Imidazolate Framework Research Articles

A novel electrochemical sensor based on mesoporous carbon hollow spheres/ZIF-67-derived Co-embedded N-doped carbon nanotubes composite for simultaneous determination of dihydroxybenzene isomers in environmental water samples

Dihydroxybenzene isomers were environmental pollutants which were potential threat to human health. Accurately and rapidly detection of them is very valuable. In this study, a dihydroxybenzene isomer sensor based on mesoporous carbon hollow spheres/zeolitic imidazolate frameworks (ZIF)-derived Co-embedded N-doped CNTs (MCHSs/Co@N-CNTs) was proposed. The MCHSs/Co@N-CNTs, with excellent conductivity and electrocatalytic, presented excellent electrochemical simultaneous detection for phenolic compounds. Under optimal conditions, the MCHSs/Co@N-CNTs/GCE showed wide linear range (CC: 2.5 μM-100 μM, HQ: 1.0 μM −150 μM, RS: 20 μM −1000 μM) and the detection limit (LOD) of CC, HQ and RS were 0.46, 0.27 and 4.21 μM (S/N = 3), respectively. Additionally, the reaction sites and mechanism of phenolic compounds were revealed by analyzing the electrochemical behavior with the help of density functional calculation. Moreover, the sensor showed satisfactory results in the determination of phenolic compounds in environmental water samples.

UV-triggered fast assembly of a high-performing stable enzyme@MOF composite membrane for efficient aquatic micropollutants removal

As conventional water purification technologies are inefficient, they put us at risk of exposure to emerging micropollutants. Here, we report a two-step method for rapid construction of a stable enzyme@MOF biomimetic membrane comprising enzyme-embedded metal–organic framework-based biocomposites for continuous and efficient removal of micropollutants from water. We first prepared a horseradish peroxidase@zeolitic imidazolate framework-8 (HRP@ZIF-8) biocomposite via ball-milling method, capable of preserving structural integrity and the entrapped enzyme bioactivity under different denaturing environments. The second step involves biocomposite membrane synthesis via stimulation of polydopamine (PDA) polymerization with UV light after successively dispersing the dopamine and HRP@ZIF-8 biocomposite molecules in a neutral pH Tris-HCl system. Accompanied by the clever codeposition with PDA, the HRP@ZIF-8 biocomposite can be “sandwiched” between the PDA layers to create a stable HRP@ZIF-8-composite membrane (HRP@ZIF-8-CM). HRP@ZIF-8-CM synergistically integrates MOF adsorption, enzyme catalysis, and membrane separation functions. The calculated encapsulation rate of the HRP@ZIF-8 biocomposite is ≤ 98.2 %. The enzyme@MOF composite membrane has a catalytic degradation efficiency of 98 % for bisphenol A (1 mg/L), membrane water flux of 32.3 L/m2 h bar, outstanding stability, and high efficiency after 7 cycles of use. Surprisingly, the bisphenol A removal rate of the enzyme@MOF composite membrane remained stable under varying denaturing conditions, including wide pH and temperature ranges and proteolytic enzymes, indicating that HRP enzyme activity is well preserved, probably owing to the bio-inertness of ZIF-8. In conclusion, we propose a new, simple, and fast method for the constructing enzyme@MOF composite membranes, which can significantly improve water purification.

ZIF-67 derived Mo-CoS2 nanoparticles embedded in hierarchically porous carbon hollow sphere for efficient overall water splitting

Regulation of active sites and intrinsic activity is essential for achieving highly efficient electrocatalysts. Herein, a dual-template route is adopted to prepare Mo-CoS2 nanoparticles embedded in hierarchically porous carbon hollow sphere (Mo-CoS2/NC (H)). The in-situ growth of phosphomolybdic acid/zeolitic imidazolate framework-67 (ZIF-67) nanoparticles on the surface of polystyrene sphere (PS) are pyrolyzed to obtain hollow sphere. Mo-CoS2/NC (H) can be obtained by subsequent vulcanization treatment. The results indicate that Mo-CoS2/NC (H) with favorable features including abundant active sites, better conductivity and optimized electronic structure contribute to superior overall water splitting performance. The intrinsic catalytic activity and electronic structure are analyzed by combining the results of characterizations and density functional theory (DFT) calculations. Consequently, Mo-CoS2/NC (H) delivers the overpotentials of 158 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) at 10 mA cm−2 in 1.0 M KOH electrolyte. Moreover, the electrolyzer assembled by Mo-CoS2/NC (H) as two-electrode delivers a low potential of 1.59 V at 10 mA cm−2 for overall water splitting. This work gives an insight about cooperative contributions of hierarchically porous structure and electron structure towards the electrocatalytic performance.

