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Significant reduction of phase-transition hysteresis for magnetocaloric (La1-xCex)(2)Fe11Si2Hy alloys by microstructural manipulation
No full textFirst-order magnetostructural phase transitions are inevitably accompanied by large hysteresis, which evokes non-ignorable energy losses a main challenge for the utilization of giant magnetocaloric effect (MCE) materials in the emerging magnetic cooling technology. In this work, we present a novel approach to reduce the hysteresis and simultaneously to remain the giant entropy change in La-Fe-Si-based MCE alloys by microstructural manipulation. The microstructure evolution is comprehensively studied by high angle annular dark field-scanning transmission electron microscope, three-dimensional atom probe and geometric phase analysis. For the LaFe13-xSix system via co-doping of Ce and H atoms, we have observed the appearance of nanograins in size range of 5 - 50 nm that is totally different from the widely reported compositions. Such refinement can be ascribed to the release of internal stress caused by the inhomogeneous distribution of hydrogen atoms. With the formation of the nanocrystals in (La1-xCex)(2)Fe11Si2Hy alloys, the value of hysteresis loss can be monotonously reduced from 48.3 to 0.6 J kg(-1). More importantly, the magnetostructural transition keeps an obvious first-order type, which leads to a large adiabatic temperature change of 2.03 K in 1.3 T upon 10(5) magnetic cycles, as well as a high reversible refrigeration capacity of 89.4 J kg(-1) for (La0.6Ce0.4)(2)Fe11Si2Hy. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Poly(1,4-butylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate) copolyester: Potential bio-based engineering plastic
No full textPoly(1,4-butylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate) (PBCFs) was synthesized from biobased 2,5-furandicarboxylic acid (FDCA), 1,4-butanediol (BDO) and 1,4-cyclohexanedimethanol (CHDM). The GPC showed that the number average molecular weight (M-n) of PBCFs were in the range of 38400-44200 g/mol and the average molecular weight (M-w) varied from 83,000 to 94,800 g/mol with the polydispersity index of 2.22-2.33. The chemical structures, compositions and sequence distributions of PBCFs were confirmed by H-1 NMR and C-13 NMR. Their thermal properties and crystallization behavior were investigated by Differential Scanning Calorimeter (DSC). Results showed that the glass transition temperature (T-g) and melting temperature (T-m) of poly(butylene 2,5-furandicarboxylate) (PBF) were increased from 38 and 171.8 degrees C to 65.8 and 211.7 degrees C for PBCF-68, respectively. Furthermore, the strength and modulus were increased from 44 and 950 MPa for PBF to 69 and 1360 MPa for PBCF-68 with the mole percentage of CHDM units of 68% in diol units. PBCFs demonstrated much better thermo-mechanical properties when compared with those of PBF, which might be used as the bio-based engineering plastic or excellent packaging materials with high transparency and good gas barrier properties
Polyamide thin-film composite membrane on polyethylene porous membrane: Fabrication, characterization and application in water treatment
No full textThe ultrafiltration membranes fabricated by the non-solvent induced phase separation (NIPS) have been widely used as the supports of the polyamide thin film composite (PA TFC) membranes, although they are usually thick, low porosity, and poor chemical stability. Instead, thin polyethylene (PE) lithium battery microporous membrane with high surface porosity and connected pores is used as the support layer. PE membrane was pre-modified by the co-deposition of tannin and 3-aminopropyltriethoxysilane improving its hydrophilicity, and then a uniform and defect-free PA active layer was successfully fabricated by interfacial polymerization. The resultant membrane exhibited high filtration performances in the forward osmosis (FO) process (2 times higher water flux and 90% lower specific salt flux than the commercial HTI-TFC membrane), and efficient separation of NaCI and dyes in nanofiltration (NF) process, outstanding chemical stability and mechanical strength. (C) 2020 Elsevier B.V. All rights reserved
Direct evidence of electron-hole compensation for extreme magnetoresistance in topologically trivial YBi
