| The last decade has witnessed tremendous growth in nanotechnology research, particularly in the synthesis of semiconductor nanocrystals (NCs) for novel applications. The synthesis of NCs, however, is difficult due to their tendency to agglomerate into bulk species. Additional obstacles such as sample heterogeneity, instability, low product yield, and high cost of preparation must be taken into account. Production of NCs in quantities suitable for large-scale applications is, therefore, problematic. The main goal of this dissertation research was to optimize a biomolecule-based synthesis technique for high-yield, gram-quantity production of semiconductor nanocrystals. Biomolecules such as glutathione (GSH), cysteine and histidine have been used to produce CdS and ZnS NCs. An additional objective was to demonstrate the applicability of thus produced NCs in photocatalytic degradation of model environmental pollutants. Parathion, p-nitrophenol (pNP) and Acid Orange 7 (AO7) were readily degraded by ZnS-mediated photocatalysis.; The biomolecule-based synthesis technique is based on metal tolerance found in some microorganisms. The yeast Candida glabrata, for example, produces US NCs in vivo upon exposure to toxic Cd ions. Sulfhydryl peptides such GSH chelate the Cd ions, forming a peptide-Cd matrix. Labile sulfide is incorporated into this matrix, resulting in CdS nanoparticles. This general mechanism was mimicked in vitro to develop the biomolecule-capped NC synthesis technique described herein. Optical spectroscopies were employed as the primary characterizational tools. Further description of the NCs was accomplished by electron microscopy and X-ray diffraction. Separation methods such as ethanol precipitation and size-exclusion chromatography proved important.; The optimum pH for synthesis was ∼10.5, and a 2:1 ratio of biomolecule cap to metal ions was needed to ensure full chelation. Sulfide concentration largely determined the properties of the NCs. Gram-quantities of NCs were readily produced per batch with yields greater than 50%. The NC powders were stable for >30 months at 4°C and could be handled like ordinary shelf chemicals. Meanwhile, the photocatalytic degradation of pNP by thus produced ZnS NCs was 3 to 6 times faster than comparable experiments employing TiO 2. Further experiments will be necessary to develop large-scale, field-applicable treatment systems. |
