Core Shell MOFs Research Articles

Highly Efficient Photoelectrochemical Detection of Cystatin C Based on a Core-Shell MOF Nanocomposite with Biomimetic-Catalysis Amplification.

Cystatin C (CysC) has been proven to be used to diagnose acute kidney injury (AKI) rapidly and sensitively early. Therefore, it is urgent to develop a sensitive, novel, and rapid method for detecting CysC. In this work, a novel photoelectrochemical (PEC) biosensor was designed for ultrasensitive CysC detection. Ti-MOF@DM-LZU1@Au as a photosensitive material was first modified on the ITO electrode surface. Then, Ab1 and CysC were assembled on the electrode via the specific immunoresponse of an antigen and antibody. Lastly, the conjugate Ab2/l-Cys bilayer/l-Cys-hemin/G-quadruplex with self-catalytic enzyme performance, as a signal amplification approach, could further react with CysC and Ab1, which resulted in a stronger photocurrent. As expected, the constructed PEC sensor realized the ultrasensitive detection of CysC, with a detection range of 10 pg/mL to 16 μg/mL and a lower limit of 8.023 pg/mL. The biosensor had excellent repeatability, selectivity, and stability. Moreover, it can provide a new method for the sensitive and rapid detection of other protein molecules in clinical practice.

Synergistically Enhanced Oxidase-like Property of Core-Shell MOF Nanozymes by Decorating Au and Ag/AgCl Nanoparticles for l-Cysteine Colorimetric Sensing.

Monitoring l-cysteine (l-Cys) is of importance for human health and food safety. Herein, we designed a novel strategy for bimetallic Au and Ag/AgCl anchoring on Ni-doped ZIF-67 to form core-shell nanocubes (Ni-ZIF-67/AuAg/AgCl) using the galvanic replacement processes. The unique properties of ZIF-67 nanocubes were conducive to generating strong synergistic catalytic effects with Au and Ag/AgCl, particularly when Ni-ZIF-67/AuAg/AgCl composites were employed as oxidase mimics for catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The Ni-ZIF-67/AuAg/AgCl composites displayed strong affinity toward TMB, displaying a lower Michaelis constant Km value of 0.25 mM and a higher maximum initial rate Vmax of 9 × 10-8 M s-1. By virtue of the nanozyme, the colorimetric sensor was constructed for l-Cys detection with a relatively low detection limit of 0.051 μM. The superior catalytic performance of the as-prepared Ni-ZIF-67/AuAg/AgCl composites can be ascribed to the core-shell structure, large specific surface area, and strong synergistic catalytic effects, which are beneficial for exposing more active sites and enhancing the conductivity to further boost their catalytic activity.

Construction of Core-Shell MOF CSMnP with Enzyme-Like Activity for Chemotherapy and Chemodynamic Therapy.

Materials with enzyme-like activity have received a lot of attention in the field of tumor catalytic therapy. Here, biocompatible core-shell MOF CSMnP with two valence states of Mn ion, which could process chemodynamic therapy (CDT), was designed and synthesized. Besides, it could also promote a series of catalytic processes in the tumor microenvironment (TME). CSMnP catalyzed endogenous hydrogen peroxide (H2O2) to oxygen (O2) via catalase-like activity and then combined with the outer layer Mn(II)-PBC to convert O2 into superoxide radicals (•O2-), exhibiting oxidase-like activity. Besides, intracellular glutathione (GSH) could be effectively consumed through the glutathione oxidase-like activity of Mn3+. The occurrence of the cascade reactions effectively amplified the enzymatic production to enhance CDT. Furthermore, the therapeutic effect of CSMnP was improved through the loading of cationic drug DOX. The loading capacity was 11.10 wt %, which was 2.2 times that of Mn(III)-PBC (4.95 wt %), and the release of DOX showed a characteristic response. Therefore, the core-shell MOF with enzyme-like activity had a potential application for tumor combination therapy.

One-Pot Synthesis of MOF@MOF: Structural Incompatibility Leads to Core-Shell Structure and Adaptability Control Makes the Sequence.

