Research On The Photosensitivity Of Quinoid Compounds

In recent years, advanced oxidation technologies based on sunlight/Fenton and sunlight/Fe2+/S2O82- methods are the new field by scholars. The methods can not only accelerate the degradation process of organic matter, but also reduce the dosage of oxidant to decrease the cost. Although sunlight method has been widely studied, the degradation mechanism of sunlight method has not been comprehensively and deeply researched. Because quinonoids and quinoneimines could be generated during the process of aromatic compounds degradation and the majority of quinonoids is induced photosensitive reaction under visible light. So the photosensitivity of benzoquinones and benzoquinoneimines was studied in this paper to reveal the photosensitization in water treatment and find out the reason of that sunlght could improve the degradation rate.This paper investigated the degradation characters of benzoquinones and benzoquinoneimines in the light/Fenton, light/H2O2, light/Fe2+/S2O82- and light/S2O82-system using benzoquinone that was the degradation intermediates of phenol, benzene and nitrobenzene, and acid methyl orange, Methylene blue and toluidine blue as the model compounds to represent benzoquinones and benzoquinoneimines respectively. The photosensitivity of benzoquinones and benzoquinoneimines was analyzed by measuring the yields of 1O2 and O2-· and the yield of OH and SO4- in the light/Fenton and light/Fe2+/S2O82- system, respectively. The results demonstrated that benzoquinones and benzoquinoneimines were both photosensitizers, and the photosensitivity of benzoquinones was superior to benzoquinoneimines. Sunlight method was better than the UV method for the degradation of benzoquinones in four systems. For benzoquinoneimines, UV/Fenton was better than sunlight/Fenton at lower concentration, sunlight/Fenton is better at higher concentration, sunlight/Fe2+/S2O82- method was superior to UV/Fe2+/S2O820 method and UV method was superior to sunlight method in light/H2O2 and light/S2O82- systems.The reason is that O2-· which can be produced by benzoquinones and benzoquinoneimines can promote the generation of OH and SO4-· in sunlight system, and that could cause more active material to be produced in this system. However, benzoquinoneimines is a worse photosensitizer than benzoquinones and is influenced by Fe2+ and its concentration. Nevertheless, benzoquinones could be generated during the degradation of benzoquinoneimines that could generate 1O2, O2-·,·OH and SO4-· in sunlight system, thereby more benzoquinones could been generated by higher concentration of benzoquinoneimines resulting fast degradation in sunlight system. So the sunlight/Fenton method and light/Fe2+/S2O82- method are more suitable for handing wastewater that contains benzoquinoneimines.