Formation and Persistence of Cadmium Sulfide Nanoparticle in Aqueous Solution PDF Download

Author: Katherine M. Mullaugh
Publisher:
ISBN: 9781109386738
Category : Cadmium sulfide
Languages : en
Pages :

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Book Description
Recent research has shown that naturally occurring nanoparticles are widespread in the environment. Among these, metal sulfides are important species in aquatic environments with regard to metal speciation and mobility, even in oxic waters. Here a multi-technique approach was adopted and includes UV/visible spectroscopy, voltammetry, fluorescence, size exclusion chromatography, dynamic light scattering and transmission electron microscopy in the characterization of metal sulfide nanoparticles. Using cadmium sulfide (CdS) as a model species, CdS nanoparticles were prepared in aqueous solution in the laboratory. The reaction of Cd 2+ and HS - in the presence of a thiol "capping agent," which prevents precipitation of the bulk material, resulted in nanoparticles typically less than 5 nm in diameter. Based on quantum confinement effects of semiconductor nanoparticles, UV/vis was used to determine CdS nanoparticle size. Nanoparticle size decreased with increasing pH, Cd(II) and thiol concentrations. Growth of nanoparticles followed a non-classical crystallization mechanism called oriented attachment and nanoparticle growth rates increased when capping agent was limited and ionic strength was increased. High ionic strength solutions induced aggregation of nanoparticles and eventual settling of nanoparticles over days whereas low ionic strength solutions were stable for over three weeks. Sulfide was recoverable as acid volatile sulfide after two weeks in fully oxygenated water, demonstrating significantly slowed sulfide oxidation. The nanoparticles were also shown to be resistant to oxidation by Fe(III) hydroxide solid. A hanging mercury drop electrode was used to monitor the solution chemistry of the nanoparticle system as well. The replacement of thiol molecules bound to Cd(II) by sulfide was demonstrated. An electrochemical signal was established for thiol-capped nanoparticles and enhanced through adsorptive stripping voltammetry (AdSV) and the effects of various analytical variables on the AdSV response are discussed. Parallel titration experiments with UV/vis and voltammetry, as well as adsorptive stripping voltammetry experiments, demonstrated the species giving peak C5 was a Cd(II) thiolate complex adsorbed on the surface of CdS nanoparticles. Size exclusion chromatography indicated these nanoparticles were relatively small, eluting after most of the UV/vis absorbing nanoparticles, but before cysteine molecules.