Huaiying Zhou

Mesoporous metal–organic frameworks: design and applications

Metal–organic frameworks (MOFs), which are constructed from the assembly of organic ligands with metal ions or metal clusters, have high potential applications in the fields of gas storage, separations and catalysis. MOFs involving mesopores are considered to have specific performance in such fields. In this mini review, we are mainly focussing on the recent developments in mesoporous MOFs including the design strategies and their most important applications.

Nanosized Cu-MOFs induced by graphene oxide and enhanced gas storage capacity

Various MOFs with tailored nanoporosities have recently been developed as potential storage media for CO2 and H2. The composites based on Cu-BTC and graphene layers were prepared with different percentages of graphene oxide (GO). Through the characterization analyses and gas adsorption experiments, we found that the nanosized and well-dispersed Cu-BTC induced by the incorporation of GO greatly improved the carbon dioxide capture and hydrogen storage performance of the composites. The materials obtained exhibited about a 30% increase in CO2 and H2 storage capacity (from 6.39 mmol g−1 of Cu-BTC to 8.26 mmol g−1 of CG-9 at 273 K and 1 atm for CO2; from 2.81 wt% of Cu-BTC to 3.58 wt% of CG-9 at 77 K and 42 atm for H2). Finally, the CO2/CH4 and CO2/N2 selectivities were calculated according to single-component gas sorption experiment data.

Preparation and thermal properties of fatty acids/CNTs composite as shape-stabilized phase change materials

A series of fatty acids/carbon nanotubes (CNTs) composite shape-stabilized PCMs were prepared through infiltration method by using the eutectic mixture of capric acid, lauric acid, and palmitic acid as phase change materials, multi-walled CNTs as a supporting material. Nitrogen adsorption–desorption curves and SEM images of composite shape-stabilized PCMs indicate that the eutectic mixture was effectively absorbed into the porous structure of the CNTs. DSC thermograms show that the composite fatty acids/CNTs possess good phase change behavior. And the latent heat of the sample absorbed with 80xa0wt% fatty acids can achieve 101.6xa0Jxa0g−1 in the melting process and its phase change temperatures and latent heat almost remain unchanged in 30 times of thermal cycling. Moreover, the thermal conductivity of the composite materials are significantly improved (up to 0.6661xa0Wxa0m−1xa0k−1) due to the addition of the highly thermal conductive CNTs.

CaCl 2 6H 2 O/Expanded graphite composite as form-stable phase change materials for thermal energy storage

In this study, CaCl2·6H2O/expanded graphite (EG) composite was prepared as a novel form-stable composite phase change material (PCM) through vacuum impregnation method. CaCl2·6H2O used as the PCM was dispersed by surfactant and then, was absorbed into the porous structure of the EG. The surfactant was used to enhance the bonding energy between CaCl2·6H2O and EG, which fulfilled the composites with good sealing performance and limited the leakage of the inside CaCl2·6H2O. Differential scanning calorimetry and thermal gravimetric analysis show that all the composite PCMs possess good thermal energy storage behavior and thermal stability. Thermal conductivity measurement displays that the conductivities of the samples have been significantly improved due to the highly thermal conductive EG. The thermal conductivity of the sample including 50xa0mass% CaCl2·6H2O (8.796xa0Wxa0m−1xa0K−1) is 14 times as that of pure CaCl2·6H2O (0.596xa0Wxa0m−1xa0K−1). Therefore, the obtained composite PCMs are promising for thermal energy storage applications.

Polarized micropores in a novel 3D metal-organic framework for selective adsorption properties.

A novel 3D porous metal-organic framework with 1D polarized channels was synthesized, and its adsorption properties for gas separation and chemical sensing were studied. The framework shows a preferential adsorption of CO(2) over N(2) with a selectivity of 22:1. It also exhibits a very good sensitivity to water with respect to most of the organic solvents in view of chemical sensing applications.

