Two-dimensional metal-organic frameworks nanosheets: Synthesis strategies and applications

Electrochemical Synthesis and Electrocatalytic Oxygen-Evolution Performance of Two-Dimensional NiCo-BPDC Materials

Metal-organic frameworks (MOFs) have been widely studied as electrocatalysts, and the research strategy to improve their electrocatalytic oxygen evolution reaction (OER) performance is to modify their structure. In this paper, two-dimensional bimetallic MOFs were constructed to improve electrocatalytic OER performance. Using a mild electrochemical method with Ni and Co as metal sources and 4, 4 '-biphenyl dicarboxylic acid (H2BPDC) as ligand, two-dimensional NiCo-BPDC was synthesized and then deposited on a carbon cloth electrode. The results show that NiCo-BPDC/CC possessed a low overpotential of 356 mV at a current density of 20 mA cm-2 with a small Tafel slope of 86 mV dec-1 in 1.0 M KOH solution. The two-dimensional NiCo-BPDC exhibits excellent electrocatalytic OER performance because the coordination of Ni and Co in the material and the interaction of the two-dimensional materials provide a large electrochemically active surface area and expose more metal active sites for OER, thus improving the reaction efficiency and indicating NiCo-BPDC as potential OER electrocatalyst.

Nanosheet-Assembled Zirconium-Porphyrin Frameworks Enabling Surface-Confined, Initiator-Free Photosynthesis of Ultrahigh Molecular Weight Polymers

Metal-organic frameworks with well-organized low-dimensional architectures provide significant thermodynamic and/or kinetic benefits for diverse applications. We present here the controlled synthesis of a novel class of hierarchical zirconium-porphyrin frameworks (ZrPHPs) with nanosheet-assembled hexagonal prism morphology. The crystal growth behaviors and structural evolution of ZrPHPs in an additive-modulated solvothermal synthesis are examined, showing an "assembly-hydrolysis-reassembly" mechanism towards the formation of 2D nanosheets with ordered arrangement. Because of the highly-accessible active sites harvesting broadband photons, ZrPHPs serve as adaptable photocatalysts to regulate macromolecular synthesis under full-range visible light and natural sunlight. An initiator-free, oxygen-tolerant photopolymerization system is established, following a distinctive mechanism involving direct photo-induced electron transfer to dormant species and hole-mediated reversible deactivation. Specifically, ZrPHPs provide a surface-confined effect towards the propagating chains which inhibits their recombination termination, enabling the highly-efficient synthesis of ultrahigh molecular weight polymers (Mn >1,500,000) with relatively low dispersity (Đ≈1.5).

Two-Dimensional Copper/Nickel Metal-Organic Framework Nanosheets for Non-Enzymatic Electrochemical Glucose Detection

Metal-organic frameworks (MOFs) have broad potential applications in electrochemical glucose detection. Herein, a green ultrasonic synthesis process is presented for preparing two-dimensional (2D) copper-nickel metal-organic framework nanosheets (CuNi-MOFNs) for glucose detection. The synthesized CuNi-MOFNs were characterized using scanning electron microscopy (SEM), scanning transmission electron microscope (STEM), X-ray diffractometer (XRD), and X-ray photoelectron spectrometer (XPS). The CuNi-MOFN nanocomposites were used to cover the glassy carbon electrode (GCE) and the CuNi-MOFNs-modified electrode was studied in alkaline media. Cyclic voltammetry (CV) and amperometric i-t curves indicated that the CuNi-MOFNs-modified electrode revealed great electrochemical performances towards glucose oxidation. Due to the ease of access to active metal sites in large specific surface of nanosheets, the CuNi-MOFNs-modified electrode can effectively improve the electronic transfer rate and enhance electrocatalytic activity of the CuNi-MOFNs-modified electrode. The CuNi-MOFNs-modified electrode showed electrochemical performances for glucose detection with a linear range from 0.01 mM to 4 mM, sensitivity of 702 μAmM-1cm-2, and detection limit of 3.33 μΜ (S/N = 3). The CuNi-MOFNs-modified electrode exhibited excellent anti-interference ability and high selectivity in glucose measurements. Hence, the CuNi-MOFNs-modified electrode has good, promising prospects in non-enzymatic electrochemical glucose detection.

