Synthesis Of Zeolitic Imidazolate Frameworks Research Articles

Sustainable synthesis of MOF for COVID-19 detection using a 23 factorial design

The emergence of the COVID-19 pandemic has underscored the urgent requirement for rapid and accurate diagnostic methods to detect the virus and control its spread. Metal Organic Frameworks (MOFs) have gained significant interest in biosensing applications because of their exceptional properties. This study investigates the microwave synthesis of zeolitic imidazolate framework-8 (ZIF-8) and explores its potential as a fluorescent biosensor for detecting COVID-19 RNA sequences. The microwave method enables a rapid, eco-friendly, and efficient synthesis of ZIF-8. Characterization tests including PXRD, FE-SEM, TGA, and FT-IR confirmed the high crystallinity and thermal stability of ZIF-8. To optimize the biosensor’s performance, a 23 factorial design is pursued. The factorial design allows determining the individual and simultaneous effects of the control parameters such as ZIF-8 concentration, buffer pH, and solution temperature on the quenching efficiency. The results demonstrate that the parameters combination of 25 °C, pH 8.0, and 0.7 mg/mL ZIF-8 concentration results in the highest quenching percentage of 72.41 %. The study of the quenching mechanism confirms that the P-DNA can form electrostatic and π-π stacking interactions with ZIF-8, to produce a P-DNA@ZIF-8 complex. It is also found that photoinduced electron transfer is more dominant than fluorescence resonance energy transfer in the quenching mechanism. The biosensor showed a high sensitivity towards the target COVID-19 RNA with a very low detection limit of 12.02 pM, a fast detection time of 40 minutes, and high selectivity to the target RNA. This study shows the potential of ZIF-8 as a feasible and environmentally friendly material for swiftly and accurately detecting COVID-19 RNA sequences.

Facile synthesis of multifunctional zeolitic imidazolate framework-8 coatings on diverse bare substrates using a one-step strategy

Rational growth of metal–organic frameworks (MOFs) with controllable morphology and surface properties has been challenging. In this study, facile synthesis of zeolitic imidazolate framework-8 (ZIF-8) in solutions as well as direct in-situ growth of ZIF-8 on various untreated substrates was studied systematically. ZIF crystals with controllable morphology and size were prepared by simply adjusting the ethanol content in the co-solvent system, achieving a rational synthesis of ZIFs in controlled environments. More importantly, co-solvent content was proved to be crucial in the inter-dimensional topotactic phase transformation from a 2-dimensional ZIF-L to a three-dimensional ZIF-8. Then, the facile in-situ crystallization of ZIF-8 on a variety of untreated substrates was studied. With the use of co-solvents, ZIF-8 crystals were formed uniformly and continuously on all substrates regardless of the nature of the support material, including organic supports such as nylon membranes, 3D printed meshes, melamine sponges, mask filter layers, fabric, metallic support stainless-steel meshes, and ceramic pellet. This facile coating strategy provided controllable crystal coating morphology, size, and coating density, without surface modification/pre-treatment steps which are commonly used in the synthesis of high-quality ZIF coatings/membranes. The ZIF-8 coated substrates prepared in a co-solvent system displayed superior performance in some environmental remediation and biomedical applications. For example, the ZIF-8-coated nylon membrane achieved an impressive 96 ∼ 98 % small oil droplet removal from emulsions while maintaining a high water flux of ∼ 1200 L m−2h−1 bar−1. The superhydrophobic ZIF-8-coated melamine sponges were effective for fast oil adsorption. Last but not least, the ZIF-8-coated masks demonstrated greatly improved antibacterial activities. Overall, the co-solvent synthesis method reported in this work has enabled a one-step universal strategy for the direct growth of zeolitic imidazolate framework coating on diverse bare substrates with controlled surface properties and thus showed significant commercial potential in environmental and biological applications.

