Rozprawy doktorskie na temat „Functional Noble Metal Nanoparticle”

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
The remarkable optical and luminescence properties of noble metal nanoparticles (with diameters < 2 nm) attract researchers due to potential applications in biomedicine, photocatalysis, and optoelectronics. Extensive experimental investigations on luminescence properties of thiolate-protected gold and silver nanoclusters during the past decade have failed to unravel their exact photoluminescence mechanism. Herein, density functional and time-dependent density functional theory (DFT and TDDFT) calculations are performed to elucidate electronic-level details of several such systems upon photoexcitation. Multiple excited states are found to be involved in photoemission from Au₂₅(SR)₁₈– nanoclusters, and their energies agree well with experimental emission energies. The Au₁₃ core-based excitations arising due to electrons excited from superatom P orbitals into the lowest two superatom D orbitals are responsible for all of these states. The large Stokes shift is attributed to significant geometrical and electronic structure changes in the excited state. The origin of photoluminescence of Ag₂₅(SR)₁₈– nanoclusters is analogous to their gold counterparts and heteroatom doping of each cluster with silver and gold correspondingly does not affect their luminescence mechanism. Other systems have been examined in this work to determine how widespread these observations are. We observe a very small Stokes shift for Au₃₈(SH)₂₄ that correlates with a relatively rigid structure with small bond length changes in its Au₂₃ core and a large Stokes shift for Au₂₂(SH)₁₈ with a large degree of structural flexibility in its Au₇ core. This suggests a relationship between the Stokes shift of gold−thiolate nanoparticles and their structural flexibility upon photoexcitation. The effect of ligands on the geometric structure and optical properties of the Au₂₀(SR)₁₆ nanocluster is explored. Comparison of the relative stability and optical absorption spectra suggests that this system prefers the [Au₇(Au₈SR₈)(Au₃SR₄)(AuSR₂)₂] structure regardless of whether aliphatic or aromatic ligands are employed. The real-time (RT) TDDFT method is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems. A systematic benchmark study is performed to demonstrate the consistency of linear-response (LR) and RT-TDDFT methods for calculating the optical absorption spectra of a variety of bare gold and silver nanoparticles with different sizes and shapes.

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
Small silver and gold clusters (less than 2 nm) display a discrete absorption spectrum characteristic of molecular systems whereas larger particles display a strong, broad absorption band in the visible. The latter feature is due to the surface plasmon resonance, which is commonly explained by the collective dipolar motion of free electrons across the particle, creating charged surface states. The evolution between molecular properties and plasmon is investigated. Time-dependent density functional theory (TDDFT) calculations are performed to study the absorption spectrum of cluster-size silver and gold nanorods. The absorption spectrum of these silver nanorods exhibits high-intensity longitudinal and transverse modes (along the long and short axis of the nanorod respectively), similar to the plasmons observed experimentally for larger nanoparticles. These plasmon modes result from a constructive addition of the dipole moments of nearly degenerate single-particle excitations. The number of single-particle transitions involved increases with increasing system size, due to the growing density of states available. Gold nanorods exhibit a broader absorption spectrum than their silver counterpart due to enhanced relativistic effects, affecting the onset of the longitudinal plasmon mode. The high-energy, high-intensity beta-peak of acenes also results from a constructive addition of single-particle transitions and I show that it can be assigned to a plasmon. I also show that the plasmon modes of both acenes and metallic nanoparticles can be described with a simple configuration interaction (CI) interpretation. The evolution between molecular absorption spectrum and plasmon is also investigated by computing the density of states of spherical thiolate-protected gold clusters using a charge-perturbed particle-in-a-sphere model. The electronic structure obtained with this model gives good qualitative agreement with DFT calculations at a fraction of the cost. The progressive increase of the density of states with particle size observed is in accordance with the appearance of a plasmon peak. The optical properties of nanoparticles can be tuned by varying their composition. Therefore, the optical behavior of the bimetallic Au[subscript](25-n)Ag[subscript]n(SH)[subscript]18[superscript]- cluster for different values of n using TDDFT is analyzed. A large blue shift of the HOMO-LUMO absorption peak is observed with increasing silver content, in accordance with experimental results.

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
Gold and silver particles with dimensions less than a nanometer possess unique characteristics and properties that are different from the properties of the bulk. They demonstrate a non–zero HOMO–LUMO gap that can reach up to 3.0 eV. These differences arise from size quantization effects in the metal core due to the small number of atoms. These nanoparticles have attracted great interest for decades both in fundamental and applied research. Small gold clusters protected by various types of ligands are of interest because ligands allow obtaining gold nanoclusters with given sizes, shapes and properties. Three main families of organic ligands are usually used for stabilization of gold nanoclusters: phosphine ligands, thiolate ligands and DNA. Usually, optical properties of these NPs are studied using optical absorption spectroscopy. Unfortunately, sometimes this type of spectrum is poorly resolved and tends to appear very similar for different complexes. In these cases, circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopy can be applied. However, the interpretation of experimental CD and MCD spectra is a complicated process. In this thesis, theoretically simulated CD and MCD spectra were combined with optical absorption spectra to study optical activity for octa– and nona– and undecanuclear gold clusters protected by mono– and bidentate phosphine ligands. Additionally, optical properties of bare and DNA protected silver NPs were studied. Theoretical CD spectra were examined to learn more about the origin of chirality in chiral organometallic complexes, and to contribute to the understanding of the difference in chiroptical activity of gold clusters stabilized by different phosphine ligands and DNA–stabilized silver clusters. Furthermore, optical properties of the small centered gold clusters Au₈(PPh₃)₈²⁺ and Au₉(PPh₃)₈³⁺ were examined by optical absorption and MCD spectra using TDDFT. Theoretical MCD spectra were also used to identify the plasmonic behavior of silver nanoparticles. These results showed that CD and MCD spectroscopy yield more detailed information about optical properties and electronic structure of the different chemical systems than optical absorption spectroscopy alone. Theoretical simulation of the CD and MCD spectra together with optical absorption spectra can be used to assist in the understanding of empirically measured CD and MCD and provide useful information about optical properties and electronic structure.

New challenges in nanotechnology arise in the assembly of nanoobjects into three-dimensional superstructures, which may carry synergetic properties and open up new application fields. Within this new class of materials nanostructured, porous functional metals are of great interest since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior and size-enhanced catalytic reactivity. Even though a large variety of preparation pathways for the fabrication of porous noble metals has already been established, several limitations are still to be addressed by research developments. The new and versatile approach that is presented in this work makes use of a templatefree self-assembly process for the fabrication of highly porous, metallic nanostructures. Thereby, nanochains are formed by the controlled coalescence of noble metal NPs in aqueous media and their interconnection and interpenetration leads to the formation of a self-supported network with macroscopic dimensions. Subsequently, the supercritical drying technique is used to remove the solvent from the pores of the network without causing a collapse of the fragile structure. The resulting highly porous, low-weighted, three-dimensional nanostructured solids are named aerogels. The exceptional properties of these materials originate from the conjunction of the unique properties of nanomaterials magnified by macroscale assembly. Moreover, the combination of different metals may lead to synergetic effects regarding for example their catalytic activity. Therefore, the synthesis of multimetallic gels and the characterization of their structural peculiarities are in the focus of the investigations. In the case of the developed preparation pathways the gelation process starts from preformed, stable colloidal solutions of citrate capped, spherical noble metal (Au, Ag, Pt, Pd) NPs. In order to face various requirements several methods for the initiation of the controlled destabilization and coalescence of the nanosized building blocks were developed and synthesis conditions were optimized, respectively. Multimetallic structures with tunable composition are obtained by mixing different kinds of monometallic NP solutions and performing a joint gel formation. The characterization of the resulting materials by means of electron microscopy reveals the formation of a highly porous network of branched nanochains that provide a polycrystalline nature and diameters in the size range of the initial NPs. Furthermore, synthesis conditions for the spontaneous gel formation of glucose stabilized Au and Pd NPs were investigated. In order to gain a detailed knowledge of the structural properties of bimetallic aerogel structures a versatile set of characterization techniques was applied. A broad pore size distribution dominated by meso- and macropores and remarkably high inner surface areas were concluded from the N2 physisorption isotherms and density measurements. As investigated, a specific thermal treatment could be used to tune the ligament size of Au-Ag aerogels, whereas Au-Pd and Pt-Pd structures provide thermal stability under mild conditions. Further investigations aimed to the enlightenment of the elemental distribution and phase composition within the nanochains of multimetallic gel structures. The different approaches provide complementary and consistent results. Phase analyses based on XRD measurements revealed separated phases of each metal in the case of Ag-Pd and Au-Pd aerogels. They further proved the possibility of temperature induced phase modifications that lead to complete alloying of Au and Pd. In addition, separated domains of Pt and Pd were established from the EXAFS analysis of the corresponding aerogel. STEM EDX high resolution elemental mappings confirmed the separated domains of different metals in the case of Au-Pd and Pt-Pd aerogels. Moreover, a complete interdiffusion and alloy formation of Au and Ag within the corresponding aerogel structure is suggested from STEM EDX results. Finally, the presented investigations further promote the field of metallic aerogels by addressing the challenging issue of processability and device fabrication. Hybrid materials with organic polymers as well as various kinds of coatings on glass substrates and glassy carbon electrodes were prepared whereas the network structure was preserved throughout all processing steps. Moreover, it was illustrated that the NP-based aerogels carry metallic properties as expressed by their low Seebeck coefficients and high electrical conductivities.

