Semiconductor nanocrystals have immense potential to make an impact in consumer products due to their narrow, tunable emission linewidths. One factor limiting their use is the ease and reproducibility of core/shell nanocrystal syntheses. This thesis aims to address this issue by providing chemical control over the formation of core/shell nanostructures by replacing engineering controls with kinetic controls. Chapter 1 contextualizes our study on nanoparticle synthesis with a brief discussion on the physics of quantum confinement and the importance of narrow size dispersities, core/shell band alignments, and low lattice mismatches and strain at core/shell nanocrystal interfaces. Next, the evolution of cadmium chalcogenide nanocrystal reagents is described, ranging from the original organometallic reagents used in the 1980s to modern approaches involving cadmium phosphonates and carboxylates. This is followed by a description of chalcogen precursors, highlighting the recent introduction of molecules whose well-controlled and tunable reaction rates allow for the size tuning of nanocrystals at 100% yield, and accompanying theories on nanocrystal nucleation. Chapter 2 covers work to expand the library of available sulfur precursors to a wider range of molecules relevant for the synthesis of cadmium sulfide nanocrystals. Using thioureas alone, only very fast or very slow precursor conversion rates can be accessed. This limits the accessible sizes of cadmium sulfide nanocrystals using a single hot injection of precursor at standardized reaction conditions. We observe that thiocarbonate and thiocarbamate precursors with varying electronic substituents allow access to intermediate precursor conversion rates and cadmium sulfide nanocrystal sizes. Interestingly, we note that these new precursor classes nucleate particles with higher monodispersity than ones synthesized from thioureas. These results indicate that in addition to precursor structure controlling precursor conversion rate, precursor structure additionally impacts nanocrystal monodispersity. Chapter 3 expands the library of sulfur and selenium precursors to include cyclic thiones and selenones which extends chemical control of precursor conversion kinetics to cover five orders of magnitude. This unprecedented breadth of rate control allows for the simultaneous hot injection of multiple precursors to generate core/shell or alloyed nanoparticles using precursor reactivity. Using this new synthetic strategy, we observe that kinetic control runs into several issues which we partially attribute to differences in cadmium sulfide and cadmium selenide critical concentrations and growth rates. Nevertheless, combined with a syringe pump shelling method, we are able to access core/shell and alloyed nanocrystals with photoluminescence quantum yields of 67-81%. Chapter 4 applies the concept of nanostructure control via precursor conversion kinetics to a better model system: two-dimensional nanoplatelets. Cadmium chalcogenide nanoplatelets are highly desirable materials due to their exceptionally narrow emission full width half max (FWHM) values which make them pure emitters relative to quantum dots or organic dyes. We synthesize 3 monolayer thick nanoplatelets whose lateral dimensions vary from 10 nm x 10 nm to 186 x 100 nm and demonstrate compositional control on the smallest platelet sizes with STEM EELS.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 268-376. / by Rakesh Agrawal. / Sc.D.

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Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

"September 2002" Includes as appendix: a list of publications by the author arising from this work; and, copies of some published journal articles Includes bibliographical references. Describes the synthesis, properties and reactions of transition metal complexes containing poly-ynyl ligands

