Ultrathin Two-dimensional Metal-organic Framework Research Articles

Synthesis of ultrathin two-dimensional metal-organic framework nanosheets for lubricant additives

Two-dimension (2D) nano materials are diffusely employed as lubricant additives. In this paper, three kinds of ultrathin 2D metal-organic framework (MOF) nanosheets with different metal ions (Ni2+, Zn2+, and Cu2+) were successfully synthesized by ultrasonic assisted self-assembly under appropriate solvent ratio. Ni-MOF nanosheets as a new additive in 500 N system exhibit the best dispersion stability and lubrication performance, which is related to its maximum absolute value of Zeta potential. Compared with pure 500 N, the best tribological properties were obtained with the addition of 0.1 wt% Ni-MOF nanosheets, reducing friction by 33.2 ± 12.4 % and wear by 98.7 ± 0.14 %. The excellent performance originates from interlayer sliding effect, polishing effect, and tribofilm with concrete structure. The iron oxide particles embedded in the tribofilm play a supporting structrue for the whole tribofilm. The carbonaceous and nitrogenous compounds are filled around the iron oxide particles, which makes tribofilm denser and more smooth. The further friction tests under higher sliding velocity and longer term reveal the potential industrial use of Ni-MOF nanosheets.

Ultrathin metal organic framework nanosheets with rich defects for enhanced fluoride removal

Herein, we present a defluoridation approach based on ultrathin two-dimensional metal organic framework (MOF, viz., Ce-DCPBA) nanosheets. The nanosized layers and ultimately exposed metal defects of Ce-DCPBA enable the high-capacity adsorption of fluoride in a wide pH window. Attributed to tailored ligand exchange at metal defects and boron-fluoride complexation, Ce-DCPBA exhibits exceptional selectivity for fluoride with a partition coefficient up to 18.805 L g−1, even in the matrixes with ultrahigh salinity (8 mol/L of nitrate). Negligible interference from other anions, superior adsorption ability and favorable reusability promotes the practical application of Ce-DCPBA for the selective and efficient removal of fluoride from complex environmental samples. These findings furnish a promising strategy for the anesis of fluoride contamination, and illuminate the application potentials and superiorities of ultrathin MOFs-based nanostructures for environmental remediation.

Ligand-Assisted Controllable Growth of Self-Supporting Ultrathin Two-Dimensional Metal-Organic Framework Nanosheet Electrodes for an Efficient Oxygen Evolution Reaction.

Rational design of metal-organic frameworks (MOFs) into ultrathin two-dimensional (2D) nanosheets with controllable thickness is significantly attractive but is also a significant challenge. Herein, the authors report, for the first time, the synthesis of ultrathin 2D nickel-based MOF nanosheets with a thickness of only about 2 nm via a ligand-assisted controllable growth strategy, which cannot be acquired from the exfoliation of their bulky counterparts or the conventional hydrothermal method. The correlation between 2D nanosheets and crystal growth preference was demonstrated through a judicious choice of a specific [Ni(BIP)(p-BDC)(H2O)2]n framework (BIP = (3,5-bis(1-imidazoly)pyridine), p-H2BDC = terephthalic acid) to underlie the geometry of the resultant morphology. Under the modulation by the dosage of terephthalic acid through a corrosion-dissolution-coordination process, the nanosheets of Ni-MOFs with a controllable thickness can be tuned to 50 and 100 nm. Ultrathin 2D Ni-MOF nanosheet-derived N-doped Ni@carbon exhibits a satisfactory electrocatalytic performance with a small overpotential of 170 mV to achieve a current density of 10 mA cm-2, much outperforming the bulk Ni-MOF and the most reported non-noble-metal oxygen evolution reaction electrocatalysts to date. It is believed that this ligand-assisted controllable growth strategy represents a novel and simple path to prepare high-performance MOF-based electrocatalysts for wide applications.

Interaction of Nucleic Acids with Metal-Organic Framework Nanosheets by Fluorescence Spectroscopy and Molecular Dynamics Simulations.

