Enhanced Hydrogen Storage by Palladium Nanoparticles Fabricated in a Redox-Active Metal-Organic Framework

The Landscape of Smart Biomaterial-Based Hydrogen Therapy

Hydrogen (H2) therapy is an emerging, novel, and safe therapeutic modality that uses molecular hydrogen for effective treatment. However, the impact of H2 therapy is limited because hydrogen molecules predominantly depend on the systemic administration of H2 gas, which cannot accumulate at the lesion site with high concentration, thus leading to limited targeting and utilization. Biomaterials are developed to specifically deliver H2 and control its release. In this review, the development process, stimuli-responsive release strategies, and potential therapeutic mechanisms of biomaterial-based H2 therapy are summarized. H2 therapy. Specifically, the produced H2 from biomaterials not only can scavenge free radicals, such as reactive oxygen species (ROS) and lipid peroxidation (LPO), but also can inhibit the danger factors of initiating diseases, including pro-inflammatory cytokines, adenosine triphosphate (ATP), and heat shock protein (HSP). In addition, the released H2 can further act as signal molecules to regulate key pathways for disease treatment. The current opportunities and challenges of H2-based therapy are discussed, and the future research directions of biomaterial-based H2 therapy for clinical applications are emphasized.

Metal-Organic Frameworks (MOFs) As Hydrogen Storage Materials At Near-Ambient Temperature

Hydrogen may play a critical role in our efforts to de-carbonize by 2050. However, there remain technical challenges in the storage and transport of hydrogen. Metal-organic frameworks (MOFs) have shown significant promise for hydrogen storage at cryogenic temperatures. A material that can meet the US department of energy (DOE) ultimate goal of 6.5 wt. % for gravimetric performance and 50 g/L for volumetric storage at near-ambient temperatures would unlock hydrogen as a future fuel source for on-board applications. Metal-organic frameworks typically have low heat of adsorptions (i. e. 4-7 kJ/mol), whereas for storing significant quantities of hydrogen at near-ambient temperatures, 15-25 kJ/mol is likely required. In this review we explore the current methods used (i. e., open-metal sites, alkali dopants and hydrogen spillover) for promoting strong adsorption within MOFs. Further we discuss MOF-based materials with respect to the technical aspects of deliverable capacity, kinetics and stability.

In situ confinement of ultra-small metal nanoparticles in redox-active zirconium MOFs for catalysis

Herein, we successfully fabricated ultra-small metal nanoparticles into two stable Zr-based metal-organic frameworks via in situ redox reactions between triphenylamine and the corresponding metal ions to afford Pd NPs@1 and Pd NPs@2, which exhibit excellent activity and reusability for Suzuki coupling reactions as heterogeneous catalysts.

A Real-Time LSPR-Based Study of Metal-Organic Framework (MOF) Growth

MOFs are known for their absorption properties and widely used for accumulation, filtering, sensorics, photothermal, catalytical and other applications. Their combination with plasmonic metal nanoparticles leads to hybrid structures that profit from the stabilizing effect and high porosity of the MOF as well as the optical and electronic properties of the nanoparticles. The growth of MOFs on plasmonic nanoparticles can be monitored in-situ using LSPR spectroscopy, simultaneously applying microfluidic reaction conditions for the fabrication of NP@MOF structures. Here, a systematic study is conducted using LSPR spectroscopy for the monitoring of the Layer-by-Layer deposition of twelve different MOFs, determining the suitability of LSPR spectroscopy for this purpose. In addition to some well-investigated materials like HKUST-1, other MOFs such as MIL-53, MIL-88 A and Cu-BDC are deposited successfully. For some MOFs such as Zn-Fum, the LSPR experiment indicates that no deposition had taken place. The results are confirmed with AFM, SEM and XPS measurements. This work shows that LSPR spectroscopy is suitable for the in-situ monitoring of LbL MOF growth and the microfluidic setup is a very promising method for the controlled manufacturing of NP@MOF hybrid structures. Further studies may include the optimization of the synthesis process or the transfer to other materials.

