M.Sc. / ZnO nanostructures with different morphologies have been prepared by using microwave and conventional heating methods. The effect of solvent, zinc precursor, time and the concentration of sodium hydroxide on the morphology of zinc oxide were investigated, when different heating methods were employed. ZnO nanoparticles were prepared using the solvothermal method. Zinc precursor impact on the shape of zinc oxide nanoparticles formed depends on the solvent used during the synthesis. Different morphologies such as spheres, rods, hexagonal prisms, hexagonal plates, diamond-like and multipods were formed by a simple solution based method. The optical features for most of the formed shapes were typical of ZnO nanoparticles. The XRD patterns of the particles showed the most stable hexagonal phase with a high degree of crystallinity. A capping molecule has an impact on the shape of the nanoparticle. In this work, we also present the results from the study of the effect of the stabilizing molecule on the shape and formation of the core shell nanoparticles of CdSe/PbS. The capping molecules used were hexadecylamine (HDA), tri-n-octylphosphine oxide (TOPO) and stearic acid. The core shell nanomaterials were synthesized by using a method in which selenium powder was converted to TOPSe.Transmission electron microscopy was used to determine the morphology and the size of the ZnO and coreshell nanomaterials. Spherical particles were obtained when TOPO was used whereas the use of HDA induced the formation of non-spherical shapes. With both capping molecules, epitaxial shell growth was not achieved. The particles formed from both capping groups (HDA and TOPO) were large due to the long reaction time that instigates lager particle sizes. However, when stearic acid was used as a capping molecule, a perfect core shell arrangement was formed. The phase and the crystallinity of the formed particles were determined by the XRD.

Ph. D., Faculty of Science, University of the Witwatersrand, 2011 / Different cadmium, cobalt and zinc complexes of substituted thioureas, dithiocarbamates and thiuram di/monosulfides were synthesized using ethanol or water as solvents. The synthesis of dithiocarbamates complexes were performed at room temperature while the rest were refluxed at 70 oC. The complexes were easy to synthesize, of low cost and stable in air and were obtained in good yields. The complexes were characterized using various instruments, such as infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy, elemental analyzer, thermogravimetric analysis (TGA) and X-ray crystallography. The complexes were found to coordinate the ligands through sulphur atom, instead of nitrogen atom. This was concluded after shifts to higher or lower wavenumbers were observed from the infrared spectra of the complexes as compared to their free ligands. The 1H NMR also depicted formation of the complexes, with complexes peaks shifting to downfield as compared to the free ligands. There were also signs of broad NH peaks especially for substituted thiourea complexes. The crystals grown from complex II (diphenylthiourea cadmium complex) depicted a tetrahedral geometry, with two sulphur and two chlorine atoms binding to the central atom which is cadmium. The easily synthesized complexes were thermolysed in HDA, TOPO or a mixture of the two to form metal sulphide nanoparticles. The role of the above capping agents or ligands was to control particles growth and prevent them from aggregation. A single source precursor route was employed in synthesizing hydrophobic semiconductor nanoparticles, which are also known as (QDs) quantum dots. Various shapes, which are rods (mono-, bi- and tripods), spheres and hexagonal were revealed through transmission electron microscope (TEM). The sizes of these particles ranged from 1 to 12 nm in diameter. Other instruments used for characterising the as-synthesized semiconductor nanoparticles include X-ray diffractometer (XRD), UV-Visible and Photoluminescence spectroscopy. The optical properties of the particles as determined by the UV-Visible spectroscopy revealed some differences as compared to the bulk materials. All the absorption spectra were blue shifted to the bulk materials signifying finite size of the particles. The XRD peaks observed were broad as compared to the bulk ones, which also signified small particles size. Two phases, which are hexagonal and cubic, were revealed from the XRD. viii The hydrophobic semiconductor nanoparticles or quantum dots synthesized were then transferred into water soluble using ligand exchange method. The chloroform and pyridine routes were used to synthesize hydrophilic semiconductor nanoparticles, with pyridine route being preferred. The shape and size of the particles were not influenced by the transfer into water soluble since the experiments were performed at room temperature. This was confirmed by TEM analysis. The capping agents used after displacing water insoluble capping agents were sugars, which were soluble in water. The XRD pattern of the semiconductor nanoparticles/QDs (CdS) capped