directly attributed to the increased effective surface area for adsorption of target contaminant molecules. Defects, in the form of interstitials and vacancies, were intentionally created by faster growth of the nanorods by microwave activation. Visible light photocatalytic activity was observed to improve by ≈8% attributed to the availability of more electron deficient sites on the nanorod surfaces. Engineered defect creation in nanostructured photocatalysts could be an attractive solution for visible light photocatalysis.

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Bilirubin (BR) is a protective antioxidant; however, when its conjugation and excretion are impaired, as in neonatal and hereditary jaundice, BR accumulates and may cause severe neurotoxicity. Here, we report a novel mechanism for ZnO nanoparticle (NP)-sensitized BR degradation via defect-mediated nonradiative energy transfer pathway. Among different sizes and shapes, ZnO particles with diameter of 5 nm having very high concentration of defect states are found to be the most effective catalyst, which particularly follows a pseudofirst-order kinetics validating the Langmuir−Hinshelwood model of surface catalysis. The nontoxic wide band gap ZnO NPs essentially transmit defect-mediated visible optical radiation, which is not supposed to interfere with the conventional phototherapy process. Therefore, the recyclable ZnO nanocatalysts essentially invite an added advantage in potential therapeutic applications and/or in a flow-device that has been explored in the present study.

Increasing water pollution by microbes has become a source of serious health concern across the globe. Production of potentially carcinogenic disinfection byproducts has marred credibility of traditional water purification techniques like chlorination. Photocatalysis has emerged as a promising alternative technique for the disinfection of water with minimal risk of harmful by-products. The process involves a wide band gap semiconductor material which, upon irradiation of light, produces electrons and holes with high redox potential to degrade organic contaminants and microbes. In this review, we analyze the research trends in photocatalytic inactivation of water borne microorganisms. This report analyzes the major factors that affect the disinfection efficiency using this process. The discussion also includes plausible mechanisms of microbial degradation as well as a kinetic model of the inactivation process. Different approaches, like doping of semiconductors or energy band engineering or plasmon coupling, have been reported for the enhancement and utilization of ambient solar light. Photocatalysis could be a cost-effective and environmentally friendly water purification technique though further research is required to enhance its efficiency with the use of solar light.

Zinc oxide has been the focus of material research due to its potential applications in a variety of novel fields. The material exhibits anisotropic growth in the form of single crystal rods/wires of length in microns and thickness in several tens of nanometers through a facile and low temperature hydrothermal route wherein size, morphology, orientation, and growth rate are strongly dependent on a number of synthesis parameters. In this review article we intend to present/discuss the effects of important growth parameters of zinc oxide that have been reported in the literature. These parameters include concentration of the precursor solution, growth time, role of hexamine, synthesis temperature, pH of the precursor, and seeding layer deposited on a substrate.