Jeffrey Pyun

Graphene Oxide as Catalyst: Application of Carbon Materials beyond Nanotechnology

Since the seminal report by Geim and co-workers, research on graphene and other two-dimensional sp-hybridized carbon nanomaterials has tremendously impacted the areas of modern chemistry, physics, and materials science and engineering. The significant attraction of these materials can be attributed to the outstanding electrical, optical, electrochemical, and mechanical properties of graphene materials, especially in comparison to other carbon materials. Although early routes to these materials were challenging, significant advances in synthetic and processing methods (e.g., synthetic “wet chemistry”, micromechanical exfoliation, oxidation/reduction protocols, epitaxial growth, and vapor deposition) have enabled access to high-quality graphene or chemically modified graphenes (CMGs) in appreciable quantities. Beyond the applications described above, the use of graphene and CMGs as catalysts for facilitating synthetic transformations is a relatively new area with outstanding potential. The use of nanostructured carbon materials (see Figure 1) as both supports and metal-free catalysts has been investigated previously with 1D, 2D, and 3D carbonaceous materials. For example, Su and co-workers elegantly demonstrated that partially oxidized carbon nanotubes (CNTs) were able to catalytically dehydrogenate n-butane to 1-butene, albeit with modest conversion (< 15% after 100 h). Other forms of carbon, including carbon molecular sieves (CMSs), have also been employed in catalytic oxidation reactions, although harsh conditions (200 + 8C and high pressures) were typically required for reasonable conversion. Likewise, natural flake graphite has been shown to catalyze the reduction of a variety of substituted nitrobenzenes to the corresponding anilines (with hydrazine as the terminal reductant). Until now, however, the catalytic application of graphene and CMGs has focused primarily on the use of these materials as supports for catalytically active transition metals. In one such example, M lhaupt and co-workers demonstrated that palladium nanoparticles dispersed on graphite oxide were able to catalyze Suzuki–Miyaura coupling reactions (see Figure 2). Although the catalytic activity of this material was high (turnover frequencies in excess of 39000 h 1 were reported), the supported metal was the active catalyst, not the carbon. Figure 1. Examples of nanostructured carbon materials for applications in catalysis: a) SEM image of mesoporous graphite microfibers of a felt; b) TEM image of multiwalled carbon nanotubes.

Colloidal Polymerization of Polymer- Coated Ferromagnetic Nanoparticles into Cobalt Oxide Nanowires

The preparation of polystyrene-coated cobalt oxide nanowires is reported via the colloidal polymerization of polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs). Using a combination of dipolar nanoparticle assembly and a solution oxidation of preorganized metallic colloids, interconnected nanoparticles of cobalt oxide spanning micrometers in length were prepared. The colloidal polymerization of PS-CoNPs into cobalt oxide (CoO and Co(3)O(4)) nanowires was achieved by bubbling O(2) into PS-CoNP dispersions in 1,2-dichlorobenzene at 175 degrees C. Calcination of thin films of PS-coated cobalt oxide nanowires afforded Co(3)O(4) metal oxide materials. Transmission electron microscopy (TEM) revealed the formation of interconnected nanoparticles of cobalt oxide with hollow inclusions, arising from a combination of dipolar assembly of PS-CoNPs and the nanoscale Kirkendall effect in the oxidation reaction. Using a wide range of spectroscopic and electrochemical characterization techniques, we demonstrate that cobalt oxide nanowires prepared via this novel methodology were electroactive with potential applications as nanostructured electrodes for energy storage.

Nanocomposite Materials from Functional Polymers and Magnetic Colloids

The synthesis of polymer coated magnetic nanoparticles is reviewed. This class of organic/inorganic materials has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. We outline the various approaches that have been investigated to encapsulate discrete magnetic colloids with functional polymer shells. An essential component of this research is the preparation of polymeric surfactants that enable synthesis, passivation, and functionalization of magnetic nanoparticles. Various polymerization techniques, namely, living and controlled polymerizations, such as, ring‐opening metathesis polymerization (ROMP) and controlled radical processes have been applied to synthesize core‐shell colloids possessing tunable film thickness, composition, and properties.

Functionalization of polymers prepared by ATRP using radical addition reactions

Low molecular weight linear poly(methyl acrylate), star and hyperbranched polymers were synthesized using atom transfer radical polymerization (ATRP) and end-functionalized using radical addition reactions. By adding allyltri-n-butylstannane at the end of the polymerization of poly(methyl acrylate), the polymer was terminated by allyl groups. When at high conversions of the acrylate monomer, allyl alcohol or 1,2-epoxy-5-hexene, monomers which are not polymerizable by ATRP, were added, alcohol and epoxy functionalities respectively were incorporated at the polymer chain end. Functionalization by radical addition reactions was demonstrated to be applicable to multi-functional polymers such as hyperbranched and star polymers.