A large-area MOF-based membrane for challenging CO2 purification and ethanol/CO2/N2 ternary mixture separation

Bioethanol has garnered widespread attention as a potential substitute for traditional fossil fuels. Focusing on the treatment of bioethanol fermentation exhaust is crucial for optimizing bioethanol recovery and achieving carbon dioxide (CO2) purification. This study successfully achieved the large-scale synthesis of zeolitic imidazolate framework-8 (LSZIF-8), which was then incorporated into polydimethylsiloxane (PDMS) to fabricate large-area ZIF-8/PDMS/PVDF mixed matrix membranes (MMMs) for bioethanol recovery from fermentation exhaust via vapor permeation (VP) processes. The ZIF-8/PDMS/PVDF MMMs exhibited a 1.5-time increase in ethanol permeability and selectivity improved by 1.7 times compared to the PDMS/PVDF membrane. The mass transport behavior of ethanol and CO2 molecules within the membrane, as well as examining the interactions between different components was systematically explored. It delves into the disparities in separation performance between PDMS/PVDF membrane and ZIF-8/PDMS/PVDF MMMs with nitrogen (N2), water vapor as the third component. Notably, high-quality LSZIF-8 crystals serves as a crucial source of raw materials for the continuous preparation of high-performance MMMs, addressing the limitation of traditional nanoparticle fillers in terms of scalability for production. This study paving new avenues for purifying fermentation exhaust and recovering bioethanol, while simultaneously present significant potential for industrial applications.

Aqueous co-solvent synthesis of Zeolitic Imidazolate Frameworks: The impact of co-solvents in the crystal growth kinetics

Zeolitic Imidazolate Frameworks (ZIFs) have been widely studied in recent decades in a variety of applications. However, a fundamental understanding of crystal growth kinetics as well as their formation mechanisms has been very limited. Underpinning such mechanisms might be of key importance for the predictable synthesis of ZIFs to rationally tune the structural and morphological properties for respective applications. Herein, the crystal growth kinetics and structural evolution of ZIF-8 crystals in various aqueous co-solvent reaction environments were studied with respect to synthesis time. By tracking the nucleation, crystal growth, stabilization and ripening, three potential kinetic formation mechanisms were proposed. More specifically, with methanol, isopropanol and acetone, a fast nucleation rate and crystal growth occurred within 60 minutes (min) at room temperature. However, ethanol and n-propanol showed prolonged nucleation which resulted in the slow formation of ZIF-L/ZIF-8 mixed phases at the early stage. Phase transformation to pure ZIF-8 was observed in longer syntheses. Nitrogen-containing solvent, N, N–dimethyl formaldehyde (DMF), was found to induce both nucleation and growth, resulting in large crystals in less than 60 min of fabrication. In each case, the crystal formation follows Avrami's classical model. Hence, by understanding the effects of co-solvents in ZIF nucleation, crystallization and phase selection, one can rationally design the crystals with predictable crystallinity, size, morphology, purity and surface properties for targeted applications such as adsorption of small molecules from aqueous mixtures.

Template Role of Long Alkyl-Chain Amides in the Synthesis of Zeolitic Imidazolate Frameworks.

Organic amides as solvents and structure directing agents (SDAs) are crucial for synthesizing zeolitic imidazolate frameworks (ZIFs). However, current research focuses only on the use of short alkyl-chain amides as solvents/SDAs. Here, we investigate the role of amides with varying alkyl-chain lengths on the structures and topologies of Zn(Im)2 polymorphs. Using short alkyl-chain amides as solvents, the Zn(Im)2 topological structures are affected by the synthesis conditions, leading to "one SDA/multiple topological structures". In contrast, when long alkyl-chain amides are used as solvents, the Zn(Im)2 topological structures are essentially unaffected by other synthesis conditions. Thus, long alkyl-chain amides are shown for the first time to exhibit a significant template role, leading to "one template/one topological structure". Specifically, the use of long alkyl-chain N,N-dimethyl-Cn amides (abbreviated as DM-Cn amides, n = 3, 4, 6, 8, and 10) can lead to only DTF-type Zn(Im)2 frameworks under broad crystallization conditions. Single-crystal X-ray diffraction confirmed that the exquisite structural compatibility between long alkyl-chain DM-Cn amides and the DFT-type Zn(Im)2 framework results in a highly regular head-to-tail arrangement of amides along the (kaa-lov) n chain of the DFT framework. The template role for long alkyl-chain amides was further identified to be multiple C-H···π interactions between DM-Cn amides and Zn(Im)2 frameworks thanks to molecular simulations.

