Bimetallic Zeolitic Imidazolate Framework Research Articles

Hierarchical Engineering on Built‐In Electric Field of Bimetallic Zeolitic Imidazolate Derivatives Towards Amplified Dielectric Loss

AbstractConstruction of built‐in electric field (BIEF) in nanohybrids has been demonstrated as an efficacious strategy to boost the dielectric loss by facilitating oriented transfer and transition of charges, thus optimizing the electromagnetic wave absorption property. However, the specific influence of BIEF on interface polarization needs to explore thoroughly and the BIEF strength should be further augmented. Herein, several dielectric systems incorporated Mott–Schottky heterojunctions and hollow structures are designed and constructed, where bimetallic zeolitic imidazolate framework are employed to derive Cu‐ZnO Mott–Schottky heterojunctions, and hierarchical structures and BIEF are further enriched by introducing hollow structure and reduced graphene oxide. The well‐established “double” BIEF verified by theoretical calculation and hollow engineering can regulate the conductivity, and enhance the polarization relaxation effectively. Especially, there always coexisted both enhanced charge separation and reversed charge distribution in this “double” BIEF, boosting the interface polarization. Attributing to the synergy of well‐matched impedance and amplified dielectric loss, the obtained hybrids exhibited superior absorption (reflection loss of −46.29 dB and an ultra‐wide effective absorption bandwidth of 7.6 GHz at only 1.6 mm). This work proves an innovative model for dissecting dielectric loss mechanisms and pioneers a novel strategy to explore advanced absorbers through enhancing BIEF.

Polyvinyl alcohol/sodium alginate-based conductive hydrogels with in situ formed bimetallic zeolitic imidazolate frameworks towards soft electronics

Bimetallic zeolitic imidazolate frameworks (BZIFs) have received enormous attention due to their unique physi-chemical properties, but are rarely reported for electrically conductive hydrogel (ECH) applications arising from low intrinsic conductivity and poor dispersion. Herein, we propose an innovative strategy to prepare highly conductive and mechanically robust ECHs by in situ growing Ni/Co-BZIFs within the polyvinyl alcohol/sodium alginate dual network (PZPS). 2-methylimidazole (MeIM) ligands copolymerize with pyrrole monomers, enhancing the electrical conductivity; meanwhile, MeIM ligands act as anchor points for in-situ formation of BZIFs, effectively avoiding phase-to-phase interfacial resistance and ensuring a uniform distribution in the hydrogel network. Due to the synergism of Ni/Co-BZIFs, the PZPS hydrogel exhibits a high areal capacitance of 630.3 mF·cm−2 at a current density of 0.5 mA·cm−2, promising for flexible energy storage devices. In addition, PZPS shows excellent mechanical strength and toughness (with an ultimate tensile strength of 405.0 kPa and a toughness of 784.2 kJ·m−3 at an elongation at break of 474.0 %), a high gauge factor of up to 4.18 over an extremely wide stress range of 0–42 kPa when used as flexible wearable strain/pressure sensors. This study provides new insights to incorporating highly conductive and uniformly dispersed ZIFs into hydrogels for flexible wearable electronics.

Improvement of optical and structural properties of ZIF-8 by producing multifunctional Zn/Co bimetallic ZIFs for wastewater treatment from copper ions and dye

In the paper, high specific surface area (SSA) mono and bimetallic zeolitic imidazolate frameworks (ZIFs) based on zinc and cobalt metals are successfully synthesized at room temperature using different ratios of Zn to Co salts as precursors and ammonium as a solvent to tailor the properties of the produced ZIF and optimize the efficiency of the particles in water treatment from dye and copper ions, simultaneously. The results declare that monometallic and bimetallic ZIF microparticles are formed using ammonium and the tuning of pore sizes and also increasing the SSA by inserting the Co ions in Zn-ZIF particles is accessible. It leads to a significant increase in the thermal stability of bimetallic Zn/Co-ZIF and the appearance of an absorption band in the visible region due to the existence of Co in the bimetallic structures. The bandgap energies of bimetallic ZIFs are close to that of the monometallic Co-ZIF-8, indicating controlling the bandgap by Co ZIF. Furthermore, the ZIFs samples are applied for water treatment from copper ions (10 and 184 ppm) and methylene blue (10 ppm) under visible irradiation and the optimized multifunctional bimetallic Zn/Co ZIF is introduced as an admirable candidate for water treatment even in acidic conditions.

