7 research outputs found
Imaging Radial Distribution Functions of Complex Particles by Relayed Dynamic Nuclear Polarization
The physical properties
of many modern multi-component
materials
are determined by their internal microstructure. Tools capable of
characterizing complex nanoscale architectures in composite materials
are, therefore, essential to design materials with targeted properties.
Depending on the morphology and the composition, structures may be
measured by laser diffraction, scattering methods, or by electron
microscopy. However, it can be difficult to obtain contrast in materials
where all the components are organic, which is typically the case
for formulated pharmaceuticals, or multi-domain polymers. In nuclear
magnetic resonance (NMR) spectroscopy, chemical shifts allow a clear
distinction between organic components and can in principle provide
the required chemical contrast. Here, we introduce a method to obtain
radial images of the internal structure of multi-component particles
from NMR measurements of the relay of nuclear hyperpolarization obtained
from dynamic nuclear polarization. The method is demonstrated on two
samples of hybrid core–shell particles composed of a core of
polystyrene with a shell of mesostructured silica filled with the
templating agent CTAB and is shown to yield accurate images of the
core–shell structures with a nanometer resolution
Synthesis and Photocatalytic Activity of Titania Monoliths Prepared with Controlled Macro- and Mesopore Structure
Herein, we report a one-pot synthesis of crack-free titania
monoliths
with hierarchical macro-mesoporosity and crystalline anatase walls.
Bimodal macroporosity is created through the polymer-induced phase
separation of poly(furfuryl alcohol). The cationic polymerization
of furfuryl alcohol is performed in situ and subsequently the polymer
becomes immiscible with the aqueous phase, which includes titanic
acid. Addition of template, Pluronic F127, increases the mesopore
volume and diameter of the resulting titania, as the poly(ethylene
glycol) block interacts with the titania precursor, leading to assisted
assembly of the metal oxide framework. The hydrophobic poly(propylene
glycol) micelle core could itself be swollen with monomeric and oligomeric
furfuryl alcohol, allowing for mesopores as large as 18 nm. Variations
in synthesis parameters affect porosity; for instance furfuryl alcohol
content changes the size and texture of the macropores, water content
changes the grain size of the titania and Pluronic F127 content changes
the size and volume of the mesopore. Morphological manipulation improves
the photocatalytic degradation of methylene blue. Light can penetrate
several millimeters into the porous monolith, giving these materials
possible application in commercial devices
One-Pot Preparation and CO<sub>2</sub> Adsorption Modeling of Porous Carbon, Metal Oxide, and Hybrid Beads
Hierarchically porous carbon (C),
metal oxide (ZrTi), or carbon–metal oxide (CZrTi) hybrid beads
are synthesized in one pot through the in situ self-assembly of Pluronic
F127, titanium and zirconium propoxides, and polyacrylonitrile (PAN).
Upon contact with water, a precipitation of PAN from the liquid phase
occurs concurrently with polymerization and phase separation of the
inorganic precursors. The C, ZrTi, and CZrTi materials have similar
morphologies but different surface chemistries. The adsorption of
carbon dioxide by each material has been studied and modeled using
the Langmuir–Freundlich equation, generating parameters that
are used to calculate the surface affinity distributions. The Langmuir,
Freundlich, Tóth, and Temkin models were also applied but gave
inferior fits, indicating that the adsorption occurred on an inhomogeneous
surface reaching a maximum capacity as available surface sites became
saturated. The carbon beads have higher surface affinity for CO<sub>2</sub> than the hybrid and metal oxide materials
Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane
Crystalline silicon
particles sustaining Mie resonances are readily
obtained from the thermal processing of hydrogen silsesquioxane (HSQ).
Here, the mechanisms involved in silicon particle formation and growth
from HSQ are investigated through real-time in situ analysis using an environmental transmission electron microscope
and X-ray diffractometer. The nucleation of Si nanodomains is observed
starting around 1000 °C. For the first time, a highly mobile
intermediate phase is experimentally observed, thus demonstrating
a previously unknown growth mechanism. At least two growth processes
occur simultaneously: the coalescence of small particles into larger
particles and growth mode by particle displacement through the matrix
toward the HSQ grain surface. Postsynthetic characterization by scanning
electron microscopy further supports the latter growth mechanism.
The gaseous environment employed during synthesis impacts particle
formation and growth under both in situ and ex situ conditions, impacting the particle yield and structural
homogeneity. Understanding the formation mechanisms of particles provides
promising pathways for reducing the energy cost of this synthetic
route
Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane
Crystalline silicon
particles sustaining Mie resonances are readily
obtained from the thermal processing of hydrogen silsesquioxane (HSQ).
Here, the mechanisms involved in silicon particle formation and growth
from HSQ are investigated through real-time in situ analysis using an environmental transmission electron microscope
and X-ray diffractometer. The nucleation of Si nanodomains is observed
starting around 1000 °C. For the first time, a highly mobile
intermediate phase is experimentally observed, thus demonstrating
a previously unknown growth mechanism. At least two growth processes
occur simultaneously: the coalescence of small particles into larger
particles and growth mode by particle displacement through the matrix
toward the HSQ grain surface. Postsynthetic characterization by scanning
electron microscopy further supports the latter growth mechanism.
The gaseous environment employed during synthesis impacts particle
formation and growth under both in situ and ex situ conditions, impacting the particle yield and structural
homogeneity. Understanding the formation mechanisms of particles provides
promising pathways for reducing the energy cost of this synthetic
route
Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane
Crystalline silicon
particles sustaining Mie resonances are readily
obtained from the thermal processing of hydrogen silsesquioxane (HSQ).
Here, the mechanisms involved in silicon particle formation and growth
from HSQ are investigated through real-time in situ analysis using an environmental transmission electron microscope
and X-ray diffractometer. The nucleation of Si nanodomains is observed
starting around 1000 °C. For the first time, a highly mobile
intermediate phase is experimentally observed, thus demonstrating
a previously unknown growth mechanism. At least two growth processes
occur simultaneously: the coalescence of small particles into larger
particles and growth mode by particle displacement through the matrix
toward the HSQ grain surface. Postsynthetic characterization by scanning
electron microscopy further supports the latter growth mechanism.
The gaseous environment employed during synthesis impacts particle
formation and growth under both in situ and ex situ conditions, impacting the particle yield and structural
homogeneity. Understanding the formation mechanisms of particles provides
promising pathways for reducing the energy cost of this synthetic
route
Understanding the Formation Mechanisms of Silicon Particles from the Thermal Disproportionation of Hydrogen Silsesquioxane
Crystalline silicon
particles sustaining Mie resonances are readily
obtained from the thermal processing of hydrogen silsesquioxane (HSQ).
Here, the mechanisms involved in silicon particle formation and growth
from HSQ are investigated through real-time in situ analysis using an environmental transmission electron microscope
and X-ray diffractometer. The nucleation of Si nanodomains is observed
starting around 1000 °C. For the first time, a highly mobile
intermediate phase is experimentally observed, thus demonstrating
a previously unknown growth mechanism. At least two growth processes
occur simultaneously: the coalescence of small particles into larger
particles and growth mode by particle displacement through the matrix
toward the HSQ grain surface. Postsynthetic characterization by scanning
electron microscopy further supports the latter growth mechanism.
The gaseous environment employed during synthesis impacts particle
formation and growth under both in situ and ex situ conditions, impacting the particle yield and structural
homogeneity. Understanding the formation mechanisms of particles provides
promising pathways for reducing the energy cost of this synthetic
route