Ultrathin Metal-organic Framework Nanosheets Research Articles

Ultrathin MOF nanosheet assembled highly oriented microporous membrane as an interlayer for lithium-sulfur batteries

Lithium sulfur (Li-S) batteries are attracting increasing attentions as promising next-generation rechargeable batteries. However, the rapid capacity fading of sulfur cathodes caused by the shuttling of polysulfide intermediates between the cathodes and anodes restricts the application of Li-S batteries. In this work, a facile wet-chemistry method is developed for the direct synthesis of few-molecular-layer thin metal-organic framework (MOF) nanosheets without using surfactant. By assembling these ultrathin MOF nanosheets with a facile vacuum filtration method, a highly oriented and flexible MOF membrane with favorable mechanical properties is achieved for the first time. The excellent features make the as-prepared MOF nanosheets ideal to fabricate lightweight interlayer modified separators for suppressing the polysulfide shuttling of Li-S batteries. When using the MOF membrane modified separator, the Li-S batteries made from commercial carbon materials exhibits the significantly enhanced cycling stabilities. This work brings new opportunities for the synthesis and application of MOF materials.

Facile synthesis of ultrathin metal-organic framework nanosheets for Lewis acid catalysis

Ultrathin metal-organic framework (MOF) nanosheets are attracting great interest in catalysis due to their unique and intriguing two-dimensional (2D) features. Although many progresses have been achieved, it is still highly desirable to develop novel strategies for controllable synthesis of the well-defined ultrathin MOF nanosheets. Herein we report a polyvinylpyrrolidone (PVP)-assisted route to synthesize the ultrathin Ni-MOF nanosheets characteristic of 1.5 nm in thickness, in which PVP is reacted with 2-aminoterephthalic acid (H2BDC-NH2) via formation of C=N bond, followed by coordination with Ni2+ ions to form the ultrathin MOF nanosheets. Impressively, when used in the Knoevenagel condensation reactions of propane dinitrile with different aldehydes, ultrathin Ni-MOF nanosheets display the significantly enhanced catalytic activity and good stability in respect with the bulk Ni-MOF, mainly owing to the exposed active sites as well as facile mass transfer and diffusion of substrates and products.

Ultrathin Metal-Organic Framework Nanosheets as a Gutter Layer for Flexible Composite Gas Separation Membranes.

Ultrathin metal-organic framework (MOF) nanosheets show great potential in various separation applications. In this study, MOF nanosheets are incorporated as a gutter layer in high-performance, flexible thin-film composite membranes (TFCMs) for CO2 separation. Ultrathin MOF nanosheets (∼3-4 nm) were prepared via a surfactant-assisted method and subsequently coated onto a flexible porous support by vacuum filtration. This produced an ultrathin (∼25 nm), extremely flat MOF layer, which serves as a highly permeable gutter with reduced gas resistance when compared with conventional polydimethylsiloxane gutter layers. Subsequent spin-coating of the ultrathin MOF gutter layer with a polymeric selective layer (Polyactive) afforded a TFCM exhibiting the best CO2 separation performance yet reported for a flexible composite membrane (CO2 permeance of ∼2100 GPU with a CO2/N2 ideal selectivity of ∼30). Several unique MOF nanosheets were examined as gutter layers, each differing with regard to structure and thickness (∼10 and ∼80 nm), with results indicating that flexibility in the ultrathin MOF layer is critical for optimized membrane performance. The inclusion of ultrathin MOF nanosheets into next-generation TFCMs has the potential for major improvements in gas separation performance over current composite membrane designs.

Synthetic Strategies for Constructing Two‐Dimensional Metal‐Organic Layers (MOLs): A Tutorial Review

AbstractTwo‐dimensional (2D) metal‐organic layers (MOLs) are the 2D version of metal‐organic frameworks (MOFs) with nanometer thickness in one dimension. MOLs are also known as 2D‐MOFs, 2D coordination polymers, ultrathin MOF nanosheets (UMOFNs) or coordination nanosheets in literature. This new category of 2D materials has attracted a lot of interests because of the opportunity in combining molecular chemistry, surface/interface chemistry and material chemistry of low dimensional materials in these systems. Several synthetic strategies have been developed for the construction of 2D MOLs, but the general synthesis of MOLs still presents a challenge. This tutorial level review summarizes the recent progress in the fabrication of novel 2D MOLs and aims to highlight challenges in this field.