Design and Application of Metal Organic Framework ZIF-90-ZnO-MoS2 Nanohybrid for an Integrated Electrochemical Liquid Biopsy

Limited healthcare capacity highlights the needs of integrated sensing systems for personalized health-monitoring. However, only limited sensors can be employed for point-of-care applications, emphasizing the lack of a generalizable sensing platform. Here, we report a metal organic framework (MOF) ZIF-90-ZnO-MoS₂ nanohybrid-based integrated electrochemical liquid biopsy (ELB) platform capable of direct profiling cancer exosomes from blood. Using a bottom-up approach for sensor design, a series of critical sensing functions is considered and encoded into the MOF material interface by programming the material with different chemical and structural features. The MOF-based ELB platform is able to achieve one-step sensor fabrication, target isolation, nonfouling and high-sensitivity sensing, direct signal transduction, and multiplexed detection. We demonstrated the capability of the designed sensing system on differentiating cancerous groups from healthy controls by analyzing clinical samples from lung cancer patients, providing a generalizable sensing platform.

Toward efficient removal of organic pollutants in water: A tremella-like iron containing metal-organic framework in Fenton oxidation

The treatment of wastewater containing organic pollutants has become a serious issue, and one of the advanced oxidation process, Fenton oxidation is recognized as an ideal way owing to its universality and environmental friendliness, thus efficient and economic catalysts are in great demand. Herein by incorporating Fe²⁺ containing compound as ligand, a tremella-like iron containing metal-organic framework (TFMOF) was synthesized with zirconium acetate and 1,1'-ferrocene-dicarboxylic acid though a facile solvothermal method. The TFMOF combined the merits of both ferrocene moiety with well dispersed Fe²⁺ sites in the molecular level and MOF films with large surface areas and exposed sites. And the morphology and crystal structure of TFMOF were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Moreover, employed as an effective catalyst in Fenton oxidation, over 99%, 95% and 97% of rhodamine B, methyl orange and reactive black V were rapidly degraded without the assistance of additional irradiation, and degradation conditions like pH, H₂O₂ and initial pollutant concentrations as well as the reaction kinetic was investigated, indicating the hydroxyl radical generated in the presence of TFMOF and H₂O₂ was able to degrade the pollutants into non-toxic molecular. Besides, the catalytic activity of TFMOF maintained well after three cycles. The good activity and universality of TFMOF make it a promising catalyst for the treatment of wastewater.

Layered Double Hydroxide@Metal-Organic Framework Hybrids for Extraction of Indole-3-Carbinol From Cruciferous Vegetables

Cruciferous vegetables are rich in glucosinolates, which can be metabolized to produce the antitumor compound indole-3-carbinol (I3C). The conventional solvent extraction method for I3C is inefficient. To improve the extraction efficiency of I3C from cruciferous vegetables, we prepared a metal-organic framework (MOF) material (Fe₃O₄@Zn-Al-LDH@B-D-MIL-100). First, Fe₃O₄ nanoparticles were introduced to layered double hydroxides by in situ polymerization. Then, the MOF material was grown on the surface of the layered double hydroxide by co-precipitation and the layer-by-layer self-assembly method. This gave Fe₃O₄@Zn-Al-LDH@B-D-MIL-100, which was characterized using a variety of techniques. The results showed that Fe₃O₄@Zn-Al-LDH@B-D-MIL-100 had a double-layer porous structure, excellent superparamagnetism (11.54955 emu/g), a large specific surface area (174.04 m²/g), and a pore volume (0.26 cm³/g). The extraction conditions for I3C were optimized. Non-linear fitting of the static adsorption model showed that the adsorption was mainly monolayer. Fe₃O₄@Zn-Al-LDH@B-D-MIL-100 had fast adsorption kinetics and could extract 95% of I3C in 45 min. It is superior to the traditional solvent extraction method because of its high enrichment efficiency in a short time and environmental friendliness. The successful preparation of the new nanomaterial will provide a new reference for the enrichment and extraction of the I3C industry.

