10 research outputs found
Photo-corrosion inhibition of Ag<sub>3</sub>PO<sub>4</sub> by polyaniline coating
<p>In this paper, polyaniline-coated silver phosphate has been successfully prepared via a facile chemisorption method in order to improve the stability of Ag<sub>3</sub>PO<sub>4</sub> under light irradiation. The crystalline phase, band gap energy, and microstructure of the obtained PANI/Ag<sub>3</sub>PO<sub>4</sub> composites were characterized by X-ray diffraction, UVāvis diffuse reflection spectroscopy, scanning electron microscopy, and transmission electron microscopy, respectively. The photocatalytic degradation of methlylene blue was performed to test the activities of PANI/Ag<sub>3</sub>PO<sub>4</sub> composites with different coating amounts and the results indicate that the stabilities of PANI/Ag<sub>3</sub>PO<sub>4</sub> composites were successfully enhanced. The correlation between photocatalytic performance and the properties of PANI/Ag<sub>3</sub>PO<sub>4</sub> composites is discussed in detail.</p
Multiscale Interfacial Strategy to Engineer Mixed Metal-Oxide Anodes toward Enhanced Cycling Efficiency
Interconnected macro/mesoporous
structures of mixed metal oxide (MMO) are developed on nickel foam
as freestanding anodes for Li-ion batteries. The sustainable production
is realized via a wet chemical etching process with bio-friendly chemicals.
By means of divalent iron doping during an in situ recrystallization
process, the as-developed MMO anodes exhibit enhanced levels of cycling
efficiency. Furthermore, this atomic-scale modification coherently
synergizes with the encapsulation layer across a micrometer scale.
During this step, we develop a quasi-gel-state tri-copolymer, i.e.,
F127āresorcinolāmelamine, as the N-doped carbon source
to regulate the interfacial chemistry of the MMO electrodes. Electrochemical
tests of the modified Fe<i><sub>x</sub></i>Ni<sub>1ā<i>x</i></sub>O@NCāNiF anode in both half-cell and full-cell
configurations unravel the favorable suppression of the irreversible
capacity loss and satisfactory cyclability at the high rates. This
study highlights a proof-of-concept modification strategy across multiple
scales to govern the interfacial chemical process of the electrodes
toward better reversibility
Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures: Topotaxial Oxidation of Fe<sub>1ā<i>x</i></sub>O|Fe<sub>3āĪ“</sub>O<sub>4</sub> Core|Shell Nanocubes to Single-Phase Particles
Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe<sub>1ā<i>x</i></sub>O|Fe<sub>3āĪ“</sub>O<sub>4</sub> nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of antiphase boundaries. Dark-field transmission electron microscopy and powder X-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe<sub>1ā<i>x</i></sub>O core is removed but that the antiphase boundaries remain. The antiphase boundaries result in anomalous magnetic behavior, that is, a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic properties of iron oxide nanoparticles
Iron Doping in Spinel NiMn<sub>2</sub>O<sub>4</sub>: Stabilization of the Mesoporous Cubic Phase and Kinetics Activation toward Highly Reversible Li<sup>+</sup> Storage
Quaternary oxide structures with
a three-dimensional macro/mesoporous
network are synthesized via a facile nanocasting method followed by
a calcination process. Structural engineering integrates multiscale
pores by using a hydrophilic membrane with tunable-porosity as the
sacrificial template. Through tailoring the metal precursor ratio,
the tetragonal sites of spinel oxide are preferentially occupied by
iron, resulting in a stabilized mesoporous cubic phase. Crystal field
theory together with compositional characterizations from energy-dispersive
spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), MoĢssbauer,
and electron energy loss spectroscopy (EELS) direct our detailed analysis
of the cation distribution in the spinel structures. Galvanostatic
tests based on the best performing electrode exhibits a robust cycle
life stable for 1200 cycles at a high current density of 1500 mA g<sup>ā1</sup>. This good Li<sup>+</sup> storage performance could
be attributed to the mutually beneficial synergy of the optimal level
of iron doping which improves the electrical conductivity and structural
robustness, as well as the presence of extended, hierarchical macro/mesoporous
network. Finally, we demonstrate three feasible surface modification
strategies for the oxide anodes toward better reversibility of Li<sup>+</sup> storage
Integrated Heterogeneous Metal/Enzymatic Multiple Relay Catalysis for Eco-Friendly and Asymmetric Synthesis
Organic synthesis is in general performed
using stepwise transformations
where isolation and purification of key intermediates is often required
prior to further reactions. Herein we disclose the concept of integrated
heterogeneous metal/enzymatic multiple relay catalysis for eco-friendly
and asymmetric synthesis of valuable molecules (e.g., amines and amides)
in one-pot using a combination of heterogeneous metal and enzyme catalysts.
