Bionanomaterials from plant viruses

Plant virus capsids have emerged as useful biotemplates for material synthesis. All plant virus capsids are assembled with high-precision, three-dimensional structures providing nanoscale architectures that are highly monodisperse, can be produced in large quantities and that cannot replicate in mammalian cells (so are safe). Such exceptional characteristics make plant viruses strong candidates for application as biotemplates for novel and new material synthesis

Predicting the conformations of peptides and proteins in early evolution. A review article submitted to Biology Direct

Considering that short, mainly heterochiral, polypeptides with a high glycine content are expected to have played a prominent role in evolution at the earliest stage of life before nucleic acids were available, we review recent knowledge about polypeptide three-dimensional structure to predict the types of conformations they would have adopted. The possible existence of such structures at this time leads to a consideration of their functional significance, and the consequences for the course of evolution

Recent Advances in Noble Metal (Pt, Ru, and Ir)-Based Electrocatalysts for Efficient Hydrogen Evolution Reaction

Noble metal (Pt, Ru, and Ir)-based electrocatalysts are currently considered the most active materials for the hydrogen evolution reaction (HER). Although they have been associated with high cost, easy agglomeration, and poor stability during the HER reaction, recent efforts to intentionally tailor noble-metal-based catalysts have led to promising improvements, with lower cost and superior activity, which are critical to achieving large-scale production of pure hydrogen. In this mini-review, we focus on the recent advances in noble-metal-based HER electrocatalysts. In particular, the synthesis strategies to enhance cost-effectiveness and the catalytic activity for HER are highlighted

Investigations on the localized surface plasmon resonances of nickel sulfide nanostructures

The main topic of this thesis was the examination of the optical properties of nanoparticles consisting of metallic nickel sulfide phases. For this, new syntheses to obtain various colloidal dispersions of Ni3S2, Ni3S4, and α-NiS nanostructures as well as core-shell particles with gold cores were developed. These materials all exhibit prominent absorbance features in the visible part of the electromagnetic spectrum which were confirmed to be caused by localized surface plasmon resonances (LSPRs). Since the field of plasmonic materials active in this spectral region is otherwise confined to noble metal nanoparticles, the novel nickel sulfide particles were evaluated with regard to their molar extinction coefficient. An analysis of the results compared to commonly used gold nanocrystals showed that Ni3S2 nanostructures could achieve very similar values while the necessary precursors for their synthesis are much less expensive than the respective noble metal precursors. Furthermore, hollow nickel sulfide nanoparticles were synthesized to be able to profit from the advantages of hollow nanostructures in regards to applications as nanosensors. This was achieved via the nanoscale Kirkendall effect starting from nickel nanoparticles. The obtained hollow nickel sulfide nanoparticles showed a much sharper LSPR absorbance band making them a more promising material for sensorics. Additionally, α-NiS and Au-α-NiS nanoparticles were investigated regarding their metal-insulator type phase transition and its influence on their LSPR. It could be shown, that the optical density of the colloidal dispersions can be tuned by varying the temperature, resulting in a temperature-switchable plasmonic material.Das Hauptthema dieser Arbeit war die Untersuchung der optischen Eigenschaften von Nanopartikeln bestehend aus metallischen Nickelsulfid-Phasen. Dazu wurden neue Synthesen entwickelt, um kolloidale Dispersionen von Ni3S2-, Ni3S4- und α-NiS-Nanostrukturen sowie Kern-Schale-Partikel mit Goldkernen zu erhalten. Diese Materialien zeigen auffällige Extinktionsbanden im sichtbaren Teil des elektromagnetischen Spektrums, die lokalisierten Oberflächenplasmonenresonanzen (LOPRs) zugeordnet werden konnten. Da das Feld der in diesem Spektralbereich aktiven plasmonischen Materialien auf Edelmetall-Nanopartikel beschränkt ist, wurden die neuartigen Nickelsulfid-Partikel hinsichtlich ihres molaren Extinktionskoeffizienten untersucht. Ein Vergleich der Ergebnisse mit denen der häufig verwendeten Goldnanokristalle zeigte, dass Ni3S2-Nanostrukturen sehr ähnliche Werte erreichen können, während die für ihre Synthese notwendigen Vorstufen deutlich günstiger sind als die der Edelmetalle. Darüber hinaus wurden hohle Nickelsulfid-Nanopartikel synthetisiert, um die Vorteile hohler Nanostrukturen im Hinblick auf Anwendungen als Nanosensoren nutzen zu können. Dies wurde über den nanoskaligen Kirkendall-Effekt ausgehend von Nickel-Nanopartikeln erreicht. Die erhaltenen hohlen Nickelsulfid-Nanopartikel zeigten eine deutlich schärfere LOPR-Extinktionsbande, was sie zu einem vielversprechenderen Material für die Sensorik macht. Darüber hinaus wurden α-NiS- und Au-α-NiS-Nanopartikel hinsichtlich ihres Metall-Isolator Übergangs und dessen Einfluss auf ihre LOPR untersucht. Es konnte gezeigt werden, dass die optische Dichte der kolloidalen Dispersionen durch Variation der Temperatur eingestellt werden kann, was sie zu einem temperaturschaltbaren plasmonischen Material macht

