Preformed Nanoparticles Research Articles

Colloidal Stability of Silica-Modified Magnetite Nanoparticles: Comparison of Various Dispersion Techniques.

The production of stable and homogeneous batches during nanoparticle fabrication is challenging. Surface charging, as a stability determinant, was estimated for 3-aminopropyltriethoxysilane (APTES) coated pre-formed magnetite nanoparticles (MNPs). An important consideration for preparing stable and homogenous MNPs colloidal systems is the dispersion stage of pre-formed samples, which makes it feasible to increase the MNP reactive binding sites, to enhance functionality. The results gave evidence that the samples that had undergone stirring had a higher loading capacity towards polyanions, in terms of filler content, compared to the sonicated ones. These later results were likely due to the harsh effects of sonication (extremely high temperature and pressure in the cavities formed at the interfaces), which induced the destruction of the MNPs.

Effect of copolymer composition of controlled (N-vinylcaprolactam/N-vinylpyrrolidone) statistical copolymers on formation, stabilization, thermoresponsiveness and catalytic properties of gold nanoparticles

The insertion of an increasing amount of N-vinylpyrrolidone (VP) in statistical copolymers based on thermoresponsive poly(N-vinylcaprolactam) (PVCL) enables one to modulate the properties of the copolymer and those of the corresponding gold nanoparticles (AuNPs)-polymer hybrid materials. The incorporation of VP not only affects the growth of AuNPs synthesized in the presence of the polymers (in situ route), but also the properties (stabilization, optical, catalytic...) of preformed nanoparticles coated by these polymers. Hence, at a molar fraction of VP in copolymer less than 40%, it is possible to increase the transition temperature of the hybrid material and improve its catalytic properties compared to counterparts comprising PVP and PVCL homopolymers. The structural difference of the two monomers allows the best compromise between the hydration level and the interaction strength of the copolymer with the surface of gold particles for a chosen application.

Gold Nanoparticles and Nanoshells Embedded as Core–Shell Architectures in Hybrid Poly(l-Histidine)-Containing Polymers for Photothermal Therapies

We present a facile strategy for the synthesis of hybrid nanoparticles containing gold nanoshells (AuNSs) that absorb at near-infrared (NIR). Poly(ethylene oxide)-b-poly(l-histidine), poly(ethylene oxide)-b-poly(l-histidine)-b-poly(l-phenylalanine), and poly(ethylene oxide)-b-poly(l-histidine)-b-poly(γ-benzyl-l-glutamate) hybrid copolypeptides were used for the development of AuNSs. Spherical nanoparticles (NPs) were initially formed by the self-assembly of the amphiphilic hybrid polypeptides in water. The addition of HAuCl4 followed by heating, resulted in the reduction of the Au(III) by poly(l-histidine) (PHis), leading to the formation of AuNSs only at the PHis layer, thus forming a nanoshell within the preformed NPs. The NPs formed are composed of a poly(ethylene oxide) (PEO) shell, a PHis layer containing the nanoshell and a poly(l-phenylalanine) (PPhe) or poly(γ-benzyl-l-glutamate) (PBLG) core. By controlling the AuNS thickness and the core diameter by the molecular characteristics of the polymeric precursors as well as the PHis/Au(III) ratio, the optical properties of the AuNSs can be fine-tuned to absorb at a specific wavelength. Thus, we achieved a shift of the absorption peak corresponding to longitudinal surface plasmon resonance to NIR wavelengths. The size and the morphology of the polymeric NPs containing AuNSs were examined by TEM and Dynamic Light Scattering. Studies on a dilute solution of polymeric nanoparticles containing AuNSs showed that by irradiation with a low power laser at 808 nm, results to significant increase of its temperature. We present an approach for the design and facile synthesis of biocompatible polymeric nanoparticles featuring AuNSs with a peak optical absorption in the NIR that can be fine-tuned. Therefore, our aim is to present a novel and facile approach for the formation of AuNSs to be used for photothermal therapy.

