Chemistry
1
Abstract：
A series of Li2-xMn1-xGaxCl4 (x=0, 0.1, 0.3, and 0.5) materials were synthesized with the mechanochemical approach. As confirmed by X-ray powder diffraction and Rietveld refinements, Ga3+can be successfully incorporated into the octahedral sites that are partially occupied by Mn2+.The as-milled materials with relatively low crystallinity generally exhibit higher ionic conductivity than the well crystallized ones produced by annealing at 250 ℃. Among all the materials studied,the as-milled Li1.9Mn0.9Ga0.1Cl4shows the highest ionic conductivity (8.3×10-5 S·cm-1), which is two orders of magnitude higher than that of the as-milled Li2MnCl4(7.12×10-7 S·cm-1). While the unit cell volume does not vary significantly with the composition, the appropriate Li vacancy content should play an important role in the optimized ionic conductivity of Li1.9Mn0.9Ga0.1Cl4.
A series of Li2-xMn1-xGaxCl4 (x=0, 0.1, 0.3, and 0.5) materials were synthesized with the mechanochemical approach. As confirmed by X-ray powder diffraction and Rietveld refinements, Ga3+can be successfully incorporated into the octahedral sites that are partially occupied by Mn2+.The as-milled materials with relatively low crystallinity generally exhibit higher ionic conductivity than the well crystallized ones produced by annealing at 250 ℃. Among all the materials studied,the as-milled Li1.9Mn0.9Ga0.1Cl4shows the highest ionic conductivity (8.3×10-5 S·cm-1), which is two orders of magnitude higher than that of the as-milled Li2MnCl4(7.12×10-7 S·cm-1). While the unit cell volume does not vary significantly with the composition, the appropriate Li vacancy content should play an important role in the optimized ionic conductivity of Li1.9Mn0.9Ga0.1Cl4.
2
Abstract：
A quantitative analysis method was developed for determination of pectin content in tobacco samples by solid state 13C CP/MAS NMR. A 5.5 mm outer diameter of dimethyl silicone rubber tubing was designed and utilized as a reference of intensity, which was packed into a 5.5 mm inner diameter zirconia NMR rotor to construct an NMR sample tubing. The powder samples filled into the sample tubing were detected to obtain 13C CP/MAS NMR spectra. The peak of C-6 at 171 ppm was processed with spectral deconvolution to eliminate interference from overlapping peaks. The calibration curve was established with the area ratios of assigned C-6 peak to intensity reference peak and the mass of the polygalacturonic acid (PGA). This method was used to determine the pectin content in six different tobacco samples. Relative errors were between -4.94% and 3.84% compared with the results measured by the standard method. The recovery of PGA from spiked tobacco samples was ranged from 94.33% to 102.77%, the RSD (n=5) was less than 2.32%. It demonstrates that the 13C CP/MAS NMR method with a novel intensity reference possesses the properties of speediness, accuracy and simplicity, which is suitable for the quantitative analysis of pectin content in tobacco.
A quantitative analysis method was developed for determination of pectin content in tobacco samples by solid state 13C CP/MAS NMR. A 5.5 mm outer diameter of dimethyl silicone rubber tubing was designed and utilized as a reference of intensity, which was packed into a 5.5 mm inner diameter zirconia NMR rotor to construct an NMR sample tubing. The powder samples filled into the sample tubing were detected to obtain 13C CP/MAS NMR spectra. The peak of C-6 at 171 ppm was processed with spectral deconvolution to eliminate interference from overlapping peaks. The calibration curve was established with the area ratios of assigned C-6 peak to intensity reference peak and the mass of the polygalacturonic acid (PGA). This method was used to determine the pectin content in six different tobacco samples. Relative errors were between -4.94% and 3.84% compared with the results measured by the standard method. The recovery of PGA from spiked tobacco samples was ranged from 94.33% to 102.77%, the RSD (n=5) was less than 2.32%. It demonstrates that the 13C CP/MAS NMR method with a novel intensity reference possesses the properties of speediness, accuracy and simplicity, which is suitable for the quantitative analysis of pectin content in tobacco.
3
Abstract：
Hydrogen activation plays a pivotal role in hydrogenation reactions over transition metal oxide catalysts. Clarifying hydrogen activation over ceria oxide (CeO2) is an important issue in the acetylene hydrogenation reaction. Employing density functional theory (DFT) calculations, we studied hydrogen activation over stoichiometric and defective CeO2(111), (110), and (100) surfaces. Hydrogen dissociates on the stoichiometric CeO2 surfaces only forming hydroxyl groups. The presence of oxygen vacancies can promote the H2 activation over the defective CeO2 surfaces. Both H+ and H- species can be found on the defective CeO2(111) and (100) surfaces, whereas only H+ species can be observed on the defective CeO2(110) surface. The structure sensitivity of the H2 activation over the stoichiometric and defective CeO2 surfaces is correlated with H+ and H- adsorption energies determined by the ability of the surface oxygen vacancy formation and charge distributions of Ce and O ions. Our work provides more insight into H2 activation on CeO2-based catalysts which will guide better catalyst design for hydrogenation reactions.
Hydrogen activation plays a pivotal role in hydrogenation reactions over transition metal oxide catalysts. Clarifying hydrogen activation over ceria oxide (CeO2) is an important issue in the acetylene hydrogenation reaction. Employing density functional theory (DFT) calculations, we studied hydrogen activation over stoichiometric and defective CeO2(111), (110), and (100) surfaces. Hydrogen dissociates on the stoichiometric CeO2 surfaces only forming hydroxyl groups. The presence of oxygen vacancies can promote the H2 activation over the defective CeO2 surfaces. Both H+ and H- species can be found on the defective CeO2(111) and (100) surfaces, whereas only H+ species can be observed on the defective CeO2(110) surface. The structure sensitivity of the H2 activation over the stoichiometric and defective CeO2 surfaces is correlated with H+ and H- adsorption energies determined by the ability of the surface oxygen vacancy formation and charge distributions of Ce and O ions. Our work provides more insight into H2 activation on CeO2-based catalysts which will guide better catalyst design for hydrogenation reactions.
