The effect of dissolved oxygen on the UV/TiO2 photocatalytic degradation mechanism of phenol

Abstract

Photocatalysis is a green technology for the degradation of persistent organic compounds in water and has been successful in the removal of several water pollutants. Degradation of organic compounds in water is often accompanied by the formation of degradation by-products, which are not well researched. In this study, aromatic intermediates formed during the photocatalytic degradation of phenol were profiled in a batch system. The carbon-13 isotopic labelling technique was used to track the degradation pathway. Photocatalytic degradation of phenol was conducted in 1L solutions of phenol (20 mg/L) in ultrapure water in a batch system. Catalyst concentration was constant at 8 mg/L Titanium dioxide (TiO2). Concentration of phenol and detection of the aromatic intermediates of phenol degradation were monitored on a Waters High Performance Liquid Chromatograph (HPLC) and Gas Chromatogram-Mass Spectrometer (GC-MS), respectively. Aromatic intermediates identified during the course of photocatalysis of the phenol include Benzoquinone, Hydroquinone and Maleic acid. Photocatalysis has shown potential for the complete mineralisation of aromatic organic pollutants as it has been demonstrated that both the pollutant and its direct intermediates can be completely removed from solution. Phenol degradation produces first aromatic dihydroxy substituted compounds that are further degraded forming acyclic compounds on cleavage of the aromatic ring. The distribution of the degradation intermediates confirms that the dominant degradation pathway is via hydroxyl radical mechanism.