As an alternative to the gold standard TiO2 photocatalyst, the use of zinc oxide (ZnO) as a robust candidate for wastewater treatment is widespread due to its similarity in charge carrier dynamics upon bandgap excitation and the generation of reactive oxygen species in aqueous suspensions with TiO2. However, the large bandgap of ZnO, the massive charge carrier recombination, and the photoinduced corrosion–dissolution at extreme pH conditions, together with the formation of inert Zn(OH)2 during photocatalytic reactions act as barriers for its extensive applicability. To this end, research has been intensified to improve the performance of ZnO by tailoring its surface-bulk structure and by altering its photogenerated charge transfer pathways with an intention to inhibit the surface-bulk charge carrier recombination. For the first time, the several strategies, such as tailoring the intrinsic defects, surface modification with organic compounds, doping with foreign ions, noble metal deposition, heterostructuring with other semiconductors and modification with carbon nanostructures, which have been successfully employed to improve the photoactivity and stability of ZnO are critically reviewed. Such modifications enhance the charge separation and facilitate the generation of reactive oxygenated free radicals, and also the interaction with the pollutant molecules. The synthetic route to obtain hierarchical nanostructured morphologies and study their impact on the photocatalytic performance is explained by considering the morphological influence and the defect-rich chemistry of ZnO. Finally, the crystal facet engineering of polar and non-polar facets and their relevance in photocatalysis is outlined. It is with this intention that the present review directs the further design, tailoring and tuning of the physico-chemical and optoelectronic properties of ZnO for better applications, ranging from photocatalysis to photovoltaics.

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Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Morphologies of zinc oxide particles and their effects on photocatalysis.

The efficiency of anodized aluminum wire was investigated as a new fiber for solid-phase microextraction (SPME). Aluminum wires were anodized by direct current in a solution of sulfuric acid at room temperature and were conditioned at 300 °C for 30 min. These fibers were used for the extraction of some aliphatic alcohols, BTEX, and petroleum products from gaseous samples. The extracted analytes were transferred to a GC injector using an (in-house-designed) SPME syringe that also allowed for an easy change of SPME fibers. The results obtained prove the ability of anodized aluminum wire as a new fiber for sampling of organic compounds from gaseous samples. This behavior is due most probably to the porous layer of aluminum oxide, which is formed on the metal surfaces. In this work, the optimum conditions for the preparation and conditioning of fibers and the extraction of analytes from gaseous samples were obtained. In the optimum conditions, one fiber was used in several equal analyses and the relative stan...

Anodized Aluminum Wire as a Solid-Phase Microextraction Fiber

The effects of various physical properties (particle size, shape, surface area, crystal structure, and phase composition) on the photocatalytic performance of nanosized TiO2 were studied through the photodegradation of Congo Red. Kinetic results showed that anatase TiO2 was a superior photocatalyst to rutile TiO2 due to the inherent difference in the two crystal structures. Anatase TiO 2 nanorods with predominantly (1 0 1) surface

Photodegradation of Congo Red catalyzed by nanosized TiO2

Simple fabrication and photocatalytic activity of ZnO particles with different morphologies

Photocatalytic ZnO films prepared by anodizing

PROBLEM TO BE SOLVED: To improve catalyst activity and photocatalyst activity by forming a catalyst film from a zinc oxide film having the X-ray diffraction peak intensity of a (100) face higher than the X-ray diffraction peak intensity of a (002) face. SOLUTION: The orientation of the (100) face of the zinc oxide film is enhanced at the time of forming the zinc oxide film having the high catalyst activity and photocatalyst activity in the case of formation of the catalyst film consisting of the zinc oxide film and photocatalyst film consisting of the zinc oxide film. Namely, the zinc oxide film having the X-ray diffraction peak intensity of the (100) face higher than the X-ray diffraction peak intensity of the (002) face is used. The zinc oxide constituting the catalyst film and photocatalyst film is a hexagonal crystal having a wurtzite type structure and the unit lattice thereof is a=3.250 angstrom and c=5.207 angstrom. The zinc oxide film having the high catalyst activity and photocatalyst activity is obtainable if the zinc oxide film having the X-ray diffraction peak intensity of the (100) face higher than the X-ray diffraction peak intensity of the (002) face is formed in such a manner.

Yasuhide Yamaguchi

Papers

Photocatalytic ZnO films prepared by anodizing

Zinc oxide catalyst film

Anodized Condition and Formed Films of Zinc Oxide

Photocatalytic Properties of Transparent ZnO Films Prepared by Anodization of Zinc Plate