Atomically precise titanium-oxo nanotube with selective water adsorption and semiconductive behaviors

Abstract

We report the first example of carbon nanotube (CNT)-like assembly of the titanium (Ti) framework, Ti oxo inorganic cluster (Ti6O6) hexagonal rings into a titanium oxide (Ti-O) nanotube, prepared by ionothermal synthesis. As determined by single-crystal X-ray diffraction analysis, the Ti-O nanotube arrays, stabilized by sulfate ligands, assumed proper parallel alignment with each other and were separated by supramolecular interactions with surrounding EMIm (1-Ethyl-3-methylimidazolium) counter cations. Our stability studies indicated that the Ti-O nanotube obtained is indeed stable in air and various solvents. Also, it could maintain its structure upon heating to ∼300 °C. Moreover, inside the pores of the Ti-O nanotubes, a rare water molecules nanoconfinement behavior was observed at room temperature. Further, our current developed Ti-O nanotube arrays exhibited selective water adsorption over methanol and ethanol, showing potential applications for miscible solvents separations. Finally, these Ti-O nanotubes demonstrated typical semiconductive characteristics, with the electrical conductivity increasing four orders of magnitude, ranging from 3.15 × 10-10-1.03 × 10-6 S/cm, as the temperature increased from 35 to 135 °C. This work represents a milestone in constructing inorganic Ti-O nanotube arrays with atomically precise structural information for applications as visible-lightinduced photocatalysts, semiconductors, sensors, and optoelectronics.