Nano sized particles of semiconductor materials have achieved great interest in recent years due to their desirable properties and applications in different areas such as agricultural, rubber industries, pharmaceutical and cosmetic, textile industries, electronic industries, sensors, photoelectronic devices and photocatalysts. These nanomaterials have unusual thermal, structural and electronic properties, which are of important scientific interests in the fundamental and applied research fields. Zinc oxide (ZnO) is a promising material which gained increasing interest in recent years owing to its distinctive properties. In this review paper an attempt has been made to elaborate the promising applications of ZnO nanoparticles in various fields.
Recently, hierarchical 3D nanostructures have attracted attention due to their multiple advantages, such as large surface area, porous structures, as well as enhanced light harvesting ability. Zinc oxide is a promising photocatalyst alternative to TiO2 used for environmental remediation of wastewater pollutants due to its high photosensitivity, non-toxic nature, low cost, and environmental friendliness. ZnO can be crystallized in three forms under different conditions i.e., wurtzite, zinc-blende, and rock-salt structures. ZnO exhibits a higher quantum efficiency and has a similar bandgap as TiO2 as it has a larger number of inherent active defect sites on the surface, which makes it capable of absorbing a larger fraction of the solar spectrum. Various approaches have been used to efficiently utilize the solar radiation and to enhance the efficiency of zinc oxide photocatalyst. These techniques enhance the photocatalytic performance ZnO under visible light by shifting the bandgap energy, suppressing the recombination rate of electron-hole pairs, increasing charge separation efficiency. In future there is a need of developing green, scalable, low-cost and highly efficient hierarchically ZnO nanostructures and nanocomposites photocatayst for remediation of wastewater pollution. In this chapter the emphasis has been on the advantages, fabrication methods, and photocatalytic applications of hierarchical ZnO nanostructures for the degradation of organic contaminants present in wastewater.
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