Ultrathin 2D Metal-organic Framework Research Articles

Synthesis of Homochiral N-Heterocyclic Carbene-Based Nanosheets for Enhanced Asymmetric Catalysis.

Utilizing ultrathin 2D metal-organic framework nanosheets (2D MONs) as supports for incorporating chiral catalysts represents a highly promising avenue in the field of asymmetric catalysis. In this study, four pairs of isostructural chiral metal-organic layers (MOLs) adorned with N-Heterocyclic carbene (NHC) groups are successfully synthesized. Notably, the obtained bulky (S)-1-Zn crystals can be readily delaminated into ultrathin MONs consisting of 1-2 layers through an ion intercalation-assisted exfoliation process. Subsequent asymmetric catalysis studies revealed that the NHC sites can be effectively activated by a proton sponge while maintaining structural integrity for the subsequent benzoin condensation. Due to their well-exposed catalytic sites, ultrathin morphology, and porous structure, the (S)-1-Zn nanosheets exhibited significantly enhanced yield and enantioselectivity compared to their bulk counterparts and organic precursors. This research highlights an efficient strategy for incorporating chiral NHC species onto 2D MONs, thereby unlocking their immense potential for heterogeneous asymmetric catalysis.

Decorating Cage-Shaped Cavities with Carboxyl Groups on Two-Dimensional MOF Nanosheet for Trace Uranium(VI) Trapping.

The efficient and complete extraction of uranium from aqueous solutions is crucial for safeguarding human health from potential radiotoxicity and chemotoxicity. Herein, an ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately constructed, based on a calix[4]arene ligand. The large molecular skeleton and cup-shaped feature of the calix[4]arene enabled the as-prepared MOFs with large layer separations, which can be readily delaminated into ultrathin single-layer (∼1.25 nm) nanosheets. The incorporation of permanent cavity structures to the MOF nanosheets can fully utilize their structural features of readily accessible adsorption groups and exposed surface area in uranium removal, reaching ultrafast adsorption kinetics; the functionalized cavity structure endowed MOF nanosheets with the ability to preconcentrate and extract uranium from aqueous solutions with ultrahigh efficiencies, even at extremely low concentrations. As a result, relatively high removal ratios (>95%) can be achieved for uranium within 5 min, even in the ultralow concentration range of 75-250 ppb, and the residual uranium was reduced to below 4.9 ppb. The MOF nanosheets also exhibited extremely high anti-interference ability, which could efficiently remove the low-level uranium (∼150 ppb) from various real samples. The characterizations and density functional theory calculations demonstrated that the synergistic effects of multiple interactions between the carboxylate groups and cage-like cavities with uranyl ions can be responsible for the efficient and selective uranium extraction.

Ultrathin 2D metal-organic framework nanosheet arrays to boost the overall efficiency of water splitting

Developing cost-effective and highly efficient electrocatalysts for water splitting has posed a significant challenge in recent research. This work presents a facile approach to synthesizing a 2D nickel-based metal-organic framework (TIT-1) using 2,3,5,6-tetracarboxyphenylpyrimidine (TCPP), 4,4′-bipyridine (BPY) and nickel nitrate hexahydrate under solvothermal conditions. The detailed structure and phase purity were characterized by X-ray analysis, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). To enhance the water electrolysis ability, the TIT-1 nanosheet (TIT-1@NS/NF) was fabricated via ultrasonic treatment of pure TIT-1 for 30 min. The TIT-1@NS/NF electrode was synthesized via an in-situ growth method and employed as an electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at ambient temperature. The results indicate that TIT-1@NS/NF achieved a current density of 10 mA cm−2 at an overpotential of 196 mV for OER and 270 mV for HER under the same conditions, so exhibiting superior performance compared to TIT-1. The electrochemical durability of TIT-1@NS/NF showed a retention rate of 87% for OER and 90% for HER. The superior electrocatalytic performance is primarily attribute to the synergistic impact of the 2D nanosheet architecture, which significantly increased the specific surface area and facilitated enhances electronic conductivity. The presence of partially deprotonated carboxylate groups and open metal sites (OMS) in TIT-1 further boosts the enhanced activity, as they exposed a multitude of unsaturated metal sites, thereby optimizing both the OER and HER process. Additionally, an asymmetric electrolytic cell comprising TIT-1@NS/NF was designed and assembled to assess its effectiveness for overall water splitting in alkaline conditions.