Core-shell metal-organic frameworks (MOF@MOF) are promising materials with sophisticated structures that cannot only enhance the properties of MOFs but also endow them with new functions. The growth of isotopic lcore-shell MOFs is mostly limited to inconvenient stepwise seeding strategies with strict requirements, and by far one-pot synthesis is still of great challenge due to the interference of different components. Through two pairs of isoreticular MOFs, it reveals that the structural incompatibility is a prerequisite for the formation of MOFs@MOFs by one-pot synthesis, as illustrated by PMOF-3@HHU-9. It further unveils that the adaptability of the shell-MOF is a more key factor for nucleation kinetic control. MOFs with flexible linkers has comparably slower nucleation than MOFs with rigid linkers (forming PMOF-3@NJU-Bai21), and structural-flexible MOFs built by flexible linkers show the lowest nucleation and the most adaptability (affording NJU-Bai21@HHU-9). This degree of adaptability variation controls the sequence and further facilitates the synthesis of a first triple-layered core-shell MOF (PMOF-3@NJU-Bai21@HHU-9) by one-pot synthesis. The insight gained from this study will aid in the rational design and synthesis of other multi-shelled structures by one-pot synthesis and the further expansion of their applications.

Facile MOF Support Improvement in Synergy with Light Acceleration for Efficient Nanoalloy-Catalyzed H2 Production from Formic Acid

Hydrogen (H2) generation and storage are actively investigated to provide a green source of energy, and formic acid (HCOOH), a major product obtained from the biomass, is regarded as a productive source of H2. Therefore, improvements in heterogeneous catalysts are called for. Here, a novel type of catalyst support is proposed involving simple addition of the mixture of metal ion precursors to core-shell ZIF-8@ZIF-67, followed by reduction with NaBH4, with performances surpassing those obtained using nanocatalysts in ZIF-8 or ZIF-67. The nanocatalysts PdxAg were optimized with ZIF-8@Pd2Ag1@ZIF-67 under visible-light illumination for selective HCOOH dehydrogenation involving a turnover frequency value of 430 h-1 under light irradiation at 353 K. These results also reveal the crucial roles of the Pd sites electronically promoted in the presence of visible light by the Ag plasmon resonance and the advantageous core-shell MOF structure. In order to examine the potential of extending this catalyst improvement principle to other catalytic reactions, 4-nitrophenol reduction, a benchmarking model of catalytic reaction, was tested, and the results also confirmed the superiority of the performance of ZIF-8@Pd2Ag1@ZIF-67 over Pd2Ag1@ZIF-8 and Pd2Ag1@ZIF-67, confirming the interest in the novel catalyst design.

Pd@Co3O4/In2O3 hollow microtubes derived from core-shell MOFs as materials for conductometric trace toluene detection

In this work, we designed and prepared Pd-loaded Co3O4/In2O3 hollow microtubes heterostructures, which are promising for trace toluene gas detection in humid atmosphere. We characterized the materials, confirmed the morphology of hollow microtubes and structure of the heterojunctions, and analyzed the effect of components and Pd NPs loading on the gas sensing performance. In gas sensing measurements, the Pd@Co3O4/In2O3 (PdCoIn-2) sensor shows high responses (21.5/16.4, 1 ppm), low limit of detections (LODs, 0.02/0.06 ppb), with fast response and recovery times (1 and 4 s/1 and 3 s) toward toluene under 54 %/95 % RH. In addition, PdCoIn-2 sensor also exhibits excellent selectivity, repeatability and long-term stability. Finally, based on the structure of this material, the enhanced sensing mechanism of PdCoIn-2 for toluene detection is discussed in depth.

PEGylation of a shell over core-shell MOFs-a novel strategy for preventing agglomeration and synergism in terms of physicochemical and biological properties.

