13 research outputs found
Structural Study of Pt–Fe Nanoparticles: New Insights into Pt Bimetallic Nanoparticle Formation with Oxidized Fe Species
A combination of
physicochemical methods allowed us to assess a
structure of comparatively monodisperse 3–4 nm Pt–Fe<sub><i>x</i></sub>O<sub><i>y</i></sub> nanoparticles
(NPs) synthesized by thermal decomposition of platinum acetylacetonate
in the presence of iron oxide NPs as an iron source. Unlike traditional
PtFe alloys composed of zerovalent Pt and Fe species with the surface
enriched by Pt atoms, the NPs discussed in this work contain Pt(0)
and oxidized Fe species (most probably Fe<sup>3+</sup> or Fe<sup>2+</sup>) as is proven by X-ray photoelectron spectroscopy (XPS). Angular
dependence XPS measurements demonstrated the absence of the core–shell
structure, although a minor enrichment of the NP surface with Fe species
was observed. High-resolution transmission electron microscopy and
X-ray powder diffraction (XRD) reveal that these Pt–Fe<sub><i>x</i></sub>O<sub><i>y</i></sub> NPs are not
alloys, but consist of different domains; i.e., they have a “cluster-in-cluster”
morphology. A comparison of the XPS and XRD data allowed us to conclude
that the NPs also include amorphous iron oxide. These results allow
better understanding of the mechanism of such NP formation and possible
predictions of their catalytic performance
Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2‑Propanol
Here,
we report transfer hydrogenation of nitroarenes to aminoarenes
using 2-propanol as a hydrogen source and Ag-containing magnetically
recoverable catalysts based on partially reduced graphene oxide (pRGO)
sheets. X-ray diffraction and X-ray photoelectron spectroscopy data
demonstrated that, during the one-pot catalyst synthesis, formation
of magnetite nanoparticles (NPs) is accompanied by the reduction of
graphene oxide (GO) to pRGO. The formation of Ag<sup>0</sup> NPs on
top of magnetite nanoparticles does not change the pRGO structure.
At the same time, the catalyst structure is further modified during
the transfer hydrogenation, leading to a noticeable increase of sp<sup>2</sup> carbons. These carbons are responsible for the adsorption
of substrate and intermediates, facilitating a hydrogen transfer from
Ag NPs and creating synergy between the components of the catalyst.
The nitroarenes with electron withdrawing and electron donating substituents
allow for excellent yields of aniline derivatives with high regio
and chemoselectivity, indicating that the reaction is not disfavored
by these functionalities. The versatility of the catalyst synthetic
protocol was demonstrated by a synthesis of an Ru-containing graphene
derivative based catalyst, also allowing for efficient transfer hydrogenation.
Easy magnetic separation and stable catalyst performance in the transfer
hydrogenation make this catalyst promising for future applications
Coat Protein-Dependent Behavior of Poly(ethylene glycol) Tails in Iron Oxide Core Virus-like Nanoparticles
Here we explore the formation of
virus-like nanoparticles (VNPs) utilizing 22–24 nm iron oxide
nanoparticles (NPs) as cores and proteins derived from viral capsids
of brome mosaic virus (BMV) or hepatitis B virus (HBV) as shells.
