Research on Photocatalytic Degradation Pathway and Degradation Mechanisms of Organics

In this review, three degradation mechanisms, pathways and intermediate products of various organic compounds for photocatalytic degradation by using different photocatalysts are discussed in detail. Three degradation mechanisms are as following: (1) Holes in valence bond and resulting OH˙ radicals generated from holes oxidize the organics, (2) resulting OH˙ radicals and the O2 ˙¯ generated from conduction band electrons oxidize the organics, (3) dye sensitization. The organic matters can be oxidized by several oxidizing species. Under the condition of various light irradiation, photocatalyst can produce electron and hole to form oxidizing species, which have enough oxidization capability to decompose those organic compounds. Most researchers agreed with the mechanisms of electron /O2 or hole oxidizing, which happened in the photodegradation process. However, dye sensitization is also an important mechanism for photodegradation. In addition, photodegradation intermediate products and pathways of 48 organic compounds are illuminated in detail. They are 1,2-diethyl phthalate, 2,3-dichlorophenol, 2-naphthol, 3,3'-dimethylbiphenyl-4,4'-diamine (o-Tolidine), 3-chloropyridine, 3- nitroacetophenone, methylene blue, trimelitic acid, 4-chlorophenol, pirimiphos-methyl, propanil, molinate, imzazpyr, 4-nitrophenol, methomyl, iodosulfuron methylester, imipramine, chlorfenvinphos, rhodamine B, atrazine, chlorfenapyr, methylparaben, malachite green, C.I. acid red, aniline, 4-chlorophenol, chlorothalonil, dichlofluanid, cyromazine, decabromodiphenyl ether, dipyrone, ethanol, fluroxypyr, hexachlorocyclohexane, maleic acid, fumaric acid, malic acid, metanil yellow, methyl orange, methyl red, methyl-tert-butyl ether, naphthalene, tetrachloroethylene, trichloroethylene, triane, Ph-triole, Ph-triane, dicyclanil. The degradation routes and the intermediate products of these 48 organic compounds will provide scientific researchers with the proof to prepare novel and ideal photocatalysts with perfect crystallinity and photodegradation methods in this field.