by sugars after ligand exchange through pyridine yielded multiple peaks which were difficult to assign. The attempt to employ ligand exchange method in transferring hydrophobic CoxSy and ZnS nanoparticles to hydrophilic CoxSy and ZnS nanoparticles proved unsuccessful. When the materials were centrifuged after the sugars were introduced as capping agents, some solid material settled at the bottom, with some floating on top of the solution. This was an indication that the materials were not miscible. The hydrophilic CdS, CoxSy and ZnS nanoparticles were also synthesized using direct method. In this method, the metal sources and capping (sugars) were dissolved in ethylene glycol at 100 oC. The sulphur sources were also dissolved separately in the same solvent. Upon completion, the latter solution was added to the former one. The particles were grown at 160 oC for an hour with ethylene glycol as a solvent. The morphology of the particles dominated through this method was spherical-like in shape. The crystallinity of CdS and ZnS nanoparticles depicted hexagonal and cubic phases depending on the complexes used. The XRD indicated the armophous nature of the cobalt sulphide nanoparticles, irrespective of the precursor used. Due to the toxicity problem of the quantum dots, especially CdS, the water soluble CdS capped by glucuronic acid, glucose and sucrose after ligand exchange were chosen for that study. However, results showed that the CdS used were not toxic. It was measured or deduced by checking the viability which remained above 90%. Add a bit of deductions about toxicity study here, just some of the general trends.

This thesis mainly consists of two parts, the synthesis of several kinds of technologically interesting crystalline metal oxide nanoparticles via high temperature nonaqueous solution processes and the formation of core-shell structure metal oxide composites using some of these nanoparticles as the core with silica, titania or polymer as shell via a modified microemulsion approach. In the first part, the experimental procedures and characterization results of successful synthesis of crystalline iron oxide (Fe3O4) and indium oxide (In2O3) nanoparticles are reported. Those nanoparticles exhibit monodispersed particle size, high crystallinity and high dispersibility in non-polar solvents. The particle size can be tuned by the seed mediated growth and the particle shape can also be controlled by altering the capping ligand type and amount. The mixed bi-metal oxides such as cobalt iron oxide and lithium cobalt oxide will be discussed as well. In the second part, the synthesis and characterization of various surface coated metal oxides, including silica, titania and polymer coated nanocomposites are reported. The silica coating process is presented as a highlight of this part. By using a microemulsion system, core-shell structure silica coated iron oxide and indium oxide nanocomposites are successfully prepared. Furthermore, the thickness of the silica coating can be controlled from 2 nm to about 100 nm by adjusting the reaction agents of the micelle system. By extending the procedure, we will also discuss the titania and polymer coating preparation and characterization.

Thesis (M.S.)--Ball State University, 2009. / Title from PDF t.p. (viewed on June 07, 2010). Includes bibliographical references (p. [65]).

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Nie, Shuming; Committee Member: Bao, Gang; Committee Member: Murthy, Niren; Committee Member: Varma, Vijay; Committee Member: Wang, Zhong Lin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / In recent years both metal and semiconductor nanoparticles have gained the attention of many research groups because of their unique properties. Synthesizing metal and semiconductor nanoparticles with narrow size distribution, uniform shape, and good crystalline nature represents a significant challenge. Our research group has taken the synthesis procedure a step forward when we discovered that “when a polydispersed colloidal solution upon heating at or near the boiling point of the solvent in presence of excess surface active ligands, the particles evolve into a thermodynamic equilibrium size regime and this phenomenon was named “Digestive Ripening”. The ability to tune the nanoparticles size with a narrow size distribution after post - preparation in a reproducible fashion is remarkable. The current dissertation research encompasses the field of metal and semiconductor nanoparticles and the major part of the work is devoted to understand the digestive ripening of gold-dodecanethiol system, and the effect of the nature of the ligand and solvent temperature on a low melting point indium metal – digestive ripening. A noteworthy achievement of the current work is the ability to extent the digestive ripening to the semiconductor materials cadmium selenide and cadmium telluride by employing different ligands and by the use of different solvents. A diverse set of instrumental techniques is used for the characterization of both metal and semiconductor nanoparticles.

