Effect of different calcination temperatures on the phase structure and photocatalytic behavior of TiO۲

Titanium dioxide (TiO۲) is a widely studied semiconductor oxide owing to its remarkable physical, chemical, and optical properties. It crystallizes mainly in three polymorphs, anatase, rutile, and brookite, each with distinct structural and electronic characteristics that determine its suitability for different applications. Anatase, with a band gap of about ۳.۲ eV and high specific surface area, generally exhibits superior photocatalytic activity and is widely used in photocatalysis, dye-sensitized solar cells, and environmental purification. Rutile, the thermodynamically most stable phase with a slightly smaller band gap (~۳.۰ eV) and high refractive index, is preferred in pigments, coatings, and applications requiring high thermal and chemical stability. Brookite, although less common and less stable, can play an important role in mixed-phase systems, where synergistic interactions between different TiO۲ phases can enhance photocatalytic performance[۱, ۲]. In this work, TiO۲ nanoparticles were synthesized via a sol-gel route using tetraisopropyl orthotitanate (TTIP) as the titanium precursor. An acidic aqueous solution of nitric acid (HNO۳) was added dropwise to an alcoholic TTIP solution under vigorous stirring at ۶۰ °C until the formation of a white gel, indicating the completion of hydrolysis and condensation reactions. The obtained gel was aged, dried at ۱۰۰ °C, and subsequently calcined at different temperatures (۶۰۰, ۹۰۰, and ۱۲۰۰ °C) to produce three samples, denoted as TiO۲-۶۰۰, TiO۲-۹۰۰, and TiO۲-۱۲۰۰. The variation in calcination temperature is expected to significantly influence the crystallite size, phase composition (anatase-rutile transformation), and particle agglomeration. The synthesized TiO۲ nanoparticles are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS). XRD is employed to identify the crystalline phases (anatase and/or rutile), determine the degree of crystallinity, and estimate crystallite size using the Scherrer equation. SEM provides high-resolution images of particle morphology, shape, and aggregation, typically revealing nanoscale particles and the evolution of grain size with increasing calcination temperature. DLS is used to measure the hydrodynamic size distribution and colloidal stability of TiO۲ nanoparticles in suspension, taking into account solvation and possible aggregation effects [۱, ۳]. By correlating the structural information obtained from XRD, the morphological observations from SEM, and the hydrodynamic size analysis from DLS, this study aims to clarify the relationship between calcination temperature and the structural, morphological, and dispersion-related properties of sol-gel-derived TiO۲ nanoparticles. These insights are expected to be valuable for tailoring TiO۲ nanomaterials for photocatalytic, coating, and biomedical applications[۴].

کلیدواژه ها:

Titanium Dioxide ، Calcination ، Crystalline Phases ، Sol-Gel Synthesis