A dissertation submitted to the Faculty of Science of the University of Witwatersrand, Johannesburg, in full fulfilment of the requirements for the degree of Master of Science. May 2017 / Nanomaterials (NMs) have been shown to exhibit unique physical and chemical properties that are highly size and shape-dependent. The ability to control synthesis of nanoparticles (NPs) with particular shapes and sizes can lead to exciting new applications or enhancements of current systems in the fields of optics, electronics, catalytics, biomedicine and biotechnology. Due to increased chemical pollution as well as health concerns, biological synthesis of NMs has quickly emerged as potentially being an eco-friendly, scalable, and clean alternative to chemical and physical synthesis. In this study, the inference that the heavy metal-resistant bacteria, Paenibacillus castaneae, has the propensity to synthesize metal NPs was validated. NP formation was achieved after the exposure of bacterial cell biomass or cell-free extracts (CFE) to excess metal ion precursors in solution. These include lead nitrate and calcium sulphate dehydrate, gold (III) chloride trihydrate and silver nitrate, respectively. All reactions were incubated at 37 °C for 72 h at 200 rpm and observed for a colour change. UV–visible (UV-Vis) spectral scans (200 nm – 900 nm) were measured on a Jasco V-630 UV-Vis spectrophotometer. For scanning electron microscopy (SEM), samples were fixed, dehydrated and loaded onto carbon-coated aluminium stubs. The stubs were then sputter-coated with either Au/Pd or Cr and analysed on the FEI Nova Nanolab 600 FEG-SEM/FIB. Size distribution analysis was done using transmission electron microscopy (TEM) using the FEI Tecnai T12 TEM and Image J software. Powder X-ray diffraction measurements were carried out on a Rigaku Miniflex-II X-ray diffractrometer. Colour changes indicative of the synthesis of PbS, Au and Ag NPs were observed as a white precipitate (PbS), purple (Au) and yellow-brown (Ag) colour, respectively. This was confirmed by absorbance peaks at 325 nm and 550 nm (PbS), 595 nm (Au) and 440 nm (Ag) from UV-Vis analyses. Exposure of P. castaneae biomass and CFE to PbS ions in solution resulted in the production of nanospheres, irregularly-shaped NPs, nanorods, nanowires as well as large nanoflowers. Exposure of P. castaneae biomass to Au3+ ions in solution produced Au nanospheres, nanotriangles, nanohexagons, nanopentagons and nanopolyhedrons. Ag/AgCl NP production occurred using both the P. castaneae biomass and CFE, and resulted in the synthesis of nanospheres only. This is the first report of the biosynthesis of such a diverse set of anisotropic NPs by P. castaneae. It is also the first instance in which anisotropic PbS nanorods and nanowires, 3-D Au nanoprisms as well as “rough” Ag/AgCl nanospheres were bacterially produced. This study serves as an eco-friendly approach for the synthesis of NPs that is a simple yet amenable method for the large-scale commercial production of nanoparticles with technical relevance. This in turn expands the limited knowledge surrounding the biological synthesis of heavy metal NMs. / MT 2017

abstract: Transition metal di- and tri-halides (TMH) have recently gathered research attention owing to their intrinsic magnetism all the way down to their two-dimensional limit. 2D magnets, despite being a crucial component for realizing van der Waals heterostructures and devices with various functionalities, were not experimentally proven until very recently in 2017. The findings opened up enormous possibilities for studying new quantum states of matter that can enable potential to design spintronic, magnetic memory, data storage, sensing, and topological devices. However, practical applications in modern technologies demand materials with various physical and chemical properties such as electronic, optical, structural, catalytic, magnetic etc., which cannot be found within single material systems. Considering that compositional modifications in 2D systems lead to significant changes in properties due to the high anisotropy inherent to their crystallographic structure, this work focuses on alloying of TMH compounds to explore the potentials for tuning their properties. In this thesis, the ternary cation alloys of Co(1-x)Ni(x)Cl(2) and Mo(1-x)Cr(x)Cl(3) were synthesized via chemical vapor transport at a various stoichiometry. Their compositional, structural, and magnetic properties were studied using Energy Dispersive Spectroscopy, Raman Spectroscopy, X-Ray Diffraction, and Vibrating Sample Magnetometry. It was found that completely miscible ternary alloys of Co(1-x)Ni(x)Cl(2) show an increasing Néel temperature with nickel concentration. The Mo(1-x)Cr(x)Cl(3) alloy shows potential magnetic phase changes induced by the incorporation of molybdenum species within the host CrCl3 lattice. Magnetic measurements give insight into potential antiferromagnetic to ferromagnetic transition with molybdenum incorporation, accompanied by a shift in the magnetic easy-axis from parallel to perpendicular. Phase separation was found in the Fe(1-x)Cr(x)Cl(3) ternary alloy indicating that crystallographic structure compatibility plays an essential role in determining the miscibility of two parent compounds. Alloying across two similar (TMH) compounds appears to yield predictable results in properties as in the case of Co(1-x)Ni(x)Cl(2), while more exotic transitions, as in the case of Mo(1-x)Cr(x)Cl(3), can emerge by alloying dissimilar compounds. When dissimilarity reaches a certain limit, as with Fe(1-x)Cr(x)Cl(3), phase separation becomes more favorable. Future studies focusing on magnetic and structural phase transitions will reveal more insight into the effect of alloying in these TMH systems. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

