16 research outputs found
Selective H<sub>2</sub>S/CO<sub>2</sub> Separation by Metal–Organic Frameworks Based on Chemical-Physical Adsorption
The
removal of hydrogen sulfide (H<sub>2</sub>S) is essential in
various industry applications such as purification of syngas for avoiding
its corrosion and toxicity to catalysts. The design of adsorbents
that can bear corrosion of H<sub>2</sub>S and overcome the competitive
adsorption from carbon dioxide (CO<sub>2</sub>) is a challenge. To
obtain insight into the stability and adsorption mechanism of metal–organic
frameworks (MOFs) during the H<sub>2</sub>S separation process, 11
MOF-based materials were employed for H<sub>2</sub>S capture from
CO<sub>2</sub>. Density functional theory, molecular dynamic studies,
and dynamic separation experiments were used to investigate selective
H<sub>2</sub>S/CO<sub>2</sub> separation. Most of these MOFs showed
one-off high capacity and selectivity to H<sub>2</sub>S. Complete
reversible physical adsorption was proven on Mg-MOF-74, MIL-101Â(Cr),
UiO-66, ZIF-8, and Ce-BTC. Incomplete reversible adsorption occurred
on UiO-66Â(NH<sub>2</sub>). Disposable chemical reaction happened on
HKUST-1, Cu-BDCÂ(ted)<sub>0.5</sub>, Zn-MOF-74, MIL-100Â(Fe) gel, and
MOF-5. Using breakthrough experiments, UiO-66, Mg-MOF-74, and MIL-101Â(Cr)
were screened out to present promising performance on the H<sub>2</sub>S capture. The present study is useful to identify and design suitable
MOF materials for high-performance H<sub>2</sub>S capture and separation
Macroscopic Architecture of Charge Transfer-Induced Molecular Recognition from Electron-Rich Polymer Interpenetrated Porous Frameworks
Fluorescent
and electron-rich polymer threaded into porous framework
provides a scaffold for sensing acceptor molecules through noncovalent
interactions. Herein, polyÂ(9-vinylcarbazole) (PVK) threaded MIL-101
with confined nanospace was synthesized by vinyl-monomer impregnation,
in situ polymerization, and interpenetration. The pore size of the
resulted hybrid could be controlled by varying the time of polymerization
and interpenetration. The interaction of PVK-threaded MIL-101 with
guest molecules showed a charge-transfer progress with an obvious
red shift in the optical spectra. Depending on the degree of the interaction,
the solution color changed from blue to green or to yellow. In particular,
electron-rich PVK-threaded MIL-101 could effectively probe electron-poor
nitro compounds, especially 1,3,5-trinitrobenzene (TNP), a highly
explosive material. This sensing approach is a colorimetric methodology,
which is very simple and convenient for practical analysis and operation
Covalent Organic Frameworks Formed with Two Types of Covalent Bonds Based on Orthogonal Reactions
Covalent
organic frameworks (COFs) are excellent candidates for
various applications. So far, successful methods for the constructions
of COFs have been limited to a few condensation reactions based on
only one type of covalent bond formation. Thus, the exploration of
a new judicious synthetic strategy is a crucial and emergent task
for the development of this promising class of porous materials. Here,
we report a new orthogonal reaction strategy to construct COFs by
reversible formations of two types of covalent bonds. The obtained
COFs consisting of multiple components show high surface area and
high H<sub>2</sub> adsorption capacity. The strategy is a general
protocol applicable to construct not only binary COFs but also more
complicated systems in which employing regular synthetic methods did
not work
Nanostructured Electrode Materials Derived from Metal–Organic Framework Xerogels for High-Energy-Density Asymmetric Supercapacitor
This work successfully demonstrates
metal–organic framework (MOF) derived strategy to prepare nanoporous
carbon (NPC) with or without Fe<sub>3</sub>O<sub>4</sub>/Fe nanoparticles
by the optimization of calcination temperature as highly active electrode
materials for asymmetric supercapacitors (ASC). The nanostructured
Fe<sub>3</sub>O<sub>4</sub>/Fe/C hybrid shows high specific capacitance
of 600 F/g at a current density of 1 A/g and excellent capacitance
retention up to 500 F/g at 8 A/g. Furthermore, hierarchically NPC
with high surface area also obtained from MOF gels displays excellent
electrochemical performance of 272 F/g at 2 mV/s. Considering practical
applications, aqueous ASC (aASC) was also assembled, which shows high
energy density of 17.496 Wh/kg at the power density of 388.8 W/kg.