New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated.

Preparation of hyperbranched polyacrylates by atom transfer radical polymerization, 4: The use of zero-valent copper

The addition of zero-valent copper to the self-condensing vinyl polymerization (SCVP) of novel AB* (meth)acrylic monomers using atom transfer radical polymerization (ATRP) catalyst systems has allowed for their successful polymerization. Polymerization under homogeneous and heterogeneous catalyst conditions without additional Cu(0) were unsuccessful. The catalyst system that was designed comprised of Cu(I) bromide, 4,4′-bis(5-nonyl)-2,2′-bipyridine, and Cu(0) metal (powder or turning). From 1H NMR spectroscopy, the degree of branching was estimated for the acrylic polymers, DB = 0.48. The degree of branching could not be determined for methacrylates by this method due to overlapping signals in the 1H NMR spectra.

Synthesis and Colloidal Polymerization of Ferromagnetic Au−Co Nanoparticles into Au−Co3O4 Nanowires

The preparation of cobalt oxide nanowires with gold nanoparticle (AuNP) inclusions (Au-Co(3)O(4) nanowires) via colloidal polymerization of dipolar core-shell NPs is reported. Polystyrene-coated ferromagnetic NPs composed of a dipolar metallic cobalt shell and a gold NP core (PS-AuCoNPs) were synthesized by thermolysis of octacarbonyldicobalt [Co(2)(CO)(8)] in the presence of AuNP seeds and polymeric ligands. The colloidal polymerization process of these dipolar PS-AuCoNPs comprises dipolar nanoparticle assembly and solution oxidation of preorganized NPs to form interconnected cobalt oxide nanowires via the nanoscale Kirkendall effect, with AuNP inclusions in every repeating unit of the one-dimensional mesostructure. Calcination of the polymer-coated nanowires afforded polycrystalline Au-Co(3)O(4) nanowires that were determined to be electroactive. Nanocomposite materials were characterized by transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, and cyclic voltammetry. We demonstrate that the optical and electrochemical properties of Au-Co(3)O(4) nanowires are significantly enhanced in comparison with hollow Co(3)O(4) nanowires prepared via colloidal polymerization.

Lanthanide(III)-Doped Magnetite Nanoparticles

Nearly monodisperse lanthanide-doped magnetite nanoparticles were obtained by thermally decomposing a mixture of Fe(acac)(3) and Ln(acac)(3) (acac = acetylacetonate; Ln = Sm, Eu, Gd) in the presence of passivating surfactants. Magnetic studies revealed room-temperature ferromagnetic behaviors of these doped nanoparticles, distinctly different from those of the undoped parent magnetite or the doped nanoparticles prepared by a coprecipitation method.

Recent approaches for the direct use of elemental sulfur in the synthesis and processing of advanced materials

Elemental sulfur is an abundant and inexpensive material obtained as a by-product of natural-gas and petroleum refining operations. Recently, the need for the development of new energy-storage systems brought into light the potential of sulfur as a high-capacity cathode material in secondary batteries. Sulfur-containing materials were also shown to have useful IR optical properties. These developments coupled with growing environmental concerns related to the global production of excess elemental sulfur have led to a keen interest in its utilization as a feedstock in materials applications. This Minireview focuses on the recent developments on physical and chemical methods for directly processing elemental sulfur to produce functional composites and polymers.

Ferrocene Functional Polymer Brushes on Indium Tin Oxide via Surface-Initiated Atom Transfer Radical Polymerization

The synthesis and electrochemical characterization of ferrocene functional polymethacrylate brushes on indium tin oxide (ITO) electrodes using surface-initiated atom transfer radical polymerization (SI-ATRP) is reported. SI-ATRP of ferrocene-containing methacrylate (FcMA) monomers from a phosphonic acid initiator-modified ITO substrate yielded well-defined homo- and block (co)polymer brushes of varying molar mass (4,000 to 37,000 g/mol). Correlation of both electrochemical properties and brush thicknesses confirmed controlled SI-ATRP from modified ITO surfaces. The preparation of block copolymer brushes with varying sequences of FcMA segments was conducted to interrogate the effects of spacing from the ITO electrode surface on the electrochemical properties of a tethered electroactive film.