As an important part of the periodic table, metal elements have attracted widespread attention due to their special physical and chemical properties, as well as effective functionalities. Many metals at the nanoscale level exhibit a wide array of applications, ranging from catalysis to photonics, electronics, energy conversion/storage, and medicine. To obtain a more effective functionality in application, it is indispensable to synthesize uniform metal nanoparticles with well-defined size, morphology, composition, and crystal structures. In this dissertation, we will demonstrate high-boiling point solvent method for synthesizing metal nanocrystals, ranging from single metal nanocrystals (e.g., iridium (Ir), ruthenium (Ru), germanium (Ge), bismuth (Bi)) to binary metal nanocrystals (e.g., Sn-Ge), and ternary intermetallic compounds (e.g., Pt1-xPdxBi). By varying different halogen ions, we can get different morphologies of metal nanocrystals. We will further study the catalytic effect of Pd metal nanocrystals supported on silicon spheres and realize the hydrodeoxygenation reaction of vanillin under mild conditions.First, we used bismuth as an example to study the shape-controlled synthesis of metal nanocrystals by adjusting the injection temperature and the added halide ions (e.g., Cl-, Br-). Our findings indicated that due to the different electronegativities, halide ions are selectively adsorbed on specific crystal planes during the growth of Bi NCs, leading to different morphologies. Then we proposed a tungsten hexacarbonyl (W(CO)6)-assisted reduction strategy for obtaining uniform metal nanoparticles (e.g., Ir, Ru, Ge, Bi) of different metal salts. This strategy was extended to the synthesis of uniform binary metal (e.g., Sn-Ge) nanoparticles, which we can get tunable bandgap (0.51 eV to 0.72 eV) based on the controlled reaction of Ge2+ precursor solution with uniform tin (Sn) nanocrystals (NCs) as the template. Next, we realized the synthesis of intermetallic Pt1-xPdxBi nanoplates with controllable compositions, including Pt0.5Pb0.5Bi, Pt0.25Pd0.75Bi, and Pt0.75Pd0.25Bi via the sequential complexation-reduction-sorting method. Furthermore, we used palladium (Pd) metal nanoparticles (NPs) as a photocatalyst to trigger the hydrodeoxygenation reaction of vanillin. We demonstrated a model to disperse free-standing Pd NP on dielectric silica nanospheres (SiOx NSs). The spherical shape of SiOx can cause scattering resonance, thereby enhancing the local electric field on or near the surface to enhance light absorption of Pd NPs, further realizing a more effective catalyze on chemical reactions. We found that the adsorption of H2 on Pd is too strong to support the reaction effectively, but light absorption can reduce the "poisoning effect" by weakening the adsorption of hydrogen on Pd surface. Overall, we use innovative strategies to effectively synthesize a variety of high-quality metal nanomaterials. Our work shows that the Pd-NP/SiOx-NS composite nanostructure using dielectric SiOx as an optical nanoantenna is a promising photocatalyst that can drive photonic chemical conversion with high efficiency. / Chemistry

This thesis deals with the preparation of materials for use in separation science and their surface modification by grafting. The overall aim is the preparation of diverse materials by combination of a set of developed tools. Included in the thesis is the synthesis of monolithic media using non-traditional crosslinkers, the characterization of their porous properties and initial testing in reversed-phase chromatographic separation of proteins. The preparation of a library of short polymer chains, telomers, with varied functionality and their characterization is reported. Included in the characterization is the gradient polymer elution chromatography of selected telomers on a monolithic column in capillary format. The technique shows promise as a tool for monitoring of polymerization processes and for the separation of telomers with similar size but different functionalities or characteristics. Finally, the combination of polymeric support materials and the prepared telomer library is used in surface modification. Surface modification is performed onto activated surfaces via a “grafting to” approach. One example is shown, the surface modification of epoxy-modified divinylbenzene particles by attachment of telomer chains introducing ion-exchange functionality. The material is tested for the separation of proteins, in ion-exchange chromatography mode.