Through employing a combination of complimentary structural, spectroscopic and high-resolution microscopy techniques, the superior properties of a [PtCl4]2- precursor to yield well-defined, isolated nanoparticles (predominantly 2-3 nm) upon microporous framework architectures, have been established. These are prepared via a one-step, in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. The catalytic activity of these materials can be intrinsically linked to the degree of nanoparticle formation. The [PtCl4]2- precursor bestows a greater propensity for nanoparticle formation across a range of activation conditions by comparison to [PdCl4]2- and [AuCl4]- precursors. This, in concert with the surrounding microporous architecture, donates superior catalytic performance for the aerobic oxidation of KA oil to cyclohexanone (precursor for adipic acid and ε-caprolactam), under continuous flow conditions. It is able to approach unrivalled yields of >90% by adapting a ‘closed-loop’ system. Detailed spectroscopic investigations into the nature of the active sites at the molecular level, coupled with high-resolution electron microscopy, reveal that the intricacies of the synthetic methodology and associated activation procedures play a vital role in regulating the locality, morphology and size of the metal nanoparticles produced. Theseinvestigations also offer insights into the potential consequences of prolonged catalytic exposure. All three (Au, Pt & Pd) nanoparticle systems demonstrate a profound influence on the activation of molecular oxygen and alkyl peroxides for a plethora of selective catalytic oxidations. Furthermore, this design strategy offers adequate scope for the creation of multi-metallic (e.g. Pd-Cu, Au-Cu & Au-Pt), multifunctional heterogeneous catalysts, in the continued quest for the activation of molecular oxygen in sustainable catalytic processes.

This thesis studies the interaction between free radical species and supported noble metal nanoparticles (silver and gold) in the context of oxidation reactions. The peroxidation of cumene is the first reaction to be discussed and the difference in peroxidation product distribution using silver nanoparticles (AgNP) versus gold nanoparticles (AuNP) is examined. Specifically, cumyl alcohol is obtained as the major product obtained when using supported AuNP, whereas cumene hydroperoxide is favoured for AgNP. Such variations in product distribution are partially explained by the differences in the nanoparticle Fenton activity, where the TiO2 support was proposed to enhance such activity due to possible electron shuttling capabilities with the nanoparticle surface. Use of hydrotalcite as a support was found to minimize this characteristic, due to its insulator properties. The stability of hydroperoxide was tested in the presence of various others supports (activated carbon, Al2O3, ZnO, SiO2 and clays) with little success, with hydroperoxide exhibiting stability in the presence of HT. Using an oxygen uptake apparatus, the interaction of the cumyl peroxyl radical with the AuNP surface was demonstrated. Furthermore, this interaction promotes decomposition leading to the corresponding alkoxyl radical and subsequent hydrogen abstraction to form the observed cumyl alcohol product. The radical interaction with supported nanoparticles, and its reversibility appear different for gold and silver and accounts for a large part of the product distribution differences observed between AuNP and AgNP, as illustrated below. The peroxidation of ethylbenzene and propylbenzene was studied and revealed the participation of a reactive surface oxygen species due to the decomposition of peroxyl radicals on the nanoparticle surface. The reactive oxygen species was found to be transient in nature in the case of AuNP . Furthermore, this surface species was found to be an important participant in hydrogen abstraction leading to peroxide product formation. Finally, supported nanoparticle catalyzed tetralin peroxidation was investigated to determine the influence of temperature on the peroxidation product distribution and how changes in the reaction temperature can effect the radical-nanoparticle surface interactions.

Noble metal nanoparticles are of great interest due to their tunable optical and radiative properties. The specific wavelength of light at which the localized surface plasmon resonance occurs is dependent upon the shape, size and composition of the particle as well as the dielectric constant of the host medium. Thus, the optical properties of noble metal nanoparticles can be systematically tuned by altering these specific parameters. The purpose of this thesis is to investigate some of these properties related to metallic nanoparticles. The first several chapters focus on theoretical modeling to predict and explain various plasmonic properties of gold and silver nanoparticles while the later chapters focus on more accurately combining experimental and theoretical methods to explain the plasmonic properties of hollow gold nanoparticles of various shapes. The appendix contains a detailed description of the theoretical methods used throughout the thesis. It is intended to serve as a guide such that a user could carry out the various types of calculations discussed in this thesis simply by reading this appendix.

Valorisation of different biomass derived molecules was successfully approached and studied in this PhD project. The focus of the thesis was addressed to the catalysts preparation, passing through an accurate catalytic designed, to be then tested in academic and industrially appealing reactions. This approach led to the synthesis of different but equally interesting catalytic systems for the valorisation of substrates derived from the first and second generation of biomass feedstock. An extended study, at first, was conducted on the oxidation of glycerol (1st generation of biomass related), both in alkaline (needed for gold monometallic systems) and free pH (high industrial relevance) conditions. The target reaction was approached starting from the simplest Au/C catalytic systems, to finally move to more complicated and innovative materials: bimetallic once. Initially, the Au on carbon Vulcan (with the highest graphitisation degree) SOL derived catalysts showed a remarkable initial activity (IA= 1091 h-1) in comparison with the other carbonaceous supports (Norit and X40S) and the SMAD derived catalysts. This result pointed out the importance of the protecting agent (a polymer that surrounded the nanoparticles and is solely present for the SOL synthetic route) beside the importance of the support’s features. Similarly, electronic effects ascribed to the interaction with the support of the nanoparticles (i.e. the strong metal support interaction (SMSI) thermally induced on Au4Ag1/TiO2) showed to be the ruling factor to determine the oxidation state of the metals. This latter, subsequentially, influence the catalytic activity: an enhanced initial catalytic activity was detected for the Au4Ag1/TiO2 catalyst (IA= 1616 h-1), in comparison with the Au4Ag1/Al2O3 (IA= 963 h-1). The SMSI have influenced also the stability of the system, avoiding the enlargement of the nanoparticles during the thermal treatments. On the other hand, the SMSI induced the presence of Ag+ species onto the bimetallic nanoparticles titania supported, leading to a quite rapid deactivation of the catalytic system. The thermal treatments pointed out also the importance of the protecting agent (polyvinyl alcohol, PVA): on one side when it is present confers resistance to the system towards the nanoparticles aggregation, on the other when it is removed from the nanoparticles’ surface (by the same thermal treatment), the catalyst acquired an enhanced initial activity. AuPt/TiO2 catalytic systems were subsequentially exploited both in alkaline and free pH conditions. The gold content positively influenced the activity of the catalytic systems in both the conditions. In particular Au9Pt1/TiO2 was the most active catalyst in the alkaline condition (IA= 7389 h−1), and Au6Pt4/TiO2 showed the highest initial activity (IA= 301 h-1) in free pH condition. For all the bimetallic system mentioned and exploited in the valorisation of glycerol, furthermore, a synergistic effect was detected. The importance of gold as modifier to confer resistance to the catalytic system by stabilizing the oxidation state of the second metal was also established. Subsequentially, completely different designed and synthesised catalysts were prepared for the valorisation of substrates related with the 2nd generation of biomass. Bare carbon nanofibers (CNFs) and functionalised CNFs (CNFs-P, CNFs-O and CNFs-N), for instance, were employed as supports for Ru nanoparticles (introduced by incipient wet impregnation). All the catalysts prepared showed activity in the valorisation of cellulose derived molecules. In particular, it was observed how N-containing functionalisation of the support, promoted by a strong interaction with the Ru nanoparticles, led to the highest catalytic activity among the set of catalysts tested for the levulinic acid (LA) hydrogenation (88 % of conversion after 3 h) with a full selectivity to y-valerolactone (GVL). On the other side, exploring the 5-hydroxymethylfurfural (HMF) valorisation, Ru/CNF-N and Ru/CNF-P showed a lower activity but also a change in selectivity. In fact, these latter two catalysts enhanced the formation of ethers due to the reaction between 2,5-dihydroxymethylfuran and/or methylfurfuryl alcohol with the solvent (2-butanol). Similar support effects were also observed in the furfural hydrogenation over platinum nanoparticles (introduced by solvated metal atoms deposition, SMAD) supported on niobia and tailor-made modified niobia. Niobia was hydrothermally synthetized pure and doped with other two different metals (W and Ti, both 10 at.%) to tune the acidity of the system. In particular, we were able to enhance to 0.191 mmolPy/gCAT (W-Nb2O5) and decrees to 0.014 mmolPy/gCAT (Ti-Nb2O5) the acidity of the pure Niobia (0.078 mmolPy/gCAT). Platinum nanoparticles, showing a narrow particle size distribution (1.1-1.2 nm) for all the supports, have allowed a proper study of the acidity effect. The acidity, indeed, showed to be the ruling factor: the most acidic material showed the highest activity coupled with a selectivity addressed to the furan ether products (acid catalysed reaction’s step) at the expenses of furfuryl alcohol (highest selectivity of FA showed for the lowest acid catalyst). Unfortunately, the condition and the type of acidity (Lewis acidity) obtained were not sufficient to observe a high fraction of diols (target product, less than 10 % in selectivity), produced from the ring-opening of the substrate. Lastly, in the benzyl alcohol oxidation (model compound for the lignin) it was highlighted how gold-based materials characterised by comparable nanoparticles dimension (Au-Pd, Au-Pt, Au-Ru and Au-Cu, all supported on carbon) could change the catalytic behaviour and the bimetallic structure just by varying the second metal. For AuPd/C and AuPt/C, for example, alloyed structures were observed. On the other hand, for the case of Ru as second metal, a core-shell structure was found. When Cu was employed, bimetallic nanoparticles with Au:Cu molar ratio lower than the nominal one were detected suggesting the presence of segregated gold nanoparticles. All the catalysts were active and highly selective towards the desired and industrial appealing product (benzaldehyde, selectivity ≥ 99 %). Only in the case of AuPd/C and AuCu/C, however, a synergistic effect was observed. In particular, the AuPd/C bimetallic sample showed the highest activity (fully conversion of the substrate after 5 min). For the interesting Au-Cu system (the only catalysts that contain a not noble metal), furthermore, the role of the Cu was clarified and the composition effect was studied. The metals were deposited on a carbonaceous support by SMAD technique in order to avoid a protecting agent influence. More in details, it was speculated how Cu, promptly oxidised at CuO (if exposed to air), is responsible of the O2 activation, while the reaction took part at the Au-CuO interface. This reactivity is guided by a specific structure of the bimetallics particles finely characterized: Aucore-CuOshell structure. This last evidence highlighted once more the importance of having a good knowledge and control on the catalyst synthetic routes. Furthermore, synergistic effect was observed for all the active AuCu/C bimetallic systems, even when the amount of gold was very low (Au13Cu1/C, IA= 329 h-1). The highest initial activity, however, was reached with Au4Cu1/C catalysts (IA= 399 h-1). All the active AuCu bimetallic catalysts showed a high selectivity towards the desired product: benzaldehyde (≥ 95%). Good stability against deactivation was also observed. For the Cu-rich sample (Au1Cu17/C) case, distinguished by the negligible activity, it was assumed how the external copper oxide shells, by entirely covering the gold atoms, have repressed any catalytic activities.

