Li-Xian Sun

High and selective CO2 uptake, H2storage and methanol sensing on the amine-decorated 12-connected MOF CAU-1

The amine-decorated microporous metal–organic framework CAU-1 was readily synthesized and activated using a home-made efficient protocol. It exhibited a high heat of adsorption for CO2, high CO2 uptake capacity, and an impressive selectivity for CO2 over N2. At 273 K and up to 1 atm, CO2 uptake capacity can reach as much as 7.2 mmol g−1. Comparatively, the CH4 and N2 uptakes at 273 K and 1 atm were only 1.34 mmol g−1 and 0.37 mmol g−1, respectively. The CO2/N2 selectivity was 101 : 1 at 273 K. The isosteric heat of adsorption (Qst) for CO2 was ∼48 kJ mol−1 at the onset of adsorption, and it decreases to ∼28 kJ mol−1 at higher CO2 pressures. Furthermore, CAU-1 can adsorb 2.0 wt% and 4.0 wt% hydrogen at 77 K under 1 atm and 30 atm, respectively. The adsorption characteristics of CAU-1 for methanol investigated in situ with a quartz crystal microbalance (QCM), indicated that this particular MOF structure can be used as a highly sensitive sensor for methanol detection such as direct methanol fuel cells.

Size effect of graphene on electrocatalytic activation of oxygen

Crystals of graphite nanosheets, achieved via a simple ball milling approach, show a significant size effect in electrocatalytic activation of oxygen.

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.

Enhanced selectivity of CO2 over CH4 in sulphonate-, carboxylate- and iodo-functionalized UiO-66 frameworks

Three new functionalized UiO-66-X (X = -SO(3)H, 1; -CO(2)H, 2; -I; 3) frameworks incorporating BDC-X (BDC: 1,4-benzenedicarboxylate) linkers have been synthesized by a solvothermal method using conventional electric heating. The as-synthesized (AS) as well as the thermally activated compounds were characterized by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric (TG), and elemental analysis. The occluded H(2)BDC-X molecules can be removed by exchange with polar solvent molecules followed by thermal treatment under vacuum leading to the empty-pore forms of the title compounds. Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that 1, 2 and 3 are stable up to 260, 340 and 360 °C, respectively. The compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N(2), CO(2) and CH(4) sorption analyses, all of the thermally activated compounds exhibit significant microporosity (S(Langmuir): 769-842 m(2) g(-1)), which are comparable to that of the parent UiO-66 compound. Compared to the unfunctionalized UiO-66 compound, all the three functionalized solids possess higher ideal selectivity in adsorption of CO(2) over CH(4) at 33 °C.

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.

Heat capacities and thermodynamic functions of p-chlorobenzoic acid

The heat capacities of p-chlorobenzoic acid were measured in the temperature range from 80 to 580 K by means of an automatic adiabatic calorimeter equipped with a small sample cell of internal volume of 7.4cm(3). The construction and procedures of the calorimetric system were described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on alpha-Al2O3. The deviations of experimental heat capacities from the corresponding smoothed values lie within +/-0.28 per cent, while the inaccuracy is within +/-0.40 per cent, compared with the recommended reference data in the whole experimental temperature range. A fusion transition at T = 512.280 K was found from the C-p-T curve of p-chlorobenzoic acid. The enthalpy and entropy of the phase transition, as well as the thermodynamic functions {G((T)) - G((298.15))}, {H-(T) - H-(298.15)} and {S-(T) - S-298.15}, were derived from the heat capacity data. The mass fraction purity of p-chlorobenzoic acid sample used in the present calorimetric study was determined to be 0.99935 by fraction melting approach

Prussian Blue electrodeposited on MWNTs-PANI hybrid composites for H2O2 detection

A Prussian Blue (PB)/polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite film was fabricated by step-by-step electrodeposition on glassy carbon electrode (GCE). The electrode prepared exhibits enhanced electrocatalytic behavior and good stability for detection of H(2)O(2) at an applied potential of 0.0V. The effects of MWNTs thickness, electrodeposition time of PANI and rotating rate on the current response of the composite modified electrode toward H(2)O(2) were optimized to obtain the maximal sensitivity. A linear range from 8x10(-9) to 5x10(-6)M for H(2)O(2) detection has been observed at the PB/PANI/MWNTs modified GCE with a correlation coefficient of 0.997. The detection limit is 5x10(-9)M on signal-to-noise ratio of 3. To the best of our knowledge, this is the lowest detection limit for H(2)O(2) detection. The electrode also shows high sensitivity (526.43muAmuM(-1)cm(-2)) for H(2)O(2) detection which is more than three orders of magnitude higher than the reported.

Simultaneous determination of the concentration of methanol and relative humidity based on a single Nafion(Ag)-coated quartz crystal microbalance

Abstract A quartz crystal microbalance (QCM) coated with Nafion ® film recast from Nafion ® (Ag) complex solution has been used to investigate the interaction between methanol, water and Nafion ® (Ag) and to determine simultaneously the concentration of methanol and water (relative humidity). The frequency shift caused by methanol and water adsorbed onto Nafion ® (Ag) was in the order: water>methanol, due to larger association constant of water than methanol. Binding rate constant analysis showed that methanol demonstrates larger binding and dissociation rate constants than water due to larger vapor pressure of methanol. Molecular mechanics calculation gave binding energy change between Nafion ® (Ag) and methanol or water molecules. Artificial neural networks (ANNs) method was utilized to process the frequency response data of the single piezoelectric crystal at different times in the light of different adsorption dynamics of methanol and water on the Nafion ® (Ag) coated QCM. Concentrations of methanol and water can be estimated simultaneously with the ANNs.

Synthesis, structure and luminescent properties of coordination polymers with 1,2-benzenedicarboxylic acid and a series of flexible dicarboxylate ligands

A series of lanthanide coordination polymers, namely, [Ln(ox)0.5(phth)(H2O)2]·0.5H2O (Ln = Tb (1), Sm (2); H2ox = oxalic acid; H2phth = 1,2-benzenedicarboxylic acid), [Ln(mal)0.5(phth)(H2O)2]·H2O (Ln = Eu (3), Sm (4); H2mal = maleic acid), [Pr3(mal′)(phth)3(H2O)3]·H2O (5) (H2mal′ = malic acid) [Eu(ad)0.5(phth)(H2O)2] (Ln = Eu (6), Sm (7); H2ad = adipic acid), [Pr2(ad)(phth)2(H2O)4] (8) have been synthesized hydrothermally from the self-assembly of the lanthanide ions (Ln3+) with different types of flexible dicarboxylate ligands and the rigid 1,2-benzenedicarboxylate ligand. All coordination polymers were characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Structural analyses reveal that the networks of all eight complexes exhibit a variety of coordination modes at the metal centers. The thermal stabilities for 1, 3, 5, 6, 8, photoluminescent properties for 1–4 and 6–7 were examined, and the results show that the complexes seem to be good candidates for novel hybrid inorganic–organic photoactive materials with excellent thermal stability.

Cluster analysis by simulated annealing

Abstract The present paper tries to apply a new clustering algorithm based on simulated annealing to chemometric research. A new stopping criterion and perturbation method which are more feasible than those proposed in the literature, are proposed. The algorithm is first tested on simulated data, and then used for the classification of Chinese tea samples. The results show that the algorithm which guaranteed obtaining a global optimum compared favourably with the traditional hierarchical technique and K-means algorithm.