Path connectivity of idempotents on a Hilbert space

Let and be two idempotents on a Hilbert space. In 2005, J. Giol in [Segments of bounded linear idempotents on a Hilbert space, J. Funct. Anal. 229(2005) 405-423] had established that, if is invertible, then and are homotopic with In this paper, we have given a necessary and sufficient condition that where denotes the minimal number of segments required to connect not only from to , but also from to in the set of idempotents.

     

层状复合氢氧化物的有机改性方法及应用研究进展

层状复合氢氧化物(LDHs)因其化学组成可调、比表面积大、生物相容性好等特点,目前在环境、能源和生物医药等领域广受关注.然而, LDHs在合成过程中由于其分子内作用力易发生团聚而导致其在基体中的分散不均匀,极大地限制了LDHs在实际中的应用.有机改性是改善LDHs分散性的有效方法,从表面改性和插层改性两个方面综述了近年来LDHs的有机改性方法,并介绍了其在阻燃、吸附、催化、气体阻隔、发光、储能和生物医药材料等领域的应用.最后对改性后LDHs未来的研究方向和应用领域进行了展望.     

Enhanced Four-Electron Oxygen Reduction Selectivity of Clamp-Shaped Cobalt(II) Porphyrin(2.1.2.1) Complexes

The molecular structure, electrochemistry, spectroelectrochemistry and electrocatalytic oxygen reduction reaction (ORR) features of two Co^II porphyrin(2.1.2.1) complexes bearing Ph or F₅Ph groups at the two meso-positions of the macrocycle are examined. Single crystal X-ray analysis reveal a highly bent, nonplanar macrocyclic conformation of the complex resulting in clamp-shaped molecular structures. Cyclic voltammetry paired with UV/Vis spectroelectrochemistry in PhCN/0.1 M TBAP suggest that the first electron addition corresponds to a macrocyclic-centered reduction while spectral changes observed during the first oxidation are consistent with a metal-centered Co^II/Co^III process. The activity of the clamp-shaped complexes towards heterogeneous ORR in 0.1 M KOH show selectivity towards the 4e⁻ ORR pathway giving H₂O. DFT first-principle calculations on the porphyrin catalyst indicates a lower overpotential for 4e⁻ ORR as compared to the 2e⁻ pathway, consistent with experimental data.     

Radical-Bridged Heterometallic Single-Molecule Magnets Incorporating Four Lanthanoceniums

The syntheses and magnetic properties of organometallic heterometallic compounds [K(THF)₆]{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 1-RE ) and [K(Crypt)]₂{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 2-RE ) containing hexaazatrinaphthylene radicals (HAN⋅³⁻) and four rare earth (RE) ions are reported. 1-RE shows isolable species with ligand-based mixed valency as revealed by cyclic voltammetry (CV) thus leading to the isolation of 2-RE via one-electron chemical reduction. Strong electronic communication in mixed-valency supports stronger overall ferromagnetic behaviors in 2-RE than 1-RE containing Gd and Dy ions. Ac magnetic susceptibility data reveal 1-Dy and 2-Dy both exhibit slow magnetic relaxation. Importantly, larger coercive field was observed in the hysteresis of 2-Dy at 2.0 K, indicating the enhanced SMM behavior compared with 1-Dy . Ligand-based mixed-valency strategy has been used for the first time to improve the magnetic coupling in lanthanide (Ln) SMMs, thus opening up new ways to construct strongly coupled Ln-SMMs.     

Two-dimensional Supramolecular Polymers Based on Selectively Recognized Aromatic Cation-π and Donor-Acceptor Motifs for Photocatalytic Hydrogen Evolution

Two-dimensional (2D) organic polymers have recently received considerable interest, especially those whose architectures are held together via supramolecular engineering. However, current approaches toward supramolecular 2D structures usually suffer from mutual interference of noncovalent interactions and lack of intrinsic functions. Herein, we report well-regulated 2D supramolecular polymers (2DSPs) through an aromatics-selective recognition strategy of cation-π and donor-acceptor (D-A) motifs, which are derived from C₄-symmetric cationic monomers and electron-withdrawing molecules. By subtly designing the strength and direction of noncovalent driving forces, the mutual interference between cation-π and D-A interactions is effectively avoided, enabling the construction of 2DSPs in aqueous solution. On this basis, the resultant 2DSPs possess boosted photocatalytic hydrogen evolution activity at a rate of 600 μmol g⁻¹ h⁻¹, which is mainly ascribed to the specific stacking mode of cation-π/D-A motifs and the ordered 2D structures.     

