Formation Of Metal-organic Frameworks Research Articles

Amino Functionality Enables Aqueous Synthesis of Carboxylic Acid-Based MOFs at Room Temperature by Biomimetic Crystallization.

Enzyme immobilization within metal-organic frameworks (MOFs) is a promising solution to avoid denaturation and thereby utilize the desirable properties of enzymes outside of their native environments. The biomimetic mineralization strategy employs biomacromolecules as nucleation agents to promote the crystallization of MOFs in water at room temperature, thus overcoming pore size limitations presented by traditional postassembly encapsulation. Most biomimetic crystallization studies reported to date have employed zeolitic imidazole frameworks (ZIFs). Herein, we expand the library of MOFs suitable for biomimetic mineralization to include zinc(II) MOFs incorporating functionalized terephthalic acid linkers and study the catalytic performance of the enzyme@MOFs. Amine functionalization of terephthalic acids is shown to accelerate the formation of crystalline MOFs enabling new enzyme@MOFs to be synthesized. The structure and morphology of the enzyme@MOFs were characterized by PXRD, FTIR, and SEM-EDX, and the catalytic potential was evaluated. Increasing the linker length while retaining the amino moiety gave rise to a family of linkers; however, MOFs generated with the 2,2'-aminoterephthalic acid linker displayed the best catalytic performance. Our data also illustrate that the pH of the reaction mixture affects the crystal structure of the MOF and that this structural transformation impacts the catalytic performance of the enzyme@MOF.

In situ synthesis of porous metal-organic frameworks NH2-UiO-66 on tea stem biochar and application in odours adsorption

Multiple odour nuisance in livestock farming is a notorious problem that has a significant impact on the living environment of surrounding communities. Adsorbents based on metal-organic framework (MOF) materials show great promise for controlling odour pollution, as they offer a high specific surface area, a controllable structure and an abundance of active sites. However, the MOF formation process is prone to problems such as pore clogging or collapse and reduced porosity, which limits its further application. In this study, a series of odour adsorbents were prepared by in situ growth of NH2-UiO-66 on tea stem biochar (TSBC) using a hydrothermal method and named UiO (Zr)-TSBCx. The physical and chemical properties and composition of UiO (Zr)-TSBCx have been systematically characterized using SEM, TEM, XRD, FT-IR, N2 adsorption-desorption and XPS. The release of odours from the pig farm effluent was monitored using in-situ continuous Proton-Transfer-Reaction Mass Spectrometry (PTR-MS), and the obtained primary compositions were tested for further adsorption. In dynamic adsorption experiments focused on butyric acid, UiO (Zr)-TSBC2 showed a high adsorption capacity of 3.99 × 105 μg/g and exceptional structural stability. UiO (Zr)-TSBC2 showed variable adsorption efficiencies for different odorous gases, with the best performance for the removal of ammonia, toluene and butyric acid. It also demonstrated the ability to rapidly mitigate instantaneous high concentrations of hydrogen sulfide (H2S), methanethiol and toluene resulting from agitation. Additionally, based on the relationship between the adsorption amount and the structural characteristics of the adsorbent as well as the nature of the odours, a possible adsorption mechanism of UiO (Zr)-TSBC2 for a variety of odours released from pig farm effluent was proposed. This work demonstrates a novel approach to promote deodorization applications in livestock and poultry farming environments by the in-situ growth of NH2-UiO-66 on biochar prepared from tea stem.

Toward Selective Transport of Monovalent Metal Ions with High Permeability Based on Crown Ether-Encapsulated Metal-Organic Framework Sub-Nanochannels.

