Heterogeneous Photodegradation of Pentachlorophenol with Maghemite and Oxalate under UV Illumination

The degradation of pentachlorophenol (PCP) in a heterogeneous system with maghemite (gamma-Fe2O3) and oxalate under UV illumination was investigated in this study. The results of adsorption experiments demonstrated competitive adsorption between PCP and oxalic acid on the surface of gamma-Fe2O3. The results of photodegradation experiments showed that the rate of PCP degradation strongly relied on the oxalic acid concentration and that an optimal tested initial concentration of oxalic acid (C-ox(0)) of 0.8 mM was obtained under our experimental conditions. It was observed that a sufficient amount of oxalic acid can be adsorbed on the gamma-Fe2O3 to form various Fe(III)-oxalate complexes at C-ox(0) = 0.8 mM. During the photoreaction Fe(C2O4)(2)- and Fe(C2O4)(3)(3-) were found to be the dominant Fe(III)-oxalate complexes at different C-ox(0), while Fe(C2O4)2 2- was the dominant Fe(II)-oxalate complex at C-ox(0) >= 0.8 mM. The mechanism of H2O2 formation and consumption in the UV-irradiated gamma-Fe2O3/oxalate system was proposed and evaluated. Furthermore, six intermediates of PCP degradation were identified by GC/MS, HPLC, and IC analyses, respectively, and a possible pathway of PCP degradation in such a system was proposed.