Elucidation of Structure-Activity Relations in Proton Electroreduction at Pd Surfaces: Theoretical and Experimental Study

The structure-activity relationship is a cornerstone topic in catalysis, which lays the foundation for the design and functionalization of catalytic materials. Of particular interest is the catalysis of the hydrogen evolution reaction (HER) by palladium (Pd), which is envisioned to play a major role in realizing a hydrogen-based economy. Interestingly, experimentalists observed excess heat generation in such systems, which became known as the debated "cold fusion" phenomenon. Despite the considerable attention on this report, more fundamental knowledge, such as the impact of the formation of bulk Pd hydrides on the nature of active sites and the HER activity, remains largely unexplored. In this work, classical electrochemical experiments performed on model Pd(hkl) surfaces, "noise" electrochemical scanning tunneling microscopy (n-EC-STM), and density functional theory are combined to elucidate the nature of active sites for the HER. Results reveal an activity trend following Pd(111) > Pd(110) > Pd(100) and that the formation of subsurface hydride layers causes morphological changes and strain, which affect the HER activity and the nature of active sites. These findings provide significant insights into the role of subsurface hydride formation on the structure-activity relations toward the design of efficient Pd-based nanocatalysts for the HER.

N-doped porous carbons derived from Zn-porphyrin-MOF

N-doped porous metal-organic framework (MOF)-derived carbons (MDCs) were directly synthesized from a new Zn-DpyDtolP-MOF (ZnDpyDtolP·1/2DMF, H2DpyDtolP = 5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) containing a 3D hexagonal network through a self-templated carbonization method. KOH-activated MDC derivatives denoted as MDC-700-nKOH were also prepared with different weight ratios of KOH activator to MDC (MDC : KOH = 1 : n, where n = 1, 2). Compared to bare MDC, MDC-700-nKOH showed effective improvements of both gas sorption and electrochemical capacitive properties. More developed microporosity by KOH activation might induce great enhancement of high operating capacitive performances. The N-doped MDC-700-2KOH had high maximum gravimetric specific capacitance (555.6 F g-1) and specific energy (40.4 W h kg-1) at 0.1 A g-1 in 1 M H2SO4. Even at a high current density of 190 A g-1 in 6 M KOH, it exhibited high capacitive performance with a large specific power of 80 423 W kg-1. MDC-700-nKOH electrodes also showed good recycling properties of electrochemical capacitance up to 30 000 cycles.

Design and Characterization of Metal Nanoparticle Infiltrated Mesoporous Metal-Organic Frameworks

The infiltration of palladium and platinum nanoparticles (NPs) into the mesoporous metal-organic framework (MOF) CYCU-3 through chemical vapor infiltration (CVI) and incipient wetness infiltration (IWI) processes was systematically explored as a means to design novel NP@MOF composite materials for potential hydrogen storage applications. We employed a traditional CVI process and a new ″green″ IWI process using methanol for precursor infiltration and reduction under mild conditions. Transmission electron microscopy-based direct imaging techniques combined with synchrotron-based powder diffraction (SPD), energy-dispersive X-ray spectroscopy, and physisorption analysis reveal that the resulting NP@MOF composites combine key NP and MOF properties. Room temperature hydrogen adsorption capacities of 0.95 and 0.20 mmol/g at 1 bar and 2.9 and 1.8 mmol/g at 100 bar are found for CVI and IWI samples, respectively. Hydrogen spillover and/or physisorption are proposed as the dominating adsorption mechanisms depending on the NP infiltration method. Mechanistic insights were obtained through the crystallographic means using SPD-based difference envelope density analysis, providing previously underexplored details on NP@MOF preparations. Consequently, important host-guest correlations influencing the global hydrogen adsorption properties are discussed, and they demonstrate that employing MOFs as platforms for NPs is an alternative approach to the development of versatile materials for improving current hydrogen storage technologies.

Retention of a Four-Fold Interpenetrating Cadmium-Organic Framework through a Three-Step Single Crystal Transformation

Controlled hydration leads to four derivatives of a metal-organic framework consisting of cadmium ions, N¹,N¹,N⁴,N⁴-tetrakis(4-(pyridin-4-yl)phenyl)benzene-1,4-diamine, and coordinated and free nitrates. The balance of water coordination and the multitude of bonding of the weakly coordinated nitrate lead to a progressive change in the coordination number of the Cd²⁺ ions from eight to seven to six without great perturbation to the 4-fold interpenetration three-dimensional framework.