Bottom-Up Fabrication of Ultrathin 2D Zr Metal–Organic Framework Nanosheets through a Facile Continuous Microdroplet Flow Reaction

Direct synthesis of the ultrathin and discrete 2D metal–organic framework (MOF) nanosheets is extremely challenging. Herein, we present the first facile continuous bottom-up strategy for preparing ultrathin (∼3 nm) 2D MOF nanosheets with high crystallinity comprising assemblies of a few layers. Unlike conventional solvothermal synthetic methods for 2D MOFs, the weak interlayer interaction in the vertical direction of the 2D materials is restricted under microdroplet flow reaction conditions. The 2D MOF nanosheets with a large lateral area and a few layers thick were directly synthesized by suppressing the lamellar stacking of the nanosheets under the dynamic growth conditions. The 2D MOF nanosheets were characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, gas adsorption, and light scattering techniques, which were supported by density functional theory (DFT) ca...

Ultrathin 2D Zirconium Metal-Organic Framework Nanosheets: Preparation and Application in Photocatalysis.

Synthesizing ultrathin 2D metal-organic framework nanosheets in high yields has received increasing research interest but remains a great challenge. In this work, ultrathin zirconium-porphyrinic metal-organic framework (MOF) nanosheets with thickness down to ≈1.5 nm are synthesized through a pseudoassembly-disassembly strategy. Owing to the their unique properties originating from their ultrathin thickness and highly exposed active sites, the as-prepared ultrathin nanosheets exhibit far superior photocatalysis performance compared to the corresponding bulk MOF. This work highlights new opportunities in designing ultrathin MOF nanosheets and paves the way to expand the potential applications of MOFs.

Ultrathin Cu-TCPP MOF nanosheets: a new theragnostic nanoplatform with magnetic resonance/near-infrared thermal imaging for synergistic phototherapy of cancers.

Nanostructures based on metal-organic frameworks (MOFs) have promising potential as theragnostic nanoplatforms for phototherapy of cancer cells. However, the MOFs alone are seldom reported to be used as photothermal agents mainly due to their poor near-infrared (NIR) light absorption.Methods: Ultrathin copper-tetrakis (4-carboxyphenyl) porphyrin (Cu-TCPP) MOF nanosheets were prepared by a facile solvothermal route. The photothermal therapy (PTT), photodynamic therapy (PDT), and T1-weighted magnetic resonance (MR) imaging capabilities and the high biocompatibility of these composite nanosheets were evaluated in vitro as well as in vivo in a mouse tumor model.Results: The ultrathin Cu-TCPP MOF nanosheets exhibited 1) strong NIR absorption because of the d-d energy band transition of Cu2+ and the ultrathin characteristic translating into excellent photothermal performance, 2) ability to produce singlet oxygen because of the inherent characteristic of TCPP, and 3) capability for MR imaging because of the unpaired 3d electrons of copper.Conclusion: Our study demonstrated that the Cu-TCPP MOF nanosheets are a promising phototherapy nanoplatform with the synergistic ability for PTT and PDT of cancer, guided by MR and infrared thermal imaging.

Ultrathin Cobalt-Based Metal-Organic Framework Nanosheets with Both Metal and Ligand Redox Activities for Superior Lithium Storage.

The controllable synthesis and structural tailoring of nanostructured metal-organic frameworks (MOFs) is of huge significance in boosting their potential for rechargeable batteries. We herein present the facile synthesis of cobalt-based ultrathin metal-organic framework nanosheets (referred to as "u-CoTDA") by using 2,5-thiophenedicarboxylic (H2 TDA) as the organic building block through a one-pot ultrasonic method for the first time. The obtained u-CoTDA exhibits high reversible capacity (790 mAh g-1 after 400 cycles at 1 A g-1 ) and excellent rate capability (694 mAh g-1 at 2 A g-1 ), which outperforms its bulk counterpart. Moreover, the detailed lithiation/delithiation processes of u-CoTDA were studied by the combination of Co K-edge X-ray absorption near edge structure (XANES), O K-edge soft X-ray spectroscopy (sXAS) and electron paramagnetic resonance (EPR) techniques, which demonstrate that both the CoII centers and organic ligands of u-CoTDA are involved in the reduction/oxidation processes.

