Abstract
Revealing the binding properties of calcium ion (Ca2+) and magnesium ion (Mg2+) to terrestrial chromophoric dissolved organic matter (CDOM) facilities understanding the effect of natural water components on the photophysics of dissolved organic matter. Steady-state and time-resolved fluorescence spectrometry, and dynamic light scattering were applied to investigate the fluorescence quenching process of CDOM by Ca2+ and Mg2+. Due to a remarkable decrease of the steady-state fluorescence intensity and a slight decrease of fluorescence lifetime, the fluorescence quenching of CDOM by cations mainly occurred through a static process. The fluorescence quenching was profound under longer excitation and emission wavelengths. The binding constant (K, L/mol) for Ca2+ to CDOM ranged from 4.29 to 5.09 (lgK), which was approximately one order of magnitude higher than that of Mg2+ to CDOM (3.86 to 4.56). Nevertheless, the efficiency of CDOM fluorescence quenching by Ca2+, Mg2+ was much lower than that by Cu2+. Fluorescence decay became faster in the presence of a high concentration of Ca2+ (>20 mg/L) and Mg2+ (>50 mg/L). In the presence of these two metal ions, particularly for Ca2+, the lifetime of CDOM excited states shifted to the relatively small value side, indicating fluorescence quenching of CDOM mainly occurred through the interaction of Ca2+/Mg2+ with relatively long-lived fluorophores.
Highlights
In a previous study [23], we found that fluorophores with a relatively short lifetime (
Results obtained in this study showed that CDOM maintained at least 10% of its original steady-state fluorescence intensity among the conducted wavelength regions
Based on the change of optical spectra and hydrodynamic size of CDOM with Ca2+ and the current findings showed that both Ca2+ and Mg2+ had a high binding constant to terrestrial source CDOM
Summary
The binding of metal ions to NOM altered the bioavailability of metal ions, and affected the photophysical and photochemical properties of NOM [5,7,8]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have