Colloidal Synthesis and Assembly of Functional Nanomaterials

In this dissertation, I present my research on the colloidal synthesis of anatase titanium dioxide nanocrystals and reversible assembly of charged gold nanoparticles as well as the applications of these novel nanomaterials. Titanium dioxide nanomaterials are well known for their photoactive properties and have been used in a variety of energy and environmental applications. Since the structural factors of TiO2 nanomaterials including size, shape, crystallinity have significant effects on their performance in these applications, it is highly demanded to develop robust synthesis methods for the production of TiO2 nanomaterials with highly configurable and predictable structure and morphology. Herein, a systematic study on shape controlled synthesis of anatase TiO2 nanocrystals was carried out. Synthesis and shape transformation of anatase TiO2 nanocrystals with controllable exposing facets were realized by a nonaqueous sol-gel pyrolysis reaction with the addition of fluorine as shape-directing agent. Anatase TiO2 nanocrystals with core-antenna morphology were further produced by a seed-mediated growth method. When used in photocatalytic reactions, the core-antenna nanocrystals were found to possess superior photocatalytic activities than those with simple morphologies. The high structural configurability of the core-antenna nanocrystals made it possible to optimize the catalyst parameters and achieve excellent photocatalytic performance. Noble metal nanoparticles possess novel optical properties due to surface plasmon resonance. Since assembly of plasmonic nanoparticles induces plasmon coupling between adjacent nanoparticles and results in optical property change, realization of reversible assembly of plasmonic nanoparticles can enable dynamic tuning of the optical properties of the materials. In our study, theoretical considerations on how to realize reversible assembly by control of colloidal interactions were first discussed. Experimentally, one-dimensional assembly and disassembly of gold nanoparticles were achieved by appropriate synthesis, surface modification and application of external stimuli. Kinetics study of the reversible assembly process was also carried out. When the as-assembled one-dimensional gold nanoparticle chain structures were transferred into polymer matrices, they can also be disrupted by mechanical forces and be used as colorimetric stress memorable sensor. Based on the results of my current research, future works of the study on colloidal synthesis of TiO2 nanocrystals and reversible assembly of plasmonic nanoparticles will also be discussed