One-pot synthesis of rod-like lignin@zeolitic imidazolate framework-8 with enhanced immobilization of β-glucosidase

Developing value-added lignin-based biomaterials for enzyme immobilization has drawn great attention. This study developed a cost-effective and eco-friendly one-pot strategy to synthesize the rod-like lignin@zeolitic imidazolate framework-8 (ZIF-8) hybrid nanomaterial by using lignin derived from lignocellulosic biofuel production. The incorporation of lignin into the ZIF-8 network not only altered the morphology, but also modified the surface properties of the material, making it an ideal support for enzyme immobilization. The synthesized nanoscale hybrid materials were used to immobilize beta-glucosidase (BG) with high immobilization capacity and about 92–166 mg/g of BG was immobilized through physical adsorption. The immobilized BG exhibited good stability, catalytic activity and recycling properties, and was reused under acidic conditions for more than 8 cycles with more than 60% activity kept. The as-prepared hybrid material can serve as a great carrier for immobilizing various biomolecules.

An efficient metal–organic framework-based drug delivery platform for synergistic antibacterial activity and osteogenesis

Bone implants for clinical application should be endowed with antibacterial activity, biocompatibility, and even osteogenesis-promoting properties. In this work, metal–organic framework (MOF) based drug delivery platform was used to modify titanium implants for improved clinical applicability. Methyl Vanillate@Zeolitic Imidazolate Framework-8 (MV@ZIF-8) was immobilized on the polydopamine (PDA) modified titanium. The sustainable release of the Zn2+ and MV causes substantial oxidative damage to Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The increased reactive oxygen species (ROS) significantly up-regulates the expression of oxidative stress and DNA damage response genes. Meanwhile, the structural disruption of lipid membranes caused by the ROS, the damage caused by Zinc active sites and the damage accelerated by the MV are both involved in inhibiting bacterial proliferation. The up-regulated expression of the osteogenic-related genes and proteins indicated that the MV@ZIF-8 could effectively promote the osteogenic differentiation of the human bone mesenchymal stem cells (hBMSCs). RNA sequencing and Western blotting analysis revealed that the MV@ZIF-8 coating activates the canonical Wnt/β-catenin signaling pathway through the regulation of tumor necrosis factor (TNF) pathway, thereby promoting the osteogenic differentiation of the hBMSCs. This work demonstrates a promising application of the MOF-based drug delivery platform in bone tissue engineering.

Novel Ag3PO4@ZIF-8 p-n heterojunction for effective photodegradation of organic pollutants

In this study, a novel silver phosphate@zeolitic imidazolate framework-8 (Ag3PO4@ZIF-8) p-n heterojunction was fabricated at room temperature using the chemical precipitation method. The photocatalytic properties of the developed p-n heterojunction were investigated with respect to organic water pollutants. The effects of the operation parameters on the photocatalytic performance of the fabricated photocatalyst were also studied. The fabricated Ag3PO4@ZIF-8 p-n heterojunction exhibited excellent photocatalytic properties with respect to organic pollutants crystal violet (CV), Congo red (CR), and rhodamine B (Rh B). The total organic carbon (TOC) measurements revealed that the developed Ag3PO4@ZIF-8 p-n heterojunction mineralized 99.0% of Rh B, 90.7% of CV, and 94.7% of CR in 120 min. The heterojunction also exhibited excellent cyclic stability, which is crucial for practical applications. The excellent photocatalytic performance of the developed Ag3PO4@ZIF-8 p-n heterojunction could be ascribed to the suppression of the photogenerated charge recombination, enhancement of the surface area, p-n heterojunction formation, and extended light absorption. Therefore, the developed heterojunction is promising for environmental remediation in general, and for photocatalysis-based treatment of organic pollutant-containing wastewater in particular.

