Mixed-Metal-Cluster Strategy for Boosting Electrocatalytic Oxygen Evolution Reaction of Robust Metal-Organic Frameworks

Green and high-yield synthesis of bimetallic zeolitic imidazolate framework-67 for efficient catalytic CO2 cycloaddition

Metal-organic frameworks (MOFs) such as ZIF-67 have been widely studied. Incorporating multi-bimetals into ZIF-67 is a strategic approach to leverage unique properties and address the limitations of traditional single metals in ZIF-67. Herein, an environmentally friendly solid-solid thermal (SST) method is developed to simultaneously incorporate heterometals (Cu, Fe, Ru, Pd, Mn, and Ni) into the ZIF structure, referred to as M@ZIF-67. The synthesis occurs in a single step by utilizing thermally treated mixed solid precursors of multi-bimetals and imidazole ligands without additional agents or solvents, which is an innovative green route for preparing multi-bimetal ZIFs. Multiple techniques confirm that heterometals are homogeneously and uniformly distributed and have a precise metal content in the iso-structure of ZIF-67. Interestingly, synthesizing M@ZIF-67 through the SST method achieves a scalable and high yield. Furthermore, M@ZIF-67 exhibits a precise heterometal content, which plays a crucial role in enhancing its catalytic performance in CO2 cycloaddition, surpassing results obtained using traditional ZIF-67.

Self-Reconstructed Metal-Organic Framework-Based Hybrid Electrocatalysts for Efficient Oxygen Evolution

Refining synthesis strategies for metal-organic framework (MOF)-based catalysts to improve their performance and stability in an oxygen evolution reaction (OER) is a big challenge. In this study, a series of nanostructured electrocatalysts were synthesized through a solvothermal method by growing MOFs and metal-triazolates (METs) on nickel foam (NF) substrates (named MET-M/NF, M = Fe, Co, Cu), and these electrocatalysts could be used directly as OER self-supporting electrodes. Among these electrocatalysts, MET-Fe/NF exhibited the best OER performance, requiring only an overpotential of 122 mV at a current density of 10 mA cm-2 and showing remarkable stability over 15 h. The experimental results uncovered that MET-Fe/NF underwent an in situ structural reconstruction, resulting in the formation of numerous iron/nickel (oxy)hydroxides with high OER activity. Furthermore, in a two-electrode water-splitting setup, MET-Fe/NF only required 1.463 V to achieve a current density of 10 mA cm-2. Highlighting its potential for practical applications. This work provides insight into the design and development of efficient MOF-based OER catalysts.

Metal-Organic Frameworks for Water Harvesting and Concurrent Carbon Capture: A Review for Hygroscopic Materials

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure-performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal-organic frameworks (MOFs) for their excellent performance in water and CO2 adsorption, and representative role of micro- and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO2 adsorption are reviewed. This review summarizes recent advances in water-harvesting porous materials with special attention on MOFs and expects to direct researchers' attention into the topic of concurrent water harvesting and carbon capture as a future challenge.

Constructing an efficient electrocatalyst for water oxidation: an Fe-doped CoO/Co catalyst enabled by in situ MOF growth and a solvent-free strategy

The development of non-precious metal electrocatalysts with high activity for the oxygen evolution reaction (OER) is a crucial and challenging task. In this work, we proposed a solvent-free in situ metal-organic framework (MOF) growth strategy for the fabrication of an Fe-doped CoO/Co electrocatalyst. This approach not only partially granted the MOF's porous structure to the catalyst but also resulted in a tighter combination between the Co metal and CoO, thereby enhancing its electrical conductivity. Furthermore, this method enabled the Fe species to be more uniformly dispersed on CoO/Co, which significantly exposed more active sites for efficient electrocatalysis. The entire synthesis process was solvent-free, except for a small amount of water and ethanol used during catalyst washing. The as-synthesized Fe-CoO/Co electrocatalyst exhibited superior OER activity on a glass carbon electrode, with η = 276 mV at a current density of 10 mA cm-2, even higher than that of the commercial precious IrO2/C catalyst. Additionally, it was also extended to prepare a Ni-doped CoO/Co electrocatalyst by the same procedure with satisfactory OER performance. This work presents a new preparation approach for MOF-derived catalysts with potential applications in energy conversion and beyond.

