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 hexa-titanate structure was assigned, in contrast to the tri-titanate 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 hexa-titanate was found to be photocatalytic in the 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 while the hydrogen-rich 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 hexa-titanate did not form anatase at temperatures up to 800 °C, and instead recrystallized.