Pristine ZIF-8 Research Articles

Boosting CO2 selectivity by mono- and dicarboxylate-based ionic liquids impregnation into ZIF-8 for post-combustion separation

Post-combustion carbon dioxide (CO2) capture/separation is considered one of the main ways to minimize the impact of global warming caused by this greenhouse gas. This work used eight mono- and dicarboxylate-based ionic liquids (ILs) to impregnate metal-organic framework (MOF) ZIF-8. This anionic effect was studied for these mostly unreported IL@MOF composites to determine its impact on gas sorption and selectivity performance. Characterization results confirmed IL impregnation into the structure of ZIF-8, along with the conservation of microporosity and crystallinity in composites. Sorption-desorption equilibrium measurements were performed, and CO2 and nitrogen (N2) isotherms were obtained at 303 K for ZIF-8 and IL@ZIF-8 composites. At 0.15 bar, the dicarboxylate-based composite [C2MIM]2[Glu]@ZIF-8 showed the highest CO2 gas sorption, showing 50 % more sorption capacity than the best monocarboxylate-base composites at this pressure. Dicarboxylate-based composites also showed remarkable N2 sorption in the low-pressure range. The ideal CO2/N2 selectivity for a typical post-combustion composition was calculated, and a trend regarding the anionic carbon chain size was observed. The composite [C2MIM][Cap]@ZIF-8 showed nearly five times more selectivity than the pristine ZIF-8 at 1 bar of total pressure. Dicarboxylate-based composites, given their low-pressure high N2 sorption capacity, were not as selective as their respective monocarboxylate-based IL@ZIF-8 materials with the same carbon chain size.

Advancements in renewable energy: Achieving milder reaction conditions in biodiesel synthesis from green seed canola oil with pristine ZIF-8

This study explores the enhancement of reaction conditions for biodiesel production from green seed canola oil through the methanolysis reaction using pristine ZIF-8 as a catalyst. The research focused on the effects of varying the methanol-to-oil molar ratio, temperature, and reaction time as well as their combined effects on biodiesel yield. To analyze these factors, Response Surface Methodology (RSM) paired with Central Composite Design (CCD) was employed. The quadratic model was identified as the best fit for the experimental data, evidenced by a high determination coefficient (R²) of 0.99, with all model parameters proving significant. A comprehensive characterization of the catalyst was conducted using various techniques. The surface and pore properties were examined using N2 adsorption-desorption measurements. X-ray diffractometry (XRD) was employed for structural analysis, while X-ray photoelectron spectroscopy (XPS) presented the binding information of the sample. Fourier transform infrared spectroscopy (FT-IR) provided insights into the functional groups present. Thermal gravimetric analysis (TGA) assessed the thermal stability of the catalyst. Results revealed that ZIF-8 significantly improved biodiesel production, with optimal conditions identified at a reaction temperature of 160 °C, a duration of 2.5 h, and methanol to oil (M/O) molar ratio of 26, resulting in a biodiesel yield of 85 %. This yield is close to the predicted value, demonstrating the reliability of the developed model. The kinetic analysis was performed under optimal reaction conditions. From this, the activation energy (Ea) and the pre-exponential factor (A) were obtained to be 14.5 kJ/mol and 3.4×10−7 min−1, respectively. The use of pristine ZIF-8 in biodiesel production from a low-quality and cheap oil offers a more efficient and milder reaction conditions, with potential for significant reductions in production costs and environmental impact.

Investigating the Structure of Defects in Heterometallic Zeolitic Imidazolate Frameworks ZIF-8(Zn/Cd) and Its Interaction with CO2 Using First-Principle Calculations

Inducing defect in metal-organic frameworks (MOFs) is one of the strategies to modify the structure and properties of this functional material. Defect may occur in a pristine MOF due to missing organic linkers, metal centres and/or other structural behaviours. In this study, the structure of defects in multicomponent MOFs especially heterometallic MOFs of zeolitic imidazolate framework (ZIF-8(Zn/Cd)) was examined to unveil the possible preference defect formation due to missing 2-methylimidazolate (MeIm) and metal centres of Cd2+ and Zn2+. Assuming defect formation due to the reaction between ZIF-8(Zn/Cd) and water, MeIm linker removal is energetically lower than removing metal centres of either Cd2+ or Zn2+. But, the MeIm linker is easier to be removed when it is connected to Cd2+ (Cd-MeIm-Cd) than when it is connected to Zn2+ (Zn-MeIm-Zn). Defect in ZIF-8(Zn/Cd) affects the band gap energy to give slightly lower value than it in pristine ZIF-8(Zn/Cd). Non-covalent interaction (NCI) and interaction region indicator (IRI) analyses were also performed to indicate possible intermolecular forces such as van der Waals and attractive forces present in non-defective and defective ZIF-8(Zn/Cd). The presence of defects in mixed-metal ZIF-8(Zn/Cd) was also tested for its potential use on CO2 adsorption. The interaction energy of CO2 inside defective ZIF-8(Zn/Cd) indicates an exothermic behaviour where CO2 molecule has a preference to be adsorbed inside the framework. This is especially when the capping agents at the defective ZIF-8(Zn/Cd) sites are removed to give open metal sites. This study provides insight how defects in multicomponent MOFs might presence affecting the structural and properties changes. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Efficient Low-Pressure CO2 capture via ZIF-8 modified by deep eutectic solvents

