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
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
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
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
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>-polyÂ(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 RuÂ(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
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
Oxidation of the NADH analogue, <i>N</i>-benzyl-1,4-dihydronicotinamide
(BNAH), by the 1e<sup>–</sup> acceptor, [OsÂ(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 [OsÂ(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
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
The mechanism of electrocatalytic
water oxidation by the water
oxidation catalyst, ruthenium 2,2′-bipyridine-6,6′-dicarboxylate
(bda) bis-isoquinoline (isoq), [RuÂ(bda)Â(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 [RuÂ(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 [RuÂ(4,4′-(PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub>bpy)Â(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
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