Ethanol Oxidation at Pt Nanoparticles Supported on Titanium Modified by Thermal Decomposition of Tin and Ruthenium Acetylacetonate Complexes

Sn and Ru oxides prepared by thermal decomposition of metal acetylacetonate (acac) complexes on Ti have a substantial support effect on platinum catalyzed oxidation of ethanol. Sn and Ru oxides and mixed Sn–Ru oxides (Ru-doped SnO2) deposited onto Ti foils were drop coated with preformed Pt nanoparticles. Cyclic voltammetry in H2SO4(aq) showed a strong synergistic effect between Ru and Sn oxide for ethanol oxidation, with a 2:1 ratio of Ru(acac)3 to Sn(acac)2 in the oxide precursor solution producing the most active catalyst. X-ray photoelectron spectroscopy revealed a significant transfer of electron density from the Ru-doped SnO2 to the Pt nanoparticles (electronic/ligand effect), and increased Pt oxide formation. Both of these effects can promote the oxidation of adsorbed CO, while the electronic effect also influences the adsorption strength of ethanol. The variation of the balance of these effects with the level of Ru doping is a plausible explanation for the dependence the ethanol oxidation activity on the composition of the oxide layer.

Porous multifunctional phenylcarbamoylated-β-cyclodextrin polymers for rapid removal of aromatic organic pollutants.

In this work, polymers containing a large number of benzene rings and multiple functional groups were designed to remove aromatic organic pollutants. Using tetrafluoroterephthalonitrile (TFTPN) as a rigid crosslinking agent to crosslink different functionalized phenylcarbamoylated-β-cyclodextrin derivatives to prepare a series of porous multifunctional cyclodextrin (CD) polymerizations, including three preliminary polymerized adsorption materials and a mix β-cyclodextrin polymer (X-CDP) prepared via a secondary crosslinking procedure of the above three materials. The X-CDP preparation process connects the pre-formed nanoparticles and increases the presence of linkers inside the particles. At the same time, X-CDP exhibited porous structure with various functional groups such as nitro, chlorine, fluorine, and hydroxyl. Those special characteristics render this material with good adsorption ability towards various aromatic organic pollutants in water, including tetracycline, ibuprofen, dichlorophenol, norfloxacin, bisphenol A, and naphthol. Especially, the maximum adsorption capacity for tetracycline at equilibrium reached 110.56 mg·g-1, which is competitive with the adsorption capacities of other polysaccharide adsorbents. X-CDP removed organic contaminants much more quickly than other adsorbents, reaching almost ~95% of its equilibrium in only 30 s, and the rate constant reaches 2.32 g·mg-1·min-1. The main adsorption process of the pollutants by X-CDP fitted the pseudo-second-order kinetic and Langmuir isotherm well, indicating that the adsorption process is monolayer adsorption. Moreover, X-CDP possessed the good reusability where the pollutant removal rate was only reduced 8.3% after five cycles. Such advantages render the polymer great potential in the rapid treatment of organic pollutants in water bodies.

Nano Spray-Dried Drugs for Oral Administration: A Review.

Spray drying is an important technology that is fast, simple, reproducible, and scalable. It has a wide application range, that is, in food, chemicals, and encapsulation of pharmaceuticals. The technology can be divided into conventional spray drying and nano spray drying. The key advantage of nano spray drying is the production of drug-loaded nanosized particles for various drug delivery applications. The recent developments in nano spray dryer technology and the market launch of the Nano Spray Dryer B-90 by Büchi Labortechnik AG in 2009 enabled the production of submicron spray-dried particles. This review focuses on nanosized drug delivery systems intended for oral administration produced by nano spray drying. First, the nano spray drying concept, the basic technologies implemented in the equipment, and the effects of the various process parameters on the final dry submicron powder properties are presented. Then, the topics of new formulation strategies of oral drugs are highlighted with examples that have entered the research literature in recent years. Next, the subjects of direct conversion of poorly water-soluble drugs, encapsulation of drugs, and drying of preformed nanoparticles are considered. Finally, topics such as morphology, particle size, size distribution, surface analysis, bioavailability, drug release, release kinetics, and solid-state characterization (by differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, nuclear magnetic resonance) of oral drug delivery systems produced by nano spray drying are discussed. The review attempts to provide a comprehensive knowledge base with current literature and foresight to researchers working in the field of pharmaceutical technology and nanotechnology and especially in the field of nano spray drying.