Fabrication of Zeolitic imidazolate framework-8 (ZIF-8) modified screen-printed electrode and its catalytic role for the electrochemical determination of biological molecule (dopamine)

Herein, we reported the simple room temperature synthesis of zeolitic imidazolate framework-8 (ZIF-8). The crystallinity and phase of the synthesized ZIF-8 was confirmed by employing powder X-ray Diffraction (PXRD) method. Field emission scanning electron microscopy (FE-SEM) results showed that synthesized ZIF-8 has rhombic dodecahedral structure. The energy-dispersive X-ray spectroscopic (EDX) and photoelectron X-ray spectroscopic (XPS) analysis showed the presence of good phase purity of the synthesized ZIF-8. The screen printed carbon electrode (SPE) has been modified using ZIF-8 as catalyst for the detection of dopamine (DA). The ZIF-8@SPE demonstrated good electrochemical performance for the sensing of DA using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The ZIF-8@SPE exhibits decent limit of detection (LOD), linear range, and sensitivity of 0.087 µM, 2–50 µM, and 4.78 µA/µM.cm2, respectively. The ZIF-8@SPE also demonstrated good reproducibility, repeatability of 50 cycles and storage stability of 30 days with insignificant change in the performance. The ZIF-8@SPE exhibited decent selectivity for the sensing of DA in presence of various interfering molecules/compounds.We believe that the present work would be beneficial for the scientific scholars working on the development of DA sensors for practical applications.

나노 크기의 금속 유기 골격체, ZIF-8 합성을 위한 이온성 액체 마이크로에멀젼 합성법의 체계적 연구

Porous Metal-Organic Frameworks (MOFs) are composed of metal ions and organic ligands. Recently, nano-sized MOFs have been widely utilized in biomedical fields, including biosensing and drug delivery. Researchers are primarily focusing on reducing their particle sizes to the nanoscale with a uniform size distribution. An ionic liquid microemulsion, the one of the MOF synthesis mehtods is in the limelight as an effective way with the following advantages: grain size uniformity and eco-friendliness. In this work, systematic study to control grain size, morphology, and yield of ZIF-8 (Zeolitic Imidazolate Framework-8) through ionic liquid microemulsion method was conducted in the new systems ‘water / surfactant (TX-100 or AOT) / CnmimX (n, the number of carbon = 2, 3, 4, 6, 8, 10 / X = Cl, Br, I)’. Furthermore, not only how the type of anion of ionic liquids, the length of carbon chain in them, the type of surfactants and the mass ratio change of the components affect the ZIF-8 synthesis results, respectively, was analyzed quantitatively through several characterization methods such as PXRD, TEM, DLS and FT-IR. Through this study, we aim to shed light on the infinite possibility of ionic liquid microemulsion method to synthesize desired size of nano-size MOF with uniformity.

Fabrication of hydrophobic drug-loaded Zeolitic Imidazolate Framework-8 (ZIF-8) for enhanced anti-bacterial activity

