Immobilizing Metal Nanoparticles to Metal–Organic Frameworks with Size and Location Control for Optimizing Catalytic Performance

Silica Confinement for Stable and Magnetic Co-Cu Alloy Nanoparticles in Nitrogen-Doped Carbon for Enhanced Hydrogen Evolution

Ammonia borane (AB) with 19.6 wt % H2 content is widely considered a safe and efficient medium for H2 storage and release. Co-based nanocatalysts present strong contenders for replacing precious metal-based catalysts in AB hydrolysis due to their high activity and cost-effectiveness. However, precisely adjusting the active centers and surface properties of Co-based nanomaterials to enhance their activity, as well as suppressing the migration and loss of metal atoms to improve their stability, presents many challenges. In this study, mesoporous-silica-confined bimetallic Co-Cu nanoparticles embedded in nitrogen-doped carbon (CoxCu1-x@NC@mSiO2) were synthesized using a facile mSiO2-confined thermal pyrolysis strategy. The obtained product, an optimized Co0.8Cu0.2@NC@mSiO2 catalyst, exhibits enhanced performance with a turnover frequency of 240.9 molH2 ⋅ molmetal ⋅ min-1 for AB hydrolysis at 298 K, surpassing most noble-metal-free catalysts. Moreover, Co0.8Cu0.2@NC@mSiO2 demonstrates magnetic recyclability and extraordinary stability, with a negligible decline of only 0.8 % over 30 cycles of use. This enhanced performance was attributed to the synergistic effect between Co and Cu, as well as silica confinement. This work proposes a promising method for constructing noble-metal-free catalysts for AB hydrolysis.

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 Frameworks/Heterojunction Structures for Surface-Enhanced Raman Scattering with Enhanced Sensitivity and Tailorability

Metal-organic frameworks (MOFs), which are composed of crystalline microporous materials with metal ions, have gained considerable interest as promising substrate materials for surface-enhanced Raman scattering (SERS) detection via charge transfer. Research on MOF-based SERS substrates has advanced rapidly because of the MOFs' excellent structural tunability, functionalizable pore interiors, and ultrahigh surface-to-volume ratios. Compared with traditional noble metal SERS plasmons, MOFs exhibit better biocompatibility, ease of operation, and tailorability. However, MOFs cannot produce a sufficient limit of detection (LOD) for ultrasensitive detection, and therefore, developing an ultrasensitive MOF-based SERS substrate is imperative. To the best of our knowledge, this is the first study to develop an MOFs/heterojunction structure as an SERS enhancing material. We report an in situ ZIF-67/Co(OH)2 heterojunction-based nanocellulose paper (nanopaper) plate (in situ ZIF-67 nanoplate) as a device with an LOD of 0.98 nmol/L for Rhodamine 6G and a Raman enhancement of 1.43 × 107, which is 100 times better than that of the pure ZIF-67-based SERS substrate. Further, we extend this structure to other types of MOFs and develop an in situ HKUST-1 nanoplate (with HKUST-1/Cu(OH)2). In addition, we demonstrate that the formation of heterojunctions facilitates efficient photoinduced charge transfer for SERS detection by applying the Mx(OH)y-assisted (where M = Co, Cu, or other metals) MOFs/heterojunction structure. Finally, we successfully demonstrate the application of medicine screening on our nanoplates, specifically for omeprazole. The nanoplates we developed still maintain the tailorability of MOFs and perform high anti-interference ability. Our approach provides customizing options for MOF-based SERS detection, catering to diverse possibilities in future research and applications.

One-pot Construction of Metal Nanoparticles Loaded COF Catalysts for Aqueous Hydrogenation Reactions

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.

A core-shell AuNRs@BUT-16 nanocomposite for enhancement SERS detection and efficient removal of deoxynivalenol

INTRODUCTION

Deoxynivalenol (DON) is widely found in grains and poses a serious threat to human health, so there is an urgent need to develop methods for its simultaneous removal and detection. The novel metal organic framework (MOF) material BUT-16 has a high adsorption capacity (79.8%) for DON. Meanwhile, surface-enhanced Raman spectroscopy (SERS) has been widely used for rapid detection of analytes.

OBJECTIVES

The aim of this work is to prepare a material that can be used for enhancement SERS detection and efficient removal of DON.

METHODS

AuNRs@BUT-16 was prepared by in-situ solvothermal method and characterized using a series of characterization tools. AuNRs@BUT-16 was used as an adsorbent and SERS substrate for the removal and detection of DON, and some factors affecting the adsorption and SERS detection were investigated. The adsorption mechanism between DON and AuNRs@BUT-16 was investigated using molecular docking. The proposed SERS method was used to detect DON contamination in real samples.

