Kinetics of C60 Fullerene Dispersion in Water Enhanced by Natural Organic Matter and Sunlight Cheng En Sung 02/15/06
Introduction NOM Enhances C60 Dispersion Kinetics Effect of NOM Concentration Effect of Solution Condition (Ionic strength) Sunlight Accelerates C60 Dispersion by NOM Potential Chemical Transformation of C60
Introduction C60 Potential Concerns: Health Ecosystem nC60 Preparation: Direct Dispersion (i.e. Spill or discharge of C60 powder) Solvent Exchange (Intermediate Solvent dissolve C60 followed by mixing water)
Various Environmental Factors Solution condition NOM Sunlight C60 dispersion measurement NOM and UV light enhanced dispersion of C60 Properties of nC60 includes: particle size, morphology, surface charge and UV/vis absorbance Chemical nature of nC60-NOM interactions in respect to sunlight exposure
NOM Enhances C60 Dispersion Kinetics NOM- Natural Organic Matter Suwannee River humic acid (SRHA) Suwannee River fulvic acid (SRFA)
Why adding NaCl ? To ensure dissolution of SRHA, the solution pH is adjusted to alkaline condition using NaOH solution
nC60 stability Steric Hindrance Effect ?? Reduce surface hydrophobicity nC60 stability Each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds and this may affect the molecule's preferred shape (conformation) and reactivity. increase electric double layer repulsion within colloids.
Effect of NOM Concentration Concentration of stable nC60 increased with increasing mixing time and NOM concentration.
Ionic strength ??
Effect of Solution Condition C60 dispersion depended on the Ionic strength of the aqueous phase. Increased electrostatic repulsion equals lower total ionic strength. Ca²⁺ reduce colloidal stability due to effective charge.
Sunlight Accelerates C60 Dispersion by NOM UV may attribute to accelerate C60 dispersion.
nC60 particle size decrease as mixing under sunlight. Fast dispersion is mainly caused by surface erosion or dissolution-recrystallization process instead of particle breakage
nC60 particle size without exposing to sunlight
Mixing under sunlight reveal that fast dispersion is mainly caused by surface erosion or dissolution-recrystallization process instead of particle breakage. NOM interact with C60 which is catalyzed by sunlight. Decreased particle size accompany electro-phorectic mobility of nC60 particles. The surface charge density of secondary crystals is greater than the primary crystals as a result of interactions with NOM.
Potential Chemical Transformation of C60
Conclusion Direct dispersing of C60 to water most closely simulates the natural pathway of C60 into the aqueous environment. Natural Organic Matter (NOM) alters dispersity, physicochemical properties, and chemical nature of C60 High concentration of C60 or C60 derivatives in form of small particles likely occur under typical aqueous environment. NOM-induced chemical transformation of C60