Functionalized zeolitic imidazolate framework F-ZIF-90 as efficient catalyst for the cycloaddition of carbon dioxide to allyl glycidyl ether

Flumequine-mediated fluorescent zeolitic imidazolate framework functionalized by Eu3+ for sensitive and selective detection of UO22+, Ni2+ and Cu2+ in nuclear wastewater

Currently, antibiotics and heavy metal contaminants have posed a great threat for ecological security and human health. Herein, the lanthanide functionalized ZIF (named ZIF-90-PABA-Eu) is constructed by coordinating with Eu³⁺ via p-aminobenzoic acid intermediate. Due to the excellent fluorescence properties, the novel fluorescent probe can selectively monitor flumequine based on "turn on" mode. Furthermore, the obtained new material (named ZIF-90-PABA-Eu-Flu) can be used as "turn off" sensor for selective detection of both radioactive and nonradioactive heavy metal ions (UO₂²⁺, Ni²⁺ and Cu²⁺) which are the main component of nuclear industrial wastewater. ZIF-90-PABA-Eu-Flu shows ultra-short fluorescence response time (3 s) and ultra-low limit of detection (9.0 × 10^-3, 1.3 × 10^-2 and 6.1 × 10^-4 ppm) for three metal ions, which may be attributed to its good affinity with UO₂²⁺, Ni²⁺ and Cu²⁺. Moreover, principal component analysis (PCA) is applied to distinguish the three metal ions. Additionally, the possible sensing mechanism is investigated by the UV-vis spectra, luminescence lifetimes and theoretical calculation analysis. Based on these results, ZIF-90-PABA-Eu possesses promising potential in practical application and provides insight for the design of novel probes to continuously monitor flumequine, radioactive and nonradioactive heavy metal ions.

Matching Bidentate Ligand Anchoring: an Accurate Control Strategy for Stable Single-Atom/ZIF Nanocatalysts

Improving metal loading and controlling the coordination environment is nontrivial and challenging for single-atom catalysts (SACs), which have the greatest atomic efficiency and largest number of interface sites. In this study, a matching bidentate ligand (MBL) anchoring strategy is designed for the construction of CuN₄ SACs with tunable coordination environments (Cu loading range from 0.4 to15.4 wt.%). The obtained Cu SA/ZIF and Cu SA/ZIF* (0.4 wt.%) (ZIF and ZIF* = Zeolitic imidazolate framework with Matching bidentate N-ligands) nanocomposites exhibit superior performance in homo-coupling of phenyl acetylene under light irradiation (TON = 580, selectivity > 99%), which is 22 times higher than that of Cu SA/NC-800 (NC = N-doped porous carbon). Experiments and density functional theory calculations confirmed that the specific Cu five-membered ring formed using the MBL anchoring strategy is the key to the immobilization of isolated Cu atoms. This strategy provides a basis for the construction of M SA/MOF, which has the potential to narrow the gap between experimental and theoretical catalysis, as further confirmed by the successful preparation of Fe SA/ZIF and Ni SA/ZIF.

Biocatalytic conversion of sunlight and carbon dioxide to solar fuels and chemicals

This review discusses the progress in the assembly of photosynthetic biohybrid systems using enzymes and microbes as the biocatalysts which are capable of utilising light to reduce carbon dioxide to solar fuels. We begin by outlining natural photosynthesis, an inspired biomachinery to develop artificial photosystems, and the rationale and motivation to advance and introduce biological substrates to create more novel, and efficient, photosystems. The case studies of various approaches to the development of CO2-reducing microbial semi-artificial photosystems are also summarised, showcasing a variety of methods for hybrid microbial photosystems and their potential. Finally, approaches to investigate the relatively ambiguous electron transfer mechanisms in such photosystems are discussed through the presentation of spectroscopic techniques, eventually leading to what this will mean for the future of microbial hybrid photosystems.

