Nanomaterials with Different Morphologies for Photocatalysis

Abstract

Photocatalysis is an important phenomenon for degrading the harmful products/by-products produced by various industrial and technological sectors. The wastes from this sector can be of any form, like solid, liquid, and gaseous. When it is in liquid form, in most of the cases, they are released untreated into the regular freshwater stream leading to water contamination, and therefore, they have to be properly treated before releasing them into water bodies. The treatment can be very well done with the advanced oxidation process, photocatalysis. This process depends on the type of photocatalyst, the type of irradiation, and the type of organic molecules to be degraded. The main player is the photocatalyst material, and its design and selection for best efficiency are challenging, because its performance depends on many parameters such as large surface area, high absorption of pollutant molecules, less charge recombination, high charge transfer rate, suitable band gap, and good light harvesting capability. Mostly, these photocatalysts are semiconductor-based material with a suitable band gap. Selecting a material with suitable parameters is highly challenging, and one such parameter is the morphology of the photocatalysts. This is because morphology of the material influences the above said parameters, to be suited as photocatalysts. In this regard, this chapter deals with the nanostructured materials with different morphologies prepared by different chemical/physical methods. Since the hydrothermal method can produce a variety of morphologies, this method has been largely used by the researchers. Different morphologies will yield different surface areas, for example, spherical particles with different particle sizes have different band gap influenced by the quantum confinement phenomenon, and similarly other parameters can also be influenced by morphology. There are reports in which particular planar arrangement of ZnO nanorods played a dominant role to have them the best photocatalytic activity. This is because the ZnO can have polar or nonpolar planes whose surfaces react differently with the reactant molecules. In some cases, the surface of the photocatalysts was decorated with metal nanoparticles such as Ag, Au, and Pd in order to increase the charge transfer rate so as to increase the lifetime of the charges and in turn enhanced photodegradation. Materials with porous morphology can have different activities. In line with these facts, the chapter presents the principle of photocatalysis, importance of photocatalysts and their design, and importance of nanomaterials with different morphologies followed by different types of photocatalysts based on quantum confinement, such as zero-dimensional, one-dimensional, two-dimensional, and three-dimensional materials. Various 0-, 1-, 2-, and 3-D nanomaterials were discussed along with their preparation, photocatalytic properties, and the reasons/mechanism for the improved photocatalytic activity with appropriate examples.