10 research outputs found
Water Dispersal and Functionalization of Hydrophobic Iron Oxide Nanoparticles with Lipid-Modified Poly(amidoamine) Dendrimers
A novel and facile method for water
dispersal of hydrophobic iron
oxide nanoparticles based on the amphiphilic PAMAM-C<sub>12</sub> dendrimer
is described. Stable and highly concentrated water dispersions of
multifunctional magnetic nanoparticles were obtained with this single-step
approach, and showed interesting relaxometric properties for MRI applications.
Importantly, this method does not require substitution of the native
hydrophobic capping under nonmild reaction conditions, thus preserving
the structural and magnetic properties of the nanoparticles, and extending
the possibility of conjugation with thermally labile groups
Mechanochemical Synthesis and Three-Dimensional Electron Diffraction Structure Solution of a Novel Cu-Based Protocatechuate MetalâOrganic Framework
Mechanochemical synthesis
is a powerful approach to obtain new
materials, limiting costs, and times. However, defected and submicrometrical-sized
crystal products make critical their characterization through classical
single-crystal X-ray diffraction. A valid alternative is represented
by three-dimensional (3D) electron diffraction, in which a transmission
electron microscope is used, like a diffractometer. This work matches
a green water-based mechanochemical synthesis and 3D electron diffraction
to obtain and characterize a Cu-based protocatechuate metalâorganic
framework (PC-MOF). Its structure has been fully refined through dynamical
diffraction theory, and free water molecules could be detected in
the channels of the framework. Thermal characterization, focused on
the dehydration profile determination, leads to the formation of a
novel high-temperature 2D coordination polymer, fully solved with
3D electron diffraction data. At last, the strong activity of the
PC-MOF against cationic dyes like methylene blue has been reported
Conducting Shrinkable Nanocomposite Based on Au-Nanoparticle Implanted Plastic Sheet: Tunable Thermally Induced Surface Wrinkling
A thermally shrinkable and conductive
nanocomposite material is prepared by supersonic cluster beam implantation
(SCBI) of neutral Au nanoparticles (Au NPs) into a commercially available
thermo-retractable polystyrene (PS) sheet. Micronanowrinkling is obtained
during shrinking, which is studied by means of SEM, TEM and AFM imaging.
Characteristic periodicity is determined and correlated with nanoparticle
implantation dose, which permits us to tune the topographic pattern.
Remarkable differences emerged with respect to the well-known case
of wrinkling of bilayer metalâpolymer. Wrinkled composite surfaces
are characterized by a peculiar multiscale structuring that promises
potential technological applications in the field of catalytic surfaces,
sensors, biointerfaces, and optics, among others
Texture and Phase Recognition Analysis of ÎČâNaYF<sub>4</sub> Nanocrystals
Texture
and phase recognition analysis (TPRA) based on electron
nanodiffraction technique is used to characterize the geometry of
up-conversion nanocrystals (UCNCs) synthesized by the common thermal-decomposition
protocol in the presence of a stoichiometric amount of NH<sub>4</sub>F. Here, we confirmed experimentally that despite the apparently
different shapes of samples (hexagons, rods, and cubes), all the nanocrystals
are actually ÎČ-phase hexagonal prisms. This is of relevance
since many biological features of nanostructures, such as cellular
internalization and cytotoxicity, are governed by their geometry.
In addition, reproducibility in biological experiments is paramount
Eu Incorporation into SolâGel Silica for Photonic Applications: Spectroscopic and TEM Evidences of αâQuartz and Eu Pyrosilicate Nanocrystal Growth
The problem of Eu
incorporation into silica as dispersed dopants,
clusters, separate-phase nanoparticles, or nanocrystals, which is
of key importance for applications in the fields of lasers and scintillators,
is faced by applying to solâgel silica doped with nine different
Eu<sup>3+</sup> concentrations (0.001â10 mol % range) various
spectroscopic techniques, including crystal field and vibrational
mode analysis by means of Fourier transform absorption and microreflectivity
(in the 200â6000 cm<sup>â1</sup> and 9â300 K
ranges), radioluminescence, and Raman scattering studies at 300 K.
The variety of methods revealed the following concordant results:
(1) amorphous Eu clusters grow when the Eu concentration is increased
up to 3 mol % and (2) SiâOH groups are completely removed and
ordered phase separation occurs at 10 mol % doping, as suggested by
the remarkable narrowing of the spectral lines. Comparison with polycrystalline
Eu oxide, Eu silicates, and α-quartz spectra allowed the unequivocal
identification of Eu<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> pyrosilicate
and α-quartz as the main components of nanocrystals in 10 mol
% Eu-doped silica. Such conclusions were brilliantly confirmed by
transmission electron microscopy and electron diffraction analysis.