Achieving selective transport of monovalent metal ions with high precision and permeability analogues to biological protein ion channels has long been explored for fundamental research and various applications, such as ion sieving, mineral extraction, and energy harvesting and conversion. However, it still remains a significant challenge to construct artificial nanofluidic devices to realize the trade-off effects between selective ion transportation and high ion permeability. In this work, we report a bioinspired functional micropipet with in situ growth of crown ether-encapsulated metal-organic frameworks (MOFs) inside the tip and realize selective transport of monovalent metal ions. The functional ion-selective micropipet with sub-nanochannels was constructed by the interfacial growth method with the formation of composite MOFs consisting of ZIF-8 and 15-crown-5. The resulting micropipet device exhibited obvious monovalent ion selectivity and high flux of Li+ due to the synergistic effects of size sieving in subnanoconfined space and specific coordination of 15-crown-5 toward Na+. The selectivity of Li+/Na+, Li+/K+, Li+/Ca2+, and Li+/Mg2+ with 15-crown-5@ZIF-8-functionalized micropipet reached 3.9, 5.2, 105.8, and 122.4, respectively, which had an obvious enhancement compared to that with ZIF-8. Notably, the ion flux of Li+ can reach up to 93.8 ± 3.6 mol h-1·m-2 that is much higher than previously reported values. Furthermore, the functional micropipet with 15-crown-5@ZIF-8 sub-nanochannels exhibited stable Li+ selectivity under various conditions, such as different ion concentrations, pH values, and mixed ion solutions. This work not only provides new opportunities for the development of MOF-based nanofluidic devices for selective ion transport but also facilitates the promising practical applications in lithium extraction from salt-like brines, sewage treatment, and other related aspects.

Efficient Adsorption of Methylene Blue Using a Hierarchically Structured Metal-Organic Framework Derived from Layered Double Hydroxide.

The growing concerns about environmental pollution, particularly water pollution, are causing an increasing alarm in modern society. One promising approach to address this issue involves engineering existing materials to enhance their effectiveness. A one-step solvothermal reconstruction approach was used to build an eco-friendly two-dimensional (2D) AlNiZn-LDH/BDC MOF composite. The characterizations confirm the formation of a metal-organic framework (MOF) at the layered double hydroxide (LDH) surface. The resulting synthesized material, 2D AlNiZn-LDH/BDC MOF, demonstrated remarkable efficacy in decontaminating methylene blue (MB), a model cationic dye found in water systems. The removal performance of 2D AlNiZn-LDH/BDC MOF was significantly higher than that of pristine 2D AlNiZn-LDH. This improvement shows the potential to increase the adsorption capabilities of nanoporous LDH materials by incorporating organic ligands and integrating meso-/microporosity through MOF formation on their surfaces. Furthermore, their kinetic, isothermal, and thermodynamic studies elucidated the adsorption behavior of this composite material. The results of synthesized MOF showed excellent removal efficiency (92.27%) of 10 ppm of MB aqueous solution as compared to pristine LDH. Additionally, the as-synthesized adsorbent could be regenerated for six successive cycles. This method holds promise for the synthesis of novel and highly effective materials to combat water pollution, laying the groundwork for potential advancements in diverse applications.

Protein–polyphenol nanoassemblies modulated construction of zeolitic imidazole framework-67 based nanofiltration membrane for effective separation of dye/salt mixtures

Metal–organic frameworks (MOFs) show great potential in various separation applications. However, fast nucleation rate and crystallization of MOFs, produce non-uniform and uncontrollable sized crystals, which are not suitable for the formation of MOF-based membranes. Herein, we propose the concept of utilizing protein polyphenol nanoassemblies (PPNs) as the building blocks for the confined growth of MOFs to fabricate zeolitic imidazolate frameworks (ZIF-67)-based membranes. We first demonstrated that colloidal PPNs as modulators in solution enables the formation of ZIF-67 MOFs with uniform and controllable crystal sizes. Subsequently, we utilized the metal salt coordinated PPNs (Co2+@PPN) as the precursor layer matrix deposited on porous polymeric support to fabricate ZIF-67 membranes via in-situ growth strategy at room temperature. The resultant membrane features a robust heterogeneous and well-integrated ZIF-67-reinforced PPN (ZIF-67@PPN) microporous networks. Benefiting from the rigid and multidimensional micropores of ZIF-67, the optimized ZIF-67@PPN1 composite membrane with improved water stability exhibited good water permeance (45.68 L m−2 h−1 bar−1), excellent dye desalination performance (Na2SO4/Congo red selectivity of 1271.47), and good antibiotic desalination performance (NaCl/Erythromycin selectivity of 21.46). The findings in this work provide important engineering concepts for the development of MOF-based membranes using sustainable nature-derived building blocks for emergent environment-relevant desalination applications in the chemical process industry.

