Defined metal atom aggregates precisely incorporated into metal-organic frameworks

Gold nanoparticles-wood nanohybrid as peroxidase-like for simple and selective detection of mercury ion

We present the design and synthesis of a gold nanoparticle-wood nanohybrid (AuNPs@Wood), synthesized via the in-situ growth of gold nanoparticles (AuNPs) within a hierarchical wood flour nanostructure under mild conditions. The AuNPs@Wood exhibited remarkable peroxidase-like activity, attributed to the unique hierarchical architecture of the wood flour. Furthermore, the use of AuNPs@Wood in conjunction with T-rich DNA (P1) results in the development of a label-free colorimetric approach for detecting mercury ions. The peroxidase-like activity of the AuNPs@Wood-P1 system was found to increase with rising concentrations of Hg (II), demonstrating a linear response to Hg (II) concentration with a correlation coefficient of 0.9917. The detection limit for Hg (II) was determined to be 0.016 μM based on three times the standard deviation (σ). Additionally, sensing Hg2+ ions remained unaffected by other metal ions, underscoring the exceptional selectivity of AuNPs@Wood-P1. In comparison to traditional methods, this approach offers advantages such as high selectivity, sensitivity, cost-effectiveness, and ease of operation without requiring complex instrumentation, thereby presenting significant potential for biosensing applications.

Recent advances in metal-organic frameworks for catalysing organic transformation

Metal-organic frameworks (MOFs) have garnered considerable attention due to their tunable properties, well-defined porosity, and structural versatility, making them effective catalysts for organic transformations. This review explores recent advances in MOF-based catalysis, emphasizing the roles of metal centres and organic linkers, as well as the synergistic effects arising from their combination. Additionally, guest molecule encapsulation and morphology modulation as effective strategies for improving catalytic efficiency are also discussed. Finally, future challenges and opportunities for MOFs as heterogenous catalysts are highlighted.

Confined Palladium Nanoparticles within a Robust Hierarchical Porous Zr-Based Metal-Organic Framework for Aromatic Alcohol Oxidation

The development of novel host-guest catalysts with nanoscale active sites provides new opportunities to gain highly efficient catalytic performance for the oxidation of aromatic alcohols into high-value compounds. In this work, we develop a green and facile synthesis method to incorporate Pd nanoparticles (PdNP) into a robust hierarchical porous Zr-metal-organic framework (Zr-IPA) through in situ solvent-free synthesis and wet reduction techniques. The optimized PdNP/Zr-IPA catalyst exhibits exceptional benzyl alcohol oxidation performance, selectively oxidizing 95.3% of benzyl alcohol to benzaldehyde (yield of 97.7%) at 70 °C within 12 h. Additionally, PdNP/Zr-IPA demonstrates superior catalytic activity for the oxidation of various aromatic alcohols using different oxidants. The turnover frequency of PdNP/Zr-IPA reaches 82.3 h-1 at 70 °C, which is 4.2 times larger than that of pre-PdNP/Zr-IPA and surpasses most reported MOF-based catalysts in benzyl alcohol oxidation reactions. Quenching and electron paramagnetic resonance tests verified that the exposed (111) faces of the PdNP in the PdNP/Zr-IPA structure can react with oxidants to generate •O2- radicals, which play a dominant role in oxidizing benzyl alcohol to benzaldehyde. Our work provides a solvent-free synthesis and a wet reduction strategy for confining nanoparticles within MOFs to enhance catalytic activity in targeted reactions.

Stable Polyoxometalate-Based Metal-Organic Framework: Synthesis, Modification, and Catalytic Activity

Metal-organic frameworks (MOFs) with polyoxometalates (POMs) as the nodes usually feature a high stability. Those with available space and modifiable groups are expected to serve as a catalytic platform. In this work, a polyoxometalate-based metal-organic framework (POMOF)-bearing channel with a transversal surface of ca. 1.1 × 1.8 nm, [Ni(en)2]4H{[Ni6(tris)(en)3(SIP)1.5][B-α-PW9O34]}2·32H2O (1), was resulted by the collaboration of multiple ligands. The channel was lined with abundant amino groups that bonded with water molecules in it via hydrogen bonds. Compound 1 exhibited excellent thermal and chemical stabilities, which was confirmed by immersion experiments, in situ variable temperature powder X-ray diffraction, and reversible dehydration-hydration behavior. Pristine 1 showed remarkable activity in the hydrogen evolution reaction. According to the presence of amino groups in the channel, 1 was modified by Pd species. Resultantly, Pd was loaded into the channel successfully. The yielding material 1-Pd smoothly catalyzed the Suzuki-Miyaura coupling reactions.