Here reagents, catalysts, and different conditions can be introduced
throughout the one-pot procedure involving multistep catalytic tandem
operations. Several novel cocatalytic relay sequences (reductive amination/amidation,
aerobic oxidation/reductive amination/amidation, reductive amination/kinetic
resolution and reductive amination/dynamic kinetic resolution) were
developed. They were next applied to the direct synthesis of various
biologically and optically active amines or amides in one-pot from
simple aldehydes, ketones, or alcohols, respectively
Investigation of the Structural and Electrochemical Properties of Mn<sub>2</sub>Sb<sub>3</sub>O<sub>6</sub>Cl upon Reaction with Li Ions
The
structural and electrochemical properties of a quaternary layered
compound with elemental composition Mn<sub>2</sub>Sb<sub>3</sub>O<sub>6</sub>Cl have been investigated upon reaction with lithium in Li
half cells. Operando XRD was used to investigate the potential impact
of this particular layered structure on the lithiation process. Although
the results suggest that the material is primarily reacted through
a conventional conversion mechanism, they also provide some hints
that the space between the slabs may act as preferential entry points
for lithium ions but not for the larger sodium ions. Cyclic voltammetry,
galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed
to unravel the details of the reaction mechanism with the lithium
ions. It is found that two pairs of reactions are mainly responsible
for the reversible electrochemical cycling of this compound, namely,
the alloying of LiāSb and the conversion of Mn<sub><i>x</i></sub>O<sub><i>y</i></sub> to metallic Mn<sup>0</sup> with concomitant formation
of Li<sub>2</sub>O upon lithium uptake. A moderate cycling stability
is achieved with a gravimetric capacity of 467 mAh g<sup>ā1</sup> after 100 cycles between 0.05 and 2.2 V vs Li<sup>+</sup>/Li despite
the large particle sizes of
the active material and its nonoptimal inclusion into composite coatings.
The electrochemical activity
of the title compound was also tested in Na half cells between 0.05
and
2 V vs Na<sup>+</sup>/Na. It was found that a prolonged period
of electrochemical milling is required to fully gain access to the
active material, after which the cell delivers a capacity of 350 mAh
g<sup>ā1</sup>. These factors are demonstrated to clearly limit
the ultimate
performances for these electrodes
Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection
We report on a novel sensing platform
for H<sub>2</sub>O<sub>2</sub> and glucose based on immobilization
of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostructures
and glucose oxidase (GOx) with Nafion on a glassy carbon electrode
(GCE). HCNFs were synthesized by a chemical vapor deposition process
on a C<sub>60</sub>-supported Pd catalyst. Pd-HCNF nanocomposites
were prepared by a one-step reduction free method in dimethylformamide
(DMF). The prepared materials were characterized by transmission electron
microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy
(SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits
excellent electrocatalytic sensitivity toward H<sub>2</sub>O<sub>2</sub> (315 mA M<sup>ā1</sup> cm<sup>ā2</sup>) as probed
by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified
electrodes significantly reduce the overpotential and enhance the
electron transfer rate. A linear range from 5.0 Ī¼M to 2.1 mM
with a detection limit of 3.0 Ī¼M (based on the S/N = 3) and
good reproducibility were obtained. Furthermore, a sensing platform
for glucose was prepared by immobilizing the Pd-HCNFs and glucose
oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting
biosensor exhibits a good response to glucose with a wide linear range
(0.06ā6.0 mM) with a detection limit of 0.03 mM and a sensitivity
of 13 mA M<sup>ā1</sup> cm<sup>ā2</sup>. We show that
small size and homogeneous distribution of the Pd nanoparticles in
combination with good conductivity and large surface area of the
HCNFs lead to a H<sub>2</sub>O<sub>2</sub> and glucose sensing platform
that performs in the top range of the herein reported sensor platforms
Clearing Up Discrepancies in 2D and 3D Nickel Molybdate Hydrate Structures
When electrocatalysts are prepared, modification of the
morphology
is a common strategy to enhance their electrocatalytic performance.
In this work, we have examined and characterized nanorods (3D) and
nanosheets (2D) of nickel molybdate hydrates, which previously have
been treated as the same material with just a variation in morphology.
