11 research outputs found
Mesoporous Gold and Palladium Nanoleaves from LiquidāLiquid Interface: Enhanced Catalytic Activity of the Palladium Analogue toward Hydrazine-Assisted Room-Temperature 4āNitrophenol Reduction
The importance of an interfacial
reaction to obtain mesoporous leafy nanostructures of gold and palladium
has been reported. A new synthetic strategy involving 1,4-dihydropyridine
ester (DHPE) as a potential reducing agent performs exceptionally
well for the desired morphologies of both the noble metals at room
temperature. The DHPE in turn transforms into its oxidized aromatic
form. The as-synthesized gold leaves exhibit high surface-enhanced
Raman scattering activity with rhodamine 6G (R6G) due to their hyperbranched
structure. It is worthwhile that as-synthesized porous architectures
of palladium support the room-temperature hydrogenation of 4-nitrophenol
(4-NP) by hydrazine hydrate (N<sub>2</sub>H<sub>4</sub>Ā·H<sub>2</sub>O), reported for the first time. Furthermore, MPL exhibits
exceptionally good catalytic activity toward electrooxidation of formic
acid. Therefore, an aromaticity driven synthetic technique achieves
a rationale to design leafy nanostructures of noble metals from the
liquidāliquid interface for multifaceted applications
Suitable Morphology Makes CoSn(OH)<sub>6</sub> Nanostructure a Superior Electrochemical Pseudocapacitor
Morphology of a material
with different facet, edge, kink, etc., generally influences the rate
of a catalytic reaction., Herein, we account for
the importance of altered morphology of a nanomaterial for a supercapacitor
device and employed CoSnĀ(OH)<sub>6</sub> as an electrode material.
Suitable fabrication of a stable aqueous asymmetric supercapacitor
(AAS) using metal hydroxide as positive electrode can be beneficial
if the high energy density is derived without sacrificing the power
density. Here we have synthesized an uncommon hierarchical mesoporous
nanostructured (HNS) CoSnĀ(OH)<sub>6</sub> to fabricate a pseudocapacitor.
In this endeavor, NH<sub>3</sub> is found to be a well-suited hydrolyzing
agent for the synthesis. Serendipitously,
HNS was transformed into favored cubic nanostructure (CNS) in NaOH
solution. In solution, NaOH acts as a structure directing as well
as an etching agent. Both the samples (HNS & CNS) were used as
pseudocapacitor electrodes in KOH electrolyte independently, which
is reported for the first time. The HNS exhibits very high specific
capacitance value (2545 F/g at 2.5 A/g specific current) with better
cyclic durability over CNS sample (851 F/g at 2.5 A/g specific current).
To examine the real cell application, we used HNS sample as the positive
electrode material with the activated carbon (AC) as the negative
electrode material for the development of an aqueous asymmetric supercapacitor
(AAS). The as-fabricated AAS exhibited very high specific capacitance
value of 713 F/g at a specific current of 1.5 A/g and retained 92%
specific capacitance value even after 10āÆ000 chargeādischarge
cycles. A maximum energy density of 63.5 Wh kg<sup>ā1</sup> and a maximum power density of 5277 W kg<sup>ā1</sup> were
ascertained from the as-fabricated AAS, HNS CoSnĀ(OH)<sub>6</sub>//AC
Advance Aqueous Asymmetric Supercapacitor Based on Large 2D NiCo<sub>2</sub>O<sub>4</sub> Nanostructures and the rGO@Fe<sub>3</sub>O<sub>4</sub> Composite
NiCo<sub>2</sub>O<sub>4</sub> nanostructure is a widely studied
pseudocapacitor material because of its high specific capacitance
value. Most of the time, the thickness of the nanostructure inhibits
the electrode material from whole-body participation and causes sluggish
charge transportation. These phenomena directly interfere with the
electrochemical performance of the electrode, such as specific capacitance
value, stability, energy density, and so forth. Here, two different
thin two-dimensional morphologies (nanosheet and nanoplate) of the
NiCo<sub>2</sub>O<sub>4</sub> nanocomposite with a large lateral size
are reported using ammonia as a hydrolyzing agent. The large size
and flat surface of the as-synthesized materials offer enormous active
sites during the electrochemical reaction, and the thin wall makes
the ion penetration and transportation very effective and facile.