Beyond Thin Films: Clarifying the Impact of c-Li15Si4 Formation in Thin Film, Nanoparticle, and Porous Si Electrodes

The formation of the c-Li15Si4 phase has well-established detrimental effects on the capacity retention of thin film silicon electrodes. However, the role of this crystalline phase with respect to the loss of capacity is somewhat ambiguous in nanoscale morphologies. In this work, three silicon-based morphologies are examined, including planar films, porous planar films, and silicon nanoparticle composite powder electrodes. The cycling conditions are used as the lever to induce, or not induce, the formation of c-Li15Si4 through application of constant-current (CC) or constant-current constant-voltage (CCCV) steps. In this manner, the role of this phase on capacity retention and Coulombic efficiency can be determined with few other convoluting factors such as alteration of the composition or morphology of the silicon electrodes themselves. The results here confirm that the c-Li15Si4 phase increases the rate of capacity decay in planar films but has no major effect on capacity retention in half-cells based on porous silicon films or silicon nanoparticle composite powder electrodes, although this conclusion is nuanced. Besides using a constant-voltage step, formation of the c-Li15Si4 phase is influenced by the dimensions of the Si material and the lithiation cutoff voltage. Porous Si films, which, in this work, comprise primary Si particle sizes that are smaller than those in the preformed Si nanoparticle slurries, do not undergo the formation of c-Li15Si4 at 50 mV, whereas Si nanoparticle slurries are accompanied by the formation of c-Li15Si4 up to 80 mV. The solid-electrolyte interphase (SEI) formed from reaction of the c-Li15Si4 with the carbonate-based electrolyte causes polarization in both nanoparticle and porous film silicon electrodes and lowers the average Coulombic efficiency. A comparison of the cumulative irreversibilities due to SEI formation between different lithiation cutoff voltages in silicon nanoparticle slurry electrodes confirmed the connection between higher SEI buildup and formation of the c-Li15Si4 phase. This work indicates that concerns about the c-Li15Si4 phase in silicon nanoparticles and porous silicon electrodes should mainly focus on the stability of the SEI and a reduction of irreversible electrolyte reactions.

Quantitatively Tracking Bio-Nano Interactions of Metal-Phenolic Nanocapsules by Mass Cytometry.

Polymer nanocapsules, with a hollow structure, are increasingly finding widespread use as drug delivery carriers; however, quantitatively evaluating the bio-nano interactions of nanocapsules remains challenging. Herein, poly(ethylene glycol) (PEG)-based metal-phenolic network (MPN) nanocapsules of three sizes (50, 100, and 150 nm) are engineered via supramolecular template-assisted assembly and the effect of the nanocapsule size on bio-nano interactions is investigated using in vitro cell experiments, ex vivo whole blood assays, and in vivo rat models. To track the nanocapsules by mass cytometry, a preformed gold nanoparticle (14 nm) is encapsulated into each PEG-MPN nanocapsule. The results reveal that decreasing the size of the PEG-MPN nanocapsules from 150 to 50 nm leads to reduced association (up to 70%) with phagocytic blood cells in human blood and prolongs in vivo systemic exposure in rat models. The findings provide insights into MPN-based nanocapsules and represent a platform for studying bio-nano interactions.

Development and Characterization of Fe3O4@Carbon Nanoparticles and Their Biological Screening Related to Oral Administration.

The current study presents the effect of naked Fe3O4@Carbon nanoparticles obtained by the combustion method on primary human gingival fibroblasts (HGFs) and primary gingival keratinocytes (PGKs)—relevant cell lines of buccal oral mucosa. In this regard, the objectives of this study were as follows: (i) development via combustion method and characterization of nanosized magnetite particles with carbon on their surface, (ii) biocompatibility assessment of the obtained magnetic nanoparticles on HGF and PGK cell lines and (iii) evaluation of possible irritative reaction of Fe3O4@Carbon nanoparticles on the highly vascularized chorioallantoic membrane of a chick embryo. Physicochemical properties of Fe3O4@Carbon nanoparticles were characterized in terms of phase composition, chemical structure, and polymorphic and molecular interactions of the chemical bonds within the nanomaterial, magnetic measurements, ultrastructure, morphology, and elemental composition. The X-ray diffraction analysis revealed the formation of magnetite as phase pure without any other secondary phases, and Raman spectroscopy exhibit that the pre-formed magnetic nanoparticles were covered with carbon film, resulting from the synthesis method employed. Scanning electron microscopy shown that nanoparticles obtained were uniformly distributed, with a nearly spherical shape with sizes at the nanometric level; iron, oxygen, and carbon were the only elements detected. While biological screening of Fe3O4@Carbon nanoparticles revealed no significant cytotoxic potential on the HGF and PGK cell lines, a slight sign of irritation was observed on a limited area on the chorioallantoic membrane of the chick embryo.

Colloidal Nanocrystals: A Toolbox for Materials Chemistry.

