Adsorption and desorption of humic and fulvic acids on SiO2 particles at nano- and micro-scales

Information on the interaction of nanoparticles with natural organic matter (NOM) is essential for understanding their environmental impacts. In this study the adsorption and desorption of humic acids (HA) and fulvic acids (FA) on SiO2 particles in size of 20, 100 and 500 nm were investigated. The adsorption of HA and FA on 20 nm SiO2 was much stronger compared with their adsorption on 100 and 500 nm SiO2, probably due to the specific surface properties of the nanoparticles. The adsorption of HA and FA was pH-dependent, particularly for HA adsorption. The adsorption of HA showed apparent difference between the ionic strength of 0.01 and 0.1 mol/L NaNO3, but no obvious difference was observed for FA adsorption. Desorption results presented obviously hysteresis with more obvious for HA desorption. The results of this study demonstrated evidently that 20 nm SiO2 particles had much higher affinity to HA and FA than did 100 and 500 nm particles, which may have significant effects on their behaviors in the environment.