6 research outputs found
Le regole del gioco: Primo incontro con l'ingegneria strategica
Cu particles decorated carbon composite
microspheres (CCMs) with
a unique sesame ball structure have been prepared by combining the
mass-producible spray drying technique with calcinations. The conventional
cuprammonium cellulose complex solution obtained by dissolving cellulose
in a cuprammonia solution has been applied as raw materials for the
preparation of CuÂ(NH<sub>3</sub>)<sub>4</sub><sup>2+</sup>/cellulose
complex microspheres via a spray drying process. The resulted CuÂ(NH<sub>3</sub>)<sub>4</sub><sup>2+</sup>/cellulose complex microspheres
are then transformed into the Cu particles homogeneously decorated
porous carbon spheres <i>in situ</i> by calcinations at
450 or 550 °C. The coordination effect between the CuÂ(NH<sub>3</sub>)<sub>4</sub><sup>2+</sup> species and the hydroxyl groups
of the cellulose macromolecules has been exploited for directing the
dispersion of the Cu particles in the resultant composite CCMs. The
antimicrobial effects of the CCMs are evaluated by determining the
minimum growth inhibitory concentrations using Staphylococcus
aureus and Escherichia coli as representatives, respectively. The CCMs show high efficiency
catalytic properties to the conversion of 4-nitrophenol to 4-aminophenol
using NaBH<sub>4</sub> as a reductant in a mild condition. The recyclability
and stability of the CCM catalysts have also been studied
Facile Synthesis of ZnFe<sub>2</sub>O<sub>4</sub> Nanoparticles with Tunable Magnetic and Sensing Properties
Nanoparticles
(NPs) and colloidal nanocrystal clusters (CNCs) of
ZnFe<sub>2</sub>O<sub>4</sub> were synthesized by using a solvothermal
method in a controlled manner through simply adjusting the solvents.
When a glycerol/water mixture was used as the solvent, ZnFe<sub>2</sub>O<sub>4</sub> NPs were obtained. However, using ethylene glycol solvent
yielded well-dispersed ZnFe<sub>2</sub>O<sub>4</sub> CNCs. X-ray diffraction
(XRD) and transmission electron microscopy (TEM) data confirmed that
the ZnFe<sub>2</sub>O<sub>4</sub> NPs were a single crystalline phase
with tunable sizes ranging from 12 to 20 nm, while the ZnFe<sub>2</sub>O<sub>4</sub> CNCs of submicrometer size consisted of single-crystalline
nanosheets. Magnetic measurement results showed that the ZnFe<sub>2</sub>O<sub>4</sub> NPs were ferromagnetic with a very small hysteresis
loop at room temperature. However, CNCs displayed a superparamagnetic
behavior due to preferred orientations of the nanosheets. Electrochemical
sensing properties showed that both the size of the NPs and the structure
of the CNCs had a great influence on their electrochemical properties
in the reduction of H<sub>2</sub>O<sub>2</sub>. Based on the experimental
results, the formation mechanisms of both the ZnFe<sub>2</sub>O<sub>4</sub> CNCs and NPs as well as their structure–property relationship
were discussed
Structural Regulation of PdCu<sub>2</sub> Nanoparticles and Their Electrocatalytic Performance for Ethanol Oxidation
Two types of PdCu<sub>2</sub> nanoparticles were prepared through one-pot synthesis and
a two-step reducing process, named as PdCu<sub>2</sub>-1 and PdCu<sub>2</sub>-2, respectively. The morphology and structure of as-prepared
samples were investigated by transmission electron microscopy, high-resolution
transmission electron microscopy, X-ray diffraction, X-ray photoelectron
spectroscopy, and inductively coupled plasma-optical emission spectrometry.
Results showed that more Pd atoms were buried in the inside of PdCu<sub>2</sub>-1, whereas more available Pd sites were distributed on the
surface of PdCu<sub>2</sub>-2. The electrochemical measurements indicated
that both PdCu<sub>2</sub>-1 and PdCu<sub>2</sub>-2 nanoparticles
showed a higher electrocatalytic activity than that for pure Pd nanoparticles.
