Soluble Metal-Nanoparticle-Decorated Porous Coordination Polymers for the Homogenization of Heterogeneous Catalysis

Understanding the roles of stabilizers and reductants in soluble Pt nanoparticle catalysts for highly efficient hydrogenation of benzoic acid under mild conditions

Stabilizers and reductants of soluble metal nanoparticle (SMNP) catalysts have particular properties that differ from those of heterogeneous catalysts and can dramatically influence the activity of catalysts. To achieve better performances of SMNP catalysts, the functions of stabilizers and reductants have to be understood. Herein, we prepared a batch of SMNP catalysts by adjusting the amount of stabilizers and the type of reductants and found that the stabilizers and reductants will affect not only the size of catalysts but also the electronic states and accessibility of active metal sites, which determine the activity of catalysts. The SMNP catalyst prepared with a suitable stabilizer and reductant presents significantly higher catalytic activity with complete conversion in the selective hydrogenation of benzoic acid to cyclohexane carboxylic acid under mild conditions (30 °C and 1 atm H2) than that of the conventional heterogeneous catalyst (Pt/C). Besides, one-step selective hydrogenation of various benzoic acid derivatives was carried out over the SMNP catalyst. These conclusions on the functions of stabilizers and reductants provide new insight into the preparation of high-efficiency SMNP catalysts.

Flexible porous organic polymers with 1,2-diol subunits favoring the high loading of Pd nanoparticles

In recent years, the flexibility of porous organic polymers has demonstrated very unique properties during their applications. This paper reports a novel soluble porous polymer (named BIT-POP-75 and BIT-POP-75-OH) with 1,2-diketone and 1,2-diol subunits in the flexible polymer chain using contorted subunits. The solubility of the porous polymer and the flexible chelating 1,2-diol moiety facilitates the high loading and uniform dispersion of Pd nanoparticles to give the catalyst Pd@BIT-POP-75-OH, which shows high efficiency (kapp = 0.965 min-1) for the catalytic reduction of 4-nitrophenol with good recyclability (10 cycles).

Highly Efficient Continuous Flow Nanocatalyst Platform Constructed with Regenerable Bacterial Cellulose Loaded with Gold Nanoparticles and a Nanoporous Membrane

With the development of society and the growing concern about environmental issues, continuous flow catalytic reactors have gained significant interest due to their resource-efficient advantages over traditional batch devices. In this study, we employed a facile one-step in situ reduction approach to construct highly dispersed gold nanoparticles loaded on regenerable bacterial cellulose nanofiber (BCN) heterogeneous catalysts. These catalysts, in combination with a nanoceramic membrane with a pore size of 1 nm, formed a fully mixed system that was favorable for the efficient continuous flow catalysis of selective reduction reactions of nitrophenol. The reaction system demonstrated remarkable catalytic activity toward nitrophenol reduction reactions at low reductant dosages (<5 equiv), achieving over 95% conversion and 99% selectivity for the aniline product in 10 min under room temperature conditions. Furthermore, continuous flow operations maintained stable catalytic activity with minimal catalyst loss after a 120-h test and were 3 times more time-efficient than batch operations. Additionally, continuous monitoring could be conducted through ultraviolet (UV) spectroscopy. A highly efficient and environmentally friendly strategy was present for designing continuous flow reactions in future applications.

Catalytic Reduction of Aromatic Nitro Compounds to Phenylhydroxylamine and Its Derivatives

Phenylhydroxylamine and its derivates (PHAs) are important chemical intermediates. Phenylhydroxylamines are mainly produced via the catalytic reduction of aromatic nitro compounds. However, this catalytic reduction method prefers to generate thermodynamically stable aromatic amine. Thus, designing suitable catalytic systems, especially catalysts to selectively convert aromatic nitro compounds to PHAs, has received increasing attention but remains challenging. In this review, we initially provide a brief overview of the various strategies employed for the synthesis of PHAs, focusing on reducing aromatic nitro compounds. Subsequently, an in-depth analysis is presented on the catalytic reduction process, encompassing discussions on catalysts, reductants, hydrogen sources, and a comprehensive assessment of the merits and drawbacks of various catalytic systems. Furthermore, a concise overview is provided regarding the progress made in comprehending the mechanisms involved in this process of catalytic reduction of aromatic nitro compounds. Finally, the main challenges and prospects in PHAs' production via catalytic reduction are outlined.

