6 research outputs found
Magnetically Triggered Release From Giant Unilamellar Vesicles: Visualization By Means Of Confocal Microscopy
Magnetically triggered release from magnetic giant unilamellar vesicles (GUVs) loaded with Alexa fluorescent dye was studied by means of confocal laser scanning microscopy (CLSM) under a low-frequency alternating magnetic field (LF-AMF). Core/shell cobalt ferrite nanoparticles coated with rhodamine B isothiocyanate (MP@SiO<sub>2</sub>(RITC)) were prepared and adsorbed on the GUV membrane. The MP@SiO<sub>2</sub>(RITC) location and distribution on giant lipid vesicles were determined by 3D-CLSM projections, and their effect on the release properties and GUV permeability under a LF-AMF was investigated by CLSM time-resolved experiments. We show that the mechanism of release of the fluorescent dye during the LF-AMF exposure is induced by magnetic nanoparticle energy and mechanical vibration, which promote the perturbation of the GUV membrane without its collapse
Understanding the Oxygen Evolution Reaction Mechanism on CoO<sub><i>x</i></sub> using <i>Operando</i> Ambient-Pressure Xāray Photoelectron Spectroscopy
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>/CoĀ(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 CoĀ(OH)<sub>2</sub> and partial conversion of the spinel Co<sub>3</sub>O<sub>4</sub> phases to CoOĀ(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 CoOĀ(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 CoĀ(OH)<sub>2</sub> enhances catalytic activity by promoting transformations
to CoOĀ(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
Gold Nanoparticles Stabilized with Aromatic Thiols: Interaction at the MoleculeāMetal Interface and Ligand Arrangement in the Molecular Shell Investigated by SR-XPS and NEXAFS
Small
gold nanoparticles capped with 4-trimethylsilylethynyl-1-acetylthiobenzene
(SEB) were prepared with spherical shape and different mean sizes
(5ā8 nm). The functionalized gold nanoparticles (AuNPs-SEB)
were deposited onto TiO<sub>2</sub> substrates, and the interaction
at the moleculeāgold 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 āflatā 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
Influence of Multistep Surface Passivation on the Performance of PbS Colloidal Quantum Dot Solar Cells
The
performance of devices containing colloidal quantum dot (CQD)
films is strongly dependent on the surface chemistry of the CQDs they
contain. Multistep surface treatments, which combine two or more strategies,
are important for creating films with high carrier mobility that are
well passivated against trap states and oxidation. Here, we examine
the effect of a number of these surface treatments on PbS CQD films,
including cation exchange to form PbS/CdS core/shell CQDs, and solid-state
ligand-exchange treatments with Cl, Br, I, and 1,2-ethanedithiol (EDT)
ligands. Using laboratory-based and synchrotron-radiation-excited
X-ray photoelectron spectroscopy (XPS), we examine the compositions
of the surface layer before and after treatment, and correlate this
with the performance data and stability in air. We find that halide
ion treatments may etch the CQD surfaces, with detrimental effects
on the air stability and solar cell device performance caused by a
reduction in the proportion of passivated surface sites. We show that
films made up of PbS/CdS CQDs are particularly prone to this, suggesting
Cd is more easily etched from the surface than Pb. However, by choosing
a less aggressive ligand treatment, a good coverage of passivators
on the surface can be achieved. We show that halide anions bind preferentially
to surface Pb (rather than Cd). By isolating the part of XPS signal
originating from the topmost surface layer of the CQD, we show that
air stability is correlated with the total number of passivating agents
(halide + EDT + Cd) at the surface
Fast One-Pot Synthesis of MoS<sub>2</sub>/Crumpled Graphene pān Nanonjunctions for Enhanced Photoelectrochemical Hydrogen Production
Aerosol processing enables the preparation
of hierarchical graphene nanocomposites with special crumpled morphology
in high yield and in a short time. Using modular insertion of suitable
precursors in the starting solution, it is possible to synthesize
different types of graphene-based materials ranging from heteroatom-doped
graphene nanoballs to hierarchical nanohybrids made up by nitrogen-doped
crumpled graphene nanosacks that wrap finely dispersed MoS<sub>2</sub> nanoparticles. These materials are carefully investigated by microscopic
(SEM, standard and HR TEM), diffraction (grazing incidence X-ray diffraction
(GIXRD)) and spectroscopic (high resolution photoemission, Raman and
UVāvisible spectroscopy) techniques, evidencing that nitrogen
dopants provide anchoring sites for MoS<sub>2</sub> nanoparticles,
whereas crumpling of graphene sheets drastically limits aggregation.
The activity of these materials is tested toward the photoelectrochemical
production of hydrogen, obtaining that N-doped graphene/MoS<sub>2</sub> nanohybrids are seven times more efficient with respect to single
MoS<sub>2</sub> because of the formation of local pān MoS<sub>2</sub>/N-doped graphene nanojunctions, which allow an efficient
charge carrier separation
Thiolāene Mediated Neoglycosylation of Collagen Patches: A Preliminary Study
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 thiolāene 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