Current study presents a novel approach for constructing small hydrophobic biomolecules embedded within zeolitic imidazolate framework-8 (ZIF-8) with exceptional antibacterial properties. In this method, ZIF-8 is synthesized from zinc acetate and 2-methylimidazole in the presence or absence of small hydrophobic bioactive molecules like rutin, rosmarinic acid, and morin. Scanning electron microscopy (SEM) analysis reveals that the synthesized ZIF-8 nanoparticles exhibit mostly hexagonal shape with size 200 nm which is further increased upon drug encapsulation. The synthesis of ZIF-8 and drug-loaded ZIF-8 is confirmed through FTIR, UV–vis spectroscopy, XRD, TGA, and EDX analyses. Zeta potential measurements show values ranging from -14.5 to -23.97 mV for both ZIF-8 and drug-loaded ZIF-8 nanoparticles. The drug loading content is determined to be 5 %, 9 %, and 16 % for morin, rutin, and rosmarinic acid, respectively. All the drug-loaded ZIF-8 formulations exhibit a pH-dependent drug release pattern, with maximal drug release observed at lower pH levels. Most importantly, these formulations demonstrate potent antibacterial activity against both Gram-positive (Enterococcus faecalis and Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial strains. Specifically, ZIF-8/RUT exhibit maximum zone of inhibition (ZOI ∼ 51 mm) against all tested bacterial strains. ZIF-8/MOR and ZIF-8/RUT exhibit MIC values ranging from 2.0 to 3.0 mg/mL and MBC values from 6 to 9 mg/mL against all the tested bacteria. Among the formulations, ZIF-8/MOR and ZIF-8/RUT exhibit synergistic antibacterial effect, whereas ZIF-8/RMA possess less antibacterial potency against all the tested bacteria and mostly exhibit additive effect. Our findings suggest that these newly developed nano-formulations hold potential for the creation of highly effective antibacterial agents.

Tribological Performance and Enhancing Mechanism of 3D Printed PEEK Coated with In Situ ZIF-8 Nanomaterial.

Polyether ether ketone (PEEK) is esteemed as a high-performance engineering polymer renowned for its exceptional mechanical properties and thermal stability. Nonetheless, the majority of polymer-based lubricating materials fail to meet the contemporary industrial demands for motion components regarding high speed, heavy loading, temperature resistance, and precise control. Utilizing 3D printing technology to design and fabricate intricately structured components, developing high-performance polymer self-lubricating materials becomes imperative to fulfill the stringent operational requirements of motion mechanisms. This study introduces a novel approach employing 3D printing technology to produce PEEK with varying filling densities and conducting in situ synthesis of zeolitic imidazolate framework (ZIF-8) nanomaterials on its surface to enhance PEEK's frictional performance. The research discusses the synthetic methodology, characterization techniques, and tribological performance evaluation of in situ synthesized ZIF-8 nanomaterials on PEEK surfaces. The findings demonstrate a significant enhancement in frictional performance of the composite material under low-load conditions, achieving a minimum wear rate of 4.68 × 10-6 mm3/N·m compared to the non-grafted PEEK material's wear rate of 1.091 × 10-5 mm3/N·m, an approximately 1.3 times improvement. Detailed characterization and analysis of the worn surface of the steel ring unveil the lubrication mechanism of the ZIF-8 nanoparticles, thereby presenting new prospects for the diversified applications of PEEK.

Organic-inorganic hybrid ZIF-8/MXene/cellulose-based textiles with improved antibacterial and electromagnetic interference shielding performance

Despite the tremendous efforts on developing antibacterial wearable textile materials containing Ti3C2Tx MXene, the singular antimicrobial mechanism, poor antibacterial durability, and oxidation susceptibility of MXene limits their applications. In this context, flexible multifunctional cellulosic textiles were prepared via layer-by-layer assembly of MXene and the in-situ synthesis of zeolitic imidazolate framework-8 (ZIF-8). Specifically, the introduction of highly conductive MXene enhanced the interface interactions between the ZIF-8 layer and cellulose fibers, endowing the green-based materials with outstanding synergistic photothermal/photodynamic therapy (PTT/PDT) activity and adjustable electromagnetic interference (EMI) shielding performance. In-situ polymerization formed a MXene/ZIF-8 bilayer structure, promoting the generation of reactive oxygen species (ROS) while protecting MXene from oxidation. The as-prepared smart textile exhibited excellent bactericidal efficacy of >99.99 % against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) after 5 min of NIR (300 mW cm−2) irradiation which is below the maximum permissible exposure (MPE) limit. The sustained released Zn2+ from the ZIF-8 layer achieved a bactericidal efficiency of over 99.99 % within 48 h without NIR light. Furthermore, this smart textile also demonstrated remarkable EMI shielding efficiency (47.7 dB). Clearly, this study provides an elaborate strategy for designing and constructing multifunctional cellulose-based materials for a variety of applications.

