Oxidation of Phenol by Tris(1,10-phenanthroline)osmium(III)

Outer-sphere oxidation of phenols is under intense scrutiny because of questions related to the dynamics of proton-coupled electron transfer (PCET). Oxidation by cationic transition-metal complexes in aqueous solution presents special challenges because of the potential participation of the solvent as a proton acceptor and of the buffers as general base catalysts. Here we report that oxidation of phenol by a deficiency of [Os­(phen)₃]³⁺, as determined by stopped-flow spectrophotometry, yields a unique rate law that is second order in [osmium­(III)] and [phenol] and inverse second order in [osmium­(II)] and [H⁺]. A mechanism is inferred in which the phenoxyl radical is produced through a rapid PCET preequilibrium, followed by rate-limiting phenoxyl radical coupling. Marcus theory predicts that the rate of electron transfer from phenoxide to osmium­(III) is fast enough to account for the rapid PCET preequilibrium, but it does not rule out the intervention of other pathways such as concerted proton–electron transfer or general base catalysis

Proton-Coupled Electron Transfer Reduction of a Quinone by an Oxide-Bound Riboflavin Derivative

The redox properties of a surface-bound phosphate flavin derivative (flavin mononucleotide, FMN) have been investigated on planar-FTO and <i>nano</i>ITO electrodes under acidic conditions in 1:1 CH₃CN/H₂O (V:V). On FTO, reversible 2e^–/2H⁺ reduction of FTO|-FMN to FTO|-FMNH₂ occurs with the pH and scan rate dependence expected for a 2e^–/2H⁺ surface-bound couple. The addition of tetramethylbenzoquinone (Me₄Q) results in rapid electrocatalyzed reduction to the hydroquinone by a pathway first order in quinone and first order in acid with <i>k</i>_H = (2.6 ± 0.2) × 10⁶ M^–1 s^–1. Electrocatalytic reduction of the quinone also occurs on derivatized, high surface area <i>nano</i>ITO electrodes with evidence for competitive rate-limiting diffusion of the quinone into the mesoporous nanostructure

Hydrogen Bond-Regulated Boron Nitride Network Structures for Improved Thermal Conductive Property of Polyamide-imide Composites

Highly thermal conductive polymer composites with minimized content of fillers are desirable for handling the issue in thermal management in modern electronics. However, the difficulty of filler dispersion restricts the heat dissipation performance of thermoplastic composites and the intermolecular interaction is another crucial factor in this problem. In the present study, the hydrogen bond was used to regulate the formation of the three-dimensional boron nitride (3D BN) interconnected network to act as a high thermal conductive network in thermoplastic polyamide-imide (PAI) materials. The prepared electrical insulated PAI/3D–BN composites have a thermal conductivity (TC) of 1.17 W·m^–1·K^–1 at a low BN loading of 4 wt %/2 vol % and exhibit a thermal conductivity enhancement of 409%. We attribute the increased TC to the construction of 3D BN interconnected network and the hydrogen bond regulated between hydroxylated BN and polyvinyl alcohol, in which an effective thermal conductive network is constructed. This study provides a guided hydrogen bond strategy for thermally conductive polymer composites with good mechanical and electrical insulation properties in thermal management and other applications

Significant Enhancement of Thermal Conductivity in Nanofibrillated Cellulose Films with Low Mass Fraction of Nanodiamond

High thermal conductive nanofibrillated cellulose (NFC) hybrid films based on nanodiamond (ND) were fabricated by a facile vacuum filtration technique. In this issue, the thermal conductivity (TC) on the in-plane direction of the NFC/ND hybrid film had a significant enhancement of 775.2% at a comparatively low ND content (0.5 wt %). The NFC not only helps ND to disperse in the aqueous medium stably but also plays a positive role in the formation of the hierarchical structure. ND could form a thermal conductive pathway in the hierarchical structures under the intermolecular hydrogen bonds. Moreover, the hybrid films composed of zero-dimensional ND and one-dimensional NFC exhibit remarkable mechanical properties and optical transparency. The NFC/ND hybrid films possessing superior TC, mechanical properties, and optical transparency can open applications for portable electronic equipment as a lateral heat spreader

Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management

An anisotropic thermally conductive film with tailorable microstructures and macroproperties is fabricated using a layer-by-layer (LbL) assembly of graphene oxide (GO) and nanofibrillated cellulose (NFC) on a flexible NFC substrate driven by hydrogen bonding interactions, followed by chemical reduction process. The resulting NFC/reduced graphene oxide (RGO) hybrid film reveals an orderly hierarchical structure in which the RGO nanosheets exhibit a high degree of orientation along the in-plane direction. The assembly cycles dramatically increase the in-plane thermal conductivity (λ_<i>X</i>) of the hybrid film to 12.6 W·m^–1·K^–1, while the cross-plane thermal conductivity (λ_<i>Z</i>) shows a lower value of 0.042 W·m^–1·K^–1 in the hybrid film with 40 assembly cycles. The thermal conductivity anisotropy reaches up to λ_<i>X</i>/λ_<i>Z</i> = 279, which is substantially larger than that of similar polymeric nanocomposites, indicating that the LbL assembly on a flexible NFC substrate is an efficient technique for the preparation of polymeric nanocomposites with improved heat conducting property. Moreover, the layered hybrid film composed of 1D NFC and 2D RGO exhibits synergetic mechnical properties with outstanding flexibility and a high tensile strength (107 MPa). The combination of anisotropic thermal conductivity and superior mechanical performance may facilitate the applications in thermal management

High Surface Area Antimony-Doped Tin Oxide Electrodes Templated by Graft Copolymerization. Applications in Electrochemical and Photoelectrochemical Catalysis

Mesoporous ATO nanocrystalline electrodes of micrometer thicknesses have been prepared from ATO nanocrystals and the grafted copolymer templating agents poly vinyl chloride-<i>g</i>-poly­(oxyethylene methacrylate). As-obtained electrodes have high interfacial surface areas, large pore volumes, and rapid intraoxide electron transfer. The resulting high surface area materials are useful substrates for electrochemically catalyzed water oxidation. With thin added shells of TiO₂ deposited by atomic layer deposition (ALD) and a surface-bound Ru­(II) polypyridyl chromophore, they become photoanodes for hydrogen generation in the presence of a reductive scavenger

Multiple Pathways in the Oxidation of a NADH Analogue

Oxidation of the NADH analogue, <i>N</i>-benzyl-1,4-dihydronicotinamide (BNAH), by the 1e^– acceptor, [Os­(dmb)₃]³⁺, and 2e^–/2H⁺ acceptor, benzoquinone (Q), has been investigated in aqueous solutions over extended pH and buffer concentration ranges by application of a double-mixing stopped-flow technique in order to explore the redox pathways available to this important redox cofactor. Our results indicate that oxidation by quinone is dominated by hydride transfer, and a pathway appears with added acids involving concerted hydride-proton transfer (HPT) in which synchronous transfer of hydride to one O-atom at Q and proton transfer to the second occurs driven by the formation of the stable H₂Q product. Oxidation by [Os­(dmb)₃]³⁺ occurs by outer-sphere electron transfer including a pathway involving ion-pair preassociation of HPO₄^2– with the complex that may also involve a concerted proton transfer

Thermal Conductive and Mechanical Properties of Polymeric Composites Based on Solution-Exfoliated Boron Nitride and Graphene Nanosheets: A Morphology-Promoted Synergistic Effect

In this work, we reported a synergistic effect of boron nitride (BN) with graphene nanosheets on the enhancement of thermal conductive and mechanical properties of polymeric composites. Here, few layered BN (s-BN) and graphene (s-GH) were used and obtained by liquid exfoliation method. The polystyrene (PS) and polyamide 6 (PA) composites were obtained via solution blending method and subsequently hot-pressing. The experimental results suggested that the thermal conductivity (TC) of the PS and PA composites increases with additional introduction of s-BN. For example, compared with the composites containing 20 wt % s-GH, additional introduction of only 1.5 wt % s-BN could increase the TC up to 38 and 34% in polystyrene (PS) and polyamide 6 (PA) matrix, respectively. Meanwhile, the mechanical properties of the composites were synchronously enhanced. It was found that s-BN filled in the interspaces of s-GH sheets and formed s-BN/s-GH stacked structure, which were helpful for the synchronously improving TC and mechanical properties of the polymeric materials

Effect of Covalent-Functionalized Graphene Oxide with Polymer and Reactive Compatibilization on Thermal Properties of Maleic Anhydride Grafted Polypropylene

The covalent functionalization of graphene oxide (GO) with bis­(3-aminopropyl)-terminated poly­(ethylene glycol) (NH₂–PEG–NH₂) and subsequent grafting with maleic anhydride grafted polypropylene (MAPP) oligomer matrix using reactive compatibilization were carefully analyzed and verified through detailed investigations. Improvements in the compatibility between the modified GO and the matrix, thermal stability, flame properties, and crystallization properties were achieved through the addition of a small amount of GO-grafted MAPP (PP-<i>g</i>-GO). Results of thermogravimetric and microscale combustion calorimetry analyses revealed an increase in <i>T</i>_max by 51 °C and reductions in the total heat release and peak heat release rate by 44.4% and 38.9%, respectively, upon the addition of 2.0 wt % PP-<i>g</i>-GO relative to pure MAPP. The approach used in this work is an efficient strategy for improving the thermal behavior of polypropylene oligomer with a view toward extending its use in advanced technological applications