L'intérêt de la recherche fondamentale pour les morceaux nanométriques de métaux nobles est principalement dû à la résonance localisée des plasmons de surface (LSPR) dans l'absorption optique. Différents aspects, liés à la compréhension théorique de la LSPR dans le cas de clusters de métaux nobles de taille dite intermédiaire, sont étudiés dans ce manuscrit. Afin d'avoir une vision plus large nous utilisons deux approches : l'approche électromagnétique classique et le formalisme ab initio en temps réel de la théorie de la fonctionnelle de la densité dépendant du temps (RT-TDDFT). Une comparaison systématique et détaillée de ces deux approches souligne et quantifie les limitations de l'approche électromagnétique lorsqu'elle est appliquée à des systèmes de taille quantique. Les différences entre les excitations plasmoniques collectives et celles impliquant les électrons d, ainsi que leurs interactions, sont étudiées grâce au comportement spatial des densités correspondantes. Ces densités sont obtenues en appliquant une transformée de Fourier dans l'espace à la densité obtenue par les simulations DFT utilisant une perturbation delta-kick. Dans ce manuscrit, des clusters de métaux nobles nus et protégés par des ligands sont étudiés. En particulier, motivé par de récents travaux sur les phénomènes d'émergence de plasmon, l'étude par TD-DFT de nano-alliages Au-Cu de taille tout juste inférieure à 2nm à fourni de subtiles connaissances sur les effets d'alliages sur la réponse optique de tels systèmes
The fundamental research interest in nanometric pieces of noble metals is mainly due to the localized surface-plasmon resonance (LSPR) in the optical absorption. Different aspects related to the theoretical understanding of LSPRs in `intermediate-size' noble-metal clusters are studied in this thesis. To gain a broader perspective both the real-time \ai formalism of \td density-functional theory (RT-TDDFT) and the classical electromagnetics approach are employed. A systematic and detailed comparison of these two approaches highlights and quantifies the limitations of the electromagnetics approach when applied to quantum-sized systems. The differences between collective plasmonic excitations and the excitations involving $d$-electrons, as well as the interplay between them are explored in the spatial behaviour of the corresponding induced densities by performing the spatially resolved Fourier transform of the time-dependent induced density obtained from a RT-TDDFT simulation using a $\delta$-kick perturbation. In this thesis, both bare and ligand-protected noble-metal clusters were studied. In particular, motivated by recent experiments on plasmon emergence phenomena, the TDDFT study of Au-Cu nanoalloys in the size range just below 2~nm produced subtle insights into the general effects of alloying on the optical response of these systems

Pollution from automobile exhaust is one of the most major environmental problems because of increasing usage of engine technologies. Diesel and lean burn gasoline engines operate under oxygen rich (lean) conditions and they emit harmfull gases to the atmosphere (CO,CO2, NO, NO2). The control of NOx emission from exhaust has become a challenging issue in engine industry because of the worldwide environmental regulations. Therefore lean-burn NOx emission control technologies have been developed to reduce emission of harmfull gases from exhausts, and the NOx storage/reduction (NSR) catalysts is one of the most promising candidates to reduce the pollution caused by lean-burn engines. In NSR systems, NO from the emission is first oxidized to NO2 over noble metal sites (Pt, Rh, Pd) during lean-burn engine operation. After that NO2 is stored as nitrites and nitrates in alkali earth oxides (BaO,MgO, CaO) particles or monolayer which is well dispersed on a substrate (Gamma-Al2O3, TiO2, SiO2). Finally, stored NOx compound are broken into N2 and O2 on noble metal sites. The Pt/BaO/Gamma-Al2O3 system is one of the most popular subjects in literature both experimentally and theoretically since this system is known to be catalytically more active and ecient in interactions between NOx and Pt-BaO components are still not clearly explained. For this reason, in this thesis, the interaction between catalytic redox components, Pt and Rh, and the support material Gamma-Al2O3 and the eects of Pt and Rh in atomic and diatomic clusters forms on the adsorption of the NO2 molecule on the Gamma-Al2O3(100) surface have been investigated by using density functional theory (DFT).

Els carburs de metalls de transició (TMC) exhibeixen propietats químiques i catalítiques similars a les dels costosos metalls nobles. La conversió d'alcohol, hidrogenació d'olefines i altres reaccions importants han demostrat l'aplicabilitat d'aquests compostos en processos industrials. També se sap que nanopartícules de metalls nobles (NMNPs) mostren una alta activitat catalítica tot i la baixa o nul • la reactivitat del metall sòlid. A més, investigacions recents assenyalen que els suports de TMC polaritzen la densitat electrònica de NMNPs adsorbits i augmenten l'activitat catalítica respecte als suports més tradicionals d'òxid metàl • lic. Aquests descobriments recents han inspirat el treball presentat en aquesta tesi, realitzat mitjançant tècniques actuals de la química quàntica. S'ha estudiat CO, CO2, H2, H2O adsorbits sobre TiC i sobre petits clústers d'or adsorbits en el suport. S'ha considerat la superfície (001), terrasses, esglaons monoatòmics i defectes, i també la reactivitat de les molècules adsorbides sobre la superfície neta de TiC (001) i en dos clústers d'or, Au4 i Au6, adsorbits. Les barreres energètiques calculades per a la formació de metà o formaldehid a partir de gas de síntesi, en TiC (001) resulten ser massa altes i aquests processos són inviables sobre el suport net. Sobre els clústers d'or suportats sobre TiC (001) hi ha una major activitat catalítica, però la reacció continua sent altament impedida. No obstant això, la reacció de desplaçament del gas d'aigua es preveu que sigui ràpida en el sistema Au4/TiC (001), superant els catalitzadors utilitzats normalment en la indústria. Experiments recents mostren que els clústers de Ni, Cu i Au estan fortament deformats un cop adsorbits sobre TMC, donant lloc a catalitzadors molt actius. S'ha investigat la interacció dels àtoms amb la fase delta de MoC. La interacció és més forta pel recobriment més baix considerat, la relaxació de la superfície és important i l'activitat es preveu que augmenti en l'ordre Ni> Cu> Au. Finalment, s'han considerat possibles reconstruccions no polars per a la superfície (001) de Mo2C centrant-se en l'energia d’escissió, la qual és proporcional a l'estabilitat de cada tipus de terminació. Les reconstruccions no polars disminueixen l'energia d’escissió, confirmant l'aplicabilitat dels conceptes clàssics de Tasker per a òxids als TMC.
Los carburos de metales de transición (TMC) exhiben propiedades químicas y catalíticas similares a las de los costosos metales nobles. La conversión de alcohol, hidrogenación de olefinas y otras reacciones importantes han demostrado la aplicabilidad de estos compuestos en procesos industriales. También se sabe que nanopartículas de metales nobles (NMNPs) muestran una alta actividad catalítica a pesar de la baja o nula reactividad del metal sólido. Además, investigaciones recientes señalan que los soportes de TMC polarizan la densidad electrónica de NMNPs adsorbidos y aumentan la actividad catalítica respecto a los soportes más tradicionales de óxido metálico. Estos descubrimientos recientes han inspirado el trabajo presentado en esta tesis, realizado mediante técnicas actuales de la química cuántica. Se ha estudiado CO, CO2, H2, H2O adsorbidos sobre TiC y sobre pequeños clusters de oro adsorbidos sobre el suport. Se ha considerado la superficie (001), terrazas, escalones monoatómicos y defectos y, también, la reactividad de las moléculas adsorbidas sobre la superficie limpia de TiC (001) y en dos clusters de oro, Au4 y Au6, adsorbidos. Las barreras energéticas calculadas para la formación de metano o formaldehído a partir de gas de síntesis en la superficie limpia de TiC (001) resultan ser demasiado altas y esos procesos son inviables sobre el soporte limpio. Sobre los clusters de oro soportados sobre TiC (001) hay una mayor actividad catalítica, pero la reacción continúa siendo altamente impedida. Sin embargo la reacción de desplazamiento del gas de agua se prevé que sea rápida en el sistema Au4/TiC (001), superando los catalizadores utilizados normalmente en la industria. Experimentos recientes muestran que los clusters de Ni, Cu y Au están fuertemente deformados una vez adsorbidos sobre TMC dando lugar en catalizadores muy activos. Se ha investigado la interacción de los átomos con la fase delta del catalizador de MoC. La interacción es más fuerte para el recubrimiento más bajo considerado, la relajación de la superficie es importante y la actividad se prevé que aumente en el orden Ni> Cu> Au. Finalmente, se han considerado posibles reconstrucciones no polares para la superficie (001) de Mo2C centrándose en la energía de escisión, que es proporcional a la estabilidad de cada tipo de terminación. Las reconstrucciones no polares disminuyen la energía de escisión, confirmando la aplicabilidad de los conceptos clásicos de Tasker para óxidos a los TMC.
Carbides of the early transition metals (TMC) exhibit chemical and catalytic properties that in many aspects are very similar to those of expensive noble metals. Alcohol conversion, hydrogenation of olefins and many others important reactions demonstrated the applicability of these compounds for industrial processes. It is also known that small noble metal nanoparticles (NMNPs) show high catalytic activity despite of the poor reactivity or inertness of the bulk metal. Additionally, recent investigations pointed out that supporting TMCs polarize the electron density of adsorbed NMNPs increasing the catalytic activity respect to more traditional metal oxide supports. These recent discoveries inspired the work reported in this thesis using state-of-the-art quantum chemical techniques. We studied CO, CO2, H2, H2O molecules adsorbed on TiC and on small gold clusters adsorbed thereon. We considered the (001) extended surface, terraces, monatomic steps and kink defective sites. The reactivity of adsorbed molecules on the clean TiC (001) surface and on two gold clusters, Au4 and Au6, adsorbed thereon were also studied. Energy barriers calculated for methane or formaldehyde formation from syngas, on the clean TiC (001) surface were by far too high and those processes are unviable on the clean support. Gold clusters supported by TiC (001) show higher catalytic activity but the reaction continues to be highly hindered. However water gas shift reaction is predicted to be fast on the Au4/TiC(001) system, overtaking catalysts normally used in industry. Recent experiments show that Ni, Cu and Au clusters are strongly perturbed upon adsorption on TMC resulting in extremely active catalysts. We investigated the interaction of those atoms with the delta phase of the MoC catalyst. The interaction is stronger for the lowest coverage considered, the relaxation of the surface important and the activity is predicted to increase in the order Ni>Cu >Au. Finally, we have studied possible non-polar reconstructions of the (001) surface of Mo2C focusing on the cleavage energy, proportional to the stability of each type of termination. The non-polar reconstructions decreased the calculated cleavage energy, confirming the applicability of the classical Tasker’s concepts for oxides to TMCs.

