Green and Rational Design of 3D Layer-by-Layer MnO<i>_x</i> Hierarchically Mesoporous Microcuboids from MOF Templates for High-Rate and Long-Life Li-Ion Batteries

Rational design and delicate control on the textural properties of metal-oxide materials for diverse structure-dependent applications still remain formidable challenges. Here, we present an eco-friendly and facile approach to smartly fabricate three-dimensional (3D) layer-by-layer manganese oxide (MnO<i>_x</i>) hierarchical mesoporous microcuboids from a Mn-MOF-74-based template, using a one-step solution-phase reaction scheme at room temperature. Through the controlled exchange of metal–organic framework (MOF) ligand with OH^– in alkaline aqueous solution and in situ oxidation of manganese hydroxide intermediate, the Mn-MOF-74 template/precursor was readily converted to Mn₃O₄ or δ-MnO₂ counterpart consisting of primary nanoparticle and nanosheet building blocks, respectively, with well-retained morphology. By X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, high-resolution TEM, N₂ adsorption–desorption analysis and other techniques, their crystal structure, detailed morphology, and microstructure features were unambiguously revealed. Specifically, their electrochemical Li-ion insertion/extraction properties were well evaluated, and it turns out that these unique 3D microcuboids could achieve a sustained superior lithium-storage performance especially at high rates benefited from the well-orchestrated structural characteristics (Mn₃O₄ microcuboids: 890.7, 767.4, 560.1, and 437.1 mAh g^–1 after 400 cycles at 0.2, 0.5, 1, and 2 A g^–1, respectively; δ-MnO₂ microcuboids: 991.5, 660.8, 504.4, and 362.1 mAh g^–1 after 400 cycles at 0.2, 0.5, 1, and 2 A g^–1, respectively). To our knowledge, this is the most durable high-rate capability as well as the highest reversible capacity ever reported for pure MnO<i>_x</i> anodes, which even surpass most of their hybrids. This facile, green, and economical strategy renews the traditional MOF-derived synthesis for highly tailorable functional materials and opens up new opportunities for metal-oxide electrodes with high performance

Exploring the Capacity Limit: A Layered Hexacarboxylate-Based Metal–Organic Framework for Advanced Lithium Storage

Our previous work suggested that more carboxylate groups might lead to higher energy density for metal–organic frameworks. In this study, we synthesized a layered metal–organic framework (MOF) Ni-BHC by use of 1,2,3,4,5,6-benzenehexacarboxylic acid. After evacuation by thermal treatment, this MOF was employed as an anode for lithium storage. For its rich lithiation sites as well as layered fast-kinetics structure, it delivers a superior reversible capacity of 1261.3 mA h g^–1 at 100 mA g^–1, far exceeding the performance of previously reported MOF-based anode materials. Density functional theory calculation and O soft X-ray absorption spectroscopy suggest that the luxuriant carboxylate–metal units play an important part in the electrochemical process

High Anodic Performance of Co 1,3,5-Benzenetricarboxylate Coordination Polymers for Li-Ion Battery

We report the designed synthesis of Co 1,3,5-benzenetricarboxylate coordination polymers (CPs) via a straightforward hydrothermal method, in which three kinds of reaction solvents are selected to form CPs with various morphologies and dimensions. When tested as anode materials in Li-ion battery, the cycling stabilities of the three CoBTC CPs at a current density of 100 mA g^–1 have not evident difference; however, the reversible capacities are widely divergent when the current density is increased to 2 A g^–1. The optimized product CoBTC-EtOH maintains a reversible capacity of 473 mAh g^–1 at a rate of 2 A g^–1 after 500 galvanostatic charging/discharging cycles while retaining a nearly 100% Coulombic efficiency. The hollow microspherical morphology, accessible specific area, and the absence of coordination solvent of CoBTC-EtOH might be responsible for such difference. Furthermore, the ex situ soft X-ray absorption spectroscopy studies of CoBTC-EtOH under different states-of-charge suggest that the Co ions remain in the Co²⁺ state during the charging/discharging process. Therefore, Li ions are inserted to the organic moiety (including the carboxylate groups and the benzene ring) of CoBTC without the direct engagement of Co ions during electrochemical cycling

Synthesis of a Water-Soluble Carboxylatobiphen[4]arene and Its Selective Complexation toward Acetylcholine

The first water-soluble biphen[4]­arene containing eight carboxylato moieties (carboxylatobiphen[4]­arene, CBP4) has been synthesized. Selective molecular recognition of acetylcholine (<b>ACh</b>) against choline (<b>Ch</b>) and betaine (<b>Bt</b>) and pH-responsive host–guest complexation in aqueous media are described