Size and shape-controlled synthesis of inorganic nanomaterials

Inorganic nanoparticles and nanostructured materials have caused rising interest over the past decades because their unique properties, such as quantumconfinement of electrons and holes, surface effects, and geometrical confinement of phonons, are totally different from those bulk materials. It is well known that these nanoparticles are intermediate between molecular and bulk materials, leading to size- and morphology- dependent properties and potential applications including electrical, optical, magnetic and catalytic fields. So one can design the size and morphology of inorganic nanoparticles and tailor these properties according to the requirements of the devices, which have important value for the practical applications. Therefore, size- and shape-controlled inorganic nanoparticles are extremely desired and the detailed growth mechanism, such as the oriented attachment and the classical crystal growth arenecessary to explore. In chapter II, the author provides a simple and practical method for the preparation of folic acid (FA)-chitosan functionalized gold nanoparticles (AuNPs) with a very small size (1–6 nm). UV–vis spectroscopy and transmission electron microscopy (TEM) are used to characterize the size distribution dependent on the mass fraction of ligand to Au. In chapter III, Chain-like chitosan modified sodium gadolinium fluoride (NaGdF4) nanocrystals are successfully synthesized through a template-free and catalyst-free method in a hydrothermal condition, in which the reaction parameters, such as the mass ratio of [Chitosan] /[Gd3+], temperature and reaction time, played important roles. Also, the author investigates that individual NaGdF4 nanoparticles grow into a chain-like structure along the (110) direction through oriented attachment. It’s worthwhile to note that the chain-like chitosan modified NaGdF4 nanocrystal possesses high quality water-soluble property and the one doped with Eu3+ demonstrates the outstanding luminescent properties. In chapter IV, morphology-controlled BaWO4 is successfully prepared in an ethanol-water system, including flower-like, dipyramid-like and shuttle-like structures, etc. The author details the formation mechanisms of BaWO4 by using SEM to examine morphologies over a wide range of conditions and time-points and in- situ AFM to investigate the generation and propagation of growth sources on BaWO4 crystal surfaces. These results demonstrate that complex BaWO4 morphologies occur through purely classical growth mechanisms influenced by ethanol as a modifier for island birth and step propagation. In chapter V, ZnO dimer and rod-like structure are successfully synthesized by the oriented attachment mechanism and characterized using ex-situ TEM technique. In order to have a better understanding of the formation mechanism, liquid phase in-situ TEM is used to study the crystal nucleation and growth process, which illustrates that ZnO worm-like structure is formed by the oriented attachment mechanism.The new technique provides the direct evidence for ZnO nanocrystal growth in solution and is expected to substantially advance our understanding of nanocrystal growth mechanism.