We demonstrate a new strategy of PEGylation over core-shell MOFs of HKUST-1 and Cu-MOF-2 by a solvothermal method. The novel synthesized PEGylated core-shell MOFs has synergistic enhancement in terms of physicochemical and biological properties. FTIR spectroscopy and XRD analysis described the bonding characteristics of the double-shelled-core MOFs PEG@HKUST-1@CuMOF-2 and PEG@CuMOF-2@HKUST-1. XPS and EDAX spectroscopy confirmed the structural features of the PEG@core-shell MOFs. The as-synthesized PEG-modified core-shell MOFs showed a readily identifiable morphology with a reduction in particle size. The significant observation from SEM and TEM was that agglomeration disappeared completely, and the morphology of individual core-shell MOFs was clearly revealed. BET analysis provided the surface characteristics of MOF compounds. The chemical states of frameworks were established by XPS. The designed PEG-modified copper MOFs were evaluated for their activity against Gram-positive (Staphylococcus aureus, Enterococcus faecalis), Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacterial species and activity against fungal species (Aspergillus niger and Candida albicans). This research work highlights a facile and synergistic approach to design promising biocompatible nano-dimensional core-shell MOFs for biological applications.

Visualization of the gas permeation in core–shell MOF/Polyimide mixed matrix membranes and structural optimization based on finite element equivalent simulation

Core-shell MOFs recently have suggested the greater potential on gas separation of mixed matrix membranes (MMMs) than the single MOFs. In this work, two core–shell MOFs (ZIF-67@ZIF-8 (ZIF-67@8) and ZIF-8@ZIF-67 (ZIF-8@67)) with adverse structure were specially designed to explore what structure is more conducive to gas separation of MMMs. Moreover, a simplified equivalent simulation based on electrical conductivity of Maxwell model was adopted to predict the gas permeability and the internal gas permeation behavior for core–shell MOF based MMMs. The simulation exhibited the better predicted results than the Felske model and revealed the gas transport pathway. As a result, ZIF-67@8 based MMM with the shell-dependent transport and a thin interlayer had the highest H2 permeability of 224 Barrer and H2/CH4 separation factor of 76.7, which are 180% and 24% higher than neat PI, respectively. Finally, core–shell MOFs based MMMs also showed the lower temperature dependence of permeation for N2 and CH4 compared to pure PI. This work provides a unique method to investigate how core–shell structure affects the gas separation performance of MMMs, especially for equivalent simulation, which not only is proved to play as an efficient tool to predict the gas permeability, but also exhibits a great potential on investigation of gas transport pathway for the further structural optimization.

Stimuli-responsive of magnetic metal-organic frameworks (MMOF): Synthesis, dispersion control, and its tunability into polymer matrix under the augmented-magnetic field for H2 separation and CO2 capturing applications

Single-crystal magnetic-responsive core-shell MOF by grafting Fe3O4 nanoparticles onto the UiO-66-NH2 and their controlled embedding into gas separation mixed matrix membranes was reported. Obtained results confirmed the stimuli-responsive character of the MMOF during their dispersion of MMOF in a well-defined arrays structure in the PMMA matrix. Contrarily, an absence of a magnetic field results in the MMOF aggregation and sedimentation of the particles at the bottom of the membrane. Compared to the non-controlled ones, gas permeability increased by 26.2% for CO2 and 76.67% for H2, and selectivity increased 2.95 and 1.49 times for the CO2/N2 and H2/CO2 gas pairs, respectively. Moreover, obtained permeability-selectivity values for the H2/CO2 gas pairs overcome the appropriate modified 2008 Robeson upper bound.

Fabrication and deployment of nanodisc ZnO@ZIF-8, ZnO@NA and ZnO@INA core–shell MOFs: enhanced NH3 and HCHO gas sensing

Three nanodisc ZnO@MOFs, ZnO@ZIF-8 (1), ZnO@NA (2) and ZnO@INA (3) with structural building units 2-methylimidazole, nicotinic acid and isotonic acid are synthesized. These are fabricated and deployed as an advanced chemical capacitive sensors to detect formaldehyde and ammonia (NH3) at room temperature. These composite materials are characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD) spectra, scanning electron microscope (SEM) analysis, energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) and Brunauer–Emmett–Teller (BET) analysis. TGA studies suggest that these MOFs are stable up to 400 to 450 °C temperature. ZnO@ZIF-8 detected ammonia, formaldehyde, acetone and ethanol, while ZnO@NA and ZnO@INA detected ammonia and formaldehyde gases from 5 to 100 ppm range. ZnO@ZIF-8 showed microporous behaviour, while ZnO@NA and ZnO@INA showed mesoporous behaviours. Sensing performances were carried out at 5, 10, 25, 50 and 100 ppm concentrations of ammonia, acetone, formaldehyde, toluene, xylene and ethanol.

