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Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / The rate of waste electrical and electronic equipment (WEEE) is growing at an alarming rate, especially in countries where markets are saturated with huge quantities of new electronic goods. Printed circuit boards (PCBs) are a substantial portion of the value contained in waste from WEEE although they are only 6% of the total weight. It is reported that WEEE is currently the fastest growing waste stream in South Africa as the general population’s access to electronic goods in the last decade has increased, especially access to mobile phones. PCBs are found in any piece of electrical or electronic equipment and consist of various metals including precious metals such as gold (Au), silver (Ag) and palladium (Pd). It is reported that gold has the highest economic incentive at 15,200 $ per ton of PCBs. The rapid introduction of new and advanced technology into mobile phones has caused mobile phones to have a relatively short life span, 1 to 2 years to be exact. Mobile phones printed circuit boards (MPPCBs) have more Au content compared to computer circuit boards. They contain 350 g/ton Au whereas computer (PC) PCBs contains 250 g/ton. This research project will recover gold from waste mobile phones PCBs pregnant ammonia thiosulphate leach solution using copper cementation. The cementation process is preferred to all the other technologies of metals extraction from solution due to ultrahigh purity metals that can be obtained and to the less consumption of materials and energy. Electronic parts on the PCBs were manually removed using pliers and screwdrivers. PCBs were then cut to smaller pieces of about 2 x 2 m. The pieces were crushed and milled respectively. Some of the particles were recycled back to the crusher to get finer particles. The particles were separated to particles of sizes between 0 and 1350 μm using a shaker. The comminuted fractions of the PCBs were then used in the leaching step. Batch cementation experiments were performed by bubbling N2 in glass reaction vessel with a working volume of 0.5 L. The reactor was connected to a circulating water bath for temperature control. The recovery percentage of gold at various temperatures, agitation speeds and different amounts of copper powder used, was determined while pH was monitored. The temperature was varied at 30 °C, 40 °C, and 50 °C and the agitation speeds at 300 RPM and 900 RPM. Copper powder was added at 0.5 g/L, 1 g/L, and 1.5 g/L. Gold concentrations were measured by atomic adsorption spectrophotometer (AAS). Scanning electron microscope (SEM) and Energy-dispersive x-ray spectrometry (EDS) analyses of the copper powder after cementation (precipitates) were used to determine the surface morphology and to evaluate the quantitative aspect of the precipitate. It was found that the recovery of gold from ammonia thiosulphate leach solution was greatly affected by agitation speed. At an agitation speed of 900 rpm, 40 °C and 0.5 g of Copper powder, 96% of the gold was recovered from the leach solution. The cementation rate increased as temperature was elevated from 30 to 40 °C, but slightly decreased as the temperature reached 50 °C. The change in experimental conditions affected the gold concentration on the precipitate recovered. This study will provide a possible solution to the WEEE problem and more specifically mobile cell phones, in South Africa.

by Lai Kwong-Yu. / Thesis submitted in: December 1998. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 90-101). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Metal Silicides --- p.1 / Chapter 1.2 --- Titanium Silicide --- p.8 / Chapter 1.3 --- Goal Of This Project --- p.10 / Chapter 2 --- Sample Preparation And Experimental Methods --- p.12 / Chapter 2.1 --- MEVVA Implantation --- p.12 / Chapter 2.2 --- Sample Preparation --- p.15 / Chapter 2.2.1 --- Implantation Condition --- p.15 / Chapter 2.2.2 --- Thermal Treatment --- p.19 / Chapter 2.3 --- Characterization Methods --- p.20 / Chapter 2.3.1 --- Sheet Resistivity Measurement --- p.22 / Chapter 2.3.2 --- X-Ray Diffraction (XRD) --- p.25 / Chapter 2.3.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.28 / Chapter 2.3.4 --- Transmission Electron Microscopy (TEM) --- p.31 / Chapter 3 --- Characterization of As-implanted Samples --- p.36 / Chapter 3.1 --- Introduction --- p.36 / Chapter 3.2 --- Dose Dependence Of As-implanted Samples --- p.37 / Chapter 3.2.1 --- Sheet Resistance Measurement --- p.37 / Chapter 3.2.2 --- X-Ray Diffraction (XRD) --- p.40 / Chapter 3.2.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.40 / Chapter 3.3 --- Implant Beam Current Dependence Of As-implanted Samples --- p.43 / Chapter 3.3.1 --- Sheet Resistance Measurement --- p.43 / Chapter 3.3.2 --- X-Ray Diffraction (XRD) --- p.44 / Chapter 3.3.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.46 / Chapter 3.4 --- Transmission Electron Microscopy (TEM) --- p.48 / Chapter 3.5 --- Summary --- p.52 / Chapter 4 --- Characterization of Annealed Samples --- p.57 / Chapter 4.1 --- Introduction --- p.57 / Chapter 4.2 --- Dose Dependence Of Annealed Samples --- p.58 / Chapter 4.2.1 --- Sheet Resistance Measurements --- p.58 / Chapter 4.2.2 --- X-Ray Diffraction (XRD) --- p.61 / Chapter 4.2.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.63 / Chapter 4.3 --- Implant Beam Current Dependence Of Annealed Samples --- p.66 / Chapter 4.3.1 --- Sheet Resistance Measurement --- p.66 / Chapter 4.3.2 --- X-Ray Diffraction (XRD) --- p.68 / Chapter 4.3.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.70 / Chapter 4.4 --- Annealing Temperature Dependence Of Annealed Samples --- p.71 / Chapter 4.4.1 --- Sheet Resistance Measurement --- p.71 / Chapter 4.4.2 --- X-Ray Diffraction (XRD) --- p.73 / Chapter 4.4.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.75 / Chapter 4.5 --- Annealing Time Dependence Of Annealed Samples --- p.78 / Chapter 4.5.1 --- Sheet Resistance Measurement --- p.78 / Chapter 4.5.2 --- X-Ray Diffraction (XRD) --- p.79 / Chapter 4.5.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.81 / Chapter 4.6 --- Transmission Electron Microscopy (TEM) --- p.82 / Chapter 4.7 --- Summary --- p.84 / Chapter 5 --- Conclusion --- p.87 / Chapter 5.1 --- Main Results Of This Work --- p.87 / Chapter 5.2 --- Suggestions To Future Works --- p.89 / Bibliography