Location-Specific Microenvironment Modulation Around Single-Atom Metal Sites in Metal-Organic Frameworks for Boosting Catalysis

Despite coordination environment of catalytic metal sites has been recognized to be of great importance in single-atom catalysts (SACs), a significant challenge remains in the understanding how the location-specific microenvironment in the higher coordination sphere influences their catalysis. Herein, a series of Cu-based SACs, namely Cu1/UiO-66-X (X=-NO2, -H, and -NH2), are successfully constructed by anchoring single Cu atoms onto the Zr-oxo clusters of metal-organic frameworks (MOFs), i.e., UiO-66-X. The -X functional groups dangling on the MOF linkers could be regarded as location-specific remote microenvironment to regulate electronic properties of the single Cu atoms. Remarkably, they exhibit significant differences in the catalysis toward the hydroboration of alkynes. The activity follows the order of Cu1/UiO-66-NO2 > Cu1/UiO-66 > Cu1/UiO-66-NH2 under identical reaction conditions, where Cu1/UiO-66-NO2 showcases the phenylacetylene conversion of 92 %, ~3.5 times higher efficiency than that of Cu1/UiO-66-NH2. Experimental and calculation results jointly support that the Cu electronic structure is modulated by the location-specific microenvironment, thereby regulating the product desorption and promoting the catalysis.

In Situ Encapsulation of Atomically Precise Nanoclusters in Reticular Frameworks via Mechanochemical Synthesis

The combination of atomically precise nanoclusters (APNCs) and reticular frameworks is promising for generating component-specific nanocomposites with emergent properties. However, traditional liquid-phase synthesis often hampers this potential by damaging APNCs and limiting combination diversity. Here, mechanochemical synthesis to explore the encapsulation of diverse oil- and water-soluble APNCs within various reticular frameworks is employed, establishing a database of 21 unique APNC-framework combinations, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and multivariate MOFs. These framework coatings not only spatially immobilize APNCs but also secure their structures, preventing aggregation and degradation while enhancing stability and activity. Encapsulating Au25 in HOFs resulted in a remarkable 315-fold increase in catalytic activity compared to Au25 homogeneous catalyst, highlighting the framework's crucial role in catalytic enhancement. The mechanochemical synthesis strategy facilitates tailored support screening, catering to specific needs, and shows promise for developing multifunctional systems, including enzyme-APNC@frameworks material for cascade reactions.

Mechanism of Electron-Beam-Induced Structural Degradation in ZIF-8 and its Electron Dose Tolerance

Zeolitic-imidazolate frameworks (ZIFs) are crystalline microporous materials with promising potential for gas adsorption and catalysis application. Further research advances include studies on integrating ZIFs into nanodevice concepts. In detail for the application, e.g., electron-beam-assisted structural modifications or patterning, there is a need to understand potential structural degradation processes caused by such electron beams. Advanced transmission electron microscopy (TEM) has demonstrated its ability to study structures at the nanoscale. Here, we systematically investigated electron-beam-induced loss in crystallinity in ZIF-8 under various experimental conditions, using as measure the attenuation of the relative intensity and the relative displacement of electron diffraction Bragg planes with increasing cumulative electron dose. The {110} Bragg planes reflect the overall stability of the ZIF-8 unit-cell structure, while the {431} Bragg planes assess the stability of its micropore structure. We considered a relative loss of Bragg plane intensity of 37% as the threshold for determining the critical electron dose, which varied for different Bragg planes, with 35.6 ± 8.4 e-Å-2 for {110} and 11.4 ± 3.0 e-Å-2 for {431}. However, the critical dose per breakage of N-Zn bonds in a ZnN4 tetrahedra per different Bragg plane was found to be ∼3 e-Å-2, which indicates continuous, simultaneous breakage of N-Zn bonds throughout the crystal, confirming radiolysis as the dominant damage mechanism. In addition, we investigated the effects of TEM experiment parameters, including acceleration voltage, electron dose rate, cryogenic sample temperature, in situ sample drying, and change in conductivity of the sample substrate (e.g., graphene). Our results unravel the degradation mechanisms in ZIF-8 and provide threshold parameters for maximizing resolution in electron-beam-assisted experiments and processes.