Preformed Au nanoparticles supported on activated carbon and TiO2 were synthesised by sol-immobilisation. Polyethylene glycol, polyvinyl pyrrolidone and polyvinyl alcohol were used as stabilisers for the gold nanoparticles at different polymer/Au wt/wt ratios for each polymer. The effect of polymer/Au wt/wt ratios was investigated on (i) the average nanoparticle size, (ii) catalytic activity for two reactions, 4-nitrophenol reduction and glucose oxidation to glucaric acid. 4-nitrophenol reduction is recognised as a model reaction for nanomaterial catalytic activity tests; glucose oxidation to glucaric acid is a reaction that is traditionally carried out with concentrated nitric acid, for which alternative reaction pathways are looked for in an effort to reduce its environmental impact. The catalysts were characterised from the nanoparticle synthesis by colloidal method by means of UV-vis spectroscopy and DLS analysis, to the immobilisation step by XRD and TEM. The effect of the polymer:Au wt/wt ratio on nanoparticle size depends on the polymer nature, and point out the need to optimise supported nanoparticle synthesis protocols in the future depending on the type of stabiliser. The catalytic tests revealed that the polymers interact with Au nanoparticles through different active sites. Activated carbon (AC) and TiO2 were compared as supports for Au nanoparticles stabilised by PVA at PVA/Au 0,65 wt/wt. AC-supported Au NPs were the most active for glucose oxidation while TiO2-stabilised Au NPs were five times more active in 4-nitrophenol reduction that AC-supported NPs. Hence support and stabiliser are important parameters that should be optimised in order to achieve high catalytic activity for a given reaction.

Cette thèse porte sur les complexes de coordinations basés sur les métaux de transitions et les lanthanides en tant qu'éléments clés pour créer des matériaux fonctionnels. Précisément, des matériaux contenant des propriétés de détection, d'auto assemblage et optique ont été conçus et optimisés. En plus d'une brève introduction sur la photophysique, les gels supramoléculaires et les nanoparticules métalliques, un résumé sur les différents instruments et techniques employés pour ces travaux est inclus. Le chapitre 3 décrit la synthèse et la caractérisation de complexe de lanthanide anionique. Des techniques analytiques, tels que la spectroscopie d'émission ou la cristallographie à rayon X ont été employé pour caractériser ces différents complexes. Dans le chapitre 4, l'étude de complexes métalliques luminescents se focalise sur les complexes de métaux de transition, et plus précisément sur les complexes d'iridium(lll). Une famille de complexes d'iridium(lll) bi-cyclométallés neutres qui montre une intense émission rouge sous photo ou electro excitation est étudié. Le chapitre 5 présente la conception et le développement d'une nouvelle famille de gelators à faible poids moléculaire, basée sur des terpyridines perfluorés.La morphologie ainsi que les propriétés mécaniques et thermodynamique de ces metallogels sont étudiées. Le chapitre 6 présente une nouvelle sonde colorimétrique, composée de nanoparticules d'or fonctionnalisées avec des complexes de Zn aminoterpyridinique via des liaisons thiol est décrite pour la détection de pyrophosphate
This thesis deals with coordination compounds based on transition metals and lanthanides as key components of functional materials. Besides a brief summary of photophysics, supramolecular gels and metal nanoparticles, an overview of the instruments and techniques employed in this work is included. This thesis is further divided into four chapters focused on optically active metalcomplexes (chapters 3 and 4), stimuli responsive metallogels (chapter 5) and functionalized nanomaterials for sensing applications (chapter 6). In chapter 3, the synthesis and characterization of anionic lanthanide complexes is reported. Analytical techniques, emission spectroscopy and X-ray crystallography were employed to characterize these complexes. ln chapter 4, the study of light emitting metal complexes is extended to transition metal complexes, in particular to iridium (lll) complexes. A family of neutral bis-cyclometallated iridium (lll) complexes that exhibit an intense red emission under photo- or electro-excitation is studied. ln chapter 5 the design and investigation of a new family of low molecular weight gelators based on perfluorinated terpyridines is reported. The morphology and mechanical and thermodynamical properties of these metallogels is studied. Chapter 6 studies the excellent cooperation between coordination compounds and nanomaterials to yield optical sensors. A new colorimetric sensor for pyrophosphate consisting of gold nanoparticles acting as reporting units functionalized with a thiol-modified aminoterpyridine-Zn complex is described

World population is continuously growing, as well as the influence we have on the ecosystem’s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity’s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today’s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices.

La réponse optique de nanostructures métalliques est caractérisée par une amplification locale du champ électromagnétique appelée Résonance Plasmon de Surface (RPS) reliée à leur nature et leur morphologie. Pour étudier la réponse optique d’une nanoparticule unique, un dispositif ultra-sensible de spectroscopie à modulation spatiale utilisant une source de lumière blanche a été développé : il permet de mesurer la section efficace d’extinction absolue de nano-objets uniques sur un large domaine spectral (300-900 nm). Des images de microscopie électronique à transmission peuvent être obtenues indépendamment sur les mêmes objets. On a ainsi une corrélation directe entre la morphologie des nanoparticules et leur signature optique. Ce travail de thèse a permis d’une part de mettre en évidence les paramètres qui entrent en jeu dans le processus de vieillissement de nanoparticules uniques d’argent sous éclairement. En particulier, l’étude de nanocubes d’argent révèle une « sphérisation » et une photo-oxydation au cours du temps due à la partie UV du spectre. D’autre part, des mesures réalisées sur des doublets de nanocubes d’argent en interaction ont montré l’importance de la morphologie à l’interface entre les deux nanoparticules sur le couplage plasmonique. Pour une excitation lumineuse longitudinale, on observe, outre le décalage de la RPS vers les basses énergies lorsque la distance interparticule diminue, un dédoublement de cette bande de résonance. Des calculs théoriques réalisés avec la méthode DDA ont permis de corréler ce phénomène de dédoublement à des variations de courbure de surface dans la zone interparticule liées principalement au rognage des arêtes des cubes
The optical properties of noble metal nanoparticles are known to be dominated by the localized surface plasmon resonance (SPR) which is highly sensitive to the size of the particles, their shape, their environment, and eventually their chemical composition in the case of mixed systems. In order to study the optical response of a single supported metallic nanoparticle, a high sensitive spectroscopic setup using a white lamp (300-900 nm) has been developed in a transmission measurement configuration. This technique, the Spatial Modulation Spectroscopy, aims to detect the overall extinction of light by a nanoparticle. Moreover, the coupling of this technique with the direct observation of the particles by Transmission Electron Microscopy allows to get an unambiguous description of their optical response in relation with their exact morphology. In this work, the optical response of single silver nano-objects has been correlated with their morphology and their structure at a sub-nanometer scale. Time evolution of the optical response of single silver nanocubes under illumination was first investigated. We observed a “spherization” and a photo-oxidation due to the UV part of the light. Moreover, we studied pairs of cubic silver nanoantennas that showed a huge sensitivity of their optical response with the interparticle distance and their morphology. Indeed, the SPR is red-shifted with decreasing interparticle distance. One can also observe a striking splitting of the resonance for very low interparticle distances. Preliminary DDA calculations seem to show that the radius of curvature at the corners and edges of both cubes plays a key role in the splitting of the resonance

Yes
The operation of many nanostructured biomolecular sensors and catalysts critically hinges on the manipulation of non-covalent adsorption of biomolecules on unfunctionalised noble-metal nanoparticles (NMNPs). Molecular-level structural details of the aqueous biomolecule/NMNP interface are pivotal to the successful realisation of these technologies, but such experimental data are currently scarce and challenging to obtain. Molecular simulations can generate these details, but are limited by the assumption of non-preferential adsorption to NMNP features. Here, via first principles calculations using a vdW-DF functional, and based on nanoscale sized NMNPs, we demonstrate that adsorption preferences to NP features vary with adsorbate chemistry. These results show a clear distinction between hydrocarbons, that prefer adsorption to facets over edges/vertices, over heteroatomic molecules that favour adsorption onto vertices over facets. Our data indicate the inability of widely used force-fields to correctly capture the adsorption of biomolecules onto NMNP surfaces under aqueous conditions. Our findings introduce a rational basis for the development of new force-fields that will reliably capture these phenomena.