The integration of nanomaterials and nucleic acids has attracted great attention in various research fields, especially biomedical applications. Designing two-dimensional nanomaterials and studying the mechanism of their interaction with nucleic acids are still attractive tasks. Herein, we designed and prepared a class of ultrathin two-dimensional metal-organic framework (MOF) nanosheets, named Zr-BTB MOF nanosheets, composed of Zr-O clusters and 1,3,5-benzenetribenzoate by a bottom-up synthesis strategy. The Zr-BTB MOF nanosheets possessed inherent excellent performance such as a high specific surface area, porosity, and biocompatibility. In addition, we clarified the interaction difference between the Zr-BTB MOF nanosheets and fluorophore-labeled double-stranded DNA and single-stranded DNA via molecular dynamics simulations and fluorescence measurement. Through molecular dynamics simulations, specific interactions between DNA and nanosheets such as forces, binding energies, and binding modes were deeply analyzed and clearly presented. Based on the affinity difference, the system showed the biosensing potential for target DNA detection with considerable specificity, sensitivity, and linearity. Our research results presented the Zr-BTB MOF nanosheet as a platform for nucleic acid detection, showing the potential for hybridization-based biosensing and related biological applications.

Ultrathin Two‐Dimensional Metal–Organic Framework Nanosheets Based on a Halogen‐Substituted Porphyrin Ligand: Synthesis and Catalytic Application in CO2 Reductive Amination

Ultrathin two-dimensional metal-organic framework nanosheets have emerged as a promising kind of heterogeneous catalysts. Herein, we report a series of 2D porphyrinic metal-organic framework nanosheets (X-PMOF, X=F, Cl, Br), which was prepared from the self-assembly of a halogen-based porphyrin ligand X-TCPP (X-TCPP=5-(4-halogenatedphenyl)-10,15,20-tris(4-carboxyphenyl)-porphyrin) and ZrCl4 in the presence of trifluoroacetic acid as the modulating reagent. The framework of X-PMOF possessed the ftw topology as in MOF-525. The lamellar X-PMOF nanosheets with the thickness of down to 4.5 nm were assembled and aggregated into a flower-like morphology. With the introduction of iridium(III) atoms into the porphyrin rings, the resultant X-PMOF(Ir) nanosheets were prepared by a similar method. Catalytic results show that Br-PMOF(Ir) nanosheets were efficient for CO2 reduction and aminolysis, giving rise to formamides in high yields under room temperature and atmospheric pressure, and can be recycled and reused for 3 runs. The total turnover number of Br-PMOF(Ir) after 3 runs was 1644 based on Ir. Mechanistic studies disclose that the high efficiency of Br-PMOF(Ir) nanosheets was ascribed to three factors, including the superior activation capability of iridium(III) porphyrin for Si-H bonds, more active sites on the external surfaces of Br-PMOF(Ir) nanosheets, and the defects caused by unsymmetrical porphyrin ligand that increased the framework's affinity towards CO2 .

Ultrafast Synthesis of Ultrathin Two-Dimensional Metal–Organic Framework Nanosheets with High Space-Time Yield

Ultrafast Synthesis of Ultrathin Two-Dimensional Metal–Organic Framework Nanosheets with High Space-Time Yield

Ultrathin Two-Dimensional Metal–Organic Framework Nanosheets with Activated Ligand-Cluster Units for Enhanced SERS

Ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets (MOFNs) comprise an emerging family of attractive materials with excellent potential for use in different catalytic, electrochemical, and sensing applications owing to their striking features such as ultrathin thickness, a large surface area, and highly ordered network structures. However, to the best of our knowledge, the ligand-cluster units activated through exfoliation into the MOFNs have rarely been realized, which is indeed crucial for surface-enhanced Raman scattering (SERS) analysis. Herein, we emphasize that the activated ligand-cluster units are based on the accessible coordination sites at the exposed cluster nodes accompanied by a complete excitation of the ligand-cluster units under incident photons, which make MOFNs highly effective SERS substrates, significantly outperforming their bulk counterparts. The SERS enhancement of MOFNs is further illustrated by an efficient integration of the inherent ligand-cluster charge-transfer (LCCT) transitions in MOFNs into interfacial charge-transfer processes through an "L"-type charge-transfer (CT) pathway, as further evidenced by an ultrahigh degree (0.98) of CT contributed to the SERS enhancement. This study provides an efficient strategy of exfoliating MOFs into ultrathin nanosheets for the design of highly efficient MOF-based SERS substrates.