Integrating Photoactive Ligands into Crystalline Ultrathin 2D Metal-Organic Framework Nanosheets for Efficient Photoinduced Energy Transfer.

3D metal-organic frameworks (MOFs) have gained attention as heterogeneous photocatalysts due to their porosity and unique host-guest interactions. Despite their potential, MOFs face challenges, such as inefficient mass transport and limited light penetration in photoinduced energy transfer processes. Recent advancements in organic photocatalysis have uncovered a variety of photoactive cores, while their heterogenization remains an underexplored area with great potential to build MOFs. This gap is bridged by incorporating photoactive cores into 2D MOF nanosheets, a process that merges the realms of small-molecule photochemistry and MOF chemistry. This approach results in recyclable heterogeneous photocatalysts that exhibit an improved mass transfer efficiency. This research demonstrates a bottom-up synthetic method for embedding photoactive cores into 2D MOF nanosheets, successfully producing variants such as PCN-641-NS, PCN-643-NS, and PCN-644-NS. The synthetic conditions were systematically studied to optimize the crystallinity and morphology of these 2D MOF nanosheets. Enhanced host-guest interactions in these 2D structures were confirmed through various techniques, particularly solid-state NMR studies. Additionally, the efficiency of photoinduced energy transfer in these nanosheets was evidenced through photoborylation reactions and the generation of reactive oxygen species (ROS).

Ozonolysis–oxidation-driven top-down strategy for the target preparation of ultrathin 2D metal–organic framework monolayers

A novel chemical exfoliation method is developed for the target preparation of 2D MOF monolayers from the 3D pillar-layered MOFs.

Fabrication of Carboxylate-Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution.

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra-low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50-500µgL-1 within 5min. Moreover, the 2D nano-material exhibits ultra-high anti-interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

Ultrathin 2D Pd/Cu Single-Atom MOF Nanozyme to Synergistically Overcome Chemoresistance for Multienzyme Catalytic Cancer Therapy.

Single-atom nanozymes (SAzymes) have obtained increasing interest to mimic natural enzymes for efficient cancer therapy, while challenged by chemoresistance from cellular redox homeostasis and the interface of reductive species in tumor microenvironment (TME). Herein, a dual single-atomic ultrathin 2D metal organic framework (MOF) nanosheet of multienzyme (Pd/Cu SAzyme@Dzy) is prepared to synergistically overcome chemoresistance for multienzyme enhanced cancer catalytic therapy. The Pd SAzyme exhibits peroxidase (POD)-like catalytic activity for overcoming chemoresistance via disturbing cellular redox balance. This is further enhanced by cascade generation of more ∙OH via Cu+ -catalyzed POD-like reactions, initiated by in situ-reduction of Cu2+ into Cu+ upon GSH depletion. This process can also avoid the consumption of ∙OH by endogenous reductive GSH in TME, ensuring the adequate amount of ∙OH for highly efficient therapy. Besides, the DNAzyme is also delivered for gene therapy of silencing cancer-cell-targeting VEGFR2 protein to further enhance the therapy. Based on both experiments and theoretical calculations, the synergetic multienzyme-based cancer therapy is examined and the enhancement by the cascade tumor antichemoresistance is revealed.

Dextran-assisted ultrasonic exfoliation of two-dimensional metal-organic frameworks to evaluate acetylcholinesterase activity and inhibitor screening

Acetylcholinesterase (AChE) is regarded as a biomarker of Alzheimer's disease (AD), and its inhibitors show great potential in AD therapy as AChE can increase the neurotoxicity of the amyloid component that induces AD. Because of this, it is crucial and significant to develop a simple and highly sensitive strategy to monitor AChE levels and screen highly efficient AChE inhibitors. Herein, we synthesize an ultrathin two-dimensional (2D) metal-organic framework (MOF) based on copper-catecholate (Cu-CAT) via dextran assisted ultrasound exfoliation, followed by construction of a sensitive sensor for the monitoring AChE and screening of its inhibitors. By adding AChE, the acetylthiocholine (ATCh) substrate is hydrolyzed to be thiocholine (TCh), which decreases the peroxidase-like activity of Cu-CAT nanosheets (Cu-CAT NSs), impairing the signal reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidized-TMB (ox-TMB). In the presence of an AChE inhibitor, the signal can be gradually restored. The newly developed sensor shows high sensitivity and selectivity for AChE and huperzine A (HA, an effective drug for AD, an acetylcholine receptor antagonist), as well as for AD drug discovery from traditional Chinese herbs. The limit of detection of the sensor for AChE is 0.01 mU mL−1 and the average IC50 value of HA is 30.81 nM under the optimal of catalysis conditions. Compared with the 3D bulk Cu-CAT, the current 2D Cu-CAT NSs exhibit higher peroxidase activity due to more catalytic active site exposure. This study provides a strategy to prepare an ultrathin 2D MOF with high catalytic activity and new insights for the construction of a biosensor to monitor AChE and new AD drugs.