Portable and sensitive detection of non-glucose target by enzyme-encapsulated metal-organic-framework using personal glucose meter

Personal glucose meter (PGM) is one of the most commercially available POC (point-of-care) devices for monitoring the level of glucose reliably, yet its non-glucose quantification ability is limited since such strategy needs ingenious interface design and tedious enzyme conjugation. Herein, we constructed a portable and sensitive platform that can detect non-glucose target by combining enzyme-encapsulated zeolitic imidazole framework-90 (ZIF-90) with personal glucose meter. ZIF-90 is an ideal carrier and susceptor due to the extraordinary capability of packaging enzyme and stimuli-responsiveness. We selected adenosine-5'-triphosphate (ATP) as the target model of non-glucose analytes. Upon ATP-induced decomposition of MOF, the released enzyme (glucose oxidase or invertase) catalyzed substrate and gave rise to the change of the glucose concentration for PGM assay. This method determined ATP with a remarkably sensitivity of 233 nM and effective recovery in real serum samples. Our strategy provides a facile and practical approach for measuring the non-glucose target using PGM, and could potentially be applied in bimolecular detection in point-of-care diagnosis.

Efficient uranium adsorbent with antimicrobial function constructed by grafting amidoxime groups on ZIF-90 via malononitrile intermediate

Herein, a dual-function Zeolitic Imidazole Frameworks (ZIFs) ZIF-90 grafted with malononitrile by Knoevenagel reaction and following with an amidoximation reaction to form an efficient U (VI) adsorbent (ZIF-90-AO). The strong chelation power of amidoxime groups (AO) with uranium and ZIF-90's mesoporous structure afforded ZIF-90-AO high maximum uranium adsorption capacity of 468.3 mg/g (pH = 5). In addition, the factors affecting uranium adsorption process were investigated by a batch of adsorption tests under different adsorption conditions. ZIF-90-AO displayed good selectivity to UO₂²⁺ in the solution containing multiple co-existing ions and good regeneration property. More importantly, ZIF-90-AO showed excellent antimicrobial property against both E. coli and S. aureus. Therefore, ZIF-90-AO is a U-adsorbent with great application value for removing U (VI) from wastewater due to the high U (VI) adsorption capacity in weak acid condition and good anti-biofouling properties.

Imidazolium-based poly(ionic liquid)s@MIL-101 for CO2 adsorption and subsequent catalytic cycloaddition without additional cocatalyst and solvent

Poly(ionic liquid)@MIL-101 incorporates an ionic liquid in a MOF and can be used in CO2 capture and conversion.

In situ activation of COOH-functionalized ZIF-90-enabled reductive CO2N-formylation

A heterogeneous COOH-functionalized ZIF-90 porous catalyst (ZIF-90-C) was prepared for enhanced CO2 adsorption/activation, and the in situ generated –COO− species can efficiently promote the N-formylation reaction.

Simultaneous transformation of 2D to 3D and doped metal transitions of zeolitic imidazole frameworks under solid phase and free-solvent conditions

The post-thermal treatment (PTT) method was applied for crystal transformation on the structure of zeolitic imidazolate frameworks (ZIFs) from 2D to 3D under solvent-free conditions. The investigation was performed based on bridging of the cobalt ions by the 2-methylimidazole linker to form the ZIF structure. Extensive characterization revealed that the reaction mechanism was a transformation in the solid crystal phase and resulted from the de-coordination of the framework and reformation of the crystalline structure. In addition, the PTT method opens the opportunity to simultaneously dope transition metals (Zn, Co, Fe, Ni, and Mn) in the framework during the transformation of ZIFs. The materials with doped metals showed enhanced properties and excellent performance for applications including gas adsorption, dye degradation, and the catalytic activity of CO₂ fixation.

Study of the Cycloaddition of CO2 with Styrene Oxide Over Six-Connected spn Topology MOFs (Zr, Hf) at Room Temperature

A series of MOFs with a 6-connected spn topology were synthesized (MOF-808-(Zr, Hf), PCN-777-(Zr, Hf), MOF-818-(Zr, Hf)). Through the in situ DRIFTS of NH₃ adsorption-desorption, we found that the activated catalyst mainly contains Lewis acid sites. The effects of different organic ligands on the Lewis acid of the Zr₆ cluster were analyzed by XPS and NH₃ -TPD, and the relative Lewis acidity of the same metal was obtained: PCN-777>MOF-808>MOF-818. In the Py-FTIR results, we confirmed that MOF-818 has a higher acid site density. In the activity test, MOFs with mesoporous structure showed better catalytic activity under normal temperature and pressure. Among them, MOF-818 can still maintain a high degree of crystallinity after catalysis. Finally, we use density functional theory to propose the mechanism of the cycloaddition reaction of carbon dioxide and styrene oxide. The results show that the metal is coordinated with styrene oxide and halogens attack the β carbon of the epoxide.

