Thermal stability of (K<inf>x</inf>Na<inf>y</inf>H<inf>1-x-y</inf>) <inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> nanofibers

Potassium-rich titanate nanofibers were produced by digesting TiO 2 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 hexatitanate structure 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 ammonium-rich material. Surprisingly, the sodium-rich hexatitanate did not form anatase at temperatures up to 800 °C and instead recrystallized. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim