Mechanism Study on Photodegradation of Nonylphenol in Water by Intermediate Products Analysis

Abstract

The photodegradation mechanisms of nonylphenol (NP) with the involvement of dissolved oxygen (DO), hydro- gen peroxide, nitrate ion and chloride ion in water by simulated sunlight were studied, respectively. The influence of each factor on the photodegradation of NP has been assessed through contrasting the residual rate of NP. And the photodegrada- tion pathways in different conditions have been proposed according to the intermediate products identified by GC-MS. DO was a key factor in the photodegradation of NP and the rate of photoreaction depended on O2 concentration; the existence of H2O2 or 3 NO - increased the NP degradation rate significantly; with the existence of H2O2, the addition of Cl - first acceler- ated then slowed down the NP degradation rate. When NP reacted with DO, 4-nonylcatechol, nonanol, nonanal and nonoic acid have been identified as the degradation products. The accumulated amount of nonoic acid was the most. The proposed mechanism was that the 4-nonylcatechol and ortho-quinone derivative were produced after the formation of 4-nonylphenoxyl radical and superoxide radical anions 2 (O ) •- , then the intermediates underwent conjugate addition, nonanol, nonanal and nonoic acid were produced. In the presence of H2O2, 4-n-akylphenol (HOC6H4-CnH2n+1, n=2~8), 4-nonylcatechol, nonanol, nonanal and nonoic acid were the degradation products. And the accumulated amount of nonanal was the most. The hydroxyl radicals (•OH) generated by the photolysis of H2O2 attacked the electronic gathered positions of NP molecules. The products detected in the presence of 3 NO - were same as which detected in the presence of H2O2. The irradiated 3 NO - can produce •OH andNO2, so 2-nitryl-4-nonylphenol was found as the product ofNO2 attacking the ortho-position of phenolic hy- droxyl. In the presence of Cl - and H2O2, the nonanoyl chloride was found. The accumulated amount of nonanal was the most, so the probable mechanism was that the chlorine radical which generated from the reaction ofOH and Cl - reacted