The direct anodic decomposition of copper-rich mattes using packed bed electrodes was investigated, because a practical solution to direct electrorefining of copper matte would lead to the potential elimination of copper converting and its associated sulphur dioxide emissions. Much greater copper extraction has been achieved experimentally at 50° C from a packed bed electrode consisting of 0.5-4mm diameter particles than from a massive or solid flat electrode composed of copper-rich matte, as found in earlier studies. This was shown to be attributable to natural convection mass transport processes within the inter-particle region that is not available in massive electrodes. However, while natural convection mass transfer is an important process in the packed bed electrodes, other factors were shown to be ultimately more important in terms of the maximum copper extraction which may be achieved prior to shut-down caused by total-bed polarization of these electrodes. Total-bed polarization of copper-rich mattes during direct anodic decomposition may be attributed to (a) deteriorating electrical contact (related to the formation of elemental sulphur and lead sulphate) between the current distributor and the adjacent particles, and in thick electrodes, between the particles across the anode, (b) relative nonreactivity of iron-containing phases and (c) physical association of these phases with the reactive phases, and under certain conditions (d) crystallization of copper sulphate within the inter-particle region, blocking ionic conduction paths. The maximum copper extraction from synthetic pure chalcocite, the predominant component of industrial copper-rich mattes, using the packed bed electrodes was found to be about 80%. The presence of 3-4wt% iron in the copper-rich mattes was shown to degrade the copper extraction considerably due to the presence of relatively nonreactive iron-rich phases which form as the matte is cooled from its liquid state. The presence of lead in copper matte was found to be a relatively unimportant impurity in terms of copper extraction, while oxygen was found to partially offset the negative effects of iron. A simple one-dimensional mathematical model was developed to estimate the variation of copper extraction across a 2cm-thick packed bed electrode. The copper extraction was found experimentally to vary by less than a factor of two across the anode. This was attributed to (a) the relatively high electrical conductivity of the electrolyte which minimizes reaction-process overpotential gradients across the anode, and (b) the increasing impedances of the decomposition processes in the most reacted particles. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Nitrogen-doped carbon materials such as carbon nanotubes and graphene have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (e.g. oxygen reduction) and biosensing (e.g. hydrogen peroxide reduction). Electrocatalytic properties of these materials have been attributed to enhanced electron transfer ability exhibited by surface nitrogen atoms compared to typical carbon structures. Screen-printing has been widely employed in the production of low-cost carbon-based electrodes for sensors and biosensors. Here, we develop nitrogen-doped screen-printed carbon (N-SPCE) electrodes for detection of hydrogen peroxide - an important analyte in biosensing. Conductive ink was formulated in the lab from nitrogen-doped graphite that was produced using a simple urea-based soft nitriding technique. N-SPCEs exhibited electrocatalytic activity towards hydrogen peroxide reduction, while SPCEs prepared from unmodified carbon showed no ability to electrocatalytically reduce H2O2. Amperometric detection of H2O2 using N-SPCEs at an applied potential of -0.4 V (vs. Ag/AgCl) displayed a wide linear range of 20 µM to 5.3 mM, and a low limit of detection (2.4 µM). These performance characteristics compare favorably to other electrodes for H2O2 sensing and indicate that the low-cost, easy-to-prepare N-SPCEs described here are promising platforms for the development of biosensors.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 1977 / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Chemistry

Thesis advisor: Michael J. Naughton / In this dissertation, I first discuss many different kinds of transparent conductors in Chapter one. In Chapter two, I focus on transparent conductors based on crackle temples. I and my colleagues developed three (one sputter-free and two fully all-solution) methods to fabricate metallic networks as transparent conductors. The first kind of all-solution process is based on crackle photolithography and the resulting silver networks outperform all reported experimental values, including having sheet resistance more than an order of magnitude lower than ITO, yet with comparable transmittance. The second kind of all-solution proceed transparent conductor is obtained by integrating crackle photolithography-based microwires with nanowires and electroplate welding. This combination results in scalable film structures that are flexible, indium-free, vacuum-free, lithographic-facility-free, metallic-mask-free, with small domain size, high optical transmittance, and low sheet resistance (one order of magnitude smaller than conventional nanowire-based transparent conductors). / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) has been successfully deposited onto nanometer-sized gold (Au) electrodes. The cyclic voltammograms obtained on a 4-ATP SAMs modified electrode show peaks and the peak height is proportional to the scan rate, which is similar to that on an electroactive SAMs modified macro electrode. The electrochemical behavior and mechanism of outer-sphere electron transfer reaction on the 4-ATP SAMs modified nanometer-sized electrode has also been studied. The 4-ATP SAMs modified electrode is further modified with platinum (Pt) nanoparticles. Electrochemical behaviors show that there is electrical communication between Pt nanoparticles and Au metal on the Pt nanoparticles/4-ATP SAMs/Au electrode. However, scanning electron microscopic image shows that the Pt nanoparticles are not evenly covered the electrode.

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3D printed on-skin electrodes are of notable interest because, unlike traditional wet silver/silver chloride (Ag/AgCl) on-skin electrodes, they can be personalized and 3D printed using a variety of materials with distinct properties such as stretchability, conformal interfaces with skin, biocompatibility, wearable comfort, and, finally, low-cost manufacturing. Dry on-skin electrodes, in particular, have the additional advantage of replacing electrolyte gel, which dehydrates and coagulates with prolonged use. However, issues arise in performance optimization with the recently discovered dry materials. These challenges become even more critical when the on-skin electrodes are scaled down to a miniaturized size, making the detection of various biosignals while keeping mechanical resilience under several conditions crucial. Thus, this thesis focuses on designing, fabricating, optimizing, and applying a personalized, fully 3D-printed permeable skin patch with miniaturized octopus-like suckers and embedded microchannels for enhanced mechanical strengths, breathability, and biosignal monitoring. The developed device showcases a rapid, cost-effective fabrication process of porous skin patches and the printing process of ink metal-based materials that expands its applications to low-resource settings and environments.

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