Dissolution of cellulose in aqueous NaOH/urea solution: role of urea

Urea can improve the solubility and stability of cellulose in aqueous alkali solution, while its role has not come to a conclusion. To reveal the role of urea in solution, NMR was introduced to investigate the interaction between urea and the other components in solution. Results from chemical shifts and longitudinal relaxation times show that: (1) urea has no strong direct interaction with cellulose as well as NaOH; (2) urea does not have much influence on the structural dynamics of water. Urea may play its role through van der Waals force. It may accumulate on the cellulose hydrophobic region to prevent dissolved cellulose molecules from re-gathering. The driving force for the self-assembly of cellulose and urea molecules might be hydrophobic interaction. In the process of cellulose dissolution, OH^? breaks the hydrogen bonds, Na⁺ hydrations stabilize the hydrophilic hydroxyl groups and urea stabilizes the hydrophobic part of cellulose.     

隔膜对双电层电容器和混合型电池-超级电容器的电化学性能的影响

隔膜是双电层电容器和混合型电池-超级电容器等电化学储能器件的重要组成元件.本文采用1 mol?L-1四乙基四氟硼酸铵的丙烯碳酸酯电解液制备了基于活性炭的扣式双电层电容器,并采用1 mol?L-1六氟磷酸锂锂离子电解液制备了(LiNi0.5Co0.2Mn0.3O2+活性炭)/石墨体系的混合型电池-超级电容器.研究了不同类型隔膜的物理化学性能,以及其对双电层电容器和混合型电池-超级电容器的电化学性能的影响.四种隔膜分别是无纺布聚丙烯毡、多孔聚丙烯薄膜、Al2O3涂层的聚丙烯薄膜和纤维素纸隔膜.进行了表面形貌、差示扫描量热、电解液吸液量和表观接触角测试表征.电化学测试表明,采用纤维素隔膜的双电层电容器具有最高的比电容和更优的倍率性能,电容器的自放电性能差别不大.而对于混合型电池-超级电容器,采用聚丙烯薄膜和无纺布聚丙烯毡隔膜器件的比容量比其它器件约高20%,且采用纤维素隔膜的器件自放电率最高.     

Modified two-derivative Runge–Kutta methods for the Schrödinger equation

A family of modified two-derivative Runge–Kutta (MTDRK) methods for the integration of the Schrödinger equation are obtained. Two new three-stage and fifth order TDRK methods are derived. The numerical results in the integration of the radial Schrödinger equation with the Woods–Saxon potential are reported to show the high efficiency of our new methods. The results of the error analysis are illustrated by the resonance problem.     

Control of N‐Heterocyclic Carbene Catalyzed Reactions of Enals: Asymmetric Synthesis of Oxindole‐γ‐Amino Acid Derivatives

A strategy to control the switch between a non‐cycloaddition reaction and a cycloaddition reaction of enals, using N‐heterocyclic carbene (NHC) catalyisis, has been developed. The new scalable protocol leads to γ‐amino‐acid esters bearing a tetrasubstituted stereocenter in good yields and high stereoselectivities by homo‐Mannich reactions of enals and isatin‐derived ketimines. By simply changing the N‐ketimine substituent to an ortho‐hydroxy phenyl group, the corresponding spirocyclic oxindolo‐γ‐lactams are obtained.     

Ultralong Phosphorescence from Organic Ionic Crystals under Ambient Conditions

A new type of materials, organic salts in the crystal state, have ultralong organic phosphorescence (UOP) under ambient conditions. The change of cations (NH₄⁺, Na⁺, or K⁺) in these phosphors gives access to tunable UOP colors ranging from sky blue to yellow green, along with ultralong emission lifetimes of over 504 ms. Single‐crystal analysis reveals that unique ionic bonding can promote an ordered arrangement of organic salts in crystal state, which then can facilitate molecular aggregation for UOP generation. Additionally, reversible ultralong phosphorescence can be realized through the alternative employment of fuming gases (ammonia and hydrogen chloride), demonstrating its potential as a candidate for visual ammonic or hydrogen chloride gas sensing. The results provide an environmental responsible and practicable synthetic approach to expanding the scope of ultralong organic phosphorescent materials as well as their applications.     

