Hydrothermal Synthesis of Rare-Earth Modified Titania: Influence on Phase Composition, Optical Properties, and Photocatalytic Activity

Abstract

In order to expand the use of titania indoor as well as to increase its overall performance, narrowing the band gap is one of the possibilities to achieve this. Modifying with rare earths (REs) has been relatively unexplored, especially the modification of rutile with rare earth cations. The aim of this study was to find the influence of the modification of TiO2 with rare earths on its structural, optical, morphological, and photocatalytic properties. Titania was synthesized using TiOSO4 as the source of titanium via hydrothermal synthesis procedure at low temperature (200 °C) and modified with selected rare earth elements, namely, Ce, La, and Gd. Structural properties of samples were determined by X-ray powder diffraction (XRD), and the phase ratio was calculated using the Rietveld method. Optical properties were analyzed by ultraviolet and visible light (UV-Vis) spectroscopy. Field emission scanning electron microscope (FE-SEM) was used to determine the morphological properties of samples and to estimate the size of primary crystals. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical bonding properties of samples. Photocatalytic activity of the prepared photocatalysts as well as the titania available on the market (P25) was measured in three different setups, assessing volatile organic compound (VOC) degradation, NOx abatement, and water purification. It was found out that modification with rare earth elements slows down the transformation of anatase and brookite to rutile. Whereas the unmodified sample was composed of only rutile, La- and Gd-modified samples contained anatase and rutile, and Ce-modified samples consisted of anatase, brookite, and rutile. Modification with rare earth metals has turned out to be detrimental to photocatalytic activity. In all cases, pure TiO2 outperformed the modified samples. Cerium-modified TiO2 was the least active sample, despite having a light absorption tail up to 585 nm wavelength. La- and Gd-modified samples did not show a significant shift in light absorption when compared to the pure TiO2 sample. The reason for the lower activity of modified samples was attributed to a greater Ti3+/Ti4+ ratio and a large amount of hydroxyl oxygen found in pure TiO2. All the modified samples had a smaller Ti3+/Ti4+ ratio and less hydroxyl oxygen.

Recent Progress in the Abatement of Hazardous Pollutants Using Photocatalytic TiO2-Based Building Materials

“…They concluded that the binder inclusion did not significantly enhance the properties of the photocatalytic paints concerning VOC emissions. Nejc Rozman et al prepared rare earth element (such as La, Gd, and Ce) modified TiO2 and assessed the photocatalytic degradation of a few VOCs [162]. A reactor comprising of a gas pump and pipes was set up to understand the degradation kinetics using Fourier-transform infrared spectroscopy.…”

“…They concluded that the binder inclusion did not significantly enhance the properties of the photocatalytic paints concerning VOC emissions. Nejc Rozman et al prepared rare earth element (such as La, Gd, and Ce) modified TiO 2 and assessed the photocatalytic degradation of a few VOCs [ 162 ].…”

Entropy-Stabilized Oxides owning Fluorite Structure obtained by Hydrothermal Treatment

“…These doped oxides are commonly used for a wide range of applications, such as sunscreen cosmetics, magneto-optical devices, catalysts, biomarkers, colorant for special glasses, solid electrolytes, etc. [15][16][17].…”

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

“…The impurity energy levels act as trapping centers for photogenerated electrons and holes, thereby favoring charge separation and reducing the electron-hole recombination [118][119][120][121]. Among these, the La dopant in titania is studied most frequently, followed by Ce doping, in recent years [116][117][118][119][120][121][122]. Kasinathan et al reported that cerium doping suppresses the recombination of photogenerated electron-hole pairs in titania and promotes a red-shift in its band gap transition.…”

“…Mo 6+ + e − → Mo 5+ (3) From the literature, rare earth metal ions are effective in extending the recombination time of charge carriers and improving their separation efficiency. Rare earth metals, such as cerium (Ce), lanthanide (La), erbium (Er) and ytterbium (Yb), with 4f, 5d, and 6s electrons are good dopants for modifying the electronic structure and optical properties of titania [116,117]. Rare earth dopants introduce several impurity energy levels due to the introduction of orbitals between the conduction and valence bands.…”