Green synthesis of SiO2 from Equisetnm arvense plant for synthesis of SiO2/ZIF-8 MOF nanocomposite as photocatalyst

Equisetnm arvense plant extract was used for preparing amorphous SiO2. For preparing of SiO2/zeolitic imidazolate framework-8 (ZIF-8) nanocomposite by solvothermal method, the synthesized SiO2 was added to synthesis mixture ZIF-8. The photocatalytic activity of SiO2/ZIF-8 was investigated systematically by degrading crystal violet as a cationic dye under UV light irradiation. The photodegradation of crystal violet by SiO2, ZIF-8 and SiO2/ZIF-8 samples was 13.7%, 25.6% and 75.6% during UV-light irradiation for 15 min. Among synthesized samples (SiO2, ZIF-8 and SiO2/ZIF-8), the SiO2/ZIF-8 exhibited highest photocatalytic activity and improved stability compared to pure SiO2 and ZIF-8. As evidenced from SEM and TEM images, ZIF-8 particles without aggregation located over SiO2. The enhancement of the photocatalytic activity is due to the fact that the introduction of insulator SiO2 in SiO2/ZIF-8 composites can modify the surface state of the composite; more importantly, the energy level of SiO2 can help accelerate the separation and transfer of electron-hole pairs of ZIF-8. The SiO2/ZIF-8 photocatalyst did not show any obvious loss of photocatalytic activity during five cycles, which indicate that the heterostructured photocatalyst was stable and can be used repeatedly.

Honeycomb-like structured ZnFe2O4@C derived from ZnFe2O4@ZIF-8 for electromagnetic wave absorption

In this paper, ZnFe2O4@Zeolitic imidazolate framework-8 (ZIF-8) composites were prepared by Sol-Gel self-propagating combustion method and in situ growth method. Honeycomb-like structured ZnFe2O4@C composites were obtained using ZnFe2O4@ZIF-8 as the precursor in Ar atmosphere carbonization at 800℃. The honeycomb-like structure is conducive to enhance the polarization and reflection on the surface of powder particles, which ameliorate the EMW absorption properties of the materials significantly. Wherein, the carbon content can be controlled by ZIF-8 coating. The composite with 5% ZIF-8 (wt%) shows excellent reflection loss value of −36.5 dB at 9.4 GHz with a matching thickness of 2.0 mm, and the corresponding effective absorption bandwidth is 3.5 GHz (7.6–11.1 GHz). The composite with 10% ZIF-8 (wt%) obtain a minimum reflection loss value of −37.8 dB at 10.0 GHz when the thickness is 2.0 mm, and the effective absorption bandwidth is 3.5 GHz (7.9–11.3 GHz).

A ratiometric electrochemical sensor for detecting lead in fish based on the synergy of semi-complementary aptamer pairs and Ag nanowires@zeolitic imidazolate framework-8.

This work describes the synergistic application of semi-complementary aptamer pairs and signals on-off ratio strategies on glassy carbon electrodes (GCE) for detecting lead ions (Pb2+) in fish. Gold nanoparticles (AuPNs) as the electrode substrate can provide added binding sites for the aptamers and improve the conductivity of the electrodes. Pb2+ aptamers containing ferrocene (Fc) molecules act as molecular recognizers in the sensing system. In the presence of target ions, Fc signals are affected by conformational changes of the aptamer. The "Ag nanowires@zeolitic imidazolate framework-8 with methylene blue (AgNWs@ZIF-8/MB)" can be semi-complementary to the Pb2+ aptamer after binding to single-stranded DNA (S1). However, S1/AgNWs@ZIF-8/MB self-assembled with Pb2+ aptamer (Apt) by hybridization incubation was quickly replaced by Pb2+ competitively, resulting in the loss of methylene blue (MB) signaling molecules. Hence, the internal reference signal (MB) and conformation change signal (Fc) comprise the ratio sensing system well. Morphology, spectroscopy, and electrochemistry methods have validated the modification and sensing behaviors. The used Apt has made considerable progress in analytical performance. In interference studies and stability checks, the ratio measurement signal IFc/IMB is a more reliable signal than the single signal readout. Following a log-linear relationship, this sensor provides a wide linear range. Furthermore, the proposed sensor can be used to determine Pb2+ in fish samples, and the results agree with those obtained using ICP-MS and recovery tests.

