A metal-organic-framework approach to engineer hollow bimetal oxide microspheres towards enhanced electrochemical performances of lithium storage

MoS2@MWCNTs with Rich Vacancy Defects for Effective Piezocatalytic Degradation of Norfloxacin via Innergenerated-H2O2: Enhanced Nonradical Pathway and Synergistic Mechanism with Radical Pathway

Molybdenum disulfide (MoS2)-based materials for piezocatalysis are unsatisfactory due to their low actual piezoelectric coefficient and poor electrical conductivity. Herein, 1T/3R phase MoS2 grown in situ on multiwalled carbon nanotubes (MWCNTs) was proposed. MoS2@MWCNTs exhibited the interwoven morphology of thin nanoflowers and tubes, and the piezoelectric response of MoS2@MWCNTs was 4.07 times higher than that of MoS2 via piezoresponse force microscopy (PFM) characterization. MoS2@MWCNTs exhibited superior activity with a 91% degradation rate of norfloxacin (NOR) after actually working 24 min (as for rhodamine B, reached 100% within 18 min) by pulse-mode ultrasonic vibration-triggered piezocatalysis. It was found that piezocatalysis for removing pollutants was attributed to the synergistic effect of free radicals (•OH and O2•-) and nonfree radical (1O2, key role) pathways, together with the innergenerated-H2O2 promoting the degradation rate. 1O2 can be generated by electron transfer and energy transfer pathways. The presence of oxygen vacancies (OVs) induced the transformation of O2 to 1O2 by triplet energy transfer. The fast charge transfer in MoS2@MWCNTs heterostructure and the coexistence of sulfur vacancies and OVs enhanced charge carrier separation resulting in a prominent piezoelectric effect. This work opens up new avenues for the development of efficient piezocatalysts that can be utilized for environmental purification.

Metal-organic framework derived bimetallic selenide embedded in nitrogen-doped carbon hierarchical nanosphere for highly reversible sodium-ion storage

Bimetallic selenides with various valence transitions and high theoretical capacities are extensively studied as anodes for sodium-ion-batteries (SIBs), but their huge volume changes and poor capacity retention limit their practicality. Herein, a facile and controllable strategy using a binary Ni-Co metal-organic framework (MOF) precursors followed by the selenization process, which produced a cobalt nickel selenide/N-doped carbon composite ((CoNi)Se₂/NC) that maintained the hierarchical nanospheres structure. Such a distinctive structure affords both Na⁺ and electron diffusion pathways in the electrochemical reactions as well as high electrical conductivity, thus leading to superior electrochemical performance when the designed composite is utilized as an anode in SIBs. The resulting nanospheres-like (CoNi)Se₂/NC hierarchical structure exhibits a high specific capacity of 526.8 mA h g^-1 at 0.2 A/g over 100 cycles, a stable cycle life with no obvious capacities loss at 1.0 and 3.0 A/g after 500 cycles, and exceptional rate capability of 322.9 mA h g^-1 at 10.0 A/g.

Bimetallic MOFs-Derived Hollow Carbon Spheres Assembled by Sheets for Sodium-Ion Batteries

Metal-organic frameworks (MOFs) have attracted extensive attention as precursors for the preparation of carbon-based materials due to their highly controllable composition, structure, and pore size distribution. However, there are few reports of MOFs using p-phenylenediamine (pPD) as the organic ligand. In this work, we report the preparation of a bimetallic MOF (CoCu-pPD) with pPD as the organic ligand, and its derived hollow carbon spheres (BMHCS). CoCu-pPD exhibits a hollow spherical structure assembled by nanosheets. BMHCS inherits the unique hollow spherical structure of CoCu-pPD, which also shows a large specific surface area and heteroatom doping. When using as the anode of sodium-ion batteries (SIBs), BMHCS exhibits excellent cycling stability (the capacity of 306 mA h g^-1 after 300 cycles at a current density of 1 A g^-1 and the capacity retention rate of 90%) and rate capability (the sodium storage capacity of 240 mA h g^-1 at 5 A g^-1). This work not only provides a strategy for the preparation of pPD-based bimetallic-MOFs, but also enhances the thermal stability of the pPD-based MOFs. In addition, this work also offers a new case for the morphology control of assembled carbon materials and has achieved excellent performance in the field of SIBs.

Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal-Organic Frameworks and Their Magnetic Characterization

The incorporation of multiple metal atoms in multivariate metal-organic frameworks is typically carried out through a one-pot synthesis procedure that involves the simultaneous reaction of the selected elements with the organic linkers. In order to attain control over the distribution of the elements and to be able to produce materials with controllable metal combinations, it is required to understand the synthetic and crystallization processes. In this work, we have completed a study with the RPF-4 MOF family, which is made of various rare-earth elements, to investigate and determine how the different initial combinations of metal cations result in different atomic distributions in the obtained materials. Thus, we have found that for equimolar combinations involving lanthanum and another rare-earth element, such as ytterbium, gadolinium, or dysprosium, a compositional segregation takes place in the products, resulting in crystals with different compositions. On the contrary, binary combinations of ytterbium, gadolinium, erbium, and dysprosium result in homogeneous distributions. This dissimilar behavior is ascribed to differences in the crystallization pathways through which the MOF is formed. Along with the synthetic and crystallization study and considering the structural features of this MOF family, we also disclose here a comprehensive characterization of the magnetic properties of the compounds and the heat capacity behavior under different external magnetic fields.

