Abstract
The ubiquity of naturally occurring nanoparticles in the aquatic environment is now widely accepted, but a better understanding
of the conditions that promote their formation and persistence is needed. Using cadmium sulfide (CdS) as a model metal sulfide
species, thiolate-capped CdS nanoparticles were prepared in the laboratory to evaluate how aquatic conditions influence metal
sulfide nanoparticle growth and stability. This work examines CdS nanoparticle growth directly in aqueous solution at room
temperature by utilizing the size-dependent spectroscopic properties of semiconductors detectable by UV/vis. CdS nanoparticle
growth was governed by oriented attachment, a non-classical mechanism of crystallization in which small precursor nanoparticles
coalesce to form larger nanoparticle products. Nanoparticle growth was slowed with increasing capping agent and decreasing
ionic strength. In addition to examining the short-term (hours) growth of the nanoparticles, a long-term study was conducted
in which cysteine-capped CdS nanoparticles were monitored over 3 weeks in solutions of various ionic strengths. The long-term
study revealed an apparent shift from small nanoparticles to nanoparticles twice their original size, suggesting nanoparticle
growth may continue through oriented attachment over longer time scales. High-ionic strength solutions resulted in salt-induced
aggregation and eventual settling of nanoparticles within days, whereas low-ionic strength solutions were stable against settling
over the course of the experiment. Sulfide recovery from cysteine-capped CdS nanoparticles as acid volatile sulfide was nearly
quantitative after 2 weeks in fully oxygenated water, demonstrating significantly slowed oxidation of sulfide when complexed
to Cd(II) within CdS nanoparticles. The nanoparticles were also shown to be resistant to oxidation by Fe(III) (hydr)oxide.
This study illustrates that aggregation, rather than chemical oxidation, is likely more important to the lifetime of many
metal sulfide nanoparticles in the aquatic environment.
of the conditions that promote their formation and persistence is needed. Using cadmium sulfide (CdS) as a model metal sulfide
species, thiolate-capped CdS nanoparticles were prepared in the laboratory to evaluate how aquatic conditions influence metal
sulfide nanoparticle growth and stability. This work examines CdS nanoparticle growth directly in aqueous solution at room
temperature by utilizing the size-dependent spectroscopic properties of semiconductors detectable by UV/vis. CdS nanoparticle
growth was governed by oriented attachment, a non-classical mechanism of crystallization in which small precursor nanoparticles
coalesce to form larger nanoparticle products. Nanoparticle growth was slowed with increasing capping agent and decreasing
ionic strength. In addition to examining the short-term (hours) growth of the nanoparticles, a long-term study was conducted
in which cysteine-capped CdS nanoparticles were monitored over 3 weeks in solutions of various ionic strengths. The long-term
study revealed an apparent shift from small nanoparticles to nanoparticles twice their original size, suggesting nanoparticle
growth may continue through oriented attachment over longer time scales. High-ionic strength solutions resulted in salt-induced
aggregation and eventual settling of nanoparticles within days, whereas low-ionic strength solutions were stable against settling
over the course of the experiment. Sulfide recovery from cysteine-capped CdS nanoparticles as acid volatile sulfide was nearly
quantitative after 2 weeks in fully oxygenated water, demonstrating significantly slowed oxidation of sulfide when complexed
to Cd(II) within CdS nanoparticles. The nanoparticles were also shown to be resistant to oxidation by Fe(III) (hydr)oxide.
This study illustrates that aggregation, rather than chemical oxidation, is likely more important to the lifetime of many
metal sulfide nanoparticles in the aquatic environment.
- Content Type Journal Article
- Category Research Paper
- DOI 10.1007/s11051-010-0045-9
- Authors
- Katherine M. Mullaugh, University of North Carolina Wilmington Wilmington NC 28403 USA
- George W. Luther, University of Delaware Department of Chemistry and Biochemistry Newark DE 19716 USA
- Journal Journal of Nanoparticle Research
- Online ISSN 1572-896X
- Print ISSN 1388-0764
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