Synthesis of TiO2 nanoparticles by spray-lyophilization process : characterization and optimization of properties of photocatalytic water purification and gas sensing applications

Abstract

Monodisperse titanium dioxide (TiO2) nanoparticles were synthesized by a novel freeze-drying process herein called lyophilization. The process of lyophilization is described in detail. The materials were characterized by scanning electron microscopy SEM) including energy dispersive x-ray spectroscopy (EDXS), high resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), Raman spectroscopy and UV-Vis-IR spectrophotometry. The TiO2 nanoparticles have narrow size distribution, mono-disperse, strained with most of the characteristics showing presence of the four phases of TiO2 thus: anatase, brookite, rutile with each lyophilization process producing its own phase mostly controlled by pH and precursor concentration and anneal/calcining temperatures. With specific reference to HRTEM, Raman spectroscopy results and XRD, it was found that the Scherrer equation, the Williamson-Hall method and others of similar nature were not enough to explain the strain and the grain sizes of these particles. Therefore the Williamson-Hall method was revised to properly explain the new results. The obtained TiO2 nanoparticles were used in three applications: (1) gas sensing (2) degradation of organic water-borne pollutants using methylene blue as an indicator (3) anti-bacterial activity.