This work aims to develop solvent extractants to recover platinum and palladium from highly acidic chloride solutions bearing other platinum group metals (PGMs). In general, metal values can be recovered by solvent extraction through three different mechanisms: metal cation extraction (1); metalate anion extraction (2); or metal salt extraction (3). Mn- + n(LH)(org) ⇌ [M(L)n](org) + nH+ (1) MClx n- + nL(org) + nH+ ⇌ [MClx(LH)n](org) (2) MClx + nL(org) ⇌ [MClxLn](org) (3) The main objective of this thesis is to establish whether ditopic extractants can be developed which have chemical functionalities that allow both mechanisms (2) and (3) to operate, co-extracting Pt(IV) and Pd(II) as their chloridometalates in an outer sphere binding site (2) and allowing their separation by raising pH to transfer the more kinetically labile Pd(II) to an inner sphere binding site (3) and releasing H2PtCl6 to the aqueous strip solution. A review of the literature is presented in Chapter 1, noting current commercially available extractants and the processes in which they are, or have been, applied. Particular attention is paid to the mode of action of the reported extractants and whether they extract metal cations, anions or metal salts. This chapter also outlines the proposed solvent extraction circuit in which new reagents developed in this thesis would be incorporated and the methods applied during the screening of candidate extractants. Chapter 2 deals exclusively with the use of reagents with inner-sphere binding sites for the selective extraction of palladium over platinum. Work on a series of oxime reagents synthesised for palladium extraction as part of preliminary MSci research (Andrew M. Wilson, MSci Thesis, University of Edinburgh, 2011) is reviewed. Studies of the hydrolytic stability of oximes indicate that they are unsuitable for incorporation into ditopic reagents for use in a circuit with a highly acidic feed solution. Thioethers were studied as alternatives as they show high kinetic selectivity for palladium over platinum and are more stable under acidic conditions. The synthesis and extraction properties of model reagents (largely arylalkyl thioethers) are reported and compared with those of the commercially available di-n-hexylsulfide. Incorporation of a polar group such as an amide provides phase transfer catalysis, accelerating the rate of transport of Pd(II) into the organic phase, but reducing selectivity over Pt(IV). The identification of functionalities that operate as receptors for chloridometalates by forming outer-sphere assemblies is explored in Chapter 3. The synthesis of amine, amide and amino-amide extractants from acid chloride streams and the effects of variations of functional groups on the extraction of PtCl6 2− are described. Secondary amides were found to be stronger extractants than tertiary amides, and aliphatic amides also show better metalate extraction than aromatic amides. The interactions between protonated aminoamide reagents and PtCl6 2− werre analysed by X-ray crystallography, noting that C-H∙∙∙Cl interactions with the “soft” chloridometalate anion are more common than with the “hard” chloride ion which shows a preference for more conventional N-H∙∙∙Cl interactions. Chapter 4 combines the reagent types explored in Chapters 2 and 3, in ditopic extractants that have both inner- and outer sphere binding sites. The synthesis and characterisation of a series of thioether amide reagents are reported and the selective extraction of platinum and palladium over other PGMs are discussed. In-house screenings of aryl- and alkylthioetheramide extractants showed selective co-extraction of Pd(II) and Pt(IV), rejecting Ir(III). Pt(IV) can be selectively water-stripped followed by ammonia-stripping of Pd(II). Industrial screenings at Johnson Matthey Technology Centre further exemplified the selectivity of these extractants over Ru(III) and Rh(III), although third phases were formed when the reagents were used for recovery from highly concentrated metal-feed solutions. The mode of action of the ditopic extractants is discussed, based on DFT calculations, crystal structure determinations and NMR studies, which support the formation of outersphere metalate assemblies and inner-sphere palladium complexes. Chapter 5 describes new difunctional (inner + outer sphere complexation) extraction by a single chemical entity, in this case an unsaturated N-heterocycle (an azole). The synthesis and characterisation of a series of hydrophobic azoles are described. These have basicities which allow protonation when contacted with strongly acidic solutions (2), but can be deprotonated in contact with water to allow their neutral forms to form inner-sphere complexes with Pd(II). Triazole-based reagents show the selective co-extraction of Pt(IV) and Pd(II) and, as with the ditopic thioetheramide reagents reported in Chapter 4, allow the selective water stripping of Pt(IV) and subsequent ammonia stripping of Pd(II).