Colloidal nanocrystals are the ideal building blocks for the fabrication of functional materials. Using various assembly, patterning or processing techniques, the nanocrystals can be arranged with unprecedented flexibility in 1-, 2- or 3-dimensional architectures over several orders of length scales, providing access to ordered or disordered, porous or non-porous, and simple as well as hierarchical structures. Careful selection of colloidal nanocrystals allows the properties of the final materials to be predefined. Moreover, by combining different nanocrystals, these properties can be fine-tuned for a specific application, opening up fascinating opportunities to create new materials for energy storage and conversion, catalysis, photocatalysis, biomedicine or optics. Indeed, functional materials made of preformed nanoparticles have been realized for metals, polymers, semiconductors, and ceramics, as well as for composites and organic-inorganic hybrids. In this review article, we introduce some concepts for the fabrication of colloidal nanocrystals and their assembly into dense and porous 3-dimensional structures. Porosity is a particularly important material property that strongly influences its application potential. Therefore, we pay special attention to this aspect and compare porous materials synthesized from nanoparticles with those from molecular routes. An additional focus is set on the degree of structural order that can be achieved on different length scales.

Porous SiO2 Nanofibers Loaded with CuO Nanoparticles for the Dosimetric Detection of H2S

Mesoporous SiO2 nanofibers were prepared by electrospinning dispersions of preformed SiO2 nanoparticles and infiltrated with soluble Cu compounds, forming CuO/SiO2 nanocomposites after heat treatme...

Structural and magnetic properties of size-controlled Fe–Ni nanoparticles synthesized by diffusing Fe atoms into preformed Ni nanoparticles

Fe–Ni nanoparticles are attractive candidates for magnetic cores of transformers and inductors that are operated at high frequencies. When applying Fe–Ni nanoparticles in magnetic cores, particle size must be controlled to enhance magnetic properties. A two-step synthetic method can be useful for fabricating size-controlled Fe–Ni nanoparticles. In the first step, Ni nanoparticles are synthesized by reducing Ni (II) acetylacetonate in oleylamine (OA) with trioctylphosphine (TOP). Thereafter, Fe (III) acetylacetonate is reduced and Fe atoms diffuse into the preformed Ni nanoparticles in OA. The size of the Fe–Ni nanoparticles depends on that of the Ni nanoparticles. However, no studies have conducted extensive investigations of their synthesis and magnetic properties with various particle sizes. Here, we attempted particle-size-controlled synthesis of Fe–Ni nanoparticles and investigated their magnetic properties. The particle size of the Fe–Ni nanoparticles was varied between 13.1. and 20.5 nm by varying the size of Ni nanoparticles. The saturation magnetization (Ms) gradually reduced with the decrease in particle size because of the increased amount of oxidized surface atoms and phosphides. Coercive forces (Hc) also decreased as the particle size decreased to 15 nm because of the increased effect of superparamagnetism, while the Hc greatly increased with the particle size reduction below 14 nm because of the ferromagnetism exhibited by the Fe layer owing to undiffused Fe atoms. Thus, using this synthetic method, Fe–Ni nanoparticles with a size of approximately 15 nm can be produced, which have a minimum Hc and are the most appropriate for magnetic cores.

G-C3N4/Ag3PO4 based binary and ternary heterojunction for improved photocatalytic removal of organic pollutants

ABSTRACT Ag3PO4 (AP) was effectively coupled with bare and modified graphitic carbon nitride through a facile wet-chemistry process for the development of hybrid organic/inorganic heterojunctions. The prepared materials were thoroughly characterised using a multimethodology approach including XRD, IR, DR-UV-Vis, nitrogen adsorption/desorption isotherms, photoluminescence and EPR spectroscopy. The photoactive hybrid materials were applied as photocatalysts for the degradation of organic pollutants, namely rhodamine B (RhB), under pure visible light irradiation. The prepared nanocomposites were proven stable under working conditions and more active than their individual counterparts. The study highlighted the importance of CN modification and the development of preformed Ag nanoparticles in photoactivity. The enhanced activity is attributed to the improved charge separation efficiency as evidenced by PL due to the formation of a heterojunction. In-situ EPR spin-trap experiments provide direct evidence for the formation of a Z-scheme heterojunction through the detection of superoxide anion radicals (). Finally, a photocatalytic mechanism is proposed based on the spectroscopic data and reference reactions using sacrificial agents to identify the predominant active species.

