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 (ZrO₂) 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 ZrO₂/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 ZrO₂. Treatment of the nanocomposites with phenylphosphonic acid was undertaken and shown to result in robust binding of the phosphonic acid to the surface of ZrO₂ particles. Incorporation of nanoscale ZrO₂ 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 m²/g and a mesopore volume of 0.34 cm³/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 (PbX₂; X = Cl, Br, or I) NWs and conversion to LHP. We present a kinetic model of the PbX₂ 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 PbI₂, we show that the NWs are single-crystalline, oriented in the ⟨1̅21̅0⟩ direction, and composed of a stoichiometric PbI₂ shaft with a spherical Pb tip. Low-temperature vapor-phase intercalation of methylammonium iodide converts the NWs to methylammonium lead iodide (MAPbI₃) 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