Atomic Imaging of Subsurface Interstitial Hydrogen and Insights into Surface Reactivity of Palladium Hydrides

Resolving interstitial hydrogen atoms at the surfaces and interfaces is crucial for understanding the mechanical and physicochemical properties of metal hydrides. Although palladium (Pd) hydrides hold important applications in hydrogen storage and electrocatalysis, the atomic position of interstitial hydrogen at Pd hydride near surfaces still remains undetermined. We report the first direct imaging of subsurface hydrogen atoms absorbed in Pd nanoparticles by using differentiated and integrated differential phase contrast within an aberration-corrected scanning transmission electron microscope. In contrast to the well-established octahedral interstitial sites for hydrogen in the bulk, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices. DFT calculations show that the amount and the occupation type of subsurface hydrogen atoms play an indispensable role in fine-tuning the electronic structure and associated chemical reactivity of the Pd surface.

Zeolite-Like Boron Imidazolate Frameworks (BIFs): Synthesis and Application

This review is devoted to discussion of the latest advances in design and applications of boron imidazolate frameworks (BIFs) that are a particular sub-family of zeolite-like metal–organic frameworks family. A special emphasis is made on nanostructured hybrid materials based on BIF matrices and their modern applications, especially in environment remediation and energy conversion.

Sustainable Carbon as Efficient Support for Metal-Based Nanocatalyst: Applications in Energy Harvesting and Storage

Sustainable activated carbon can be obtained from the pyrolysis/activation of biomass wastes coming from different origins. Carbon obtained in this way shows interesting properties, such as high surface area, electrical conductivity, thermal and chemical stability, and porosity. These characteristics among others, such as a tailored pore size distribution and the possibility of functionalization, lead to an increased use of activated carbons in catalysis. The use of activated carbons from biomass origins is a step forward in the development of more sustainable processes enhancing material recycling and reuse in the frame of a circular economy. In this article, a perspective of different heterogeneous catalysts based on sustainable activated carbon from biomass origins will be analyzed focusing on their properties and catalytic performance for determined energy-related applications. In this way, the article aims to give the reader a scope of the potential of these tailor-made sustainable materials as a support in heterogeneous catalysis and future developments needed to improve catalyst performance. The selected applications are those related with H2 energy and the production of biomethane for energy through CO2 methanation.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

In-situ synthesis of metal nanoparticles@metal-organic frameworks: Highly effective catalytic performance and synergistic antimicrobial activity

M-NP@Zn-BIF (M-NP = Ag or Cu nanoparticle; Zn-BIF is a zinc-based boron imidazolate framework, Zn₂(BH(2-mim)₃)₂(obb); 2-mim = 2-methylimidazole; obb = 4,4'-oxybis(benzoate)) composites were successfully in-situ synthesized by utilizing the reducing ability of the BH bond contained in the Zn-BIF at room temperature without any additional chemical reduction reagents. These composites (225 μg/mL) exhibited excellent catalytic activity to convert 4-nitrophenol to 4-aminophenol in 2.5 min and 6 min with a conversion rate of 99.9 %, respectively. In addition, Ag@Zn-BIF (50 μg/mL) showed highly synergistic antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with a bactericidal rate of approximately 99.9 %. An antibacterial mechanism was proposed for the generation of intracellular reactive oxygen species (ROS) levels. Superoxide radicals (O^2-) and hydroxyl radicals (OH) formed during the antibacterial process were shown to accelerate the death of bacteria. They also exhibited highly photocatalytic activity for Rhodamine B (RhB). When the concentration of the composites is 1000 μg/mL, the photocatalytic efficiency of Ag@Zn-BIF and Cu@Zn-BIF increased by 31.62 and 18.13 times compared with Zn-BIF, respectively. All in all, this study developed a simple and versatile integrated platform for the removal of nitrophenols, organic dyes, and the effective inactivation of bacteria in water.

