Transformation of 4-tert-octylphenol by UV irradiation and by an H_2O_2/UV process in aqueous solution

摘要

The transformation of the organic pollutant 4-(l,l,3,3-tetramethylbutyl)phenol(4-tert-octylphenol;OP)upon irradiation at 253.7 nm and by hydroxyl radicals generated by the photolysis(gamma)exc)=253.7 nm)of hydrogen peroxide in aqueous solution has been studied.The quantum yield of direct OP photolysis in pure aqueous solution was evaluated to be 0.058(+-)0.004 in aerated conditions(O_2=272 muM).The rate of photoreaction depends on oxygen concentration;it increases with increasingO_2.4-tert-Octylcatechol has been identified as one of the degradation products,together with a dimeric structure.The probable mechanism of OP photolysis involves photoejection of an electron from the singlet state,leading to the formation of the 4-tert-octylphenoxyl radical.In the presence of hydrogen peroxide,the degradation of octylphenol by hydroxyl radicals has been observed.The second-order rate constant was found to be(6.4 ± 0.5)x 10~9 M~(-1)s~(-1)by direct measurement at various high concentrations of hydrogen peroxide and competitive kinetic measurements using atrazine as the competitor.The degradation products are 4-tert-octylcatechol,again,and 2-hydroxy-5-tert-octylbenzoquinone.The later product may arise from the oxidation of 4-tert-octylcatechol by hydrogen peroxide or from a subsequent reaction of hydroxyl radicals with 4-tert-octylcatechol.Kinetic modelling when using either purified water or natural water successfully simulated the elimination of 4-tert-octylphenol by UV and H_2O_2/UV processes.