Ordered mesoporous materials have attracted much attention recently for use in a wide range of applications. The oxidising materials, ceria (CeO₂) and CGO (Ce₀.₉Gd₀.₁O[subscript(2-δ)]) have both been synthesised with ordered mesopores, but a method for the simple fabrication of these materials in high yields with crystalline pore walls has not yet been reported in the literature. This thesis details the development of the vacuum impregnation method for the synthesis of ordered mesoporous materials with emphasis on ceria and CGO. Using the vacuum impregnation method both materials were successfully prepared. The materials exhibited the porous single crystal morphology in high yields, with unusual crystallographic features. Nitrogen physisorption, transmission electron microscopy (TEM), TEM tomography and temperature programmed studies were employed. Temperature programmed studies showed the materials to be catalytically active at lower temperatures than traditionally-prepared ceria. Photovoltaic studies showed that the materials exhibited efficient exciton quenching. The observation of nanowire extrusion during the synthetic procedure assisted in the postulation of a mechanism for product formation in the vacuum impregnation method. The vacuum impregnation method was subsequently shown to be applicable to the synthesis of other materials, with encouraging results presented for ordered mesoporous carbon and Zr₀.₈₄Y₀.₁₆O[subscript(2-δ)]. The syntheses of ordered mesoporous La₀.₈₅Sr₀.₁₅GaO[subscript(3-δ)] and La₀.₇₆Sr₀.₁₉CoO[subscript(3-δ)] were unsuccessful.

Au cours des dernières années, de nombreuses recherches se sont concentrées sur les batteries afin de satisfaire leur demande croissante pour de nombreuses applications. Les matériaux hybrides métal/carbone ont fait l'objet d'une grande attention en tant qu'anodes pour les batteries ioniques Li et Na en raison de leur capacité plus élevée par rapport aux anodes graphite/carbone dur. Cependant, l'expansion de la taille des NPs métalliques et la forte capacité irréversible pendant le 1ercycle sont les principaux inconvénients à surmonter et représentent l'objectif principal de cette thèse. Trois types d'hybrides ont été étudiés (C@Sn et C@SiO2pour les LIBs, et C@Sb pour les NIBs) et des voies de synthèse originales ont été développées qui ont permis d'obtenir des matériaux avec des NPs petites et homogènes distribuées dans le réseau de carbone. Plusieurs paramètres expérimentaux ont été optimisés, conduisant à une vaste palette de matériaux avec des porosités, des structures et des granulométries différentes. La température et la charge de particules se sont avérées être les principaux paramètres affectant la porosité et la taille des particules ainsi que les performances électrochimiques. L'augmentation de la température et de la charge de NPs ont conduit à une porosité plus faible qui a permis de diminuer la capacité irréversible et d'améliorer la capacité réversible. En même temps, le cycle à long terme a été affecté négativement en raison de la formation de particules non confinées et agglomérées. Un compromis entre la charge de carbone/porosité/structure a été déterminé pour chaque système et les mécanismes électrochimiques traités sur la base d'analyses post-mortem. / During the last years a lot of research has been focused on batteries to satisfy their increasing demand for a broad application. Metal-based/carbon hybrid materials received great attention as anodes for Li and Na ion batteries due to their higher capacity compared to graphite/hard carbons anodes. However, the metal particle size expansion and the high irreversible capacity during cycling are the main inconvenients to be overcome and represent the main goal of this thesis. Three type of hybrids were studied(C@Sn and C@SiO2for LIBs, and C@Sb for NIBs) and original synthesis pathways were developed which allowed to obtain materials with small and homogeneous distributed particles in the carbon network. Several experimental parameters were tuned leading to a large pallet of materials exhibiting different porosities, structures and particle size/distribution. The temperature and the particle loading were found to be the main parameters affecting the porosity and the particle size and further the electrochemical performances. The increase of both temperature and particle loading lead to smaller porosity which successfully allowed to diminish the irreversible capacity and to improve the reversible capacity. In the same time, the long-term cycling was negatively affected due to the formation of un-confined and agglomerated particles. The extent of particle agglomeration and consequently of capacity fading was found to depend on the type of metal and synthesis route. A compromise between the carbon loading/porosity/structure was determined for each system and the electrochemical mechanisms addressed based on post-mortem analyses.