RESULTS

The prepared core-shell AuNRs@BUT-16 showed a synergistic effect in improving DON adsorption and SERS response. 97.6 % of DON was removed by AuNRs@BUT-16 in aqueous solution, and 70 % in 80 % methanol. The pre-enrichment effect of BUT-16 could trap more DON molecules in the "hot spots" of AuNRs, thus the proposed SERS sensor based on AuNRs@BUT-16 substrate displayed outstanding SERS response and the limit of detection of DON was 3.87 × 10-3 μg/mL. Molecular docking revealed that hydrogen bond and π-alkyl interaction were the main reasons for high affinity between BUT-16 and DON, and Au-O bonds facilitated the adsorption of DON on AuNRs.

CONCLUSIONS

AuNRs@BUT-16 with superior enrichment and SERS detection capabilities has been used for simultaneous removal and SERS detection of DON, and it also has great potential to realize sensitive and selective detection and removal of DON in multiple disciplines.

Highly-dispersed nickel species on nitrogen-doped porous carbon: Significant local pH-buffering capacity and favorable CO desorption for efficient and robust electro-reduction of CO2

Electrocatalytic reduction of CO2 (CO2RR) to value-added fuels and chemicals can potentially serve as a promising strategy to curb CO2 accumulation and carbon neutral cycle, but is still plagued by sluggish kinetics, poor selectivity and weak durability. Herein, we developed highly-dispersed nickel species on the nitrogen-doped carbon materials (Ni/NC) via the double solvent method (DSM), followed by the pyrolysis. The as-prepared Ni/NC possesses high CO2-to-CO selectivity of 93.2%∼98.6% at broad potential range (0.57 ∼ 0.97 VRHE), decent jCO of 57.9 mAcm-2 at -1.07 VRHE, and significant robustness (retaining 96.3% of the initial faradaic efficiency for CO formation after 50 h electrolysis). As manifested by the rotating ring-disk electrode (RRDE) tests, the DSM-based Ni/NC possesses more significant pH-buffering capacity than Ni nanoparticles, thus promotes the CO2-to-CO. DFT calculations unveil that Ni/NC exhibits relatively lower d-band center, hence resulting in favorable desorption of CO from the catalyst surface that intrinsically boost the CO2-to-CO compared with the nanoparticle catalyst. These results suggest that the DSM-derived Ni/NC catalysts is a promising candidate towards large-scale application of CO2-to-CO.

Hydrothermal synthesis of a bimetallic metal-organic framework (MOF)-derived Co3O4/SnO2 composite as an effective material for ethanol detection

This study utilized a hydrothermal method and air calcination to prepare a bimetallic metal-organic framework (MOF) derived Co3O4/SnO2 nanocomposite material, which was employed as a sensing material for ethanol detection. The structure, elemental composition, and surface morphology of Co3O4/SnO2 nanocomposite materials were defined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Compared to SnO2 nanoparticles derived from metal-organic frameworks, the bimetallic metal-organic framework-derived Co3O4/SnO2 nanocomposite material exhibits significantly superior ethanol sensing performance. At 225 °C, the response value (R = Ra/Rg) to 100 ppm ethanol is 135, demonstrating excellent repeatability, selectivity and stability. Gas sensitivity assessment findings indicate that the 3 at% (Co/Sn) Co3O4/SnO2 nanocomposite is an excellent gas sensing material, providing strong technical support for ethanol detection and environmental monitoring.

Heterostructured Ag@MOF-801/MIL-88A(Fe) Nanocomposite as a Biocompatible Photocatalyst for Degradation of Reactive Black 5 under Visible Light

Heterostructured Ag@MOF-801/MIL-88A(Fe) nanocomposite was synthesized through template effects in metal-organic frameworks (MOFs). MIL-88A(Fe) was fabricated on a MOF-801 template using the internal extended growth method (IEGM) via polyvinylpyrrolidone (PVP) as the structure-director agent to create the MIL-88A(Fe)-on-MOF-801 heterostructure. The MOF-801/MIL-88A(Fe) heterostructure was used as a template for the formation of Ag nanoparticles (NPs) inside it via a double solvents method (DSM) combined with a photoreduction route (PR). To characterize synthesized samples to a high level of detail, PXRD, FT-IR, EDX, N2 adsorption-desorption isotherms, TEM, DRS, PL, EIS, and Mott-Sckottky measurements were used. The resulting Ag@MOF-801/MIL-88A(Fe) nanocomposite demonstrated the highest photocatalytic activity of 91.72% for the degradation of Reactive Black 5, after 30 min under visible light irradiation.

