Optimization of reaction conditions on titanium dioxide with various co-catalysts for phenol removal

Abstract

Titanium oxide, TiO2 is commonly used as a photocatalyst for photocatalytic degradation of organic pollutants such as phenol. In order to improve the photocatalytic efficiency of TiO2, modification and reaction condition optimizations were carried out in this study. Three types of TiO2 were used, which were anatase, rutile, and mixture of anatase and rutile. It was confirmed that the anatase structure gave the highest photocatalytic activity with 22% of phenol removal after 2 hours reaction under UV light irradiation. Modification of anatase TiO2 was conducted using various co-catalysts, such as Pt, Ni, ZnO, and Fe2O3. Among the examined cocatalysts, only Pt showed its potential as co-catalyst for TiO2 in this photocatalyst system. The Pt/TiO2 series were then characterized by X-ray diffraction (XRD), particle size analyser, Diffuse Reflectance UV-Visible spectroscopy (DR UVVisible), and fluorescence spectroscopy. XRD patterns showed that the addition of Pt resulted in the higher peak intensity of the TiO2, without detection of other diffraction peaks. This result suggested that the addition of Pt might induce the high crystallinity and increase the particle size of prepared samples. The increase of the particle size was in good agreement with the particle size distribution. DR UVvisible spectra showed the strong absorption peak of TiO2 at 320 nm, indicating that all of these samples possess the ability to be active in UV light region. Additional of absorbance at background level above 400 nm suggested the presence of Pt in the Pt/TiO2 samples. Fluorescence spectra showed that the emission intensity of TiO2 increased with the addition of Pt, suggesting the Pt can act as an electron trapper. The effect of co-catalyst loading on TiO2 anatase was then investigated and it was found that 0.5 wt% loading on TiO2 gave higher photocatalytic phenol removal (28%) than the unmodified TiO2. Optimization of the reaction conditions was carried out by varying the amount of catalyst, pH of the solution, and addition of H2O2 into the phenol solution. It was observed that the best condition for the Pt/TiO2 to give the highest activity (54%) was obtained when using 50 mg of catalyst, phenol solution pH of 6.4 and ratio of H2O2 to phenol solution of 10.5. The kinetic study showed that the reactions followed first order reaction and the rate of reaction increased with the addition of H2O2 under optimized conditions.