Bimetallic zeolitic imidazolate framework derived hollow layered double hydroxide with tailorable interlayer spacing for nickel-zinc batteries

Bimetallic zeolitic imidazolate framework derived hollow layered double hydroxide with tailorable interlayer spacing for nickel-zinc batteries

Bi-metallic zeolitic imidazolate framework (ZIF) derived ZnO/Co3O4 heterostructure: effect of calcination temperature on microstructural and photocatalytic properties

Bi-metallic zeolitic imidazolate framework (ZIF) derived ZnO/Co3O4 heterostructure: effect of calcination temperature on microstructural and photocatalytic properties

High performance bimetallic ZIF-CoZn@PVDF-HFP composite nanofiber membrane for membrane distillation based on coaxial electrospinning technology

Membrane Distillation (MD) technology stands out for its cost-effectiveness and sustainability in diverse applications, such as high-salinity wastewater treatment and seawater desalination. However, conventional MD membranes frequently encounter challenges associated with inadequate permeate flux and insufficient anti-wetting performance. In the present study, we fabricated a series of ZIF-CoZn@PVDF-HFP composite nanofiber membranes with a core–shell structure via coaxial electrospinning. Here, PVDF-HFP functions as the core, while a blend of bimetallic Zeolitic imidazolate framework ZIF-CoZn nanoparticles and PVDF-HFP constitutes the shell. Through the utilization of the coaxial technology, functional nanoparticles achieve uniform and stably dispersed on the nanofiber surface, leading to the creation of a secondary rough structure in addition to the inherent roughness of single-nozzle electrospinning. This results in a surface with a 3D-hierarchical structure. The significantly amplifies the evaporation area on the surface of the composite nanofiber membrane, thereby bolstering the permeate flux in the MD process. Additionally, the incorporation of bimetallic ZIF-CoZn nanoparticles, recognized for their superior hydrophobicity and low thermal conductivity, improves the anti-wetting and heat-insulating properties of the composite nanofiber membrane, further advancing permeate flux performance. Using a 35 g L−1 NaCl as the feed solution, the optimal 1 % ZIF-CoZn@PVDF-HFP composite nanofiber membrane demonstrated a permeate flux of 21.8 L m−2 h−1, coupled with a salt rejection rate exceeding 99.9 %. Even during long-term MD testing, it maintained excellent insulation and anti-wetting capabilities. Our research offers a convenient and effective approach for fabricating anti-wetting composite nanofiber membranes.

Less solvent solid state reaction method synthesis of zeolitic imidazolate frameworks and the adsorption properties of their derived carbon materials

In recent years, a variety of nanomaterial synthesis methods have been used to explore the preparation of metal–organic frameworks (MOFs). The zeolitic imidazolate frameworks (ZIFs), are typically synthesized through high cost and environmentally unfriendly solvothermal methods, require a large amount of organic solvents, and have extremely low yields. Therefore, exploring scalable and environmentally friendly synthesis routes for ZIFs is crucial. The metal oxide and 2-methylimidazole are completely converted into submicron size ZIFs in stoichiometric ratio via less solvent solid state reaction (LSR) method. The ZIFs synthesized by LSR method have good crystallinity, large specific surface area, and the use of tiny solvent amount can achieve a yield of nearly 100%, which solves the problems of low yield and serious waste of solvent in the synthesis of ZIFs by traditional methods. Additionally, the fabricated ZIFs derived materials through high-temperature pyrolysis have high specific surface area, nitrogen rich content, and excellent chemical stability, being favorable for promoting the adsorption of organic dyes. The adsorption capacity of ZIF-8 derived materials fabricated by the LSR method for organic dyes is significantly better than that of ZIF-67 and bimetallic ZIFs (BZIFs) derived materials. Compared with the traditional method, the LSR method is a green and scalable manner to synthesize submicron ZIFs materials, paving the way for the preparation of various ZIFs with different metal centers, and also providing a new strategy for the commercial production of ZIFs derived materials widely used in the environment protection.