Zwitterionic Luminescent 2D Metal-Organic Framework Nanosheets (LMONs): Selective Turn-On Fluorescence Sensing of Dihydrogen Phosphate

While a plethora of organic linkers based on carboxylic acids have been utilized in the construction of MOFs, zwitterionic linkers that typify the attributes of naturally occurring amino acids have been exploited only scarcely to the best of our knowledge. Zwitterionic interior characteristics should be expected to impart unique properties to the resultant MOFs with a high potential to interact with guest species through electrostatic interactions. In our investigations with bis(p-carboxyphenyl)imidazolylarenes as a novel class of linkers for the development of functional MOFs, we have found that bisimidazole-tetracarboxylic acid H₄DMBI undergoes metal-assisted self-assembly with Zn(NO₃)₂ to yield a layered MOF (Zn-DMBI). In the latter, the linker serves as a two-connecting linker with imidazoles and carboxylic acids behaving as zwitterions. The layers are offset stacked in the crystal structure and are bound firmly by hydrogen bonds between imidazolium and carboxylate ions. Such a packing precludes fluorescence from being observed due to self-quenching. However, exfoliation into zwitterionic 2D metal-organic nanosheets (MONs) by sonication in methanol for 1 h liberates palpable fluorescence. Furthermore, the suspension of luminescent MONs (LMONs) in methanol permits selective sensing of anions; in particular, dihydrogen phosphate (H₂PO₄^-) that is complementary to the zwitterions in terms of hydrogen bond donor and acceptor sites is observed with fluorescence enhancement by 120%, leading to its detection at a sub-parts-per-million (0.13 ppm) level. Thus, access to zwitterionic 2D MONs and their application for selective anion sensing with "turn-on" fluorescence are demonstrated by a rational de novo bottom-up approach.

Converging 2D Nanomaterials and 3D Bioprinting Technology: State-of-the-Art, Challenges, and Potential Outlook in Biomedical Applications

The development of next-generation of bioinks aims to fabricate anatomical size 3D scaffold with high printability and biocompatibility. Along with the progress in 3D bioprinting, 2D nanomaterials (2D NMs) prove to be emerging frontiers in the development of advanced materials owing to their extraordinary properties. Harnessing the properties of 2D NMs in 3D bioprinting technologies can revolutionize the development of bioinks by endowing new functionalities to the current bioinks. First the main contributions of 2D NMS in 3D bioprinting technologies are categorized here into six main classes: 1) reinforcement effect, 2) delivery of bioactive molecules, 3) improved electrical conductivity, 4) enhanced tissue formation, 5) photothermal effect, 6) and stronger antibacterial properties. Next, the recent advances in the use of each certain 2D NMs (1) graphene, 2) nanosilicate, 3) black phosphorus, 4) MXene, 5) transition metal dichalcogenides, 6) hexagonal boron nitride, and 7) metal-organic frameworks) in 3D bioprinting technology are critically summarized and evaluated thoroughly. Third, the role of physicochemical properties of 2D NMSs on their cytotoxicity is uncovered, with several representative examples of each studied 2D NMs. Finally, current challenges, opportunities, and outlook for the development of nanocomposite bioinks are discussed thoroughly.

2D metal-organic framework-based materials for electrocatalytic, photocatalytic and thermocatalytic applications

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have recently attracted extensive interest in various catalytic fields (e.g., electrocatalysis, photocatalysis, thermocatalysis) due to their ultrathin thickness, large surface area, abundant accessible unsaturated active sites and tunable surface properties. Besides tuning the intrinsic properties of pristine 2D MOFs by changing the metal nodes and organic ligands, one of the hot research trends is to develop 2D MOF hybrids and 2D MOF-derived materials with higher stability and conductivity in order to further increase their activity and durability. Here, the synthesis of 2D MOF nanosheets is briefly summarized and discussed. More attention is focused on summaries and discussions about the applications of these 2D MOFs, their hybrids and their derived materials as electrocatalysts, photocatalysts and thermocatalysts. The superior properties and catalytic performance of these 2D MOF-based catalysts compared to their 3D MOF counterparts in electrocatalysis, photocatalysis and thermocatalysis are highlighted. The enhanced activities of 2D MOFs, their hybrids and derivatives come from abundant accessible active sites, a high density of unsaturated metal nodes, ultrathin thickness, and tunable microenvironments around the MOFs. Views regarding current and future challenges in the field, and new advances in science and technology to meet these challenges, are also presented. Finally, conclusions and outlooks in this field are provided.

