A Cyclic Titanium-Oxo Cluster with a Tetrathiafulvalene Connector as a Precursor for Highly Efficient Adsorbent of Cationic Dyes.

Titanium-oxo clusters (TOCs) have been studied for applications in catalysis, energy storage and transfer, light emission, and so on; however, use of TOCs for the selective adsorption of dyes has not yet been reported. Herein, a TOC compound formulated as [TiO(OPr)(TTFTC)] (, TTFTC = tetrathiafulvalene-tetracarboxylate) was successfully prepared and crystallographically characterized. Compound has a cyclic structure assembled by four Ti clusters and four rodlike TTFTC connectors. Red compound self-condenses to form a black polymeric organic-inorganic hybrid material (denoted as B-), which was characterized by various techniques. B- is an amorphous TiO material that is formed by the irregular condensation of by the removal of alkoxyl groups. B- exhibits high dye adsorption efficiency toward cationic dyes with a value of 651.3 mg/g at 298 K for methylene blue (MB). Moreover, B- can be used to selectively remove MB not only from mixed cationic-anionic dye solutions but also from some mixed cationic dyes, which is related to their structures. Kinetic, isotherm, and thermodynamic studies demonstrated that the pseudo-second-order kinetic model and Freundlich model show a good fit to the experimental data. The adsorption process involves an exothermic and entropy decreasing process. In addition, dye-adsorbed B- can be further used as a photocurrent-responsive material. The work opens up a new field for the application of TOCs in the selective adsorption and removal of dyes.