Pd nanoparticles decorated ultrathin 2D metal-organic framework nanosheets with enhanced peroxidase-mimic activity and colorimetric assay of glucose.

In addition to size, shape and morphology, enzyme-mimetic property could be efficiently regulated by controlling composition, forming complexes or hybrids, and surface modification. Herein, Pd nanoparticles with an average diameter of 2.52 nm were decorated on ultrathin 2D copper(ii)-porphyrin derived metal-organic framework (MOF) nanosheets by a simple reduction method for catalytic activity regulation. In comparison with other nanozymes, the as-synthesized Pd modified 2D MOF hybrid nanosheets (Pd@Cu-TCPP(Fe)) presented excellent peroxidase-mimic activity, exhibiting an even superior catalytic ability towards H2O2 with a Michaelis-Menten constant as low as 2.33 mM. Based on a cascade reaction between glucose oxidase and Pd@Cu-TCPP(Fe), a colorimetric method for the detection of glucose was established and validated with a wide linear range (0.2-8.0 mM), good recovery (89.5-94.2%) and nice reproducibility (3.65%). All these features guaranteed its excellent ability for glucose determination in human cerebrospinal fluids. This study could offer a valuable reference for constructing novel optical biosensors.

Microneedle-Assisted Transdermal Delivery of 2D Bimetallic Metal-Organic Framework Nanosheet-Based Cascade Biocatalysts for Enhanced Catalytic Therapy of Melanoma.

Current conventional treatments for malignant melanoma still face limitations, especially low therapeutic efficacy and serious side effects, and more effective strategies are urgently needed to develop them. Delivering biocatalysts into tumors to efficiently trigger in situ cascade reactions has shown huge potential in producing more therapeutic species or generating stronger tumoricidal effects for augmented tumor therapy. Recently, ultrathin 2D metal-organic framework (MOF) nanosheets have acquired great interest in biocatalysis owing to their large surface areas and abundant accessible active catalytic sites. Herein, an enhanced catalytic therapeutic strategy against melanoma is developed by biocompatible microneedle (MN)-assisted transdermal delivery of a 2D bimetallic MOF nanosheet-based cascade biocatalyst (Cu-TCPP(Fe)@GOD). Profiting from the constructed dissolving MN system, the loaded Cu-TCPP(Fe)@GOD hybrid nanosheets can be accurately delivered into the melanoma sites through skin barriers, and subsequently, trigger the specific cascade catalytic reactions in response to the acidic tumor microenvironment to effectively generate highly toxic hydroxyl radical (• OH) and deplete glucose nutrient for inducing the death of melanoma cells. The ultimate results prove the high melanoma inhibition effect and biosafety of such therapeutic modality, exhibiting a new and promising strategy to conquer malignant melanoma.

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.

Flow-homogeneous electrochemical sensing system based on 2D metal-organic framework nanozyme for successive microRNA assay

Considering DNA-based homogeneous electrochemical assay allows identification of targets to be carried out in a homogeneous solution, it would be of significance to develop the successive homogeneous assay system in dynamic solution for rapid disease diagnosis and high-throughput bioanalysis. In homogeneous assay, the work electrodes generally have capability of DNA capture but lack signal amplification, restricting its sensitivity. Here, a flow-homogeneous sensing system was proposed to realize the successive assay of microRNA, a model biomarker. Ultrathin 2D metal-organic framework (MOF) nanozymes with thickness of about 1 nm were facilely prepared by ultrasonic approach. Due to the excellent enzyme-like activity and adsorption capacity towards single-strand DNA (ssDNA), MOF nanozymes adsorbed on electrode simultaneously played two roles of ssDNA collector and signal-amplifier. To adapt the recoverable electrode to on-line monitoring, duplex-specific nuclease-assisted circle reaction was conducted to produce the turn-on amplified signal. Flow injection device was employed to realize the recycling of electrodes and the successive microRNA assay. The assay strategy showed low limit of detection (0.12 pM, S/N = 3) for microRNA, excellent renewability and acceptable reliability for real sample assay. The established system exerts the advantages of DNA-based homogeneous electrochemical sensing strategy. This work would not only expand homogeneous electrochemical assay to successive bioassay, but also provide the possibility for practical application of homogeneous sensing strategy.