Synthesis of Cu and Zr-based coordination polymers with N/O donors and investigation of their photocatalytic activity against dye

The coordination polymers (CPs) of Cu and Zr were synthesized by the hydrothermal method. The orotic acid potassium salt (H3KL) was used as a linker, which coordinates via O-O. Whereas, 4,4'-trimethylenedipyridine (4,4'-TMDP) was used as a bifunctional monomer, which coordinates via N-N. The synthesized CPs were characterized by FTIR, P-XRD, TGA, DSC and SEM. The photocatalytic activity was investigated against methylene blue (MB) under sunlight irradiation. Both Cu-CP and Zr-CP exhibited potential activity for the degradation of MB, which was 72 % for Cu-CP and 93 % for Zr-CP. The band gap of the CPs was also investigated, and the observed value was 2.2 eV. The band gap indicates that these compounds could bring breakthroughs as photocatalysts instead of semiconductors. These kinds of CPs could be used for multiple purposes in industry and in a green environment.

A Soluble Porous Coordination Polymer for Fluorescence Sensing of Explosives and Toxic Anions under Homogeneous Environment

In the past decades, porous coordination polymers (PCPs) based fluorescent (FL) sensors have received intense attention due to their promising applications. In this work, a soluble Zn-PCP is presented as a sensitive probe towards explosive molecules, chromate, and dichromate ions. In former reports, PCP sensors were usually ground into fine powders and then dispersed in solvents to form FL emulsion for sensing applications. However, their insoluble characters would cause the sensing accuracy which is prone to interference from environmental effects. While in this work, the as-made PCP could be directly soluble in organic solvents to form a clear solution with bright blue emission, representing the first soluble PCP based fluorescence sensor to probe explosive molecules under a homogeneous environment. Moreover, the FL PCP solution also shows sensitive detection behaviors towards the toxic anions of CrO42- and Cr2O72-, which exhibit a good linear relationship between the fluorescence intensity of Zn-PCP and the concentrations of both analytes. This work provides a reference for designing task-specific PCP sensors utilized under a homogeneous environment.

Emerging Liquid Metal Catalysts

Catalysts serve pivotal roles in facilitating the development of sustainable energy systems on a global scale. Liquid metal usually refers to metal that is liquid below 330 °C, also known as low melting point metal. Liquid metal has emerged as an intriguing catalyst due to its commendable electrical conductivity, favorable fluidity, solubility in metals, phase transition capabilities, and modifiable oxide surface, thereby presenting a plethora of prospects for diverse catalytic reactions. In this Perspective, we elucidate the four primary merits of liquid metal catalysts: resistance to coking, the ability to tune elemental composition, the potential for structural transformation, and the capacity to inhibit coalescence. In light of this, a comprehensive summary is presented on the research advancements pertaining to liquid metal in methane pyrolysis, alkane dehydrogenation, carbon dioxide reduction, alcohol oxidation, and various other catalytic reactions. Finally, the challenges and prospects of liquid metal catalysts are elucidated.

Efficient Reduction in Methylene Blue Using Palladium Nanoparticles Supported by Melamine-Based Polymer

In this work, palladium nanoparticles, supported by polyaminals (Pd@PAN-NA), were synthesized via a reverse double solvent approach and used as a nano catalyst. The thermogravimetric and the elemental analysis revealed that the catalyst had good dispersity and improved thermal stability. The catalytic activity of the prepared Pd@PAN-NA catalyst was studied for a methylene blue chemical reaction in the presence of NaBH4 as a reducing agent. The effect of the catalyst dose, pH, and dye initial concentration were examined to optimize the chemical reduction conditions. The prepared catalyst Pd@PAN-NA removed 99.8% of methylene blue organic dye, indicating its potential effect for treating waste and contaminated water.

