Fluorescence Quenching of Humic Acid by Coated Metallic Silver Particles

Natural organic matter is an important component of the aquatic environments, which has attracted wide attention to its influence of interaction with other pollutants. The present work aimed to investigate its fluorescence quenching (FQ) by coated metallic silver particles (AgNPs). In this work, using fluorescence spectroscopy in conjunction with UV-Vis spectroscopy and dynamic light scattering, the effect of coated AgNPs on fluorescence quenching intensity (FQI) of humic acid (HA) was assessed. In addition, the influence of electrolytes (NaCl, NaNO₃ and CaNO₃) in the FQI was observed. Results showed that with AgNPs dosage increased (>1.17X10^-3 mM), fluorescence quantum yield of HA gradually decreased, which implies that the FQ occurred. Furher observation showed that the FQ process followed both first-order and second-order Stern-Volmer functions. The FQ process was affected by the electrolytes: NaCl had an effect on reduction of FQI, possibly resulting from dissolution of AgNPs; Both of NaNO₃ and Ca(NO₃)₂ had an effect on the FQ of HA but Ca(NO₃)₂ presented greater degree. As a result, the FQ degree of HA by alone electrolyte was listed in descent order as Ca(NO₃)₂ > NaNO₃ > NaCl, which also implies the subsequent experimental results, indicating the FQ degree of HA by mutual electrolytes as Ca(NO₃)₂ + NaNO₃ > Ca(NO₃)₂ + NaCl > NaNO₃ + NaCl.