The high energy density and excellent capacity retention of the developed
materials show great promise for the practical utilization of these
energy storage devices
Kinetic and Thermodynamic Insights into Advanced Energy Storage Mechanisms of Battery-Type Bimetallic Metal–Organic Frameworks
The engineering of high-performance battery-type electrode
materials
highly depends on the guidance from the combination of experimental
analysis and theoretical simulation. Herein, the joint experimental–theoretical
investigation provides a mechanistic explanation for the electrochemical
performance enhancement in bimetallic metal–organic frameworks
(MOFs). The superior CoNi-MOF in our study exhibits advanced electrochemical
energy storage performance, achieving a high specific capacity of
382 C g–1 (1 A g–1), 2.0 and 1.4
times that of Co-MOF and Ni-MOF, respectively. Such a significant
enhancement results from the surface-controlled reaction kinetics
and the low onset potential contributed by the well-tuned electronic
structures of bimetallic MOFs. Our study opens up new perspectives
for understanding the advantages of mixed metal sites in MOFs for
electrochemical energy storage
A Triazole-Containing Metal–Organic Framework as a Highly Effective and Substrate Size-Dependent Catalyst for CO<sub>2</sub> Conversion
A highly porous metal–organic
framework (MOF) incorporating
both exposed metal sites and nitrogen-rich triazole groups was successfully
constructed via solvothermal assembly of a clicked octcarboxylate
ligand and CuÂ(II) ions, which presents a high affinity toward CO<sub>2</sub> molecules clearly verified by gas adsorption and Raman spectral
detection. The constructed MOF featuring CO<sub>2</sub>-adsorbing
property and exposed Lewis-acid metal sites could serve as an excellent
catalyst for CO<sub>2</sub>-based chemical fixation. Catalytic activity
of the MOF was confirmed by remarkably high efficiency on CO<sub>2</sub> cycloaddition with small epoxides. When extending the substrates
to larger ones, its activity showed a sharp decrease. These observations
reveal that MOF-catalyzed CO<sub>2</sub> cycloaddition of small substrates
was carried out within the framework, while large ones cannot easily
enter into the porous framework for catalytic reactions. Thus, the
synthesized MOF exhibits high catalytic selectivity to different substrates
on account of the confinement of the pore diameter. The high efficiency
and size-dependent selectivity toward small epoxides on catalytic
CO<sub>2</sub> cycloaddition make this MOF a promising heterogeneous
catalyst for carbon fixation
Tailoring Carbon Nanotube Density for Modulating Electro-to-Heat Conversion in Phase Change Composites
We report a carbon nanotube array-encapsulated
phase change composite
in which the nanotube distribution (or areal density) could be tailored
by uniaxial compression. The <i>n</i>-eicosane (C20) was
infiltrated into the porous array to make a highly conductive nanocomposite
while maintaining the nanotube dispersion and connection among the
matrix with controlled nanotube areal density determined by the compressive
strains along the lateral direction. The resulting electrically conductive
composites can store heat at driven voltages as low as 1 V at fast
speed with high electro-to-heat conversion efficiencies. Increasing
the nanotube density is shown to significantly improve the polymer
crystallinity and reduce the voltage for inducing the phase change
process. Our results indicate that well-organized nanostructures such
as the nanotube array are promising candidates to build high-performance
phase change composites with simplified manufacturing process and
modulated structure and properties
Experimental and Theoretical Investigation of Mesoporous MnO<sub>2</sub> Nanosheets with Oxygen Vacancies for High-Efficiency Catalytic DeNO<sub><i>x</i></sub>
A solvent-free
synthetic method was employed for the construction
of mesoporous α-MnO<sub>2</sub> nanosheets. Benefiting from
