6 research outputs found

    Room Temperature Metalation of 2H-TPP Monolayer on Iron and Nickel Surfaces by Picking up Substrate Metal Atoms

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    Here, it is demonstrated, using high-resolution X-ray spectroscopy and density functional theory calculations, that 2<i>H</i>-tetraphenyl porphyrins metalate at room temperature by incorporating a surface metal atom when a (sub)monolayer is deposited on 3d magnetic substrates, such as Fe(110) and Ni(111). The calculations demonstrate that the redox metalation reaction would be exothermic when occurring on a Ni(111) substrate with an energy gain of 0.89 eV upon embedding a Ni adatom in the macrocycle. This is a novel way to form, <i>via</i> chemical modification and supramolecular engineering, 3d-metal–organic networks on magnetic substrates with an intimate bond between the macrocycle molecular metal ion and the substrate atoms. The achievement of a complete metalation by Fe and Ni can be regarded as a test case for successful preparation of spintronic devices by means of molecular-based magnets and inorganic magnetic substrates

    Understanding the Oxygen Evolution Reaction Mechanism on CoO<sub><i>x</i></sub> using <i>Operando</i> Ambient-Pressure X‑ray Photoelectron Spectroscopy

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    Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water-splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active Co<sub>3</sub>O<sub>4</sub>/Co­(OH)<sub>2</sub> biphasic electrocatalyst on Si by means of <i>operando</i> ambient-pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that the catalyst undergoes chemical-structural transformations as a function of the applied anodic potential, with complete conversion of the Co­(OH)<sub>2</sub> and partial conversion of the spinel Co<sub>3</sub>O<sub>4</sub> phases to CoO­(OH) under precatalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core-level regions to emerge under oxygen evolution reaction conditions on CoO­(OH). The <i>operando</i> photoelectron spectra support assignment of these newly observed features to highly active Co<sup>4+</sup> centers under catalytic conditions. Comparison of these results to those from a pure phase spinel Co<sub>3</sub>O<sub>4</sub> catalyst supports this interpretation and reveals that the presence of Co­(OH)<sub>2</sub> enhances catalytic activity by promoting transformations to CoO­(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design

    Silicon Monomer Formation and Surface Patterning of Si(001)‑2 × 1 Following Tetraethoxysilane Dissociative Adsorption at Room Temperature

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    The adsorption of tetraethoxysilane (TEOS, Si­[OC<sub>2</sub>H<sub>5</sub>]<sub>4</sub>) on the Si(001)-2 × 1 surface at 300 K is studied through a joint experimental and theoretical approach, combining scanning tunneling microscopy (STM) and synchrotron radiation X-ray photoelectron spectroscopy (XPS) with first-principles simulations within the density functional theory (DFT). XPS shows that all Si–O bonds within the TEOS molecules are broken upon adsorption, releasing one Si atom per dissociated molecule, while the ethoxy (−OC<sub>2</sub>H<sub>5</sub>) groups form new Si–O bonds with surface Si dimers. A comparison between experimental STM images and DFT adsorption configurations shows that the four ethoxy groups bind to two second-neighbor silicon dimers within the same row, while the released silicon atom is captured as a monomer on an adjacent silicon dimer row. Additionally, the surface displays alternate ethoxy- and Si adatom-covered rows as TEOS coverage increases. This patterning, which spontaneously forms upon TEOS adsorption, can be used as a template for the nanofabrication of one-dimensional self-organized structures on Si(001)-2 × 1

    Gold Nanoparticles Stabilized with Aromatic Thiols: Interaction at the Molecule–Metal Interface and Ligand Arrangement in the Molecular Shell Investigated by SR-XPS and NEXAFS

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    Small gold nanoparticles capped with 4-trimethylsilylethynyl-1-acetylthiobenzene (SEB) were prepared with spherical shape and different mean sizes (5–8 nm). The functionalized gold nanoparticles (AuNPs-SEB) were deposited onto TiO<sub>2</sub> substrates, and the interaction at the molecule–gold interface, the molecular layer thickness, and the ligand organization on the surface of Au nanospheres were investigated by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and angular dependent near edge X-ray absorption spectroscopy (NEXAFS) at the C K-edge. In order to obtain better insight into the molecular shell features, the same measurements were also carried out on a self-assembling monolayer (SAM) of SEB anchored on a “flat” gold surface (Au/Si(111) wafer). The comparison between angular dependent NEXAFS spectra collected on the self-assembling monolayer and AuNPs-SEB allowed for successfully probing the molecular arrangement of SEB molecules on the gold nanospheres surface. Furthermore, DFT calculations on the free SEB molecule as well as bonded to a small cluster of gold atoms were developed. The comparison with experimental results allowed better understanding of the spectroscopic signatures in the experimental absorption spectra and rationalization of the molecular organization in the SAM, NPs having a thin molecular shell, and NPs covered by a thick layer of ligands

    Chemical Bonds and Charge-Transfer Dynamics of a Dye–Hierarchical-TiO<sub>2</sub> Hybrid Interface

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    The adsorption of Zn-tetraphenylporphyrin (ZnTPP) on nanoporous hierarchically organized anatase TiO<sub>2</sub> structures and the properties of the corresponding hybrid interface were studied by synchrotron radiation experiments. The molecular structure, electronic properties, and bonding with nanostructured TiO<sub>2</sub> surfaces were analyzed by photoemission (XPS and UPS) and X-ray absorption spectroscopy (XAS). The charge transfer at the interface was investigated by means of valence band resonant photoemission experiments (ResPES) at the C K-edge. We show that the charge-transfer dynamics between the photoexcited ZnTPP and TiO<sub>2</sub> is strongly influenced by the presence of defects on the TiO<sub>2</sub> surface. On a stoichiometric anatase nanostructure, ZnTPP bonding occurs primarily via carbon atoms belonging to the molecular phenyl rings, and this creates a preferential channel for the charge transfer. This phenomenon is reduced in the case of defective TiO<sub>2</sub> surface, where ZnTPP interacts mainly through the molecule macrocycle. Our results represent a surface science study of the dye molecule behavior on a nanoporous TiO<sub>2</sub> photoanode relevant to dye-sensitized or hybrid solar cell applications, and they show the importance of the surface oxidation state for the charge-transfer process

    Thiol–ene Mediated Neoglycosylation of Collagen Patches: A Preliminary Study

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    Despite the relevance of carbohydrates as cues in eliciting specific biological responses, the covalent surface modification of collagen-based matrices with small carbohydrate epitopes has been scarcely investigated. We report thereby the development of an efficient procedure for the chemoselective neoglycosylation of collagen matrices (patches) via a thiol–ene approach, between alkene-derived monosaccharides and the thiol-functionalized material surface. Synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), Fourier transform-infrared (FT-IR), and enzyme-linked lectin assay (ELLA) confirmed the effectiveness of the collagen neoglycosylation. Preliminary biological evaluation in osteoarthritic models is reported. The proposed methodology can be extended to any thiolated surface for the development of smart biomaterials for innovative approaches in regenerative medicine
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