Η νήσος της Τήνου (εικόνα 1), με εμβαδό περίπου 200 km2, βρίσκεται στη δυτική Ελλάδα και είναι τρίτη σε έκταση μεταξύ των νήσων που συγκροτούν το σύμπλεγμα των Κυκλάδων, στο Αιγαίο πέλαγος. Από γεωτεκτονικής απόψεως υπάγεται στην γεωτεκτονική ενότητα, γνωστή ως ‘Αττικοκυκλαδική Κρυσταλλοσχιστώδης Μάζα’. Από διάφορες γεωλογικές μελέτες που έχουν συνταχθεί κατά καιρούς, έχει προκύψει ότι στην γεωλογική της δομή μετέχουν μεταμορφίτες, μαγματίτες και τεταρτογενή ιζήματα. Από τα πετρώματα αυτά οι μεν μεταμορφίτες καλύπτουν το 79%, τα δε υπόλοιπα το 17% και 4%, αντίστοιχα, της επιφάνειας της νήσου.Με βάση μελέτες που πραγματοποιήθηκαν στις οφιολιθικές εμφανήσεις της Τήνου, προέκυψε πως η σύσταση του μανδυακού περιδοτίτη είναι χαρζβουργιτική, μέσα στον οποίο υπήρχαν αρκετές μικρές εμφανήσεις χρωμίτη. Οι χαρακτήρες που έχουν μελετηθεί γεωχημικά και ορυκτολογικά-πετρογραφικά, αφορούν κυρίως τον διάσπαρτο τύπο σπινελλίου και τον τεκτονίτη-περιδοτίτη που είναι ο δυνητικός ξενιστής κοιτασμάτων χρωμίτη.Το ενδιαφέρον της νήσου της Τήνου από απόψεως οικονομικής γεωλογίας περιορίζεται – σύμφωνα τουλάχιστον με τα δεδομένα που έχουν προκύψει από τις μέχρι τώρα έρευνες – αποκλειστικά και μόνο στα μάρμαρα και στα βιομηχανικά ορυκτά και πετρώματα (τάλκης). Μεταλλικά ορυκτά απατώνται μεν, σε φυσικές όμως συγκεντρώσεις τέτοιες, ώστε ούτε οι διαστάσεις τους ούτε και η περιεκτικότητά τους σε μέταλλο να αφήνουν περιθώρια για θετικές εκτιμήσεις. Παλαιότερα, έγινε προσπάθεια εκμεταλλεύσεως, σε διάφορες θέσεις, χωρίς θετικά αποτελέσματα όμως. Τα μεταλλευτικά έργα είναι μικρών διαστάσεων, συνήθως εκσκαφές, και σε λίγες περιπτώσεις στοές και κεκλιμένα. Σημειώνεται ότι σε πολλές από τις εκσκαφές δεν υπάρχουν σήμερα ίχνη μεταλλεύματος, ούτε στα τοιχώματά τους, ούτε στα μπάζα. Η συγκέντρωση της ομάδας του λευκόχρυσου (PGE) και του χρυσού στους χρωμιτίτες των οφιολίθων της Τήνου είναι της τάξεως των εκατοντάδων ppb. Αυτά τα στοιχεία συγκεντρώνονται κυρίως θειούχα μεταλλικά ορυκτά (σουλφίδια), όπως ο χαλκοπυρίτης, και σχηματίζονται στο ορθομαγματικό στάδιο, σχηματίζοντας ομάδες, μέσα στους κόκκους του χρωμίτη. / Tinos island (picture 1), with an area of about 200 km2, is located in weastern Greece and is the third largest island of the Cyclades group of islands, in the Aegean Sea. Geologically, is regarded, to belong to the geotectonic unit, known as the ‘Atticocycladic Crystalline Massif’. As a result of many geological studies, it was found that the geological structure of the island is made up from metamorphic and magmatic rocks, as well as Quaternary sediments. These rocks cover an area of about 79%, 17% and 4%respectively of the island’s surface area. Based on studies performed in the Tinos ophiolitic complex, showed that the composition of the mantle peridotites is harzburgitic, in which there were several small commulations of chromite. The characters studied geochemical and mineralogical-petrographical, mainly concern the disseminated spinel type and the peridotite which is a potential host rock for chromite deposits. The interest of Tinos island in terms of economic geology is limited - at least according to the data derived from the surveys so far - to marbles and industrial minerals and rocks (talc). Metallic minerals are occured, but in natural concentrations such that neither the dimensions nor the content of metal allow for positive evaluations. Previously, an exploitation attempt was made, in various positions, but without positive results. Mining projects are small, usually excavations, and in a few cases tunnels and ramps. Note that in many of the excavation does not exist today mines traces neither in their walls, nor in the rubble. The concentration of platinum group (PGE) and gold in chromitites of serpentines of Tinos are about of hundreds of ppb. These components are mainly concentrated sulphurous metallic minerals (sulfides) such as chalcopyrite, and formed in orthomagmatic stage, forming groups within the granules of the chromite.