Ultrathin Manganese-Based Metal-Organic Framework Nanosheets: Low-Cost and Energy-Dense Lithium Storage Anodes with the Coexistence of Metal and Ligand Redox Activities.

We herein demonstrate the fabrication of Mn- and Ni-based ultrathin metal-organic framework nanosheets with the same coordination mode (termed "Mn-UMOFNs" and "Ni-UMOFNs", respectively) through an expedient and versatile ultrasonic approach and scrutinize their electrochemical properties as anode materials for rechargeable lithium batteries for the first time. The obtained Mn-UMOFNs with structure advantages over Ni-UMOFNs (thinner nanosheets, smaller metal-ion radius, higher specific surface area) exhibit high reversible capacity (1187 mAh g-1 at 100 mA g-1 for 100 cycles), excellent rate capability (701 mAh g-1 even at 2 A g-1), rapid Li+ diffusion coefficient (2.48 × 10-9 cm2 s-1), and a reasonable charge-discharge profile with low average operating potential at 0.4 V. On the grounds of the low-cost and environmental benignity of Mn metals and terephthalic acid linkers, our Mn-UMOFNs show alluring promise as a low-cost high-energy anode material for future LIBs. Furthermore, the lithiation-delithiation chemistry of Mn-UMOFNs was unequivocally studied by a combination of magnetic measurements, electron paramagnetic resonance, and synchrotron-based soft X-ray spectroscopy (O K-edge and Mn L-edge) experiments, the results of which substantiate that both the aromatic chelating ligands and the Mn2+ centers participate in lithium storage.

Controlled Intercalation and Chemical Exfoliation of Layered Metal-Organic Frameworks Using a Chemically Labile Intercalating Agent.

Creating ordered two-dimensional (2D) metal-organic framework (MOF) nanosheets has attracted extensive interest. However, it still remains a great challenge to synthesize ultrathin 2D MOF nanosheets with controlled thickness in high yields. In this work, we demonstrate a novel intercalation and chemical exfoliation approach to obtain MOF nanosheets from intrinsically layered MOF crystals. This approach involves two steps: first, layered porphyrinic MOF crystals are intercalated with 4,4'-dipyridyl disulfide through coordination bonding with the metal nodes; subsequently, selective cleavage of the disulfide bond induces exfoliation of the intercalated MOF crystals, leading to individual freestanding MOF nanosheets. This chemical exfoliation process can proceed efficiently at room temperature to produce ultrathin (∼1 nm) 2D MOF nanosheets in ∼57% overall yield. The obtained ultrathin nanosheets exhibit efficient and far superior heterogeneous photocatalysis performance compared with the corresponding bulk MOF.

Lanthanide-based metal-organic framework nanosheets with unique fluorescence quenching properties for two-color intracellular adenosine imaging in living cells

Two-dimensional (2D) materials have attracted tremendous interest as fluorescence quenchers of dye-labeled biomolecules for application in biosensing. Metal-organic framework (MOF) nanosheets, as a new type of 2D material, have rarely been studied as bioanalytical platforms. Herein, we synthesize a series of ultrathin lanthanide-based MOF (MOF-Ln) nanosheets as a dye-labeled aptamer platform. The fluorescence quenching or recovery on the MOF-Ln nanosheets is determined by the charge properties (positive or negative) of the labeled fluorophores. The negatively charged fluorophores experience a fluorescence ‘turn-down followed by turn-down’ process, whereas the positively charged fluorophores experience a fluorescence ‘turn-down followed by turn-up’ process. The interesting fluorescence quenching properties of the MOF-Ln nanosheets make them an excellent two-color sensing platform for the intracellular detection of biomolecules.

In situ synthesis of ultrathin metal–organic framework nanosheets: a new method for 2D metal-based nanoporous carbon electrocatalysts

Ultrathin ZIF-67 nanosheets are synthesized for the first time via a salt-template confined in situ growth strategy. And the directly carbonized Co,N-doped nanoporous carbon nanosheets greatly boost the oxygen reduction reaction (ORR) as well.