The use of mixed thiol collectors in the flotation of Nkomati sulphide ore

Includes bibliographical references.Mixtures of collectors are widely used in sulfide and platinum group mineral (PGM) flotation, and a range of performance benefits have been reported for many different systems. An increase in paymetal recovery and grade as well as increased rates of recovery at lower collector dosages has been observed when single collectors are replaced with multi-collector suites. These benefits have been attributed to increased carrying capacity of the froth phase, faster kinetics and increased recovery of middling or course particles. However, the mechanism of action of such collector suites is not clearly understood. Candidate selection of mixed collector suites is currently based on experience and contextual knowledge. The overall objective of this study was to experimentally identify a three component collector suite consisting of conventional collectors which could enhance the metallurgical performance of Nkomati nickel-copper sulfide ore. A three component collector suite consisting of sodium isobutyl xanthate (SIBX), sodium ethyl xanthate (SEX) and either sodium ethyl dithiophosphate (DTP) or sodium ethyl dithiocarbamate (DTC) was used. The scope of this work was confined to the use of xanthates, DTC’s and DTP’s since they are in common use in industry, are supplied over a relatively low price range and have shown potential performance enhancements when used as mixtures. The standard University of Cape Town (UCT) batch flotation procedure was used in this investigation and changes in electrochemical potential were monitored as collector was added to the flotation cell. It is hypothesised that the benefits of collector mixtures are only evident at low dosages, thus, dosages were carefully controlled. The study aimed to determine whether benefits of collector mixtures were dominant in the pulp or froth phase and suggest a possible mechanism of action

Investigating depressant behaviour in the flotation of selected Merensky ores

Includes abstract.Includes bibliographical references (p. 109-116).This study utilised laboratory batch flotation tests to characterise the flotation performance, with respect to sulfide and gangue minerals, of two Merensky ores with different mineralogy, in the presence of depressants; and contributes to the increased understanding of depressant behaviour in the flotation of Merensky ores. The ores were obtained from the southern section of the Merensky reef in the Bushveld Igneous Complex

Synthetic fabrication of nanoscale MoS₂-based transition metal sulfides

2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Anisotropic Particles: Preparation and Study