Characterization, catalytic, and recyclability studies of nano-sized spherical palladium particles synthesized using aqueous poly-extract (turmeric, neem, and tulasi)

Green synthesis of noble metal nanoparticles (NPs) has gained immense significance compared to other metal ions owing to their unique properties. Among them, palladium 'Pd' has been in the spotlight for its stable and superior catalytic activity. This work focuses on the synthesis of Pd NPs using the combined aqueous extract (poly-extract) of turmeric (rhizome), neem (leaves), and tulasi (leaves). The bio-synthesized Pd NPs were characterized to study its physicochemical and morphological features using several analytical techniques. Role of Pd NPs as nano-catalysts in the degradation of dyes (1 mg/2 mL stock solution) was evaluated in the presence of a strong reducing agent (sodium borohydride; SBH). In the presence of Pd NPs and SBH, maximum reduction of methylene blue (MB), methyl orange (MO), and rhodamine-B (Rh-B) dyes was observed under 20nullmin (96.55 ± 2.11%), 36nullmin (96.96 ± 2.24%), and 27nullmin (98.12 ± 1.33%), with degradation rate of 0.1789 ± 0.0273 min^-1, 0.0926 ± 0.0102 min^-1, and 0.1557 ± 0.0200 min^-1, respectively. In combination of dyes (MB + MO + Rh-B), maximum degradation was observed under 50nullmin (95.49 ± 2.56%) with degradation rate of 0.0694 ± 0.0087 min^-1. It was observed that degradation was following pseudo-first order reaction kinetics. Furthermore, Pd NPs showed good recyclability up to cycle 5 (72.88 ± 2.32%), cycle 9 (69.11 ± 2.19%) and cycle 6 (66.21 ± 2.72%) for MB, MO and Rh-B dyes, respectively. Whereas, up to cycle 4 (74.67 ± 0.66%) during combination of dyes. As Pd NPs showed good recyclability, they can be used for several cycles thus influencing the overall economics of the process.

Synergetic argentophilic and through space electronic interactions in a single-crystal-to-single-crystal photocycloaddition reaction: a mechanistic study

Ag(I) is able to mediate single-crystal-to-single-crystal transformation through [2+2] photocycloaddition to prepare high-conductivity materials. However, the intrinsic mechanism of Ag(I) mediation, the detailed photophysical and photochemical processes as well as the origin of the enhanced conductivity of nanocrystals are still unclear. In this work, the comprehensive kinetic scheme and regulation mechanism are established by the accurate QM/MM calculations at the CASPT2//CASSCF/AMBER level of theory with consideration of the crystal environment. We find that the argentophilic interaction and through space electronic interaction are the key factors that promote Ag(I)-mediated [2+2] PCA reactions and may account for the enhancement of conductivity. These mechanistic insights into the Ag(I)-regulated photo-dimerization in the crystal surrounding are beneficial for the design of the structurally and electrically favorable skeletons of a metal-organic coordination polymer.

Heterogeneous Iridium Single-Atom Molecular-like Catalysis for Epoxidation of Ethylene

Developing efficient and simple catalysts to reveal the key scientific issues in the epoxidation of ethylene has been a long-standing goal for chemists, whereas a heterogenized molecular-like catalyst is desirable which combines the best aspects of homogeneous and heterogeneous catalysts. Single-atom catalysts can effectively mimic molecular catalysts on account of their well-defined atomic structures and coordination environments. Herein, we report a strategy for selective epoxidation of ethylene, which exploits a heterogeneous catalyst comprising iridium single atoms to interact with the reactant molecules that act analogously to ligands, resulting in molecular-like catalysis. This catalytic protocol features a near-unity selectivity (99%) to produce value-added ethylene oxide. We investigated the origin of the improvement of selectivity for ethylene oxide for this iridium single-atom catalyst and attributed the improvement to the π-coordination between the iridium metal center with a higher oxidation state and ethylene or molecular oxygen. The molecular oxygen adsorbed on the iridium single-atom site not only helps to strengthen the adsorption of ethylene molecule by iridium but also alters its electronic structure, allowing iridium to donate electrons into the double bond π* orbitals of ethylene. This catalytic strategy facilitates the formation of five-membered oxametallacycle intermediates, leading to the exceptionally high selectivity for ethylene oxide. Our model of single-atom catalysts featuring remarkable molecular-like catalysis can be utilized as an effective strategy for inhibiting the overoxidation of the desired product. Implementing the concepts of homogeneous catalysis into heterogeneous catalysis would provide new perspectives for the design of new advanced catalysts.