MOFs as Versatile Catalysts: Synthesis Strategies and Applications in Value-Added Compound Production

Catalysts played a crucial role in advancing modern human civilization, from ancient times to the industrial revolution. Due to high cost and limited availability of traditional catalysts, there is a need to develop cost-effective, high-activity, and nonprecious metal-based electrocatalysts. Metal-organic frameworks (MOFs) have emerged as an ideal candidate for heterogeneous catalysis due to their physicochemical properties, hybrid inorganic/organic structures, uncoordinated metal sites, and accessible organic sections. MOFs are high nanoporous crystalline materials that can be used as catalysts to facilitate polymerization reactions. Their chemical and structural diversity make them effective for various reactions compared to traditional catalysts. MOFs have been applied in gas storage and separation, ion-exchange, drug delivery, luminescence, sensing, nanofilters, water purification, and catalysis. The review focuses on MOF-enabled heterogeneous catalysis for value-added compound production, including alcohol oxidation, olefin oligomerization, and polymerization reactions. MOFs offer tunable porosity, high spatial density, and single-crystal XRD control over catalyst properties. In this review, MOFs were focused on reactions of CO2 fixation, CO2 reduction, and photoelectrochemical water splitting. Overall, MOFs have great potential as versatile catalysts for diverse applications in the future.

Anchoring ultrasmall Pd nanoparticles by bipyridine functional covalent organic frameworks for semihydrogenation of acetylene

Acetylene hydrogenation is a well-accepted solution to reduce by-products in the ethylene production process, while one of the key technical difficulties lies in developing a catalyst that can provide highly dispersed active sites. In this work, a highly crystalline layered covalent organic framework (COF) material (TbBpy) with excellent thermal stability was synthesized and firstly applied as support for ultrasmall Pd nanoparticles to catalyze acetylene hydrogenation. 100% of C2H2 conversion and 88.2% of C2H4 selectivity can be obtained at 120 °C with the space velocity of 70 000 h-1. The reaction mechanism was elucidated by applying a series of characterization techniques and theoretical calculation. The results indicate that the coordination between Pd and N atom in the bipyridine functional groups of COFs successfully increased the dispersibility and stability of Pd particles, and the introduction of COFs not only improved the adsorption of acetylene and H2 onto catalyst surface, but enhanced the electron transfer process, which can be responsible for the high selectivity and activity of catalyst. This work, for the first time, reported the excellent performance of Pd@TbBpy as a catalyst for acetylene hydrogenation and will facilitate the development and application of COFs materials in the area of petrochemicals.

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.

Photoactive MOF-Derived Bimetallic Silver and Cobalt Nanocomposite with Enhanced Antibacterial Activity

Conventional antibiotic-based treatment of bacterial infections remains one of the most difficult challenges in medicine because of the threat of multidrug resistance caused by indiscriminate abuse. To solve these problems, it is essential to develop an effective antibacterial agent that can be used at a small dose while minimizing the occurrence of multiple resistance. Metal-organic frameworks (MOFs), which are hyper-porous hybrid materials containing metal ions linked by organic ligands, have recently attracted attention because of their strong antibacterial activity through metal-ion release, unlike conventional antibiotics. In this study, we developed a photoactive MOF-derived cobalt-silver bimetallic nanocomposite (Ag@CoMOF) by simply depositing silver nanoparticles on a cobalt-based MOF through nanoscale galvanic replacement. The nanocomposite structure continuously releases antibacterial metal ions (i.e., Ag and Co ions) in the aqueous phase and exhibits a strong photothermal conversion effect of Ag nanoparticles, accompanied by a rapid temperature increase of 25-80 °C under near-infrared (NIR) irradiation. Using this MOF-based bimetallic nanocomposite, superior antibacterial activities were achieved by 22.1-fold for Escherichia coli and 18.3-fold for Bacillus subtilis enhanced inhibition of bacterial growth in a liquid culture environment compared with the generally used chemical antibiotics. In addition, we confirmed the synergistic enhancement of the antibacterial ability of the bimetallic nanocomposite induced by NIR-triggered photothermal heating and bacterial membrane disruption even when using a small amount of the nanocomposites. We envision that this novel antibacterial agent using MOF-based nanostructures will replace traditional antibiotics to circumvent multidrug resistance and present a new approach to antibiotic development.

Zr-MOF-Induced Smart Accumulation Enables Surface-Enhanced Raman Spectroscopic Detection of Dioxin at ppt Level in Food Samples

The fast and economical detection of trace polychlorinated dibenzo-p-dioxins (PCDDs) in food samples by current mass spectrum-based methods is hindered by tedious sample preparation and bulky & expensive analytical instruments. Surface-enhanced Raman spectroscopy (SERS) successfully detects many organic pollutants in foods but not dioxins because the employed metal nanoparticles weakly adsorb hydrophobic PCDDs. Herein, we report the detection of PCDDs in milk with SERS for the first time using a bifunctional substrate consisting of Au nanoparticles embedded in a zirconium-based metal-organic framework shell (AuNP/Zr-MOF). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), as the most toxic PCDD, is detected as low as 1.2 parts per trillion (ppt) in real milk samples with massive interfering substances in 30 min, which is the lowest among all reported methods. The aromatic rings of Zr-MOF promote the smart accumulation of TCDD through π-π interactions, and Au-Cl interactions drive TCDD onto Au surfaces. Zr-MOF shells with pore sizes of 12.7 and 20 Å block the accessibility of larger interfering molecules. A one-step apparatus and protocol are established to be superior to traditional methods in terms of time and cost. This work provides new insight into a rational screening method for the detection of persistent organic pollutants in a real sample matrix.

