https://iris.unipa.it/bitstream/10447/74239/1/Di%20Paola-J%20hzardous%20mater%202012-survey.pdf

A survey of photocatalytic materials for environmental remediation.

Review on the improvement of the photocatalytic and antibacterial activities of ZnO

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

Nanoparticles: Their potential toxicity, waste and environmental management

In this paper, TiO2 nanoparticles doped with different amounts of Zn were prepared by a sol−gel method and were mainly characterized by means of X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and surface photovoltage spectrum (SPS). The effects of surface oxygen vacancies (SOVs) of Zn-doped TiO2 nanoparticles on photophysical and photocatalytic processes were investigated along with their inherent relationships. The results show that the SOVs easily bind photoinduced electrons to further give rise to PL signals. The SOVs can result in an interesting sub-band SPS response near the band edge in the TiO2 sample consisting of much anatase and little rutile, except for an obvious band-to-band SPS response. Moreover, the intensities of PL and SPS signals of TiO2, as well as the photocatalytic activity for degrading phenol solution, can be enhanced by doping an appropriate amount of Zn. These improvements are mainly attributed to the increase in the SOV amount. It can be suggested that the SOVs ...

Effects of surface oxygen vacancies on photophysical and photochemical processes of Zn-doped TiO2 nanoparticles and their relationships.

The photocatalytic degradation of isothiazolin-3-ones has been studied using the catalytically active TiO2 and ZnO and the inactive paint grade TiO2, under various illumination and chemical conditions. The reaction follows a pseudo-first-order kinetics. Three types of lamps have been used. The photocatalytic degradation is faster under UV lamp, when it is compared to reaction under suntest and fluorescent lamps. In the presence of oxygen and H2O2, the reaction proceeds faster than in air atmosphere. ZnO exhibits comparable activity with TiO2 and in some cases it was found to be even better than TiO2. The reaction was studied in aqueous suspensions as well as on gas–solid interfaces. The degradation of isothiazolin-3-ones in paint formulations was also studied.

H Kastien

Papers

Photocatalytic degradation of isothiazolin-3-ones in water and emulsion paints containing nanocrystalline TiO2 and ZnO catalysts