科研之友
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摘要
Production of hydroxyl radical ((OH)-O-center dot) is of significant concern in engineered and natural environment. A simple in situ method was developed to measure (OH)-O-center dot formation in UV/H2O2, UV/Fe(III), and UV/NO3- systems using trapping of (OH)-O-center dot by benzoic acid (BA) and measuring fluorescence signals from hydroxylated products of BA. Method development included characterization of (OH)-O-center dot trapping mechanism and measurement of quantum yields (phi center dot OH) for (OH)-O-center dot. The distribution of OHBA isomers was in the order of o-OHBA > p-OHBA > m-OHBA, although it changed with the H2O2 concentration and light intensity. This supports that (OH)-O-center dot attacks dominantly on the benzene rings. The quantum yields for (OH)-O-center dot formation in the UV/H2O2 process were 1.02 and 0.59 at 254 and 313 run, which were in good agreement with the literature values. Confirming that the method is suitable for the measurement of (OH)-O-center dot production from UV/H2O2 processes. Using the continuous flow method developed, quantum yields for (OH)-O-center dot in UV/H2O2, UV/Fe(III), and UV/NO3- systems were measured varying the initial concentration of (OH)-O-center dot precursors. The phi center dot OH values increased with increasing concentrations of H2O2, Fe(III), and NO3- and approached constant values as the concentration increased. The phi center dot OH values were 0.009 for H2O2 at 365 nm, showing that (OH)-O-center dot production is not negligible at such high wavelength. The phi center dot OH values during the photolysis of Fe(OH)(2+) (pH 3.0) and Fe(OH)(2)(+) (pH 6.0) at 254 nun were 0.34 and 0.037, respectively. The phi center dot OH values for NO3- approached a constant value of 0.045 at 254 nm at the initial concentration of 10 mm.
- 出版日期2010-3-25
