Using Density Functional Theory to Model Realistic TiO2 Nanoparticles, Their Photoactivation and Interaction with Water

Abstract

Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable spherical titania nanoparticles of increasing size, with diameter from 1.5 nm (~300 atoms) to 4.4 nm (~4000 atoms). We use first self-consistent-charge density functional tight-binding (SCC-DFTB) methodology to perform thermal annealing simulations to obtain globally optimized structures and then hybrid density functional theory (DFT) to refine them and to achieve high accuracy in the description of structural and electronic properties. This allows also to assess SCC-DFTB performance in comparison with DFT(B3LYP) results. As a further step, we investigate photoexcitation and photoemission processes involving electron/hole pair formation, separation, trapping and recombination in the nanosphere of medium size by hybrid DFT. Finally, we show how a recently defined new set of parameters for SCC-DFTB allows for a proper description of titania/water multilayers interface, which paves the way for modeling large realistic nanoparticles in aqueous environment.

Charge Carriers Cascade in a Ternary TiO2/TiO2/ZnS Heterojunction: A DFT Study

“…Now, we try to go beyond this approximation by explicitly simulating the photogeneration of charge carriers in the model, to complement the picture arising from the band alignment. This is done starting from the relaxed heterojunction in its electronic ground state and forcing the system into a triplet solution . This simulates a vertical excitation of an electron from the valence band to the conduction band.…”

“…This is done starting from the relaxed heterojunction in its electronic ground state and forcing the system into a triplet solution. [49,89,90] This simulates a vertical excitation of an electron from the valence band to the conduction band. As reported in Figure 5a, this procedure has a cost of 2.1 eV, and the electron is delocalized over several Ti sites in the TiO 2 (001) region, while the hole is A subsequent geometry relaxation of the system leads to a full localization of the photoexcited electron on a Ti 3 + center at TiO 2 (001) while the hole is fully localized on a S site of the ZnS (110) surface, Figure 5(b), with formation of two polarons.…”

Recent Advancements in the Understanding of the Surface Chemistry in TiO2 Photocatalysis

“…Selli et al [17] modeled spherically shaped TiO 2 nanoparticles containing 300 to 4000 atoms. They compared the precision of computations carried out using the semiempirical method DFTB (matsci-0-3 parameters set) versus the traditionally used B3LYP hybrid functional.…”

Properties of hydrated TiO2and SiO2nanoclusters: dependence on size, temperature and water vapour pressure

“…11 A number of recent theoretical studies have used top-down bulk cut nanoparticles containing 10s -1000s of atoms in order to investigate the electronic properties of nano-TiO2 photocatalysts 12,13,14,15 and their interactions with water. 16,17,18,19,20,21 Although such calculations can provide important new insights, in most cases the nanoparticles used are still relatively small idealised model systems compared to experimental systems where larger and more complex nanoparticles are typically used. Detailed spectroscopic experiments probing the interaction of water with small oxide (i.e.…”