To accomplish that, hydrophobic FeO/Fe<sub>3</sub>O<sub>4</sub> NPs
prepared by thermal decomposition of iron oleate were coated with
poly(maleic acid-<i>alt</i>-octadecene) modified with poly(ethylene
glycol) (PEG) tails of different lengths and grafting densities. MRI
studies show high <i>r</i><sub>2</sub>/<i>r</i><sub>1</sub> relaxivity ratios of these NPs that are practically
independent of the polymer coating type. The versatility and flexibility
of the viral capsid protein are on display as they readily form shells
that exceed their native size. The location of the long PEG tails
upon shell formation was investigated by electron microscopy and small-angle
X-ray scattering. PEG tails were located differently in the BMV and
HBV VNPs, with the BMV VNPs preferentially entrapping the tails in
the interior and the HBV VNPs allowing the tails to extend through
the capsid, which highlights the differences between intersubunit
interactions in these two icosahedral viruses. The robustness of the
assembly reaction and the protruding PEG tails, potentially useful
in modulating the immune response, make the systems introduced here
a promising platform for biomedical applications
Viruslike Nanoparticles with Maghemite Cores Allow for Enhanced MRI Contrast Agents
Here, for the first time, we demonstrate
formation of virus-like
nanoparticles (VNPs) utilizing gold-coated iron oxide nanoparticles
as cores and capsid protein of brome mosaic virus (BMV) or hepatitis
B virus (HBV) as shells. Further, utilizing cryo-electron microscopy
and single particle methods, we are able to show that the BMV coat
on VNPs assembles into a structure very close to that of a native
virion. This is a consequence of an optimal iron oxide NP size (∼11
nm) fitting the virus cavity and an ultrathin gold layer on the maghemite
cores, which allows for utilization of SH-(CH<sub>2</sub>)<sub>11</sub>-(CH<sub>2</sub>-CH<sub>2</sub>-O)<sub>4</sub>-OCH<sub>2</sub>-COOH
as capping molecules to provide sufficient stability, charge density,
and small form factor. MRI studies show unique relaxivity ratios that
diminish only slightly with gold coating. A virus protein coating
of a magnetic core mimicking the wild-type virus makes these VNPs
a versatile platform for biomedical applications
Functionalization of Monodisperse Iron Oxide NPs and Their Properties as Magnetically Recoverable Catalysts
Here we report the functionalization of monodisperse
iron oxide
nanoparticles (NPs) with commercially available functional acids containing
multiple double bonds such as linolenic (LLA) and linoleic (LEA) acids
or pyridine moieties such as 6-methylpyridine-2-carboxylic acid, isonicotinic
acid, 3-hydroxypicolinic acid, and 6-(1-piperidinyl)pyridine-3-carboxlic
acid (PPCA). Both double bonds and pyridine groups can be reacted
with noble metal compounds to form catalytically active species in
the exterior of magnetic NPs, thus making them promising magnetically
recoverable catalysts. We determined that both LLA and LEA stabilize
magnetic iron oxide NPs, allowing the formation of π-complexes
with bis(acetonitrile)dichloropalladium(II) in the NP shells. In both
cases, this leads to the formation of NP aggregates because of interparticle
complexation. In the case of pyridine-containing ligands, only PPCA
with two N-containing rings is able to provide NP stabilization and
functionalization whereas other pyridine-containing acids did now
allow sufficient steric stabilization. The interaction of PPCA-based
particles with Pd acetate also leads to aggregation because of interparticle
interactions, but the aggregates that are formed are much smaller.
Nevertheless, the catalytic properties in the selective hydrogenation
of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol were the
best for the catalyst based on LLA, demonstrating that the NP aggregates
in all cases are penetrable for DMEC. Easy magnetic separation of
this catalyst from the reaction solution makes it promising as a magnetically
recoverable catalyst
Insights into Sustainable Glucose Oxidation Using Magnetically Recoverable Biocatalysts
Here,
we developed magnetically recoverable biocatalysts for enzymatic
oxidation of d-glucose to d-gluconic acid with high
product yields. The catalyst support is based on nanoparticle clusters
(NPCs) composed of magnetite particles and coated with the amino terminated
silica layer to facilitate further functionalization. It involves
the attachment of the glutaraldehyde linker followed by the covalent
attachment of glucose oxidase (GOx) via its amino groups. It was established
that the NPCs with a diameter of ∼430 nm attach 33% more GOx
molecules than NPCs with a diameter of ∼285 nm, although the
surface area of the former is lower than that of the latter. At the
same time, the biocatalyst based on the smaller NPCs shows higher
relative activity of 94% than that (87%) of the biocatalyst based
on the larger NPCs, both at 50 °C and pH 7 (optimal reaction
conditions). This surprising result has been explained by a combination
of two major factors such as GOx crowding on the support surface which
should prevent denaturation (similar to the enzyme behavior in cells)
and the enzyme mobility which should be preserved upon immobilization.
