Fluorescence quenching of fulvic acids by fullerene in water.

Fullerene can be suspended in water as nanoscaled-fullerene-aggregates (nC(60)). However, little is known about its biogeochemical cycling in natural waters. In this paper, the interactions between nC(60) and fulvic acids were investigated using fluorescence spectroscopy and fluorescence quenching titration. The results show that the intrinsic fluorescence of fulvic acids was static quenched by adding nC(60). The association constants (log K) of fulvic acids and nC(60) were estimated using a modified Ryan-Weber nonlinear model, and ranged from 6.76 to 7.41 l/mol. The log K was not significantly affected by the concentration levels of fulvic acids from 5.0 to 20.0 mg/l. The log K increased at low pH 3-5, but remained constant at high pH ranging from 5 to 11. The hydrophobic and π-π interactions were the likely primary mechanisms. The present observation will be helpful in understanding the environmental behavior of fullerene in natural aquatic ecosystems.