期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 43, 期 12, 页码 4348-4354出版社
AMER CHEMICAL SOC
DOI: 10.1021/es802964m
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资金
- IHSS Training Bursary
Peat humic acid was fractionated by tangential ultrafiltration into six nominal molecular weight (NMW) fractions, HA(5-10), HA(10-20), HA(20-50), HA(50-100), HA(100-300) and HA(>300), which were purified by dialysis using a 0.5 kDa membrane. The absorbing and emission properties of the separated fractions were compared and their ability to generate singlet oxygen under light excitation was evaluated, using furfuryl alcohol (FFA) as a singlet oxygen scavenger. The absorbance, the emission intensity, and the apparent first order rate constants of FFA loss were normalized per mole of organic carbon (a*, I-F*, and k*, respectively). The fraction absorbance decreased with NMW, except for HA(>300) which was less absorbing than HA(100-300). The low NMW fractions and the HA(>300) fraction generally showed lower k* and I-F* values compared to the HA(50-100) and HA(100-300) fractions. A plot of k* versus I-F* indicates that the first order rate constant of FFA photo-oxygenation increased with the intensity of fluorescence at 380, 430, and 500 nm (R-2 = 0.77-0.84). This shows that the distribution of fluorescent centers among fractions paralleled that of photosensitizing centers. Plotting k* or I-F* versus a* at 365 nm reveals the apparent relative quantum efficiency of the different fractions. Higher values for low NMW fractions and HA(50-100) are either due higher percentages of absorbing centers able to produce singlet oxygen or exhibit fluorescence or to lower quenching processes.
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