Photodegradation of methyl green using visible irradiation in ZnO suspensions: Determination of the reaction pathway and identification of intermediates by a high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry

Heterogeneous photocatalytic treatment of a dye called methyl green (MG), which was simulating textile wastewater from associated auxiliary chemicals, was investigated using ZnO. A detailed investigation of the photodegradation of MG has been carried out in the ZnO suspension irradiated with visible light. The effects of various factors – viz. pH values, amount of catalyst, initial dye concentration, and the presence of NaCl, Na2CO3, H2O2, and Na2S2O8 – on the degradation efficiency were studied. Thirty-two intermediates were separated, identified, and characterized by high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry (HPLC–ESI-DAD-MS) technology, giving us insight into the pathways of the degradation process.