Graphene, since its first isolation, carries many promises on its superior properties. However, unlike its conventional two-dimensional (2D) counterparts, e.g. Si and GaAs systems, graphene represents the first 2D systems built on an atomically thin structure. With every atoms on the surface, graphene is severely affected by the environment and the measured properties have not reaching its full potential. Avoiding all possible external contamination sources is the key to keep graphene intact and to maintain its high quality electronic properties. To achieve this, it requires a revolution in the graphene device structure engineering, because all factors in a conventional process are scattering sources, i.e. substrate, solvent and polymer residues. With our recent two inventions, i.e. the van der Waals transfer method and the metal-graphene edge-contact, we managed to completely separate the layer assembly and metallization processes. Throughout the entire fabrication process, the graphene layer has never seen any external materials other than hexagonal boron nitride, a perfect substrate for graphene. Both optical and electrical characterizations show our device properties reach the theoretical limit, including low-temperature ballistic transport over distances longer than 20 micrometers, mobility larger than 1 million cm²/Vs at carrier density as high as 2 ×10^12 cm^-2, and room-temperature mobility comparable to the theoretical phonon-scattering limit. Moreover, for the first time, we demonstrate the post-fabrication cleaning treatments, annealing, is no longer necessary, which greatly eases integration with various substrate, such as CMOS wafers or flexible polymers, which can be damaged by excessive heating. Therefore the progress made in this work is extremely important in both fundamental physics and applications in high quality graphene electronic devices. Furthermore, our work also provides a new platform for the high quality heterostructures of the 2D material family.

The discipline of organic electronics encompasses the design and synthesis of molecules for use in organic field effect transistors, organic photovoltaics, organic photodetectors, single molecule electronics, sensors, and many more. The rationale for studying organic electronic materials is compelling: organics have the potential to be low cost, processable, and flexible complements to silicon technologies to combat some of the most pressing environmental issues. Organic molecules that transport carriers are used as the active layer in many device applications. Molecules that possess energy levels that allow for electron or hole transport are typically π-conjugated materials. There has been swift progress on the design and synthesis of π-conjugated materials that possess a large density of high energy electrons such as acenes. Yet there has been less growth on materials with low energy vacant orbitals to accept an electron. Fullerenes are the ubiquitous acceptor materials used in organic electronics. Over the past few years, there have been several groups, including our own, that have synthesized non-fullerene materials for use in organic field effect transistors and solar cells. In particular, the Nuckolls laboratory has pioneered the design and synthesis of a class of molecules called contorted aromatics and studied these molecules in range of organic electronic applications. Conjugated macrocycles are one sub-class of the contorted aromatic family. This Thesis describes a body of research on the design, synthesis, and application of a new class of electronic materials made from conjugated macrocycles. Each of the macrocycles comprises perylenediimide cores wound together with various electronic linkers. The perylenediimide building block endows each macrocycle with the ability to transport electrons, while the synthetic flexibility to install different linkers allows us to create macrocycles with different electronic and physical properties. We use these materials in organic photovoltaics, field effect transistors, sensors, and photodetectors. The macrocycles possess vivid colors, absorb in the visible range of the solar spectrum, and are an exemplary class of materials to study how rigidity and strain affect device performance. We find that the strained and rigid macrocyclic framework affords each macrocycle with the ability to absorb lower energy visible light with respect to acyclic counterparts and the macrocycles outperform in photovoltaic applications. Rigidity was an important concept in our organic photodetector study: we found rigidity was one of the reasons our macrocycles outperformed both fullerenes and acyclic controls. The macrocycles all possess intramolecular cavities, and our recent studies focused on using this nanospace for sensing applications. Each of the studies described in this Thesis will demonstrate how macrocyclization is a design technique to enhance organic electronic performance.