Particle Size Evolution during the Synthesis of Gold Nanoparticles Using In Situ Time-Resolved UV–Vis Spectroscopy: An Experimental and Theoretical Study Unravelling the Effect of Adsorbed Gold Precursor Species

The quantitative analysis of nanomaterials synthesis kinetics is valuable both for understanding the synthesis and for development of manufacturing processes, and it usually requires the use of synchrotron-based instrumentation, making it challenging to perform experiments in the large parametric space needed to develop quantitative kinetic models. UV–vis spectroscopy represents a convenient technique to circumvent such difficulties, as it is available in most chemistry laboratories and allows fast data acquisition. This technique can in theory be used for the characterization of plasmonic nanomaterials synthesis kinetics. However, linking UV–vis spectra with characteristic features of the produced nanomaterials, such as size and shape, is a challenging task. This work presents a detailed spectroscopic analysis of gold nanoparticles syntheses via in situ time-resolved UV–vis spectroscopy, with emphasis on the role of gold precursor adsorption on the particle surface during nanoparticle growth. We show that the classic Turkevich synthesis and the growth of preformed gold nanoparticles with two different methods exhibit significant commonalities in the spectra evolution, explained in terms of the interaction between gold precursor species and the nanoparticle surface. Such interaction was accounted for in a model based on the Mie theory, describing the growing nanoparticles as core–shell spheres with an outer shell of few Ångströms characterized by reduced conductivity and increased electron damping rate. The proposed model led to the determination of the nanoparticle size and concentration evolution throughout the synthesis with good quantitative agreement against literature SAXS data. Furthermore, the core–shell model enabled the reproduction of the progressive blue-shift in the SPR peak position observed during the synthesis. Thus, this work reconciles the “seed-mediated growth” mechanism for the Turkevich synthesis with the temporal evolution of the spectra within the framework of the Mie theory, showing that the distinctive purple-greyish hue observed during the synthesis can be related to the interaction of gold precursor with the growing gold nanoparticles.

Effect of complexing lipids on cellular uptake and expression of messenger RNA in human skin explants

Messenger RNA (mRNA) represents a promising next-generation approach for both treatment and vaccination. Lipid based particles are one of the most investigated delivery systems for mRNA formulations. Here we explore how the complexing lipid affects uptake and translation of lipoplex-delivered RNA in resident cells in human skin explants and, we explore a more modular delivery system that utilizes mRNA added to pre-formed nanoparticles prior to dosing. We prepared formulations of lipoplexes with ionizable, cationic or zwitterionic lipids, externally complexed these with mRNA, and observed which cells internalized and/or expressed the mRNA over 72 h after intradermal injections into primary, human, skin explants. Using a flow cytometry panel to assess cellular phenotypes, mRNA uptake and mRNA expression, we found that, unlike other cell types, adipocytes expressed mRNA efficiently at 4 and 24 h after mRNA-lipoplex injection and contributed the greatest proportion of total RNA-encoded protein expression, despite being the lowest frequency cell type. Other cell types (epithelial cells, fibroblasts, T cells, B cells, dendritic cells, monocytes, NK cells, Langerhans cells, and leukocytes) had increasing mRNA expression over the course of 72 h, irrespective of lipoplex formulation. We observed that overall charge of the particle, but not the complexing lipid classification, was predictive for the pattern of mRNA uptake and expression among resident cell types in this model.This study provides insight into maximizing protein expression, using modular mRNA lipoplexes that are more compatible with product development, in a clinically relevant, human skin explant model.

CO Total and Preferential Oxidation over Stable Au/TiO2 Catalysts Derived from Preformed Au Nanoparticles

CO preferential oxidation (PROX) is an effective method to clean reformate H2 streams to feed low-temperature fuel cells. In this work, the PROX and CO oxidation reactions were studied on preformed Au nanoparticles (NPs) supported on TiO2 anatase. Preformed Au NPs were obtained from gold cores stabilized by dodecanethiols or trimethylsilane-dendrons. A well-controlled size of ca. 2.6 nm and narrow size distributions were achieved by this procedure. The catalysts were characterized by high-resolution transmission electron microscopy and ex situ and in situ X-ray photoelectron spectroscopy (XPS). The XPS results showed that the preformed Au NPs exhibited high thermal stability. The different ligand-derived Au catalysts, as well as a conventional gold catalyst for comparison purposes, were loaded onto cordierite supports with 400 cells per square inch. The activity and selectivity of the samples were evaluated for various operation conditions. The catalyst prepared using dodecanethiol-capped Au NPs showed the best performance. In fact, CO conversions of up to 70% at 40% CO2 selectivity and 90% O2 conversion were observed operating at 363 K in H2-rich atmospheres. The performance of the best catalysts was subsequently tested on stainless steel microreactors. A 500-hour stability test was carried out under a real post-reformate stream, including 18 vol.% CO2 and 29 vol.% H2O. A mean CO conversion of ca. 24% was measured for the whole test operating at 453 K and a gas hourly space velocity (GHSV) of 1.3 × 104 h−1. These results reveal our dodecanethiol- and carbosilane-derived Au catalysts as extremely promising candidates to conduct a PROX reaction while avoiding deactivation, which is one of the major drawbacks of Au/TiO2 catalysts.