Improved dehydrogenation/rehydrogenation performance of LiBH4 by doping mesoporous Fe2O3 or/and TiF3

The LiBH4xa0+xa0mesoporous Fe2O3 (defined as M-Fe2O3) mono-doped and LiBH4xa0+xa0M-Fe2O3xa0+xa0TiF3 co-doped hybrid materials were prepared by ball milling process. A variety of characterization methods, such as thermogravimetric, differential scanning calorimetry, X-ray diffraction, and pressure–composition–temperature instrument, were used for examinations of the two materials’ performances of storage/release of hydrogen, catalytic activity, kinetics, and thermodynamics. All the results showed that the M-Fe2O3 prepared in laboratory exhibited a good catalytic effect. Compared with the performance of M-Fe2O3 mono-doped system, M-Fe2O3 and TiF3 co-doped mode exhibits a better performance using the same additive content. Thus, the M-Fe2O3 and TiF3 co-doped mode possesses a collaborative catalytic utility with the LiBH4 hydrogen performance improved, showing a promising application.

Heat capacities and thermodynamic properties of Co(3,5-PDC)(H2O)

A novel metal-organic frameworks Co(3,5-PDC)(H2O) (CoMOF, 3,5-PDCxa0=xa0pyridine-3,5-dicarboxylic acid) has been synthesized hydrothermally and characterized by single-crystal XRD and FT-IR spectra. The thermal stability and the decomposition mechanism of CoMOF were investigated by thermogravimetry-mass spectrometry, and a two-stage shape curve of mass loss was observed. Moreover, the low-temperature molar heat capacities were measured by temperature-modulated differential scanning calorimetry for the first time. The thermodynamic parameters such as entropy and enthalpy relative to reference temperature 298.15xa0K were derived based on the molar heat capacity data.

Hydrogen storage and selective carbon dioxide capture in a new chromium(III)-based infinite coordination polymer

A new chromium(III)-based infinite coordination polymer (ICP) was synthesized under solvothermal conditions. The morphology, particle size and the textural porosity of the resulting solids could be monitored and controlled by adjusting the volume ratio of the solvent mixture (1,4-dioxane/N,N′-dimethylformamide). Two differently textured samples were further compared using powder X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, solid-state UV-Vis spectroscopy and thermogravimetric analysis. Their sorption capacities for H2, CO2 and CH4 were measured by using volumetric gas adsorption, while the isosteric heats of adsorption for the same gasses were calculated based on gas sorption data at different temperatures. Both samples showed a remarkable selectivity for CO2 over CH4 at 273 K. H2 and CO2 sorption capacities, (respectively 16.9 mg g−1 at 77 K and 817 mm Hg and 168 mg g−1 at 273 K and 760 mm Hg) of the sample composed of the nanosized particles, are comparable or even superior to values reported for most MOFs and ZIFs under similar conditions.

Structure and electrochemical performance of nanosized Li1.1(Ni0.35Co0.35Mn0.30)O2 powders for lithium-ion battery

Pure Li1.1Ni0.35Co0.35Mn0.30O2 nanosized powders have been successfully synthesized by improved hydroxide co-precipitation method, and characterized with X-ray powder diffraction and scanning electron microscopy (SEM). The electrochemical properties of cathodes and Li1.1Ni0.35Co0.35Mn0.30O2/Li4Ti5O12 full cells have been studied by charge–discharge tests and cyclic voltammetry. The Li1.1Ni0.35Co0.35Mn0.30O2 powders have a typical layered hexagonal crystal structure with an average particle size of about 780 nm. The cathodes exhibit high capacities and good cycling performance. The initial discharge capacity of the cathodes is 154.8 mAhg-1 at 0.5 C between 2.5 V and 4.3 V, and the capacity retention keeps 80.6% after 50 charge–discharge cycles. The Li1.1Ni0.35Co0.35Mn0.30O2/Li4Ti5O12 cells also deliver high specific capacities, good cycling stability and rate capability. This work demonstrates that Li1.1Ni0.35Co0.35Mn0.30O2 is a promising cathode material for lithium-ion batteries.

First-principles studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7 *

The detailed theoretical studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7 are carried out by using first-principle density functional theory calculations. Our calculated results indicate that γ-Bi2Sn2O7 is the p-type semiconductor with an indirect band gap of about 2.72 eV. The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi2Sn2O7. The calculated complex dielectric function and macroscopic optical constants including refractive index, extinction coefficient, absorption coefficients, reflectivity, and electron energy-loss function show that γ-Bi2Sn2O7 is an excellent light absorbing material. The analysis on mechanical properties shows that γ-Bi2Sn2O7 is mechanically stable and highly isotropic.