Chiral Ligand-Decorated Rhodium Nanoparticles Incorporated in Covalent Organic Framework for Asymmetric Catalysis

While metal nanoparticles (NPs) have demonstrated their great potential in catalysis, introducing chiral microenvironment around metal NPs to achieve efficient conversion and high enantioselectivity remains a long-standing challenge. In this work, tiny Rh NPs, modified by chiral diene ligands (Lx) bearing diverse functional groups, are incorporated into a covalent organic framework (COF) for the asymmetric 1,4-addition reactions between arylboronic acids and nitroalkenes. Though Rh NPs hosted in the COF are inactive, decorating Rh NPs with Lx creates the active Rh-Lx interface and induces high activity. Moreover, chiral microenvironment modulation around Rh NPs by altering the groups on chiral diene ligands greatly optimizes the enantioselectivity (up to 95.6 % ee). Mechanistic investigations indicate that the formation of hydrogen-bonding interaction between Lx and nitroalkenes plays critical roles in the resulting enantioselectivity. This work highlights the significance of chiral microenvironment modulation around metal NPs by chiral ligand decoration for heterogeneous asymmetric catalysis.

Lanthanide-Doped Nanoparticles Anchoring on Metal-Organic Frameworks with Thermally Enhanced Upconversion Luminescence for Sensitive Nanothermometers

Nanothermometers can detect changes in the local temperature in living cells and in vivo, revealing fundamental biological properties. Despite the exploration of different temperature-responsive materials, the design and development of temperature-sensing probes with high brightness and high sensitivity remain a daunting challenge. Here, we employed the UiO-66 type metal-organic frameworks (MOFs) to anchor UNCPs on the surface of the MOFs for constructing MOF@UCNPs nanohybrids. The in situ composite method with MOFs leads to the coordination interaction between the ligands and the surface of UCNPs, enabling controlled composite formation between different MOFs and UCNPs. Remarkably, the surface interaction favors the anomalous thermo-enhanced luminescence, achieving a 35-fold enhancement of UiO-66@NaYF4:Yb/Tm at 413 K. Furthermore, these MOF@UCNPs nanohybrids with thermo-enhanced luminescence are developed as multifunctional biological probes for bioimaging and intracellular temperature sensing, demonstrating a high thermal sensitivity of 1.92% K-1 in the physiological temperature range. Based on these findings, temperature monitoring of the local position was successfully carried out by the designed MOF@UCNPs nanoprobes in vivo. These findings underscore the potential of MOF@UCNPs nanohybrids, opening up new avenues for the development of a multifunctional platform for biological analysis.

High-loading ficin@AuNPs on polymer-UiO-66 surface with enhanced peroxidase-mimetic catalytic activity for colourimetric detection of dopamine

Recently, MOFs@AuNPs composites-based catalysts via anchoring of AuNPs onto metal-organic-frameworks (MOFs) have attracted great attention. However, the influence of the AuNPs loading amounts on the catalytic activity of MOFs@AuNPs composites remains largely unexplored. Here, ficin (Fic) protected AuNPs (Fic@AuNPs) anchored onto the surface of UiO-66-NH2 (UiO) modified with poly(2-vinyl-4,4-dimethyl-2-oxazolidine) (PV) were designed and constructed. The UiOPVFic@AuNPs composites with longer PV chains leading to high-loading Fic@AuNPs exhibited intense peroxidase (POD)-mimetic activity in 3,3'5,5'-tetramethylbenzidine (TMB) oxidation. Further, following the colour-fading, dopamine (DA) was sensitively and selectively monitored in the composites-TMB-H2O2 system. The portable smartphone sensing platform-based colourimetric method had good linearity ranging from 3.34 to 36.7 μM (R2 = 0.995), with a limit of detection of 0.3 μM. This protocol explores high-loading AuNPs on polymer-MOFs composites, providing deep insights into understanding catalytic activity improvements of polymer-MOFs@AuNPs catalysts and revealing their application potential in real biological samples analysis.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Metal-Organic Frameworks-Derived Nanocarbon Materials and Nanometal Oxides for Photocatalytic Applications