Zirconium metal-organic frameworks incorporating tetrathiafulvalene linkers: robust and redox-active matrices for in situ confinement of metal nanoparticles

Redox-active metal-organic frameworks (MOFs), with highly ordered porous structures and redox tunability, have attracted research interest in the fields of catalysis, energy storage, and electrochemical sensing. However, the chemical lability has limited the application scope of many redox-active MOFs. Herein, we selected stable Zr₆ inorganic nodes and redox-active tetrathiafulvalene (TTF)-based linkers to construct two robust, redox-active MOFs, namely compounds 1 ([Zr₆(TTFTB)₂O₈(OH₂)₈]) and 2 ([Zr₆(Me-TTFTB)_1.5O₄(OH)₄(C₆H₅COO)₆]) (TTFTB = tetrathiafulvalene tetrabenzoate; Me-TTFTB = tetrathiafulvalene tetramethylbenzoate). The structure and topology of the MOFs were controlled by tuning the linker conformation through steric effects, resulting in a variety of pore structures from microporous channels (compound 1) to hierarchically micro/mesoporous cages (compound 2). Compound 2 shows high porosity with a BET surface area of 1932 m² g^-1 and strong chemical stability in aqueous solutions with pH ranging from 1 to 12. Furthermore, the reductive TTF moieties allow for in situ generation and stabilization of ultra-small noble metal (Ag, Pd, and Au) nanoparticles by incubating MOFs in the respective metal salt solution. Single crystal structures, TEM images, and pore size distribution data from N₂ adsorption measurements indicated that the metal nanoparticles were mostly placed in the small cubic cavities of hierarchically porous compound 2, leaving the large cages open for substrate diffusion. As a proof of concept, Pd NPs@compound 2 was utilized as a heterogeneous catalyst for aerobic oxidation of alcohols, showing noteworthy activity and recyclability.

Pillar–template strategy switching the redox activity and magnetic properties of trisphenylamine-based coordination polymers

A pillar–template strategy was used to modify the redox activity and magnetic properties of trisphenylamine-based coordination polymers via a single-crystal-to-single-crystal transformation method.

Molecular sieving property adjusted by the encapsulation of Ag nanoparticles into ZnO@ZIF-71 nanorod arrays

Ag NPs are encapsulated into ZIF-71 via a deposition-reduction method. The resulting products are tested as adjustable molecular sieves for hydrogen and acetone. The gas sensing performances show that the response to acetone is reduced and that to hydrogen increased, demonstrating an engineered selectivity. A novel design of molecular sieving MOF materials for gas separation in gas-sensing selectivity is thus provided.

Frontiers and progress in cation-uptake and exchange chemistry of polyoxometalate-based compounds

Cation-uptake and exchange has been an important topic in both basic and applied chemistry relevant to life and materials science. For example, living cells contain appreciable amounts of Na+ and K+, and their concentrations are regulated by the sodium-potassium pump. Solid-state cation-exchangers such as clays and zeolites both natural and synthetic have been used widely in water softening and purification, separation of metal ions and biomolecules, etc. Polyoxometalates (POMs) are robust, discrete, and structurally well-defined metal-oxide cluster anions, and have stimulated research in broad fields of sciences. In this perspective, cation-uptake and exchange in POM and POM-based compounds are categorized and reviewed in three groups: (i) POMs as inorganic crown ethers and cryptands, (ii) POM-based ionic solids as cation-exchangers, and (iii) reduction-induced cation-uptake in POM-based ionic solids, which is based on a feature of POMs that they are redox-active and multi-electron transfer occurs reversibly in multiple steps. This method can be utilized to synthesize mixed-valence metal clusters in metal ion-exchanged POM-based ionic solids.

Polar functional groups anchored to a 2D MOF template for the stabilization of Pd(0) nps for the catalytic C-C coupling reaction

A 2D porous MOF, {[Cu(1,2,3-btc)(bpe)(H₂O)]·H₂O}_n (1), has been synthesized using a mixed linker system. The structural determination showed non-coordinated carboxylate groups decorating the pore surface. The desolvated MOF (1a) with pendant carboxylate groups was used as a template for the stabilization of Pd nps (2-3 nm) and the resulting composite Pd(0)@1a showed efficient catalytic activity for the Suzuki-Miyaura C-C coupling reaction.

Hydrogen in Palladium and Storage Properties of Related Nanomaterials: Size, Shape, Alloying, and Metal-Organic Framework Coating Effects

One of the key issues for an upcoming hydrogen energy-based society is to develop highly efficient hydrogen-storage materials. Among the many hydrogen-storage materials reported, transition-metal hydrides can reversibly absorb and desorb hydrogen, and have thus attracted much interest from fundamental science to applications. In particular, the Pd-H system is a simple and classical metal-hydrogen system, providing a platform suitable for a thorough understanding of ways of controlling the hydrogen-storage properties of materials. By contrast, metal nanoparticles have been recently studied for hydrogen storage because of their unique properties and the degrees of freedom which cannot be observed in bulk, i. e., the size, shape, alloying, and surface coating. In this review, we overview the effects of such degrees of freedom on the hydrogen-storage properties of Pd-related nanomaterials, based on the fundamental science of bulk Pd-H. We shall show that sufficiently understanding the nature of the interaction between hydrogen and host materials enables us to control the hydrogen-storage properties though the electronic-structure control of materials.

