Thermal Stability of (KxNayH1–x–y)2Ti6O13 Nanofibers

Abstract

Potassium-rich titanate nanofibers were produced by digesting TiO2 in concentrated KOH solutions under hydrothermal conditions. The nanofibers were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and thermogravimetric analysis. A hexatitanatestructure was assigned, in contrast to the trititanate structure usually resulting from NaOH treatment of TiO2. The potassium cations could be exchanged with others, such as sodium, hydrogen, and ammonium. The potassium-rich hexatitanate was found to be photocatalytic in its as-synthesized condition. The thermal stability of the fibers during calcination was followed in situ using X-ray diffraction and was found to be strongly dependent on the chemical composition. The potassium-rich titanate converted to anatase at only 480 °C, whereas the hydrogen- and ammonium-rich materials had to be heated to over 600 °C before conversion took place. Conversion was notably slowest in the ammoniumrich material. Surprisingly, the sodium-rich hexatitanate did not form anatase at temperatures up to 800 °C and insteadrecrystallized.