Anisotropic particles have received significant attention in self-assembly for the large scale fabrication of hierarchical structures. Janus particles, a specific class of anisotropic particles, have two hemispheres with different materials. Due to the anisotropic nature of the particle shape and interactions, Janus particles have demonstrated interesting properties in interfacial assembly, switchable devices, cargo transport, and optical sensing. The objective of this research is to fabricate novel anisotropic Janus particles and explore their potential unique properties.;One of the driving forces arises from the previous work of bimetallic nanorods and their autonomous motion. The bimetallic nanorod systems undergo chemically powered non- Brownian motion due to the asymmetric distribution of catalytic source for a chemical fuel solution. However, the approach used to prepare the bimetallic nanorods is rather complex. The original design of bimetallic Janus particles is based on a general physical vapor deposition technique -- electron beam evaporation. The resulting bimetallic Janus particles are colloidal silica spheres coated with two differing metals on each hemisphere. This approach allows fabricating bimetallic Janus particles with various combinations of metals that are available for electron beam evaporation.;Chemical transformation of bimetallic Janus particles into other species provides an opportunity to expand the scope of anisotropic particles. The metals on the Janus particles are possible to convert to their corresponding metal oxides and metal sulfides through solid-gas heterogeneous reactions, and therefore, the chemical transformation of the parent bimetallic Janus particles produces a wide array of previously unavailable Janus particle types, including metal/metal oxide, metal/metal sulfide, metal oxide/metal oxide, metal sulfide/metal sulfide, and metal oxide/metal sulfide, which allows tuning their optical, electronic, magnetic and catalytic properties. This vast library of anisotropic particulate building blocks provides a powerful arsenal for engineering the assembly of specific targeted structures and systems.;Autonomous motion is distinctive from Brownian motion. Platinum half-coated Janus particles undergo self-propelled motion, which is induced by the catalytic decomposition of hydrogen peroxide. The average speed of the self-propelled Pt-SiO2 Janus particles increases with increasing the concentration of hydrogen peroxide. Motion direction analyses show that the probability for the Janus particles continuing to travel in nearly same direction goes higher in higher concentrations of hydrogen peroxide. Microscopic observation of the particle motion demonstrates that these Janus particles move, on average, with the platinum-coated region oriented opposite to the direction of motion. The trajectories of the autonomous motion exhibit a directed motion at short time scale but with an overall random behavior at long time scales. Huge benefit can be garnered by taking advantage of the self-propulsion component in the system. The control of the motion of the magnetic Janus particles in solutions of hydrogen peroxide is demonstrated using the external magnetic field. The magnetic Janus particles orient themselves with the equatorial plane parallel to the applied field and the motion direction is perpendicular to the field. The directed motion has a more distinct preferred direction compared to the case in the absence of magnetic field, and the applied field is verified to control the orientation, not influence the speed of the particle motion.;Anisotropic particles are unique building blocks to assemble complex structures. The surface functionalized Janus particles with alkanethiols are adsorbed at the interfaces of liquid-air and liquid-liquid, forming monolayers with metal hemispheres pointing to the same direction. By changing the liquid oil phase, the orientation of the Janus particles can be manipulated, which provides an opportunity to selectively modify the surface in either phase. The preferential orientation in the same direction at interfaces allows for direct transfer of the Janus particles while the desired faces remain in either a face-down or face-up configuration. An external intervention, magnetic field, is also sought to direct the assembly of the magnetic Janus particles. In the presence of uniform magnetic field, the magnetic Janus particles form staggered chain structures with the chain direction parallel to the direction of the applied field. These chain structures are destroyed due to the capillary force during solvent evaporation. However, these soft structures are successfully locked in place after the solution dries by the addition of ammonium carbonate to the solution, which suggests a promising way to achieve 2D or 3D super structures for the fabrication of photonic crystals and photonic devices

Notes and laboratory reports on “Technology of Structural materials and Material Science” Part 2

“Technology of Structural materials and Material Science” is one of the basic technical disciplines in the syllabus for “Engineering mechanics” field of study. During the implementation of laboratory work considerable attention is given to the educational and experimental work for the study of materials that are used in different branches of an industry; alloy’s properties dependance on the chemical composition; structure, methods of treatment and external environments. The study of the theory and practice of different methods of materials strengthening is to provide a high reliability and longevity of the machine’s details, devices, tools etc. After every practical class in the laboratory, students will fill the laboratory report. The content of the laboratory class corresponds with the syllabus of the course “Material Science” for students of the “Engineering mechanics” field of study. The purpose of this manual is to provide guidelines for the students in preparation for independent laboratory work and to project its results in the laboratory reports