Metal-Organic Frameworks for Hydrogen Energy Applications: Advances and Challenges

Hydrogen is in limelight as an environmental benign alternative to fossil fuels from few decades. To bring the concept of hydrogen economy from academic labs to real world certain challenges need to be addressed in the areas of hydrogen production, storage, and its use in fuel cells. Crystalline metal-organic frameworks (MOFs) with unprecedented surface areas are considered as potential materials for addressing the challenges in each of these three areas. MOFs combine the diverse chemistry of molecular linkers with their ability to coordinate to metal ions and clusters. The unabated flurry of research using MOFs in the context of hydrogen energy related activities in the past decade demonstrates the versatility of this class of materials. In the present review, we discuss major strategical advances that have taken place in the field of "hydrogen economy and MOFs" and point out issues requiring further attention.

Metal-Bonded Redox-Active Triarylamines and Their Interactions: Synthesis, Structure, and Redox Properties of Paddle-Wheel Copper Complexes

Four new triphenylamine ligands with different substituents in the para position and their corresponding copper(II) complexes are reported. This study includes their structural, spectroscopic, magnetic, and electrochemical properties. The complexes possess a dinuclear copper(II) paddle-wheel core, a building unit that is also common in metal-organic frameworks. Electrochemical measurements demonstrate that the triphenylamine ligands and the corresponding complexes are susceptible to oxidation, resulting in the formation of stable radical cations. The square-wave voltammograms observed for the complexes are similar to those of the ligands, except for a slight shift in potential. Square-wave voltammetry data show that, in the complexes, these oxidations can be described as individual one-electron processes centered on the coordinated ligands. Spectroelectrochemistry reveals that, during the oxidation of the complexes, no difference can be detected for the spectra of successively oxidized species. For the absorption bands of the oxidized species of the ligands and complexes, only a slight shift is observed. ESR spectra for the chemically oxidized complexes indicate ligand-centered radicals. The copper ions of the paddle-wheel core are strongly antiferromagnetic coupled. DFT calculations for the fully oxidized complexes indicate a very weak ferromagnetic coupling between the copper ions and the ligand radicals, whereas a very weak antiferromagnetic coupling is found among the ligand radicals.

In situ Stabilization of Au and Co Nanoparticles in a Redox-Active Conjugated Microporous Polymer Matrix: Facile Heterogeneous Catalysis and Electrocatalytic Oxygen Reduction Reaction Activity

We report a novel in situ method for synthesis of metal nanoparticles (NPs)-CMP (conjugated microporous polymer) composites based on a redox-active, donor-acceptor CMP, tris-(4-aminophenyl)amine (TPA)-perylenediimide (PDI). The TPA-PDI CMP, comprising triphenylamine as an electron donor and PDI as an acceptor, showed stable charge-separated state and semiconducting behavior. Further, TPA-PDI CMP has been exploited for in situ stabilization of metal (Au and Co) NPs, and two novel nanocomposites (Au@TPA-PDI and Co@TPA-PDI) were prepared. The catalytic reduction of nitro aryls to amino aryls was studied using Au@TPA-PDI, which showed excellent yields and fast kinetics. The CMP itself was found to show good activity as a metal-free oxygen reduction reaction (ORR) electrocatalyst with an onset potential of 0.82 V. Stabilizing merely 2.56 wt % Co nanoparticles in the CMP matrix improved the electrochemical ORR activity of as-synthesized TPA-PDI immensely and showed an onset potential of 0.91 V, which has also been supported by density functional theory (DFT) calculations.

Ultrasmall Metal Nanoparticles Confined within Crystalline Nanoporous Materials: A Fascinating Class of Nanocatalysts

Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal-organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high-efficiency nanocatalysts. The nanopore-encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore-encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic-scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore-encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.