No full textThe prediction of topological states in rare-earth monopnictide compounds has attracted renewed interest. Extreme magnetoresistance (XMR) has also been observed in several nonmagnetic rare-earth monopnictide compounds. The origin of XMR in these compounds could be attributed to several mechanisms, such as topologically nontrivial electronic structures and electron-hole carrier balance. YBi is a typical rare-earth monopnictide exhibiting XMR and is expected to have a nontrivial electronic structure. In this work, we perform a direct investigation of the electronic structure of YBi by combining angle-resolved photoemission spectroscopy and theoretical calculations. Our results show that YBi is topologically trivial without the expected band inversion, and they rule out the topological effect as the cause of XMR in YBi. Furthermore, we directly observed nearly perfect electron-hole compensation in the electronic structure of YBi, which could be the primary mechanism accounting for the XMR
Interface engineering of mesoporous triphasic cobalt-copper phosphides as active electrocatalysts for overall water splitting
No full textEfficient electrocatalysts for water splitting are essential for viable generation of highly purified hydrogen. Hence there is a need to develop robust catalysts to eliminate barriers associated with sluggish kinetics associated with both anodic oxygen and cathodic hydrogen evolution reactions. Herein, we report a two-step nanocasting-solid phase phosphorization approach to generate ordered mesoporous triphasic phosphides CoP@Cu2P-Cu3P. We show that it is a highly efficient bifunctional electrocatalyst useful for overall water splitting. The mesoporous triphasic CoP@Cu2P-Cu3P only requires a low overpotential of 255 mV and 188 mV to achieve 10 mA cm(-2) for oxygen and hydrogen evolution reactions, respectively. The combination of mesoporous pores (similar to 5.6 nm) with very thin walls (similar to 3.7 nm) and conductive networks in triphasic CoP@Cu2P-Cu3P enable rapid rate of electron transfer and mass transfer. In addition, when CoP@Cu2P-Cu3P is used to fabricate symmetric electrodes, the high surface area mesoporous structure and synergetic effects between phases together contribute to a low cell voltage of 1.54 V to drive a current density 10 mA cm(-2). This performance is superior to noble-metal-based Pt/C-IrO2/C. This work provides a new approach for the facile design and application of multiphase phosphides as highly active bifunctional and stable electrocatalysts for water-alkali electrolyzers
Microstructural design in LaCe misch-metal substituted 2:14:1-type sintered magnets by dual-alloy method
No full textLaCe-based sintered magnets with different microstructural features and distinct rare earth elemental distribution were designed by dual-alloy method. The sample prepared by fine LaCe-containing powder and coarse LaCe-free powder possesses higher remanence (similar to 13.41 kGs), whereas another sample prepared by fine LaCe-free powder and coarse LaCe-containing powder possesses higher coercivity (similar to 5.67 kOe). Additionally, these samples are with the same nominal compositions and their elemental distribution features are obviously different in matrix grains respectively. Their remanence difference is mainly affected by the saturation magnetization difference caused by the distribution variation of the rare earth elements at the matrix phase. The coercivity difference is affected by the component of the grain boundary phase between the adjacent grains and the distribution variation of the rare earth elements at the matrix phase. These findings may provide a new prospect for the utilization of LaCe misch-metal in 2:14:1-type permanent magnets. (C) 2020 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths
A novel Cl- modification approach to develop highly efficient photocatalytic oxygen evolution over BiVO4 with AQE of 34.6%
No full textWater oxidation with multielectron transfer is regarded as the crucial step in photocatalytic water splitting. However, a facile but efficient method to promote its slow kinetics is still highly demanding. This work demonstrates that Clsurface modification drastically enhances photocatalytic water oxidation over BiVO4 as well as WO3. The optimal modified BiVO4 achieves a photocatalytic activity of 4.2 orders enhancement relative to the pristine BiVO4, giving up to an excellent apparent quantum efficiency of 34.6% at 420 nm. Cl--modified 30-facet BiVO4 with 2.6 times enhancement confirms that the surface reaction involved with photogenerated holes can be dramatically accelerated by Clmodification in addition to enhanced charge carrier separation. Our results highlight the impact of Clmodification on the reaction kinetics and pathway during the photocatalytic water oxidation process, which has been mostly overlooked. Systematic studies (DFT simulations, kinetic experiments) reveal that Clmodification remarkably reduces the photocatalytic water oxidation energy barrier and alters reaction pathway, which is also manifested in facilitated H2O molecule activation in synchronous illumination XPS (SI-XPS) study. The EXAFS and angle-resolved XPS (AR-XPS) results show that Cl bonds to Bi and mainly concentrates on the surface of modified BiVO4. Our findings provide an effective and facile approach to exploring efficient O-2 evolution semiconductors for photocatalytic water splitting