Integrating Ultrasmall Pd NPs into Core-Shell Imidazolate Frameworks for Photocatalytic Hydrogen and MeOH Production

The construction of photoactive units in the proximity of a stable framework support is one of the promising strategies for uplifting photocatalysis. In this work, the ultrasmall Pd NPs implanted onto core-shell (CS) metal organic frameworks (MOFs), i.e., CS@Pd nanoarchitectures with tailored electronic and structural properties are reported. The all-in-one heterogeneous catalyst CS@Pd3 improves the surface functionalities and exhibits an outstanding hydrogen evolution reaction (HER) activity rate of 12.7 mmol g^-1 h^-1, which is 10-folds higher than the pristine frameworks with an apparent quantum efficiency (AQE) of 9.02%. The bifunctional CS@Pd shows intriguing results when subjected to photocatalytic CO₂ reduction with an impressive rate of 71 μmol g^-1 h^-1 of MeOH under visible-light irradiation at ambient conditions. Spectroscopic data reveal efficient charge migrations and an extended lifetime of 2.4 ns, favoring efficient photocatalysis. The microscopic study affirms the formation of well-ordered CS morphology with precise decoration of Pd NPs over the CS networks. The significance of active Pd and Co sites is addressed by congruent charge-transfer kinetics and computational density functional theory calculations of CS@Pd, which validate the experimental findings with their synergistic involvement in improved photocatalytic activity. This present work provides a facile and competent avenue for the systematic construction of MOF-based CS heterostructures with active Pd NPs.

Recent Advances and Perspectives on Supported Catalysts for Heterogeneous Hydrogen Production from Ammonia Borane

Ammonia borane (AB), a liquid hydrogen storage material, has attracted increasing attention for hydrogen utilization because of its high hydrogen content. However, the slow kinetics of AB hydrolysis and the indefinite catalytic mechanism remain significant problems for its large-scale practical application. Thus, the development of efficient AB hydrolysis catalysts and the determination of their catalytic mechanisms are significant and urgent. A summary of the preparation process and structural characteristics of various supported catalysts is presented in this paper, including graphite, metal-organic frameworks (MOFs), metal oxides, carbon nitride (CN), molybdenum carbide (MoC), carbon nanotubes (CNTs), boron nitride (h-BN), zeolites, carbon dots (CDs), and metal carbide and nitride (MXene). In addition, the relationship between the electronic structure and catalytic performance is discussed to ascertain the actual active sites in the catalytic process. The mechanism of AB hydrolysis catalysis is systematically discussed, and possible catalytic paths are summarized to provide theoretical considerations for the designing of efficient AB hydrolysis catalysts. Furthermore, three methods for stimulating AB from dehydrogenation by-products and the design of possible hydrogen product-regeneration systems are summarized. Finally, the remaining challenges and future research directions for the effective development of AB catalysts are discussed.

Electronic State and Microenvironment Modulation of Metal Nanoparticles Stabilized by MOFs for Boosting Electrocatalytic Nitrogen Reduction

Modulation of the local electronic structure and microenvironment of catalytic metal sites plays a critical role in electrocatalysis, yet remains a grand challenge. Herein, PdCu nanoparticles with an electron rich state are encapsulated into a sulfonate functionalized metal-organic framework, UiO-66-SO₃ H (simply as UiO-S), and their microenvironment is further modulated by coating a hydrophobic polydimethylsiloxane (PDMS) layer, affording PdCu@UiO-S@PDMS. This resultant catalyst presents high activity toward the electrochemical nitrogen reduction reaction (NRR, Faraday efficiency: 13.16%, yield: 20.24 µg h^-1 mg_cat. ^-1 ), far superior to the corresponding counterparts. Experimental and theoretical results jointly demonstrate that the protonated and hydrophobic microenvironment supplies protons for the NRR yet suppresses the competitive hydrogen evolution reaction reaction, and electron-rich PdCu sites in PdCu@UiO-S@PDMS are favorable to formation of the N₂ H* intermediate and reduce the energy barrier of NRR, thereby accounting for its good performance.

Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis

Ultrasmall metal nanoparticles (NPs) show high catalytic activity in heterogeneous catalysis but are prone to reunion and loss during the catalytic process, resulting in low chemoselectivity and poor efficiency. Herein, a locking effect strategy is proposed to synthesize high-loading and ultrafine metal NPs in metal-organic frameworks (MOFs) for efficient chemoselective catalysis with high stability. Briefly, the MOF ZIF-90 with aldehyde groups cooperating with diamine chains via aldimine condensation was interlocked, which was employed to confine in situ formation of Au NPs, denoted as Au@L-ZIF-90. The optimized Au@L_a-ZIF-90 has highly dispersed Au NPs (2.60 ± 0.81 nm) with a loading amount around 22 wt % and shows a great performance toward 3-aminophenylacetylene (3-APA) from the selective hydrogenation of 3-nitrophenylacetylene (3-NPA) with a high yield (99%) and excellent durability (over 20 cycles), far superior to contrast catalysts without chains locking and other reported catalysts. In addition, experimental characterization and systematic density functional theory calculations further demonstrate that the locked MOF modulates the charge of Au nanoparticles, making them highly specific for nitro group hydrogenation to obtain 3-APA with high selectivity (99%). Furthermore, this locking effect strategy is also applicable to other metal nanoparticles confined in a variety of MOFs, and all of these catalysts locked with chains show great selectivity (≥90%) of 3-APA. The proposed strategy in this work provides a novel and universal method for precise control of the inherent activity of accessible metal nanoparticles with a programmable MOF microenvironment toward highly specific catalysis.

Metal organic frameworks derived functional materials for energy and environment related sustainable applications

With the vigorous development of industrial economy, energy and environmental problems have become the most serious issues affecting people's production and life. Therefore, the demand for clean energy production, effective separation and storage is growing. Metal-organic frameworks (MOFs), as a kind of porous crystalline materials with large surface area and porosity, which is self-assembled by metal ions or clusters and organic ligands through coordination bonds. Thanks to a number of unique characteristics such as adjustable pore environment, homogeneous void structure, abundant active sites, unprecedented chemical composition tunability and functional versatility, it has been widely studied, especially for the clean energy conversion in catalysis. In this review, we focus on the research progress of clean energy in catalysis based on MOFs. Emphasis is placed on MOFs with different structures of compositions and their applications in catalytic for clean energy conversion, such as CO oxidation, CO₂ reduction and H₂ evolution. In addition, the situation of MOFs assisting environmental remediation is also briefly described. Finally, the prospects and challenges of MOFs in clean energy and the remaining issues in this field are presented.

Defined metal atom aggregates precisely incorporated into metal-organic frameworks

Nanosized metal aggregates (MAs), including metal nanoparticles (NPs) and nanoclusters (NCs), are often the active species in numerous applications. In order to maintain the active form of MAs in "use", they need to be anchored and stabilised, preventing agglomeration. In this context, metal-organic frameworks (MOFs), which exhibit a unique combination of properties, are of particular interest as a tunable and porous matrix to host MAs. A high degree of control in the synthesis towards atom-efficient and application-oriented MA@MOF composites is required to derive specific structure-property relationships and in turn to enable design of functions on the molecular level. Due to the versatility of MA@MOF (derived) materials, their applications are not limited to the obvious field of catalysis, but increasingly include 'out of the box' applications, for example medical diagnostics and theranostics, as well as specialised (bio-)sensoring techniques. This review focuses on recent advances in the controlled synthesis of MA@MOF materials en route to atom-precise MAs. The main synthetic strategies, namely 'ship-in-bottle', 'bottle-around-ship', and approaches to achieve novel hierarchical MA@MOF structures are highlighted and discussed while identifying their potential as well as their limitations. Hereby, an overview of standard characterisation methods that enable a systematic analysis procedure and state-of-art techniques that localise MA within MOF cavities are provided. While the perspectives of MA@MOF materials in general have been reviewed various times in the recent past, few atom-precise MAs inside MOFs have been reported so far, opening opportunities for future investigation.

Spatial directional separation and synergetic treatment of Cr(VI) and Rhodamine B mixed pollutants on three-layered Pd@MIL-101/P25 photocatalyst

The development of efficacious photocatalysts for removal of heavy metal and dyes coexisting pollutants simultaneously remains a challenge. Herein, we designed a three-layered Pd@MIL-101/P25 composite photocatalyst, which had the characteristics of directional photogenerated carrier separation. Pd nanoparticles were encapsulated in the MIL-101 to enrich the e^-, while P25 was loaded on the outer surface of MIL-101 as the valence band of the heterojunction with MIL-101 to enrich the h⁺. The photocatalytic kinetic constants (K) of Pd@MIL-101/P25 for the removal of Cr (VI) and RhB were 3.4 and 4.2 times greater than that of MIL-101, respectively. The photocatalytic efficiency of the catalyst in the mixed pollutants of Cr(VI) and RhB was much higher than that when Cr(VI) and RhB were present separately. Due to the 1.2 and 1.6 nm windows of MIL-101, two target pollutants can be directionally separated. Cr (VI) was reduced by e^- on the inner surface, and RhB was blocked on the outer surface and oxidized by h⁺. These results suggested that the directional spatially separation of target pollutants are able to separate the reaction sites of oxidation and reduction, improving the utilization efficiency of photogenerated carriers. This work not only provided a new strategy for the design and construction of photocatalytic materials, but also provided a new idea for the treatment of mixed pollutants.