4
Abstract：
The thermal conductivity of polymer composites filled with hollow microspheres is closely related to the content and structure of hollow microspheres. In this paper, micron-sized monodisperse polystyrene (PS) microspheres are synthesized as the sacrificial template to prepare a series of hollow SiO2 (H-SiO2) microspheres with different inner and outer radius ratios (r/R).The r/R value is controlled by the relative content of PS microspheres and tetraethyl orthosilicate (TEOS). The chemical composition and morphology of H-SiO2 microspheres are characterized by infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Further, H-SiO2 microspheres are blended with polydimethylsiloxane (PDMS) at a certain content to obtain H-SiO2/PDMS composite rubbers. The effect of the content and the r/R value of H-SiO2 microspheres on the thermal conductivity of the composite rubber are investigated.Combined with the theoretical model calculation on the thermal conductivity of the silicone rubber,it can be concluded that the addition of H-SiO2 microspheres with a complete hollow structure and an r/R value higher than 0.963 can reduce the thermal conductivity of H-SiO2/PDMS composite rubbers.The more the H-SiO2 microspheres, the smaller the thermal conductivity of the composite rubber.At the same time, when the mass fraction of H-SiO2 microspheres is no more than 5%, the mechanical properties of the H-SiO2/PDMS composite rubber are also enhanced with the increase of the weight content of H-SiO2 microspheres. This work provides theoretical and experimental guidance for the design and preparation of high-performance hollow microspheres filled with polymer thermal insulation materials.
The thermal conductivity of polymer composites filled with hollow microspheres is closely related to the content and structure of hollow microspheres. In this paper, micron-sized monodisperse polystyrene (PS) microspheres are synthesized as the sacrificial template to prepare a series of hollow SiO2 (H-SiO2) microspheres with different inner and outer radius ratios (r/R).The r/R value is controlled by the relative content of PS microspheres and tetraethyl orthosilicate (TEOS). The chemical composition and morphology of H-SiO2 microspheres are characterized by infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Further, H-SiO2 microspheres are blended with polydimethylsiloxane (PDMS) at a certain content to obtain H-SiO2/PDMS composite rubbers. The effect of the content and the r/R value of H-SiO2 microspheres on the thermal conductivity of the composite rubber are investigated.Combined with the theoretical model calculation on the thermal conductivity of the silicone rubber,it can be concluded that the addition of H-SiO2 microspheres with a complete hollow structure and an r/R value higher than 0.963 can reduce the thermal conductivity of H-SiO2/PDMS composite rubbers.The more the H-SiO2 microspheres, the smaller the thermal conductivity of the composite rubber.At the same time, when the mass fraction of H-SiO2 microspheres is no more than 5%, the mechanical properties of the H-SiO2/PDMS composite rubber are also enhanced with the increase of the weight content of H-SiO2 microspheres. This work provides theoretical and experimental guidance for the design and preparation of high-performance hollow microspheres filled with polymer thermal insulation materials.
5
Abstract：
The effect of the matching relation between the cation and anion exchange membranes on the electrodialysis (ED) concentration performance was investigated through evaluating the salt flux, water flux, the flux ratio of salt to water and the salt content of the ED concentrate. Results indicate that the water uptake of the cation exchange membrane (CEM) is a key factor for the ED concentration performance when the ion exchange capacity of CEM has a feasible value; while for the anion exchange membrane (AEM), the ion permeability maybe is more important compared with the ion exchange capacity and the water uptake for the ED concentration performance. Besides, CEM has a greater significance for the ED concentration performance compared with AEM when both membranes have a relatively high ion permeability.
The effect of the matching relation between the cation and anion exchange membranes on the electrodialysis (ED) concentration performance was investigated through evaluating the salt flux, water flux, the flux ratio of salt to water and the salt content of the ED concentrate. Results indicate that the water uptake of the cation exchange membrane (CEM) is a key factor for the ED concentration performance when the ion exchange capacity of CEM has a feasible value; while for the anion exchange membrane (AEM), the ion permeability maybe is more important compared with the ion exchange capacity and the water uptake for the ED concentration performance. Besides, CEM has a greater significance for the ED concentration performance compared with AEM when both membranes have a relatively high ion permeability.
6
Abstract：
An efficient and mild method to prepare carbamoyl azides from NHP (N-hydroxyphthalimide) esters and TMSN3 was developed. The structure of carbamoyl azide was confirmed by the X-ray analysis. Corresponding carbamoyl azides were converted into carbamates for isolation. This methodology allows an efficient access to primary, secondary, tertiary alkyl and aryl carbamates. Mechanistic studies reveal that Curtius rearrangement is responsible for the generation of carbamoyl azides.
An efficient and mild method to prepare carbamoyl azides from NHP (N-hydroxyphthalimide) esters and TMSN3 was developed. The structure of carbamoyl azide was confirmed by the X-ray analysis. Corresponding carbamoyl azides were converted into carbamates for isolation. This methodology allows an efficient access to primary, secondary, tertiary alkyl and aryl carbamates. Mechanistic studies reveal that Curtius rearrangement is responsible for the generation of carbamoyl azides.