Enhancing the Catalytic Activity of Zeolitic Imidazolate Frameworks (ZIFs) via an Etching and Regrowth Method for CO2 Cycloaddition Reaction.

Zeolitic imidazolate frameworks (ZIFs) bearing rich accessible Lewis acidic/basic active sites and hierarchical pores are favorable to catalyze the cycloaddition of CO2 and epoxides with high yields of the target product under mild conditions. In this context, a facile etching and regrowth method is developed here to convert unstable leaf-like zinc-based ZIF-L to one kind of bimetallic ZIF (namely, ZnFe-ZIF) with a rough surface, a porous and accessible three-dimensional structure, and abundant Lewis acidic sites. Owing to the high Fe-doping content functioning as rich Lewis acidic sites and the high CO2 adsorbing capability together with the structural advantages to favor the mass diffusion, the yield of target cyclic carbonate can be up to >99% for the cycloaddition of CO2 and epichlorohydrin by ZnFe-ZIF at 6 h under mild conditions (0.1 MPa and 80 °C) with the selectivity of 100%. More importantly, unlike ZIF-L, which is unstable in the reaction system, the synthesized ZnFe-ZIF displays a satisfactory chemical stability without a loss in catalytic activities after five recycling runs as well as good substrate tolerance, making ZnFe-ZIF a potential high-performance catalyst for CO2 conversion.

Bimetallic ZIF-derived heteroatomic-doped bioanode catalysts for enhanced power production in microbial fuel cells

Binary composite nanoparticles (NPs) are considered anode materials with development potential. Herein, we synthesized two composite NPs, namely Mn-Co3O4/NPs and Mn-Co9S8/NPs, by codoping O, S and C based on bimetallic zeolitic imidazolate framework (Co-Mn-ZIF) precursors. The modified carbon felt (CF) Mn-Co3O4/NPs@CF and Mn-Co9S8/NPs@CF integrated into the microbial fuel cells (MFCs) exhibited the highest volume power densities of 4.58 ± 0.11 and 5.12 ± 0.15 W m−3, respectively, which were higher than that of the precursor anode Co-Mn-ZIF (2.70 ± 0.07 W m−3). In addition, microbial community structure analysis showed that the Mn-Co3O4/NPs@CF and Mn-Co9S8/NPs@CF bioanodes were substantially enriched with electricity-producing bacteria such as Geoalkalibacter, Thermovirga, and Desulfuromonas. The synergistic effect of the binary metal composites along with their oxides and sulfides, facilitated the extracellular electron transfer and biofilm formation. These results demonstrate the advantageous properties of heteroatom-doped binary metal NPs, including high electrical conductivity and good biocompatibility. These NPs serve as excellent anode materials for fabricating high-performance MFCs.

Atomically Dispersed Co2 MnN8 Triatomic Sites Anchored in N-Doped Carbon Enabling Efficient Oxygen Reduction Reaction.