This thesis is submitted as a portfolio of peer-reviewed publications. / For many geochemical systems, reaction kinetics determines the system's current status and evolution. It might also be the key to unraveling their thermal history. In metal sulfide systems, kinetic studies have been carried out on four sets of solid-state transitions/transformations in Fe-Ni-S and Ni-S systems. In this work, a new kinetic model, the Refined Avrami method, has been developed to account for reactions involving changes in reaction mechanisms. Nonstoichiometric compounds are commonly present in these reactions. The exsolution of pentladite from the monosulfide solid solution (mss) is an important reaction in the formation of nickel ores. For near equimolar mss compositions, the reaction rate is rapid even in the low temperature ranges. For bulk composition Fe₀.₇₇ Ni₀.₁₉ S, the experimental results show the reaction rates ( mss → pentlandite ) vary from 1.6x10⁻⁵ to 5.0x10⁻⁷ s⁻¹ at 200 °C and from 9.4x10⁻⁵ to 4.1x10⁻⁷ s⁻¹ at 300 °C. The activation energy, E [subscript a], varies during the course of reaction from 49.6 kJ.mol⁻¹ at the beginning of reaction (nucleation mechanism is dominant) to 20.7 kJ.mol⁻¹ at the end (crystal growth mechanism is dominant). Monosulfide solid solution (mss) is a common intermediate phase observed during the oxidation of nickel ores, such as violarite and pentlandite. The investigation of mss oxidation is of benefit in understanding the thermal behavior of economically important metal sulfides during smelting. The oxidation products of mss vary in our samples depending on their compositions. Apart from the common oxidation products hematite and Ni₁ ₇ S₁₈, Fe₂ (SO₄) ₃ was observed during the oxidation of Fe₇ . ₉ S₈ and pentlandite for Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ . The activation energy was determined using a model-free method. The oxidation of Fe₆.₄ Ni₁.₆ S₈ exhibited a higher E [subscript a] than Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ over the course of the reaction. The E [subscript a] increases with reaction extent (y) from 67.1 to 103.3 kJ.mol⁻¹ for mss composition Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ and from 76.1 to 195.0 kJ.mol⁻¹ for Fe₆.₄ Ni₁.₆ S₈ . The kinetic study of the α - Ni₁₋ ₓ S → β - NiS transition shows that initial compositions of α - Ni₁₋ ₓ S plays an important role in the kinetics of the transition. The activation energy ( E [subscript a] ) for this α - to β - phase transition is 16.0 ( ± 0.5 ) kJ.mol⁻¹ for NiS in the temperature range 70 to 150 °C, and 13.0 (± 0.5) kJ.mol⁻¹ in the temperature range 250 to 350 °C. For Ni₀. ₉₇ S, however, E [subscript a] deceases from 73.0 ( ± 0.5 ) to 17.0 ( ± 0.5 ) kJ.mol⁻¹ over the course of the reaction in the temperature range 300 to 320 °C. The relationship between E [subscript a] and extent of transition (y) for the initial bulk Ni₀. ₉₇ S was derived using the Refined Avrami method. For Ni deficient compositions, α - Ni₁₋ₓ S, the transformation to β-NiS is accompanied by the exsolution of either a progressively more Ni deficient α-Ni₁₋ₓ S and Ni₃ S₄ , and the reactions become more sluggish for more metal deficient compositions. The study of oxidation kinetics of α-NiS is of metallurgical interest, as α-NiS related phases may occur when nickel ores are flash smelted to produce nickel matte. In an open air environment, the oxidation mechanisms of α-NiS are constant at 670 and 680 °C, dominated by the direct oxidation of α-NiS → NiO. The dominant oxidation mechanism changes to a chain reaction : α-NiS → [superscript k] ₁ Ni₃ S₂ → [superscript k] ₂ NiO at 700 °C. Therefore, different kinetic models need to be applied to these two distinct reaction mechanisms. Activation energy for the oxidation, α-NiS → NiO, in the temperature range 670 to 680 °C was calculated to be 868.2 kJ.mol⁻¹ using Avrami/Arrhenius method. Rate constant k₁ and k₂ are approximated to be 3 x 10⁻⁴ s⁻¹ and 5 x 10⁻⁴ s⁻¹ for the first part and second part of the chain reaction respectively at 700 ° C. The study of the variation in reaction rate with oxidation time illustrates the optimum oxidation time zone for each temperature, where NiO can be produced at the fastest rate. / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2005.

"September 2002" / Includes as appendix: a list of publications by the author arising from this work; and, copies of some published journal articles / Includes bibliographical references. / [12], 209 leaves, [35] pages : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Describes the synthesis, properties and reactions of transition metal complexes containing poly-ynyl ligands / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 2002

Bibliography: p.61-65.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, December 1997. / Includes bibliographical references. Also available on the Internet.

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