Photocatalytic degradation of polycyclic aromatic hydrocarbons in GaN:ZnO solid solution-assisted process: Direct hole oxidation mechanism

The photooxidation of four polycyclic aromatic hydrocarbons (PAHs), namely phenanthrene (PHE), anthracene (ANT), acenaphthene (ACE), and benz[a]anthracene (BaA), were investigated. The solid solution GaN:ZnO before and after Pt modification were employed as photocatalysts. The intermediates from photodegradation were analyzed by gas chromatography-mass spectrometer. Active species in the present photocatalytic systems were monitored by the electron paramagnetic resonance spin-trap technique and hydrogen peroxide test strip. The effects of radicals and hole scavengers on the photocatalytic degradation of PAHs were also evaluated. The experimental results show that GaN:ZnO exhibits excellent activity for the photodegradation of PAHs, and the activity can be obviously improved by loading Pt. The reactivity of PAHs decreases in the order of PHE > BaA > ANT > ACE. On the catalyst of Pt-GaN:ZnO, PHE, BaA, ANT, and ACE can be degraded completely after 1, 3, 6, and 8 h visible light irradiation respectively. The mechanism examination evidences that the degradation of PAHs is induced by the formation of holes and active H species in the present photocatalytic system. The holes interact with PAHs to produce PAHs(+center dot), which are active enough to react with O-2 and active H species. The theoretical calculation results display that the active positions of PAHs without sp(3) orbital hybridization can be predicted by the frontier electron density (f(r)). (C) 2010 Elsevier B.V. All rights reserved.