Preparation of Trimetallic-Organic Framework Film Electrodes via Secondary Growth for Efficient Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) are promising electrocatalysts for clean energy conversion systems. However, developing MOF-based electrodes with high performance toward oxygen evolution reaction (OER) is still challenging. In this work, a series of MOF film electrodes derived from Ni-btz were prepared by employing the secondary growth strategy under solvothermal conditions. Fe and Co ions were also incorporated into the Ni-btz framework to produce a trimetallic coupling effect to obtain enhanced OER activity. The as-prepared FeCoNi-btz/NF exhibited not only good stability but also excellent OER performance under alkaline conditions. Furthermore, the possible intermediates including metal oxides and metal oxyhydroxides were confirmed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

An iron(III) complex-based supramolecular organic framework (SOF) as a theranostic platform via magnetic resonance imaging-guided chemotherapy

It is crucially important to explore the additional metal-endowed functions of supramolecular organic frameworks (SOFs) for expanding their applications. In this work we have reported the performance of a SOF (designated as Fe(III)-SOF) as a theranostic platform via magnetic resonance imaging (MRI)-guided chemotherapy. The Fe(III)-SOF may be used as an MRI contrast agent for cancer diagnosis because the building unit (iron complex) contains high spin iron(III) ions. Additionally, the Fe(III)-SOF may also be used as a drug carrier because it possesses stable internal voids. We loaded doxorubicin (DOX) into the Fe(III)-SOF to obtain a DOX@Fe(III)-SOF. The Fe(III)-SOF showed good loading content (16.3%) and high loading efficiency (65.2%) for DOX. Additionally, the DOX@Fe(III)-SOF had a relatively modest relaxivity value (r₂ = 19.745 mM^-1 s^-1) and exhibited the strongest negative contrast (darkest) at 12 h of post-injection. Furthermore, the DOX@Fe(III)-SOF effectively inhibited tumor growth and showed high anticancer efficiency. In addition, the Fe(III)-SOF was biocompatible and biosafe. Therefore, the Fe(III)-SOF was an excellent theranostic platform and may have potential applications in tumor diagnosis and treatment in the future. We believe that this work will initiate extensive research endeavors not only on the development of SOFs, but also on the construction of theranostic platforms based on SOFs.

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal-Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction

Three new metal organic frameworks (ZnTIA-1mc, CuTIA-1mc, and CoTIA-1mc) were synthesized by the mechanochemical grinding (mc) method in the unadulterated form. They compared with their solvothermally synthesized (st) counterparts, where the mixtures of isomeric forms have been isolated. Kinetics study with the function of grinding time during the mechanosynthesis process revealed the formation of new metastable phases. Less crystallinity and short of mechanical defects in the structure of synthesized mc metal organic frameworks showed enhanced electrocatalytic activity toward oxygen evolution reaction (OER). Among all, CoTIA-1mc showed high OER activity with 289 mV overpotential, 10 mA cm^-2 current density, and 55.4 mV dec^-1 Tafel slope in 1 M KOH which is close to the commercially used RuO₂.

Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal-Organic Frameworks and Their Magnetic Characterization

The incorporation of multiple metal atoms in multivariate metal-organic frameworks is typically carried out through a one-pot synthesis procedure that involves the simultaneous reaction of the selected elements with the organic linkers. In order to attain control over the distribution of the elements and to be able to produce materials with controllable metal combinations, it is required to understand the synthetic and crystallization processes. In this work, we have completed a study with the RPF-4 MOF family, which is made of various rare-earth elements, to investigate and determine how the different initial combinations of metal cations result in different atomic distributions in the obtained materials. Thus, we have found that for equimolar combinations involving lanthanum and another rare-earth element, such as ytterbium, gadolinium, or dysprosium, a compositional segregation takes place in the products, resulting in crystals with different compositions. On the contrary, binary combinations of ytterbium, gadolinium, erbium, and dysprosium result in homogeneous distributions. This dissimilar behavior is ascribed to differences in the crystallization pathways through which the MOF is formed. Along with the synthetic and crystallization study and considering the structural features of this MOF family, we also disclose here a comprehensive characterization of the magnetic properties of the compounds and the heat capacity behavior under different external magnetic fields.

Hetero-metallic metal-organic frameworks for room-temperature NO2 sensing

Metal-organic frameworks (MOFs) with exceptional features such as high structural diversity and surface area as well as controlled pore size has been considered a promising candidate for developing room temperature highly-sensitive gas sensors. In comparison, the hetero-metallic MOFs with redox-active open-metal sites and mixed metal nodes may create peculiar surface properties and synergetic effects for enhanced gas sensing performances. In this work, the Fe atoms in the Fe₃ (Porous coordination network) PCN-250 MOFs are partially replaced by transition metal Co, Mn, and Zn through a facile hydrothermal approach, leading to the formation of hetero-metallic MOFs (Fe₂^IIIM^II, M = Co, Mn, and Zn). While the PCN-250 framework is maintained, the morphological and electronic band structural properties are manipulated upon the partial metal replacement of Fe. More importantly, the room temperature NO₂ sensing performances are significantly varied, in which Fe₂Mn PCN-250 demonstrates the largest response magnitude for ppb-level NO₂ gas compared to those of pure Fe₃ PCN-250 and other hetero-metallic MOF structures mainly attributed to the highest binding energy of NO₂ gas. This work demonstrates the strong potential of hetero-metallic MOFs with carefully engineered substituted metal clusters for power-saving and high-performance gas sensing applications.

Label-Free Bimetallic In Situ-Grown 3D Nickel-Foam-Supported NH2-MIL-88B(Fe2Co)-MOF-based Impedimetric Immunosensor for the Detection of Cardiac Troponin I

In this study, a simple and competent metal-organic framework (MOF)-based nickel foam (NF)-supported three-dimensional (3D) immunosensor (Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF) was constructed and utilized for the specific recognition of the biomarker cardiac troponin (I) (cTnI). In the present work, biosensor fabrication was progressed through the modification of the NF substrate with the MOF material (NH₂-MIL-88B(Fe₂Co)-MOF) to enable an amine-functionalized electrode. This amine-functionalized NF electrodes (NH₂-MIL-88B(Fe₂Co)-MOF/NF) were then biointerfaced with anti-cTnI antibodies, which ended up as Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF electrodes. Analytical executions of the constructed bioelectrode were investigated for the quantitative analysis of cTnI in both buffered and serum solutions. Then, the electrochemical studies were carried out using the electrochemical impedance spectroscopy (EIS) method by monitoring changes concerning the charge transfer resistance (R_ct) characteristics. The limit of detection (LOD) of the Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF immunosensor was achieved to be 13 fg/mL with great specificity. This kind of immunosensor imparts a new platform for the construction and application of MOF-hybrid 3D electrode materials with enhanced electrochemical behavior in cTnI sensing for the first time.

Three-Dimensional Transition Metal Phosphide Heteronanorods for Efficient Overall Water Splitting

The development of low-cost electrocatalysts with excellent activity and durability for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) poses a huge challenge in water splitting. In this study, a simple and scalable strategy is proposed to fabricate 3 D heteronanorods on nickel foam, in which nickel molybdenum phosphide nanorods are covered with cobalt iron phosphide (P-NM-CF HNRs). As a result of the rational design, the P-NM-CF HNRs have a large surface area, tightly connected interfaces, optimized electronic structures, and synergy between the metal atoms. Accordingly, the P-NM-CF HNRs exhibit a remarkably high catalytic activity for the OER under alkaline conditions and wide-pH HER. For overall water splitting, the catalyst only requires a voltage of 1.53 V to reach a current density of 10 mA cm^-2 in 1 m KOH with prominent stability, and the activity is not degraded after stability testing for 36 h. This new strategy can inspire the design of durable nonprecious-metal catalysts for large-scale industrial water splitting.

