Titanium dioxide (TiO2) has been widely used in industry as a photocatalyst due to its superior photoactivity, high photo- and chemical-stability, non-toxicity, abundance, and low cost. Many of its applications in clean energy generation and environmental remediation involve interactions between organic species and TiO2 materials. Such interactions not only depend on the intrinsic properties of TiO2, but also on its surfaces structure. Specifically, the capacity of the TiO2 surface to adsorb organic species is vital for TiO2 photocatalytical performance. Understanding the adsorption properties of organic compounds on various crystalline TiO2 surfaces is essential for further technological development. In this project, theoretical studies initially demonstrated that TiO2 is the most photoactive all Ti-O based materials. A combined photoelectrochemical (PEC) and theoretical study was conducted to understand the adsorption properties of organic molecules on anatase (001) and rutile (111) TiO2 surfaces. PEC measurements can provide quantitative thermodynamic and kinetic information on the adsorption properties of organic species on the TiO2 surface under operational, practical conditions. The theoretical studies provide further information on interactions at the atomic level.