To enhance CO2 sorption efficiency under low-pressure conditions and effectively compete with N2 sorption in flue gas, modifications are implemented aimed at improving the adsorption capacity and selectivity of ZIF-8, renowned for their robust stability. Deep eutectic solvent (DES) comprising tetraethylammonium chloride (TEAC), tetrapropylammonium chloride (TPAC), and tetrabutylammonium bromide (TBAB) as hydrogen-bond acceptors, along with ethanolamine (MEA) as the hydrogen-bond donor, were meticulously prepared for this purpose. ZIF-8 underwent modification through DES loading, resulting in the distinctive emergence of a “core-membrane” structure. Characterization revealed that the DES effectively adhered to the surface of ZIF-8 in a membrane-like structure, without altering the chemical structure or pore size of ZIF-8. The most significant enhancement in sorption capacity was observed with TPAC&MEA modification. Considering the presence of N2 partial pressure in the flue gas, at 0.05 and 1 bar, the CO2 adsorption capacities reached 1.92 and 3.03 mmol g−1, respectively, increasing 71.11 and 4.00 times compared to pristine ZIF-8. The ZIF-8 exhibited a CO2/N2 separation coefficient of 72.77, which increased to a maximum of 997.50 after DES modification. Additionally, the modified material demonstrated exceptional cyclic and thermal stability during testing. This study significantly elevates the CO2 adsorption capacity and selectivity of solid materials within the low-pressure range, providing pivotal support for CO2 capture and decarbonization efforts.

Synthesis of magnetic layered double hydroxide (Fe3O4@CuCr-LDH) decorated with ZIF-8 for efficient sonocatalytic degradation of tetracycline

A series of Fe3O4@CuCr-LDH hybrids decorated with different amount of ZIF-8 (FLZ, 10–40 wt%) was prepared using simple methods and characterized with different techniques. The activity of the synthesized nanocomposites was investigated in the sonocatalytic degradation of tetracycline (TC) antibiotic from wastewater. When the content of ZIF-8 in the nanocomposite structure was 20 wt%, the FLZ-20 sonocatalyst exhibited the high performance in the sonocatalytic removal of TC. At optimum conditions (0.7 g/L catalyst dosage, pH of 7, 50 mg/L initial concentration of antibiotic, and 15 min sonication time) of the sonocatalytic removal of TC approached to 91.4% under ultrasonic irradiation (USI) using FLZ-20. This efficiency was much higher than those of obtained results by Fe3O4@CuCr-LDH and pristine ZIF-8. The formed ●OH and ●O2− exhibited the major roles in the sonocatalytic TC degradation process. The excellent performance of FLZ-20 can be attributed to the heterojunctions created between composite components, which could improve the electron transfer ability and effectively separate e−/h+ pairs. In addition, FLZ-20 showed the superior reusability and stability during three successive recycling. Moreover, the facile magnetically separation of the sonocatalyst from the aqueous solution was another outstanding feature, which prevents the formation of secondary pollutants. It can be concluded that the fabrication of heterojunctions is an efficient procedure to promote the sonocatalytic acting of the catalyst.

ZIF-8@Hydroxyapatite Composite as a High Potential Material for Prolonged Delivery of Agrochemicals.

Although agrochemical practices can enhance agricultural productivity, their intensive application has resulted in the deterioration of ecosystems. Therefore, it is necessary to develop more efficient and less toxic methods against pests and infections while improving crop productivity. Moving toward sustainable development, in this work, we originally described the preparation of a composite (ZIF-8@HA) consisting of the coating of zeolitic-like metal-organic framework (MOF) ZIF-8 (based on Zn, an essential micronutrient in plants with antibacterial, antifungal, and antifouling properties) with hydroxyapatite (HA) nanoparticles (i.e., nanofertilizer). The interaction between the HA and ZIF-8 has been characterized through a combination of techniques, such as microscopic techniques, where the presence of a HA coating is demonstrated; or by analysis of the surface charge with a dramatic change in the Z-potential (from +18.7 ± 0.8 to -27.6 ± 0.7 mV for ZIF-8 and ZIF-8@HA, respectively). Interestingly, the interaction of HA with ZIF-8 delays the MOF degradation (from 4 h for pristine ZIF-8 to 168 h for HA-coated material), providing a slower and gradual release of zinc. After a comprehensive characterization, the potential combined fertilizer and bactericidal effect of ZIF-8@HA was investigated in wheat (Triticum aestivum) seeds and Pseudomonas syringae (Ps). ZIF-8@HA (7.3 ppm) demonstrated a great fertilizer effect, increasing shoot (9.4 %) and root length (27.1 %) of wheat seeds after 11 days at 25 °C under dark conditions, improving the results obtained with HA, ZIF-8, or ZnSO4 or even physically mixed constituents (HA + ZIF-8). It was also effective in the growth inhibition (>80 % of growth inhibition) of Ps, a vegetal pathogen causing considerable crop decline. Therefore, this work demonstrates the potential of MOF@HA composites and paves the way as a promising agrochemical with improved fertilizer and antibacterial properties.