Bimetallic metal organic frameworks with precisely positioned metal centers for efficient H2 storage

We demonstrated that the ratio and position of two different metal ions, Pd and Cu, can be precisely controlled within MOFs through predesigned metal clusters. These MOF structures incorporating Pd-Cu paddle wheel units were synthesised simply by reacting Pd-Cu acetate metal clusters and tritopic organic linkers at room temperature. Pd-Cu open metal sites were found to be uniformly distributed throughout the MOFs with a ca. 1 : 1 ratio. The incorporation of Pd into the MOF structure also led to enhanced affinity towards H2 with Qst values up to 8.9 kJ mol-1.

Polyaniline/palladium nanohybrids for moisture and hydrogen detection

Palladium nanoparticles display fascinating electronic, optical and catalytic properties, thus they can be used for various applications such as sensor fabrication. Conducting polymers such as polyaniline have also been widely used in sensor technology due to its cost effectiveness, versatility, and ease of synthesis. In this research, attention was given to unify the exceptional properties of these two materials and construct palladium nanoparticle coated polyaniline films to detect hydrogen and moisture. Electrochemical polymerization of aniline was carried out on gold sputtered epoxy resin boards. Polyaniline film was generated across a gap of 0.2 mm created by a scratch made on the gold coating prior to electrochemical polymerization. A palladium nanoparticle dispersion was prepared using sonochemical reduction method and coated on to polyaniline film using drop-drying technique. Polyaniline only films were also fabricated for comparative analysis. Sensitivity of films towards humidity and hydrogen was evaluated using impedance spectroscopy in the presence of the respective species. According to the results, polyaniline films exhibited an impedance drop in the presence of humidity and the response was significantly improved once palladium nanoparticles were incorporated. Interestingly, polyaniline only films did not respond to hydrogen. Nevertheless, palladium nanoparticle coated polyaniline films exhibited remarkable response towards hydrogen.

The Electronic State of Hydrogen in the α Phase of the Hydrogen-Storage Material PdH(D)x : Does a Chemical Bond Between Palladium and Hydrogen Exist?

The palladium-hydrogen system is one of the most famous hydrogen-storage systems. Although there has been much research on β-phase PdH(D)_x , we comprehensively investigated the nature of the interaction between Pd and H(D) in α-phase PdH(D)_x (x<0.03 at 303 K), and revealed the existence of Pd-H(D) chemical bond for the first time, by various in situ experimental techniques and first-principles theoretical calculations. The lattice expansion, magnetic susceptibility, and electrical resistivity all provide evidence. In situ solid-state ¹ H and ² H NMR spectroscopy and first-principles theoretical calculations revealed that a Pd-H(D) chemical bond exists in the α phase, but the bonding character of the Pd-H(D) bond in the α phase is quite different from that in the β phase; the nature of the Pd-H(D) bond in the α phase is a localized covalent bond whereas that in the β phase is a metallic bond.

Biosynthesis of palladium nanoparticles using Diospyros kaki leaf extract and determination of antibacterial efficacy

Palladium, the building block of white gold, has been found to exhibit extraordinary properties in nanotechnological products produced in recent years. The most prominent feature of palladium is adsorbing and storing high levels of hydrogen. Therefore, the demand for palladium in the world increased excessively in the 2000s. In the present study, palladium nanoparticles (PdNPs) were biosynthesized by the extract of Diospyros kaki leaves as bio-stimulator. D. kaki, also called persimmon, was collected in a local area in Istanbul Turkey. PdNP formation was screened by analyzing UV-Vis spectrophotometer at 250-550 nm. The nanoparticles were characterized by scanning electron microscope which revealed that the biosynthesized PdNPs were in sizes ranging from 50 to 120 nm. Fourier transform infrared spectroscopy applied on both D. kaki leaf extract and PdNPs was used to decide on the reactive groups managing the reduction of the biosynthesized nanoparticles. Also, the PdNPs showed reasonably proficient antibacterial efficacy for both Escherichia coli and Staphylococcus aureus and the zones of inhibition were found as 18 and 10.5 mm, respectively.

Post-synthetically modified MOF for the A3-coupling reaction of aldehyde, amine, and alkyne

A new heterogeneous NHC catalyst (Ag-NHC-MOF) was synthesized by the post-synthetic modification of an azolium-containing metal–organic framework.

