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Oxygen-enriched carbon nanotubes as a bifunctional catalyst promote the oxygen reduction/evolution reactions in Li-O(2 )batteries
No full textThe aprotic lithium-oxygen (Li-O-2) batteries based on carbon-based oxygen cathodes usually suffer from low round-trip efficiency. Here we adopt oxygen-enriched carbon nanotubes (CNTs) by acid etching treatment as the cathode, in which a low voltage plateau at similar to 3.5 V during charge is exhibited and the initial round-trip efficiency is increased from 69.9% to 76.0%. An optimized integration of electrocatalytic property and electrical conductivity is crucial for the oxidized CNTs cathode to enhance the capacity and cycling performance. In particular, the surface oxygen groups can facilitate the electrocatalysis of O-2 with the enhanced oxygen reduction reaction activity and induce defective lithium peroxide (Li-O-2 ) formation due to their preferential adsorption of O-2 on the oxidized CNTs. Compared to the high crystalline Li-O-2 toroids, the defective Li-O-2 with poor crystallinity could be decomposed at a lower charge potential, contributing to the enhanced round-trip efficiency of Li-O(2 )batteries. (C) 2018 Elsevier Ltd. All rights reserved
Production of 1,2-Cyclohexanedicarboxylates from Diacetone Alcohol and Fumarates
No full text1,2-Cyclohexanedicarboxylates, which are one of the most commonly used plasticizers in the poly(vinyl chloride) (PVC) industry, are generally prepared via the oxidation/esterification/hydrogenation of o-xylene (or naphthalene). Herein, we develop an alternative route toward cyclohexane-based plasticizers using diacetone alcohol and fumarates as the starting materials. The process includes a mild Raney Ni-catalyzed hydrogenation of diacetone alcohol, an one-step dehydration/Diels-Alder reaction of resulting 2-methyl-2,4-pentandiol and fumarates in a choline chloride (ChCl) based deep eutectic solvent (DES), and a further Pd/C-catalyzed hydrogenation. The toxicological tests indicate that the as-synthesized di(2-ethylhexyl) 3,5-dimethylcyclohexane-1,2-dicarboxylate can serve as a safe plasticizer for PVC materials
Hollow metal organic frameworks composite prepared via an "escape from the cage" strategy
No full textA step-by-step self-assembly and concurrent self-etching strategy that differs from previous methods used to prepare SiO2@UiO-66-NH2 hollow composite has been reported. The magnetic core was selectively etched to generate a hollow metal-organic framework superstructure. The physical and chemical properties were characterized by TEM and SEM techniques, composition by SEM-EDX. Benefit from the efficient mass transfer and enhanced active sites accessibility, the hollow SiO2@UiO-66-NH2 composite showed higher or comparable catalytic activity than the nano-sized UiO-66-NH2 in the Knoevenagel condensation as a solid basic catalyst. Furthermore, it could be recovered and stable in terms of activity and structure when recycled for at least four times. (C) 2019 Elsevier B.V. All rights reserved
In vitro immunomodulatory effects of human milk oligosaccharides on murine macrophage RAW264.7 cells
No full textHuman milk plays an important role in the child's immune system. The human milk oligosaccharides (HMOs) may affect breast-fed infants both locally and systemically. In the present study, HMOs were separated, characterized and investigated for the immunomodulatory effects on RAW264.7 macrophages and its underlying molecular mechanisms. Our results revealed that HMO-7, one of the neutral HMOs fractions can significantly induce the production of nitric oxide (NO) and PGE2 via up-regulating nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) expression. Additionally, HMO-7 was found to stimulate the release of ROS, TNF-alpha and cytokines including IL-1 beta, IL-2, IL-6 and IL-10 in RAW264.7 macrophages. Further study showed that macrophage activated by HMO-7 involved in nuclear factor (NF)-kappa B and mitogen-activated protein kinase (MAPK) signaling pathways. Our study provides additional evidence that HMOs are the functional components in human milk and that HMOs may have the potential application in healthcare industry
Ni catalysts supported on nanosheet and nanoplate gamma-Al2O3 for carbon dioxide methanation
No full textNanosheet (S) and nanoplate (P) gamma-Al2O3 were synthesized by simple hydrothermal methods and employed as supports for Ni catalysts in CO2 methanation. Both of the nanostructured Ni/Al2O3 catalysts displayed good activity. In comparison, the Ni/Al2O3-S catalyst showed higher CO2 conversion than the Ni/Al2O3-P counterpart at the reaction temperature ranging from 250 to 400 degrees C. The physical and chemical properties of the catalysts were systematically characterized by N-2 sorption, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), hydrogen temperature-programmed reduction (H-2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) techniques. Higher specific surface area and stronger metal-support interactions were confirmed on the Ni/Al2O3-S catalyst, which may lead to smaller particle size of Ni nanoparticles. Moreover, the Ni/Al2O3-S catalyst possessed more abundant weak and medium basic sites, which would benefit the activation of CO2. The smaller Ni size and more suitable basic sites may rationalize the superior activity of the Ni/Al2O3-S catalyst. Besides, the Ni/Al2O3-S catalyst exhibited excellent stability at 325 degrees C for 40 h. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier By, and Science Press. All rights reserved
Enhanced hydrogen evolution reaction over molybdenum carbide nanoparticles confined inside single-walled carbon nanotubes