Effect of MAF-6 Crystal Size on Its Physicochemical and Catalytic Properties in the Cycloaddition of CO2 to Propylene Oxide

Zeolitic imidazolate frameworks MAF-5 and MAF-6 based on Zn2+ and 2-ethylimidazole were demonstrated to be efficient heterogeneous catalysts in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. Activity of MAF-5 was lower in comparison with MAF-6 due to the difference in their structural and textural characteristics. MAF-6 samples with particle size of 190 ± 20, 360 ± 30, and 810 ± 30 nm were prepared at room temperature from [Zn(NH3)4](OH)2 and 2-ethylimidazole. Control of particle size was achieved by variation of type of alcohol in alcohol/cyclohexane media for the preparation of MAF-6. According to this comprehensive study, the yield of PC was found to decrease with increasing crystal size of the MAF-6 material, which was related to the change in textural properties and the number and localization of active sites. The combination of MAF-6 with particle size of with particle size of 190 ± 20 nm and tetrabutylammonium bromide ([n-Bu4N]Br) as co-catalyst led to an approximately 4-fold enhancement in the yield of PC (80.5%). Compared with reported ZIFs catalysts, the efficiencies of MAF-5/[n-Bu4N]Br and MAF-6/[n-Bu4N]Br binary systems were comparable and higher under similar reaction conditions.

Trifunctional Metal-Organic Framework Catalyst for CO2 Conversion into Cyclic Carbonates

Herein, we reported a facile strategy for the preparation of trifunctional ionic metal-organic frameworks (MOFs) incorporating imidazolium cation functionalities. This strategy exploits the Debus-Radziszewski reaction to create the cationic imidazole ring by postsynthetic modification, meanwhile introducing exchangeable counteranions. On the basis of this strategy, MIL-101-IMOH-Br^- has been synthesized, which combines Lewis acidic sites, Brønsted acidic sites, and nucleophilic centers to achieve catalysis for the carbon dioxide-epoxide cycloaddition into cyclocarbonate without any cocatalyst and solvent.

MOF Embedded and Cu Doped CeO2 Nanostructures as Efficient Catalyst for Adipic Acid Production: Green Catalysis

Greatly efficient chemical processes are customarily based upon a catalyst activating the process pathway to achieve higher yields of a product with desired specifications. Catalysts capable of achieving good performance without compromising green credentials are a pre-requisite for the development of a sustainable process. In this study, CeO2 nanoparticles were tested for their catalytic activity with two different configurations, one as a hybrid of CeO2 nanoparticles with Zeolitic Immidazole Framework (ZIF-67) and second being doped Cu cations into CeO2 nanoparticles. Physicochemical and catalytic activity was investigated and compared for both systems. Each hybrid was synthesized by embedding the CeO2 nanoparticles into the microporous structure of ZIF-67, and Cu doped CeO2 nanoparticles were prepared by a facile hydrothermal route. As a catalytic test, it was employed for the oxidation of cyclohexene to adipic acid (AA) as an alternative to expensive noble metal-based catalysts. Heterogeneous ZIF-67/CeO2 found catalytical activity towards the oxidation of cyclohexene with nearly complete conversion of cyclohexene into AA under moderate and co-catalyst free reaction conditions, whereas Cu doped CeO2 nanoparticles have shown no catalytic activity towards cyclohexene conversion, depicting the advantages of the porous ZIF-67 structure and its synergistic effect with CeO2 nanoparticles. The large surface area catalyst could be a viable option for the green synthesis of many other chemicals.

