Preparation, Surface Modification and Application of Nanometer Zinc Oxide
Abstract：
Nanometer zinc oxide (ZnO), a white powder with wide spectra of bandgap, has found numerous applications ranging from photodetectors to gas sensors. Owing to its versatile characters, remarkable structure and surface composition, scientists have designed and developed many surface modification methods to yield a variety of nanometer ZnO from visible light to photocatalytic activities. In this article, we review the preparation and surface modification methods of nanometer ZnO, as well as recent progress in the application of nanometer ZnO in gas sensor and photocatalysis. We further give our insights regarding their future prospects.
Keywords：Nanometer ZnO, Preparation, Surface modification, Application
1 Introduction
Nanometer ZnO, also known as zinc oxide nano-material (ZnO-NT), is one of the most important inorganic nanomaterials. It exhibits strong ultraviolet (UV) absorption and luminescence capability and is considered as an attractive material for the potential applications in the fields of photo-detection, solar energy conversion, lighting, and gas sensor technology [1]. Nanometer ZnO has a wide bandgap (3.3 eV) that is suitable for visible light absorption, chemical stability, origin of non-toxicity, and small size [2, 3]. As a result, nanometer ZnO has emerged as an ideal material for light harvesting and photocatalyst. To make full use of the properties of nanometer ZnO, scientists start to study the synthesis, surface modification and application of nanometer ZnO [4, 5]. In this article, we review the preparation and surface modification methods of nanometer ZnO, and the recent progress in the application of nanometer ZnO in photocatalysis and gas sensor technology.
2 Preparation and Surface Modification of Nanometer ZnO
Nanometer ZnO can be easily prepared by either chemical or physical methods. The most frequently used methods for preparating nanometer ZnO in chemical method include hydrothermal synthesis, chemical vapor deposition, sputtering and chemical bath deposition, etc. In physical method, the most popular ones are chemical vapor deposition, laser-induced vaporization and shock wave synthesis. Each for the above mentioned method has its advantages and disadvantages, and their selection depends on the available equipment and cost of materials.
Surface modification of nanometer ZnO is the process by which the surface of the nanometer ZnO is altered in order to more effectively respond to the environment or to enhance performance of the nanometer ZnO. This can be accomplished by a number of techniques such as chemical modification, doped modification, and coating with organic films. Chemical modification, for instance, one of the most common method for surface modification of nanometer ZnO, involves the deposition of a thin layer of a chemical or organic compound on the surface of the particle in order to modify the surface properties of the particle [6]. The chemical or organic compound can be a self-assembled monolayer, a polymer, or an inorganic compound such as a metal oxide. In addition to chemical modification, nanometer ZnO can also be modified by doping with different element or coating with other thin films.
3 Applications of Nanometer ZnO
Due to its low cost and excellent properties, nanometer ZnO has been widely used in many different application areas such as gas sensor technology, photocatalysis, and light harvesting materials.
3.1 Gas Sensor Applications
Gas sensing is a critical technology to the modern industrialized world. Gas sensors based on nanometer ZnO have been explored in the range of viscous fluids, such as alcohols, fuel (gasoline) and other hydrocarbon molecules. Due to its high sensitivity to gas molecules, nanometer ZnO gas sensors can be used for both qualitative and quantitative analysis. The sensors can detect changes in the concentrations of different gases with a high resolution. Moreover, due to the low cost nature of nanometer ZnO based gas sensors, they can be made on a large scale at a low cost.
3.2 Photocatalytic Applications
Due to its ability to absorb visible light, nanometer ZnO has become an attractive material for photodegradation of pollutants. In particular, nanometer ZnO has been used in degradation of organic dyes, organic compounds and pharmaceutical compounds. Nanometer ZnO based photocatalysts are effective in removing organic and inorganic contaminants, and they have been applied in various industries such as wastewater treatment, air purification and hazardous waste disposal.
4 Conclusion
In this review paper, we discussed the synthesis, surface modification and application of nanometer ZnO. As the technology advances and more efficient and cost-effective methods for preparation and surface modification are developed, nanometer ZnO will be increasingly used in gas sensor technology and photocatalysis for improving the efficiency of environmental pollutant control. We believe that nanometer ZnO will become one of the most promising nanomaterials in the future.
References：
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[2]Kumar R.S., et al., 2013, Recent advances in ZnO based field emission devices, Nanomaterials, 3(4), 695-715.
[3]Geida J.S., et al., 2010, ZnO nanostructures for gas sensing applications, Sensors, 10(4), 3454-3485.
[4]Biswas S., et al., 2014, Surface modifications of ZnO nanostructures and their application as efficient photocatalysts, Journal of Materials Chemistry A, 2(8), 2705-2713.
[5]Zhang Y., et al., 2011, A review of ZnO-based gas sensors, Journal of Sensors, 11, 2763.
[6]Liu T.-Y., et al., 2012, Surface modification of ZnO nanoparticles by self-assemble monolayers, Journal of Materials Chemistry, 22(5),1922-1929.