No full textCarbon nanotubes (CNTs) have shown as unique nanoreactors to tune the catalytic activity of confined nano-catalysts. Here we report that the catalytic performance of molybdenum carbide nanoparticles (MoCx NPs) for the hydrogen evolution reaction (HER) process can be enhanced by encapsulation within single-walled carbon nanotubes (SWNTs) with a diameter of 1-2 nm. The catalyst with MoCx NPs located on the interior surface of SWNTs (MoCx@SWNTs) exhibits a lower onset over-potential and a smaller Tafel slope than the one with MoCx NPs attached on the exterior surface (MoCx/SWNTs). This is likely attributed to the much smaller particle size and the more reduced states of the confined MoCx NPs, as well as the larger specific surface area of MoCx@SWNTs compared with MoCx/SWNTs. In addition, the electronic structure of the confined MoCx NPs might be modified by the confinement effects of SWNTs, and hence the adsorption free energy of H atoms on the confined MoCx NPs, which could also contribute to their higher performance. These results suggest that the SWNTs can be further explored for constructing novel catalysts with beneficial catalytic performance. (C) 2018 Published by Elsevier B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Science
Hydrodynamics and mass transfer characteristics of liquid-liquid slug flow in microchannels: The effects of temperature, fluid properties and channel size
No full textImmiscible liquid-liquid flow patterns and mass transfer were investigated in circular PTFE capillaries, with toluene-sulfuric acid, toluene-water and ethyl acetate-water systems. By comparing the slug flow operation range at different temperatures and capillary diameters, the results revealed the roles of inertia and viscous force in the transition from slug flow to droplet flow, and from slug flow to annular flow. A universal flow map based on composite terms of Ca(C)Re(C)(0.5)andCa(D)(0.7)Re(D)(0.5) was proposed to represent the competition between interfacial tension and the inertia/viscous force, which can excellently predict experimental data and literature results with fluid viscosity ranging from 0.85 to 1200 mPa.s. Additionally, the effect of temperature on the dispersed phase slug velocity, specific surface area and mass transfer was investigated and discussed, providing incremental understanding on the flow hydrodynamics and better guidance for optimized reactor design
Capturing CO2 to reversible ionic liquids for dissolution pretreatment of cellulose towards enhanced enzymatic hydrolysis
No full textTo overcome the natural recalcitrance of cellulose for glucose production in aqueous media catalyzed by enzyme, in this study, a dissolution pretreatment strategy was developed by using in situ formed CO2-based reversible ionic compounds (RICs)/DMSO mixed organic electrolytes under mild conditions. The influences of the constitution of RICs, CO2 pressure, dissolution pretreatment time on the physic-chemical structure of cellulose were investigated systematically by FTIR, XRD, SEM, AFM towards in-depth understanding of the correlations between the pretreatment conditions, micro-scale structure and enzymatic saccharification of cellulose. The results showed that the tetramethyl guanidine (TMG) based RICs solvent system [TMGH](2)(+)[O2COCH2CH2OCO2](2-)/DMSO (X-RICs = 0.1, X-RICs: the mole fraction of the formed RICs in the mixture) presented the best performance, which was evidenced by 100% glucose yield after the dissolution-regeneration pretreatment strategy under mild conditions (T = 60 degrees C, PCO2 = 2.0 MPa, t = 2 h). Furthermore, the solvent system have good recyclability and usability
Design, synthesis and evaluation of a series of alkylsiloxane-bonded stationary phases for expanded supercritical fluid chromatography separations
No full textSupercritical fluid chromatography (SFC) today represents an alternative technique in analytical chemistry due to its obvious benefits in kinetic performance and its complementarity to liquid chromatography. In this paper, a series of alkylsiloxane-bonded stationary phases were synthesized and evaluated to expand their SFC applications. Five kinds of non-endcapped C8 stationary phases (C8-1 to C8-5) with increasing bonding density were synthesized, and the carbon content was 3.91%, 6.07%, 7.97%, 8.65% and 9.10% respectively. Retention mechanism of the C8 phases in SFC in SFC was investigated by the use of a linear solvation energy relationship (LSER) model. Results underlined a close relationship between the bonding density of alkyl chain and the dispersion and polar interactions of the stationary phase. Complementary evaluation was studied based on the calculation of vector angle (theta), and the widest theta of 123 degrees was found between silica and C8 with the highest bonding density. Selective diversity also existed between the two C8 phases with the highest and lowest bonding densities. In addition, the effect of modifier on the SFC mechanism was investigated. Modifiers (methanol, ethanol, isopropanol and acetonitrile) had insignificant influence on the dispersion interaction but they mainly affected the hydrogen bonding interaction by changing the LSER parameters a and b. Finally, C8 and silica columns were applied for separation of eight amide alkaloids of Piper kadsura. Silica provided better retention but limited selectivity while C8 can distinguish alkaloids different in alkyl chain, double bond and cis-trans structure. This research further contributed to demonstrate the potential of alkylsiloxane-bonded stationary phase in improving selectivity of SFC. (C) 2019 Elsevier B.V. All rights reserved
Identification of different carbenium ion intermediates in zeolites with identical chabazite topology via(13)C-C-13 through-bond NMR correlations
No full textC-13-C-13 through-bond NMR correlation experiments reveal the stabilization of different carbenium ion intermediates in two zeolites possessing identical CHA topology (H-SAPO-34 and H-SSZ-13) during the methanol to olefins reaction