A ZIF-90 nanoplatform loaded with an enzyme-responsive organic small-molecule probe for imaging the hypoxia status of tumor cells

Hypoxia is one of the most common and important features occurring across a wide variety of malignancies, which can have adverse effects on the therapeutic outcomes of chemotherapy and radiotherapy. Therefore, the characterization of tumor hypoxia is of great importance in clinical tumor treatment. Herein, we firstly develop a new spectroscopic off-on probe with high sensitivity (detection limit: 5.8 ng mL^-1) and good selectivity for fluorescence imaging the hypoxic status of tumor cells via its enzymatic reaction with nitroreductase in vitro and in vivo in the presence of dimethyl sulfoxide (DMSO) as a co-solvent. Inspired by the recent investigations on metal-organic frameworks (MOFs), a dual pH and ATP-responsive ZIF-90 nanoplatform was synthesized, and then PEG was post-modified through a Schiff base reaction. This allows the platform to serve as a carrier to load the hypoxia-responsive probe to investigate its response to enzyme in cells and in mice without using dimethyl sulfoxide as a co-solvent. Consequently, the two probes we synthesized here can successfully respond to nitroreductase for turn-on fluorescence imaging at a cellular level and in tumor-bearing mice. This is the first time that an enzyme-responsive organic small-molecule probe has been mounted on one of the MOFs. Our results open up a promising way for the design and application of both enzyme-responsive probes and MOFs.

Metal–organic frameworks for the energy-related conversion of CO2 into cyclic carbonates

MOFs are promising heterogeneous catalysts for chemical fixation of CO₂ and epoxides into cyclic carbonates.

Hollow Zn-Co Based Zeolitic Imidazole Framework as a Robust Heterogeneous Catalyst for Enhanced CO2 Chemical Fixation

The efficient chemical conversion of carbon dioxide (CO₂ ) into value-added fine chemicals is an intriguing but challenging route in sustainable chemistry. Herein, a hollow-structured bimetallic zeolitic imidazole framework composed of Zn and Co as metal centers (H-ZnCo-ZIF) has been successfully prepared via a post-synthetic strategy based on controllable chemical-etching of the preformed solid ZnCo-ZIF in tannic acid. The creation of hollow cavities inside each monocrystalline ZIFs could be achieved without destroying the intrinsic frameworks, as characterized by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction technologies. The as-synthesized H-ZnCo-ZIF exhibited remarkable catalytic activity in the cycloaddition of CO₂ with epoxides to the corresponding cyclic carbonates, outperforming the solid ZnCo-ZIF analogue due to the improved mass transfer originating from the hollow structure. More importantly, due to stabilization of metal centers in the ZIF framework by the tannic acid shell, H-ZnCo-ZIF exhibited good recyclability, and no activity loss could be observed in six runs. The present study provides a simple and effective strategy to enhance the catalytic performance of ZIFs by creating a hollow structure via chemical etching.

Schiff-base reaction induced selective sensing of trace dopamine based on a Pt41Rh59 alloy/ZIF-90 nanocomposite

Zeolitic imidazole frameworks (ZIFs) are a new class of functional porous materials with attractive characters, such as gas storage, selective separation, catalysis, and drug delivery. We report herein using nanoscale ZIF-90 crystals with free aldehyde group of imidazole-2-carboxaldehyde (ICA) ligand for the selective electrochemical detection of dopamine. The averaged adsorption enthalpy ΔH (i.e., isosteric heat) of ZIF-90 to dopamine is estimated as 72 kJ mol^-1 according to grand canonical Monte Carlo (GCMC) simulation. With further modification of a Pt₄₁Rh₅₉ alloy nanocatalyst, the electrochemical sensing performances towards dopamine are improved. The synergetic effect generated by a Pt₄₁Rh₅₉/ZIF-90 nanocomposite endows it a low detection limit of 1 nM and good specificity. The different anti-interference mechanisms to coexisting redox active species and amino analogues are also included in this work. The strategy demonstrated here may be extended to tune metal nodes as well as ligands of ZIFs crystals and further regulating their functionalities for different target molecules identification.