Assembling your nanowire: an overview of composition tuning in ternary III-V nanowires

The ability to grow defect-free nanowires in lattice-mismatched material systems and to design their properties has made them ideal candidates for applications in fields as diverse as nanophotonics, nanoelectronics and medicine. After studying nanostructures consisting of elemental and binary compound semiconductors, scientists turned their attention to more complex systems-ternary nanowires. Composition control is key in these nanostructures since it enables bandgap engineering. The use of different combinations of compounds and different growth methods has resulted in numerous investigations. The aim of this review is to present a survey of the material systems studied to date, and to give a brief overview of the issues tackled and the progress achieved in nanowire composition tuning. We focus on ternary III _x III_1-x V nanowires (AlGaAs, AlGaP, AlInP, InGaAs, GaInP and InGaSb) and IIIV _x V_1-x nanowires (InAsP, InAsSb, InPSb, GaAsP, GaAsSb and GaSbP).

Interface synthesis for controllable construction of 2D Zn(Bim)(OAc) nanosheets via oil/water system and their application in oil

Fabrication of 2D Zn(Bim)(OAc) MOFs-structured nanosheets based on the oil/water interface.

Photothermal-Responsive Microporous Nanosheets Confined Ionic Liquid for Efficient CO2 Separation

2D materials hold promising potential for novel gas separation. However, a lack of in-plane pores and the randomly stacked interplane channels of these membranes still hinder their separation performance. In this work, ferrocene based-MOFs (Zr-Fc MOF) nanosheets, which contain abundant of in-plane micropores, are synthesized as porous supports to fabricate Zr-Fc MOF supported ionic liquid membrane (Zr-Fc-SILM) for highly efficient CO₂ separation. The micropores of Zr-Fc MOF nanosheets not only provide extra paths for CO₂ transportation, and thus increase its permeance up to 145.15 GPU, but also endow the Zr-Fc-SILM with high selectivity (216.9) of CO₂ /N₂ through the nanoconfinement effect, which is almost ten times higher than common porous polymer SILM. Furthermore, based on the photothermal-responsive properties of Zr-Fc MOF, the performance is further enhanced (35%) by light irradiation through a photothermal heating process. This provides a brand new way to design light facilitating gas separation membranes.

Superior absorption capacity of tremella like ferrocene based metal-organic framework in removal of organic dye from water

Removal of organic dyes from water by porous materials is considered as an efficient and low-cost way. Herein for the first time novel tremella-like ferrocene based metal-orgainc framework (TMOF) nanosheets designated as TFMOF were synthesized through a traditional solvothermal method. This ferrocene based TFMOF exhibit outstanding removal efficiency towards organic dye Congo red (CR) from water. After optimizing the reaction conditions, the highest adsorption capacity of 252.25 mg g^-1 could be achieved within 10 min. Furthermore, the investigation of adsorption kinetic indicated this adsorption process could be described as a pseudo-second order kinetic model with k₂ and q_e of 0.0488 g mg^-1 min^-1 and 241.5 mg g^-1, respectively. The adsorption isotherm could also be described as the Sips isotherm model according to the fitting calculation. The removal efficiency could maintain around 50 % with adsorption capacity of 124.38 mg g^-1 after 3 cycles, giving the TFMOF promising potential in the practical water treatment.

General synthesis of hierarchical sheet/plate-like M-BDC (M = Cu, Mn, Ni, and Zr) metal-organic frameworks for electrochemical non-enzymatic glucose sensing

Two-dimensional metal-organic frameworks (2D MOFs) are an attractive platform to develop new kinds of catalysts because of their structural tunability and large specific surface area that exposes numerous active sites. In this work, we report a general method to synthesize benzene dicarboxylic acid (BDC)-based MOFs with hierarchical 3D morphologies composed of 2D nanosheets or nanoplates. In our proposed strategy, acetonitrile helps solvate the metal ions in solution and affects the morphology, while polyvinylpyrrolidone (PVP) serves as a shape-control agent to assist in the nucleation and growth of MOF nanosheets. PVP also acts as a depletion agent to drive the assembly of the hierarchical sheet/plate-like M-BDC under solvothermal conditions. Further, we also demonstrate the flexibility of the proposed method using numerous coordinating metal ions (M = Cu, Mn, Ni, and Zr). The potential of these MOFs for electrochemical glucose sensing is examined using the hierarchical sheet-like Ni-BDC MOF as the optimum sample. It drives the electrocatalytic oxidation of glucose over a wide range (0.01 mM to 0.8 mM) with high sensitivity (635.9 μA mM-1 cm-2) in the absence of modification with carbon or the use of conductive substrates. It also demonstrates good selectivity with low limit of detection (LoD = 6.68 μM; signal/noise = 3), and fast response time (<5 s).