Rational Design of a N,S Co-Doped Supermicroporous CoFe-Organic Framework Platform for Water Oxidation

It remains a challenge to rational design of a new metal-organic framework (MOF) as highly efficient direct electrocatalysts for the oxygen evolution reaction (OER). Herein, we developed a simple and effective method to explore a new pillared-layered MOF with syringic acid as a promising OER electrocatalyst. The isostructural mono-, heterobimetallic MOF and N,S co-doped MOF by mixing thiourea were quickly synthesized in a high yield under solvothermal condition. Moreover, the optimized N,S co-doped MOF exhibits the lowest overpotential of 254 mV at 10 mA cm^-2 on a glass carbon electrode and a small Tafel slope of 50 mV dec^-1 , especially, this catalyst also possesses long-term electrochemical durability for at least 16 h. According to the characterization, the incorporation of N and S atoms into this heterobimetallic CoFe-based MOF could modify its pore structure, tune the electronic structure, accordingly, improve the mass and electron transportation, and facilitate the formation of active species, as a consequence, the improved activity of this new N,S co-doped MOF for OER should be mainly be ascribed to higher electrochemical activation toward the active species via in situ surface modification during the OER process.

Mimic of Ferroalloy To Develop a Bifunctional Fe-Organic Framework Platform for Enhanced Gas Sorption and Efficient Oxygen Evolution Electrocatalysis

It is well-known that the formation of ferroalloy with the addition of the second or third metal during the steel-making process usually can improve the performance of the iron. Inspired by ferroalloy materials, it is speculated that the pore environment, framework charge, and catalytic properties of metal-organic frameworks (MOFs) could be optimized dramatically via the introduction of ferroalloy-like inorganic building blocks. However, different to ferroalloy, the accurate integration of different metals into one MOF platform is still challenging. Herein, taking advantages of the good compatibility for metals in trigonal prismatic trinuclear cluster, a series of Fe-based alloy-like [M₃O(O₂C)₆] motifs (M₃ = Fe₃, Fe_1.5Ni_1.5, Fe_1.5Co_1.5, Fe_1.5Ti_1.5, FeCoNi, and FeTiCo) are successfully generated, which further lead to a robust Fe-MOF material family (SNNU-5s). These multicomponent MOFs not only provide a good chance to explore the impact of pore environment on gas adsorption/separation but also offer an opportunity to the efficient electrocatalytic reaction directly. Accordingly, compared with the SNNU-5-Fe parent structure, the pore characters of heterometallic SNNU-5 MOFs are clearly regulated by the type of alloy-like building blocks. SNNU-5-FeTi displays more superior gas separation performance for CO₂/CH₄, C₂H₂/CH₄, C₂H₄/CH₄, and C₂H₂/CO₂ gas mixtures. What is more, benefited from the multimetallic active sites and their catalytic synergy, FeCoNi-ternary alloy-like cluster-based SNNU-5 MOF material exhibits an exceptional oxygen evolution reaction activity in aqueous solution at pH = 13, which delivers a low overpotential (η_j=10 = 317 mV), a fast reaction kinetics (Tafel slope = 37 mV dec^-1), and excellent catalytic stability. This facile multialloy-like building block strategy holds promise to accurately design and improve the performance of MOFs, as well as open an avenue to understand the related mechanisms.

Evolution of metal organic frameworks as electrocatalysts for water oxidation

The development of metal organic framework based water oxidation catalysts is discussed here in connection with various design strategies.