Rapid microwave-assisted synthesis of a magnetic biochar@ZIF-67: an efficient nanocomposite-based adsorbent for the dye-contaminated water cleanup

A magnetic waste date seed-derived biochar@zeolitic imidazolate framework-67 was fabricated by the microwave-assisted synthesis method, and used as an efficient nanocomposite-based adsorbent for the removal of Tartrazine and Sunset yellow dyes from contaminated water.

Zn2+-Loaded adhesive bacterial cellulose hydrogel with angiogenic and antibacterial abilities for accelerating wound healing.

Wound healing is a process that requires angiogenesis and antibacterial activities and it remains a challenge for both experimental and clinical research worldwide. Zn2+ has been reported to be widely involved in angiogenesis and exerts antibacterial effects, making it suitable as a treatment to promote wound healing. Therefore Zn2+-loaded adhesive bacterial cellulose hydrogel was designed to observe its angiogenic and antibacterial abilities in the wound healing process. The characterization, tensile strength, swelling behaviors and antibacterial activity of bacterial cellulose/polydopamine/zeolitic imidazolate framework-8 (BC/PDA/ZIF8) hydrogels were tested. Cell-Counting-Kit-8 (CCK8), transwell, tube formation and real time qunantitative PCR (qRT-PCR) assays were performed to evaluate the cell compatibility of BC/PDA/ZIF8 hydrogels in vitro. A full-thickness defect wound model and histological assays were used to evaluate the BC/PDA/ZIF8 hydrogels in vivo. The prepared BC/PDA/ZIF8 hydrogels exhibited suitable mechanical strength, excellent swelling properties, good tissue adhesion, efficient angiogenic and antibacterial effects and good performance as a physical barrier. In vivo experiments showed that the BC/PDA/ZIF8 hydrogels accelerated wound healing in a full-thickness defect wound model by stimulating angiogenesis. This study proved that BC/PDA/ZIF8 hydrogels possess great potential for promoting satisfactory wound healing in full-thickness wound defects through antibacterial effects and improved cell proliferation, tissue formation, remodeling and re-epithelialization.

Ultrasensitive Luteolin Electrochemical Sensor Based on Novel Lamellar CuZn@ Nitrogen-Containing Carbon Nanosheets.

The Cu/Zn-zeolitic imidazolate framework (Cu/Zn-ZIF) was synthesized using the traditional hydrothermal method, and its surface morphology was controlled by adding polyvinylpyrrolidone (PVP) during its synthesis. It was then calcined at 800 °C to form the nitrogen-containing carbon material CuZn@NC, which improved the electron transfer rate. Scanning electron microscopy (SEM), X-ray crystal diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface morphology and structure. Finally, the electrochemical sensing platform for luteolin was effectively constructed by changing the metal-ion ratio during synthesis to achieve the most suitable electrode material. The sensor platform detects luteolin well, with an operating curve equation of Ip (A) = 0.0571C (nM) - 1.2913 and a minimum detection limit of 15 nM, and the platform has been successfully employed for luteolin detection in real samples.

Front Cover: How to Harness Electrochemical Mediators for Photocatalysis – A Systematic Approach Using the Phenanthro[9,10‐d]imidazole Framework as a Test Case (ChemCatChem 1/2023)

Front Cover: How to Harness Electrochemical Mediators for Photocatalysis – A Systematic Approach Using the Phenanthro[9,10‐<i>d</i>]imidazole Framework as a Test Case (ChemCatChem 1/2023)

Fe2O3/ZIF-8 architectures with enhanced thermocatalytic performance for efficient degradation of nitrocellulose

Fe2O3/zeolitic imidazolate framework-8 (ZIF-8) architectures were successfully prepared by a polyvinylpyrrolidone (PVP)-assisted method, which can be as an effective potential catalyst for promoting the thermal degradation of nitrocellulose (NC). Thermal behavior and degradation kinetics of catalyst-NC mixtures were studied using the TG/DTG and DSC methods, and found that the Fe2O3/ZIF-8-NC pyrolysis possessed a total degradation of 77.96%, a maximum pyrolysis rate temperature of 194.5 °C, and the lowest activation energy of 179.4 ± 16.1 kJ mol−1, confirming a better thermocatalytic performance of Fe2O3/ZIF-8 when compared to Fe2O3 and ZIF-8 for NC thermolysis. Furthermore, it can be inferred from the isoconversional analysis, which employs a modified fitting algorithm, that catalyst-NC mixtures and pure NC adhere to the reconstructed “n-order” reaction models. This work showed how a catalyst of the metal oxide/metal-organic frameworks (MOFs) type could improve the pyrolysis of NC, which could serve as a significant reference for the development of additional catalysts of the metal oxide/MOFs for use in NC-based energetic materials.