Nanoparticle/metal-organic framework hybrid catalysts: elucidating the role of the MOF

Hybrid materials of metal-organic frameworks (MOFs) and nanoparticles (NPs) have attracted significant attention because of the wide variety of attractive properties derived from the two components. In the last decade, the development of synthesis techniques for NP/MOF composites was particularly significant. In the field of catalysis in particular, various synergistic effects that make the composites attractive catalysts have been reported. However, the role of MOFs in the composite catalysts is still not well understood and is being elucidated. In this feature article, we focus on recent progress in NP/MOF composite catalysts, concentrating on the analysis of the interaction between NPs and MOFs and the reaction mechanisms, together with the synthetic techniques used for NP/MOF hybrid materials.

Size-Selective Suzuki-Miyaura Coupling Reaction over Ultrafine Pd Nanocatalysts in a Water-Stable Indium-Organic Framework

Metal nanoparticles stabilized by crystalline metal-organic frameworks (MOFs) are highly promising for green heterogeneous catalysis. In this work, in situ formed ultrafine Pd nanocatalysts with an average size of 3.14 nm have been successfully immobilized into the mesopores or defects of a water-stable indium-based MOF by the double-solvent method and subsequent reduction. Significantly, the obtained Pd@InOF-1 displays an obvious and satisfactory size-selective effect in the Suzuki-Miyaura coupling reaction between arylboronic acids and aryl bromides. On the basis of the synergistic effect, microporous InOF-1 nanorods afford a confined space for improving the selectivity of target products while Pd nanoparticles endow abundant active sites for catalysis. Herein, choosing the smallest size reactant with only one benzene ring gives the highest isolated yield of 90%, and if the size is larger, the yield is obviously reduced or even the target product could not be collected. Looking forward, this demonstrated study not only assembles a well-designed Pd@MOF composite with unique micro-nanostructures but also delivers an impressive option for cross-coupling reaction, which has implications for the further development of MOF hybrids for sustainable applications.

Pt-embodiment ZIF-67-derived nanocage as enhanced immunoassay for infectious virus detection

A facile and general strategy has been employed to develop highly-active nanozyme for immunoassay purposes. The hollow nanostructure of the Co₃O₄ nanocages (NCs) was anchoring the platinum nanoparticles (PtNPs) enclosed by the exposed oxides framework nd formed PtNPs@Co₃O₄ NCs. The embodiment of PtNPs was considered an ideal hybrid nanozyme that efficiently catalyzed the oxidation of the substrate molecules with enhanced activity. The PtNPs@Co₃O₄ NCs were revisited and repurposed on showing its nanozyme's activity with optimization done for the immunoassay platform. The embodiment of 32.44% Pt in the hollow nanostructures demonstrated the highest signal-to-noise responses in the immunoassay. In addition, the stepwise analysis highlighted the enhancement factor of the nanocages' catalytic mechanism. Based on their catalytic activity, these nanocages have been demonstrated to enable sub-femtogram level biosensing of norovirus-like particles (NoV-LPs) with highly selective signals in the capture-detect immunoassay format. The detection limit of the prepared immunoassay achieved 33.52 viral NoV copies/mL of the detection limit, which is 321-folds lower magnitude of the commercial ELISA. This nanocage's enhanced synergic catalytic properties could have great potential applications, including catalysis, biological labeling, and bioassays.

Thermoplasmonics in Solar Energy Conversion: Materials, Nanostructured Designs, and Applications

The indispensable requirement for sustainable development of human society has forced almost all countries to seek highly efficient and cost-effective ways to harvest and convert solar energy. Though continuous progress has advanced, it remains a daunting challenge to achieve full-spectrum solar absorption and maximize the conversion efficiency of sunlight. Recently, thermoplasmonics has emerged as a promising solution, which involves several beneficial effects including enhanced light absorption and scattering, generation and relaxation of hot carriers, as well as localized/collective heating, offering tremendous opportunities for optimized energy conversion. Besides, all these functionalities can be tailored via elaborated designs of materials and nanostructures. Here, first the fundamental physics governing thermoplasmonics is presented and then the strategies for both material selection and nanostructured designs toward more efficient energy conversion are summarized. Based on this, recent progress in thermoplasmonic applications including solar evaporation, photothermal chemistry, and thermophotovoltaic is reviewed. Finally, the corresponding challenges and prospects are discussed.

