Enhancement of Sono-Fenton by P25-Mediated Visible Light Photocatalysis: Analysis of Synergistic Effect and Influence of Emerging Contaminant Properties

The main purpose is to figure out the involved synergistic effects by combining sono-Fenton using in situ generated H2O2 and the photocatalytic process of P25 under visible light (Vis/P25). Two emerging contaminants, dimethyl phthalate (DMP) and diethyl phthalate (DEP), with similar structure but different properties were selected to examine the influence of hydrophilic and hydrophobic properties of target pollutants. Results show that there is synergy between sono-Fenton and Vis/P25, and more significant synergy can be obtained with low dose of Fe3+ or Fe2+ (0.02 mM) and for more hydrophilic DMP. Based on systematic analysis, the primary mechanism of the synergy is found to be the fast regeneration of Fe2+ by photo-electrons from P25 photocatalysis, which plays the dominant role when the Fe3+/Fe2+ concentration is low (0.02 mM). However, at high Fe3+/Fe2+ concentration (0.5 mM), the photoreduction of Fe(III) to Fe2+ can play a key role with relatively low efficiency. By studying the degradation intermediates of both DMP and DEP, the degradation pathways can be determined as the hydroxylation of aromatic ring and the oxidation of the aliphatic chain. Better mineralization performance is achieved for DMP than that for DEP due to the enhanced utilization efficiency of H2O2 by accelerating Fe2+ regeneration.