Atomically dispersed transition metal-nitrogen/carbon (M-N/C) catalysts have emerged as the most promising substitutes to precious platinum counterparts toward oxygen reduction reaction (ORR). However, the reported M-N/C catalysts are usually in the form of common M-N4 moieties with only one single metal active site and suffer from insufficient activity. Herein, we elaborately developed an unusual trinuclear active structure with nitrogen-coordinated one Mn atom adjacent two Co atoms (Co2 MnN8 ) anchored in N-doped carbon as highly efficient ORR catalyst via adsorption-pyrolysis of bimetallic zeolitic imidazolate framework precursor. Atomic structural investigations and density functional theory (DFT) calculations revealed that Co2 MnN8 would experience a spontaneous OH binding to form Co2 MnN8 -2OH as the real active site, leading to a single electron-filled state in the orbital and an optimized binding energy of intermediates. Accordingly, the as-developed Co2 MnN8 /C exhibited an unprecedented ORR activity with a high half-wave potential of 0.912V and outstanding stability, not only surpassing the Pt/C catalyst but also representing a new record for the Co-based catalyst. This article is protected by copyright. All rights reserved.

Co/N co‐doped flower‐like carbon‐based phase change materials toward solar energy harvesting

AbstractThe photothermal conversion capacity of pristine organic phase change materials (PCMs) is inherently insufficient in solar energy utilization. To upgrade their photothermal conversion capacity, we developed bimetallic zeolitic imidazolate framework (ZIF) derived Co/N co‐doped flower‐like carbon (Co/N‐FLC)‐based composite PCMs toward solar energy harvesting. 3D interconnected carbon framework with low interfacial thermal resistance, abundant carbon defects and high content of nitrogen doping, excellent localized surface plasmon resonance (LSPR) effect of Co nanoparticles, and light absorber Co3ZnC in Co/N‐FLC synergistically upgrade the photothermal capacity of (polyethylene glycol) PEG@Co/N‐FLC composite PCMs with an ultrahigh photothermal conversion efficiency of 94.8% under 0.16 W/cm2. Uniformly anchored Co and Co3ZnC nanoparticles in carbon framework guarantee excellent photon capture ability. Bridging carbon nanotubes (CNTs) in 2D carbon nanosheets further accelerate the rapid transport of phonons by constructing cross‐connected heat transfer paths. Additionally, PEG@Co/N‐FLC exhibits a thermal energy storage density of 100.69 J/g and excellent thermal stability and durable reliability. Therefore, PEG@Co/N‐FLC composite PCMs are promising candidates to accelerate the efficient utilization of solar energy.

Hydroxyapatite nanoparticles decorated with metal–organic framework, Co‐Cu/ZIF@HAp, and evaluation of photocatalytic performance of the prepared nanocomposite in the degradation of organic pollutants

In this study, a novel hydroxyapatite (HAp)‐based composite, Co‐Cu/ZIF@HAp, was constructed through in situ growth and simultaneous sonication followed by magnetic string. Herein, the HAp‐based nanocomposite was obtained in which HAp was coated with cobalt–copper bimetallic zeolitic imidazolate framework (ZIF) in one‐pot synthesis method. The as‐synthesized composite was characterized by PXRD, FTIR, FE‐SEM, EDS, HR‐TEM, TGA‐DTG, XPS, BET, and UV‐DRS techniques, which suggested that HAp was well coated with bimetallic ZIF. The prepared composite was utilized as a catalyst in degradation of organic pollutants. Removal of organic pollutants such as organic dyes has become indispensable due to their higher stability, toxicity, and mutagenic nature. Two commonly found organic dyes, namely, Eosin Yellow (EY) and Brilliant Green (BG), were chosen for the investigation of photocatalytic activity of the as‐prepared catalyst. The degradation process was carried out under solar radiation, and there was no utilization of any oxidizing and reducing agent. Several parameters such as amount of catalyst dose, initial concentration of the dye solution, and effect of different pH conditions were evaluated for better understanding of photocatalytic performance of Co‐Cu/ZIF@HAp composite. Both EY and BG dyes were almost degraded up to 98.3% and 99.5%, respectively, within 50 min by the as‐prepared nanocomposite. Also, quenching test was performed that confirmed the formation of superoxide radicals (O2−.) as reactive oxygen species (ROS) in the photodegradation process. The as‐synthesized catalyst was repeatedly used for five times to ascertain the stability and reusability of catalyst.