Pressure-induced amorphous zeolitic imidazole frameworks with reduced toxicity and increased tumor accumulation improves therapeutic efficacy In vivo
No full textZeolitic Imidazole Frameworks (ZIFs) are widely applied in nanomedicine for their high drug loading, suitable pore size, pH-responsive drug release, and so on. However, fast drug release during circulation, unexpected toxicity to mice major organs, undesirable long-term accumulation in the lung and even death currently hinder their in vivo biomedical applications. Herein, we report an amorphous ZIF-8 (aZIF-8) with high loading of 5-Fu through pressure-induced amorphization. This nano-system avoids early drug release during circulation and provides tumor microenvironment-responsive drug release with improved in vitro cell viability, and survival rate in in vivo evaluations as compared to ZIF-8. Furthermore, aZIF-8 shows longer blood circulation and lower lung accumulation than ZIF-8 at same injected doses. Less drug release during circulation, longer blood circulation, and better biocompatibility of aZIF-8/5-Fu significantly improves its therapeutic efficacy in ECA-109 tumor-bearing mouse, and result in 100% survival rate over 50 days after treatment. Therefore, aZIF-8 with favorable biocompatibility and long blood circulation is expected to be a promising nano-system for efficacious cancer therapy in vivo
Heterogeneous single-cluster catalysts (Mn-3, Fe-3, Co-3, and Mo-3) supported on nitrogen-doped graphene for robust electrochemical nitrogen reduction
No full textElectrochemical nitrogen reduction reaction (NRR) is one of the most promising alternatives to the traditional Haber-Bosch process. Designing efficient electrocatalysts is still challenging. Inspired by the recent experimental and theoretical advances on single-cluster catalysts (SCCs), we systematically investigated the catalytic performance of various triple-transition-metal-atom clusters anchored on nitrogen-doped graphene for NRR through density functional theory (DFT) calculation. Among them, Mn-3-N4, Fe-3-N4, Co-3-N4, and Mo-3-N4 were screened out as electrocatalysis systems composed of non-noble metal with high activity, selectivity, stability, and feasibility. Particularly, the Co-3-N4 possesses the highest activity with a limiting potential of -0.41 V through the enzymatic mechanism. The outstanding performance of Co-3-N4 can be attributed to the unique electronic structure leading to strong it backdonation, which is crucial in effective N-2 activation. This work not only predicts four efficient non-noble metal electrocatalysts for NRR, but also suggest the SCCs can serve as potential candidates for other important electrochemical reactions. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved
Synthesis and gas separation performances of intrinsically microporous polyimides based on 4-methylcatechol-derived monomers
No full textNovel dibenzodioxane-containing dianhydride (MMBMDA) and diamine (FDBDA and MMBDA) monomers with sterically hindered contortion sites and pendent fluorene or trimethylbenzene moieties were prepared using 4-methylcatechol as a major reactant. High temperature polycondensation of these monomers and 4,4'-(hexafluomisopropylidene) diphthalic anhydride (6FDA) enabled the synthesis of intrinsically microporous polyimides (PIM-PI) with adequately high molecular weights. The surface area, fractional free volume, and d-spacing of these PIM-PIs were 385-543 m(2)g(-1), 0.179-0.212, and 0.672-0.683 nm, respectively, following the order of MMBMDA-FDBDA > MMBMDA-MMBDA > 6FDA-FDBDA > 6FDA-MMBDA. Moreover, the high rigidity of MMBMDA-based PIM-PIs induced the formation of ultramicropores (<0.7 nm), which enhanced their gas-sieving capability. The PIM-PIs developed in this study showed favorable O-2/N-2, CO2/N-2, and CO2/CH4 separation performances because of their rigid, sterically hindered and contorted architectures. In particular, MMBMDA-FDBDA exhibited comparable gas separation performances to the benchmark PIM-1 membrane