Constructing 3D hierarchical MOFs nanospheres for oxygen evolution from high-throughput calculations

In order to realize outstanding electrochemical performance in oxygen evolution reactions (OER), it is important to construct 3D hierarchical nanospheres consisting of 2D bimetal metal–organic framework (MOF) nanosheets. Based on high-throughput density-functional theory (DFT) calculations, we chose Ni and V as central ions and prepared Ni-V bimetal MOFs nanospheres (NiV-MNs) assembled from ultrathin 2D MOFs nanosheets through a simple one-step solvothermal method. So far, V-based ultrathin 2D MOFs have been firstly reported. Gradient experiments demonstrated that NiV-MNs shows the best catalytic activity when the amount of Ni is equal to that of V (denoted as Ni1V1-MNs). The Ni1V1-MNs can deliver a high current density of 50 mA·cm−2 at a low over-potential of 370 mV in alkaline condition even after 10000 s continuous catalytic testing. Coincidentally, the DFT calculations further confirmed that the ΔG of Ni1V1-MNs is much lower compared with Ni1V2-MNs and Ni2V1-MNs. Based upon the experimental results and DFT calculations, we propose that the better performance of Ni1V1-MNs should be attributed to the grater intrinsic activity of Ni and the coupling effect between Ni and V, as they are crucial for tuning the electrochemical activity.

Ionic liquid-mediated catalytic oxidation of β-caryophyllene by ultrathin 2D metal-organic framework nanosheets under 1 atm O2

An ionic liquid (IL)-mediated facile method was established for the epoxidation of β-caryophyllene with molecular oxygen using ultrathin (∼3−6 nm) 2D Cu-, Co- or Ce-based MOF nanosheets. Under the optimum conditions, high selectivity (92.4%) and excellent yield (86.7%) for β-caryophyllene epoxide were obtained over ultrathin (∼5.5 nm) Cu-TCPP nanosheets (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with the aid of [C12mim]Cl at 313 K and 1 atm O2. Notably, a small amount of [C12mim]Cl (1-dodecyl-3-methylimidazolium chloride, 5.0 mol %) played pivotal roles in forming a favorable microenvironment in-situ, thus significantly improving the catalytic performances of above-mentioned Cu-TCPP nanosheets containing PVP stabilizer. Moreover, ultrathin Cu-TCPP nanosheets showed better stability during β-caryophyllene transformation in the presence of amphiphilic [C12mim]Cl, as supported by TEM and XRD analyses. Importantly, the addition of TBHP (tert-butyl hydroperoxide, 13.0 mol %) initiator is also crucial for the aerobic oxidation of β-caryophyllene viaCu-TCPP nanosheets/[C12mim]Cl/TBHP/O2 nanosystem. Further insights into the synergistic effects and free radical mechanism were achieved by fluorescence, DRUV-Vis, UV-vis and XPS measurements.

Ultrathin nanosheet-assembled accordion-like Ni-MOF for hydrazine hydrate amperometric sensing.

The ultrathin 2D metal-organic framework structure effectively increases the metal sites of the active molecules and endows Ni-MOF with good current sensing performance. The ultrathin 2D nanosheet Ni-MOF assemblies have been successfully synthesized by using (Ni3(OH)2(C8H4O4)2(H2O)4)·2H2O as the molecular formula. The sensor performance of Ni-MOF assemble was investigated by amperometric method. The resulting products are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electric signal generated by the electrochemical reaction on the electrode surface indicates that the assemble of Ni-MOF with ultrathin folded-like structure and special aggregation state has high electrocatalytic performance. In the detection of hydrazine hydrate, Ni-MOF assemble shows good stability, low detection limit (0.23nm), and high selectivity in the range of 0.5μM to 8.0mM at a voltage of 0.25V. This study provides a new idea for the application of MOF assemble in hydrazine hydrate sensor. Graphical abstract Schematic of illustration of the synthesis of the Ni-MOF and the Ni-MOF applied for catalyzing N2H4.

Encapsulating Pt Nanoparticles inside a Derived Two-Dimensional Metal-Organic Frameworks for the Enhancement of Catalytic Activity.

