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Low temperature synthesis of cubic phase zinc sulfide quantum dots

100%

Shahid R., Toprak M., Soliman H., Muhammed M.

In this study, we report on a new method for the synthesis of ZnS quantum dots (QDs). The synthesis was carried out at low temperature by a chemical reaction between zinc ions and freshly reduced sulfide ions in ethanol as reaction medium. Zinc chloride and elemental sulfur were used as zinc and sulfur sources, respectively and hydrazine hydrate was used as a strong reducing agent to convert elemental sulfur (S8) into highly reactive sulfide ions (S2−) which react spontaneously with zinc ions. This facile, less toxic, inexpensive route has a high yield for the synthesis of high quality metal sulfide QDs. Transmission electron microscopy (TEM) image analysis and selected area electron diffraction (SAED) reveal that ZnS QDs are less than 3 nm in diameter and are of cubic crystalline phase. The UV-Vis absorption spectrum shows an absorption peak at 253 nm corresponding to a band gap of 4.9 eV, which is high when compared to the bulk value of 3.68 eV revealing strong quantum confinement. PL emission transitions are observed at 314 nm and 439 nm and related to point defects in ZnS QDs.

Fabrication and characterization of nanostructured thermoelectric FexCo1-xSb3

76%

Tafti M. Y., Saleemi M., Toprak M. S., Johnsson M., Jacquot A., Jägle M., Muhammed M.

Open Chemistry

2015

vol. 13

issue 1

A novel synthesis route for the fabrication of p-type nanostructured skutterudite, FexCo1-xSb3 in large quantity is reported. This scalable synthesis route provides nano-engineered material with less impact on the environment compared to conventional synthesis procedures. Several Fe substituted compositions have been synthesized to confirm the feasibility of the process. The process consists of a nano-sized precursor fabrication of iron and cobalt oxalate, and antimony oxides by chemical co-precipitation. Further thermochemical processes result in the formation of iron substituted skutterudites. The nanopowders are compacted by Spark Plasma Sintering (SPS) technique in order to maintain nanostructure. Detailed physicochemical as well as thermoelectric transport properties are evaluated. Results reveal strongly reduced thermal conductivity values compared to conventionally prepared counterparts, due to nanostructuring. P-type characteristic was observed from the Seebeck measurements while electrical conductivity is high and shows metallic behavior. The highest TE figure of merit of 0.25 at 800 K has been achieved, which is strongly enhanced with respect to the mother compound CoSb3. This suggests the promise of the utilized method of fabrication and processing for TE applications with improved performance.

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2 Open Chemistry

1 2014

1 2012

2 Muhammed M.

1 Jacquot A.

1 Johnsson M.

1 Jägle M.

1 Saleemi M.

1 Shahid R.

1 Soliman H.

1 Tafti M. Y.

1 Toprak M.

1 Toprak M. S.

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Low temperature synthesis of cubic phase zinc sulfide quantum dots

Fabrication and characterization of nanostructured thermoelectric FexCo1-xSb3