A facile hybrid method to synthesize metal and metal chalcogenide nanoparticles using various capping groups
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Date
2014
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Abstract
The synthesis of bismuth (Bi), antimony (Sb) and tin (Sn) metal and metal chalcogenide nanoparticles is presented using a novel hybrid solution based high temperature method. Furthermore is the synthesis of zinc telluride (ZnTe) and cadmium telluride (CdTe) nanostructured materials also described. The nanomaterials are predominantly capped by organic ligands. The use of water soluble ligands such as triethanolamine (TEA) and cysteine is also reported. The synthetic method involves the reduction of a metal salt followed by the introduction of the chalcogenide source in the case of metal chalcogenide nanoparticle synthesis. The metal or metal chalcogenide prepared is thermolysed into a high boiling point ligand at high temperature. For the water soluble nanoparticles after reduction there is a simultaneous addition of a chalcogenide source and a ligand at room temperature.
The Bi and Sb nanoparticles showed similar spherical morphology when capped with tri-noctylphosphine oxide (TOPO). Bismuth particles in the form of dots, branched nanorods and self assembled cubes were obtained at different reaction conditions. The cubed shaped Bi and Sb nanoparticles which appear to self-assemble were obtained when using oleylamine (OA) as a capping group. The Bi2S3, Bi2Se3 and Bi2Te3 nanoparticles were elongated when capped using alkylamines such as hexadecylamine (HDA) and OA, however at low temperature of 90oC they appeared to be close to spherical. The antimony chalcogenides, Sb2S3, Sb2Se3 and Sb2Te3 gave a similar rod shape morphology. The Sn nanoparticles appeared aggregated to some extent. A triangular shaped morphology is observed for the OA capped SnS nanoparticles. HDA capped ZnTe nanoparticles were synthesized using NaHTe and ZnCl2 as the tellurium and zinc sources respectively. The particles synthesized at reaction temperatures of 230 oC and 270 oC were spherical in shape. The blue shift in the absorption spectra confirms that the particles undergo quantum confinement. The photoluminescence studies show that the particles emit at a wavelengths close to their band edge. The water soluble cysteine and TEA capped ZnTe particles appear as nanorods which are aggregated. Finally water soluble CdTe nanoparticles were synthesized using TEA and cysteine as capping groups. The results showed that both cysteine and TEA are effective capping groups for water soluble CdTe nanoparticles. The optical properties of the particles synthesized in both capping groups revealed absorption features due to the Cd-ligand complex. The photoluminescence spectra showed reasonably narrow emission peaks. The cadmium salt was varied to study its effect on the morphology of the CdTe nanoparticles. The nitrate source gave well defined, crystalline, close to spherical nanoparticles. The FT-IR measurements confirmed the presence of the capping ligand on the surface of CdTe nanoparticles.
Description
A thesis submitted to the Faculty of Science and Agriculture in fulfilment of the requirements for the Degree of Doctor of Science in the Department of Chemistry at the University of Zululand, South Africa, 2014
Keywords
metal chalcogenide --nanoparticles --hybrid --capping