Novel Ce-based coordination polymer nanoparticles with excellent oxidase mimic activity applied for colorimetric assay to organophosphorus pesticides

Cerium, as a lanthanide, has attracted considerable interest because of its excellent catalytic activity. Here, we propose a novel cerium-based coordination polymer nanoparticles named DPA-Ce-GMP, which have excellent oxidase-mimicking properties. Furthermore, a colorimetric probe that can act as an inhibitor to suppress the activity of acetylcholinesterase (AChE) was developed for detecting organophosphorus pesticides (OPs). DPA-Ce-GMP catalyzes colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue color, and AChE catalyzes acetylthiocholine to produce thiocholine (TCh), which can weaken DPA-Ce-GMP-catalyzed TMB. After the addition of OPs, the enzymatic activity of AChE was inhibited to produce less amount of TCh, resulting in more DPA-Ce-GMP-catalyst oxidized TMB to show an increasing blue color. Dichlorvos, as the samples, with the limit of 0.024 μg/L. Overall, we believe that the colorimetric probe can be used for the rapid, low-cost, and large-scale field detection of OPs in food samples.

Modulating the Chemical Microenvironment of Pt Nanoparticles within Ultrathin Nanosheets of Isoreticular MOFs for Enhanced Catalytic Activity

The catalytic activity of metal nanoparticles (MNPs) embedded in metal-organic frameworks (MOFs) is affected by the electronic interactions between MNPs and MOFs. In this report, we fabricate a series of ultrathin nanosheets of isoreticular MOFs (NMOFs) with different metal nodes as supports and successfully encapsulate Pt NPs within these NMOFs, affording Pt@NMOF-Co, Pt@NMOF-Ni₁Co₁, Pt@NMOF-Ni₃Co₁, and Pt@NMOF-Ni nanocomposites. The microchemical environment on the surface of Pt NPs can be modulated by varying the metal nodes of NMOFs. The catalytic activity of the nanocomposites toward liquid-phase hydrogenation of 1-hexene shows obvious difference, in which Pt@NMOF-Ni possesses the highest activity followed by Pt@NMOF-Ni₃Co₁, Pt@NMOF-Ni₁Co₁, and Pt@NMOF-Co in a decreasing order of activity. Obviously, increasing gradually the amount of Ni²⁺ nodes in the carriers can improve the catalytic activity. The difference of catalytic activity of the nanocomposites might originate from the distinct electron interactions between Pt NPs and NMOFs, as ascertained by X-ray photoelectron spectroscopy spectrum and density functional theory calculations. This work provides a rare example that the catalytic activity of MNPs could be controlled by accurately regulating the microchemical environment using ultrathin NMOFs as supports.

Precise fabrication of porous polymer frameworks using rigid polyisocyanides as building blocks: from structural regulation to efficient iodine capture

Porous materials have recently attracted much attention owing to their fascinating structures and broad applications. Moreover, exploring novel porous polymers affording the efficient capture of iodine is of significant interest. In contrast to the reported porous polymers fabricated with small molecular blocks, we herein report the preparation of porous polymer frameworks using rigid polyisocyanides as building blocks. First, tetrahedral four-arm star polyisocyanides with predictable molecular weight and low dispersity were synthesized; the chain-ends of the rigid polyisocyanide blocks were then crosslinked, yielding well-defined porous organic frameworks with a designed pore size and narrow distribution. Polymers of appropriate pore size were observed to efficiently capture radioactive iodine in both aqueous and vapor phases. More than 98% of iodine could be captured within 1 minute from a saturated aqueous solution (capacity of up to 3.2 g g-1), and an adsorption capacity of up to 574 wt% of iodine in vapor was measured within 4 hours. Moreover, the polymers could be recovered and recycled for iodine capture for at least six times, while maintaining high performance.