Nanoparticles of MoS2 and WS2 were synthesized by decomposing the appropriate metal hexacarbonyl in the presence of sulfur dissolved in decalin at 140°C. A significant fraction of the nanoparticles was ≤ 15 nm in diameter as verified by Transmission Electron Microscopy. The process was repeated in the presence of silica and then titania to produce supported metal sulfides. The unsupported nanoparticles were found to exhibit a size-dependent shift in their threshold UV-visible absorption due to quantum confinement. Photocatalytic properties of each sulfide from synthesis in decalin were explored by using each as a catalyst in the photodegradation of methylene blue by visible light. These sulfides were also used to catalyze the photodegradation of acetone. Unsupported MoS2 and WS2 nanoparticles catalyzed the photodegradation of acetone under visible light of ≥ 400 nm wavelength. This is the first study reporting the photocatalytic properties of the unsupported WS2 nanoparticles. Photodegradation of methylene blue under ≥ 435 nm irradiation was detected using unsupported WS2 but not unsupported MoS2, likely because activity was masked by the likely photobleaching of the dye. When deposited on silica or titania, the nanosized MoS2 and WS2 could be uniformly distributed in aqueous solutions to maximize the photocatalytic efficiency. Correcting the absorbance measurements for light scattering by solids proved to be beneficial for extracting kinetic information. Both silica deposited sulfides were found to significantly increase the rate of methylene blue photodegradation, and deposited WS2 increased this rate significantly more than deposited MoS2. Similarly, both titania deposited sulfides significantly increased the rate of methylene blue photodegradation, and the deposited WS2 increased this rate significantly more than the deposited MoS2 / Synthesis of the sulfide photocatalysts -- Characterization of synthesized nanoparticles -- Photocatalytic degradation tests : setup and protocols -- Photocatalytic degradation tests : results. / Department of Chemistry

Engineering particles at the nanoscale demands a high degree of control over process parameters during synthesis. For nanocrystal synthesis, solution-based techniques typically include application of external convective heat. This process often leads to slow heating and allows decomposition of reagents or products over time. Microwave-assisted heating provides faster, localized heating at the molecular level with near instantaneous control over reaction parameters. In this work, microwave-assisted heating has been applied for the synthesis of II-VI semiconductor nanocrystals namely, ZnO nanopods and CdX (X = Se, Te) quantum dots (QDs). Based on factors such as size, surface functionality and charge, optical properties of such nanomaterials can be tuned for application as sensors. ZnO is a direct bandgap semiconductor (3.37 eV) with a large exciton binding energy (60 meV) leading to photoluminescence (PL) at room temperature. A microwave-assisted hydrothermal approach allows the use of sub-5 nm ZnO zero-dimensional nanoparticles as seeds for generation of multi-legged quasi one-dimensional nanopods via heterogeneous nucleation. ZnO nanopods, having individual leg diameters of 13-15 nm and growing along the [0001] direction, can be synthesized in as little as 20 minutes. ZnO nanopods exhibit a broad defect-related PL spanning the visible range with a peak at ~615 nm. Optical sensing based on changes in intensity of the defect PL in response to external environment (e.g., humidity) is demonstrated in this work. Microwave-assisted synthesis was also used for organometallic synthesis of CdX(ZnS) (X = Se, Te) core(shell) QDs. Optical emission of these QDs can be altered ased on their size and can be tailored to specific wavelengths. Further, QDs were incorporated in Enhanced Green-Fluorescent Protein – Ultrabithorax (EGFP-Ubx) fusion protein for the generation of macroscale composite protein fibers via hierarchal self-assembly. Variations in EGFP- Ubx·QD composite fiber surface morphology and internal QD distribution were studied with respect to (i) time of QD addition (i.e., pre or post protein self-assembly) and (ii) QD surface charge — negatively charged QDs with dihydrolipoic acid functionalization and positively charged QDs with polyethyleneimine coating. Elucidating design motifs and understanding factors that impact the protein-nanoparticle interaction enables manipulation of the structure and mechanical properties of composite materials.