Integrating multiple energy storage in 1D–2D bridged array carbon‐based phase change materials

AbstractIn response to global energy scarcity, frontiers in multifunctional composite phase change materials (PCMs) with photo‐/electro‐/magnetothermal triggers show great potential in multiple energy utilization. However, most available composite PCM candidates are inadequate for multiple energy storage applications simultaneously. Herein, a green synthetic route is proposed to develop bimetallic zeolitic imidazolate framework (ZIF)‐derived 1D–2D bridged array carbon‐based composite PCMs for simultaneous photo‐/electro‐/magnetothermal energy storage applications. As graphitization‐induced catalyst, Co nanoparticles greatly boost the formation of ZIF‐derived 1D–2D bridged array carbon framework with high graphitization and low interface electrical/thermal resistance. Benefiting from the broadband intense photon capture, fast photon/electron/phonon transport, and surface plasma resonance effect of Co nanoparticles, the resulting composite PCMs integrate advanced photo‐, electro‐, and magnetothermal storage functions. Furthermore, composite PCMs also exhibit long‐lasting shape stability, structural stability, thermal storage stability, and photo‐/electro‐/magnetothermal storage stability after undergoing multiple heating–cooling cycles. This study is promising to accelerate the major breakthroughs of advanced multifunctional carbon‐based composite PCMs toward multiple energy utilization.

Electrospun fibers integrating enzyme-functionalized metal-organic frameworks for postoperative tumor recurrence inhibition and simultaneously wound tissue healing

The tumor recurrence and infected wound tissue defect are the major clinical challenges after the surgical treatment of primary chest wall cancer. Herein, to address the above issues, blending electrospinning was applied to incorporate glucose oxidase (GOx) loaded Zn/Cu-based bimetallic zeolitic imidazolate frameworks (GOx/BMOFs) into polyurethane (PU) fibers, which were designed for effective cancer therapy with improved wound healing. The release of Cu2+ and GOx could accomplish the conversion from Cu2+ to Cu+ through the glutathione (GSH) depletion and provide additional H2O2 from glucose by GOx catalysis, respectively, which further underwent the Fenton-like reaction to produce toxic hydroxyl radical (OH). The tumor cells (human fibrosarcoma cells) could be effectively killed in vitro and in vivo through the synergistic chemodynamic therapy and starvation therapy. Moreover, the electrospun fiber platform could support the adhesion and proliferation of wound tissue cells, and also show the antibacterial ability owing to the functional agents in the fibers, thereby accelerating the infected wound repair in vivo. This work may offer a reliable and effective fiber biomaterial for localized chest wall tumor therapy and simultaneous tissue regeneration.

Co-N/Zn@NPC derived from bimetallic zeolitic imidazolate frameworks: A dual mode simultaneous electrochemical sensor for uric acid and ascorbic acid

Bimetallic Co-N/Zn@NPC (nanoporous carbon) derived from bimetallic zeolitic imidazolate frameworks (BMZIFs) has been synthesized using the co-precipitation method followed by carbonization 800 °C for 4 h in a nitrogen atmosphere. The synthesized Co-N/Zn@NPC was characterised by numerous physiochemical techniques such as Fourier-Transform infrared (FTIR), Raman spectroscopy, Scanning Electron Microscope (SEM), Tunnelling Electron Microscope (TEM), Selected Area Electron Diffraction (SAED) and X-ray Photoelectron Spectroscopy (XPS). The as-synthesized nanocomposite was utilized as an electrocatalyst to modify the glassy carbon electrode (GCE) for the electrochemical evaluation of uric acid (UA) and ascorbic acid (AA) in individual and dual modes in phosphate buffer solution (PB) in pH-6. The electrode kinetic behaviour of the Co-N/Zn@NPC has been studied by electrochemical impedance spectroscopy (EIS). The prepared electrode material demonstrates high electroactive surface area and appraisable electron transfer ability. It expresses an exquisite linear range of 0.1 to 14.7 μM for uric acid (UA) and 0.1 to 157.1 μM for ascorbic acid (AA), respectively. The present Co-N/Zn@NPC system has an excellent detection of limit (LOD) with 0.21 nM for UA and 7.65 nM for AA. The practical feasibility analysis shows a recovery of 99.62% and 99.00% for UA and AA in human blood serum samples.