Co/N co-doped carbonaceous polyhedron as efficient peroxymonosulfate activator for degradation of organic pollutants: Role of cobalt

• Synthesized a novel Co,N co-doped carbon material with Core-shell MOFs. • Co@N-C-2 showed superb catalytic performance and low cobalt leaching. • Nonradical way including 1 O 2 and electron transfer dominated oxidation process. • Co species regulated the structure and determined the activation mechanism. • Co@N-C-2/PMS system is resistant to the inorganic anions and NOM. In this study, Co/N co-doped polyhedron carbonaceous catalyst (Co@N-C-2) with abundant mesoporous, high graphitization degree and cobalt content was synthesized via the pyrolysis of core–shell MOFs composite (ZIF-8@ZIF-67). The two cobalt species (Co NPs and Co-N x ) coexisted in Co@N-C-2 were unveiled to play different role in PMS activation. Concretely, the Co-N x served as active sites for 1 O 2 evolution pathway, while Co NPs greatly improved the graphitization degree and thus enhanced the electron transfer pathway. Owing to the novel structure, the as-prepared Co@N-C-2 presented superior catalytic performance upon PMS activation for the removal of several organic pollutants in comparison with the catalysts derived from single MOFs (ZIF-8 and ZIF-67) and the transition metal oxides. Moreover, Co@N-C-2 could be recovered by thermal treatment, and the Co@N-C-2/PMS system also showed high resistance to inorganic anions and natural organic matter (NOM). This study reveals the crucial role of cobalt species in regulating the structure of catalyst and determining the PMS activation pathway.

Hyaluronic acid-drug conjugate modified core-shell MOFs as pH responsive nanoplatform for multimodal therapy of glioblastoma.

Multimodal therapeutic approach has been gaining lot of attention for effective therapy of cancer. In the present work, a novel and unique pH responsive nanoplatform have been developed for multimodal therapy of glioblastoma using protein, biopolymer and MOFs. Lactoferrin (Lf) has been used as protein matrix for loading titanocene which was then enclosed in ZIF-8 framework along with 5-FU (ZIF-8@Lf-TC). The ZIF-8 was further coated with Lenalidomide-HA conjugate linked via hydrazone linkage (LND-HA@ZIF-8@Lf-TC). The developed nanocomposite was extensively characterized using spectroscopic, x-ray and electron microscopic techniques. The nanocomposites were evaluated for pH responsive drug release, stability, bio-interaction, and haemocompatibility which confirmed pH responsive nature of nanocomposite, stability and absence of any significant interaction with biomolecules. In obtained results for in vitro cell line studies performed in U87MG and RAW264.7 cells demonstrated enhanced cell cytotoxicity against cancer cells which was further supported by results of cellular ROS generation and surface ROS generation by nanocomposites. The Zinc and Lf mediated disruption of intracellular IL-6 and TNFα levels was observed with synthesized nanocomposites. They demonstrated pH responsive release of 5-FU and LND along with sustained release of both drugs in simulated medium. The LND-HA@ZIF-8@Lf-TC demonstrated superior cell growth supressing ability compared to ZIF-8@Lf-TC and ZIF-8. The nanocomposites were stable in biomimicking environment as well as did not show any significant interaction with RBC, plasma or CSF. The overall results suggest that LND-HA@ZIF-8@Lf-TC can be explored as promising platform for dual drug delivery mediated multimodal therapy of cancer.

Frontispiece: Modulating Guest Uptake in Core–Shell MOFs with Visible Light

Frontispiece: Modulating Guest Uptake in Core–Shell MOFs with Visible Light

Unveiling the mechanism of lattice-mismatched crystal growth of a core-shell metal-organic framework.

