Pathway analysis of phenol degradation by UV/TiO2 photocatalysis utilising the C-13 isotopic labelling technique

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 several intermediate compounds, some of which are feared to be more toxic than the original compound being treated. 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 (20mg/L) in ultrapure water in a batch system. Catalyst concentration was constant at 8mg/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 hydroquinone, benzoquinone catechol and resorcinol. The concentration of phenol was determined from the calibration curve of standards of phenol. Photocatalysis is a promising technology for the complete mineralization 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 cycling compounds on cleavage of the aromatic ring. The distribution of the degradation intermediates confirms that the dominant degradation pathway is via hydroxyl radical mechanism.