Harnessing low-density solar energy and converting it into high-density chemical energy through photocatalysis has emerged as a promising avenue for the production of chemicals and remediation of environmental pollution, which contributes to alleviating the overreliance on fossil fuels. In recent years, metal-organic frameworks (MOFs) have gained widespread application in the field of photocatalysis due to their photostability, tunable structures, and responsiveness in the visible light range. However, most MOFs exhibit relatively low response to light, limiting their practical applications. MOFs-derived nanomaterials not only retain the inherent advantages of pristine MOFs but also show enhanced light adsorption and responsiveness. This review categorizes and summarizes MOFs-derived nanomaterials, including nanocarbons and nanometal oxides, providing representative examples for the synthetic strategies of each category. Subsequently, the recent research progress on MOFs-derived materials in photocatalytic applications are systematically introduced, specifically in the areas of photocatalytic water splitting to H2, photocatalytic CO2 reduction, and photocatalytic water treatment. The corresponding mechanisms involved in each photocatalytic reaction are elaborated in detail. Finally, the review discusses the challenges and further directions faced by MOFs-derived nanomaterials in the field of photocatalysis, highlighting their potential role in advancing sustainable energy production and environmental remediation.

Heteroatom-Doped Ag25 Nanoclusters Encapsulated in Metal-Organic Frameworks for Photocatalytic Hydrogen Production

Atomically precise metal nanoclusters (NCs) with unique optical properties and abundant catalytic sites are promising in photocatalysis. However, their light-induced instability and the difficulty of utilizing the photogenerated carriers for photocatalysis pose significant challenges. Here, MAg24 (M=Ag, Pd, Pt, and Au) NCs doped with diverse single heteroatoms have been encapsulated in a metal-organic framework (MOF), UiO-66-NH2, affording MAg24@UiO-66-NH2. Strikingly, compared with Ag25@UiO-66-NH2, the MAg24@UiO-66-NH2 doped with heteroatom exhibits much enhanced activity in photocatalytic hydrogen production, among which AuAg24@UiO-66-NH2 presents the best activity up to 3.6 mmol g-1 h-1, far superior to all other counterparts. Moreover, they display excellent photocatalytic recyclability and stability. X-ray photoelectron spectroscopy and ultrafast transient absorption spectroscopy demonstrate that MAg24 NCs encapsulated into the MOF create a favorable charge transfer pathway, similar to a Z-scheme heterojunction, when exposed to visible light. This promotes charge separation, along with optimized Ag electronic state, which are responsible for the superior activity in photocatalytic hydrogen production.

Bottom-Up Construction of Metal-Organic Framework Loricae on Metal Nanoclusters with Consecutive Single Nonmetal Atom Tuning for Tailored Catalysis

The introduction of single or multiple heterometal atoms into metal nanoparticles is a well-known strategy for altering their structures (compositions) and properties. However, surface single nonmetal atom doping is challenging and rarely reported. For the first time, we have developed synthetic methods, realizing "surgery"-like, successive surface single nonmetal atom doping, replacement, and addition for ultrasmall metal nanoparticles (metal nanoclusters, NCs), and successfully synthesized and characterized three novel bcc metal NCs Au38I(S-Adm)19, Au38S(S-Adm)20, and Au38IS(S-Adm)19 (S-Adm: 1-adamantanethiolate). The influences of single nonmetal atom replacement and addition on the NC structure and optical properties (including absorption and photoluminescence) were carefully investigated, providing insights into the structure (composition)-property correlation. Furthermore, a bottom-up method was employed to construct a metal-organic framework (MOF) on the NC surface, which did not essentially alter the metal NC structure but led to the partial release of surface ligands and stimulated metal NC activity for catalyzing p-nitrophenol reduction. Furthermore, surface MOF construction enhanced NC stability and water solubility, providing another dimension for tunning NC catalytic activity by modifying MOF functional groups.

