Photodegradation of nonylphenol in aqueous solution by simulated solar UV-irradiation: The comprehensive effect of nitrate, ferric ion and bicarbonate

摘要

A Suntest-CPS+ sunlight simulator was used to investigate the direct and indirect photolysis of nonylphenol (NP) exposing to simulated sunlight in aqueous solution. The degradation reaction of NP obeyed a pseudo-first-order kinetics. Based on the pseudo-first-order rate constant (k) obtained from experimental data, the half-life of NP was calculated under different conditions, which ranged from 0.41 to 2.39 h. The affecting factors (NO3-, Fe3+ and HCO3-), especially their interactions on NP photodegradation, were systematically studied for the first time in the present study. The results showed that NO3- significantly influenced the photodegradation of NP and had a degradation ceiling. NO3- and HCO3- exhibited a synergistic effect on the photodegradation of NP and this interaction was very strong, which showed an abnormal phenomenon in dynamics, whereas the influence of Fe3+/HCO3- was slight on the photodegradation of NP. In addition, Fe3+ contributed little to the interaction in combining with other ions (NO3- and HCO3-). The light-absorbing ions (NO3- and Fe3+) with low concentration could inhibit the photolysis of NP only at the beginning of degradation process, indicating that the competition for energy and photons between NP molecule and light-absorbing ions is stronger than the photosensitizing effect at the initial stage. But this effect diminished with prolonged irradiation. Additionally, it was proved that the formation of free radicals during the photodegradation reaction was not the rate-determining step in NP indirect photodegradation. Meanwhile, compared with HO center dot, CO3-center dot had a higher oxidation rate on NP degradation, attributed to the generation of the more stable transition state between NP and CO3-center dot during the degradation process. (C) 2016 Elsevier B.V. All rights reserved.