M.Sc. / This report illustrates the synthesis and characterization of CdS and CdSe nanoparticles in TOPO, HDA and hexamethylenediamine. The prepared nanoparticles were characterized using UV-visible and photoluminescence spectrophotometers for optical properties, transmission electron microscopy for shapes and sizes as well as powder X-ray diffractometer for structural analysis. The effect of monomer concentration and temperature were investigated on the growth of nanocrystals. The monomer concentration was varied by changing the amount of stabilizer. The particle sizes increased with an increase in monomer concentration. Higher monomer concentration resulted in polydispersed nanoparticles due to faster uncontrolled growth. Increasing the temperature resulted in a faster growth thus increasing the size of the particles. The growth also affected the shapes of the particles as the particles tend to grow anisotropical ly at higher monomer concentration and high temperatures. The formation of tretrapods at high temperatures was due to a kinetically driven reaction as a result of increased temperature. Hexamethylenediamine was found to be a poor capping agent for the prepared CdS nanoparticles. The particles prepared in the compound agglomerated at all temperatures used in preparation. Such results were associated with lower steric hindrance due to a shorter molecular chain. The polymer nanofibres were fabricated via electrospinning technique while varying the concentrations of the polymer solutions. Solutions of low viscosity gave beaded fibres as mixtures of droplets and fibres due to the collection of wet fibres. An increase in the concentration (viscosity) of the solutions resulted in the deposition of solid fibres with bigger diameters. The TGA results show that PMMA electrospun fibres demonstrate a significant increase in thermal stability compared to the powder polymer. However the changes were very minimal on the PEO fibres. CdS and CdSe nanoparticles were incorporated into PMMA and PEO and electrospun to fabricate composite fibres. The incorporation of the quantum dots caused an increase in the viscosity of the solutions and resulted in the collection of fibres with spiral morphology. However this increase of concentration caused an increase in the diameters of the composite fibres as evaluated from the SEM analysis. The EDS analysis showed the presence of Cd, S, and Se elements in the composite fibres due to the presence of CdS and CdSe. The XRD analysis of the composite showed no effect of the quantum dots on the amorphous peak of the PMMA. However on the PEO it showed a decrease in the intensity as the peaks as they become broader due to the decrease of crystallinty. The FTIR spectra showed that the presence of the quantum dots in the polymers on both PMMA and PEO. The optical analysis showed absorption and emissions peaks on the composites fibres due to the showed incorporated light emitter. These peaks were not affected by any change in the concentrations as a result of increased wt % of the quantum dots. Thermal analysis of the composite fibres demonstrates an increase in the thermal stability of the polymers after the incorporation of the quantum dots. Very small changes were observed for the quantum dots doped-PEO material compared to the doped PMMA. DSC analysis showed an increase in the glass transition temperature of the PMMA with increasing wt % of the CdS and CdSe. The addition of CdS and CdSe nanoparticles into PEO caused a decrease in the melting temperature of the polymer due to a decrease in the polymer crystallinity.

