Structure and Electronic Properties of TiO2 Nanoclusters and Dye–Nanocluster Systems Appropriate to Model Hybrid Photovoltaic or Photocatalytic Applications

Abstract

We report the results of a computational study of TiO2 nanoclusters of various sizes as well as of complex systems with various molecules adsorbed onto the clusters to set the ground for the modeling of charge transfer processes in hybrid organic–inorganic photovoltaics or photocatalytic degradation of pollutants. Despite the large number of existing computational studies of TiO2 clusters and in spite of the higher computing power of the typical available hardware, allowing for calculations of larger systems, there are still studies that use cluster sizes that are too small and not appropriate to address particular problems or certain complex systems relevant in photovoltaic or photocatalytic applications. By means of density functional theory (DFT) calculations, we attempt to find acceptable minimal sizes of the TinO2n+2H4 (n = 14, 24, 34, 44, 54) nanoclusters in correlation with the size of the adsorbed molecule and the rigidity of the backbone of the molecule to model systems and interface processes that occur in hybrid photovoltaics and photocatalysis. We illustrate various adsorption cases with a small rigid molecule based on coumarin, a larger rigid oligomethine cyanine dye with indol groups, and the penicillin V antibiotic having a flexible backbone. We find that the use of the n = 14 cluster to describe adsorption leads to significant distortions of both the cluster and the molecule and to unusual tridentate binding configurations not seen for larger clusters. Moreover, the significantly weaker bonding as well as the differences in the density of states and in the optical spectra suggest that the n = 14 cluster is a poor choice for simulating the materials used in the practical applications envisaged here. As the n = 24 cluster has provided mixed results, we argue that cluster sizes larger than or equal to n = 34 are necessary to provide the reliability required by photovoltaic and photocatalytic applications. Furthermore, the tendency to saturate the key quantities of interest when moving from n = 44 to n = 54 suggests that the largest cluster may bring little improvement at a significantly higher computational cost.

Photoexcitation Processes in Oligomethine Cyanine Dyes for Dye-Sensitized Solar Cells—Synthesis and Computational Study

“…In a previous study, following the work of Persson et al [52] and De Angelis et al [53] we showed that (TiO 2 ) n clusters with n less than 24 cannot properly describe the complex dye-oxide systems [54]. It was concluded that the n = 24 cluster was the smallest one that can be used well for qualitative calculations, particularly when the adsorbed molecule is rigid, as it is the case here [54,55].…”

“…The model clusters used has a slight deviation from the TiO 2 stoichiometry which circumvents the problem of the surface states in the gap. We introduced H atoms or -OH groups to terminate the peripheral dangling bonds, resulting in the Ti 24 O 50 H 4 , and we showed that the presence of the four H atoms does not affect the nature of the electronic spectrum [54,55].…”

Isolation and Characterization of Ochrobactrum tritici for Penicillin V Potassium Degradation

“…Several methods have been used for PVK degradation. For example, penicillin V can be degraded under visible light when TiO 2 is used as a photocatalyst (21). It has also been reported that simulated sunlight is able to degrade PVK (22).…”

“…The 16S rRNA gene sequences were compared with other 16S rRNA gene sequences available in GenBank by using the Basic Local Alignment Search Tool (BLASTN) program and BLASTn database and aligned with similar sequences by using multiple sequence alignment software (21). A phylogenetic tree was constructed by applying the neighbor-joining method using the MEGA 7.0 program based on Kimura-2 parameters with 1,000 replicates of bootstrap values.…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Relatively few studies so far have faced the theoretical modeling of the structural and electronic features of the dye-semiconductor interface and its effect on photocatalytic activity. A dedicated DFT investigation considered TiO 2 nanoclusters with different adsorbed dyes: a small rigid molecule based on coumarin, a larger rigid oligomethine cyanine dye with indole groups, and the penicillin V antibiotic, with a flexible backbone [79].…”