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Adsorption and desorption of hydrocarbons and heavy metals from C60 and anatase particles

By Mason B. Tomson, Professor, Center for Biological and Environmental Nanotechnology, Civil and Environmental Engineering Department, Rice University, Houston, TX 77005.
Phone: 713-348-6048, E-mail: mtomson@rice.edu

The introduction of large amounts of nanomaterials into ecosystems may have unforeseeable environmental impacts. Sorption and desorptiona are important processes which could possibly control the fate and transport of both nanomaterials and environmental contaminants. The objective of this study is to understand the impact of nanomaterials on contaminant transport through investigating the sorptive interactions of pollutants with C60 fullerene and anatase nanoparticles.

The adsorption and desorption of naphthalene and Cd²⁺ to large and nanometer scale C60 fullerene and anatase crystals have been studied to determine the relationship between hydrocarbon and heavy metal adsorption properties and particle sizes. Adsorption and desorption of naphthalene to/from C60 fullerene solids in different aggregation forms was studied, where C60 was used as purchased (20-50 µm); dispersed in water by magnetic mixing (1-3 µm) or by high-energy sonication probe (nanometer sized). Sorption partition coefficients could vary by orders of magnitude and have been observed to relate to different C60 aggregation forms. Sorption/desorption hysteresis, a common phenomenon observed in natural soils and sediments, was also observed in this work with naphthalene sorbed to well dispersed C60 aggregates. Data showed that adsorption and desorption to/from C60 was analogous to that reported for soils.

Adsorption and desorption of Cd to/from 10 to 140 nm sizes TiO2 anatase were studied. On a surface area basis, it was found that large and nanometer scale anatase particles had similar maximum Cd²⁺ adsorption capacities, while their adsorption slopes differed by more than one order of magnitude. The particle-size effect on adsorption is constant over a pH range of 4 to 7.5. The desorption of Cd²⁺ from both particle sizes is completely reversible. The adsorption data have been modeled by the Basic Stern model using three monodentate surface complexes. It is proposed that intraparticle electrostatic repulsion may reduce the adsorption free energy significantly for nanometer sized particles.

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