| Increasing interest in the photoelectrochemical activity of TiO 2 has led to the consideration of using TiO2 nanoparticles in renewable energy generation. To better understand the electronic properties of nanoscale TiO2 structures, it is important to understand fundamental components that are synthesis precursors of TiO2 nanomaterials. Knowing the properties of basic building blocks of TiO2 materials, such as titanium hydroxide, Ti(OH)4, helps in a better understanding of the properties of larger scale structures. In this work, Ti(OH)4 is computationally modeled in an explicit aqueous environments to recreate realistic conditions. In this study, computational methods are employed to calculate the changes in electronic structure following photoexcitation. The top goal of this work is to gain insight on mechanisms of how the charge carriers relax and recombine. On the molecular size scale, one is able to study the direct effects of molecular coordination and surrounding environment on charge carrier migration. Density functional theory is used to model the Ti(OH) 4 with and without an aqueous environment, showing the effect solvation brings to the electronic structure. The electronic structure of Ti(OH) 4 is dramatically affected by the addition of an aqueous environment, quantum size effects, and the coordination of the hydroxyl ligands to the metal ion. Realistic molecular motion, which facilitates charge carrier migration, is modeled using first principles molecular dynamics (MD) at ambient temperatures. Combining Redfield Theory with MD results provides the electron and hole energy dissipation rates. It was found that quantum size effects and metal coordination deplete the density of states within the conduction band, resulting in slow charge carrier relaxation rates. Comparison of charge carrier relaxation rates show a faster relaxation time for holes, providing charge separation between the valence and conduction band. The charge separation process is facilitated by energy dissipation via non-radiative relaxation occurring within a stepwise cascade thermalization mechanism. The results show the possibility for design of novel, promising, and efficient materials for solar driven water splitting reactions. |