A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

Encapsulation of Metal Clusters within Porous Organic Materials: From Synthesis to Catalysis Applications

Metal clusters (MCs) with dimensions between a single metal atom and nanoparticles of >2 nm usually possess distinct geometric and electronic structures, their outstanding performance in catalysis applications have underpinned a broad research interest. However, smaller-sized MCs are easily deactivated by migration coalescence during the catalysis process because of their high surface energy. Therefore, the search of an appropriate stabilizer for MCs is urgently demanded. In recent years, porous organic polymers (POPs) and organic molecular cages (OMCs), as emerging functional materials, have attracted significant attention. Benefiting from the spatial confinement, encapsulating MCs into these porous organic materials is a promising approach to guarantee the uniform size distribution and stability. In this review, we aim to provide a comprehensive summary of the recent progress in the synthetic strategies and catalysis applications of the encapsulated MCs, and seek to uncover promising ideas that can stimulate future developments at both the fundamental and applied levels.

Development of Au-Pd@UiO-66-on-ZIF-L/CC as a self-supported electrochemical sensor for in situ monitoring of cellular hydrogen peroxide

Integrating metal-organic frameworks (MOFs) of different components or structures together and exploiting them as electrochemical sensors for electrochemical sensing has aroused great interest. Furthermore, the incorporation of noble metals with MOFs is conducive to the improvement of catalytic performance. In this work, Pd@UiO-66-on-ZIF-L nanomaterials were successfully synthesised onto a self-supported flexible carbon cloth (Pd@UiO-66-on-ZIF-L/CC) through a novel strategy called MOF-on-MOF. Then, Au nanoparticles were electrodeposited onto Pd@UiO-66-on-ZIF-L/CC to obtain Au-Pd@UiO-66-on-ZIF-L/CC, which can serve as an excellent electrocatalyst for the reduction of hydrogen peroxide (H₂O₂). The obtained flower-like Pd@UiO-66-on-ZIF-L/CC hybrid MOF changes the structure of the monomeric MOF alone and adds more attachment sites. The synergy of the bimetals greatly improved the catalytic performance of the as-developed sensor. Electrochemical experiment results show that the proposed sensor based on Au-Pd@UiO-66-on-ZIF-L/CC has an extended linear range from 1 μM to 19.6 mM with a sensitivity of 390 μA mM^-1 cm^-2, and a low limit of detection (LOD) of 21.2 nM (S/N = 3). Moreover, it has good anti-interference, reproducibility, repeatability and excellent stability. Furthermore, the real-time in situ detection of H₂O₂ secreted from human adenocarcinomic alveolar basal epithelial cells (A549 cells) was achieved by culturing cells on Au-Pd@UiO-66-on-ZIF-L/CC, which indicates the potential of the sensor for applications in cancer pathology. Both the synthesis strategy and the sensor design provide new methods and ideas for the production of ultrasensitive H₂O₂ electrochemical sensors.

Construction of CuII Defects on CuCl Nanoparticles in Metal-Organic Frameworks toward Composite Catalysts with Superior Activity

Metal-organic frameworks (MOFs) represent an ideal platform for the construction of highly active composite catalysts. However, loading metastable and/or multicomponent metal compounds into MOFs remains a synthetic bottleneck due to the great challenge of keeping the guest and matrix intact during the preparation of a composite. In this work, we develop a new impregnation reduction surface modification (IRSM) strategy to give a new composite catalyst CuCl@MIL-101(Cr), which is successfully postmodified by in situ construction of Cu^II defects on the surface of loaded CuCl inside MOF pores, leading to the new composite material Cu^II/Cu^I@MIL-101(Cr). The new dual-component composite catalyst exhibits a hierarchical structure and superior catalytic activity in C-C homocoupling of arylboronic acids under green conditions. This study presents a facile strategy for improving the catalytic activity by constructing defects on the surface of MOF-based catalysts as well as for forming multiple-component composite materials.

