20 research outputs found

    Direct Conversion of Sugars and Ethyl Levulinate into γ‑Valerolactone with Superparamagnetic Acid–Base Bifunctional ZrFeO<sub><i>x</i></sub> Nanocatalysts

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    Acid–base bifunctional superparamagnetic FeZrO<sub><i>x</i></sub> nanoparticles were synthesized via a two-step process of solvothermal treatment and hydrolysis–condensation, and were further employed to catalyze the conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) using ethanol as both H-donor and solvent. ZrFeO(1:3)-300 nanoparticles (12.7 nm) with Fe<sub>3</sub>O<sub>4</sub> core covered by ZrO<sub>2</sub> layer (0.65 nm thickness) having well-distributed acid–base sites (0.39 vs 0.28 mmol/g), moderate surface area (181 m<sup>2</sup>/g), pore size (9.8 nm), and strong magnetism (35.4 Am<sup>2</sup> kg<sup>–1</sup>) exhibited superior catalytic performance, giving a high GVL yield of 87.2% at 230 °C in 3 h. The combination of the nanoparticles with solid acid HY2.6 promoted the direct transformation of sugars to produce GVL in moderate yield (around 45%). Moreover, the nanocatalyst was easily recovered by a magnet for six cycles with an average GVL yield of 83.9% from EL

    Amorphous Ge/C Composite Sponges: Synthesis and Application in a High-Rate Anode for Lithium Ion Batteries

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    A Ge/C spongelike composite is prepared by the facile and scalable single-step pyrolysis of the GeO<sub><i>x</i></sub>/ethylenediamine gel process, which has a feature with three-dimensional interconnected pore structures and is hybridized with nitrogen-doped carbon. A detailed investigation shows that the pore in the sponge is formed for the departure of the gaseous products at the evaluated temperature. As an anode for lithium ion batteries, the obtained composite exhibits superior specific capacity in excess of 1016 mA h g<sup>–1</sup> at 100 mA g<sup>–1</sup> after 100 cycles. Moreover, the amorphous Ge/C sponge electrode also has a good rate capacity and stable cycling performance. The obtained amorphous Ge/C sponges are a good candidate anode for next-generation lithium ion batteries

    Mechanical Properties, Electronic Structures, and Potential Applications in Lithium Ion Batteries: A First-Principles Study toward SnSe<sub>2</sub> Nanotubes

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    First-principles calculations were carried out to investigate the mechanical and electronic properties as well as the potential application of SnSe<sub>2</sub> nanotubes. It was found that the mechanical properties are closely dependent on diameter and chirality: the Young’s modulus (<i>Y</i>) increases with the enlargement of diameter and converges to the monolayer limit when the diameter reaches a certain degree; with a comparable diameter, the armchair nanotube has a larger Young’s modulus than the zigzag one. The significantly higher Young’s modulus of SnSe<sub>2</sub> nanotubes with the larger diameter demonstrates that the deformation does not easily occur, which is beneficial to the application as anode materials in lithium ion batteries because a large volume expansion during charge–discharge cycling will result in serious pulverization of the electrodes and thus rapid capacity degradation. On the other hand, band structure calculations unveiled that SnSe<sub>2</sub> nanotubes display a diversity of electronic properties, which are also diameter- and chirality-dependent: armchair nanotubes (ANTs) are indirect bandgap semiconductors, and the energy gaps increase monotonously with the increase of tube diameter, while zigzag nanotubes (ZNTs) are metals. The metallic SnSe<sub>2</sub> ZNTs exhibit terrific performance for the adsorption and diffusion of Li atom, thus they are very promising as anode materials in the Li-ion batteries

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

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    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 TiO<sub>2</sub> 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

    Production of Liquefied Oil Palm Empty Fruit Bunch Based Polyols via Microwave Heating

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    Optimization of microwave-assisted liquefaction of oil palm empty fruit bunch fiber (EFB) and cellulose (EFBC) in ethylene glycol (EG) was carried out to produce polyols. The liquefaction residues and hydroxyl numbers of the resultant polyols from respective sources were studied and compared. EFB produced a minimum residue of 3.22% at the optimal parameters of 160 °C and 15 min. Meanwhile, optimum liquefaction of EFBC produced 1.03% residue at 175 °C and 40 min. The maximum hydroxyl numbers of both EFB (749.22 mg KOH/g) and EFBC (639.91 mg KOH/g) polyols were obtained at optimum conditions. FTIR analysis revealed the degradation mechanism of cellulose and lignin in EFB at different temperatures. Lignin was found to be liquefied easily at lower temperatures (130 and 145 °C). However, most of the cellulose began to be liquefied at the optimum temperature (160 °C) and severely degraded at higher temperatures (175 and 190 °C)