Two-dimensional metal-organic frameworks and their derivatives for electrochemical energy storage and electrocatalysis

Two-dimensional (2D) metal-organic frameworks (MOFs) and their derivatives with excellent dimension-related properties, e.g. high surface areas, abundantly accessible metal nodes, and tailorable structures, have attracted intensive attention as energy storage materials and electrocatalysts. A major challenge on the road toward the commercialization of 2D MOFs and their derivatives is to achieve the facile and controllable synthesis of 2D MOFs with high quality and at low cost. Significant developments have been made in the synthesis and applications of 2D MOFs and their derivatives in recent years. In this review, we first discuss the state-of-the-art synthetic strategies (including both top-down and bottom-up approaches) for 2D MOFs. Subsequently, we review the most recent application progress of 2D MOFs and their derivatives in the fields of electrochemical energy storage (e.g., batteries and supercapacitors) and electrocatalysis (of classical reactions such as the HER, OER, ORR, and CO2RR). Finally, the challenges and promising strategies for the synthesis and applications of 2D MOFs and their derivatives are addressed for future development.

Chemical transformation of a luminescent two-dimensional Eu(iii) coordination polymer in the aqueous phase

We report a 2D Eu-based MOF that give promising applications in several areas, especially in luminescence sensing. This compound can be exfoliated in nanosheets and also, transformed into a hydrated polýmer with strong red luminescence by naked eye.

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.

2D Metal-Organic Frameworks as Multifunctional Materials in Heterogeneous Catalysis and Electro/Photocatalysis

Metal-organic frameworks (MOFs) are composed of particles with 3D geometry and are currently among the most widely studied heterogeneous catalysts. To further increase their activity, one of the recent trends is to develop related 2D materials with a high aspect ratio derived from a large lateral size and a small thickness. Here, the use of these 2D MOFs as catalysts, electrocatalysts, and photocatalysts is summarized, illustrating the advantages of these 2D materials compared to analogous 3D MOFs. The state of the art is summarized in tables and, when possible, pertinent turnover number (TON) and frequency (TOF) values. This enhanced activity of 2D MOFs derives from the accessibility of the active sites, the presence of a higher density of defects, and exchangeable coordination positions around the MOFs, as well as from their ability to form thin films on electrodes or surfaces. The importance of providing convincing evidence of the stability of 2D MOFs under reaction conditions and general characterization data of the used 2D material after catalysis is highlighted. In the last part, views regarding challenges in the field and new developments that can be expected are presented.

Delamination of 2D coordination polymers: The role of solvent and ultrasound

Two novel cadmium-based 2D coordination polymers have been synthesized and characterized. Experimental results evidence that the best delamination processes occurs when weak interactions dominate the cohesion between layers and solvent molecules are occluded within the crystalline network. In this case, the delamination of the crystals occurs spontaneously in water. On top of that, and thanks to the high stability of the resulting (flake) colloidal dispersions, we have completed a detailed study of the sonication assisted delamination impact by: I) comparison of two different sonication approaches (bath vs. tip sonication) and II) optimization of final flake morphology and yield by controlling solvent and sonication time. Our results definitely pave the way for the fabrication and implementation of 2D coordination polymers using ultrasound.

Structural Engineering of Low-Dimensional Metal-Organic Frameworks: Synthesis, Properties, and Applications

Low-dimensional metal-organic frameworks (LD MOFs) have attracted increasing attention in recent years, which successfully combine the unique properties of MOFs, e.g., large surface area, tailorable structure, and uniform cavity, with the distinctive physical and chemical properties of LD nanomaterials, e.g., high aspect ratio, abundant accessible active sites, and flexibility. Significant progress has been made in the morphological and structural regulation of LD MOFs in recent years. It is still of great significance to further explore the synthetic principles and dimensional-dependent properties of LD MOFs. In this review, recent progress in the synthesis of LD MOF-based materials and their applications are summarized, with an emphasis on the distinctive advantages of LD MOFs over their bulk counterparties. First, the unique physical and chemical properties of LD MOF-based materials are briefly introduced. Synthetic strategies of various LD MOFs, including 1D MOFs, 2D MOFs, and LD MOF-based composites, as well as their derivatives, are then summarized. Furthermore, the potential applications of LD MOF-based materials in catalysis, energy storage, gas adsorption and separation, and sensing are introduced. Finally, challenges and opportunities of this fascinating research field are proposed.