Modulating the Electronic States of Pt Nanoparticles on Reducible Metal-Organic Frameworks for Boosting the Oxidation of Volatile Organic Compounds

The adsorption and activation of pollutant molecules and oxygen play a critical role in the oxidation reaction of volatile organic compounds (VOCs). In this study, superior adsorption and activation ability was achieved by modulating the interaction between Pt nanoparticles (NPs) and UiO-66 (U6) through the spatial position effect. Pt@U6 exhibits excellent activity in toluene, acetone, propane, and aldehyde oxidation reactions. Spectroscopic studies, 16O2/18O2 kinetic isotopic experiments, and density functional theory (DFT) results jointly reveal that the encapsulated Pt NPs of Pt@U6 possess higher electron density and d-band center, which is conducive for the adsorption and dissociation of oxygen. The toluene oxidation reaction and DFT results indicate that Pt@U6 is more favorable to activate the C-H of toluene and the C═C of maleic anhydride, while Pt/U6 with lower electron density and d-band center exhibits a higher oxygen dissociation temperature and higher reactant activation energy barriers. This study provides a deep insight into the architecture-performance relation of Pt-based catalysts for the catalytic oxidation of VOCs.

Progress in the Elimination of Organic Contaminants in Wastewater by Activation Persulfate over Iron-Based Metal-Organic Frameworks

The release of organic contaminants has grown to be a major environmental concern and a threat to the ecology of water bodies. Persulfate-based Advanced Oxidation Technology (PAOT) is effective at eliminating hazardous pollutants and has an extensive spectrum of applications. Iron-based metal-organic frameworks (Fe-MOFs) and their derivatives have exhibited great advantages in activating persulfate for wastewater treatment. In this article, we provide a comprehensive review of recent research progress on the significant potential of Fe-MOFs for removing antibiotics, organic dyes, phenols, and other contaminants from aqueous environments. Firstly, multiple approaches for preparing Fe-MOFs, including the MIL and ZIF series were introduced. Subsequently, removal performance of pollutants such as antibiotics of sulfonamides and tetracyclines (TC), organic dyes of rhodamine B (RhB) and acid orange 7 (AO7), phenols of phenol and bisphenol A (BPA) by various Fe-MOFs was compared. Finally, different degradation mechanisms, encompassing free radical degradation pathways and non-free radical degradation pathways were elucidated. This review explores the synthesis methods of Fe-MOFs and their application in removing organic pollutants from water bodies, providing insights for further refining the preparation of Fe-MOFs.

A zero-valent palladium cluster-organic framework

Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd3} cluster-based organometallic framework from a molecular triangulo-Pd3(CNXyl)6 (Xyl = xylyl; Pd3) cluster under chemically mild conditions. The formally zero-valent Pd3 cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd3-MOF). The structure of Pd3-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd3-MOF displays Pd03 cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd3-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.

Selectivity Control in the Direct CO Esterification over Pd@UiO-66: The Pd Location Matters

The selectivity control of Pd nanoparticles (NPs) in the direct CO esterification with methyl nitrite toward dimethyl oxalate (DMO) or dimethyl carbonate (DMC) remains a grand challenge. Herein, Pd NPs are incorporated into isoreticular metal-organic frameworks (MOFs), namely UiO-66-X (X=-H, -NO2 , -NH2 ), affording Pd@UiO-66-X, which unexpectedly exhibit high selectivity (up to 99 %) to DMC and regulated activity in the direct CO esterification. In sharp contrast, the Pd NPs supported on the MOF, yielding Pd/UiO-66, displays high selectivity (89 %) to DMO as always reported with Pd NPs. Both experimental and DFT calculation results prove that the Pd location relative to UiO-66 gives rise to discriminated microenvironment of different amounts of interface between Zr-oxo clusters and Pd NPs in Pd@UiO-66 and Pd/UiO-66, resulting in their distinctly different selectivity. This is an unprecedented finding on the production of DMC by Pd NPs, which was previously achieved by Pd(II) only, in the direct CO esterification.

