Quantification of photocatalytically-generated hydrogen peroxide in the presence of organic electron donors: Interference and reliability considerations

Photocatalytic H2O2 production is an innovative on-site H2O2 synthesis method to treat organic pollutants through Fenton-like reactions, avoiding the need and potential liability of H2O2 storage and transportation. Accurate quantification of H2O2 is crucial to explore the mechanism of photocatalytic H2O2 production and optimize reaction parameters. In this work, three common H2O2 quantification methods (i.e., titration with potassium permanganate (KMnO4), and colorimetry with ammonium metavanadate (NH4VO3) or N,N-diethylp-phenylenediamine-horseradish peroxidase (DPD-POD)) were compared and their susceptibility to interference by seven types of representative organics were considered. Interference mechanisms were explored based on the electron-donating (Egap) and electron-accepting (ELUMO) ability of the present organics. The accuracy of the KMnO4 titration method is greatly compromised by aromatic compounds even at 0.1 mM due to the increased KMnO4 consumption by direct oxidation. The presence of p-benzoquinone that directly reacts with NH4VO3 and DPD compromises these colorimetric methods, especially DPD-POD colorimetry at concentrations as low as 0.1 mM. The DPD-POD method should also be scrutinized in the presence of phenols due to significant disturbance by oxidation byproducts (e.g. hydroquinone inducing immediate color disappearance). A flowchart was generated to provide guidelines for selecting an appropriate H2O2 quantification method for different water matrices treated by Fenton-like reactions.