6 research outputs found
Photoluminescent Nanostructures from Graphite Oxidation
The graphite intercalation compound (GIC) of 3:1 sulfuric
to nitric
acid mixture was used to produce photoluminescent (PL) nanostructures
by oxidizing micrographite, nanographite, nanographite platelets,
onion-like-carbon, and highly oriented pyrolytic graphite. The GIC
used in this work is a Stage I intercalation compound that expands
the graphitic planes to a maximum degree; this expansion was visible
as a blue color for these graphitic materials in suspension with the
GIC solution. The GIC intercalates into the graphitic layers to facilitate
oxidation, resulting in graphite oxide, which may be fully exfoliated
to graphene oxide. This treatment produced carbon nanostructures that
were colloidally stable and photoluminesced across the visible wavelength
range. It was possible to control the PL color of the reaction suspension
by tuning the reaction temperature or reaction time; higher temperatures
or longer reaction times caused a blue shift in the PL wavelength.
Various graphitic oxide nanostructures were observed in the reaction
suspension with increasing reaction time, including nanoribbons, graphene-like
nanoplatelets, and round single-digit nanoparticles. Using separation
methods for a PL orange reaction supernatant solution, it was possible
to isolate individual PL colors spanning the visible wavelength region.
These PL colors exhibit a blue shift in emission wavelength with filters
that decreased in molecular weight or as the migration distanced increased
in a denaturing polyacrylamide gel. Chemical functionalization of
the PL blue carbon product from the oxidation of nanographite platelet
allowed for the fluorescent coating of silica beads
Mesoporous Carbon/Zirconia Composites: A Potential Route to Chemically Functionalized Electrically-Conductive Mesoporous Materials
Mesoporous nanocomposite materials in which nanoscale
zirconia
(ZrO<sub>2</sub>) particles are embedded in the carbon skeleton of
a templated mesoporous carbon matrix were prepared, and the embedded
zirconia sites were used to accomplish chemical functionalization
of the interior surfaces of mesopores. These nanocomposite materials
offer a unique combination of high porosity (e.g., ∼84% void
space), electrical conductivity, and surface tailorability. The ZrO<sub>2</sub>/carbon nanocomposites were characterized by thermogravimetric
analysis, nitrogen-adsorption porosimetry, helium pychnometry, powder
X-ray diffraction, Raman spectroscopy, scanning electron microscopy,
transmission electron microscopy, and X-ray photoelectron spectroscopy.
Comparison was made with templated mesoporous carbon samples prepared
without addition of ZrO<sub>2</sub>. Treatment of the nanocomposites
with phenylphosphonic acid was undertaken and shown to result in robust
binding of the phosphonic acid to the surface of ZrO<sub>2</sub> particles.
Incorporation of nanoscale ZrO<sub>2</sub> surfaces in the mesoporous
composite skeleton offers unique promise as a means for anchoring
organophosphonates inside of pores through formation of robust covalent
Zr–O–P bonds
Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules
Here,
we report the synthesis of surfactant-templated mesoporous carbons
from lignin, which is a biomass-derived polymeric precursor, and their
potential use as a controlled-release medium for functional molecules
such as pharmaceuticals. To the best of our knowledge, this is the
first report on the use of lignin for chemical-activation-free synthesis
of functional mesoporous carbon. The synthesized carbons possess the
pore widths within the range of 2.5–12.0 nm. In this series
of mesoporous carbons, our best result demonstrates a Brunauer–Emmett–Teller
(BET) surface area of 418 m<sup>2</sup>/g and a mesopore volume of
0.34 cm<sup>3</sup>/g, which is twice the micropore volume in this
carbon. Because of the dominant mesoporosity, this engineered carbon
demonstrates adsorption and controlled release of a representative
pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale
utilization of these sustainable mesoporous carbons in applications
involving adsorption, transport, and controlled release of functional
molecules is desired for industrial processes that yield lignin as
a coproduct
Single-Handed Helical Wrapping of Single-Walled Carbon Nanotubes by Chiral, Ionic, Semiconducting Polymers
We establish the requisite design
for aryleneethynylene polymers
that give rise to single-handed helical wrapping of single-walled
carbon nanotubes (SWNTs). Highly charged semiconducting polymers that
utilize either an (<i>R</i>)- or (<i>S</i>)-1,1′-bi-2-naphthol
component in their respective conjugated backbones manifest HRTEM
and AFM images of single-chain-wrapped SWNTs that reveal significant
preferences for the anticipated helical wrapping handedness; statistical
analysis of these images, however, indicates that ∼20% of the
helical structures are formed with the “unexpected”
handedness. CD spectroscopic data, coupled with TDDFT-based computational