Philosophiae Doctor - PhD / Nowadays, the pollution of surface waters with chemical contaminants is one of the most crucial environmental problems. These chemical contaminants enter rivers and streams resulting in tremendous amount of destruction, so the detection and monitoring of these chemical contaminants results in an ever-increasing demand. This thesis describes the search for a suitable method for the determination of platinum group metals (PGMs) in environmental samples due to the toxicity of mercury films and the limitations with methods other than electroanalytical methods. This study focuses on the development of a novel bismuth-silver bimetallic nanosensor for the determination of PGMs in roadside dust and soil samples. Firstly, individual silver, bismuth and novel bismuth-silver bimetallic nanoparticles were chemically synthesised. The synthesised nanoparticles was compared and characterised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy, and transmission electron microscopy (TEM) analysis to interrogate the electrochemical, optical, structural, and morphological properties of the nanomaterials. The individual silver, bismuth, and bismuth-silver bimetallic nanoparticles in the high resolution transmission electron microscopy results exhibited an average particle size of 10-30 nm. The electrochemical results obtained have shown that the bismuth-silver bimetallic nanoparticles exhibit good electro-catalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible spectroscopy, Fourier-transformed infrared spectroscopy, and Raman spectroscopy results confirmed the structural properties of the novel bismuth-silver bimetallic nanoparticles. In addition the transmission electron microscopy and selected area electron diffraction morphological characterisation confirmed the nanoscale nature of the bismuth-silver bimetallic nanoparticles. Secondly, a sensitive adsorptive stripping voltammetric procedure for palladium, platinum and rhodium determination was developed in the presence of dimethylglyoxime (DMG) as the chelating agent at a glassy carbon electrode coated with a bismuth-silver bimetallic nanofilm. The nanosensor further allowed the adsorptive stripping voltammetric detection of PGMs without oxygen removal in solution. In this study the factors that influence the stripping performance such as composition of supporting electrolyte, DMG concentration, deposition potential and time studies, and pH have been investigated and optimised. The bismuth-silver bimetallic nanosensor was used as the working electrode with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. The differential pulse adsorptive stripping peak current signal was linear from 0.2 to 1.0 ng/L range (60 s deposition), with limit of detections for Pd (0.19 ng/L), Pt (0.20 ng/L), Rh (0.22 ng/L), respectively. Good precision for the sensor application was also obtained with a reproducibility of 4.61% for Pd(II), 5.16% for Pt(II) and 5.27% for Rh(III), for three measurements. Investigations of the possible interferences from co-existing ions with PGMs were also done in this study. The results obtained for the study of interferences have shown that Ni(II) and Co(II) interfere with Pd(II), Pt(II) and Rh(III) at high concentrations. The interference studies of Cd(II), Pb(II), Cu(II) and Fe(III) showed that these metal ions only interfere with Pd(II) and Pt(II) at high concentrations, with no interferences observed for Rh(III). Phosphate and sulphate only interfere at high concentrations with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. Based on the experimental results, this bismuth-silver bimetallic nanosensor can be considered as an alternative to common mercury electrodes, carbon paste and bismuth film electrodes for electrochemical detection of PGMs in environmental samples. Thirdly, this study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry (DPAdSV) of PGMs in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the SPCEs. Optimisation parameters such as pH, DMG concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng/L. The detection limit for Pd(II), Pt(II) and Rh(III) was found to be 0.07 ng/L, 0.06 ng/L and 0.2 ng/L, respectively. Good precision for the sensor application was also obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II) and 5.37% for Rh(III), for three measurements. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42- and PO43- does not interfere with Pd(II) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. These possible interference ions only interfere with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) as the supporting electrolyte solution.