3D-printing of alginate/gelatin scaffold loading tannic acid@ZIF-8 for wound healing: In vitro and in vivo studies

In the present study, ZIF-8 metal-organic framework (MOF) modified with Tannic acid (TA@ZIF-8) was synthesized and impregnated in alginate-gelatin (Alg-Gel) hydrogel. The Alg-Gel scaffolds containing 0, 5, and 10 % of TA@ZIF-8 were fabricated through the 3D printing method specifically denoted as Alg-Gel 0 %, Alg-Gel 5 %, and Alg-Gel 10 %. XRD, FTIR, FESEM, and EDX physically and chemically characterized the synthesized ZIF-8 and TA@ZIF-8 MOFs. Besides, Alg-Gel containing TA@ZIF-8 prepared scaffolds and their biological activity were also evaluated. SEM images verified the nano-size formation of MOFs. Improved swelling and decreased degradation rates after adding TA@ZIF-8 were also reported. Increased compression strength from 0.628 to 1.63 MPa in Alg-Gel 0 % and Alg-Gel 10 %, respectively, and a 2.19 increase in elastic modulus in Alg-Gel 10 % scaffolds were exhibited. Biological activity of scaffolds, including Live-dead and Cell adhesion, antibacterial, in-vivo, and immunohistochemistry assays, demonstrated desirable fibroblast cell proliferation and adhesion, increased bacterial growth inhibition zone, accelerated wound closure and improved expression of anti-inflammatory cytokines in Alg-Gel 10 % scaffolds. The findings of this study confirm that Alg-Gel 10 % scaffolds promote full-thickness wound healing and could be considered a potential candidate for full-thickness wound treatment purposes.

Glyme-functionalized ligand based MOF: A comprehensive study on copper and zirconium frameworks

In this study, the synthesis of a series of novel glyme-modified ligands and their corresponding copper and zirconium metal-organic frameworks (MOF) has been successfully realized. In addition, while using copper salts, it was possible to yield a water-stable MOF. Besides, the utilization of zirconium salts resulted in the formation of MOF exhibiting a UiO-68 type structure. The thorough characterization of these MOF was performed using Single Crystal X-ray Diffraction (SCXRD), Powder X-ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and nitrogen adsorption-desorption isotherms.Furthermore, the CO2 adsorption capacity of these MOF was also evaluated. Despite the significant differences in their crystalline networks, all MOF exhibited appreciable CO2 adsorption capacities, ranging from 0.6 to 1.3 mmol g−1 at ambient pressure and 0 °C.

Comparison of In Situ‐Fabricated Ternary NiCoMn‐Metal–Organic Frameworks versus Slurry Deposition on Porous Ni‐Foam: A Facile Approach for Enhancing Supercapacitor Performance

Owing to the worldwide energy requirements, metal–organic frameworks (MOFs) have been extensively used as electrode material. Ternary MOFs have been of prime importance because of their characteristic of a variety of oxidation states than mono‐ and bimetallic MOFs. Herein, a novel comparison and superiority of binder‐free MOF deposition known as in situ (IN) on the substrate have been investigated over the slurry deposition method involving the excellent properties of ternary MOFs. Confirmation of MOF formation using X‐ray diffraction and investigation of its morphological features have been explored using field‐emission scanning electron microscopy. Energy dispersive X‐ray area mapping has also been integrated for conformity of uniform elemental distribution. The electrochemical properties of NiCoMn‐MOF have been investigated and the results obtained for NiCoMn deposited using IN methodology are superior due to excellent penetration of MOF inside substrate that provides the basis of excellent electrochemical properties. A specific capacitance of 1000 C g−1 at 4 A g−1 in 3‐electrode assembly has been achieved accompanied by energy and power density of 55 Wh kg−1 and 2467 W kg−1 in 2‐electrode setup. An excellent cyclic stability of about 97% has been obtained after subjecting the asymmetric supercapacitor device to 5000 charge/discharge cycles at 20 A g−1. Diffusive nature dominancy over capacitive is also observed by manipulating Dunns’ model. The superior and novel aspect of using IN deposition may pave the way for their efficient use in energy storage devices.

In situ monitoring of mechanochemical MOF formation by NMR relaxation time correlation.

