From titania to titanates: Phase and morphological transition in less alkaline medium under mild conditions

Abstract

In this work, nine products were prepared by modifying the experimental conditions (6, 12 and 18 h at 110, 135 and 160 °C) of hydrothermal treatment of starting nanoanatase in significantly less concentrated alkaline medium than usual in order to obtain a pure titanate phase. The nanocrystalline samples were characterized by XRPD, FESEM, HRTEM/SAED, EDS, TG, FT-IR, UV-Vis and BET analyses. The results revealed that the structure, texture, morphology and band gap energy of samples strongly depend on conditions of hydrothermal treatment. The intensification of hydrothermal treatment significantly increases the solubility of TiO2 promoting the changes in morphology from nearly spherical titania nanoparticles to elongated titanate nanosheets. The single titanate phase was obtained after energetically the most intensive treatment, i.e. 18 h at 160 °C. The step-by-step optimization was thus necessary to finally distinguish the titanates from titania in terms of structural and spectral properties and to finally allow the clarification of long-standing confusion between titania and titanates. The obtained single titanate phase was furtherly used to fabricate a humidity sensor, which showed remarkably rapid response and quick recovery time.