In-situ-grown multidimensional Cu-doped Co1-xS2@MoS2 on N-doped carbon nanofibers as anode materials for high-performance alkali metal ion batteries

Transition metal sulfides with the high theoretical capacity and low cost have been considered as advanced anode candidate for alkali metal ion batteries, but suffered from unsatisfactory electrical conductivity and huge volume expansion. Herein, a multidimensional structure Cu-doped Co1-xS2@MoS2 in-situ-grown on N-doped carbon nanofibers (denoted as Cu-Co1-xS2@MoS2 NCNFs) have been elaborately constructed for the first time. The bimetallic zeolitic imidazolate framework CuCo-ZIFs were encapsulated in the one-dimensional (1D) NCNFs through an electrospinning route and then on which the two-dimensional (2D) MoS2 nanosheets were in-situ grown via a hydrothermal process. The architecture of 1D NCNFs can effectively shorten ion diffusion path and enhance electrical conductivity. Besides, the formed heterointerface between MOF-derived binary metal sulfides and MoS2 can provide extra active centers and accelerate reaction kinetics, which guarantee a superior reversibility. As expected, the resulting Cu-Co1-xS2@MoS2 NCNFs electrode delivers excellent specific capacity of Na-ion batteries (845.6 mAh/g at 0.1 A/g), Li-ion batteries (1145.7 mAh/g at 0.1 A/g), and K-ion batteries (474.3 mAh/g at 0.1 A/g). Therefore, this innovative design strategy will bring a meaningful prospect for developing high-performance multi-component metal sulfides electrode for alkali metal ion batteries.

CoSe2 nanoparticles anchored on CoNC carbon nanoplates as bifunctional electrocatalyst for flexible rechargeable Zn-air batteries

A flexible solid rechargeable Zn-air battery for advanced energy conversion and storage has extensive applications in portable electric sources, wildlife rescue and flexible wearable systems. Herein, the CoSe2 nanoparticles anchored on cobalt-embedded N-doping carbon nanoplates (CoSe2/CoNC) is developed as a highly active bifunctional catalyst via pyrolysis and selenization of bimetallic zeolitic imidazolate frameworks containing Zn and Co. The introduction of inactive Zn generates strong electrochemically active surface areas due to the synergistic effect between CoSe2 nanoparticles and CoNC matrix. Further, CoSe2/CoNC exhibits prominent Zn–air battery performance and even outperforms the commercially available noble-metal catalysts. Notably, a high-rate flexible Zn-air battery enabled by an alkaline composite polyacrylic acid-carboxymethyl cellulose electrolyte delivers the open-circuit potential of 1.51 V. The battery offers high wearability and performs very well under various conditions, such as soaking, drilling and sewing.

Cobalt doping amount determines dominant reactive species in peroxymonosulfate activation via porous carbon catalysts co-doped by cobalt and nitrogen