    Multiple Pathways in the Oxidation of a NADH Analogue

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    Oxidation of the NADH analogue, <i>N</i>-benzyl-1,4-dihydronicotinamide (BNAH), by the 1e<sup>–</sup> acceptor, [Os­(dmb)<sub>3</sub>]<sup>3+</sup>, and 2e<sup>–</sup>/2H<sup>+</sup> 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 H<sub>2</sub>Q product. Oxidation by [Os­(dmb)<sub>3</sub>]<sup>3+</sup> occurs by outer-sphere electron transfer including a pathway involving ion-pair preassociation of HPO<sub>4</sub><sup>2–</sup> with the complex that may also involve a concerted proton transfer

    Ultrathin Nanosheets Assembled Hierarchical Co/NiS<sub><i>x</i></sub>@C Hollow Spheres for Reversible Lithium Storage

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    Cobalt sulfides are good candidate anode materials for lithium ion storage for their high theoretical capacities. However, their electrochemical performance is restricted by their volume change during the cycles, leading to a sharp capacity fading in the subsequent process. To overcome these disadvantages, ultrathin nanosheets assembled hierarchical cobalt sulfides@C hollow spheres are fabricated by a hydrothermal and subsequent carbon enwrapping strategy. The as-prepared hierarchical Co<sub>9</sub>S<sub>8</sub>@C hollow spheres deliver an enhanced electrochemical performance with both long-term cyclability and reversible specific capacities. 823 mA h g<sup>–1</sup> reversible capacity could be maintained after 200 cycles at a current density of 100 mA g<sup>–1</sup>. More importantly, the present synthesis strategy shows good generality for the synthesis of nickel sulfide and Ni–Co bimetal sulfides hollow spheres with improved performance in anode materials of lithium ion batteries

    Electron Transfer Mediator Effects in the Oxidative Activation of a Ruthenium Dicarboxylate Water Oxidation Catalyst

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    The mechanism of electrocatalytic water oxidation by the water oxidation catalyst, ruthenium 2,2′-bipyridine-6,6′-dicarboxylate (bda) bis-isoquinoline (isoq), [Ru­(bda)­(isoq)<sub>2</sub>], <b>1</b>, at metal oxide electrodes has been investigated. At indium-doped tin oxide (ITO), diminished catalytic currents and increased overpotentials are observed compared to glassy carbon (GC). At pH 7.2 in 0.5 M NaClO<sub>4</sub>, catalytic activity is enhanced by the addition of [Ru­(bpy)<sub>3</sub>]<sup>2+</sup> (bpy = bipyridine) as a redox mediator. Enhanced catalytic rates are also observed at ITO electrodes derivatized with the surface-bound phosphonic acid derivative [Ru­(4,4′-(PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub>bpy)­(bpy)<sub>2</sub>]<sup>2+</sup>, <b>RuP</b><sup>2+</sup>. Controlled potential electrolysis with measurement of O<sub>2</sub> at ITO with and without surface-bound RuP<sup>2+</sup> confirm that water oxidation catalysis occurs. Remarkable rate enhancements are observed with added acetate and phosphate, consistent with an important mechanistic role for atom-proton transfer (APT) in the rate-limiting step as described previously at GC electrodes

    Soluble Reduced Graphene Oxide Sheets Grafted with Polypyridylruthenium-Derivatized Polystyrene Brushes as Light Harvesting Antenna for Photovoltaic Applications

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    Soluble graphene nanosheets, prepared by grafting polystyrene-based polymer chains from the surface of reduced graphene oxide (RGO), have been functionalized with pendant Ru(II) polypyridine chromophores. <i>N</i>-Hydroxysuccinimide (NHS) derivatized <i>p</i>-vinylbenzoic acid polymer chains were grown from methyl bromoisobutyrate initiation sites on the surface of RGO by atom transfer radical polymerization (ATRP). Deprotection of the resulting NHS polystyrene chains followed by amide coupling with the amine-derivatized Ru(II) polypyridyl complex [Ru(4-CH<sub>2</sub>NH<sub>2</sub>-4′-CH<sub>3</sub>-bpy)(bpy)<sub>2</sub>]<sup>2+</sup> (4-CH<sub>2</sub>NH<sub>2</sub>-4′-CH<sub>3</sub>-bpy = 4-aminomethyl-4′-methyl 2,2′-bipyridine and bpy = 2,2′-bipyridine) afforded the covalently linked RGO-metallopolymer. The hybrid graphene-polymer assembly has been fully characterized with clear evidence for covalent attachment of the metallopolymer brushes to the graphene substrate. On the basis of thermal gravimetric analysis, one polymer strand is grafted to the surface of RGO for every hundred graphene carbons. The covalently linked polymer brushes feature controlled chain lengths of ∼30 repeat units with a small polydispersity index (PDI, ∼ 1.2). Photovoltaic cells based on the derivatized polymers and graphene-polymer assemblies were evaluated. The graphene-polymer assembly in the configuration, ITO/PEDOT:PSS/RGO-PSRu/PC<sub>60</sub>BM/Al, exhibited enhanced photocurrent and power conversion efficiencies (∼5 fold) relative to devices with the configuration, ITO/PEDOT:PSS/PSRu/PC<sub>60</sub>BM/Al
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