Photochemical degradation of 2,4,6-trichlorophenol in the presence of a nonionic surfactant : pH control on reaction kinetics

摘要

The photochemical degradation of 2,4,6-trichlorophenol (2,4,6-TCP) has been studied in the presence of a nonionic surfactant. A faster decay of 2,4,6-TCP could be achieved by the addition of surfactant depending on the pH levels. By examining the TCP decay at different solution pH and surfactant concentrations, the variations in photodecay rates were dominated by the existence of surfactant micelles. In water or when surfactant dosage was below the critical micellar concentration, the photodecay of 2,4,6-TCP was found to be faster at high pH levels, mainly due to the higher absorption of TCP and additional hydrogen source (from surfactant monomer). On the contrary, in the presence of micelles, faster decay of 2,4,6-TCP was obtained at lower pH levels. This was possibly due to the domination of both photochemical homolysis and electron transfer processes in acidic condition, but the latter was inhibited at alkaline condition. In addition, the cage effect of surfactant micelles may possibly hinder the O H- -catalyzed photohydrolysis in the solution, so the TCP decay in micellar solution was reduced at high pH levels.