Stability of C60 nanoparticles in aquatic systems

The influences of storage time, pH, electrolytes and organic matters on the stability of two different suspensions of C60 nanoparticles were investigated. The results showed that the C60 nanoparticles prepared by solvent substitution (C60/son) were more stable than that prepared by prolonged stirring (C60/aq), and kept stable for a period of time. Higher pH enhanced the stability of C60 nanoparticles. The presence of electrolyte made a dramatic decrease in the surface zeta potential and an increase in the particle size. The aggregation process of C60 nanoparticles exhibited slow and rapid regions, which was found to be consistent with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. The critical coagulation concentration (CCC) values of C60/son, obtained from the intersection of the interpolated lines through the slow and fast regions, were estimated as 321 mmol x L(-1) NaCl, 316 mmol x L(-1) KCl, 9.6 mmol x L(-1) MgCl2 and 6.7 mmol x L(-1) CaCl2. The CCC values of C60/aq were estimated as 295 mmol x L(-1) NaCl, 278 mmol x L(-1) KCl, 7.8 mmol x L(-1) MgCl2 and 5.9 mmol x L(-1) CaCl2, which were much higher than their concentrations in natural waters. The presence of humic acid enhanced the stability of C60 nanoparticles, which was attributable to steric repulsion. Therefore, C60 nanoparticles will keep relatively stable in typical aquatic environments.