Green Approach To Metal Chalcogenide Semiconductor Nanomaterials: Syntheses And Characterization Of Cds, Pbs, Zns, Mns And Mnxzn1-Xs Nanoparticles
No Thumbnail Available
Date
2018-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
KNUST
Abstract
Metal chalcogenide nanomaterials such as CdS, PbS, ZnS, MnS and MnxZn1-xS are very useful compound semiconductors with potential applications in sensing, bioimaging, drug delivery, data storage and photovoltaic devices as well as in catalysis. However, the syntheses of good quality nanomaterials usually include toxic chemical reagents and therefore limit their application and adaptation to large scale production. Castor oil and single source precursors (SSPs) are suitable alternative green reagents for the syntheses of undoped and doped metal chalcogenide nanocrystals. In this thesis, green syntheses of (i) CdS nanoclusters and PbS nanorods/belts via thermal decomposition of xanthate complexes in castor oil, and (ii) ZnS, MnS and MnxZn1-xS nanocrystals via the thermal decomposition of diricinoleate carboxylate and heterocyclic dithiocarbamate complexes in oleylamine are reported. The dopant (Mn) feed concentration was varied in the range 0 ≤ x ≤ 0.1. The CdS displayed a band gap of 2.63 – 2.84 eV and a strong emission in the near-UV (λmax = 393 nm) region and formed small clusters of nanocrystals with average particle size of 6.78 1.89 nm. The PbS nanocrystals showed variety of morphologies. The average width and length of the PbS nanorods observed were 22.2 ( 2.3) nm and 225.9 ( 23.3) nm respectively. The activation energy obtained for the growth of ZnS nanoparticles in oleylamine was 53.41 kJ/mol. Powder-X-ray diffraction (p-XRD) patterns showed that the ZnS and MnxZn1-xS nanocrystals synthesized by different precursor routes were sphalerite and the shift in the lattice parameter indicated distortion due to the incorporation of the Mn(II) into the ZnS. The MnS nanocrystals were pure alabandite. The p-XRD patterns of the nanocrystals synthesized by the dithiocarbamate route showed some wurtzitic characteristics of ZnS and MnxZn1-xS. The band gap energy was found to decrease with increasing Mn(II) dopant concentration which indicated the introduction of trap states into the forbidden zone of the host ZnS. Luminescence was observed for MnxZn1-xS (for x ≤ 0.01) nanocrystals at 587 – 599.7 nm characteristic of Mn 4T16A1 transition suggesting possible incorporation of the Mn(II) into the
ZnS host lattice. Electron paramagnetic resonance (EPR) studies confirmed the presence of Mn(II) ions dispersed at substitutionary sites for x ≤ 0.01 MnxZn1-xS nanocrystals. However, at high concentrations of Mn dopant (≥ 0.01), the Mn(II) ions were found bound to the surface/interstitial sites in ZnS. Thus, useful morphologies and interesting properties of important metal chalcogenide semiconductors were achieved by the use of environmentally benign materials.
Description
A THESIS SUBMITTED TO THE DEPARTMENT OF CHEMISTRY, KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, KUMASI, IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF DOCTOR OF PHILOSOPHY IN PHYSICAL CHEMISTRY