Therefore, the NiCo<sub>2</sub>O<sub>4</sub> nanosheet and nanoplate
structures exhibited high specific capacitance values of 1540 and
1333 F/g, respectively, with excellent rate and good cycling stability.
Here also, two different advance aqueous asymmetric supercapacitors
have been reported utilizing two NiCo<sub>2</sub>O<sub>4</sub> nanostructure
materials as positive electrodes and the rGO@Fe<sub>3</sub>O<sub>4</sub> composite as a negative electrode, which exhibited excellent rate
and high specific energy without sacrificing the specific power. We
also studied the electrochemical activity of the rGO@Fe<sub>3</sub>O<sub>4</sub> composite at different compositions
Superb Dye Adsorption and Dye-Sensitized Change in Cu<sub>2</sub>OāAg Crystal Faces in the Dark
Hybrid Cu<sub>2</sub>OāAg is attractive because of its many
applications in the fields of photocatalysis, surface-enhanced Raman
scattering (SERS), and optical features. In this article, we have
presented a newer application of Cu<sub>2</sub>OāAg. Cu<sub>2</sub>OāAg has been found to exhibit excellent anionic dye
adsorption properties together with organic transformation for effective
water remediation. Cu<sub>2</sub>OāAg was prepared through
a facile but controlled galvanic reaction between cuprous oxide (Cu<sub>2</sub>O) and silver nitrate (AgNO<sub>3</sub>), rendering stability
and porosity. The experimental results of adsorption showed that Cu<sub>2</sub>OāAg bears an exceptionally high adsorption capacity
toward methyl orange (501.23 mg g<sup>ā1</sup>), which is higher
than most reported results. The adsorption of MO on Cu<sub>2</sub>OāAg happens because of the definite chemical interaction
between CuĀ(I) and the SO<sub>3</sub><sup>ā</sup> functionality
of MO. A kinetic study revealed that the MO adsorption on Cu<sub>2</sub>OāAg primarily followed the pseudo-second-order kinetic model.
The kinetic model followed the Langmuir adsorption isotherm. A very
significant feature that emerged during MO adsorption by Cu<sub>2</sub>OāAg is the transformation of the 3-D morphology of Cu<sub>2</sub>OāAg into 2-D nanosheets under ambient and dark conditions.
This morphology change corroborates that the adsorption occurred through
chemical interaction, i.e., the chemisorption process. This feature,
a morphology change in the dark, presumably happened through the participation
of the highly interactive exposed high-index facet of spherical Cu<sub>2</sub>OāAg nanoparticles. This unique recrystallization of
Cu<sub>2</sub>OāAg due to the chemisorption of MO is reported
for the first time. Cu<sub>2</sub>OāAg was also found to have
a high adsorption capacity (976.30 mg g<sup>ā1</sup>) even
for Congo red (an anionic azo dye), which is also higher than the
reported adsorption capacities of various materials. In another water
remediation aspect, Cu<sub>2</sub>OāAg has also been applied
to the transformation of organic toxic pollutant, 4-nitrophenol (4-NP),
into its nontoxic and medicinally important amino derivative through
catalytic reduction. The catalysis of 4-NP reduction by Cu<sub>2</sub>OāAg in the presence of sodium borohydride (NaBH<sub>4</sub>) exhibited a high rate constant value (<i>k</i> = 0.38
min<sup>ā1</sup>). Thus, two novel properties, adsorption and
catalytic reduction on organic pollutants, of Cu<sub>2</sub>OāAg
have been ascertained for water remediation
A Gel-Based Approach To Design Hierarchical CuS Decorated Reduced Graphene Oxide Nanosheets for Enhanced Peroxidase-like Activity Leading to Colorimetric Detection of Dopamine
Supramolecular colorless copperĀ(I)āthiourea
hydrogel (Cu-TU
gel) has been made a mechanically strong functional hybrid material
in the graphene oxide (GO) framework. Mild heat treatment (85 Ā°C)
of the hybrid material fetches black product containing hierarchical
copper sulfide decorated reduced graphene oxide nanosheets (CuS-rGO)
through an obvious in-house redox transformation reaction between
CuĀ(I) and GO without any additive. The as-synthesized CuS-rGO nanocomposite
exhibits impressive peroxidase-like activity where oxidation of colorless
3,3ā²,5,5ā²-tetramethylbenzidine (TMB) to blue product
is observed in solution phase with H<sub>2</sub>O<sub>2</sub>. Systematic
control experiments suggest that strong covalent interaction between
CuS and rGO synergistically enhances the catalytic activity of CuS-rGO
in comparison to its individual counterparts. Furthermore, an important
biomolecule, dopamine, has been found to selectively inhibit, in succession,
the oxidizing action of H<sub>2</sub>O<sub>2</sub> for TMB oxidation
reaction. Thus, dopamine-dependent successive inhibition reaction
creates a one-pot reporter platform to sense dopamine down to the
0.48 Ī¼M concentration level by UVāvis spectrophotometry
Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor
Although aqueous
asymmetric supercapacitors are promising technologies
because of their high-energy density and enhanced safety, their voltage
window is still limited by the narrow stability window of water. Redox
reactions at suitable electrodes near the water splitting potential
can increase the working potential. Here, we demonstrate a kinetic
approach for expanding the voltage window of aqueous asymmetric supercapacitors
using <i>in situ</i> activated Mn<sub>3</sub>O<sub>4</sub> and VO<sub>2</sub> electrodes. The underlying mechanism indicates
a specific potential of ā¼1 V <i>vs</i> Ag/AgCl for
the oxidation of Mn<sup>4+</sup>-to-Mn<sup>7+</sup> at the positive
electrode and ā¼āÆā0.8 V <i>vs</i> Ag/AgCl
for the reduction of V<sup>3+</sup>-to-V<sup>2+</sup> at the negative
electrode, which limits oxygen and hydrogen evolution reactions, respectively.