Hierarchically Structured CA@ZIF-8 Biohybrids for Carbon Dioxide Mineralization.

Carbonic anhydrase (CA) is a powerful biocatalyst for carbon dioxide (CO2) mineralization, of which immobilization is usually used for maintaining its catalytic activity against harsh external stimuli. However, the incorporated materials for CA immobilization would commonly increase the internal diffusion resistance during the catalytic process, thereby decreasing the catalytic efficiency. In our study, poly-L-glutamic acid (PLGA) as the structure regulator was used to induce the synthesis of CA@zeolitic imidazolate framework-8 (CA@ZIF-8) biohybrids. The introduction of PLGA that could coordinate with Zn2+ interfered the crystallization of ZIF-8, thereby changing the morphological structure of CA@ZIF-8 biohybrids. With the increase of PLGA amount from 0 to 60mg, PLGA(x)-CA@ZIF-8 biohybrids were gradually transformed from a dodecahedron structure to a 3D lamellar nano-flower structure, which caused elevated exposed surface area. Accordingly, the loading ratio was increased from 34.6 to 49.8mg gcat-1, while the catalytic activity was elevated from 20.6 to 23.4%. The CO2 conversion rate was enhanced by nearly two folds compared to PLGA(0)-CA@ZIF-8 under the optimized condition. The final CaCO3 yield could reach 5.6mg mgcat-1, whereas the reaction system could remain above 80% of the initial reaction activity after 8 cycles.

Bimetallic zeolite imidazolium framework derived multiphase Co/HNC as pH-universal catalysts with efficient oxygen reduction performance for microbial fuel cells

Here, the metallic Co encapsulated in hierarchical porous nitrogen-doped carbon (Co/HNC) catalysts is synthesized by pyrolysis of bimetallic (Co, Zn) zeolite imidazolium framework (ZIF) precursors to facilitate oxygen reduction reaction (ORR) in microbial fuel cell (MFC). Importantly, the highly dispersed cobalt nanoparticles are completely encapsulated in the N-doped hierarchical porous carbon, with abundant metal-nitrogen active sites and high degree of graphitization, which is very favorable for the ORR process. As a result, the Co/HNC as pH-universal catalyst shows remarkable ORR properties in alkaline, acidic and neutral environments. More notably, the density functional theory (DFT) calculation demonstrates that the introduction of cobalt can reduce the ORR overpotential and improves the ORR catalytic activity. Furthermore, the assembled MFCs with Co/HNC as cathode catalysts also exhibit high power density of 1324.5 mWm−2, and an output voltage of 0.48 V. Consequently, the investigation provides a new perspective for preparing high-performance and stable electrocatalysts for MFC devices.

Preparation of F and N Co‐Doped Fe–N–C Catalyst and Evaluation of its Oxygen Reduction Performance

The problems of underdeveloped pores and high electrochemical impedance of oxygen reduction reaction (ORR) catalysts need to be urgently addressed. Heteroatoms F and N are doped on precursor Fe‐zeolitic imidazolate framework (ZIF)‐8 to increase the activity of Fe‐ZIF‐8‐derived porous carbon materials and a noble metal‐free high‐activity ORR catalyst F–N/FeNC with 3D interconnected porous structure and high conductivity is successfully prepared. Experiments show that the synergistic effect of CF ionic bonds, pyridinic‐N, pyrrolic‐N, graphitic‐N, FeNx sites, and CF semi‐ionic bonds in F–N/FeNC can improve the ORR activity of the F–N/FeNC. The developed F–N/FeNC is advantageous with excellent specific surface area, ultra‐high electrical conductivity, and extremely high ORR mass transfer efficiency. As such, the F–N/FeNC has a high onset potential of 0.95 V (vs RHE) and a half‐wave potential of 0.84 V (vs RHE), implying excellent ORR performance even better than commercially available Pt/C catalyst. In addition, the carefully prepared F–N/FeNC demonstrated higher long‐term durability and excellent resistance to methanol influence compared with commercially available Pt/C catalyst. The developed strategy provides new insights into heteroatom‐doped metal–organic frameworks as a precursor of ORR catalysts.