This dissertation describes the synthesis and characterization of fluorescent semiconductor nanoparticles (NPs) in order to optimize their biomedical utility for imaging and sensing applications. While both direct and indirect bandgap semiconductor NPs have been studied, control over their emission properties vary. Quantum confinement (QC), which primarily controls the emission wavelength of nanosized semiconductors, dictates that as the size of semiconductor NPs decrease, the magnitude of the bandgap increases, resulting in changes in the observed emission wavelength: smaller NPs have a larger bandgap, and thus a bluer emission. However, surface, interfacial, or shell defects can act as non-radiative or radiative recombination sites for excitons formed within the NP; the latter results in emission competition with the bandgap transition, as described Chapters 1 and 2. Because the emission wavelengths of direct bandgap semiconductor NPs correlate with size according to the expectations of QC, and are stable in aqueous environments with high quantum efficiencies (quantum yield, QY), current research focuses on their potential biomedical applications. Chapter 3 describes red-emitting CdSe/ZnS quantum dots (QDs) that exhibit a concentration-dependent decrease in fluorescence intensity in response to the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). A mechanistic study was performed to understand a 5-HT-dependent decrease in QD emission and calibration curves relating QD intensity loss to 5-HT concentration in ensemble and single QD studies were generated. Unfortunately, the known toxicity of CdSe-based QDs has generated interest in more benign semiconductor NPs to replace these QDs in biological applications, while maintaining the same degree of control over the emission color and QY. Bulk indirect bandgap semiconductors, such as Si, have low efficiency inter-band transitions, and Si NPs are known to contain radiative defects that can alter the emission wavelength from QC-based size expectations; these competitive emission pathways must be controlled in order for Si NPs to be successfully used in biological applications. In general, synthetic methods that gives precise control over both the particle size and surface termination are needed in order to produce emission controlled Si NPs. Relative to groups II and VI QDs, synthetic routes to prepare Si NPs are few in numbers, and the size vs. defect emission events are difficult to assign. Not only do these assignments vary amongst reports, but they also vary with particle size, solvent, sample age, and identities of the surface ligands. Si NPs have been prepared through two synthetic routes using the Zintl salt, sodium silicide (NaSi) and ammonium bromide (NH4Br) as precursors. Chapter 4 describes the synthesis performed in the solvent N,N,-dimethylformamide (DMF). This reaction produces blue-emitting Si NPs (5.02 ± 1.21 nm) that bear partial hydride surface termination. However, it was determined that the solvent was able to interact with the Si NP surface, and prevent subsequent functionalization. This observation was used advantageously, and Chapter 5 describes a one-pot Zintl salt metathesis of Si NPs (3.9 + 9.8 nm) performed in a bi-functional (amine or carboxylic acid) solvent ligand, where the observations indicated that the solvent ligands coordinate to the Si NP. The emission maxima of the Si NPs prepared from the Zintl salt metathesis exhibited a dependence on the excitation energy, and is indicative of emission that is influenced by QC, which likely originates from deeply oxide embedded 1-2 nm crystalline cores. The Si NPs prepared from the one-pot Zintl salt metathesis were exposed to metals salt ions of varying reduction potentials to determine the band edges by what will or will not be reduced (Chapter 6). By monitoring the emission intensity of the Si NPs, in addition to the UV-Vis of the metal ions, the band edge of Si NPs may be determined. The value of the band edge may lend insight into the origin of Si NP emission. To utilize fluorescent Si NPs for biological applications, red emission is strongly preferred. Unfortunately, when preparing aqueous Si NPs, red emission usually changes to blue, likely from the oxidation of the Si NP surface. Therefore, the red emission needs to be efficiently protected from surface oxidants. Because both increased chain lengths and steric modalities have been found to protect the emission properties of Si NPs, red-emitting, ester-functionalized Si NPs (5.51+1.35 nm) with varying chain lengths and ester termination moieties were prepared to determine the best method of preserving the observed red emission in the presence of potential alcoholic oxidants. By determining the best was to protect Si NPs emission, the red-emission from Si NPs may be preserved for biological applications.