The as-fabricated aqueous asymmetric supercapacitor exhibited a working
voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power
density of ā¼1.1 kW/kg. This mechanism improves the voltage
window and energy and power densities
Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor
Although aqueous
asymmetric supercapacitors are promising technologies
because of their high-energy density and enhanced safety, their voltage
window is still limited by the narrow stability window of water. Redox
reactions at suitable electrodes near the water splitting potential
can increase the working potential. Here, we demonstrate a kinetic
approach for expanding the voltage window of aqueous asymmetric supercapacitors
using <i>in situ</i> activated Mn<sub>3</sub>O<sub>4</sub> and VO<sub>2</sub> electrodes. The underlying mechanism indicates
a specific potential of ā¼1 V <i>vs</i> Ag/AgCl for
the oxidation of Mn<sup>4+</sup>-to-Mn<sup>7+</sup> at the positive
electrode and ā¼āÆā0.8 V <i>vs</i> Ag/AgCl
for the reduction of V<sup>3+</sup>-to-V<sup>2+</sup> at the negative
electrode, which limits oxygen and hydrogen evolution reactions, respectively.
The as-fabricated aqueous asymmetric supercapacitor exhibited a working
voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power
density of ā¼1.1 kW/kg. This mechanism improves the voltage
window and energy and power densities
Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor
Although aqueous
asymmetric supercapacitors are promising technologies
because of their high-energy density and enhanced safety, their voltage
window is still limited by the narrow stability window of water. Redox
reactions at suitable electrodes near the water splitting potential
can increase the working potential. Here, we demonstrate a kinetic
approach for expanding the voltage window of aqueous asymmetric supercapacitors
using <i>in situ</i> activated Mn<sub>3</sub>O<sub>4</sub> and VO<sub>2</sub> electrodes. The underlying mechanism indicates
a specific potential of ā¼1 V <i>vs</i> Ag/AgCl for
the oxidation of Mn<sup>4+</sup>-to-Mn<sup>7+</sup> at the positive
electrode and ā¼āÆā0.8 V <i>vs</i> Ag/AgCl
for the reduction of V<sup>3+</sup>-to-V<sup>2+</sup> at the negative
electrode, which limits oxygen and hydrogen evolution reactions, respectively.
The as-fabricated aqueous asymmetric supercapacitor exhibited a working
voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power
density of ā¼1.1 kW/kg. This mechanism improves the voltage
window and energy and power densities
Enhanced Catalytic Activity of Ag/Rh Bimetallic Nanomaterial: Evidence of an Ensemble Effect
A synergistic electronic interaction
between the constituent metals
in a bi/multimetallic system fine-tunes its catalytic property to
be enhanced compared to those of the individual metal analogues. Such
a proposition toward enhancing the catalytic activity of precious
Rh metal by otherwise inactive Ag is done here in a cost-effective
dilution method. The generated heterostructure of Ag/Rh independently
drives two industrially important model reactions: 4-nitrophenol (4-NP)
reduction and hydrogen peroxide (HP) decomposition. An impressive
catalytic activity parameter for 4-NP reduction (256.67 s<sup>ā1</sup> g<sup>ā1</sup>) with hydrazine and HP decomposition (39 Ć
10<sup>ā3</sup> min<sup>ā1</sup> g<sup>ā1</sup>) at room temperature ensures the importance of the āensemble
effectā. Spectroscopic evidence also certifies the dilution
range to justify improved catalytic activities relating to the ensemble
effect. Moreover, our theoretical study rationalizes the experimental
observation where the enhanced charge transfer or occurrence of charge
separation within the bimetallic system is responsible for the chemical
reactivity of these bimetallic systems. Finally, the thermodynamics
of formation of bimetallic nanoparticles finds support from the experimentally
observed results and electronic interactions between Ag and Rh for
improved catalytic activity that complies with spectral information
Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor
Although aqueous
asymmetric supercapacitors are promising technologies
because of their high-energy density and enhanced safety, their voltage
window is still limited by the narrow stability window of water. Redox
reactions at suitable electrodes near the water splitting potential
can increase the working potential. Here, we demonstrate a kinetic
approach for expanding the voltage window of aqueous asymmetric supercapacitors
using <i>in situ</i> activated Mn<sub>3</sub>O<sub>4</sub> and VO<sub>2</sub> electrodes. The underlying mechanism indicates
a specific potential of ā¼1 V <i>vs</i> Ag/AgCl for
the oxidation of Mn<sup>4+</sup>-to-Mn<sup>7+</sup> at the positive
electrode and ā¼āÆā0.8 V <i>vs</i> Ag/AgCl
for the reduction of V<sup>3+</sup>-to-V<sup>2+</sup> at the negative
electrode, which limits oxygen and hydrogen evolution reactions, respectively.
The as-fabricated aqueous asymmetric supercapacitor exhibited a working
voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power
density of ā¼1.1 kW/kg. This mechanism improves the voltage
window and energy and power densities