Apparently, for the biocatalyst based on 285 nm NPCs, the lower GOx
crowding is compensated by its higher mobility. The high stability
of these GOx based biocatalysts in 10 consecutive reactions as well
as facile magnetic recovery combined with excellent catalytic activity
in “tolerant” pH range make this biocatalyst design
promising for other types of enzymatic catalysts
Multifunctional Nanohybrids by Self-Assembly of Monodisperse Iron Oxide Nanoparticles and Nanolamellar MoS<sub>2</sub> Plates
Here, we report the synthesis, characterization,
and properties
of novel nanohybrids formed by self-assembly of negatively charged
MoS<sub>2</sub> nanoplates and positively charged iron oxide nanoparticles
(NPs) of two different sizes, 5.1 and 11.6 nm. Iron oxide NPs were
functionalized with an amphiphilic random copolymer, quaternized poly(2-(dimethylamino)ethyl
metacrylate-<i>co</i>-stearyl metacrylate), synthesized
for the first time using atom transfer radical polymerization. The
influence of the MoS<sub>2</sub> fraction and the iron oxide NP size
on the structure of the nanohybrids has been studied. Surprisingly,
larger NPs retained a larger fraction of the copolymer, thus requiring
more MoS<sub>2</sub> nanoplates for charge compensation. The nanohybrid
based on 11.6 nm NPs was studied in oxidation of sulfide ions. This
reaction could be used for removing the dangerous pollutant from wastewater
and in the production of hydrogen from water using solar energy. We
demonstrated a higher catalytic activity of the NP/MoS<sub>2</sub> nanohybrid than that of merely dispersed MoS<sub>2</sub> in catalytic
oxidation of sulfide ions and facile magnetic recovery of the catalyst
after the reaction
Multicore Iron Oxide Mesocrystals Stabilized by a Poly(phenylenepyridyl) Dendron and Dendrimer: Role of the Dendron/Dendrimer Self-Assembly
We report the formation of multicore
iron oxide mesocrystals using
the thermal decomposition of iron acetyl acetonate in the presence
of the multifunctional and rigid poly(phenylenepyridyl) dendron and
dendrimer. We thoroughly analyze the influence of capping molecules
of two different architectures and demonstrate for the first time
that dendron/dendrimer self-assembly leads to multicore morphologies.
Single-crystalline ordering in multicore NPs leads to cooperative
magnetic behavior: mesocrystals exhibit ambient blocking temperatures,
allowing subtle control over magnetic properties using a minor temperature
change
Multicore Iron Oxide Mesocrystals Stabilized by a Poly(phenylenepyridyl) Dendron and Dendrimer: Role of the Dendron/Dendrimer Self-Assembly
We report the formation of multicore
iron oxide mesocrystals using
the thermal decomposition of iron acetyl acetonate in the presence
of the multifunctional and rigid poly(phenylenepyridyl) dendron and
dendrimer. We thoroughly analyze the influence of capping molecules
of two different architectures and demonstrate for the first time
that dendron/dendrimer self-assembly leads to multicore morphologies.
Single-crystalline ordering in multicore NPs leads to cooperative
magnetic behavior: mesocrystals exhibit ambient blocking temperatures,
allowing subtle control over magnetic properties using a minor temperature
change
Metal-Ion Distribution and Oxygen Vacancies That Determine the Activity of Magnetically Recoverable Catalysts in Methanol Synthesis
Here,
we report on the development of novel Zn-, Zn–Cr-, and Zn–Cu-containing
catalysts using magnetic silica (Fe<sub>3</sub>O<sub>4</sub>–SiO<sub>2</sub>) as the support. Transmission electron microscopy, powder
X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) showed
that the iron oxide nanoparticles are located in mesoporous silica
pores and the magnetite (spinel) structure remains virtually unchanged
despite the incorporation of Zn and Cr. According to XPS data, the
Zn and Cr species are intermixed within the magnetite structure. In
the case of the Zn–Cu-containing catalysts, a separate Cu<sub>2</sub>O phase was also observed along with the spinel structure.
The catalytic activity of these catalysts was tested in methanol synthesis
from syngas (CO + H<sub>2</sub>). The catalytic experiments showed
an improved catalytic performance of Zn- and Zn–Cr-containing
magnetic silicas compared to that of the ZnO–SiO<sub>2</sub> catalyst. The best catalytic activity was obtained for the Zn–Cr-containing
magnetic catalyst prepared with 1 wt % Zn and Cr each. X-ray absorption
spectroscopy demonstrated the presence of oxygen vacancies near Fe
and Zn in Zn-containing, and even more in Zn–Cr-containing,
magnetic silica (including oxygen vacancies near Cr ions), revealing
a correlation between the catalytic properties and oxygen vacancies.
The easy magnetic recovery, robust synthetic procedure, and high catalytic
activity make these catalysts promising for practical applications