Controlled synthesis of functional nanostructures is of paramount interest due to their novel properties and efficient functionalities. The size and morphology of each particle in the nanoscale contribute to their optical and electronic properties. Also, the collective arrangement of these nanostructures in 3D space maximizes active sites available for the cost-effective catalysis. Recent advances in the field show a vast range of nanostructures with unique designs that affect their catalytic properties. In this dissertation, utilizing silver halides as a unique platform to develop high-performance catalysts were discussed with their respective synthesis strategies, structural evolution, and structure-related properties. Initially, we synthesized well-defined silver chlorobromide (AgCl0.5Br0.5) nanostructures investigating the effects of various reaction parameters on the synthesis. Simple reaction parameters were overlooked to gain additional controllability on determining the morphology of the nanocrystals regardless of the composition. Thus, the influence of the size and exposed surface facets was investigated towards photocatalytic activity performing methylene blue degradation on AgCl0.5Br0.5 with different sizes and morphologies, under visible light. Then, the ability to use these AgCl0.5Br0.5 nanocubes were investigated as a reactive and sacrificial template for the synthesis of nanoplates and nanoshells. As an example, fast precipitation reaction between Ag+ and benzenethiol (BT–) results in an uncontrollable growth leading to aggregated structures. The low solubility and the planer surfaces of the silver halide cubes were utilized to reduce the reaction rate and promote the growth of layered AgBT as plates, which can be organized into hollow nanostructures. Time-dependent microscopic and spectroscopic measurements showed the structural evolution and associated kinetics of the conversions. Developing a comprehensive understanding enabled generalizing the procedure to synthesize other silver-based hollow nanostructures. Mechanistic studies showed two different hollowing mechanisms involving, that depends on the anion being exchanged. The degree of nucleation and the crystal structure of silver-sulfur compounds determined the relative diffusion of ions leading to their overall size and morphology. The hollow morphology was shown to have higher stability with a large surface area relative to its aggregated solid counterpart. Next, highly porous Ag nanostructures were synthesized electrochemically, using silver thiolate nanocages. High porosity and their arrangement as plates enhanced available active sites and mass transport for CO2 electroreduction. Furthermore, the strategy was extended to design bimetallic nanostructures with enhanced bimetallic boundaries where selectivity of ethanol formation from CO2 electroreduction can be increased. Overall, the study explores the novel approaches to utilize chemical and physical properties of silver halides for various material designs that determines their enhanced performance. / Chemistry

Les matériaux thermoélectriques (TE) permettent de convertir directement de la chaleur en électricité et vice-versa. Les objectifs de cette thèse étaient de tenter d'améliorer les performances TE de trois familles de matériaux et de mieux comprendre le lien entre les propriétés physiques (électriques, thermiques, magnétiques) généralement mesurées dans une large gamme de température (5–700 K) et les microstructures/compositions chimiques observées. Généralement, les matériaux ont été synthétisés par des techniques de métallurgie des poudres et densifiés par spark plasma sintering. La majeure partie de nos travaux a concerné la famille des matériaux tétraédrites, dérivés du minéral naturel (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13, présentant des propriétés TE prometteuses, récemment mises en évidence. D’abord, les propriétés TE de huit tétraédrites naturelles de provenance différente ont été étudiées. Nous avons montré que leurs propriétés physiques sont plutôt prévisibles selon leur composition chimique et finalement peu différentes selon leur origine. Les propriétés TE de mélanges de tétraédrites naturelles et synthétiques obtenus par broyage mécanique ont ensuite été déterminées. Ce procédé fortement énergétique produit des particules de taille nanométrique des deux phases qui forment une solution solide pendant le frittage. Par contre, un broyage manuel conserve la présence des deux phases, ce qui conduit