A highly efficient synthetic strategy for de novo NP encapsulation into metal-organic frameworks: enabling further modulated control of catalytic properties

De novo encapsulation is a prevalent method to prepare composite materials where the structure-tunable metal nanoparticles (NPs) are holistically coated with metal-organic frameworks (MOFs). This method has been demonstrated to have promise in various fields but the extensive application of this approach is still challenging. This study proposed, for the first time, leveraging a specific surface-energy-dominated (SED) mechanism to achieve a highly efficient synthetic strategy for de novo NP encapsulation. The generality of this strategy is proved in applying to various MOFs, reaction conditions and the use of capping agents. By applying the strategy, Pd NPs with different morphologies are encapsulated in UiO-67, which is prone to self-assembly without coating, and an interesting enhancement is investigated in the selective semihydrogenation of alkynes on different Pd surfaces. These results demonstrate that the control of surface energy is a feasible method for efficient NP encapsulation which sheds light on the rational design of MOF-based composites for future applications.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

Integration of Metal-Organic Frameworks and Metals: Synergy for Electrocatalysis

Electrocatalysis is a highly promising technology widely used in clean energy conversion. There is a continuing need to develop advanced electrocatalysts to catalyze the critical electrochemical reactions. Integrating metal active species, including various metal nanostructures (NSs) and atomically dispersed metal sites (ADMSs), into metal-organic frameworks (MOFs) leads to the formation of promising heterogeneous electrocatalysts that take advantage of both components. Among them, MOFs can provide support and protection for the active sites on guest metals, and the resulting host-guest interactions can synergistically enhance the electrocatalytic performance. In this review, three key concerns on MOF-metal heterogeneous electrocatalysts regarding the catalytic sites, conductivity, and catalytic stability are first presented. Then, rational integration strategies of MOFs and metals, including the integration of metal NSs via surface anchoring, space confining, and MOF coating, as well as the integration of ADMSs either with the metal nodes/linkers or within the pores of MOFs, along with their recent progress on synergistic cooperation for specific electrochemical reactions are summarized. Finally, current challenges and possible solutions in applying these increasingly concerned electrocatalysts are also provided.

Atomically dispersed Ni activates adjacent Ce sites for enhanced electrocatalytic oxygen evolution activity

Manipulating the intrinsic activity of heterogeneous catalysts at the atomic level is an effective strategy to improve the electrocatalytic performances but remains challenging. Here, atomically dispersed Ni anchored on CeO₂ particles entrenched on peanut-shaped hollow nitrogen-doped carbon structures (a-Ni/CeO₂@NC) is rationally designed and synthesized. The as-prepared a-Ni/CeO₂@NC catalyst exhibits substantially boosted intrinsic activity and greatly reduced overpotential for the electrocatalytic oxygen evolution reaction. Experimental and theoretical results demonstrate that the decoration of isolated Ni species over the CeO₂ induces electronic coupling and redistribution, thus resulting in the activation of the adjacent Ce sites around Ni atoms and greatly accelerated oxygen evolution kinetics. This work provides a promising strategy to explore the electronic regulation and intrinsic activity improvement at the atomic level, thereby improving the electrocatalytic activity.

NH2-Modified UiO-66: Structural Characteristics and Functional Properties

The development of new functional materials based on metal-organic frameworks (MOFs) for adsorption and catalytic applications is one of the promising trends of modern materials science. The Zr-based MOFs, specifically UiO-66, are considered as the supports for metallic catalysts for the 5-hydroxymethylfurfural platform molecule reduction into valuable products. The present work focused on the effect of NH₂ modification of UiO-66 on its structure and functional properties. The samples were prepared by a solvothermal method. The structure of the obtained materials was studied by X-ray diffraction, IR spectroscopy, UV-visible spectroscopy, and low-temperature nitrogen adsorption. Basic properties were investigated by HCl and CH₃COOH adsorption, and electrokinetic properties were studied by electrophoretic light scattering. UiO-66-NH₂ samples with different contents of aminoterephthalate linkers were successfully prepared. A gradual decrease in the specific surface area and the fraction of micropores with a diameter of ~0.9 nm was observed with an increase in the aminoterephthalate content. A proportional increase in the total number of basic sites in UiO-66-NH₂ samples was established with an increase in the aminoterephthalate content up to 75%. At the same time, a noticeable decrease in the total number of basic sites and an increase in their strength with higher aminoterephthalate content was observed.