Switching the reaction routes in peroxymonosulfate (PMS)-based advanced oxidation processes have attracted much attention but remain challenging. Herein, a series of Co-N/C catalysts with different compositions and structures were prepared by using bimetallic zeolitic imidazolate frameworks based on ZIF-8 and ZIF-67 (xZn/Co-ZIFs). Results show that Co doping amount could mediate the transformation of the activation pathway of PMS over Co-N/C. When Co doping amount was less than 10%, the constructed xCo-N/C/PMS system (x ≤ 10%) was singlet oxygen-dominated reaction; however further increasing Co doping amount would lead to the generation and coexistence of sulfate radicals and high-valent cobalt, besides singlet oxygen. Furthermore, the nitrogen-coordinated Co (Co-NX) sites could serve as main catalytically active sites to generate singlet oxygen. While excess Co doping amount caused the formation of Co nanoparticles from which leached Co ions were responsible for the generation of sulfate radicals and high-valent cobalt. Compared to undoped N/C, Co doping could significantly enhance the catalytic performance. The 0.5% Co-N/C could achieve the optimum degradation (0.488 min−1) and mineralization abilities (78.4%) of sulfamethoxazole among the investigated Co-N/C catalysts, which was superior to most of previously reported catalysts. In addition, the application prospects of the two systems in different environmental scenarios (pH, inorganic anions and natural organic matter) were assessed and showed different degradation behaviors. This study provides a strategy to regulate the reactive species in PMS-based advanced oxidation process.

Synergetic metal-Nx and metal nanoparticles derived from Zn/Co-zeolitic imidazolate frameworks boosted conversion of microalgal lipids

In order to enhance acid-base active sites and their utilization efficiency to efficiently convert microalgal lipids into biodiesel, an acid-base catalyst was synthesized through pyrolyzing ZnCo bimetallic zeolitic imidazolate frameworks (ZIFs). Pyrolysis destroyed saturated coordinated metal-N4 sites in ZIFs and produced more unsaturated metal-Nx and metal nanoparticles, which enhanced Lewis acidity. The increased pyridinic N and unsaturated metal-Nx promoted Lewis basicity. Meanwhile, Zn doping reduced sizes of catalyst crystals and metal nanoparticles, which improved utilization efficiency of active sites. Hence, compared with pyrolyzed ZIF-67, the acidity of optimal catalyst increased from 0.205 to 1.535 mmol/g, whereas basicity increased from 0.069 to 0.405 mmol/g. DFT calculations revealed that catalytic performances of metal nanoparticles and unsaturated metal-Nx were better than that of saturated metal-N4. Therefore, the catalytic efficiency of C-Zn/Co-ZIF = 4 (molar ratio of Zn to Co was 4) catalyst was highest at 96.2%, because of the minimal catalyst crystals and metal nanoparticles.

Fabrication of Hierarchical, Porous, Bimetallic, Zeolitic Imidazolate Frameworks with the Incorporation of Square Planar Pd and Its Catalytic Application.

Bimetallic zeolitic imidazolate frameworks (ZIFs) containing two different metal ions can exhibit superior performances when applied in heterogeneous catalysis. Herein, we present a facile one-pot synthesis method for PdCo-ZIFs with various Pd/Co ratios, where Pd(II) ions are successfully incorporated into the Co node sites of the ZIF structure. The local structure of the bimetallic ZIFs was comprehensively investigated by pore-structure, X-ray absorption fine structure, and in situ CO adsorption Fourier transform infrared analyses. The results demonstrated that the framework comprises different coordination geometries of Co (tetrahedral) and Pd (square planar) ions connected by the benzimidazolate ligand. Notably, the inherently nonporous, 2D Co-ZIF structure was transformed into a hierarchical porous structure, and the PdCo-ZIFs exhibited a significantly increased concentration of defects and distorted Co sites. Based on these results, the catalytic performances of the synthesized ZIFs in the cycloaddition of CO2 to epoxides were evaluated under a cocatalyst and solvent-free conditions. The PdCo-ZIFs exhibited significantly higher catalytic activity (maximum turnover frequency, TOF = 2501 h-1) than Co-ZIF (TOF = 65 h-1) and Pd-ZIF (no activity), which revealed that the undercoordinated Co sites with distorted structure are the active sites rather than the incorporated Pd ions. This study provides a facile one-pot method for synthesizing bimetallic ZIFs with mixed-coordination modes, hierarchical porous structures, and modified defect concentrations, which would expand the library of structurally diverse bimetallic ZIFs toward various applications.