Functional nanomaterials are gaining attention due to their excellent shape and size dependent optical, electrical and catalytic properties. Synthesizing nanoparticles is no longer novel with the availability of a host of synthesis protocols for a variety of shapes and sizes of particles. What is currently needed is an understanding the fundamentals of shape and size controlled synthesis to produce functional nanomaterials that is simple and general. In addition to simple metallic nanostructures, synthesizing bimetallic and hybrid nanostructures are important for applications. Instead of trying to add functionality to the preformed nanomaterials, it is advantageous to look for cost effective and general synthetic protocols that can yield bimetallic, hybrid nanostructures along with the shape and size control. In this dissertation, a novel synthetic protocol for the synthesis of ultrfine single crystalline nanowires, metallic and bimetallic nanostructures and hybrid nanostructures has been investigated. The key point of the synthesis is that all different functional nanostructures are achieved by the use of noble metal intermediates in organic medium without phase transfer reagents. The roles of capping agents, oriented attachment and aggregation phenomenon have been studied in order to understand the formation mechanisms. Along with the synthesis, formation mechanisms, the optical and catalytic properties of the functional, noble metal, bimetallic and hybrid nanostructures have been studied. The entire thesis based on the results and findings obtained from the present investigation is organized as follows: Chapter I provides a general introduction to functional nanomaterials, their properties and some general applications, along with a brief description of conventional methods for size and shape-controlled synthesis. Chapter II deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter III presents a novel method of for synthesizing noble metals nanostructures starting from an intermediate solid phase. The method involves the direct synthesis of noble metal intermediates in organic medium without the use of any phase transfer reagent. Controlled reduction of these intermediates leads to the formation of ultrafine nanocrystallite building blocks. Controlled aggregation of the nanocrystallites under different conditions leads to the formation of different nanostructures ranging from single crystalline nanowires to porous metallic clusters. In this chapter, the details of synthesis of the intermediate phase of gold are presented. This intermediate phase is the rocksalt phase of AuCl that has been experimentally realized for the first time. Manipulation of the AuCl nanocubes leads to the formation of a variety of nanostructures of Au starting from hollow cubes to extended porous structures. Mechanistic details of the formation of the intermediate and the nanostructures are presented in this chapter. Chapter IV deals with the symmetry breaking of an FCC metal (gold) by oriented attachment of metal nanoparticles by the preferential removal of capping agent from certain facets and followed by the attachment of gold nanoparticles along those bare facets. This kind of oriented attachment leads to the formation of 1D nanostructures with high aspect ratios. In this chapter, the synthesis, characterisation, formation mechanism and optical properties of high aspect ratio, molecular scale single crystalline gold nanowires has been described. This represent the first ever successful method to produce ultrafine 1D metallic nanostructures approaching molecular dimensions. Chapter V deals with the formation of hybrid nanostructures by attaching the cubic intermediate phase to a substrate like carbon nanotubes followed by the reduction of the attached intermediates on the tubes. The Pt intermediates have been synthesized and attached on the wall of functionalized CNTs and reduced. The PtCNT nanocomposites been characterized by several spectroscopic and microscopic techniques. The electrocatalytic activity of these nanocomposites towards the methanol oxidation has also been investigated. The composites exhibit high catalytic activity and good long term performance. The presence of functional groups on the CNT surface overcomes some of the limitations of current single metal catalysts that suffer from CO poisoning. Chapter VI deals with the formation of palladium nanostructures ranging from nanoparticles to hierarchical aggregates by controlled aggregation of nanoparticles in an organic medium that is tuned by the dielectric constant of the system. A crystalline intermediate of palladium salt has been synthesized and this intermediate of palladium has been used as the precursor solution for the synthesis of palladium nanostructures. The formation mechanism of the nanoporous Pd cluster is investigated using the modified DLVO approach. The catalytic efficiency of the Pd nanostructures has been investigated using the reduction of pnitrophenol and electrocatalytic hydrogen storage as model reactions. Chapter VII discusses the possibility of achieving functional bimetallic alloys by simultaneous reduction of the cubic intermediate of two different metals with experimental evidences. The synergistic effect of the two different metals gives rise to better catalytic activity. This chapter mainly deals with the synthesis of bimetallic porous nanoclusters of goldpalladium and goldplatinum in an organic medium. Detailed microstructural and spectroscopic characterisation of the bimetallic nanoclusters has been carried out and their electrocatalytic performance, morphological stability also investigated.

Functional nanomaterials are gaining attention due to their excellent shape and size dependent optical, electrical and catalytic properties. Synthesizing nanoparticles is no longer novel with the availability of a host of synthesis protocols for a variety of shapes and sizes of particles. What is currently needed is an understanding the fundamentals of shape and size controlled synthesis to produce functional nanomaterials that is simple and general. In addition to simple metallic nanostructures, synthesizing bimetallic and hybrid nanostructures are important for applications. Instead of trying to add functionality to the preformed nanomaterials, it is advantageous to look for cost effective and general synthetic protocols that can yield bimetallic, hybrid nanostructures along with the shape and size control. In this dissertation, a novel synthetic protocol for the synthesis of ultrfine single crystalline nanowires, metallic and bimetallic nanostructures and hybrid nanostructures has been investigated. The key point of the synthesis is that all different functional nanostructures are achieved by the use of noble metal intermediates in organic medium without phase transfer reagents. The roles of capping agents, oriented attachment and aggregation phenomenon have been studied in order to understand the formation mechanisms. Along with the synthesis, formation mechanisms, the optical and catalytic properties of the functional, noble metal, bimetallic and hybrid nanostructures have been studied. The entire thesis based on the results and findings obtained from the present investigation is organized as follows: Chapter I provides a general introduction to functional nanomaterials, their properties and some general applications, along with a brief description of conventional methods for size and shape-controlled synthesis. Chapter II deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter III presents a novel method of for synthesizing noble metals nanostructures starting from an intermediate solid phase. The method involves the direct synthesis of noble metal intermediates in organic medium without the use of any phase transfer reagent. Controlled reduction of these intermediates leads to the formation of ultrafine nanocrystallite building blocks. Controlled aggregation of the nanocrystallites under different conditions leads to the formation of different nanostructures ranging from single crystalline nanowires to porous metallic clusters. In this chapter, the details of synthesis of the intermediate phase of gold are presented. This intermediate phase is the rocksalt phase of AuCl that has been experimentally realized for the first time. Manipulation of the AuCl nanocubes leads to the formation of a variety of nanostructures of Au starting from hollow cubes to extended porous structures. Mechanistic details of the formation of the intermediate and the nanostructures are presented in this chapter. Chapter IV deals with the symmetry breaking of an FCC metal (gold) by oriented attachment of metal nanoparticles by the preferential removal of capping agent from certain facets and followed by the attachment of gold nanoparticles along those bare facets. This kind of oriented attachment leads to the formation of 1D nanostructures with high aspect ratios. In this chapter, the synthesis, characterisation, formation mechanism and optical properties of high aspect ratio, molecular scale single crystalline gold nanowires has been described. This represent the first ever successful method to produce ultrafine 1D metallic nanostructures approaching molecular dimensions. Chapter V deals with the formation of hybrid nanostructures by attaching the cubic intermediate phase to a substrate like carbon nanotubes followed by the reduction of the attached intermediates on the tubes. The Pt intermediates have been synthesized and attached on the wall of functionalized CNTs and reduced. The PtCNT nanocomposites been characterized by several spectroscopic and microscopic techniques. The electrocatalytic activity of these nanocomposites towards the methanol oxidation has also been investigated. The composites exhibit high catalytic activity and good long term performance. The presence of functional groups on the CNT surface overcomes some of the limitations of current single metal catalysts that suffer from CO poisoning. Chapter VI deals with the formation of palladium nanostructures ranging from nanoparticles to hierarchical aggregates by controlled aggregation of nanoparticles in an organic medium that is tuned by the dielectric constant of the system. A crystalline intermediate of palladium salt has been synthesized and this intermediate of palladium has been used as the precursor solution for the synthesis of palladium nanostructures. The formation mechanism of the nanoporous Pd cluster is investigated using the modified DLVO approach. The catalytic efficiency of the Pd nanostructures has been investigated using the reduction of pnitrophenol and electrocatalytic hydrogen storage as model reactions. Chapter VII discusses the possibility of achieving functional bimetallic alloys by simultaneous reduction of the cubic intermediate of two different metals with experimental evidences. The synergistic effect of the two different metals gives rise to better catalytic activity. This chapter mainly deals with the synthesis of bimetallic porous nanoclusters of goldpalladium and goldplatinum in an organic medium. Detailed microstructural and spectroscopic characterisation of the bimetallic nanoclusters has been carried out and their electrocatalytic performance, morphological stability also investigated.

