Modelling rutile TiO2nanorod growth preferences: A density functional theory study

Synthesis of 1D TiO(2)nanorods is promising nowadays owing to their broad applications in photocatalytic devices. A groundbreaking synthesis procedure of one-step producing large-scale, free-standing and heterogeneous phase (anatase and rutile) 1D TiO2 nanorod array which efficiently enhances the photocatalytic activity has been previously proposed. However, the detailed growth mechanism of this catalyst remains unclear, mainly because the synthesis takes place in a closed autoclave. This study presents a complementary approach to understand the growth mechanism using computer modeling based on density functional theory (DFT). The interaction of the precursor (titanium butoxide in hydrochloric acid media, modelled by TiCl4) and solvent (water) with preexisting rutile titania is computed to derive the thermodynamic trends to grow additional TiO2 layers. Five different termination models of the rutile surfaces were built: (001), (100), (101), (110) and (111), and their interaction with precursor and water was computed. Molecular and dissociative adsorption are considered as well as coadsorption. Our results point to a preferential growth of the (001) termination of rutile TiO2 through intermediates involving TiCl3+, Cl- and hydroxyl groups. The results obtained show how computational chemistry can be used to resolve experimental growth information. The protocol used i.e. computing different terminations and their explicit interaction with both the precursor and the solvent, can be extended to other materials in which the growth takes place following well-defined preferential directions.