In this paper, we present a new approach to monitoring mechanochemical transformations, based on a magnetic resonance (MR) method in which relaxation time correlation maps are used to track the formation of the popular metal-organic framework (MOF) materials Zn-MOF-74 and ZIF-8. The two-dimensional (2D) relaxation correlation measurement employed yields a spectrum which visually and analytically identifies different 1H environments in the sample of interest. The measurement is well-suited to analyzing solid mixtures, and liquids, in complex systems. Application in this work to monitoring MOF formation shows changes in signal amplitudes, and their MR lifetime coordinates, within the 2D plots as the reaction progresses, confirming reaction completion. This new measurement provides a simple way to analyse solid-state reactions without dissolution, and there is a logical pathway to benchtop measurement with a new generation of permanent magnet-based MR instruments. The methodology described permits measurement in an MR compatible milling container, which may be directly transferred from the shaker assembly to the MR magnet for in situ measurement of the entire reaction mixture.

Vapor-phase zeolitic imidazolate framework-8 growth on fibrous polymer substrates

The use of metal-organic frameworks (MOFs) in practical applications is often hindered by synthesis related challenges. Conventional solution-based approaches rely on hazardous solvents and often form powders that are difficult to integrate into practical devices. On the other hand, vapor-phase approaches generally result in MOF films on silicon substrates that make it difficult to characterize the MOF surface area, which is an important quality indicator. We address these challenges by introducing a solvent-free synthesis method to form MOF–fiber composites, which can be more easily integrated into devices. Additionally, these vapor-phase-formed MOF–fiber composites are compatible with Brunauer–Emmett–Teller surface area analysis to characterize MOF quality. Atomic layer deposition is used to form a ZnO film on polypropylene, polyester, and nylon fibrous substrates, which is subsequently converted to zeolitic imidazolate framework-8 (ZIF-8) using 2-methylimidazole vapor. We describe the effects of the ZnO film thickness and MOF conversion conditions on MOF crystallinity and surface area. We report a ZIF-8 surface area of ∼1300 m2/gMOF, which is comparable to reported surface areas of ∼1250–1600 m2/gMOF from conventional synthesis techniques, demonstrating good quality of the solvent-free MOF–fiber composites. We expect these results to extend vapor-phase MOF formation to new, practical substrates for advanced sensing and catalytic applications.

Development of anti-corrosive coating on AZ31 Mg alloy modified by MOF/LDH/PEO hybrids

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability. In this work, a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide (LDH) films using novel metal-organic frameworks (MOFs). Initially, Mg-Al LDH nanocontainers, grown on a magnesium oxide layer produced through plasma electrolytic oxidation (PEO) of AZ31 Mg alloy substrate, were intercalated with cobalt via an oxidation route, providing the metallic coordination center for the MOF formation. In the subsequent step, a pioneering technique is introduced, utilizing tryptophan as the organic linker for the first time at a pH of 10. The self-assembly of cobalt- tryptophan complex, driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites, facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH's film. The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.% NaCl solution, surpassing the performance of PEO and pure LDH coatings. This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF, effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate. The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

Nanocomposites Based on Magnetic Nanoparticles and Metal-Organic Frameworks for Therapy, Diagnosis, and Theragnostics.

In the last two decades, metal-organic frameworks (MOFs) with highly tunable structure and porosity, have emerged as drug nanocarriers in the biomedical field. In particular, nanoscaled MOFs (nanoMOFs) have been widely investigated because of their potential biocompatibility, high drug loadings, and progressive release. To enhance their properties, MOFs have been combined with magnetic nanoparticles (MNPs) to form magnetic nanocomposites (MNP@MOF) with additional functionalities. Due to the magnetic properties of the MNPs, their presence in the nanosystems enables potential combinatorial magnetic targeted therapy and diagnosis. In this Review, we analyze the four main synthetic strategies currently employed for the fabrication of MNP@MOF nanocomposites, namely, mixing, in situ formation of MNPs in presynthesized MOF, in situ formation of MOFs in the presence of MNPs, and layer-by-layer methods. Additionally, we discuss the current progress in bioapplications, focusing on drug delivery systems (DDSs), magnetic resonance imaging (MRI), magnetic hyperthermia (MHT), and theragnostic systems. Overall, we provide a comprehensive overview of the recent advances in the development and bioapplications of MNP@MOF nanocomposites, highlighting their potential for future biomedical applications with a critical analysis of the challenges and limitations of these nanocomposites in terms of their synthesis, characterization, biocompatibility, and applicability.