Innovative Synthesis of Zeolitic Imidazolate Framework by a Stovetop Kitchen Pressure Cook Pot for Triboelectric Nanogenerator

This study presents a novel approach utilizing solvothermal techniques to synthesize zeolitic imidazolate framework (ZIF‐4) particles. Various properties of the ZIF‐4 particles are investigated to shed light on the structural and morphological characteristics. These ZIF‐4 particles act as a positive triboelectric layer in the fabrication of a triboelectric nanogenerator (TENG) designed for powering electronic devices. The solvothermal‐assisted synthesis ensures the controlled and efficient production of ZIF‐4, optimizing its characteristics for enhanced performance in the TENG. The generated TENG, based on ZIF‐4 particles, determines promising capabilities in converting mechanical energy into electrical power. The highest power of TENG is obtained to be 18 μW at a load resistance of 50 MΩ. This work contributes major insights to the search for sustainable and effective power solutions for electronic gadgets. It emphasizes the potential of ZIF‐4 as a crucial triboelectric material, demonstrating its importance in the advancement of TENGs.

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.

Green conversion of waste alkaline battery material to zeolitic imidazolate framework-8 and its iodine capture mechanism

Zeolitic imidazolate framework-8 (ZIF-8) exhibits excellent performance in capturing iodine. However, the solvent-based procedures and raw materials for ZIF-8 synthesis often lead to secondary pollution. We developed a solvent-minimizing method for preparing ZIF-8 via ball milling of raw material obtained from spent alkaline batteries, and studied its iodine-capture performance and structural changes. Exposure of the ZIF-8 to iodine vapor for 60 min demonstrated that it exhibited industrially competitive iodine-capture performance (the adsorbed amount reaches to 1123 mg g−1 within 60 min). Spectroscopic studies showed that ZIF-8 underwent a structural transformation upon iodine loading. Iodine molecules were adsorbed onto the surface of ZIF-8 and also formed C–I bond with the methyl groups on the imidazole rings, reducing iodine release. This work represents a comprehensive revelation of long-range order and short-range order evolution of ZIF-8 during iodine vapor adsorption over time. Moreover, this green synthesis of ZIF-8 is of lower cost and generates fewer harmful by-products than existing methods, and the produced ZIF-8 effectively entraps toxic iodine vapor. Thus, this synthesis enables a sustainable and circular material flow for beneficial utilization of waste materials.

Sustainable Synthesis of Zeolitic Imidazolate Frameworks at Room Temperature in Water with Exact Zn/Linker Stoichiometry.

Zeolitic imidazolate frameworks (ZIFs) are widely used MOFs because of certain characteristics, but also because they can be prepared at room temperature using water as the unique solvent. However, these a priori sustainable conditions inevitably entail a huge and somehow unusable excess of linker. Here, we present the formation of ZIFs at room temperature in water, starting from mixtures with a linker/metal ratio of two, that is, coinciding with the stoichiometry found in the final MOFs, in the presence of amines. ZIF-8 can be prepared with triethylamine (TEA), giving a yield of Zn of 96.6%. Other bases, like NaOH, tetraethylammonium hydroxide or ammonium hydroxide, do not lead to ZIF-8 under the same conditions. The so-obtained ZIF-8 contains TEA inside its cavities, making it less porous than its conventionally prepared counterparts. Amine can be removed by mild thermal treatments (200-250 °C). Such thermal treatments induce the generation of g-C3N4-like species which could give added value to these materials as potential photocatalysts, increasing their affinity to CO2, as proved in this work. This methodology can be successfully extended to other amines, like N,N-dicyclohexylmethylamine, as well as to other prepared ZIFs, like Co-based ZIF-67, isostructural to ZIF-8.