à de plus faibles performances TE. Ensuite, nous avons montré que la substitution Sb <-> As, usuelle dans les spécimens naturels, n’influence que faiblement les propriétés TE. Enfin, les propriétés TE de manganites de calcium et de polymères conducteurs ont également été étudiées / Thermoelectric (TE) materials allow direct conversion between heat and electricity. The aim of this thesis was to try to improve the thermoelectric performance of three different families of materials and to better understand the link between the various physical properties (electrical, thermal, magnetic) generally measured in a broad temperature range (5–700 K) and the observed microstructure/chemical composition. In general, the materials were synthesized by powder metallurgy techniques and densified by spark plasma sintering (SPS). The major part of our studies concerns the tetrahedrite family of materials, derived from the mineral tetrahedrite, (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13, whose promising thermoelectric properties were only recently discovered. In a first approach, the TE properties of eight natural tetrahedrites of different geographic origin are studied. It is shown that they all behave rather predictably and uniformly. Next, the properties of ball milled mixtures of natural and synthetic tetrahedrites are investigated. This high-energy process yields nanoscale particles of the two phases, which form a solid solution during the sintering. Low-energy hand grinding preserves the two-phase nature and results in inferior TE performance. Because arsenic is a common substituent in natural specimens, several As-substituted tetrahedrites are synthesized and characterized. It is shown that the TE properties are only weakly influenced by the substitution of As for Sb. Besides tetrahedrites, calcium manganese oxides and conductive polymers are also studied

Doctor of Philosophy / Mechanical and Nuclear Engineering / Douglas S. McGregor / There is a need for compact, rugged neutron detectors for a variety of applications including national security and oil well logging. A solid form neutron detector would have a higher efficiency than present day gas filled ³He and ¹⁰BF ₃ detectors, which are standards currently used in the industry today. A sub-branch of the III-V semiconductors is the filled tetrahedral compounds, known as Nowotny-Juza compounds (A[superscript I]B[superscript II]C[superscript V]). These materials are desirable for their cubic crystal structure and semiconducting electrical properties. Originally studied for photonic applications, Nowotny-Juza compounds have not been fully developed and characterized. Nowotny-Juza compounds are being studied as neutron detection materials here, and the following work is a study of LiZnP and LiZnAs material development and device characterization. Precursor binaries and ternary materials of LiZnAs and LiZnP were synthesized in-house in vacuum sealed quartz ampoules with a crucible lining. Synthesized powders were characterized by x-ray diffraction, where lattice constants of 5.751 ± .001 Å and 5.939 ± .002 Å for LiZnP and LiZnAs, respectively, were determined. A static vacuum sublimation in quartz was performed to help purify the synthesized ternary material. The resulting material from the sublimation process showed characteristics of a higher purity ternary compound. Bulk crystalline samples were grown from the purified material. Ingots up to 9.0 mm in diameter and 13.0 mm in length were harvested. Individual samples were characterized for crystallinity on a Bruker AXS Inc. D2 CRYSO, energy dispersive x-ray diffractometer, and a Bruker AXS D8 DISCOVER, high-resolution x-ray diffractometer with a 0.004° beam divergence. High-resolution XRD measurements indicated reasonable out-of-plane and in-plane ordering of LiZnP and LiZnAs crystals. Devices were fabricated from the LiZnP and LiZnAs crystals. Resistivity of devices were determined within the range of 10⁶ – 10¹¹ Ω cm. Charge carrier mobility and mean free drift time products were characterized for electrons at 8.0 x 10⁻⁴ cm² V⁻¹ ± 4.8% and 9.1 x 10⁻⁴ cm² V⁻¹ ± 4.4% for LiZnP and LiZnAs respectively. Sensitivity to 337 nm laser light (3.68 eV photons) was observed, where an absorption coefficient of 0.147 mm⁻¹ was determined for LiZnAs devices. Thermal neutron sensitivity was evaluated with unpurified and purified LiZnP and LiZnAs devices. Sensitivity was observed, however material quality and crystalline quality significantly hindered device performance.