Phonon coupling and anharmonicity were analyzed and are discussed
for a few vibrational modes of nanocrystals
Catalyst Composition Tuning: The Key for the Growth of Straight Axial Nanowire Heterostructures with Group III Interchange
Au-catalyzed
IIIâV nanowire heterostructures based on the group III interchange
usually grow straight only in one of the two growth sequences, whereas
the other sequence produces kinked geometries; thus, the realization
of double heterostructures remains challenging. Here, we investigate
the growth of Au-assisted InAsâGaAs and GaAsâInAs axial
nanowire heterostructures. A detailed study of the heterostructure
morphology as a function of growth parameters and chemical composition
of the catalyst nanoparticle is performed by means of scanning electron
microscopy, transmission electron microscopy, and energy-dispersive
X-ray analysis. Our results clearly demonstrate that the nanoparticle
composition, rather than other growth parameters, as postulated so
far, controls the growth mode and the resulting nanowire morphology.
Although GaAs easily grows straight on InAs, straight growth of InAs
on GaAs is achieved only if the nanoparticle composition is properly
tuned. We find that straight InAs segments on GaAs require high group
III-to-Au ratios in the nanoparticle (greater than 0.8); otherwise,
the droplet wets the sidewalls and the nanowire kinks. We discuss
the observed behavior within a theoretical model that relates the
nanoparticle stability to the group III-to-Au ratio. Based on this
finding, we demonstrate the growth of straight nanowire heterostructures
for both sequences. The proposed strategy can be extended to other
IIIâV nanowire heterostructures based on the group III interchange,
allowing for straight morphology regardless of the growth sequence,
and ultimately for designing nanowire heterostructures with the required
properties for different applications
Ionic Strength Responsive Sulfonated Polystyrene Opals
Stimuli-responsive
photonic crystals (PCs) represent an intriguing class of smart materials
very promising for sensing applications. Here, selective ionic strength
responsive polymeric PCs are reported. They are easily fabricated
by partial sulfonation of polystyrene opals, without using toxic or
expensive monomers and etching steps. The color of the resulting hydrogel-like
ordered structures can be continuously shifted over the entire visible
range (405â760 nm) by changing the content of ions over an
extremely wide range of concentration (from about 70 ÎŒM to 4
M). The optical response is completely independent from pH and temperature,
and the initial color can be fully recovered by washing the sulfonated
opals with pure water. These new smart photonic materials could find
important applications as ionic strength sensors for environmental
monitoring as well as for healthcare screening
<i>Ab Initio</i> Structure Determination of Cu<sub>2â<i>x</i></sub>Te Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging
We
investigated pseudo-cubic Cu<sub>2â<i>x</i></sub>Te nanosheets using electron diffraction tomography and high-resolution
HAADF-STEM imaging. The structure of this metastable nanomaterial,
which has a strong localized surface plasmon resonance in the near-infrared
region, was determined <i>ab initio</i> by 3D electron diffraction
data recorded in low-dose nanobeam precession mode, using a new generation
background-free single-electron detector. The presence of two different,
crystallographically defined modulations creates a 3D connected vacancy
channel system, which may account for the strong plasmonic response
of this material. Moreover, a pervasive rotational twinning is observed
for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry
Ultrafast Electron Diffraction Tomography for Structure Determination of the New Zeolite ITQ-58
In
this work a new ultrafast data collection strategy for electron
diffraction tomography is presented that allows reducing data acquisition
time by one order of magnitude. This methodology minimizes the radiation
damage of beam-sensitive materials, such as microporous materials.
This method, combined with the precession of the electron beam, provides
high quality data enabling the determination of very complex structures.
Most importantly, the implementation of this new electron diffraction
methodology is easily affordable in any modern electron microscope.
As a proof of concept, we have solved a new highly complex zeolitic
structure named ITQ-58, with a very low symmetry (triclinic) and a
large unit cell volume (1874.6 Ă
<sup>3</sup>), containing 16
silicon and 32 oxygen atoms in its asymmetric unit, which would be
very difficult to solve with the state of the art techniques
An Advanced Lithium-Ion Battery Based on a Graphene Anode and a Lithium Iron Phosphate Cathode
We report an advanced lithium-ion
battery based on a graphene ink
anode and a lithium iron phosphate cathode. By carefully balancing
the cell composition and suppressing the initial irreversible capacity
of the anode in the round of few cycles, we demonstrate an optimal
battery performance in terms of specific capacity, that is, 165 mAhg<sup>â1</sup>, of an estimated energy density of about 190 Wh kg<sup>â1</sup> and a stable operation for over 80 chargeâdischarge
cycles. The components of the battery are low cost and potentially
scalable. To the best of our knowledge, complete, graphene-based,
lithium ion batteries having performances comparable with those offered
by the present technology are rarely reported; hence, we believe that
the results disclosed in this work may open up new opportunities for
exploiting graphene in the lithium-ion battery science and development