Tuning the selectivity of phenol hydrogenation using Pd, Rh and Ru nanoparticles supported on ceria- and titania-modified silicas

The large-scale production of biomass-derived fuels generates large amounts of lignocellulosic residues that may further be converted into bio-derived value-added chemicals. Here, we investigate the selective hydrogenation of phenol as a model compound for lignocellulosic derivatives. Pre-formed PVP-stabilized nanoparticles (NPs) of Pd, Ru and Rh prepared using an organometallic approach were immobilized on different magnetic silica-based supports modified with TiO2 or CeO2. In phenol hydrogenation studies, the Pd NP catalysts show high selectivity towards cyclohexanone, while Ru and Rh NP catalysts primarily afford cyclohexanol. Titania-containing supports increase the selectivity towards cyclohexanol for both Pd- and Rh-based catalysts. Interestingly, the combination of Ru NPs and titania-modified silica results in 100 % selectivity of cyclohexanol. After removal of the PVP-stabilizer by thermal treatment, the catalyst combining Pd NPs and titania-modified silica leads to 100 % selectivity towards cyclohexanone. Despite the difficulties associated with the de-polymerization of biomass residues, the development of new catalyst materials for highly selective transformations of biomass-derived platform molecules contributes to a sustainable production of various value-added chemicals for several applications.

An Approach for Magnetic Halloysite Nanocomposite with Selective Loading of Superparamagnetic Magnetite Nanoparticles in the Lumen

We present for the first time a method for the preparation of magnetic halloysite nanotubes (HNT) by loading of preformed superparamagnetic magnetite nanoparticles (SPION) of diameter size ∼6 nm with a hydrodynamic diameter of ∼10 nm into HNT. We found that the most effective route to reach this goal relies on the modification of the inner lumen of HNT by tetradecylphosphonic acid (TDP) to give HNT–TDP, followed by the loading with preformed oleic acid (OA)-stabilized SPION. Transmission electron microscopy evidenced the presence of highly crystalline magnetic nanoparticles only in the lumen, partially ordered in chainlike structures. Conversely, attempts to obtain the same result by exploiting either the positive charge of the HNT inner lumen employing SPIONs covered with negatively charged capping agents or the in situ synthesis of SPION by thermal decomposition were not effective. HNT–TDP were characterized by infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and ζ-potential, and all of the techniques confirmed the presence of TDP onto the HNT. Moreover, the inner localization of TDP was ascertained by the use of Nile Red, a molecule whose luminescence is very sensitive to the polarity of the environment. The free SPION@OA (as a colloidal suspension and as a powder) and SPION-in-HNT powder were magnetically characterized by measuring the ZFC-FC magnetization curves as well as the hysteresis cycles at 300 and 2.5 K, confirming that the super-paramagnetic behavior and the main magnetic properties of the free SPION were preserved once embedded in SPION-in-HNT.

(Invited) Pt/Metal Oxide/Ti and Pt/Metal Oxide/Carbon Composite Films for Ethanol Oxidation

Metal oxides prepared by thermal decomposition of metal acetylacetonate (acac) complexes have a significant support effect on platinum catalyzed oxidation of ethanol. Ru and Sn oxides and mixed Ru-Sn oxides deposited onto Ti foils and high surface area carbon support materials were drop coated with preformed Pt nanoparticles. Cyclic voltammetry in H2SO4(aq) and polarization experiments in proton exchange membrane cells have demonstrated great versatility for screening the co-catalytic effects of oxide layers and scale-up to fuel cell testing. A strong synergistic effect has been observed between Ru and Sn oxide in both environments, with a 2:1 ratio of Ru(acac)3 to Sn(acac)2 ratio in the oxide precursor solution producing the most active catalyst. Electrodes prepared by using Pb(acac)2, In(acac)3 and MoO2(acac)2 also provided substantially enhanced activities for ethanol oxidation.

A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.