State-of-the-art with the prospects of cobalt-based metal-organic frameworks for solar cell applications

The characteristics of metal–organic framework (MOF) composites make them the most significant materials for energy conversion applications. MOFs are hybrid molecular frameworks synthesized using metal ions like Copper, Cobalt, Zinc, Nickel, etc and organic ligands such as BTC, NDC, etc. To meet and fulfill futuristic energy demands and needs, it is feasible to expand cost-effective energy conversion solar cell devices using MOF materials, therefore in the present work, the Cobalt-based MOFs (Co-MOF) are synthesized by coordinating Cobalt nitrate and 1,3,5 Benzene tricarboxylic acid (BTC or Trimesic acid) ligand using the Solvothermal method. To study the physiochemical properties of synthesized Co-BTC MOFs, these have gone through a variety of characterization processes where the structural exploration unveils that the intensity of the dominant peak obtained at 18.7° gradually decreases with a decrease in the concentration of trimesic acid ligand. First and second weight losses, corresponding to release of the solvent molecules and breakdown of the frameworks, respectively, were detected by thermogravimetric analysis (TGA) measurements. In the FTIR spectra, metal-oxide, modified benzene, carboxylic, and hydroxyl groups with different modes of vibrations are observed. Analysis of surface morphology demonstrated creation of rod-like geometry to the synthesized materials, whereas elemental studies inveterate effective formation of the Co-BTC MOFs. Additionally, the optimized Co-BTC MOF is applied as a potential interfacial layer in solar cells and the outcome implies that the device designed with 10 Co-BTC LBL cycle evolutions provided relatively desirable solar cell performance parameters. The present findings recommended that material progression is necessary to develop cost-effective and high-performance MOF-based solar cell devices.

Interfacial and Electronic Modulation of M-Bridged Heterostructures with L-Tryptophan and Transition Metallic Oxides: Enhancing Corrosion Resistance and Photocatalytic Activity.

Despite remarkable advancements in multilayer composite materials, achieving controlled growth on stationary platforms for optimal corrosion protection and photocatalytic capabilities remains a challenge. In this study, we introduce an innovative approach by integrating bifunctional metal-organic frameworks (MOFs) into plasma-electrolyzed layers made on AZ31 Mg alloy. Metallic oxides of Zr, Ti, and W serve as new pivotal centers for MOF formation, while L-tryptophan (Trp) acts as an organic linker. This innovative approach establishes an efficient electron transport system that acts as a functional pathway for creating highly effective and versatile materials. The tunable structure of the MOF/plasma electrolyzed layer enables it to concurrently display electrochemical stability and photocatalytic activity for the photodegradation of organic pollutants. Remarkably, the WOF complex emerges as a standout performer, effectively shielding the substrate from corrosive anion attacks. This sample showcases exceptional photocatalytic efficiency of 99.61% for crystal violet solution, with sustained performance after five cycles and a 72 h corrosion test (96.55% and 98.39% degradation, respectively). Moreover, DFT calculations elucidate the fundamental bonding modes between MOFs and inorganic constituents, delivering comprehensive insights into their structural formation. Our research addresses the critical challenge of achieving controlled growth for enhanced corrosion resistance and photocatalytic activity, demonstrating a novel pathway for creating multifunctional materials with practical applications across various fields.

Tuning the Cerium-Based Metal-Organic Framework Formation by Template Effect and Precursor Selection.

