作者：NAVIDB. SALEH, LISAD. PFEFFERLE, AND MENACHEM ELIMELECH
（Department of Chemical Engineering, Yale University, New Haven, Connecticut 06520-8286）
摘要：The initial aggregation kinetics of multiwalled carbon nanotubes （MWNTs） were examined through time-resolved dynamiclight scattering. Aggregation of MWNTs was evaluated by varying solution pH and the concentration of monovalent （NaCl） and divalent （CaCl2 and MgCl2） salts. Suwannee River humic acid （SRHA） was used to study the effect of background natural organic matter on MWNT aggregation kinetics. Increasing salt concentrationandaddition of divalent calciumandmagnesiumions induced MWNT aggregation by suppressing electrostaticrepulsion, similar to observations with aquatic colloidal particles. The critical coagulation concentration （CCC） values for MWNTs were estimated as 25 mM NaCl, 2.6 mM CaCl2, and 1.5 mM MgCl2. An increase in solution pH from acidic （pH 3） to basic （pH 11） conditions resulted in a substantial （over 2 orders of magnitude） decrease in MWNT aggregation kinetics, suggesting the presence of ionizable functional groups on the MWNT carbon scaffold. The presence of humic acid in solution markedly enhanced the colloidal stability of MWNTs, reducing the aggregation rate by nearly 2 orders of magnitude. The enhanced MWNT stability in the presence of humic acid is attributable to steric repulsion imparted by adsorbed humic acid macromolecules. Our results suggest that MWNTs are relatively stable at solution pH and electrolyte conditions typical of aquatic environments.
