Speciation of Gold Nanoparticles by Ex Situ Extended X‑ray Absorption Fine Structure and X‑ray Absorption Near Edge Structure

A combined X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methodology is here presented on a series of partially and fully reduced Au^III samples. This allows monitoring the relative fraction of Au^III and Au⁰ in the studied samples, displaying a consistent and independent outcome. The strategy followed is based, for the first time, on two structural models that can be fitted simultaneously, and it evaluates the correlation among strongly correlated parameters such as coordination number and the Debye–Waller factor. The results of the present EXAFS and XANES approach can be extended to studies based on X-ray absorption spectroscopy experiments for the in situ monitoring of the formation of gold nanoclusters

Synthesis Route to Supported Gold Nanoparticle Layered Double Hydroxides as Efficient Catalysts in the Electrooxidation of Methanol

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells

Silica modification of titania nanoparticles enhances photocatalytic production of reactive oxygen species without increasing toxicity potential in vitro

Titania (TiO2) nanoparticles were surfacemodified using silica and citrate to implement a ‘safe-by-design’ approach for managing potential toxicity of titania nanoparticles by controlling surface redox reactivity. DLS and zeta-potential analyses confirmed the surface modification, and electron microscopy and surface area measurements demonstrated nanoscale dimensions of the particles. Electron paramagnetic resonance (EPR) was used to determine the exogenous generation of reactive oxygen species (ROS). All the produced spray dried nanotitania lowered levels of ROS when compared to the corresponding dispersed nanotitania, suggesting that the spray drying process is an appropriate design strategy for the control of nano TiO2 ROS reactivity. The modification of nanotitania with silica and with citrate resulted in increased levels of ROS generation in exogenous measurements, including photoexcitation for 60 minutes. The dichlorodihydrofluorescein (DCFH) assay of dose-dependent production of oxidative stress, generated by pristine and modified nanotitania in macrophages and alveolar epithelial cells, found no significant change in toxicity originating from the generation of reactive oxygen species. Our findings show that there is no direct correlation between the photocatalytic activity of nanotitania and its oxidative stress-mediated potential toxicity, and it is possible to improve the former, for example adding silica as a modifying agent, without altering the cell redox equilibrium

Role of Coating-Metallic Support Interaction in the Properties of Electrosynthesized Rh-Based Structured Catalysts

Rh-structured catalysts for the catalytic partial oxidation of CH₄ to syngas were prepared by electrosynthesis of Rh-containing hydrotalcite-type (HT) compounds on FeCrAlloy foams followed by calcination at 900 °C. During the calcination the simultaneous decomposition of the layered HT structure and formation of the protective FeCrAlloy outer shell in alumina occurred. Here, we studied the role of the coating-metallic support interaction in the properties of the catalysts after calcination, H₂ reduction, and catalytic tests, by a combination of electron (FEG-SEM/EDS) and synchrotron X-ray (XRF/XRPD and XRF/XANES) microscopic techniques. The characterization of crystalline phases in the metallic support and coating and distribution of Rh active species was carried out on several samples prepared by modifying the Rh content in the electrolytic solution (Rh/Mg/Al = 11.0/70.0/19.0, 5.0/70.0/25.0, 0/70.0/30.0 atomic ratio). A sample was also prepared with no aluminum in the electrolytic solution (Rh/Mg/Al = 13.6/86.4/0.0 atomic ratio) and calcined at 550 and 900 °C. The interaction between the elements of the metallic support and the catalytic coating increased the film adhesion during the thermal treatment and catalytic tests and modified the catalyst crystalline phases. A chemical reaction between Al coming from the foam and Mg in the coating occurred during calcination at high temperature leading to the formation of spinel phases in which rhodium is solved, together with some Rh₂O₃ and Rh⁰. The metallic support was oxidized forming the corundum scale and chromium oxides, moreover ι-Al₂O₃ was identified. For the Rh_11.0Mg_70.0Al_19.0 catalyst the inclusion of Rh in the spinel phase decreased its reducibility in the H₂ pretreatment. The reduction continued during catalytic tests by feeding diluted CH₄/O₂/He gas mixtures, evidenced by the catalyst activation. While under concentrated gas mixtures the deactivation occurred, probably by oxidation

Iridium(III) Complexes with Phenyl-tetrazoles as Cyclometalating Ligands

Ir­(III) cationic complexes with cyclometalating tetrazolate ligands were prepared for the first time, following a two-step strategy based on (i) a silver-assisted cyclometalation reaction of a tetrazole derivative with IrCl₃ affording a bis-cyclometalated solvato-complex <b>P</b> ([Ir­(ptrz)₂­(CH₃CN)₂]⁺, Hptrz = 2-methyl-5-phenyl-2<i>H</i>-tetrazole); (ii) a substitution reaction with five neutral ancillary ligands to get [Ir­(ptrz)₂L]⁺, with L = 2,2′-bypiridine (<b>1</b>), 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine (<b>2</b>), 1,10-phenanthroline (<b>3</b>), and 2-(1-phenyl-1<i>H</i>-1,2,3-triazol-4-yl)­pyridine (<b>4</b>), and [Ir­(ptrz)₂L₂]⁺, with L = <i>tert</i>-butyl isocyanide (<b>5</b>). X-ray crystal structures of <b>P</b>, <b>2</b>, and <b>3</b> were solved. Electrochemical and photophysical studies, along with density functional theory calculations, allowed a comprehensive rationalization of the electronic properties of <b>1</b>–<b>5</b>. In acetonitrile at 298 K, complexes equipped with bipyridine or phenanthroline ancillary ligands (<b>1</b>–<b>3</b>) exhibit intense and structureless emission bands centered at around 540 nm, with metal-to-ligand and ligand-to-ligand charge transfer (MLCT/LLCT) character; their photoluminescence quantum yields (PLQYs) are in the range of 55–70%. By contrast, the luminescence band of <b>5</b> is weak, structured, and blue-shifted and is attributed to a ligand-centered (LC) triplet state of the tetrazolate cyclometalated ligand. The PLQY of <b>4</b> is extremely low (<0.1%) since its lowest level is a nonemissive triplet metal-centered (³MC) state. In rigid matrix at 77 K, all of the complexes exhibit intense luminescence. Ligands <b>1</b>–<b>3</b> are also strong emitters in solid matrices at room temperature (1% poly­(methyl methacrylate) matrix and neat films), with PLQYs in the range of 27–70%. Good quality films of <b>2</b> could be obtained to make light-emitting electrochemical cells that emit bright green light and exhibit a maximum luminance of 310 cd m^–2. Tetrazolate cyclometalated ligands push the emission of Ir­(III) complexes to the blue, when compared to pyrazolate or triazolate analogues. More generally, among the cationic Ir­(III) complexes without fluorine substituents on the cyclometalated ligands, <b>1</b>–<b>3</b> exhibit the highest-energy MLCT/LLCT emission bands ever reported