Thermal degradation; Evolved gas analysis; High temperature X-ray diffraction; (Peroxo)titanates; TiO2 properties; Amines

This report describes the thermal behaviour of nanotitania precursors and the influence of various amines and peroxide treatment on properties of TiO2. Thermal degradation of amine-containing amorphous (peroxo)titanates was examined via TG-DTA coupled with evolved gas analysis (EGA) by mass spectrometry in inert and oxidizing atmosphere. Crystallization to anatase and subsequent transformation to rutile are studied by in situ HT-XRD, which provided information about particle growth and mutual ratio between allotropic phases. In argon, the samples underwent a two-step degradation process, involving the release of moisture and decomposition or evaporation of amine, up to 450 degrees C, while in air conditions, the organic component could be oxidized in an additional third step at even higher temperatures. EGA confirmed the presence of the original amine in the amino-titanates, while the organic parts reacted with oxygen evolved from the peroxide group to form oxidation products (H2O, CO2 and NOx). The crystallization of nanoanatase began simultaneously/subsequently with the second degradation step. While peroxide treatment increased the initial particle size (from 5 to 40 nm), the choice of amine had a significant impact on the anatase formation temperature (325-425 degrees C). The anatase particle size increased with higher formation temperature after H2O2 treatment, while the particle size of amino-titanates decreased. The rutile formation temperature was directly dependent on the anatase particle size. Hitherto prepared amine-treated (peroxo)titanates demonstrated good thermal endurance of anatase nanoparticles (800-900 degrees C), which could be advantageous for various photocatalytic applications. The obtained results provide a method to synthetize tailored TiO2 with desired properties by adjusting the synthetic conditions (selection of precipitation agent and peroxide treatment) and annealing temperatures.