Complex Nanostructures from Materials based on Metal-Organic Frameworks for Electrochemical Energy Storage and Conversion

Metal-organic frameworks (MOFs) have drawn tremendous attention because of their abundant diversity in structure and composition. Recently, there has been growing research interest in deriving advanced nanomaterials with complex architectures and tailored chemical compositions from MOF-based precursors for electrochemical energy storage and conversion. Here, a comprehensive overview of the synthesis and energy-related applications of complex nanostructures derived from MOF-based precursors is provided. After a brief summary of synthetic methods of MOF-based templates and their conversion to desirable nanostructures, delicate designs and preparation of complex architectures from MOFs or their composites are described in detail, including porous structures, single-shelled hollow structures, and multishelled hollow structures, as well as other unusual complex structures. Afterward, their applications are discussed as electrode materials or catalysts for lithium-ion batteries, hybrid supercapacitors, water-splitting devices, and fuel cells. Lastly, the research challenges and possible development directions of complex nanostructures derived from MOF-based-templates for electrochemical energy storage and conversion applications are outlined.

Preparation and characterization of a novel macroporous silica-bipyridine asymmetric multidentate functional adsorbent and its application for heavy metal palladium removal

The effective removal of heavy metal ¹⁰⁷Pd(II) from highly active liquid waste (HLW) is very valuable for reducing its hazardous and risk to public health and environment. For this purpose, a novel silica-bipyridine multidentate functional adsorbent was synthesized by vacuum infusing a new asymmetric N-donor ligand CA-MTBP (bipyridine derivative) into the macroporous SiO₂-P support. SEM, N₂ adsorption-desorption isotherms, TGA, XRD, FT-IR, ²⁹Si solid-state NMR and XPS spectroscopy were utilized to systematically characterize the physicochemical properties of the adsorbent. The characterization results indicated that CA-MTBP was successfully immobilized onto the pores of SiO₂-P by intermolecular interaction. Strong hydrogen-bonding interactions identified by single crystal structure of the ligand and ²⁹Si NMR may play a key role in achieving this immobilization. TGA and TOC studies showed that CA-MTBP/SiO₂-P had excellent thermal stability and highly HNO₃ resistance. EDS and XPS investigations provided directly evidences for Pd(II) being selectively adsorbed onto the adsorbent. The adsorbent had excellent adsorption capability, fast adsorption kinetics and high selectivity for Pd(II) over other typical tested metals in HNO₃ media.

A Coordination Network with Ligand-Centered Redox Activity Based on facial-[CrIII (2-mercaptophenolato)3 ]3- Metalloligands

The design of redox-active metal-organic frameworks and coordination networks (CNs), which exhibit metal- and/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me₄ N]₃ fac-[Cr^III (mp)₃ ] (1) (mp=2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K⁺ ions led to the formation of the two-dimensional honeycomb sheet-structured [K₃ fac-{Cr^III (mp)₃ }(H₂ O)₆ ]_n (2⋅6 H₂ O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2⋅6 H₂ O in the solid state.

Modification of as Synthesized SBA-15 with Pt nanoparticles: Nanoconfinement Effects Give a Boost for Hydrogen Storage at Room Temperature

In this work, Pt nanoparticles were incorporated into SBA-15 to prepare the materials for hydrogen spillover adsorption. We provide a direct modification (DM) strategy to improve the content of Pt nanoparticles inside the channels of SBA-15. In this strategy, the Pt precursor was directly incorporated into as synthesized SBA-15 by a solid-state grinding method. The subsequent calcination in air, then H₂/Ar gases was conducted to obtain the resultant materials of PtAS. For the samples of PtAS, Pt nanoparticles up to 5.0 wt% have a high dispersion inside the channels of SBA-15. The size of nanoparticles is in control of 3.7 nm. Although much work so far has focused on modification of SBA-15 with Pt nanoparticles. Here, it is the first time the loading amount of Pt nanoparticles raises up to 5.0 wt%, and the location of the Pt nanoparticles is interior channels of SBA-15. We reveal that the high dispersion behaviors of Pt nanoparticles are ascribed to the nanoconfinement effects provided by as synthesized SBA-15. However, the samples derived from template free SBA-15 (PtCS) show sparsely dispersion of Pt nanoparticles with the size of 7.7 nm. We demonstrate that the PtAS samples show better hydrogen adsorption performance than PtCS.