Enhanced direct sunlight photocatalytic oxidation of methanol using nanocrystalline TiO2 calcined at different temperature

Abstract

The present study focused on photocatalytic oxidation of methanol to formaldehyde using nanocrystalline TiO2 (Degussa P-25) photocatalyst calcined at different temperature having different ratio of anatase (A)–rutile (R) phase composition under direct sunlight irradiation. The calcined nanocrystalline TiO2 was characterized using powder X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and UV–Visible diffuse reflectance spectroscopy techniques. The determination of hydroxyl radical formation during the course of the reaction was carried out using fluorescence technique with terephthalic acid as a probe molecule. The photocatalytic activity of catalysts was evaluated by methanol oxidation under direct sunlight irradiation and activity was compared with pure anatase TiO2. The result revealed that nanocrystalline TiO2 (P-25) calcined at 500 °C displays higher photocatalytic activity and the order of rate of HCHO formation is P25-500 (A74 %:R26 %) > P25 (A80 %:R20 %) > AT (A100 %) > P25-600 (A12 %:R88 %) > P25-700 (R100 %). The result also infers that TiO2 with mixed phase exhibit higher photocatalytic activity than TiO2 with pure anatase or rutile phase. The rapid transfer of photogenerated electron from rutile to anatase leads to increase in the charge separation and enhances the photocatalytic activity under direct sunlight irradiation. Effect of operational parameters like amount of catalyst and effect of reaction atmosphere have been investigated on the photocatalytic oxidation of methanol under direct sunlight irradiation.