In occupational settings where rhodium is produced or used, such as the mining industry, refineries and catalytic industries, workers are at risk of being dermally exposed to this metal in either the metallic form or its salt compounds. A considerable amount of contradictory literature has been published with regard to the sensitising abilities of rhodium and no published information is available on the occupational dermal exposure of rhodium as well as its ability to permeate through the skin. Previous studies conducted on the in vitro permeation of metals, such as nickel, cobalt and chromium, have indicated that certain metals undergo oxidation in the presence of sweat and form ions which are able to permeate through skin. For some metals, this ionisation takes place more rapidly in an acidic environment and a decrease in the environmental pH would cause an increase in the release of ions from those metals. Aim: The aim of this study was to determine whether rhodium in the form of rhodium trichloride (RhCl3) would be able to permeate through the skin in vitro, as well as to determine whether any differences exist between the in vitro permeation of rhodium at a pH of 4.5 and a pH of 6.5. Methods: Full thickness abdominal skin was obtained as biological waste after surgery from Caucasian females ranging between 39 and 42 years of age. The Franz diffusion cell method was used in which the experimental cells contained synthetic sweat with RhCl3 and the blanks did not contain any RhCl3 in the donor compartment. All of the cells contained a physiological receptor solution in the receptor compartment. At intervals of 8, 12 and 24 hours, 2 ml of the receptor solution were removed for analysis. The receptor compartment was rinsed with 2 ml receptor solution which was also removed for analysis and 2 ml of fresh receptor solution was added to the compartment. After 24 hours, the receptor and donor solution was removed respectively for analysis and the skin was removed for digestion, prior to analysis. The mass of rhodium in the receptor solutions were determined using Inductively Coupled Plasma Mass Spectrometry. The donor solutions and digested skin solutions were analysed using Inductively Coupled Plasma Optical Emission Spectrometry. Results: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin with a cumulative increase in permeation over prolonged exposure time. After 8, 12 and 24 hours, the amount of rhodium that permeated through the skin was higher at pH 4.5 than for pH 6.5. After 12 hours, the permeation of rhodium was statistically significantly higher for pH 4.5 than for pH 6.5 (p = 0.02). At both pH values, the percentage of rhodium that accumulated in the skin was higher than the percentage of rhodium that diffused through the skin and the lag time was less than six hours. Conclusion: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin. A decrease in the pH of synthetic sweat led to an increase in the permeation of rhodium and it is recommended that future in vitro permeation studies be conducted at a pH of 4.5, as the skin surface pH of workers are generally considered to be below 5. A higher percentage of rhodium was retained in the skin than the percentage that diffused through, indicating the ability of rhodium to accumulate in the skin, from where it may exert health effects, such as sensitisation. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

In occupational settings where rhodium is produced or used, such as the mining industry, refineries and catalytic industries, workers are at risk of being dermally exposed to this metal in either the metallic form or its salt compounds. A considerable amount of contradictory literature has been published with regard to the sensitising abilities of rhodium and no published information is available on the occupational dermal exposure of rhodium as well as its ability to permeate through the skin. Previous studies conducted on the in vitro permeation of metals, such as nickel, cobalt and chromium, have indicated that certain metals undergo oxidation in the presence of sweat and form ions which are able to permeate through skin. For some metals, this ionisation takes place more rapidly in an acidic environment and a decrease in the environmental pH would cause an increase in the release of ions from those metals. Aim: The aim of this study was to determine whether rhodium in the form of rhodium trichloride (RhCl3) would be able to permeate through the skin in vitro, as well as to determine whether any differences exist between the in vitro permeation of