AIE-MOF materials for biological applications

Metal-Organic Frameworks (MOFs), coming under the realm of coordination chemistry, are unparalleled and the most studied among the group of porous materials. Structurally, these are well-defined three-dimensional crystalline products that can be tuned for various potential applications with a range of physico-chemical properties. More recently, aggregation-induced emission (AIE) and AIE of MOF material has attracted tremendous attention due to promising applications in biology. However, a chapter summarizing the work in AIE-MOFs materials has never been reported till date. A comprehensive review on the AIE and MOFs separately is beyond the reach of this chapter. Hence, we have summarized overview of recent developments in the syntheses and biological applications such as cell imaging, heparin detection, and drug delivery. In the end, conclusion, prospects and challenges in the arena of AIE-MOF materials are also highlighted.

Interfacial Microenvironment Modulation Boosting Electron Transfer between Metal Nanoparticles and MOFs for Enhanced Photocatalysis

Interfacial electron transfer between cocatalyst and photosensitizer is key in heterogeneous photocatalysis, yet the underlying mechanism remains subtle and unclear. Surfactant coated on the metal cocatalysts, greatly modulating the microenvironment of catalytic sites, is largely ignored. Herein, a series of Pt co-catalysts with modulated microenvironments, including polyvinylpyrrolidone (PVP) capped Pt nanoparticles (denoted as Pt_PVP ), Pt with partially removed PVP (Pt_rPVP ), and clean Pt without PVP (Pt), were encapsulated into a metal-organic framework (MOF), UiO-66-NH₂ , to afford Pt_PVP @UiO-66-NH₂ , Pt_rPVP @UiO-66-NH₂ , and Pt@UiO-66-NH₂ , respectively, for photocatalytic hydrogen production. The PVP appears to have a negative influence on the interfacial electron transfer between Pt and the MOF. Compared with Pt_PVP @UiO-66-NH₂ , the removal of interfacial PVP improves the sluggish kinetics of electron transfer, boosting photocatalytic hydrogen production.

Porous noria polymer: a cage-to-network approach toward a robust catalyst for CO2 fixation and nitroarene reduction

The advantages of the cage-to-network design strategy were demonstrated by knitting a waterwheel-like preporous molecular cage, noria, with a rigid aromatic linker to obtain a highly microporous organic polymer (NPOP, SBET: 748 ± 25 m2 g-1). The NPOP was employed for the catalytic conversion of CO2 to cyclic carbonates under solvent-free reaction conditions. Furthermore, a silver nanoparticle encapsulated NPOP exhibited remarkable catalytic activity for nitroarene reduction with excellent recyclability.

Cyclometalated Half-Sandwich Iridium(III) Complexes: Synthesis, Structure, and Diverse Catalytic Activity in Imine Synthesis Using Air as the Oxidant

Four air-stable cyclometalated half-sandwich iridium complexes 1-4 with C,N-donor Schiff base ligands were prepared through C-H activation in moderate-to-good yields. These complexes have been well characterized, and their exact structure was elaborated on by single-crystal X-ray analysis. The iridium(III) complexes 1-4 showed good catalytic activity in the imine synthesis under open-flask conditions (air as the oxidant) from primary amine oxidative homocoupling, secondary amine dehydrogenation, and the cross-coupling reaction of amine and alcohol. Substituents bonded on the ligands of the iridium complexes displayed little effect on the catalytic efficiency. The stability and good catalytic efficiency of the iridium catalysts, mild reaction conditions, and substrate universality showed their potential application in industrial production.