A Facile and Versatile "Click" Approach Toward Multifunctional Ionic Metal-organic Frameworks for Efficient Conversion of CO2

Ionic metal-organic frameworks (IMOFs) that integrate synergistic Lewis-acid sites (intrinsic metal centers of the frameworks) and nucleophilic anions (halides encapsulated within pores) are intriguing platforms for the design of fully heterogeneous catalytic systems for cycloaddition of CO₂ to epoxides. A new, facile and versatile synthetic approach has been used to fabricate triazolium-based IMOFs for the first time. The approach makes use of azide-alkyne click chemistry and subsequent N-alkylation to post-synthetically create a cationic triazolium ring and introduce exchangeable counteranions at the same time. The IMOFs are efficient and recyclable heterogeneous catalysts for CO₂ conversion under mild and cocatalyst-free conditions. In particular, the click-accessible triazolium ring provides a handle to incorporate further functionality. The MIL-101-tzmOH-Br catalyst, which integrates hydrogen-bonding hydroxy groups besides metal centers and bromide anions, shows superior catalytic performance under mild conditions.

Liquid-Phase Catalytic Oxidation of Limonene to Carvone over ZIF-67(Co)

Liquid-phase catalytic oxidation of limonene was carried out under mild conditions, and carvone was produced in the presence of ZIF-67(Co), cobalt based zeolitic imidazolate framework, as catalyst, using t-butyl hydroperoxide (t-BHP) as oxidant and benzene as solvent. As a heterogeneous catalyst, the zeolitic imidazolate framework ZIF-67(Co) exhibited reasonable substrate–product selectivity (55.4%) and conversion (29.8%). Finally, the X-ray diffraction patterns of the catalyst before and after proved that ZIF-67(Co) acted as a heterogeneous catalyst, and can be reused without losing its activity to a great extent.

New Set of Multicomponent Crystals as Efficient Heterogeneous Catalysts for the Synthesis of Cyclic Carbonates

Three new multicomponent crystals 1a-1c of Zn(II), Mn(II), and Co(II), respectively, were synthesized by the reaction of 2,6-bis(hydroxymethyl)pyridine, the respective metal salts, and sodium benzoate in a 1:1:2 ratio. One component of these multicomponent crystals 1a-1c is the dicationic 2,6-bis(hydroxymethyl)pyridine metal complex and the other component is the dianionic tetrabenzoate complex of the same metal. The complexes were fully characterized by single-crystal X-ray structure determination. The X-ray structure of these compounds 1a-1c reveals the formation of 1D supramolecular chain parallel to the crystallographic b axis via H-bonding interactions between the dicationic and dianionic parts of the respective compound. The Mn(II) (1b) and Co(II) (1c) complexes show antiferromagnetic coupling between the two associated metal centers via the H-bonding interaction pathway. All the three compounds 1a-1c were tested as heterogeneous catalytic systems for the successful conversion of epoxides to cyclic carbonates in solvent-free condition under approximately 10 bar of pressure of CO2 and temperature ranging between 60 and 80 °C along with tetrabutyl ammonium bromide acting as a cocatalyst. All the three compounds 1a-1c were found to have turnover number more than 1000 for the respective epoxides except for the conversion of cyclohexene oxide to cyclohexene carbonate.

Construction of a 3D porous Co(ii) metal–organic framework (MOF) with Lewis acidic metal sites exhibiting selective CO2 capture and conversion under mild conditions

The application of a 3D Co(ii)-MOF as a recyclable heterogeneous catalyst for conversion of CO₂ to cyclic carbonates is reported.

Immobilization of zeolitic imidazolate frameworks with assist of electrodeposited zinc oxide layer and application in online solid-phase microextraction of Sudan dyes

Herein a facile method for immobilization of zeolitic imidazolate frameworks (ZIFs) was developed. The ZIFs grew on electrochemically deposited zinc oxide (ZnO) layer while carbon fiber bundle served as substrate. The synthesized ZIFs-ZnO composite was packed into PEEK tube as sorbent for online solid phase microextraction (SPME)-HPLC-UV analysis of Sudan dyes. Good enrichment efficiency (200-461 fold), low limits of detection (0.002 ng mL^-1) and wide linear ranges (0.02-20 ng mL^-1, correlation coefficient > 0.9996) were achieved. The analytical method was demonstrated to be practical for analysis of Sudan dyes in environmental water samples with good recoveries (83.5%~95.0%).