studies that correlate the spectral signatures of semiconducting polymer-wrapped
SWNT assemblies with the structural properties of the chiral 1,1′-binaphthyl
unit, suggest strongly that two distinct binaphthalene SWNT binding
modes, <i>cisoid-facial</i> and <i>cisoid-side</i>, are possible for these polymers, with the latter mode responsible
for inversion of helical chirality and the population of polymer-SWNT
superstructures that feature the unexpected polymer helical wrapping
chirality at the nanotube surface. Analogous aryleneethynylene polymers
were synthesized that feature a 2,2′-(1,3-benzyloxy)-<i>bridged</i> (b)-1,1′-bi-2-naphthol unit: this 1,1′-bi-2-naphthol
derivative is characterized by a <i>bridging</i> 2,2′–1,3
benzyloxy tether that restricts the torsional angle between the two
naphthalene subunits along its C1–C1′ chirality axis
to larger, oblique angles that facilitate more extensive van der Waals
contact of the naphthyl subunits with the nanotube. Similar microscopic,
spectroscopic, and computational studies determine that chiral polymers
based on conformationally restricted <i>transoid</i> binaphthyl
units direct preferential <i>facial</i> binding of the polymer
with the SWNT and thereby guarantee helically wrapped polymer-nanotube
superstructures of fixed helical chirality. Molecular dynamics simulations
provide an integrated picture tying together the global helical superstructure
and conformational properties of the binaphthyl units: a robust, persistent
helical handedness is preferred for the conformationally restricted <i>transoid</i> binaphthalene polymer. Further examples of similar
semiconducting polymer-SWNT superstructures are reported that demonstrate
that the combination of single-handed helical wrapping and electronic
structural modification of the conjugated polymer motif opens up new
opportunities for engineering the electro-optic functionality of nanoscale
objects
Silylated Precision Particles for Controlled Release of Proteins
With
the recent advances in the development of novel protein based therapeutics,
controlled delivery of these biologics is an important area of research.
Herein, we report the synthesis of microparticles from bovine serum
albumin (BSA) as a model protein using Particle Replication in Non-wetting
Templates (PRINT) with specific size and shape. These particles were
functionalized at room temperature using multifunctional chlorosilane
that cross-link the particles to render them to slowly-dissolving
in aqueous media. Mass spectrometric study of the reaction products
of diisopropyldichlorosilane with individual components of the particles
revealed that they are capable of reacting and forming cross-links.
Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy
(XPS) were also used to confirm the functionalization of the particles.
Cross sectional analysis using focused ion beam (FIB) and EDS proved
that the functionalization occurs throughout the bulk of the particles
and is not just limited to the surface. Circular dichroism data confirmed
that the fraction of BSA molecules released from the particles retains
its secondary structure thereby indicating that the system can be
used for delivering protein based formulations while controlling the
dissolution kinetics
Self-Catalyzed Vapor–Liquid–Solid Growth of Lead Halide Nanowires and Conversion to Hybrid Perovskites
Lead
halide perovskites (LHPs) have shown remarkable promise for
use in photovoltaics, photodetectors, light-emitting diodes, and lasers.
Although solution-processed polycrystalline films are the most widely
studied morphology, LHP nanowires (NWs) grown by vapor-phase processes
offer the potential for precise control over crystallinity, phase,
composition, and morphology. Here, we report the first demonstration
of self-catalyzed vapor–liquid–solid (VLS) growth of
lead halide (PbX<sub>2</sub>; X = Cl, Br, or I) NWs and conversion
to LHP. We present a kinetic model of the PbX<sub>2</sub> NW growth
process in which a liquid Pb catalyst is supersaturated with halogen
X through vapor-phase incorporation of both Pb and X, inducing growth
of a NW. For PbI<sub>2</sub>, we show that the NWs are single-crystalline,
oriented in the ⟨1̅21̅0⟩ direction, and
composed of a stoichiometric PbI<sub>2</sub> shaft with a spherical
Pb tip. Low-temperature vapor-phase intercalation of methylammonium
iodide converts the NWs to methylammonium lead iodide (MAPbI<sub>3</sub>) perovskite while maintaining the NW morphology. Single-NW experiments
comparing measured extinction spectra with optical simulations show
that the NWs exhibit a strong optical antenna effect, leading to substantially
enhanced scattering efficiencies and to absorption efficiencies that
can be more than twice that of thin films of the same thickness. Further
development of the self-catalyzed VLS mechanism for lead halide and
perovskite NWs should enable the rational design of nanostructures
for various optoelectronic technologies, including potentially unique
applications such as hot-carrier solar cells