Influence of morphology and surface characteristics on the photocatalytic activity of rutile titania nanocrystals

This article presents the synthesis of phase-pure rutile titania with different morphologies via hydrothermal method at significantly low temperatures (40-150 °C) without any additives and their application as efficient photocatalyst for environmental remediation. Phase and morphology has been determined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ultra violet diffuse reflectance spectroscopy (UV-DRS) shows the optical band-gap in the range of ∼2.8-3.1 eV and Brunauer-Emmett-Teller specific surface area is found to be between 70 and 140 m²/g depending on the synthesis conditions. Raman spectroscopic analyses of the samples provide valuable insights into the structural and stoichiometric details. Photodegradation of the pollutant azo-dye, methyl orange (MO) in presence and absence of oxygen was performed to study the photocatalytic efficiency of the synthesized materials. Complete photodegradation of the dye is confirmed with high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) study. Dependence of dye photodegradation rate on morphology, specific surface area, surface nonstoichiometry and acidity were investigated in detail. Catalyst performance was compared from the rate constants obtained for each reaction using non-linear least square fitting (NLSF) to the experimental data in a concentration ratio (C₀/C_t) versus time (t) plot which shows extraordinarily high activity for all samples compared to commercial reference. Among them the catalyst synthesized at 40 °C for 16 h showed best activity. Kinetic study of the reaction matches well with simulated fit to experimental data and confirms to be pseudo-first order reaction.