La/LaF3 co-modified MIL-53(Cr) as an efficient adsorbent for the removal of tetracycline

Chromium based metal-organic framework (MIL-53(Cr)) has enormous potential in the removal of organic contaminants from aqueous solutions due to its outstanding water stability, whereas its poor adsorption capacity limits the application. In this study, La/LaF₃-MIL-53(Cr) was successfully synthesized by taking the advantages of La doping and LaF₃ encapsulation with one-step hydrothermal method. Diverse analysis tools were utilized to verify that La not only existed in the framework, but also was loaded in the pores in the form of LaF₃. The adsorption experiment results demonstrated that 0.3-La/LaF₃-MIL-53(Cr) exhibited significantly improved adsorption capacity by four times compared with the pristine MIL-53(Cr) material. XPS and FTIR revealed that the affinity of La to tetracycline was significantly stronger than that of Cr and the excellent dispersion of LaF₃ in the material may also be the cause of the increase in adsorption capacity. This study described a simple method to combine two different forms of modification and the modified material was potential for tetracycline adsorption.

Core-shell Cu@C@ZIF-8 composite: a high-performance electrode material for electrochemical sensing of nitrite with high selectivity and sensitivity

Herein, an efficient electrochemical sensing platform is proposed for selective and sensitive detection of nitrite on the basis of Cu@C@Zeolitic imidazolate framework-8 (Cu@C@ZIF-8) heterostructure. core-shell Cu@C@ZIF-8 composite was synthesized by pyrolysis of Cu-metal-organic framework@ZIF-8 (Cu-MOF@ZIF-8) in Ar atmosphere on account of the difference of thermal stability between Cu-MOF and ZIF-8. For the sensing system of Cu@C@ZIF-8, ZIF-8 with proper pore size allows nitrite diffuse through the shell, while big molecules cannot, which ensures high selectivity of the sensor. On the other hand, Cu@C as electrocatalyst promotes the oxidation of nitrite, thereby resulting high sensitivity of the sensor. Accordingly, the Cu@C@ZIF-8 based sensor presents excellent performance for nitrite detection, which achieves a wide linear response range of 0.1-300.0μM, and a low limit of detection of 0.033μM. In addition, the Cu@C@ZIF-8 sensor possesses excellent stability and reproducibility, and was employed to quantify nitrite in sausage samples with recoveries of 95.45%-104.80%.

Support effects of metal-organic frameworks in heterogeneous catalysis

Catalytic support effects have been widely studied as a key factor for creating highly active heterogeneous catalysts with limited amounts of rare metal elements. Recently, support effects of metal-organic frameworks (MOFs) started to be investigated using their wide variety in pore size, electronic state, and selective adsorption property. Three types of support effects, namely molecular sieving, charge transfer, and substrate adsorption effects, have been reported on composite catalysts of metal nanoparticles supported on MOFs (M/MOFs). The current reports on heterogeneous catalysis in M/MOFs clearly demonstrated that both catalytic activity and product selectivity can be drastically enhanced and modulated by MOF supports through these support effects, and that application of MOFs as the supports is beneficial for creating novel high performance catalysts with metal nanoparticles. This minireview summarizes the catalytic properties and support effects observed on M/MOFs.

Rational Functionalization of UiO-66 with Pd Nanoparticles: Synthesis and In Situ Fourier-Transform Infrared Monitoring

Functionalization of metal-organic frameworks (MOFs) with noble metal nanoparticles (NPs) is a challenging task. Conventional impregnation by metals often leads to agglomerates on the surface of MOF crystals. Functional groups on linkers interact with metal precursors and promote the homogeneous distribution of NPs in the pores of MOFs, but their uncontrolled localization can block channels and thus hinder mass transport. To overcome this problem, we created nucleation centers only in the defective pores of the UiO-66 MOF via the postsynthesis exchange. First, we have introduced defects into UiO-66 using benzoic acid as a modulator. Second, the modulator was exchanged for amino-benzoic acid. As a result, amino groups have decorated mainly the defective pores and attracted the Pd precursor after impregnation. The interaction of the metal precursor with amino groups and the growth of NPs were monitored by in situ infrared spectroscopy. Three processes were distinguished: the gaseous HCl release, NH₂ reactivation, and growth of extended Pd surfaces. Uniform Pd NPs were located in the pores because of the homogeneous distribution of the precursor and pore diffusion-limited nucleation rate. Our work demonstrates an alternative approach of controlled Pd incorporation into UiO-66 that is of great importance for the rational design of heterogeneous catalysts.

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

Urchin-like hybrid nanostructures of CuOx/Fe2O3 from Cu-mediated pyrolysis of Fe-MOFs for catalytic reduction of organic pollutants

MOFs have been widely used as templates to design and construct catalysis materials, such as LDH, metal oxides, and carbon. Herein, we developed a Cu-mediated pyrolysis protocol for the synthesis of urchin-like CuO_x/Fe₂O₃ hybrid nanostructures using Fe-MOFs as the precursor. The hierarchical hybrids were composed of an inner CuO_x-dispersed Fe₂O₃ octahedral matrix covered with radially grown Fe₂O₃ nanorods. This novel hierarchical hybrid nanostructure was generated likely due to the difference in the inward contraction rates between the Cu and Fe species during pyrolysis. Given the structural and compositional benefits, the urchin-like CuO_x/Fe₂O₃ hybrids exhibited outstanding catalytic activity for the chemical reduction of 4-nitrophenol (4-NP) and dyes. Besides, CuO_x/Fe₂O₃ was found to be highly catalytic in the reduction of 4-NP even after 30 consecutive runs, manifesting outstanding durability for continuous operation.