<div>Metal-zeolites are promising materials for passive adsorber technologies for the abatement of nitrogen oxides (NOx, x = 1,2) and aldehydes during low-temperature operation in automotive exhaust aftertreatment systems. The aqueous-phase exchange processes used commonly to prepare metal-zeolites typically require mononuclear, transition metal complexes to diffuse within intrazeolite pore networks with their solvation shells and replace extra framework cations of higher chemical potential. When metal complexes are larger than the zeolite pore-limiting diameter, this imposes intracrystalline transport restrictions; thus, complexes and agglomerates tend to preferentially deposit near the surfaces of crystallites, requiring post-synthetic treatments to disperse metal species more uniformly throughout zeolite crystallites via solid-state ion-exchange processes. Here, we address the influence of post-synthetic gas treatments and zeolite material properties on the structural interconversion and exchange of extra framework Pd in CHA zeolites with a focus on the thermodynamic, kinetic, and mechanistic factors that dictate the Pd site structures and spatial distributions that form.<br></div><div><br></div><div>Pd-amine complexes introduced via incipient wetness impregnation on CHA zeolites were found to preferentially site near crystallite surfaces. Post-synthetic treatments in flowing air results in Pd-amine decomposition and agglomeration to metallic Pd0and supersequent oxidation to PdO, before converting to mononuclear Pd²⁺cations through an Ostwald ripening mechanism at high temperatures (>550 K). Progressively higher air treatment temperatures (up to 1023 K) were found to (1) thermodynamically favor the formation of mononu-clear Pd²⁺cations relative to agglomerated PdO particles, (2) increase the apparent rate of structural interconversion to mononuclear Pd²⁺, and (3) facilitate longer-range mobility of molecular intermediates involved in Ostwald ripening processes that allow Pd cations to form deeper within zeolite crystallites to form more uniformly dispersed Pd-zeolite materials. Additionally, the controlled synthetic variation of the atomic arrangement of 1 or 2Al sites in the 6-membered ring of CHA was used to show a thermodynamic preference to form mononuclear Pd2+cations charge-compensated by 2 Al sites over [PdOH]⁺complexes at 1 Al site. Colloidal Pd nanoparticle syntheses and deposition methods were used to prepare monodisperse Pd-CHA materials to isolate the effects of Pd particle size on structuralinterconversion to mononuclear Pd²⁺under a range of external environments. Consistent with computational thermodynamic predictions, smaller Pd particle sizes favor structural interconversion to mononuclear Pd²⁺under high-temperature air treatments (598–973 K),while adding H2O to the air stream inhibits the thermodynamics but not the kinetics of mononuclear Pd²⁺formation, demonstrating that water vapor in exhaust streams may be deleterious to the long-term stability of Pd-zeolite materials for passive NOx adsorption.<br></div><div><br></div><div>The influence of metal-zeolite material properties on the adsorption, desorption, and conversion of formaldehyde, a government-regulated automotive pollutant, under realistic conditions was investigated to identify beneficial material properties for this emerging application in mobile engine pollution abatement. A suite of Beta zeolite materials was synthesized with varied adsorption site identity (Brønsted acid, Lewis acid, silanol groups, and extra framework metal oxide) and bulk site densities. All materials stored formaldehyde and converted a large fraction of formaldehyde to more environmentally benign CO and CO₂, demonstrating the efficacy of silanol defects and zeolitic supports for the storage of formaldehyde. Sn-containing zeotypes, containing either Lewis acidic framework Sn sites or extra framework SnO_x particles, resulted in the greatest selectivity to CO and CO₂ formed during formaldehyde desorption, suggests that Sn species are a beneficial component in metal-zeolite formulations for the abatement of formaldehyde in automotive exhaust streams.<br></div><div><br></div><div>This work demonstrates how combining precise synthesis of metal-zeolites of varied bulk and atomic properties with site-specific characterization and titration methods enables systematically disentangling the influence of separate material properties (e.g., Pd particle size, zeolite framework Al arrangement, silanol density, heteroatom identify) and external environment on changes to metal structure, speciation, and oxidation state. This approach provides thermodynamic, kinetic, and mechanistic insights into the factors that influence metal re-structuring under the practical conditions encountered in automotive exhaust after treatment applications and guidance for materials design and treatment strategies to form desired metal structures during synthesis and after regeneration protocols.<br></div>