Atomic Hydrogen Activated TiO2 Nanocluster: DFT Calculations

The reduction of TiO2 nanoparticle through interaction with H atom and characterization of resulting defect species with O-2 molecule adsorption were investigated b) DFT calculations in a molecular cluster approach. The isolated cluster Ti8O16 was used as a nanoparticle model. It was found that interaction between atomic hydrogen and every oxygen atom in Ti8O16 has the following features: (1) formation of stable OH group, (2) low activation energy of the process, and (3) appearance of reduced Ti3+ ion together with one corresponding d-type singly occupied level in the cluster's band gap. Molecular hydrogen, in contrast with its atomic form, weakly interacts only with Ti atoms. Simulation of O-2 adsorption on each Ti3+ ion of reduced Ti8O16H clusters shows the following: (1) formation of stable molecular O-2(-) species, (2) the process has no any energetic barrier, and (3) disappearance of T3+ defect center and corresponding d-type singly occupied level. The obtained results agree well with general experimental regularities of both H plasma TiO2 reduction and interaction of reduced TiO2 with oxygen. Specifically, calculations of g-tensor provide plausible quantitative description of Ti3+ and O-2(-) paramagnetic species. Consistently the computational approach under consideration can be therefore applied to local surfaces phenomena associated with nanoscaled TiO2.