貴金屬納米顆粒催化劑因其獨特的性質而備受關注。他們的高比表面積和可控的形貌使得他們表現出於同類體相材料所不同的催化性能。為了避免催化反應過程中由於納米顆粒本身形貌的改變而引起的催化活性降低，貴金屬納米顆粒通常被負載在固體氧化物載體上。同時，由於協同作用的產生，固體金屬氧化物載體在反應過程中也能對納米顆粒的催化效果產生影響。本論文系統介紹了利用超聲噴霧法製備貴金屬納米顆粒負載的金屬氧化物微納米球的過程，以及為研究這種微纳米球的催化性能而進行的實驗檢測。氧化物存在不仅为催化剂提供了载体，而且其介孔结构亦有利于反应物扩散到纳米催化剂的周围，从而提高反应的速率。
本論文首先介紹了一步法製備貴金屬納米顆粒負載的金屬氧化物微纳米球及其在催化反应中的應用。我們選擇了金、鉑和鈀來分別負載在二氧化鈦、二氧化鋯和三氧化二鋁微納米球上。這幾種貴金屬和氧化物都是在環境污染控制、石油化工產業和醫藥產業中具有代表性的催化劑及襯底。除了檢測我們所製備的微納米顆粒的結構形貌等特徵外，我們還利用對硝基苯酚還原為對胺基苯酚的這個催化反應檢驗了這些貴金屬納米顆粒負載的氧化物微納米球的催化活性。考慮到三種貴金屬和三種氧化物的排列組合，以及金屬含量可能產生的影響，我們準備了九類共18份樣品，逐個進行催化反應。最後的結果顯示，含鈀0.1%摩爾比例的二氧化鈦表現出最強的催化活性。同时，這種方法也可以推廣到其他的貴金屬以及氧化物襯底，從而可以簡單方便地製備各种氧化物负载貴金屬催化劑，并可以對他們之間的協同作用進行研究。
此外，我根據同樣的超聲噴霧法製備了貴金屬負載的空心介孔氧化物微納米球。這個研究課題引入了聚苯乙烯球作為模板。同時利用聚苯乙烯球表面修飾過的金屬納米顆粒之间的相互作用，實現了金屬納米顆粒在球表面的吸附，进而聚苯乙烯球可以作為載體將金屬納米顆粒帶入介孔氧化物中。通過熱分解將聚苯乙烯球除去後，金屬納米顆粒就可以吸附在空心介孔氧化物球的內表面。在這個實驗中，我們先製備好據有特殊形貌的金屬納米顆粒，比如金納米棒、鈀納米立方体和金納米棒外面包覆鈀的納米殼鞘結構。然後借助聚苯乙烯球將其帶入介孔二氧化鈦和二氧化鋯及二氧化硅中。在對硝基苯酚還原的實驗中，这种介孔微纳米球表现出良好的催化性能并在一定程度上提高了催化剂的循环性。
为了尽可能的提高催化剂的循环性，我希望能獲得據有良好磁性的介孔微納米球。我們嘗試了兩種方法，一是將磁性納米顆粒比如鐵的氧化物納米顆粒引入介孔氧化物微納米球，另一種方法是製備據有磁性的介孔氧化鐵微納米球。我们相信通過這種方法，貴金屬納米顆粒負載的介孔氧化物微納米球的催化性能，尤其是循環性能必然會顯著的提高。
Noble metal nanoparticles/nanocrystals have attracted much attention as catalysts due to their unique characteristics, including high surface areas and well-controlled facets, which are not often possessed by their bulk counterparts. To avoid the loss of their catalytic activities brought about by their size and shape changes during catalytic reactions, noble metal nanoparticles/nanocrystals are usually dispersed and supported finely on solid oxide supports to prevent agglomeration, nanoparticle growth, and therefore the decrease in the total surface area. Moreover, metal oxide supports can also play important roles in catalytic reactions through the synergistic interactions with loaded metal nanoparticles/nanocrystals. In this thesis, I use ultrasonic aerosol spray to produce hybrid microspheres that are composed of noble metal nanoparticles/nanocrystals embedded in mesoporous metal oxide matrices. The mesoporous metal oxide structure allows for the fast diffusion of reactants and products as well as confining and supporting noble metal nanoparticles.
I will first describe my studies on noble metal-loaded mesoporous oxide microspheres as catalysts. Three types of noble metals (Au, Pt, Pd) and three types of metal oxide substrates (TiO₂, ZrO₂, Al₂O₃) were selected, because they are widely used for practical catalytic applications involved in environmental cleaning, pollution control, petrochemical, and pharmaceutical syntheses. By considering every possible combination of the noble metals and oxide substrates, nine types of catalyst samples were produced. I characterized the structures of these catalysts, including their sizes, morphologies, crystallinity, and porosities, and their catalytic performances by using a representative reduction reaction from nitrobenzene to aminobenzene. Comparison of the catalytic results reveals the effects of the different noble metals, their incorporation amounts, and oxide substrates on the catalytic abilities. For this particular reaction, I found that Pd nanoparticles supported on mesoporous TiO₂ exhibit the best catalytic performance. The demonstrated low-cost and high-productivity preparation method can be extended to other catalysts, which can contain various metals and oxide substrates and will have high potential for industrial applications. Our preparation method also provides a platform for the studies of the synergetic catalytic effects between different oxide substrates and metals.
I further fabricated hollow mesoporous microspheres containing differently shaped noble metal nanocrystals. Hollow structures are strongly desired in many applications because of their high pore volumes, surface areas, and possible light-trapping effect. In my study, the hollow structures were obtained by simply dispersing polystyrene (PS) nanospheres into the precursor solution for aerosol spray. The PS spheres were removed by thermal calcination to produce hollow mesoporous microspheres. In my first study, the noble metal salts were dissolved in the precursor solutions, and the noble metal nanoparticles were obtained through thermal calcination. In this way, the size and shape of the metal nanoparticles cannot be well controlled. In my second study, I first grew noble metal nanocrystals and then incorporated them into the oxide supports. This preparation route allowed me to incorporate metal nanocrystals with controlled sizes, shapes, and compositions into the oxide matrices. The metal nanocrystals I used in this experiment included Pd nanocubes, Au nanorods, and Au corePd shell nanorods. These nanocrystals were functionalized with thiol-terminated methoxypoly(ethylene glycol) . The surface functionalization allowed them to adsorb on the PS spheres. After thermal calcination, the noble metal nanocrystals were left inside and adsorbed on the inner surface of the hollow mesoporous metal oxide microspheres. I investigated the catalytic activities of the Pd nanocube-embedded hollow mesoporous TiO₂ and ZrO₂ microspheres for the reduction of 4-nitrophenol to 4-aminophenol. I also examined the recyclability of the Pd nanocube-embedded hollow mesoporous ZrO₂ microsphere catalysts. The results showed that the combination of the noble metal nanocrystals and oxides prevents the aggregation of the nanostructures and reduces the loss of the catalysts during the recycling processes, leading to the remarkable recyclability of the hybrid catalyst. This method for the preparation of noble metal nanostructure-embedded hollow mesoporous oxide microspheres can greatly facilitate the investigation on the catalytic properties of noble metal nanocrystal and metal oxide hybrid nanostructures and therefore guide the design and fabrication of high-performance catalysts.
Last but not least, I investigated the magnetic mesoporous microspheres to enable a better recyclability of the mesoporous oxide catalysts. Both magnetic nanoparticle-included mesoporous metal oxides and mesoporous magnetic oxides were presented. The successfully syntheses of these microspheres will greatly improve the catalytic performance of the noble metal nanoparticle-loaded mesoporous oxide microspheres.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Jin, Zhao = 貴金屬納米顆粒負載的介孔金屬氧化物微納米球及其催化應用 / 金釗.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Jin, Zhao = Gui jin shu na mi ke li fu zai de jie kong jin shu yang hua wu wei na mi qiu ji qi cui hua ying yong / Jin Zhao.
Abstract --- p.i
摘要 --- p.iii
Acknowledgement --- p.v
Table of Contents --- p.vii
List of Figures --- p.x
List of Tables --- p.xvii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Mesoporous metal oxide materials --- p.1
Chapter 1.1.1 --- Overview on mesoporous materials --- p.1
Chapter 1.1.2 --- Syntheses of mesoporous metal oxides --- p.3
Chapter 1.1.2.1 --- Preparation of mesoporous metal oxides through soft-templating methods --- p.3
Chapter 1.1.2.2 --- Preparation of mesoporous metal oxides through hard-templating methods --- p.8
Chapter 1.1.3 --- Applications of mesoporous metal oxides --- p.11
Chapter 1.1.3.1 --- Catalysis --- p.12
Chapter 1.1.3.2 --- Energy conversion and storage --- p.13
Chapter 1.1.3.3 --- Sensing --- p.13
Chapter 1.2 --- Noble metal nanopartilces --- p.15
Chapter 1.2.1 --- Overview of noble metal nanoparticles --- p.15
Chapter 1.2.2 --- Catalytic applications of noble metal nanoparticles --- p.19
Chapter 1.2.2.1 --- Automotive converter --- p.19
Chapter 1.2.2.2 --- Suzuki cross-coupling reaction --- p.20
Chapter 1.3 --- The overview of this thesis --- p.22
References --- p.24
Chapter 2 --- Ultrasonic Aerosol Spray --- p.30
Chapter 2.1 --- Working principle and our ultrasonic aerosol spray system --- p.30
Chapter 2.2 --- Materials synthesized by the AASA method --- p.34
References --- p.37
Chapter 3 --- Materials Characterization Methods and Catalytic Studies --- p.39
Chapter 3.1 --- Characterization methods --- p.39
Chapter 3.2 --- Model catalytic reaction --- p.41
References --- p.45
Chapter 4 --- Noble Metal Nanoparticle-Loaded Mesoporous Oxide Microspheres --- p.46
Chapter 4.1 --- Experiments --- p.48
Chapter 4.2 --- Results and discussion --- p.50
Chapter 4.2.1 --- Mesoporous metal oxide microspheres --- p.50
Chapter 4.2.2 --- Noble metal nanoparticle-loaded mesoporous oxide microspheres --- p.55
Chapter 4.3 --- Summary --- p.73
References --- p.75
Chapter 5 --- Metal Nanostructure-Embedded Hollow Mesoporous Oxide Microspheres Prepared with Polystyrene Nanospheres as Carriers and Templates --- p.78
Chapter 5.1 --- Experiments --- p.83
Chapter 5.2 --- Results and discussion --- p.88
Chapter 5.2.1 --- Hollow mesoporous oxide microspheres prepared with the PS spheres as templates --- p.88
Chapter 5.2.2 --- Noble metal nanostructure-embedded hollow mesoporous oxide microspheres --- p.90
Chapter 5.3 --- Summary --- p.106
References --- p.108
Chapter 6 --- Magnetic Mesoporous Microspheres --- p.113
Chapter 6.1 --- Experiment --- p.115
Chapter 6.2 --- Results and discussion --- p.117
Chapter 6.2.1 --- Magnetic nanoparticle-included mesoporous TiO₂ microspheres --- p.117
Chapter 6.2.2 --- Mesoporous iron oxide microspheres --- p.125
Chapter 6.3 --- Summary --- p.128
References --- p.130
Chapter 7 --- Conclusions --- p.131