rhodium at a pH of 4.5 and a pH of 6.5. Methods: Full thickness abdominal skin was obtained as biological waste after surgery from Caucasian females ranging between 39 and 42 years of age. The Franz diffusion cell method was used in which the experimental cells contained synthetic sweat with RhCl3 and the blanks did not contain any RhCl3 in the donor compartment. All of the cells contained a physiological receptor solution in the receptor compartment. At intervals of 8, 12 and 24 hours, 2 ml of the receptor solution were removed for analysis. The receptor compartment was rinsed with 2 ml receptor solution which was also removed for analysis and 2 ml of fresh receptor solution was added to the compartment. After 24 hours, the receptor and donor solution was removed respectively for analysis and the skin was removed for digestion, prior to analysis. The mass of rhodium in the receptor solutions were determined using Inductively Coupled Plasma Mass Spectrometry. The donor solutions and digested skin solutions were analysed using Inductively Coupled Plasma Optical Emission Spectrometry. Results: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin with a cumulative increase in permeation over prolonged exposure time. After 8, 12 and 24 hours, the amount of rhodium that permeated through the skin was higher at pH 4.5 than for pH 6.5. After 12 hours, the permeation of rhodium was statistically significantly higher for pH 4.5 than for pH 6.5 (p = 0.02). At both pH values, the percentage of rhodium that accumulated in the skin was higher than the percentage of rhodium that diffused through the skin and the lag time was less than six hours. Conclusion: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin. A decrease in the pH of synthetic sweat led to an increase in the permeation of rhodium and it is recommended that future in vitro permeation studies be conducted at a pH of 4.5, as the skin surface pH of workers are generally considered to be below 5. A higher percentage of rhodium was retained in the skin than the percentage that diffused through, indicating the ability of rhodium to accumulate in the skin, from where it may exert health effects, such as sensitisation. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

Nitrogen oxides (NOx) are atmospheric pollutants that pose a serious threat to both the environment and human health. Although catalytic deNOx technologies for engines working under stoichiometric air-to-fuel ratios (i.e., most gasoline engines) are already available, their performance is unsatisfactory under excess air conditions like those under which diesel engines operate. The selective catalytic reduction of NOx with hydrocarbon reductants (HC-SCR) is a potential deNOxsolution for diesel engines, whose operating temperatures are 150-500 ºC. Given that is unlikely for a single catalyst to show acceptable activity throughout this entire temperature span, the use of two catalysts is proposed in this dissertation. Whereas several catalysts active at high temperatures (>300 ºC) are already available, a catalyst showing an acceptable performance at low temperatures (<300 ºC) is yet to be found. Platinum group metals (PGMs) supported on activated carbon have been identified as promising low temperature HC-SCR catalysts. However, these materials show three main drawbacks: 1) the propensity of the carbon support to undergo combustion in an oxidizing environment, 2) a narrow temperature window of operation; and 3) a high selectivity towards N2O (as opposed to N2). To address the first limitation, the use of multi-walled carbon nanotubes (MWCNTs) as the support has been investigated and found to yield catalysts displaying a higher resistance to oxidation. Further, the acid activation of MWCNTs prior to their use as catalyst support has been explored, following reports than link carrier acidity with improved catalyst performance. In turn, the use of PGM alloys as the active phase has been examined as a means to improve catalyst activity and selectivity. Additionally, kinetic, spectroscopic and mechanistic studies have been performed in an attempt to probe structure-activity relationships in the MWCNTs-based formulations showing the best deNOx performance. The fundamental insights gained through these studies may inform further improvements to HC-SCR catalysts. Finally, the synthesis of the most promising formulations has been scaled-up using commercial metal monoliths as the catalyst substrate and the resulting monolithic catalysts have been tested in a diesel engine for activity in the HC-SCR reaction.