Synthesis of zeolitic imidazolate framework-8 using an electric field in a gelled medium

A direct electric field can be used to control the synthesis of the metal–organic framework in a gelled medium. The average size and dispersity of the crystals can be directed by the electric field strength.

Controlled synthesis of metal-organic frameworks via AC electrokinetic mixing-assisted microfluidics: A case study of ZIF-8

Metal-organic frameworks (MOFs) have great potential for a wide range of applications given their flexible structures and pore networks. Morphology control directly affects the properties and applications of MOFs. Unfortunately, governing the desired dimension and shape of MOFs is often limited by macrosystems that require organic solvents and additives while including time-consuming treatments. Microfluidics as a practical alternative provides precise manipulation of microscale liquid, has the potential to be a superior platform for directed crystal generation. Here we reported an AC electrokinetic (EK) mixing-assisted micro-synthesis method, which allowed the actively controlled synthesis of MOFs in aqueous phase. The effects of flow rate, molar-ratio of precursors, electric field intensity, and frequency on the synthesis of zeolitic imidazolate framework-8 (ZIF-8) were investigated. Using this method, the particle size of ZIF-8 were varied, and the geometry were changed between flower-like polyhedra, cubes, spheres, and rhombic dodecahedra. Furthermore, the synthesized various ZIF-8 provide different levels of immobilization sites based on their morphological deviations. The flower-like cubic ZIF-8 had defect structures and exhibited a maximum horseradish peroxidase (HRP) loading of about 16%. The study provides a simple, green and reliable tuning strategy for breaking the single morphological form of MOFs to enhance their physicochemical properties.

Synthesis, characterization, and application of ZIF-8 for removal of Cd, Ni, and Pb ions from aqueous solutions: Optimization of the process by Response Surface Methodology (RSM) based on Central Composite Design (CCD) technique

A Zeolitic imidazolate framework-8 (ZIF-8) was synthesized by the solvothermal method of zinc nitrate hexahydrate and 2-methylimidazole in DMF to remove Cd(II), Ni(II), and Pb(II) ions from aqueous solutions. The synthesized ZIF-8 was distinguished by XRD, FT-IR, BET, SEM, EDX, TEM methods. Several significant variables were optimized with response surface methodology (RSM) to obtain the highest removal of metal ions. According to the achieved results, the aqueous solution pH values of 6.5, 6.5, and 6.0, ZIF-8 dosages of 0.05, 0.06, and 0.05 g⸳L-1, and metal ions initial concentrations of 50, 60, and 60 mg⸳L-1 were chosen as the optimum amount of these variables for Cd(II), Ni(II), and Pb(II) ions adsorption from solution, respectively. The equilibrium time for metal ions adsorption was found at 50 min. Three-dimensional plots demonstrate relationships between the metal ion uptakes with the paired factors, which illustrate the behavior of the sorption system in a batch process. Based on the experimental results and model parameters, maximum adsorption efficiencies were achieved 89.76, 72 and 68.43% for Cd(II), Ni(II) and Pb(II), respectively. It can be suggested that the synthetized ZIF-8 has excellent potential as an effective adsorbent and used for heavy metal sorption from water environment.

Optimizing the Green Synthesis of ZIF-8 by Reactive Extrusion Using In Situ Raman Spectroscopy

We report the scale-up of a batch solid synthesis of zeolitic imidazolate framework-8 (ZIF-8) for reactive extrusion. The crystalline product forms in the extruder directly under the mixture of solid 2-methylimidazole and basic zinc carbonate in the presence of a catalytic amount of liquid. The process parameters such as temperature, liquid type, feeding rate, and linker excess were optimized using the setup specifically designed for in situ Raman spectroscopy. Highly crystalline ZIF-8 with a Brunauer–Emmett–Teller (BET) surface area of 1816 m2 g–1 was quantitatively prepared at mild temperature using a catalytic amount of ethanol and a small excess of the linker. Finally, we developed a simple and comprehensive approach to evaluating the environmental friendliness and scalability of metal–organic framework (MOF) syntheses in view of their large-scale production.