Ferric Single-Site Catalyst Confined in a Zeolite Framework for Propane Dehydrogenation

Non-oxidative dehydrogenation of propane is a highly efficient approach for industrial preparation of propene that is commonly catalyzed by noble Pt or toxic Cr catalysts and suffers from coking. In this work, ferric catalyst confined in a zeolite framework was synthesized by a hydrothermal procedure. The isolated Fe in the framework formed distorted tetrahedra, which were beneficial for the selective dehydrogenation of propane and reached over 95 % propene selectivity and over 99 % total olefins selectivity. This catalyst had a silanol-free structure and was oxygen tolerant, hydrothermally stable, and coke free, with a deactivation constant of 0.01 h⁻¹. This study provided guidance for the synthesis of structural heteroatomic zeolite and efficient propane non-oxidative dehydrogenation over early transition metals.     

Stabilizing Solid-state Lithium Metal Batteries through In Situ Generated Janus-heterarchical LiF-rich SEI in Ionic Liquid Confined 3D MOF/Polymer Membranes

Pursuing high power density lithium metal battery with high safety is essential for developing next-generation energy-storage devices, but uncontrollable electrolyte degradation and the consequence formed unstable solid-electrolyte interface (SEI) make the task really challenging. Herein, an ionic liquid (IL) confined MOF/Polymer 3D-porous membrane was constructed for boosting in situ electrochemical transformations of Janus-heterarchical LiF/Li₃N-rich SEI films on the nanofibers. Such a 3D-Janus SEI-incorporated into the separator offers fast Li⁺ transport routes, showing superior room-temperature ionic conductivity of 8.17×10⁻⁴ S cm⁻¹ and Li⁺ transfer number of 0.82. The cryo-TEM was employed to visually monitor the in situ formed LiF and Li₃N nanocrystals in SEI and the deposition of Li dendrites, which is greatly benefit to the theoretical simulation and kinetic analysis of the structural evolution during the battery charge and discharge process. In particular, this membrane with high thermal stability and mechanical strength used in solid-state Li||LiFePO₄ and Li||NCM-811 full cells and even in pouch cells showed enhanced rate-performance and ultra-long life spans.     

Improving Low-temperature Performance and Stability of Na2Ti6O13 Anodes by the Ti−O Spring Effect through Nb-doping

Na₂Ti₆O₁₃ (NTO) with high safety has been regarded as a promising anode candidate for sodium-ion batteries. In the present study, integrated modification of migration channels broadening, charge density re-distribution, and oxygen vacancies regulation are realized in case of Nb-doping and have obtained significantly enhanced cycling performance with 92 % reversible capacity retained after 3000 cycles at 3000 mA g⁻¹. Moreover, unexpected low-temperature performance with a high discharge capacity of 143 mAh g⁻¹ at 100 mA g⁻¹ under −15 °C is also achieved in the full cell. Theoretical investigation suggests that Nb preferentially replaces Ti3 sites, which effectively improves structural stability and lowers the diffusion energy barrier. What's more important, both the in situ X-ray diffraction (XRD) and in situ Raman furtherly confirm the robust spring effect of the Ti−O bond, making special charge compensation mechanism and respective regulation strategy to conquer the sluggish transport kinetics and low conductivity, which plays a key role in promoting electrochemical performance.     

A mechanistic study of selective propane dehydrogenations on MoS2 supported single Fe atoms

On-purpose propane dehydrogenation (PDH) has emerged as a profitable alternative to the traditional cracking of oil products for propylene production. By means of density functional theory (DFT) calculations, the present work demonstrates that Fe atoms may atomically disperse on MoS₂ (Fe₁/MoS₂) and serve as a promising single-atom catalyst (SAC) for PDH. The catalytic activity of Fe₁/MoS₂ is attributed to the highly exposed d orbitals of single Fe atoms, while the propylene selectivity is originated from the kinetic inhibition of propylene dehydrogenation resulting from fast propenyl hydrogenation. The unique catalytic selectivity of Fe₁/MoS₂ may inspire further investigations of on-purpose dehydrogenations of propane on SACs.     

Research progress on electrolytes for fast-charging lithium-ion batteries

Fast-charging is considered to be a key factor in the successful expansion and use of electric vehicles.Current lithium-ion batteries(LIBs) exhibit high energy density, enabling them to be used in electric vehicles(EVs) over long distances, but they take too long to charge. In addition to modifying the electrode and battery structure, the composition of the electrolyte also affects the fast-charging capability of LIBs. This review provides a comprehensive and in-depth overview of the research pr...