Precise and Wide-Ranged Band-Gap Tuning of Ti6-Core-Based Titanium Oxo Clusters by the Type and Number of Chromophore Ligands.

Sensitization with dyes is the most promising option to narrow the band gap and improve visible-light absorption of TiO2. As ideal structure and reaction models of TiO2, titanium oxo clusters (TOCs) with exact crystal structure are beneficial for further understanding the structure-property relationship of TiO2. Most reports mainly focus on the synthesis and properties of TOCs, but research on the band-gap tuning of TOCs at the large range of 3.7-2.0 eV by chromophore ligands (CLs) has been lacking. Herein, six new Ti6-core-based TOCs (Ti6-TOCs) were successfully synthesized by using CLs in a simple and general approach. Each Ti6-TOC structure contains two Ti3(µ3-O) units featuring a flat or pyramidal mode as building blocks. Five Ti6-core structure types were present among the six Ti6-TOCs, which enriched the family of hexanuclear TOCs. To be noted, the band-gap values were tuned at a wide range of 3.41-1.98 eV by controlling the type and number of the CLs 2-hydroxypyridine, salicylaldoxime, and catechol in the structure. Density functional theory calculation revealed that the lowest-energy bands of these Ti6-TOCs are attributed to the CL-to-TiO core charge-transfer bands. This work provides a precise and wide-ranged band-gap tuning method for TOCs. Additionally, the six Ti6-TOCs exhibit good photocurrent response.

A series of silver doped butterfly-like Ti8Ag2 clusters with two Ag ions panelled on a Ti8 surface.

Silver doped TiO2 (Ag-TiO2) materials show high activity and good stability in photocatalysis, but the mechanism could not be illustrated clearly due to their imprecise and inhomogeneous characteristics. Ag-doped titanium-oxo clusters (Ag-TOCs) with an exact crystal structure, which are rarely reported, are beneficial for further understanding structure-property relationships. Herein, six new Ag-TOCs with a butterfly-like Ti8Ag2 core have been synthesized through facile solvothermal reactions, in which two Ag ions are successfully linked to the surface of the Ti8 core. Of interest, the Ti6 unit of the Ti8Ag2 core is similar to that found in the anatase structure and may be a promising model for Ag-TiO2 materials. The band gaps of these Ag-TOCs show different values mainly affected by different ligands. DFT calculations revealed that the lowest energy bands of Ag-TOCs are attributed to the Ag-to-TiO core charge transfer bands. Additionally, all Ag-TOCs exhibit good photoelectric response and high photodegradation activity towards organic dyes.