Enhanced Photocatalytic Performance of Titania-Based Binary Metal Oxides:  TiO₂/SiO₂ and TiO₂/ZrO₂

Abstract

Sol-gel prepared mixtures of silica or zirconia with titania are shown to have significantly higher activities than pure titania for the complete photocatalytic oxidation of ethylene. These higher activities are only apparent when the respective catalysts are stabilized by sintering. The differences become even more pronounced when the catalysts are used in a tubular reactor. Optimum mixture concentrations are found to be 12 wt % zirconia and 16 wt % silica in titania. Both catalyst types exhibit activity maxima with respect to sintering temperature. It is hypothesized that the maxima arise from opposing effects of densification and phase transformation versus beneficial sintering. A comparison of our catalyst compositions with literature in this area suggests that the increase in activity due to the addition of silica or zirconia may be a result of higher surface acidity. However, isoelectric point measurements employing the unsintered and sintered catalysts show no conclusive increase in surface acidity. The effects of sintering temperature on the surface area, porosity, and crystal structure of the catalysts are also presented.

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

“…Until now, TiO 2 -ZrO 2 films prepared by sol-gel methods and used as powders or annealed on diverse substrates at a few hundred degrees have been used in industrial processes as catalysis, electronic devices and in optical applications [26,27]. The effect of Cu at very low concentrations related to TiO 2 -ZrO 2 -Cu films will be investigated for their role hindering the TiO 2 charges recombination.…”

Synthesis, characterization and photocatalytic applications of Zn-doped TiO2 nanoparticles by sol–gel method

“…The photocatalytic activity of titania can be improved by decrease in grain size, increasing surface area, sensitization using dye molecules and doping with metals and non-metals Fu et al 1996). Doping with transition metal ions like Fe 2?…”

Characterisation, phase stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

“…The reason for the larger number of metal-OH groups with increasing doping concentration can be found in the surface acidity. Incorporation of dopant cations creates a charge imbalance resulting in Brønsted or Lewis acid sites depending on the coordination geometry and valence of the dopant [17,69]. Utilising the model of mixed oxides by Tanabe et al [69], which states that the dopant cation enters the host oxide while maintaining its coordination number, it can be predicted whether Brønsted or Lewis acid sites are formed.…”

“…The reason for this is believed to be the larger radius of Zr 4+ cation and concomitant relaxation of the anatase structure [27]. An improved activity of Zr-TiO 2 and sintered ZrO 2 -TiO 2 has also been reported for the photodegradation of methylcyclohexane and ethylene, respectively, which was attributed to an increased surface acidity and larger surface area [4,17]. The reported optimal metal dopant concentration for anatase TiO 2 in photocatalysis applications generally falls between 1% and 10% [21,22,28].…”

“…Several strategies have been employed to achieve visible-active photocatalytic materials. So far the most common strategies have been to modify TiO 2 by metal dopants [4][5][6] or anion dopant atoms such as sulphur [7][8][9], carbon [10,11] and nitrogen [12][13][14], as well as by mixtures of metal oxides [15][16][17][18]. More recently complex heterostructured materials have been reported, such as diode structures made of p-and n-type semiconductors [19].…”