The novel metal-organic framework [(CH3)2NH2]2[Ce2(bdc)4(DMF)2]·2H2O (Ce-MOF, H2bdc-terephthalic acid, DMF-N,N-dimethylformamide) was synthesized by a simple solvothermal method. Ce-MOF has 3D connectivity of bcu type with a dinuclear fragment connected with eight neighbors, while three types of guest species are residing in its pores: water, DMF, and dimethylammonium cations. Dimethylamine was demonstrated to have a decisive templating effect on the formation of Ce-MOF, as its deliberate addition to the solvothermal reaction allows the reproducible synthesis of the new framework. Otherwise, the previously reported MOF Ce5(bdc)7.5(DMF)4 (Ce5) or its composite with nano-CeO2 (CeO2@Ce5) was obtained. Various Ce carboxylate precursors and synthetic conditions were explored to evidence the major stability of Ce-MOF and Ce5 within the Ce carboxylate-H2bdc-DMF system. The choice of precursor impacts the surface area of Ce-MOF and thus its reactivity in an oxidative atmosphere. The in situ PXRD and TG-DTA-MS study of Ce-MOF in a nonoxidative atmosphere demonstrates that it eliminates H2O and DMF along with (CH3)2NH guest species in two distinct stages at 70 and 250 °C, respectively, yielding [Ce2(bdc)3(H2bdc)]. The H2bdc molecule is removed at 350 °C with the formation of novel modification of Ce2(bdc)3, which is stable at least up to 450 °C. According to the total X-ray scattering study with pair distribution function analysis, the most pronounced local structure transformation occurs upon departure of DMF and (CH3)2NH guest species, which is in line with the in situ PXRD experiment. In an oxidative atmosphere, Ce-MOF undergoes combustion to CeO2 at a temperature as low as 390 °C. MOF-derived CeO2 from Ce-MOF, Ce5, and CeO2@Ce5 exhibits catalytic activity in the CO oxidation reaction.

Synthesis and structure of anhydrous Zn2EDTA metal-organic framework

Metal-organic frameworks (MOFs) have gained significant attention in materials science due to their unique properties such as high surface area, porosity, and tunable electrochemical characteristics. Among various MOFs, Zn-EDTA compounds have shown potential for electrochemical applications. This paper presents the accident discovery and investigation of a new anhydrous Zn2(EDTA) MOF and its electrochemical performance as an electrode material for aqueous sodium-ion batteries. The study systematically explores the influence of pH and stoichiometric ratio on the formation of Zn2(EDTA) and Zn2(EDTA)(H2O) MOFs using X-ray diffraction analysis. The single-phase anhydrous Zn2(EDTA) compound is synthesized, offering advantages over the hydrated form regarding stability and electrochemical activity. Zn2(EDTA) structure is characterized, revealing a 3D network of channels suitable for interstitial ionic mobility. Thermogravimetric analysis (TGA) is used to study the thermal behavior of Zn2(EDTA), showing two weight loss steps attributed to water and carbon dioxide elimination during decomposition. Electrochemical measurements using cyclic voltammetry in alkaline and neutral electrolytes demonstrate the electrochemical activity of Zn2(EDTA) as an anode material for aqueous sodium-ion batteries. The results suggest that the electrochemical process in both electrolytes involves the reversible stripping/deposition of zinc ions. The anhydrous Zn2(EDTA) MOF exhibits higher peak current intensities and more positive potentials than the hydrated form. The study provides valuable insights for synthesizing and controlling Zn2(EDTA) MOF formation, opening the prospects for searching for new structures in considered-to-be-studied phase regions.

Surface-engineered carbon nanofibers enriched with metallic particles for effective bimetallic MOF formation toward hybrid supercapacitors

Metal-organic frameworks (MOFs) are commonly used as positive electrode materials in hybrid supercapacitors (HSCs) because of their high specific surface area, tunable pore structure, and battery-like charge-storage nature. However, the redox-mediated charge-storage mechanism in MOFs affects the rate capability and cycle stability. To address this problem, herein, bimetallic MOFs (NiCo MOFs) are successfully synthesized on surface-engineered carbon nanofibers (NiCo CNFs) enriched with metallic (Ni and Co) nanoparticles by a hydrothermal method and named NiCo MOF@NiCo CNF. In the NiCo MOF@NiCo CNF composites, the NiCo CNF can boost the electrochemical activity and simultaneously enhance the effective growth of NiCo MOF due to the presence of metal contents in the NiCo CNF, which act as nucleation points and further facilitate metal‑carbon and metal‑oxygen interactions at the surface of the NiCo CNF and NiCo MOF. The unique structure of NiCo MOF@NiCo CNF helps to improve the electrochemical performance, and the specific capacity is found to be 295.4 mA h g−1 (1063.4 C g−1) at 1 A g−1. The fabricated NiCo MOF@NiCo CNF//ZIF CNF HSC device depicts an energy density of 45.4 Wh kg−1 at a power density of 800 W kg−1 and cycle stability with a capacitance retention of 70 % after 4000 cycles, demonstrating that NiCo MOF@NiCo CNF composites are a promising electrode for supercapacitor applications. The engineered CNF surfaces with the required metallic contents can generate a unique engineered composite structure, by the effective interaction from the metal-based functional materials, to enhance the composite properties and charge-storage kinetics.