>Magister Scientiae - MSc / The purpose of this study was to develop a high performance-lower cost catalyst to be applied in Direct Methanol Fuel Cells (DMFC). The study also aimed to prepare plurimetallic supported platinum (Pt), platinum-ruthenium (PtRu), platinum-ruthenium-vanadium (PtRuV) and platinum ruthenium-vanadium-iron (PtRuVFe) upon multi-walled carbon nanotube (MWCNT) as well as upon multiwalled carbon nanotube-titanium oxide (MWCNT/TiO2) supports. Platinum is very active but prone to poisoning by carbon monoxide (CO), which may be present in the fuel used in fuel cells. The focus on the use of methanol was because of its better reaction kinetics, and better performance in direct methanol fuel cells (DMFC) better than proton exchange membrane fuel cell (PEMFC). When Pt is alloyed with another platinum group metals (PGM) the alloying decreases the over-potential for reactions critical in the fuel cells. Proton exchange membrane fuel cell (PEMFC) performance may be improved at low metal loading, when supported pluri-metallic catalysts are applied since the trimetallic catalysts may promote high catalyst utilisation. In practice, DMFC require electrodes with a Pt loading to achieve acceptance fuel cell (FC) power performance. The aim of this study was therefore the reduction of the catalyst loading through further improvement of mass activity of Pt based catalysts by partial substitution of the noble metal/metals, and the use of a carbon support that will provide high surface area, good electrical conductivity and high stability. MWCNT supported pluri-metallic (PtRuVFe,) and bimetallic (PtRu) nanoparticles possessed characteristic of increased surface area, improved electron transfer rate, enhance electro-catalytic activity and promoted stability.

In this study, various techniques of hydrometallurgy and ultrasound-assisted solvent extraction were used to recover the platinum group metals (PGM¡¦s) from a composite sample of honeycomb-type autocatalysts. After they were removed from the converter casings, the autocatalyst substrates were first crushed and then ground by a ball mill. The recovery procedures employed are shown as follows: (1) dissolve PGM¡¦s from ground spent autocatalyst by aqua regia leaching; (2) separate PGM¡¦s from base metals in the aqua regia leachate by metal cementation using zinc powder so that PGM¡¦s can be precipitated out; (3) the PGM¡¦s precipitate was first dissolved by aqua regia, then proceed to remove nitrate and hydrochloride within. The residue was further dissolved in hydrochloride acid as a preparation step for solvent extraction; (4) the PGM¡¦s pregnant solution of hydrochloride acid was treated by solvent extraction and stripping to separate and purify each component of PGM¡¦s. Effects of ultrasound agitation on the efficiency of solvent extraction was also evaluated in this work. Results of aqua regia leaching experiments have shown that the quantity of dissolved PGM¡¦s increased as the solid-to-liquid ratio decreased. The maximum dissolved quantity of PGM¡¦s could be obtained by a 3-hr leaching time. At this stage, the PGM¡¦s recoveries are 80-90% for platinum and rhodium and greater than 99% for palladium. The result of a preliminary test has indicated that acetic acid can not effectively separate the PGM¡¦s and base metals. Thus, the method of cementation by zinc powder was employed to separate PGM¡¦s from base metals. Before cementation, the aqua regia leachate was diluted and pH-adjusted to greater than 2. In so doing, an almost complete cementation (>99%) could be obtained by the least quantity of zinc powder. In addition, the base metals occurred with the PGM¡¦s precipitate have been minimized except lead and zinc. While palladium was extracted by di-n-octyl sulfide (DOS), ultrasound assistance has rendered a complete extraction within a few minutes. At this stage, the extraction efficiency was found to be independent of the HCl concentration. It was found that platinum and rhodium were not extracted by DOS. When platinum was extracted by tri-n-octylamine (TOA) and assisted by ultrasound, rhodium will be extracted at the HCl concentration higher than 4M. Thus, TOA is not an effective chemical for selective extraction of platinum. TOA was then replaced by tributyl phosphate (TBP). Experimental results have indicated that the extraction of platinum using TBP was affected by the HCl concentration. The best result was obtained when the HCl concentration was 5M. Extraction by TBP was found to be fast. It took only 20-30 seconds to reach the equilibrium even with no ultrasound assistance. But multi-stage extractions are generally required to extract platinum completely. Rhodium was found to be not extracted by TBP. After palladium and platinum were extracted, only rhodium was remained in the reffinate. In summary, solvent extraction using DOS and TBP has made it possible to separate palladium, platinum, and rhodium effectively. In the palladium stripping solution almost no base metals was determined. However, zinc and lead were found in the platinum stripping solution and the rhodium-containing raffinate. These base metals should be removed to achieve a better purity for each precious metal. The TCLP (i.e., a leaching test for toxicity) result of the autocatalyst substrate after aqua regia leaching has found to be non-hazardous. However, several streams of wastewater and acid gas generated in the recovery process should be properly managed to avoid the secondary pollution.

