Photolysis is a chemical reaction in which a chemical compound is broken down by the high photon energy provided by a short wavelength light (typically UV) after absorbing light of sufficient energy. Many compounds absorb light in the UV-C range of200-280 nm, which has sufficient energy to break the chemical bonds in the molecule. The photolytic reaction performed in the absence of a catalyst (photolysis) typically exhibits very slow kinetics, compared to that in the presence of a catalyst (photocatalysis). For chlorophenol decomposition, TiO2 photocatalysis at 340 nm is more efficient than direct photolysis at 290 nm with higher photon energy because the photocatalytic reaction occurs through the formation of hydroxyl radicals . It was also reported that the mineralization of humic acid by TiO2 photocatalysis was two times faster than that by photolysis under the same UV irradiation . Direct photolysis even under short wavelength UV irradiation is not significant for many organic compounds because of low absorption of the radiation.
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