a solid interface reaction, the obtained MnO<sub>2</sub> nanosheets
with large oxygen vacancies exhibit a high surface area of up to 339
m<sup>2</sup>/g and a mesopore size of 4 nm. The MnO<sub>2</sub> nanosheets
as a catalyst were applied in NH<sub>3</sub>-assisted selective catalytic
reduction (NH<sub>3</sub>-SCR) of DeNO<sub><i>x</i></sub> at a relatively low temperature range. The conversion efficiency
could reach 100% under a gas hourly space velocity (GHSV) of 700000
h<sup>–1</sup> at 100 °C. To gain insight into the mechanism
about NH<sub>3</sub>-SCR of nitric oxide on the MnO<sub>2</sub> nanosheets,
temperature-programmed desorption of NH<sub>3</sub>, a density functional
theory study, and in situ diffuse reflectance infrared Fourier transform
spectra were carried out, revealing the cooperative effect of catalytic
sites on the reduction of nitric oxide. This work provides a strategy
for the facile preparation of porous catalysts in low-temperature
DeNO<sub><i>x</i></sub>
DataSheet1_Effect of grain boundary resistance on the ionic conductivity of amorphous xLi2S-(100-x)LiI binary system.docx
Solid-state electrolytes (SSEs) hold the key position in the progress of cutting-edge all-solid-state batteries (ASSBs). The ionic conductivity of solid-state electrolytes is linked to the presence of both amorphous and crystalline phases. This study employs the synthesis method of mechanochemical milling on binary xLi2S-(100-x)LiI system to investigate the effect of amorphization on its ionic conductivity. Powder X-ray diffraction (PXRD) shows that the stoichiometry of Li2S and LiI has a significant impact on the amorphization of xLi2S-(100-x)LiI system. Furthermore, the analysis of electrochemical impedance spectroscopy (EIS) indicates that the amorphization of xLi2S-(100-x)LiI system is strongly correlated with its ionic conductivity, which is primarily attributed to the effect of grain boundary resistance. These findings uncover the latent connections between amorphization, grain boundary resistance, and ionic conductivity, offering insight into the design of innovative amorphous SSEs.</p
Functionalized Bimetallic Hydroxides Derived from Metal–Organic Frameworks for High-Performance Hybrid Supercapacitor with Exceptional Cycling Stability
A hybrid
supercapacitor consisting of a battery-type electrode
and a capacitive electrode could exhibit dramatically enhanced energy
density compared with a conventional electrical double-layer capacitor
(EDLCs). However, advantages for EDLCs such as stable cycling performance
will also be impaired with the introduction of transition metal-based
species. Here, we introduce a facile hydrothermal procedure to prepare
highly porous MOF-74-derived double hydroxide (denoted as MDH). The
obtained 65%Ni-35%Co MDH (denoted as 65Ni-MDH) exhibited a high specific
surface area of up to 299 m<sup>2</sup> g<sup>–1</sup>. When
tested in a three-electrode configuration, the 65Ni-MDH (875 C g<sup>–1</sup> at 1 A g<sup>–1</sup>) exhibited excellent
cycling stability (90.1% capacity retention after 5000 cycles at 20
A g<sup>–1</sup>). After being fabricated as a hybrid supercapacitor
with N-doped carbon as the negative electrode, the device could exhibit
not only 81 W h kg<sup>–1</sup> at a power density of 1.9 kW
kg<sup>–1</sup> and 42 W h kg<sup>–1</sup> even at elevated
working power of 11.5 kW kg<sup>–1</sup>, but also encouraging
cycling stability with 95.5% capacitance retention after 5000 cycles
and 91.3% after 10 000 cycles at 13.5 A g<sup>–1</sup>. This enhanced cycling stability for MDH should be associated with
the synergistic effect of hierarchical porous nature as well as the
existence of interlayer functional groups in MDH (proved by Fourier
transform infrared spectroscopy (FTIR) and in situ Raman spectroscopy).
This work also provides a new MOF-as-sacrificial template strategy
to synthesize transition metal-based hydroxides for practical energy
storage applications