Determining the effect of severe lattice mismatch on the crystal growth mechanism and form of epitaxially grown materials is vital to understand and direct the form and function of such materials. Herein, we report the use of atomic force microscopy to reveal the growth of a shell metal-organic framework (MOF) on all faces of a core MOF that has similar a, b-lattice parameters but a ∼32% mismatch in the c-lattice parameter. The work shows the mechanism through which the shell MOF overcomes the core terrace height mismatch depends on that mismatch being reduced before overgrowth of continuous shell layers can occur. This reduction is achieved via a process of growth of non-continuous shell layers that are terminated by terrace edges of the core. The crystal form of the shell MOF is heavily influenced by the lattice mismatch which hinders continuous spreading of the interfacial and subsequent shell layers on some facets. The results exemplify the crystal growth versatility of MOFs to accommodate large lattice mismatch, to house many more functional defects in a core-shell MOF than either of the component MOFs, and has broader implications for engineering lattice-mismatched core-shell materials in general.

Seaming the interfaces between topologically distinct metal-organic frameworks using random copolymer glues.

Creating novel and multifunctional MOF-on-MOF hetero-architectures to achieve desired properties is a new frontier in MOF research. Herein, we demonstrate a generalizable method to construct core-shell MOFs using rationally designed random copolymer (RCP) glues as mediators to seam the interfaces between MOFs with mismatched topologies and coordination chemistry. The key advantage of this method is that the composition and functionality of the RCPs can be systematically tuned through judicious monomer selection to optimize the shell quality and potentially meet the demand for different core-shell MOFs.

Hollow shell-in-shell Ni3S4@Co9S8 tubes derived from core–shell Ni-MOF-74@Co-MOF-74 as efficient faradaic electrodes

Unique shell-in-shell hierarchical structures fabricated through transition from core–shell MOFs would have great potential for hybrid supercapacitor applications.

Increasing both selectivity and permeability of mixed-matrix membranes: Sealing the external surface of porous MOF nanoparticles

A novel approach to improve the selectivity of mixed matrix membrane (MMM) systems was developed. MOF nanoparticles (NPs) were chemical coated by a PEG based shell and then incorporated into a polymer matrix to yield a MMM. The unique design of the core-shell MOF NPs can enhance both the membrane permeability and selectivity simultaneously. This membrane material exhibits excellent CO2/N2 separation performance that surpasses the latest upper bound through the most direct way. This filler was also applied to the thin-film composite membrane system, showing promising performance and placing it in the optimal zone for post-combustion CO2 capture.

Conducting polymer coated metal-organic framework nanoparticles: Facile synthesis and enhanced electromagnetic absorption properties

A hybrid polyaniline coated metal organic framework (MOF/PANI) was designed and fabricated via hydrothermal and in situ chemical polymerization methods The microstructure and morphology were examined by XRD, FTIR, FESEM and TEM. The results showed that MOF (Fe) particles were completely coated by PANI and formed a core-shell composite. The hybrid MOF (Fe)/PANI composite exhibited enhanced EM wave absorption capability compared with MOF (Fe), including the higher absorption intensity (−41.4dB at 11.6GHz) and excellent absorption bandwidth (5.5GHz exceeding −10dB with an only thickness of 2mm), which was due to enhanced interfacial effects, attenuation constant and the synergic effect between MOF (Fe) and PANI. Therefore, such a core-shell MOF (Fe)/PANI composite is a promising absorber for application in microwave absorption field.

Dynamically controlled one-pot synthesis of heterogeneous core-shell MOF single crystals using guest molecules.

A new mixed guest approach for the synthesis of heterogeneous core-shell MOF crystals was exemplified by one-pot assembly of photoactive guests into an anionic host framework. The formation mechanism, photophysical properties and oxygen gas sensing properties of as-synthesized core-shell MOF crystals were also investigated.

Facile fabrication of magnetically recyclable metal-organic framework nanocomposites for highly efficient and selective catalytic oxidation of benzylic C-H bonds.

HKUST-1@Fe3O4 chemically bonded core-shell nanoparticles have been prepared by growing HKUST-1 thin layers joined by carboxyl groups onto Fe3O4 nanospheres. These magnetic core-shell MOF nanostructures show exceptional catalytic activity for the oxidation of benzylic C-H bonds and they can be recovered by magnetic separation and reused without losing any activity.