Modern computing and mobile device technologies are now based on semiconductor technology with nanoscale components, i.e., nanoelectronics, and are used in an increasing variety of consumer, scientific, and space-based applications. This rise to global prevalence has been accompanied by a similarly precipitous rise in fabrication cost, toxicity, and technicality; and the vast majority of modern nanotechnology cannot be repaired in whole or in part. In combination with looming scaling limits, it is clear that there is a critical need for fabrication technologies that rely upon clean, inexpensive, and portable means; and the ideal nanoelectronics manufacturing facility would harness micro- and nanoscale fabrication and self-assembly techniques. The field of molecular electronics has promised for the past two decades to fill fundamental gaps in modern, silicon-based, micro- and nanoelectronics; yet molecular electronic devices, in turn, have suffered from problems of size, dispersion and reproducibility. In parallel, advances in DNA nanotechnology over the past several decades have allowed for the design and assembly of nanoscale architectures with single-molecule precision, and indeed have been used as a basis for heteromaterial scaffolds, mechanically-active delivery mechanisms, and network assembly. The field has, however, suffered for lack of meaningful modularity in function: few designs to date interact with their surroundings in more than a mechanical manner. As a material, DNA offers the promise of nanometer resolution, self-assembly, linear shape, and connectivity into branched architectures; while its biological origin offers information storage, enzyme-compatibility and the promise of biologically-inspired fabrication through synthetic biological means. Recent advances in DNA chemistry have isolated and characterized an orthogonal DNA base pair using standard nucleobases: by bridging the gap between mismatched cytosine nucleotides, silver(I) ions can be selectively incorporated into the DNA helix with atomic resolution. The goal of this thesis is to explore how this approach to “metallize” DNA can be combined with structural DNA nanotechnology as a step toward creating electronically-functional DNA networks. This work begins with a survey of applications for such a transformative technology, including nanoelectronic component fabrication for low-resource and space-based applications. We then investigate the assembly of linear Ag+-functionalized DNA species using biochemical and structural analyses to gain an understanding of the kinetics, yield, morphology, and behavior of this orthogonal DNA base pair. After establishing a protocol for high yield assembly in the presence of varying Ag+ functionalization, we investigate these linear DNA species using electrical means. First a method of coupling orthogonal DNA to single-walled carbon nanotubes (SWCNTs) is explored for self-assembly into nanopatterned transistor devices. Then we carry out scanning tunneling microscope (STM) break junction experiments on short polycytosine, polycationic DNA duplexes and find increased molecular conductance of at least an order of magnitude relative to the most conductive DNA analog. With an understanding of linear species from both a biochemical and nanoelectronic perspective, we investigate the assembly of nonlinear Ag+-functionalized DNA species. Using rational design principles gathered from the analysis of linear species, a de novo mathematical framework for understanding generalized DNA networks is developed. This provides the basis for a computational model built in Matlab that is able to design DNA networks and nanostructures using arbitrary base parity. In this way, DNA nanostructures are able to be designed using the dC:Ag+:dC base pair, as well as any similar nucleobase or DNA-inspired system (dT:Hg2+:dT, rA:rU, G4, XNA, LNA, PNA, etc.). With this foundation, three general classes of DNA tiles are designed with embedded nanowire elements: single crossover Holliday junction (HJ) tiles, T-junction (TJ) units, and double crossover (DX) tile pairs and structures. A library of orthogonal chemistry DNA nanotechnology is described, and future applications to nanomaterials and circuit architectures are discussed.