Enhanced Photoelectrochemical Water Oxidation Using TiO2-Co3O4 p-n Heterostructures Derived from in Situ-Loaded ZIF-67.

Exposing catalytically active metal sites in metal-organic frameworks (MOFs) while maintaining porosity is beneficial for increasing electron transport to achieve better electrochemical energy conversion performance. Herein, we propose an in situ method for MOF formation and loading onto TiO2 nanorods (NR) using a simple solution-processable method followed by annealing to obtain TiO2-Co3O4. The as-prepared TiO2-ZIF-67 based photoanodes were annealed at 350, 450, and 550 °C to study the effect of carbonization on photo-electrochemical water oxidation. The successful loading of ZIF-67 on TiO2 and the formation of TiO2-Co3O4 heterojunction were confirmed by XRD, XPS, FE-SEM, and HRTEM analyses. TiO2-Co3O4-450 (the sample annealed at 450 °C) showed an enhanced photocurrent of 2.4 mA/cm2, which was 2.6 times larger than that of pristine TiO2. The improved photocurrent might be ascribed to the prepared p-n heterostructures (Co3O4 and TiO2), which promote electron-hole separation and charge transfer within the system and improve the photoelectrochemical performance. Moreover, the preparation of Co3O4 from the MOF carbonization process improved the electrical conductivity and significantly increased the number of exposed active sites and enhanced the photoresponse performance. The as-prepared ZIF-67 derived TiO2-Co3O4 based photoanodes demonstrate high PEC water oxidation, and the controlled carbonization method paves the way toward the synthesis of low-cost and efficient electrocatalysts.

Recycling of stainless steel pickling wastewater and polyethylene terephthalate plastic: A total-waste synthesis of metal-organic framework

Metal-organic frameworks (MOFs) attract considerable interests in various fields while relatively high cost limits their industrial-level use. Herein, we proposed a total-waste preparation route for Fe/Cr-MIL-88B (MIL, Matérial Institut Lavoisier), in which stainless steel pickling wastewater (PW) and waste polyethylene terephthalate (PET) act the total raw materials. Interestingly, PET is easily decomposed to terephthalic acid (H2BDC) under the strong acid environment of PW. Benefited from that, the formation of MOFs from PET and PW can be achieved via one-pot hydrothermal reaction, superior to the traditional two-step method. The obtained MIL-88B exhibits long-term acid/base stability and high removal efficiency for zirconium (IV) ion. Besides, the structure and adsorption performance of the products are not controlled by the discharge batch of the pickling wastewater, indicating the feasibility for continuous production in industry. Thus, our work provides a feasible route for preparing low-cost MOFs and recycling industrial wastes.

Isoreticular Contraction of Metal-Organic Frameworks Induced by Cleavage of Covalent Bonds.

Isoreticular chemistry, in which the organic or inorganic moieties of reticular materials can be replaced without destroying their underlying nets, is a key concept for synthesizing new porous molecular materials and for tuning or functionalization of their pores. Here, we report that the rational cleavage of covalent bonds in a metal-organic framework (MOF) can trigger their isoreticular contraction, without the need for any additional organic linkers. We began by synthesizing two novel MOFs based on the MIL-142 family, (In)BCN-20B and (Sc)BCN-20C, which include cleavable as well as noncleavable organic linkers. Next, we selectively and quantitatively broke their cleavable linkers, demonstrating that various dynamic chemical and structural processes occur within these structures to drive the formation of isoreticular contracted MOFs. Thus, the contraction involves breaking of a covalent bond, subsequent breaking of a coordination bond, and finally, formation of a new coordination bond supported by structural behavior. Remarkably, given that the single-crystal character of the parent MOF is retained throughout the entire transformation, we were able to monitor the contraction by single-crystal X-ray diffraction.