3D Porous Polymeric-Foam-Supported Pd Nanocrystal as a Highly Efficient and Recyclable Catalyst for Organic Transformations

The efficient recovery of noble metal nanocrystals used in heterogeneous organic transformations has remained a significant challenge, hindering their use in industry. Herein, highly catalytic Pd nanoparticles (NPs) were first prepared having a yield of >98% by a novel hydrothermal method using PVP as the reducing cum stabilizing agent that exhibited excellent turnover frequencies of ∼38,000 h^-1 for Suzuki-Miyaura cross-coupling and ∼1200 h^-1 for catalytic reduction of nitroarene compounds in a benign aqueous reaction medium. The Pd NPs were more efficient for cross-coupling of aryl compounds with electron-donating substituents than with electron-donating ones. Further, to improve their recyclability, a strategy was developed to embed these Pd NPs on mechanically robust polyurethane foam (PUF) for the first time and a "dip-catalyst" (Pd-PUF) containing 3D interconnected 100-500 μm pores was constructed. The PUF was chosen as the support with an expectation to reduce the fabrication cost of the "dip-catalyst" as the production of PUF is already commercialized. Pd-PUF could be easily separated from the reaction aliquot and reused without any loss of activity because the leaching of Pd NPs was found to be negligible in the various reaction mixtures. We show that the Pd-PUF could be reused for over 50 catalytic cycles maintaining a similar activity. We further demonstrate a scale-up reaction with a single-reaction 1.5 g yield for the Suzuki-Miyaura cross-coupling reaction.

Ultrastable and Highly Catalytically Active N-Heterocyclic-Carbene-Stabilized Gold Nanoparticles in Confined Spaces

Controlling the size and surface functionalization of nanoparticles (NPs) can lead to improved properties and applicability. Herein, we demonstrate the efficiency of the metal-carbene template approach (MCTA) to synthesize highly robust and soluble three-dimensional polyimidazolium cages (PICs) of different sizes, each bearing numerous imidazolium groups, and use these as templates to synthesize and stabilize catalytically active, cavity-hosted, dispersed poly-N-heterocyclic carbene (NHC)-anchored gold NPs. Owing to the stabilization of the NHC ligands and the effective confinement of the cage cavities, the as-prepared poly-NHC-shell-encapsulated AuNPs displayed promising stability towards heat, pH, and chemical regents. Most notably, all the Au@PCCs (PCC=polycarbene cage) exhibited excellent catalytic activities in various chemical reactions, together with high stability and durability.

C2-H Arylation of Indoles Catalyzed by Palladium-Containing Metal-Organic-Framework in γ-Valerolactone

An efficient and selective procedure was developed for the direct C2-H arylation of indoles using a Pd-loaded metal-organic framework (MOF) as a heterogeneous catalyst and the nontoxic biomass-derived solvent γ-valerolactone (GVL) as a reaction medium. The developed method allows for excellent yields and C-2 selectivity to be achieved and tolerates various substituents on the indole scaffold. The established conditions ensure the stability of the catalyst as well as recoverability, reusability, and low metal leaching into the solution.

Utilization of Ag nanoparticles anchored in covalent organic frameworks for mercury removal from acidic waste water

Metal nanoparticles (NPs) have high reaction rate and atom utilization with respect to pollutants in aqueous environments. However, the aggregation and instability in acidic solution limit their practical applications. Mercury removed from acidic solution are still a big problem. In this study, we used a tunable porous covalent organic framework (COF) material as a support for in situ growth of Ag NPs via a one-step solution infiltration method, to enhance the spatial dispersion of NPs and their stability in acidic solution, and for the first time studying the mercury adsorption performance. More importantly, the Ag NPs@COF composite exhibited high removal rate (99 %), ultrahigh Ag atom utilization (150 %), high selectivity and stability, and reusability for Hg(II) removal from acidic aqueous solutions. Meantime, through common characterizations and density functional theory calculations verifying the microscopic adsorption process, we found COF material played an important role in the entire purification process because it provided some electrons to Hg(II) ions via Ag NPs, finally generating an amalgam. Therefore, the present work not only provides a COF-supported Ag NPs material for Hg(II) ions removal from acidic waste water but also opens a new field of design of functionalized COFs material for applications in environmental pollutions control.