We thoroughly investigated the materials and report that they contain
fundamentally different compounds with different crystal structures,
chemical compositions, and chemical stabilities. The 3D nanorod structure
exhibits the chemical formula NiMoO4Ā·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet
structures can be rationalized with Ni3MoO5ā0.5x(OH)xĀ·(2.3 ā
0.5x)H2O, with a mixed valence of both
Ni and Mo, which enables a layered crystal structure. The difference
in structure and composition is supported by X-ray photoelectron spectroscopy,
ion beam analysis, thermogravimetric analysis, X-ray diffraction,
electron diffraction, infrared spectroscopy, Raman spectroscopy, and
magnetic measurements. The previously proposed crystal structure for
the nickel molybdate hydrate nanorods from the literature needs to
be reconsidered and is here refined by ab initio molecular dynamics
on a quantum mechanical level using density functional theory calculations
to reproduce the experimental findings. Because the material is frequently
studied as an electrocatalyst or catalyst precursor and both structures
can appear in the same synthesis, a clear distinction between the
two compounds is necessary to assess the underlying structure-to-function
relationship and targeted electrocatalytic properties
Clearing Up Discrepancies in 2D and 3D Nickel Molybdate Hydrate Structures
When electrocatalysts are prepared, modification of the
morphology
is a common strategy to enhance their electrocatalytic performance.
In this work, we have examined and characterized nanorods (3D) and
nanosheets (2D) of nickel molybdate hydrates, which previously have
been treated as the same material with just a variation in morphology.
We thoroughly investigated the materials and report that they contain
fundamentally different compounds with different crystal structures,
chemical compositions, and chemical stabilities. The 3D nanorod structure
exhibits the chemical formula NiMoO4Ā·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet
structures can be rationalized with Ni3MoO5ā0.5x(OH)xĀ·(2.3 ā
0.5x)H2O, with a mixed valence of both
Ni and Mo, which enables a layered crystal structure. The difference
in structure and composition is supported by X-ray photoelectron spectroscopy,
ion beam analysis, thermogravimetric analysis, X-ray diffraction,
electron diffraction, infrared spectroscopy, Raman spectroscopy, and
magnetic measurements. The previously proposed crystal structure for
the nickel molybdate hydrate nanorods from the literature needs to
be reconsidered and is here refined by ab initio molecular dynamics
on a quantum mechanical level using density functional theory calculations
to reproduce the experimental findings. Because the material is frequently
studied as an electrocatalyst or catalyst precursor and both structures
can appear in the same synthesis, a clear distinction between the
two compounds is necessary to assess the underlying structure-to-function
relationship and targeted electrocatalytic properties
Amorphous Calcium Carbonate Constructed from Nanoparticle Aggregates with Unprecedented Surface Area and Mesoporosity
Amorphous
calcium carbonate (ACC), with the highest reported specific
surface area of all current forms of calcium carbonate (over 350 m<sup>2</sup> g<sup>ā1</sup>), was synthesized using a surfactant-free,
one-pot method. Electron microscopy, helium pycnometry, and nitrogen
sorption analysis revealed that this highly mesoporous ACC, with a
pore volume of ā¼0.86 cm<sup>3</sup> g<sup>ā1</sup> and
a pore-size distribution centered at 8ā9 nm, is constructed
from aggregated ACC nanoparticles with an estimated average diameter
of 7.3 nm. The porous ACC remained amorphous and retained its high
porosity for over 3 weeks under semi-air-tight storage conditions.
Powder X-ray diffraction, large-angle X-ray scattering, infrared spectroscopy,
and electron diffraction exposed that the porous ACC did not resemble
any of the known CaCO<sub>3</sub> structures. The atomic order of
porous ACC diminished at interatomic distances over 8 Ć
. Porous
ACC was evaluated as a potential drug carrier of poorly soluble substances
in vitro. Itraconazole and celecoxib remained stable in their amorphous
forms within the pores of the material. Drug release rates were significantly
enhanced for both drugs (up to 65 times the dissolution rates for
the crystalline forms), and supersaturation release of celecoxib was
also demonstrated. Citric acid was used to enhance the stability of
the ACC nanoparticles within the aggregates, which increased the surface
area of the material to over 600 m<sup>2</sup> g<sup>ā1</sup>. This porous ACC has potential for use in various applications where
surface area is important, including adsorption, catalysis, medication,
and bone regeneration