A novel core-shell structured Fe@CeO2-ZIF-8 catalyst for the reduction of NO by CO

Zeolitic imidazolate framework-8 (ZIF-8) based catalysts are considered as promising candidates for the selective catalytic reduction of NO by CO (CO-SCR) reaction due to their large specific surface area. However, the structure of ZIF-8 will be damaged during the synthesis procedure of the catalyst, leading to a decrease in their physical properties, which in turn affects the catalytic performance of the catalyst. Herein, a CeO2-ZIF-8 core-shell structure was synthesized and doped with Fe, resulting in the formation of Fe@CeO2-ZIF-8, for CO-SCR reaction. Characterization results show that the Fe@CeO2-ZIF-8 core-shell catalyst has better morphology, thermal stability, and higher specific surface area than the FeCe co-impregnated ZIF-8 catalyst (FeCe@ZIF-8 (IM)). Moreover, the reducibility of the reactive Fe species in the Fe@CeO2-ZIF-8 core-shell catalyst is also enhanced. As a result, the Fe@CeO2-ZIF-8 core-shell catalyst exhibited higher low-temperature CO-SCR catalytic activity with its NO conversion reaching 99% at 250 °C versus the FeCe@ZIF-8 (IM) catalyst (89% at 250 °C). The experimental results were further verified by density functional theory (DFT) calculations including Electron Localization Function (ELF), Valence Charge Density Difference (VCDD), Projected Density of States (PDOS) and Bader charge analyses. The calculation results revealed that the core-shell configured Fe@CeO2-ZIF-8 catalyst has a stronger active metal-support charge transfer and better capacity for the adsorption of the reactants. The reaction mechanism over Fe@CeO2-ZIF-8 core-shell catalyst was investigated via in situ DRIFTS experiments, and results showed that the nitro compounds and formate species are critical intermediates in this reaction at a higher temperature range (300–350 °C). This work provides a new strategy for the synthesis of ZIF-8 based catalysts with better properties for CO-SCR reaction.

Sustainable Synthesis of Zeolitic Imidazolate Framework-8 Nanoparticles and Application in the Adsorption of the Drug Chlorhexidine

In an attempt to synthesize nanomaterial concerning chemistry, the sustainable synthesis of Zeolitic Imidazolate Framework-8 (ZIF-8) nanoparticles by a low-cost approach through the recycling of waste mother liquors was explored and then indicated the potential to remove chlorhexidine (CHLX) from an aqueous solution. ZIF-8 was produced under solvothermal reaction at 25°C and characterized by Fourier Transform Infrared Spectroscopy, X-ray diffraction, adsorption/desorption of N<sub>2</sub>, dynamic light scattering and contact angle. The water Chemical stability test was conducted using ZIF-8 and it was immersed in pure water for 24 h at room temperature. Batch-type adsorption was used to check the potential of ZIF-8 (first and second generation) for the adsorption of the chlorhexidine with initial chlorhexidine concentration (0.05, 0.06 and 0.07 mol/L), agitation time (1, 3.5 and 6 h) and the mass of nano-adosrbent (0.04, 0.05 and 0.06 g). Process optimization was performed through a Factorial experimental design. The optimum conditions were selected for the nano-adsorbent mass of 0.04 g, agitation time of 1 h and initial chlorhexidine concentration 0.07 mmol/L. The ZIF-8 sustainable synthesis was efficient and generated a crystalline nanomaterial. The result shows that ZIF-8 is stable in water under ambient conditions. The ZIF-8 first generation and ZIF-8 second generation exhibit a high adsorption capacity (27.17 mg/g and 30.96 mg/g). It was found that, under the synthesis conditions, the recycled mother liquor user did not affect the final characteristics of this nanomaterial. The results indicated that the initial concentration of chlorhexidine and nano-adsorbent mass influenced the adsorption capacity. Experimental design provided the process optimum conditions (1 h, 0.04 g of adsorbent mass and 0.07 mmol/L).