New challenges in nanotechnology arise in the assembly of nanoobjects into three-dimensional superstructures, which may carry synergetic properties and open up new application fields. Within this new class of materials nanostructured, porous functional metals are of great interest since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior and size-enhanced catalytic reactivity. Even though a large variety of preparation pathways for the fabrication of porous noble metals has already been established, several limitations are still to be addressed by research developments. The new and versatile approach that is presented in this work makes use of a templatefree self-assembly process for the fabrication of highly porous, metallic nanostructures. Thereby, nanochains are formed by the controlled coalescence of noble metal NPs in aqueous media and their interconnection and interpenetration leads to the formation of a self-supported network with macroscopic dimensions. Subsequently, the supercritical drying technique is used to remove the solvent from the pores of the network without causing a collapse of the fragile structure. The resulting highly porous, low-weighted, three-dimensional nanostructured solids are named aerogels. The exceptional properties of these materials originate from the conjunction of the unique properties of nanomaterials magnified by macroscale assembly. Moreover, the combination of different metals may lead to synergetic effects regarding for example their catalytic activity. Therefore, the synthesis of multimetallic gels and the characterization of their structural peculiarities are in the focus of the investigations. In the case of the developed preparation pathways the gelation process starts from preformed, stable colloidal solutions of citrate capped, spherical noble metal (Au, Ag, Pt, Pd) NPs. In order to face various requirements several methods for the initiation of the controlled destabilization and coalescence of the nanosized building blocks were developed and synthesis conditions were optimized, respectively. Multimetallic structures with tunable composition are obtained by mixing different kinds of monometallic NP solutions and performing a joint gel formation. The characterization of the resulting materials by means of electron microscopy reveals the formation of a highly porous network of branched nanochains that provide a polycrystalline nature and diameters in the size range of the initial NPs. Furthermore, synthesis conditions for the spontaneous gel formation of glucose stabilized Au and Pd NPs were investigated. In order to gain a detailed knowledge of the structural properties of bimetallic aerogel structures a versatile set of characterization techniques was applied. A broad pore size distribution dominated by meso- and macropores and remarkably high inner surface areas were concluded from the N2 physisorption isotherms and density measurements. As investigated, a specific thermal treatment could be used to tune the ligament size of Au-Ag aerogels, whereas Au-Pd and Pt-Pd structures provide thermal stability under mild conditions. Further investigations aimed to the enlightenment of the elemental distribution and phase composition within the nanochains of multimetallic gel structures. The different approaches provide complementary and consistent results. Phase analyses based on XRD measurements revealed separated phases of each metal in the case of Ag-Pd and Au-Pd aerogels. They further proved the possibility of temperature induced phase modifications that lead to complete alloying of Au and Pd. In addition, separated domains of Pt and Pd were established from the EXAFS analysis of the corresponding aerogel. STEM EDX high resolution elemental mappings confirmed the separated domains of different metals in the case of Au-Pd and Pt-Pd aerogels. Moreover, a complete interdiffusion and alloy formation of Au and Ag within the corresponding aerogel structure is suggested from STEM EDX results. Finally, the presented investigations further promote the field of metallic aerogels by addressing the challenging issue of processability and device fabrication. Hybrid materials with organic polymers as well as various kinds of coatings on glass substrates and glassy carbon electrodes were prepared whereas the network structure was preserved throughout all processing steps. Moreover, it was illustrated that the NP-based aerogels carry metallic properties as expressed by their low Seebeck coefficients and high electrical conductivities.

碩士
國防大學理工學院
化學工程碩士班
102
In this study, the preparation of St-co-MPS copolymer with both styrene(St) monomer and γ-methacryloxypropyltrimethoxysilane (γ-MPS) monomer by free radical polymerization. Poly(St-co-MPS)/Pd was prepared via self-reduction of palladium ions by St-co-MPS oligomer without using any reducing agent or surfactant. It was shown that Pd was reduced by the chain-end sulfate groups of styrene when copolymer reacted with the metallic ions. These St-co-MPS copolymer was characterized by 13C-NMR, 29Si-NMR and FTIR to confirm polymer composition and quantity sulfonation, and those self-assembly polymer-metal nanocomposites were characterized by electron microscopy (TEM), observe the stability of LU Misizer(LUM). The Poly(St-co-MPS)/Pd used as ink for catalytic pattern of glasses, which allows to from the metallic pattern by electroless deposition. The cross-linking extend of Poly(St-co-MPS)/Pd ink and glasses dipping with different pH condition was characterized by X-ray photoelectron spectroscope(XPS) to enhance the adhesion of the Poly(St-co-MPS)/Pd ink and glass substrate. The pattern thickness of Ni layer about 8.51 μm. Finally, we used Inkjet printing metallization process has been used in the fabricated of mobile antenna on special glass case, The WWAN five band antenna was made on the new glass case substrate by the printing of the catalyst activation and electroless plating forming the metal pattern. It will simplify the institutions of the antenna, and resolve the configuration problems of the limited space in the mobile phone's.

Incorporating metallic nanoparticles (NPs) in glass has been of intense artistic interest and scientific and technical enthusiasm, since the localized surface plasmon resonance (LSPR) of metallic nanoparticles enrich glass with light modulation capability, which allows applications from colored glasses to photonic devices. The conventional method of generating metallic NPs in glass comprises two steps: (1) prepare a parent glass containing metal ions over the entire glass volume by the melting-quenching technique; (2) strike the parent glass by post heat-treatment, during which the metal ions are reduced to metal atoms, which subsequently nucleate and grow into metallic NPs. However, to efficiently stimulate the reduction of metal ions in the striking step, a co-doping reducing agent in the glass batch is often used, which limits the glass compositions/types and/or requires toxic and environmentally hazardous chemicals. Initiated by an accidental discovery (Chapter 1), the research presented in this thesis is dedicated to the development of a novel and universal powder reheating technique capable of creating noble metal (Au, Ag, or Au-Ag alloy) NPs in a wide range of glass types/compositions (Chapter 3 and 4), and further employing this technique to produce eco-friendly coloured glass for glass art application (Chapter 5) and to study the modulation of upconversion emissions of Er³⁺ in glass by the in-situ created Au NPs taking into account both near-field and far-field LSPR effects (Chapter 6).
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019

The aim of this thesis is to assess the possible applications of noble metal nanoparticles (NPs) in the fields of solar energy production and chemical sensing. The research project arises directly from the well-known extraordinary properties of noble metal NPs, namely the optical and electrical properties, high surface area, high catalytic activity and surface enhanced Raman scattering effect. More specifically, concerning the energy production field, the first part of the thesis will deal with the application of Au NPs as counter electrode material in dye sensitized solar cells (DSSCs). This study was conducted in the S.O.L.A.R.E. laboratory at the Istituto per i Processi Chimico-Fisici of the Italian National Research Council (IPCF-CNR) in Messina, under the supervision of Dr. Giuseppe Calogero. To the best of our knowledge, the role of noble metal NPs as exclusive counter electrode material in DSSCs has not been explored yet, despite their catalytic activity (i.e. applications in water purification) and electron conductivity have been massively studied. On the other hand, gold mirror thin films were used in combination with graphene nanoplatelets for the fabrication of the counter electrode in the most efficient DSSC reported in literature. For this reason, the work conducted towards the realisation of this thesis has been focused on the development of an efficient and reproducible method for the fabrication of Au based counter electrodes for DSSCs. Two different methods have been proposed, namely the thermal decomposition of HAuCl4 as bottom-up method and the pulsed laser ablation of a gold target as top-down method. They were compared on the basis of the counter-electrodes optical properties, surface morphology, catalytic activity and performance both in dummy cells and fully assembled DSSCs. In the latter case, the adequate photoanode configuration has been studied, in order to reduce the electron recombination and maximize the solar-to-electric power conversion efficiency. In addition, the fabricated gold counter-electrodes were compared to standard platinum ones. In the second part of the thesis, the use of Ag NPs for the fabrication of multiresponsive plasmonic sensing platforms for surface enhanced Raman scattering (SERS) and chemiresistive sensing will be presented. This work has been conducted in the Nanochimie laboratory at the Institut de Science et d'Ingénierie Supramoléculaires (ISIS) in Strasbourg, under the supervision of Prof. Paolo Samorì. The development of SERS based sensors has experienced an enormous growth in the last decades, as a consequence of their high versatility, high sensitivity, ease of fabrication and low cost. However, despite the inherently higher SERS activity of Ag compared to Au, sensing platforms based on Au NPs are already commercially available, while Ag NPs are mainly employed as colloidal dispersions, due to their lower chemical stability arising from oxidation. On the other hand, the extraordinary electrical properties of noble metal NPs made them suitable as active conductive materials in chemiresistors. Within this context, different synthetic procedures have been used to obtain citrate stabilized Ag NPs, tannic acid stabilized Ag NPs and Au@Ag core@shell NPs. Besides the study of their optical properties in colloidal solutions, they were compared by means of their ability to give rise to uniform thin films on chemiresistive devices, using both the cross-linking with dithiols and the electrostatic layer-by-layer deposition. The best results were obtained with the electrostatic layer-by-layer deposition of tannic acid stabilized Ag NPs, so that the optical properties, surface morphology, SERS and chemiresistive activity of these devices was largely studied. Furthermore, the possibility to use the fabricated sensing platforms for the sensing of mercury ions in water by both indirect SERS and resistance variation was explored.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.
Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3724. Adviser: Jennifer A. Lewis. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