Ultrathin two-dimensional metal–organic framework nanosheets for efficient electrochemical CO2 reduction

A novel two dimensional (2D) ultrathin sheet-like Zn-TCPP(Co)-MOF (TCPP= 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin) was developed and used to assemble a cathode on carbon paper (Zn-TCPP(Co)-MOF/CP) for highly efficient and selective electrochemical reduction of CO 2 in neutral aqueous solution. Deeply studies revealed that Co atom in the Zn-TCPP(Co)-MOF was the real catalytic active site for CO 2 reduction. • A novel 2D ultrathin Zn-TCPP(Co)-MOF was used to assemble a cathode for CO 2 reduction. • The cathode displayed high efficiency and selectivity on electrochemical reduction of CO 2 . • The coordinative metal atoms and the sp2 C at the pyrrole ligand were identified as active sites.

Ultrathin two-dimensional metal-organic framework nanosheets decorated with tetra-pyridyl calix[4]arene: Design, synthesis and application in pesticide detection

Chemical pesticides are highly toxic and widely spread as environmental pollutants. New strategies are being developed to selectively and sensitively detect pesticides. Herein, we prepared ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets, decorated with tetra-pyridyl calix[4]arene, for determination of pesticide based on host-guest chemistry. The 3D layered MOF {[Cd2(5-NO2-BDC)2L(MeOH)]∙2MeOH}n (MOF-Calix; 5-NO2-H2BDC = 5-nitro-1,3-benzenedicarboxylic acid; L = 25,26,27,28-tetra-[(4-pyridylmethyl)oxy]calix[4]arene) was elaborately constructed, with features of 2D layered structure that are held together by weak π…π interactions. Due to the cup-shaped characteristic of calix[4]arene ligand and easy-to-departure MeOH molecules in the interspaces of the 2D layers in MOF-Calix, the 3D bulk MOF-Calix can be readily exfoliated into ultrathin single (2.20 nm) or double-layer (3.73 nm) of 2D nanosheets by ultrasound method with high efficiency. We take the intrinsic advantages of calix[4]arene and the highly accessible active site of calix[4]arene on the surface of the 2D MOF-Calix nanosheets for selective and sensitive sensing of glyphosate via fluorescence enhancement effect with a detection limit of 2.25 μM. This work demonstrates the simple preparation of a 2D MOF nanosheet as fluorescent sensor for glyphosate detection.

Ultrathin two-dimensional metal-organic framework nanosheets-an emerging class of catalytic nanomaterials.

The development of ultrathin two-dimensional metal-organic framework nanosheets (2D MONs) has recently attracted increasing interest due to their extensive application potential originating from their ultrathin thickness, large surface area, and innumerable accessible surface-active sites. In this frontier article, we highlight the recent developments of 2D MONs for highly efficient heterogeneous catalysts; they can be grouped into three sections in terms of their functions: (i) as catalysts capable of showing outstanding intrinsic reactivity, (ii) as support materials for prevalent catalysts, and (iii) as catalysts with multifunctional catalytic activity for diverse organic transformations. In addition, the present challenges and future opportunities in this field are also discussed.

Boosting Enantioselectivity of Chiral Organocatalysts with Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets.

