Nucleation and Growth of TiO2 Nanoparticles

Abstract

Crystallization is one of the most important and interesting phenomena in human life. For instance, many purifications and productions of materials are based on crystallization. In pharmacology, more than 90% of all pharmaceutical products are used in the crystalline form of solid material. Hence, the controlling of the crystallization process has a critical role on the properties of products and allows manufacturers to prepare materials with desired and reproducible properties. The recent interest in nanocrystals and other types of nanomaterials is a further illustration of the crystallization importance in the science and technology (Mehranpour et al., 2010). It is well known that at the nanometer scale, the optical, the electronic, and the catalytic properties of nanomaterials are highly sensitive to their size and shape (Finney & Finke, 2008). Consequently, the crystallization process (nucleation & growth) plays an important role in determining the crystal structure, shape, size and size distribution of the nanomaterials. Therefore, a theoretical approach to understand the mechanism of nanocrystal formation provides a greater control over the size, shape, and composition of nanocrystals and results an ability to tune the abovementioned properties simply by varying the crystallization conditions. One of the main goals of this theoretical approach of the nanocluster science is the ability to prepare nanocrystals that have very narrow size distributions (so-called “near-monodisperse”). That is the main reason to know why the nucleation and the growth mechanism of nanocrystals in solution have been the subject of increasing study. On the other hand, the agreement between the theoretical models and experimental results is not very good. This is a general shortcoming of nucleation theories. As a result, the nucleation theories in general have a little predictive power. It seems that a main goal of nucleation study is to improve the accuracy of theory (Finney & Finke, 2008). Titanium dioxide (TiO2) is one of the semiconductor materials with unique photocatalytic properties that make it an interesting candidate for different applications such as white pigment, cosmetics, catalysis support and a photocatalyst. During last two decades, this act has been highlighted that the physical and the chemical properties of nano-TiO2 depend on its size, morphology and crystalline polymorph strongly. That is well known that these specifications of TiO2 nanopowders are controlled by crystallization and phase transformation. Since the employed synthesis method has critical role on the crystallization and phase transformation of obtained material, many attempts have been done to use a procedure