In particular, PdCu<sub>2</sub>-2 predictably exhibited a better stability
and durability as well as a lower onset potential and a higher catalytic
current density than that of PdCu<sub>2</sub>-1 toward ethanol oxidation
in alkaline media. On the basis of these studies, the formation mechanisms
of both the PdCu<sub>2</sub> catalysts and the relationship between
their structure and properties were discussed in this paper
Spray-Drying-Induced Assembly of Skeleton-Structured SnO<sub>2</sub>/Graphene Composite Spheres as Superior Anode Materials for High-Performance Lithium-Ion Batteries
Three-dimensional
skeleton-structured assemblies of graphene sheets
decorated with SnO<sub>2</sub> nanocrystals are fabricated via a facile
and large-scalable spray-drying-induced assembly process with commercial
graphene oxide and SnO<sub>2</sub> sol as precursors. The influences
of different parameters on the morphology, composition, structure,
and electrochemical performances of the skeleton-structured SnO<sub>2</sub>/graphene composite spheres are studied by XRD, TGA, SEM,
TEM, Raman spectroscopy, and N<sub>2</sub> adsorption–desorption
techniques. Electrochemical properties of the composite spheres as
the anode electrode for lithium-ion batteries are evaluated. After
120 cycles under a current density of 100 mA g<sup>–1</sup>, the skeleton-structured SnO<sub>2</sub>/graphene spheres still
display a specific discharge capacity of 1140 mAh g<sup>–1</sup>. It is roughly 9.5 times larger than that of bare SnO<sub>2</sub> clusters. It could still retain a stable specific capacity of 775
mAh g<sup>–1</sup> after 50 cycles under a high current density
of 2000 mA g<sup>–1</sup>, exhibiting extraordinary rate ability.
The superconductivity of the graphene skeleton provides the pathway
for electron transportation. The large pore volume deduced from the
skeleton structure of the SnO<sub>2</sub>/graphene composite spheres
increases the penetration of electrolyte and the diffusion of lithium
ions and also significantly enhances the structural integrity by acting
as a mechanical buffer
Carrageenan Asissted Synthesis of Palladium Nanoflowers and Their Electrocatalytic Activity toward Ethanol
Palladium (Pd) nanoflowers with tunable
thorns were prepared by
a facile and rapid route with the assistance of carrageenan. The superior
nature of well-dispersed Pd nanoflowers has been disclosed by X-ray
diffraction, scanning electron microscopy, and transmission electron
microscopy measurements. The growth of thorns of Pd nanostructures
was first stimulated with the continuous introduction of l-ascorbic acid in the synthesis system and then reached a maximum
length of about 132 nm, followed by a slight decrease in concentration.
Electrochemical data showed that Pd nanoflowers with the longest thorns
exhibited the highest catalytic current density of 1160 mA/mg, optimized
tolerance to the poisoning, and the lowest onset potential while others
showed a better cycle stability with a catalytic activity maintenance
of above 96% after 300 cycles. It is suggested that the structure
of thin thorns of Pd nanoflowers should be easier to damage than thick
thorns during the electrocatalysis of ethanol. The relationship between
Pd nanoflowers and properties as well as the key factors to form the
nanoflower structure were discussed based on the experimental data
Formic Acid-Assisted Synthesis of Palladium Nanocrystals and Their Electrocatalytic Properties
Palladium (Pd) nanocrystals have
been synthesized by using formic
acid as the reducing agent at room temperature. When the concentration
of formic acid was increased continuously, the size of Pd nanocrystals
first decreased to a minimum and then increased slightly again. The
products have been investigated by a series of techniques, including
X-ray diffraction, high-resolution transmission electron microscopy
(HRTEM), UV–vis absorption, and electrochemical measurements.
The formation of Pd nanocrystals is proposed to be closely related
to the dynamical imbalance of the growth and dissolution rate of Pd
nanocrystals associated with the adsorption of formate ions onto the
surface of the intermediates. It is found that small Pd nanocrystals
showed blue-shifted adsorption peaks compared with large ones. Pd
nanocrystals with the smallest size display the highest electrocatalytic
activity for the electrooxidation of formic acid and ethanol on the
basis of cyclic voltammetry and chronoamperometric data. It is suggested
that both the electrochemical active surface area and the small size
effect are the key roles in determining the electrocatalytic performances
of Pd nanocrystals. A “dissolution–deposition–aggregation”
process is proposed to explain the variation of the electrocatalytic
activity during the electrocatalysis according to the HRTEM characterization