The development of methodologies for inducing and tailoring enantioselectivities of catalysts is an important issue in asymmetric catalysis. In this work, we demonstrate for the first time that chiral molecular catalysts can be boosted from completely nonselective to highly enantioselective when installed in nanostructured metal-organic frameworks (MOFs). Exfoliation of layered crystals is one of the most direct synthetic routes to unltrathin nanosheets, but its use in MOFs is limited by the availability of layered MOFs. We illustrate that layered MOFs can be designed using ligand-capped metal clusters and angular organic linkers. This leads to the synthesis of two three-dimensional (3D) layered porous MOFs from Zn4-p-tert-butylsulfonyl calix[4]arene and chiral angular 1,1'-binaphthol/-biphenol dicarboxylic acids, which can be ultrasonic exfoliated into one- and two-layer nanosheets. The obtained MOF materials are efficient catalysts for asymmetric cascade condensation and cyclization of 2-aminobenzamide and aldehydes to produce 2,3-dihyroquinazolinones. While both binaphthol and biphenol display no enantioselectivity, restriction of their freedom in the MOFs leads to 56-90% and 46-72% ee, respectively, which are increased to 72-94% and 64-82% ee after exposure to external surfaces of the flexible nanosheets. Moreover, the MOF crystals and nanosheets exhibit highly sensitive fluorescent enhancement in the presence of chiral amino alcohols with enantioselectivity factors being, respectively, increased up to 1.4 and 2.3 times of the values of the diols, allowing them to be utilized in chiral sensing. Therefore, the observed enantioselectivities increase in the order organocatalyst < MOF crystals < MOF nanosheets in both catalysis and sensing. This work not only provides a strategy to make 3D layered MOFs and their untrathin nanosheets but also paves the way to utilize nanostructured MOFs to manipulate enantioselectivities of molecular catalysts.

Specific Generation of Singlet Oxygen through the Russell Mechanism in Hypoxic Tumors and GSH Depletion by Cu-TCPP Nanosheets for Cancer Therapy.

The generation of singlet oxygen (1 O2 ) during photodynamic therapy is limited by the precise cooperation of light, photosensitizer, and oxygen, and the therapeutic efficiency is restricted by the elevated glutathione (GSH) levels in cancer cells. Herein, we report that an ultrathin two-dimensional metal-organic framework of Cu-TCPP nanosheets (TCPP=tetrakis(4-carboxyphenyl)porphyrin) can selectively generate 1 O2 in a tumor microenvironment. This process is based on the peroxidation of the TCPP ligand by acidic H2 O2 followed by reduction to peroxyl radicals under the action of the peroxidase-like nanosheets and Cu2+ , and their spontaneous recombination reaction by the Russell mechanism. In addition, the nanosheets can also deplete GSH. Consequently, the Cu-TCPP nanosheets can selectively destroy tumor cells with high efficiency, constituting an attractive way to overcome current limitations of photodynamic therapy.

Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets with the Inherent Open Active Sites as Electrocatalysts in Aprotic Li-O2 Batteries.

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have the potential to improve the performance of Li-O2 batteries with high O2 accessibility, open catalytic active sites, and large surface areas. To obtain highly efficient cathode catalysts for aprotic Li-O2 batteries, a facile ultrasonicated method has been developed to synthesize three kinds of 2D MOFs (2D Co-MOF, Ni-MOF, and Mn-MOF). Contributing from the inherent open active sites of the Mn-O framework, the discharge specific capacity of 9464 mAh g-1 is achieved with the 2D Mn-MOF cathode, higher than those of the 2D Co-MOF and Ni-MOF cathodes. During the cycling test, the 2D Mn-MOF cathode stably operates more than 200 cycles at 100 mA g-1 with a curtailed discharge capacity of 1000 mAh g-1, quite longer than those of others. According to further electrochemical analysis, we observe that the 2D Mn-MOF outperforms 2D Ni-MOF and Co-MOF due to a superior oxygen reduction reactions and oxygen evolution reactions activity, in particular, the efficient oxidation of both LiOH and Li2O2. The present study provides new insights that the 2D MOF nanosheets can be well applied as the Li-O2 cells with high energy density and long cycling life.

Assembly of highly efficient photocatalytic CO2 conversion systems with ultrathin two-dimensional metal–organic framework nanosheets

An ultrathin two-dimensional Zn porphyrin-based metal–organic framework (Zn-MOF nanosheets) is developed and used for the first time in photoreduction of CO2 to CO. Consequently, two novelty noble-metal-free hybrid photocatalytic systems are established and displayed outstanding photocatalytic activity and selectivity for CO evolution under mild photocatalytic reaction conditions. The insight revealed Zn-MOF nanosheets as photosensitizer displays a better charge transport ability and longer lifetime of the photogenerated electron-hole pairs than the Zn-MOF bulk, which are confirmed by photoelectrochemical impedance and photoluminescence (PL) measurements. These studies show that the development of noble-metal-free photocatalytic systems and various MOF-based materials for photocatalytic applications are promising.