碩士
國立中正大學
化學暨生物化學研究所
102
This thesis consists of three chapters. In chapter 1, we applied the multi-coefficient density functional theory (MC-DFT) to a few recent Minnesota functionals. In chapter 2, we have developed a new method using mixed functionals and we tested it on 70 bond energies of 3d transition-metal-containing molecules. In chapter 3, we investigated the kinetic isotope effects and tunneling effects of noble-gas exchange reactions. 　　 　　In chapter 1, we have applied MC-DFT method to four recent Minnesota functionals, including M06-2X, M08-HX, M11, and MN12-SX on the performance of thermochemical kinetics. The results indicated that the accuracy can be improved significantly by using two or three basis sets. We further included the SCS-MP2 energies into MC-DFT, and the resulting mean unsigned errors (MUE) decreased by ~0.3 kcal/mol for the most accurate basis set combinations. The M06-2X functional with the simple [6-311+G(d,p)/6-311+G(2d,2p)] combination gave the best performance/cost ratios for the MC-DFT and MC-SCS-MP2 | MC-DFT methods with MUE of 1.58 and 1.22 kcal/mol, respectively. 　　 　　In chapter 2, we have developed a new method using mixed functionals for transition metals. This method was tested against a database including 70 bond energies of 3d transition-metal-containing molecules with small experimental uncertainties. The best mixed functional method was the τ-HCTHhyb/mPW2-PLYP combination, and it yielded an MUE of 5.49 kcal/mol. In comparison, the single τ-HCTHhyb and mPW2-PLYP functional gave MUEs of 6.14 and 12.88 kcal/mol, respectively. We also applied the MC-DFT approach into the mixed functional and it yielded an MUE of 4.94 kcal/mol. We further added the MP2 and CCSD energies into the new method, and obtained MUE of 4.75 kcal/mol and 4.51 kcal/mol, respectively. 　　 　　In chapter 3, we used VTST/MT method to investigate four noble-gas exchange reactions: Ng’ + HNBNg+ (Ng, Ng’ = He, Ne, and Ar). The barrier heights of these four reactions were predicted to be 5－9 kcal/mol. The calculated results showed significant tunneling effects even at room temperature, especially for the He + HNBHe+ reaction. All reactions showed very significant tunneling effects at low temperature. For helium exchange reactions, the internal helium atom (in the cation) contributed more in the tunneling effects than the external helium atom (the neutral reactant) at low temperature.

Computational techniques based on density functional theory (DFT) and experimental methods based on electrochemistry (EC), electrochemical scanning tunneling microscopy (EC-STM), and high-resolution electron energy loss spectroscopy (HREELS) were employed to study the adsorption of (i) sulfuric acid on Pd(111), (ii) benzene on Pd(111), (iii) hydroquinone/benzoquinone on Pd(111), (iv) hydroquinone sulfonate/benzoquinone sulfonate on Pd(111), (v) 2,3-dimethylhydroquinone/2,3-dimethylbenzoquinone on Pd(111) and polycrystalline Pd, (vi) hydrogen on 1-6 monolayers (ML) of Pd deposited on a Pt(111) substrate, and (vii) a thiolated iron hydrogenase model complex on polycrystalline Au. In situ EC-STM and DFT investigations of sulfuric acid on a Pd(111) surface indicated that two layers of water molecules and hydronium ions are assembled, non-co-planar with one another, between the rows of surface-coordinated sulfate anions; the layer that is slightly elevated is composed of hydronium counter cations. The STM images of benzene chemisorbed on a Pd(111) electrode surface were simulated and the results suggested that, when the potential of the Pd electrode is held at 0.3 V, benzene is chemisorbed on a 3-fold site; while at 0.55 V, the molecule is adsorbed on a position between a 3-fold and a 2-fold site. Computational and experimental results implied that at low concentrations, hydroquinone sulfonate undergoes oxidative chemisorption forming benzoquinone sulfonate (BQS) on the Pd(111) surface, BQS adopts a flat orientation in which the quinone ring is centered over a 2-fold site, and the C–H and C–S bonds are no longer co-planar with the quinone ring and are slightly tilted, directed away from the surface. At very dilute concentrations, when hydroquinone (H_(2)Q) undergoes oxidative chemisorption producing benzoquinone oriented flat, albeit with a slight tilt, on the Pd(111) surface, the flat-adsorbed quinone ring is centered on a bridge site where the C_(2) axis is rotated 30degree from the [110] direction of the metal substrate, the p-oxygen atoms are located above two-fold sites, and the ring is slightly puckered with the C–H bonds tilted away from the surface at approximately 20degree. When 2,3-dimethylH_(2)Q is chemisorbed on the Pd surface, at low concentrations, 2,3-dimethylH_(2)Q is oxidatively chemisorbed producing 2,3-dimethyl-1,4-benzoquinone oriented flat on the surface, the flat-adsorbed rings are centered above 2-fold sites wherein the C=O bonds are pointing 30degree from the [110] direction of the substrate, the para-oxygen atoms are located above bridge sites, the peripheral bonds are tilted away from the surface at ca. 20degree, and at higher concentrations, oxidative chemisorption occurs through activation of the ring’s C–H bonds yielding edge-oriented 2,3-dimethylH_(2)Q. Electrochemistry and DFT results also implied that at 1-2 ML of Pd on Pt(111), hydrogen is only adsorbed on a hollow site while at 3 ML of Pd or more, atomic hydrogen may be chemisorbed on the 3-fold site or absorbed in the octahedral hole underneath the hollow site. Using Au electrodes, an unbound iron hydrogenase analogue complex studied was found to slightly catalyze the H_(2) evolution process. However, when the complex was immobilized unto the Au surface, the electrocatalytic activity was greatly improved.

There are many challenges in materializing the applications utilizing inorganic nanoparticles. The primary drawback is the degradation of properties due to aggregation and sintering either due to elevated temperatures or prevailing chemical/electrochemical conditions. In this thesis, various wet chemical synthesis methods are developed to obtain metal nanostructures with enhanced thermal stability. The thesis is organized as below: Chapter 1 presents the problems and challenges in materializing the application of nanomaterials associated with the thermal stability of nanomaterials. A review of the existing techniques to improve the thermal stability and the scope of the thesis are presented. Chapter 2 gives a summary of the various materials synthesized, the method adopted for the synthesis and the characterization techniques used in the material characterization. Chapter 3 presents a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long term stability and CO tolerance. Chapter 4 presents a detailed study on the thermal stability of spherical mesoporous aggregates consisting of nanoparticles. The thermal stability study leads to a general conclusion that nanoporous structures transform to hollow structures on heating to elevated temperatures before undergoing complete densification. Chapter 5 presents a simple and facile method for the synthesis of single crystalline intermetallic PtBi hollow nanoparticles. A mechanism is proposed for the formation of intermetallic PtBi hollow structures. The intermetallic PtBi hollow structures synthesised show excellent electrocatalytic activity for formic acid oxidation reaction. Chapter 6 presents a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene. The method involves the nucleation of a metal precursor phase on graphite oxide surfaces and subsequent reduction with a strong reducing agent. The electrocatalytic activity of the composites is investigated for methanol oxidation reaction. Chapter 7 presents a microwave-assisted synthesis method for selective heterogeneous nucleation of metal nanoparticles on oxide supports leading to the synthesis of high activity catalysts. The catalytic activity of the hybrids synthesized by this method for investigated for H2 combustion. Chapter 8 presents thermal stability studies carried out on nanostructures by in-situ heating in transmission electron microscope. The microstructural changes during the sintering process are observed in real time and the observations lead to the understanding of the mechanism of particle growth and sintering. At the end, the results of the investigations were summarized with conclusions drawn.

There are many challenges in materializing the applications utilizing inorganic nanoparticles. The primary drawback is the degradation of properties due to aggregation and sintering either due to elevated temperatures or prevailing chemical/electrochemical conditions. In this thesis, various wet chemical synthesis methods are developed to obtain metal nanostructures with enhanced thermal stability. The thesis is organized as below: Chapter 1 presents the problems and challenges in materializing the application of nanomaterials associated with the thermal stability of nanomaterials. A review of the existing techniques to improve the thermal stability and the scope of the thesis are presented. Chapter 2 gives a summary of the various materials synthesized, the method adopted for the synthesis and the characterization techniques used in the material characterization. Chapter 3 presents a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long term stability and CO tolerance. Chapter 4 presents a detailed study on the thermal stability of spherical mesoporous aggregates consisting of nanoparticles. The thermal stability study leads to a general conclusion that nanoporous structures transform to hollow structures on heating to elevated temperatures before undergoing complete densification. Chapter 5 presents a simple and facile method for the synthesis of single crystalline intermetallic PtBi hollow nanoparticles. A mechanism is proposed for the formation of intermetallic PtBi hollow structures. The intermetallic PtBi hollow structures synthesised show excellent electrocatalytic activity for formic acid oxidation reaction. Chapter 6 presents a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene. The method involves the nucleation of a metal precursor phase on graphite oxide surfaces and subsequent reduction with a strong reducing agent. The electrocatalytic activity of the composites is investigated for methanol oxidation reaction. Chapter 7 presents a microwave-assisted synthesis method for selective heterogeneous nucleation of metal nanoparticles on oxide supports leading to the synthesis of high activity catalysts. The catalytic activity of the hybrids synthesized by this method for investigated for H2 combustion. Chapter 8 presents thermal stability studies carried out on nanostructures by in-situ heating in transmission electron microscope. The microstructural changes during the sintering process are observed in real time and the observations lead to the understanding of the mechanism of particle growth and sintering. At the end, the results of the investigations were summarized with conclusions drawn.