Experimental Evidence for a Triboluminescent Antiperovskite Ferroelectric: Tris(trimethylammonium) catena‐Tri‐μ‐chloro‐manganate(II) Tetrachloromanganate(II)

The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M₃AB‐type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic–inorganic hybrid X₃AB antiperovskite structure, which exhibits a clear ferroelectric phase transition 6/mmmF6mm with a high Curie point of 480 K. The physical properties across the phase transition are obviously changed along with the symmetry requirements, providing solid experimental evidence for the ferroelectric phase transition. More interestingly, the discovered antiperovskite shows intense photoluminescence and triboluminescence properties. The confirmation of the triboluminescent ferroelectric antiperovskite will open new avenues to explore excellent optoelectronic properties in the antiperovskite family.     

Introducing Fe2+ into Nickel–Iron Layered Double Hydroxide: Local Structure Modulated Water Oxidation Activity

Exploring materials with regulated local structures and understanding how the atomic motifs govern the reactivity and durability of catalysts are a critical challenge for designing advanced catalysts. Herein we report the tuning of the local atomic structure of nickel–iron layered double hydroxides (NiFe‐LDHs) by partially substituting Ni²⁺ with Fe²⁺ to introduce Fe‐O‐Fe moieties. These Fe²⁺‐containing NiFe‐LDHs exhibit enhanced oxygen evolution reaction (OER) activity with an ultralow overpotential of 195 mV at the current density of 10 mA cm^?2, which is among the best OER catalytic performance to date. In‐situ X‐ray absorption, Raman, and electrochemical analysis jointly reveal that the Fe‐O‐Fe motifs could stabilize high‐valent metal sites at low overpotentials, thereby enhancing the OER activity. These results reveal the importance of tuning the local atomic structure for designing high efficiency electrocatalysts.     

合成高密度烃类燃料研究进展

本文对合成高密度烃类燃料的进展进行了总结,分别对多环烃类燃料、高张力笼状烃类燃料和添加纳米级微粒的燃料进行了评述.以烃类物质为原料,通过聚合、加氢、异构等工艺合成的多环高密度燃料拥有较高的能量密度和较佳的稳定性能,是目前高密度燃 料的发展重点.高张力笼状烃类燃料和添加纳米级微粒的燃料拥有更大的密度(一般大于1g/ cm3)和燃烧热值,是极具发展前景的新一代燃料。     

线型共轭Cx桥联双金属有机化合物

分子电子器件是近年来的一个热门课题。线型共轭Cx桥联双金属有机化合物是分子导线、分子开关等分子电子器件的模型化合物之一。本文介绍了线型共轭Cx桥联双金属有机化合物的结构、合成及光电性质。     

Dual-Polarity Ion Trap Mass Spectrometry: Dynamic Monitoring and Controlling Gas-phase Ion–Ion Reactions

A dual-polarity linear ion trap (LIT) mass spectrometer was developed in this study, and the method for simultaneously controlling and detecting cations and anions was proposed and realized in the LIT. With the application of an additional dipolar DC field on the ejection electrodes of an LIT, dual-polarity mass spectra could be obtained, which include both the mass-to-charge (m/z) ratio and charge polarity information of an ion. Compared with conventional method, the ion ejection and detection efficiency could also be improved by about one-fold. Furthermore, ion–ion reactions within the LIT could be dynamically controlled and monitored by manipulating the distributions of ions with opposite charge polarities. This method was then used to control and study the reaction kinetics of ion–ion reactions, including electron transfer dissociation (ETD) and charge inversion reactions. A dual-polarity collision-induced dissociation (CID) experiment was proposed and performed to enhance the sequence coverage of a peptide ion. Ion trajectory simulations were also carried out for concept validation and system optimization.

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