Formation of active radicals and mechanism of photocatalytic degradation of phenol process using eosin sensitized TiO₂ under visible light irradiation

Abstract

The role of oxygen and the generation of active radicals in the photocatalitic degradation of phenol were investigated using the eosin sensitized TiO₂ as photocatalyst under visible light irradiation. Diffuse reflectance spectra show that the absorbancy range of eosin/TiO₂ is expanded from 378 nm (TiO₂) to about 600 nm. The photocatalitic degradation of phenol is almost stopped when the eosin/TiO₂ system is saturated with N₂, which indicates the significance of O₂. The addition of NaN₃ (a quencher of single oxygen) causes about a 62% decrease in the phenol degradation. The phenol degradation ratio is dropped from 92% to 75% when the isopropanol (a quencher of hydroxyl radical) is present in the system. The experimental results show that there are singlet oxygen and hydroxyl radical generated in the eosin/TiO₂ system under visible light irradiation. The changes of absorbancy indicate that the hydrogen peroxide might be produced. Through the analysis and comparison, it is found that the singlet oxygen is the predominant active radical for the degradation of phenol.

Keywords

eosin sensitized TiO₂ / visible light / photocatalytic degradation / reaction mechanism

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