Masters of Science / The electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.

Les nanoparticules de platine (Pt) représentent environ la moitié du coût de fabrication des piles à combustible à membrane échangeuses de protons (PEMFC), ce qui constitue un frein à leur commercialisation à grande échelle. La récupération du Pt contenu dans les piles usagées apparaît donc nécessaire. Les voies de traitement habituellement mises en œuvre pour le recyclage de catalyseurs à base de Pt sont des procédés pyro-hydrométallurgiques, générateurs d’émissions polluantes (CO2, NO2). Une voie de traitement électrochimique en milieu liquide ionique (LI), plus respectueuse de l'environnement, est proposée ici. Elle combine dans une seule cellule la lixiviation du Pt par dissolution anodique et sa récupération par électrodéposition, dans des conditions de température "douces", sans émission de gaz nocifs. L’étude de nombreux électrolytes a permis de sélectionner les mélanges BMIMTFSI + BMIMCl (bis(trifluorométhylsulfonyl) imidure + chlorure de 1-butyl-3-méthylimidazolium), en raison du caractère complexant des chlorures facilitant la lixiviation du Pt et de la bonne stabilité électrochimique du BMIMTFSI. L’anion TFSI-, peu coordonnant, permet de moduler le caractère complexant de l’électrolyte, paramètre clé du procédé influant sur la nature et la stabilité électrochimique du complexe de Pt formé par lixiviation. Au cours de ce travail, les conditions expérimentales permettant de lixivier et d’électrodéposer le Pt dans une cellule unitaire ont été définies et appliquées avec succès aux électrodes de PEMFC. L’électrolyte sélectionné, faiblement hygroscopique, permet la récupération du Pt en atmosphère ambiante / The platinum nanoparticles used as catalyst in Proton Exchange Membrane Fuel Cells (PEMFCs) represent around the half of the total price of the cell and is one of the limitations for their large scale commercialization. The treatment of spent PEMFC through the recovery of platinum catalyst is a major concern for their development. Usual recovery routes for platinum-containing catalysts are pyro-hydrometallurgical processes that generate pollutant emissions (CO2, NO2). An electrochemical recovery route by coupling electrochemical leaching and electrodeposition in ionic liquids (ILs) is proposed here, more environmentally friendly, performed in "soft" temperature conditions and without any gases emission. Studies of several electrolytes lead us to select BMIMTFSI + BMIMCl melts (bis(trifluorométhylsulfonyl) imidure + 1-butyl-3-méthylimidazolium chloride), due to the complexing ability of chloride against platinum and the good electrochemical stability of the RMIM+ cation. TFSI-, a weakly coordinate anion, allows us to modulate the complexing ability of the electrolyte, which is a key parameter affecting the nature and the electrochemical stability of the Pt complex formed after leaching. The optimal conditions of the leaching and electrodeposition steps have been determined during this work and successfully applied to PEMFC’s electrode. The selected electrolyte, which is weakly hygroscopic, allows the Pt recovery under ambient atmosphere