Role of Nitrite Ions and Natural Organic Matters as Photosensitizers on Photolysis of Phenol

Nitrite and natural organic matters (NOM) are well known to be involved in photochemical processes occurring in natural waters. In this study, phenol is chosen as model molecule to investigate the role of nitrite ions or NOM towards the transformation of organic matters in aqueous solutions under simulated sunlight irradiation. All experiments were performed in pure water at pH 7. The results indicated that phenol phototransformation rate increased with increasing nitrite or NOM concentrations as expected. And •OH radical was demonstrated to be the main relative free radical according to the electron paramagnetic resonance (EPR) and isopropanol quenching experiments. But unexpectedly, the presence of NOM would inhibit nitrite ions-sensitized photolysis of phenol, and it might be attributed to the ROS quenching and light screening effect of NOM. The results imply that for accurate ecological risk assessment of organic pollutants, the integrated effect of water constituent on the environmental photochemical behavior of organic pollutants should not be ignored.

The fluorescence analysis of laser photolysis of phenols in water

Photolysis of phenol andp-chlorophenol exposed to KrCl- and Nd-YAG laser light is studied by electron spectroscopy and fluorescence and quantum chemical techniques. The decrease of the quantum yield of phenol fluorescence with increase in the excitation energy is not related to dynamic changes in the intramolecular photophysical processes; rather this is a result of increased photoreaction efficiency. Chlorine substitution for para-state of phenol is shown to strengthen the OH-bond in excitation into the long wavelength absorption band.

Quantum Yields for the Photodegradation of Pollutants in Dilute Aqueous Solution: Phenol, 4-Chlorophenol and N-Nitrosodimethylamine

A broadband method has been applied to determine the quantum yields for the photochemical removal of three common pollutants: phenol, 4-chlorophenol and N-nitrosodimethylamine (NDMA) in dilute aqueous solution. Flash photolysis (xenon flash lamps) was used to cause a significant amount of photolysis without photolyzing intermediates. The analysis of reactant depletion following a single flash was carried out by high- performance liquid chromatography (HPLC) or UV/visible absorption spectroscopy. The method for determining quantum-yields employed p-benzoquinone as an actinometer and was validated by determining the average (200-400 nm) quantum yield for the generation of hydroxyl radicals from the photolysis of hydrogen peroxide (0.90 ± 0.10) and the quantum yields for the photolysis of phenol (0.13 ± 0.02) and 4-chlorophenol (0.24 ± 0.04). The values determined agree very well with the literature ones obtained with monochromatic radiation. The quantum yield for the direct photolysis of NDMA was found to be 0.11 ± 0.03 at neutral pH and 0.27 ± 0.02 at pH 2-4. Under conditions where hydrogen peroxide is the principal absorber, the NDMA quantum yield is 0.32 ± 0.04, independent of pH in the range 2-8.