Classical spin liquid state in a rhombic lattice metal-organic framework

Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter.Here,we report spin-liquid-like behavior in a two-dimensional(2D)rhombic lattice Fe-metal-organic framework(Fe-MOF)with frustrated antiferromagnetism.This Fe-MOF exhibits a high frustration factor f=|θCW|/TN≥315,and its long-range magnetic order is suppressed down to 180 mK.Detailed theoretical calculations demonstrate strong antiferromagnetic coupling between adjacent Fe3+ions,indicating the potential of a classical spin-liquid-like behavior.Notably,a T-linear heat capacity parameter,γ,originating from electronic contributions and with magnetic field independence up to 8 T,can be observed in the specific heat capacity measurements at low-temperature,providing further proof for the spin-liquid-like behavior.This work highlights the potential of MOF materials in geometrically frustrated systems,and will promote the research of exotic quantum physics phenomena.

Probing surface structure on two-dimensional metal-organic layers to understand suppressed interlayer packing

Two-dimensional metal-organic layers(MOLs)from alternatively connected benzene-tribenzoate ligands and Zr6(μ3-O)_(4)(μ3-OH)_(4) or Hf6(μ3-O)_(4)(μ3-OH)_(4) secondary building units can be prepared in gram scale via solvothermal synthesis.However,the reason why the monolayers did not pack to form thick crystals is unknown.Here we investigated the surface structure of the MOLs by a combination of sum-frequency generation spectroscopy,nanoscale infrared microscopy,atomic force microscopy,aberration-corrected transmission electron microscopy,and compositional analysis.We found a partial coverage of the monolayer surface by dangling tricarboxylate ligands,which prevent packing of the monolayers.This finding illustrates low-density surface modification as a strategy to prepare new two-dimensional materials with a high percentage of exposed surface.

Thermal expansion-quench of nickel metal-organic framework into nanosheets for efficient visible light CO_(2) reduction

Metal-organic framework nanosheets (MOF NNs) offer potential opportunities for many applications,but an efficient strategy for the scalable preparation of few-layered two-dimensional (2D) MOF NNs are still a major challenge.Herein,we present an efficient top-down method for the synthesis of the Ni-BDC(Ni_(2)(OH)_(2)(1,4-BDC);1,4-BDC=1,4-benzenedicarboxylate) nanosheets utilizing a novel thermal expansionquench method of the flowerlike bulky MOFs in liquid N2.The obtained Ni-BDC nanosheets exhibit significantly enhanced photocatalytic performance of reductive CO_(2)deoxygenation (7.0μmol h^(-1)mg^(-1)) under visible light illumination compared with the bulky MOFs,due to much higher surface area for CO_(2)adsorption,more abundant active sites exposed and stronger electron transport ability of the nanosheets.More importantly,this synthetic strategy can be extended to fabricate other MOF nanosheets which also exhibit significantly improved performance for deoxygenative CO_(2)reduction compared to their bulky counterparts.This work may provide a guideline for preparing other 2D layered photocatalysts materials to realize energy conversion applications.

Heterointerface engineering of assembled CoP_(2) on N-modified carbon as efficient trifunctional electrocatalysts for Zn-Air batteries and overall water splitting

Enhancing catalytic activity through modulating the interaction between N-doped carbon and metal phosphides clusters is an effective approach.Herein,the electronic structure modulation of CoP_(2) supported N-modified carbon(CoP_(2)/NC)has been designed and prepared as efficient electrocatalysts for oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER).Notably,CoP_(2)/NC-1 catalyst exhibits impressive performance in alkaline media,with an ORR half-wave potential of 0.84 V,as well as OER and HER overpotentials of 290 and 129 mV(at 10 mA·cm^(−2)),respectively.In addition,CoP_(2)/NC-1 produces a power density as high as 172.9 mW·cm^(−2),and excellent reversibility of 100 h at 20 mA·cm^(−2) in home-made Zn-air batteries.The experimental results demonstrate that the synergistic interactions between N modified carbon substrate and CoP_(2) material significantly enhance the kinetics of ORR,OER,and HER.Density functional theory(DFT)calculations reveal the strong electrons redistribution of CoP_(2) induced by high-density N atoms at the interface,thus optimizing the key intermediates and significantly lower the energy barrier of reactions.These electronic adjustments of CoP_(2) greatly enhance its kinetics of ORR/OER/HER,leading to faster reactions.This study provides profound insights into the specific modification of CoP_(2) by N-doped carbon,enabling the construction of efficient catalysts.

Multistep evolution from a metal–organic framework to ultrathin nanosheets

Two-dimensional (2D) materials and ultrathin nanosheets have attracted tremendous research interests [1-4]. Exfoliation of porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) with 2D coordination structures is emerging as a viable strategy for preparation of new types of 2D materials [5-8]. The relatively weak bonding within and strong interactions between 2D coordination networks are the main problems for successful exfoliation [9]. Pretreatments of the layered MOFs to expand the interlayer distances can be helpful [10-12]. Capturing the exfoliation intermediates and visualizing their structures are valuable for understanding the exfoliation mechanism and confirming the structures of the final 2D materials [11,12].

High-loading single cobalt atoms on ultrathin MOF nanosheets for efficient photocatalytic CO_(2) reduction

Based on suitable scaffolds,constructing high-loading single-atom catalysts is a promising strategy to achieve highly efficient catalysis.Herein,using ultrathin metal-organic framework(MOF)nanosheets(2.4±0.5 nm)as the support,single-atom catalysts with high cobalt loading(6.0 wt%)were constructed(denoted as Co-MNSs)by a simple bottom-up synthetic strategy.The catalytic system of Co-MNSs exhibited an outstanding photocatalytic CO_(2)-to-CO evolution rate of 7,041μmol g^(-1)h^(-1)and a selectivity of 86%in aqueous media under visible-light irradiation,which has reached the top level of the reported MOF-based photocatalysts.The control experiments and theoretical calculation revealed that the Co-N_(4)moiety in the MOF nanosheets acted as the active site for the photocatalytic CO_(2)-to-CO conversion.The boosted photocatalytic performance could be ascribed to the high aspect-ratio of layered Co-MNSs providing abundant accessible active sites on their surfaces,which reduced the energy barrier,improved the charge separation efficiency,and also facilitated the adsorption of CO_(2)to form the reactive radicals of*COOH.Our study provides an appealing strategy for constructing high-loading single-atom catalysts and demonstrates the significance of 2D ultrathin MOF nanosheets as the support in boosting CO_(2)photoreduction efficiency.

Emerging porous nanosheets:From fundamental synthesis to promising applications

Metal-organic framework(MOF)nanosheets and covalent organic framework(COF)nanosheets as emerging porous materials nanosheets have captured increasing attention owing to their attractive properties originating from the advantages of large lateral size,ultrathin thickness,tailorable physiochemical environment,flexibility and highly accessible active sites on surface,and the applications of them have been explored in a wide range of fields.Although MOF and COF nanosheets own many similar properties,their applications in various fields show significant differences,probably due to their different compositions and bonding modes.Hence,we summarize the recent progress of MOF and COF nanosheets by comparative analysis on their advantages and limitations in synthesis and applications,providing a more profound and full-scale perspective for researchers or beginners to understand this field.Herein,the categories of preparation methods of MOF and COF nanosheets are firstly discussed,including top-down and bottom-up methods.Secondly,the applications of MOF and COF nanosheets for separation,catalysis,sensing and energy storage are summarized.Finally,based on current achievements,we put forward our personal insights into the challenges and outlooks on the synthesis,characterizations,and promising applications for future research of MOF and COF nanosheets.