Realization of an Optical Thermometer via Structural Confinement and Energy Transfer

The influence of temperature on a variety of physiological or chemical processes has generated considerable interest, and recently noninvasive lanthanide-incorporated optical thermometers have been considered as promising candidates for monitoring its changes at different scales. Herein, a novel Bi³⁺-activated Sr_3-xGd_xGaO_4+xF_1-x phosphor with tunable color has been constructed by a cooperative cation-anion substitution strategy with to the replacement of [Sr²⁺-F^-] by [Gd³⁺-O^2-]. When x = 0, the sample Sr₃GaO₄F/Bi³⁺ possesses a peak wavelength at 438 nm, and this value will shift to 470 nm if x is equal to 1 (Sr₂GdGaO₅/Bi³⁺). In addition, photoluminescence tuning from blue to red has been realized successfully by an efficient Bi³⁺ → Eu³⁺ energy migration model in Sr_2.6Gd_0.4GaO_4.4F_0.6 samples. The specific Bi³⁺ → Eu³⁺ energy transfer has been explained by dipole-dipole interactions derived from a model of the Dexter pathway. Intriguingly, the two dopants (a blue signal from Bi³⁺ and a red signal from Eu³⁺) possess different thermal responses to increasing temperature. Accordingly, the intensity ratio values are sensitive to the temperature changes. The energy level cross relaxation causes the quenching effect of Bi³⁺, and the multi-phonon de-excitation mode leads to the thermal quenching of Eu³⁺. At room temperature (298 K), the determined maximum relative sensitivity (S_r) is 1.27% K^-1. Moreover, the absolute sensitivity (S_a) is 0.067 K^-1 since the temperature is elevated to 523 K. The collected results are superior to most of the reported optical thermometry materials.

Ultra-small Fe3O4 nanodots encapsulated in layered carbon nanosheets with fast kinetics for lithium/potassium-ion battery anodes

Iron oxides are regarded as promising anodes for both lithium-ion batteries (LIBs) and potassium-ion batteries (KIBs) due to their high theoretical capacity, abundant reserves, and low cost, but they are also facing great challenges due to the sluggish reaction kinetics, low electronic conductivity, huge volume change, and unstable electrode interphases. Moreover, iron oxides are normally prepared at high temperature, forming large particles because of Ostwald ripening, and exhibiting low electronic/ionic conductivity and unfavorable mechanical stability. To address those issues, herein, we have synthesized ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheets (Fe₃O₄@LCS), using the coordination interaction between catechol and Fe³⁺, demonstrating fast reaction kinetics, high capacity, and typical capacitive-controlled electrochemical behaviors. Such Fe₃O₄@LCS nanocomposites were derived from coordination compounds with layered structures via van der Waals's force. Fe₃O₄@LCS-500 (annealed at 500 °C) nanocomposites have displayed attractive features of ultra-small particle size (∼5 nm), high surface area, mesoporous and layered feature. When used as anodes, Fe₃O₄@LCS-500 nanocomposites delivered exceptional electrochemical performances of high reversible capacity, excellent cycle stability and rate performance for both LIBs and KIBs. Such exceptional performances are highly associated with features of Fe₃O₄@LCS-500 nanocomposites in shortening Li/K ion diffusion length, fast reaction kinetics, high electronic/ionic conductivity, and robust electrode interphase stability.

Ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheet nanocomposites were synthesized, showing fast reaction kinetics, high conductivity, and robust stability.

Study on Rh(I)/Ru(III) Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid

In this study, a Rh(I)/Ru(III) catalyst with a bimetallic space structure was designed and synthesized. The interaction between the metals of the bimetallic catalyst and the structure of the bridged dimer can effectively reduce the steric hindrance effect and help speed up the reaction rate while ensuring the stability of the catalyst. X-ray photoelectron spectroscopy (XPS) results show that rhodium accepts electrons from chlorine, thereby increasing the electron-rich nature of rhodium and improving the catalytic activity. This promotes the nucleophilic reaction of the catalyst with methyl iodide and reduces the reaction energy barrier. The methanol carbonylation performance of the Rh/Ru catalyst was evaluated, and the results show that the conversion rate of methyl acetate and the yield of acetic acid are 96.0% under certain conditions. Furthermore, during the catalysis, no precipitate is formed and the amount of water is greatly reduced. It can be seen that the catalyst has good stability and activity.

Ternary TiO2/SiOx@C nanocomposite derived from a novel titanium-silicon MOF for high-capacity and stable lithium storage

A novel titanium-silicon MOF precursor was first designed and constructed via a facile solvothermal process. After subsequent pyrolysis, the derived ternary TiO₂/SiO_x@C nanocomposite exhibited superior lithium storage performances, which was attributed to their all-in-one architecture of synergistic components, including stable-cycling nanostructured TiO₂, high-capacity SiO_x and high-conductivity carbon matrix.

Co/Ni-MOF-74-derived CoNi2S4 nanoparticles embedded in porous carbon as a high performance anode material for sodium ion batteries

In this study, Co/Ni-MOF-74-derived CoNi₂S₄ nanoparticles embedded in porous carbon (CoNi₂S₄@C) were successfully prepared using Co/Ni-MOF-74 as precursor. And, CoNi₂S₄@C exhibits excellent electrochemical performance as an anode material for sodium ion batteries.

Application of MOF-derived transition metal oxides and composites as anodes for lithium-ion batteries

Research progress of MOF-derived metal oxides and composites in lithium ion batteries has been presented based on different organic linkers.

Construction of 1D conductive Ni-MOF nanorods with fast Li+ kinetic diffusion and stable high-rate capacities as an anode for lithium ion batteries

1D Ni-MOFs with a hexagonal honeycomb structure, good electronic conductivity and fast Li⁺ kinetic diffusion were hydrothermally prepared, and they exhibited excellent lithium storage performance in terms of high-rate reversible capacity and long-duration cycling behavior as the anode material in lithium ion batteries.