Construction of Ni‐Co‐Fe Hydr(oxy)oxide@Ni‐Co Layered Double Hydroxide Yolk‐Shelled Microrods for Enhanced Oxygen Evolution

The exploration of earth-abundant and efficient electrocatalysts toward the oxygen evolution reaction (OER) is critical for sustainable energy storage and conversion devices. In this work, we report a self-engaged strategy to fabricate a yolk-shelled OER electrocatalyst. Starting with a metal-organic framework, Co-Fe layered double hydroxide (LDH)@zeolitic imidazolate framework-67 (ZIF-67) yolk-shelled structures are formed in one step. Afterwards, these ZIF-67 building blocks are transformed into Ni-Co LDH nanocages to form the Ni-Co-Fe hydr(oxy)oxide@Ni-Co LDH yolk-shelled microrods (NiCoFe-HO@NiCo-LDH YSMRs) through an ion-exchange reaction. Owing to the structural and compositional merits, the NiCoFe-HO@NiCo-LDH YSMR electrocatalyst exhibits an overpotential of 278 mV to reach the current density of 10 mA cm-2 , a small Tafel slope of 49.7 mV dec-1 , and good stability in alkaline media.

Heterostructured ZnCdS@ZIF-67 as a Photocatalyst for Fluorescent Dye Degradation and Selectively Nonenzymatic Sensing of Dopamine.

Dopamine (DA) plays the role of the transmitter of information in the brain. Neurological diseases and depression are in close relationship with DA release. In this study, we developed a co-catalyst Zn0.2Cd0.8S@zeolitic imidazolate framework-67 (Zn0.2Cd0.8S@ZIF-67) to improve the photocatalyst efficacy of Rhodamine B (RhB) and electrochemical sensing of DA. Results show that Zn0.2Cd0.8S@ZIF-67 exhibits optimal photocatalytic activity with the addition of 80 mg ZIF-67. The degradation percentage of RhB by Zn0.2Cd0.8S@ZIF-67 reached 98.40% when the co-catalyst was 50 mg. Radical trapping experiments show that ·O2- played a significant role in the photocatalytic degradation of RhB. The catalytic mechanism of the Zn0.2Cd0.8S@ZIF-67 was found as a Z-type photocatalysis. Finally, a DA biosensor was constructed and displayed a high response and selectivity to DA. This can be attributed to the heterojunction between Zn0.2Cd0.8S and ZIF-67, which can significantly enhance the separation of e-/h+ and improve charge transfer. These findings will play a positive role in the in-situ monitoring of neurological diseases and depression.

Flexible Aggregation-Induced Emission-Active Hydrogel for On-Site Monitoring of Pesticide Degradation.

Benefiting from the stimuli-responsive property and powerful loading capacity, functionalized hydrogels are favorable for the fabrication of sensing devices. Herein, we design aggregation-induced emission (AIE)-active hydrogel discs by embedding gold nanoclusters@zeolite-like imidazole framework (AuNCs@ZIF) composites in double-network hydrogels to build a sensitive pesticide biosensor. The hydrogel discs integrate an AIE effect of AuNCs, a stimuli-responsive property of ZIF, and a porous network structure of the hydrogel, which enhances the sensing sensitivity via boosting the stable fluorescent signal and antifouling performance. In conjunction with a homemade device, the fluorescence images of hydrogel discs could be transduced into data information for accurate quantification of chlorpyrifos pesticide with a detection limit of 0.2 ng/mL. The dynamic degradation of chlorpyrifos in Chinese cabbage is demonstrated to confirm the practical application of hydrogel discs. Such AIE-active hydrogel discs could be a plant health sensor for the on-site quantification of pesticide residues on crops, holding great promise for precision agriculture.