Solvent-Mediated Synthesis of Hierarchical MOFs and Derived Urchin-Like Pd@SC/HfO2 with High Catalytic Activity and Stability

Carbon materials with hierarchical morphologies, pores, and compositions have attracted extraordinary attention due to their unique structural advantages and widespread applications. However, their controllable synthesis remains a grand challenge. Herein, a solvent-mediated strategy was demonstrated for the preparation of an urchin-like superstructure via modulating the hydrothermal condition (acetic acid/water ratio) of metal-organic frameworks (MOFs). The direct pyrolysis of a hierarchical NUS-6 precursor produced a well-defined carbon-based composite consisting of sulfur-doped carbon (SC) and HfO₂ with an urchin-like morphology and micro-/mesoporosity, while the doped S sites and oxygen vacancies of HfO₂ can help to anchor and activate Pd nanoparticles (NPs) through the strong host-guest interaction, which was further confirmed by the calculated results of the binding energy and differential charge density through density functional theory (DFT). The synthesized Pd@SC/HfO₂ composite exhibited extremely high catalytic activity and stability toward the water-phase hydrodeoxygenation of vanillin (conversion >99%, selectivity >99%), as well as good universality for the hydrogenation of a series of unsaturated hydrocarbons in an aqueous system. Remarkably, the catalytic activity and structural stability of Pd@SC/HfO₂ were largely maintained even after successive 10 cycles.

Hybridization of green synthesized silver nanoparticles with poly(ethylene glycol) methacrylate and their biomedical applications

In the present research, a rapid, simple and efficient green method is used for the incorporation of silver nanoparticles (AgNPs) into poly(ethylene glycol) methacrylate (PEGMA) to create biocatalysts with excellent properties for pharmaceutical purpose. In the first phase, Caralluma tuberculata capped AgNPs (Ca-AgNPs) were prepared using green synthetic approach and in the second phase Caralluma tuberculata capped AgNPs were hybridized with poly(ethylene glycol) methacrylate to form PEGMA-AgNPs. Both the virgin (naked or uncapped) and polymer-capped materials were characterized spectroscopically and their results were compared. Fourier transform infrared spectroscopy showed no new peak after the capping procedure, showing that only physical interactions takes place during capping. After PEGMA capping, the spectra of the AgNPs red shifted (from 450 nm to 520 nm) and the overall particle size of AgNPs increased. Catalytic activity of the nanoparticles and hybrid system were tested by choosing the catalytic reduction of 4-nitrophenol (4-NP) as a model reaction. Both synthesized NPs and polymer capped NPs exhibits catalytic activity for the reduction of 4-NP to 4-aminophenol. The polymer hybrid exhibits remarkable antiproliferative, antioxidant, cytotoxic, antidiabetic and antileishmanial activities.

A coordination cage hosting ultrafine and highly catalytically active gold nanoparticles

Ultrafine metal nanoparticles (MNPs) with size <2 nm are of great interest due to their superior catalytic capabilities. Herein, we report the size-controlled synthesis of gold nanoparticles (Au NPs) by using a thiacalixarene-based coordination cage CIAC-108 as a confined host or stabilizer. The Au NPs encapsulated within the cavity of CIAC-108 (Au@CIAC-108) show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108 (Au/CIAC-108). The cage-embedded Au NPs can be used as a homogeneous catalyst in a mixture of methanol and dichloromethane while as a heterogeneous catalyst in methanol. The homogeneous catalyst Au@CIAC-108-homo exhibits significantly enhanced catalytic activities toward nitroarene reduction and organic dye decomposition, as compared with its larger counterpart Au/CIAC-108-homo and its heterogeneous counterpart Au@CIAC-108-hetero. More importantly, the as-prepared Au@CIAC-108-homo possesses remarkable stability and durability.

The size-controlled synthesis of Au NPs was achieved by using a coordination cage CIAC-108 as a support. The Au NPs encapsulated within the cavity of CIAC-108 show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108.

Mind the gap! tailoring sol–gel ceramic mesoporous coatings on labile metal–organic frameworks through kinetic control

Kinetic control allows for the synthesis of mesoporous silica shells on top of labile ZIF-8 cores without compromising MOF stability.

Synthesis and characterization of thermally stable energetic complexes with 3,5-diaminopyrazolone-4-oxime as a nitrogen-rich ligand

Two thermally stable complexes based on DAPO were synthesized. The thermal decomposition temperatures were 287 °C and 344 °C, respectively. The detonation properties of the complexes were excellent with good detonation velocity and detonation pressure superior to that of TNT.