The development of highly active and stable electrocatalysts toward oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is a key for commercial application of fuel cells and water splitting. Here, we report a highly active and stable Pt nanoparticles (NPs) encapsulated in ultrathin two-dimensional (2D) carbon layers derived from the ultrathin 2D metal-organic framework precursor (ZIF-67). Electrochemical tests reveal that our approach not only stabilized Pt NPs successfully but also boosted Pt activities toward ORR and HER. We found that our Pt catalysts encapsulated in ultrathin 2D carbon layers exhibited an ORR activity of 5.9 and 12 times greater than those of the commercial Pt/C and Pt/RGO without 2D carbon layer protection. Our encapsulated Pt catalysts also show more than nine times higher stability than those of Pt/C catalysts. In addition to ORR, our novel encapsulated Pt catalysts display an extraordinary stability and activity toward HER, with a lower overpotential (14.3 mV in acidic media and 37.2 mV in alkaline media) at a current density of 10 mA cm-2 than Pt/C catalysts (23.1 mV in acidic media and 92.1 mV in alkaline media). The enhanced electrochemical activities and stability of our encapsulated Pt catalysts are attributed to the synergistic effect of Pt-based NPs and ultrathin 2D carbon layers derived from ZIF-67 with enriched active sites Co-Nx. First-principles simulations reveal that the synergistic catalysis of Pt-based NPs and Co-Nx derived from ZIF-67 improves the activity for ORR and HER.

Two-Dimensional Metal-Organic Framework Nanosheets with Cobalt-Porphyrins for High-Performance CO2 Electroreduction.

The electrochemical reduction of CO2 presents a promising strategy to mitigate the greenhouse effect and reduce excess carbon dioxide emission to realize a carbon-neutral energy cycle, but it suffers from the lack of high-performance electrocatalysts. In this work, catalytic active cobalt porphyrin [TCPP(Co)=(5,10,15,20)-tetrakis(4-carboxyphenyl)porphyrin-CoII ] was precisely anchored onto water-stable 2D metal-organic framework (MOF) nanosheets (Zr-BTB) to obtain ultrathin 2D MOF nanosheets [TCPP(Co)/Zr-BTB] with accessible catalytic sites for the CO2 reduction reaction. Compared with molecular cobalt porphyrin, the TCPP(Co)/Zr-BTB exhibits an ultrahigh turnover frequency (TOF=4768 h-1 at -0.919 V vs. reversible hydrogen electrode, RHE) owing to high active-site utilization. In addition, three post-modified 2D MOF nanosheets [TCPP(Co)/Zr-BTB-PABA, TCPP(Co)/Zr-BTB-PSBA, TCPP(Co)/Zr-BTB-PSABA] were obtained, with the modifiers of p-(aminomethyl)benzoic acid (PABA), p-sulfobenzoic acid potassium (PSBA), and p-sulfamidobenzoic acid (PSABA), to change the micro-environments around TCPP(Co) through the tuning of steric effects. Among them, the TCPP(Co)/Zr-BTB-PSABA exhibited the best performance with a faradaic efficiency (FECO ) of 85.1 %, TOF of 5315 h-1 , and jtotal of 6 mA cm-2 at -0.769 V (vs. RHE). In addition, the long-term durability of the electrocatalysts is evaluated and the role of pH buffer is revealed.

Removal of arsenic(iii) from water by 2D zeolitic imidazolate framework-67 nanosheets

Ultrathin 2D metal–organic framework nanosheets can efficiently and rapidly capture arsenate from water.

Ultrathin 2D metal–organic framework (nanosheets and nanofilms)-basedxD–2D hybrid nanostructures as biomimetic enzymes and supercapacitors

xD–2D hybrid nanostructures based on ultrathin 2D TCPP MOF exhibit great potential for application in biomimetic catalase and supercapacitors.

Ultrathin 2D metal-organic framework nanosheets prepared via sonication exfoliation of membranes from interfacial growth and exhibition of enhanced catalytic activity by their gold nanocomposites.

Ultrathin two-dimensional (2D) metal–organic framework (MOF) nanosheets were prepared by a facile sonication exfoliation of MOF membranes from interfacial growth. The stacked form of nanosheets constituting the MOF membranes was significantly different to that of its layered MOF counterparts. This led to decreased interaction between nanosheets, so they could exfoliate readily from the MOF membranes. Moreover, Au nanoparticles were introduced to form nanocomposites. Enhanced catalytic activity and long-term stability of these nanocomposites were observed by a model reaction of the reduction of 4-nitrophenol to 4-aminophenol. This preparation method could be extended to other 2D MOF nanosheets and their nanocomposites.