Efficient Selective Carbon Dioxide Separation via Task-Specific Ionic Liquids Incorporated in ZIF-8.

Owing to the rapid increase in anthropogenic emission of carbon dioxide (CO2) in the atmosphere, which has resulted in a number of global climate challenges, a decrease in CO2 emissions is urgently needed in the current scenario. This study focuses on the development and characterization of composites for carbon dioxide (CO2) separation. The composites consist of two task-specific ionic liquids (TSILs), namely, tetramethylgunidinium imidazole [TMGHIM] and tetramethylgunidinium phenol [TMGHPhO], impregnated in ZIF-8. The performance of CO2 separation, including sorption capacity and selectivity, was evaluated for pristine ZIF-8 and composites of TMGHIM@ZIF-8 and TMGHPhO@ZIF-8. To demonstrate the thermal stability of the material, thermogravimetric analysis (TGA) was performed. Additionally, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to showcase the crystal structures and morphology. Fourier transform infrared spectroscopy (FTIR) and BET were also utilized to confirm the successful incorporation of TSILs into ZIF-8. The composite synthesized with TMGHIM@ZIF-8 demonstrated superior CO2 sorption performance as compared with TMGHPhO@ZIF-8. This is attributed to its strong attraction toward CO2, resulting in a higher CO2/CH4 selectivity of 110 while pristine MOFs showed 12 that is 9 times higher than that of the pristine ZIF-8. These TSILs@ZIF-8 composites have significant potential in designing sorbent materials for efficient acid gas separation applications.

Synthesis of bimetallic Mn@ZIF–8 nanostructure for the adsorption removal of methyl orange dye from water

In this research, manganese-based Mn@ZIF-8 nanocomposite was prepared using solvothermal strategy. The resultant Mn@ZIF-8 nanostructure was assessed for the adsorption of methyl orange (MO) dye from water. The pristine ZIF-8 and Mn@ZIF-8 nanocomposite have demonstrated a rhombic dodecahedral morphology having a reasonable microporous structure. Besides, they have also displayed an outstanding specific surface area and porosity. The impact of contact time, concentration and variation in pH were analyzed in detail for the investigation of adsorption capacity. From the interpretation of the adsorption isotherms, it has been discovered that adsorption of MO over Mn@ZIF-8 follows the monolayer mechanism (Langmuir isotherm). Remarkable maximum adsorption capacity (qmax, 406 mg.g−1) has been recorded for the Mn@ZIF-8 which is sufficiently high as compared to pristine ZIF-8. The kinetic study explored that experimental data best fitted to the pseudo second order kinetics with relatively high R2 values (0.997) of Mn@ZIF-8. Thermodynamic study reconnoitered the adsorption process is spontaneous in nature. The synthesized Mn@ZIF-8 material also displays exceptional reusability capability of up to 92 % at 4th cycle compared to 1st cycle. Overall, the Mn@ZIF-8 could be a good contestant for the treatment of MO containing wastewater of industries.

Unveiling the mechanisms behind high CO2 adsorption by the selection of suitable ionic liquids incorporated into a ZIF-8 metal organic framework: A computational approach

There is growing focus on the crucial task of effectively capturing carbon dioxide (CO2) from the atmosphere to mitigate environmental consequences. Metal-organic frameworks (MOFs) have been used to replace many conventional materials in gas separation, and the incorporation of ionic liquids (ILs) into porous MOFs has shown promise as a new technique for improving CO2 capture and separation. However, the driving force underlying the electronic modulation of MOF nanostructures and the mechanisms behind their high CO2 adsorption remain unclear. This study reports the effect of encapsulating different imidazolium ILs in porous ZIF-8, to clarify the adsorption mechanism of CO2 using density functional theory (DFT)-based approaches. For this purpose, a range of anions, including bis(trifluoromethylsulfonyl)imide [NTf2], methanesulfonate [MeSO3], and acetate [AC], were combined with the 1-ethyl-3-methylimidazolium [EMIM]+ cation. [EMIM]+-based ILs@ZIF-8 composites were computationally investigated to identify suitable materials for CO2 capture. First, the intermolecular and intramolecular interactions between [EMIM]+ and different anions were examined in detail, and their effects on CO2 adsorption were explored. Subsequently, the integration of these ILs into the ZIF-8 solid structure was studied to reveal how their interactions influenced the CO2 adsorption behavior. Our results demonstrate that the incorporation of ILs strongly affects the adsorption capability of CO2, which is highly dependent on the nature of the ILs inside the ZIF-8 framework. DFT simulations further confirmed that the incorporation of ILs into ZIF-8 led to superior CO2 capture compared to isolated ILs and pristine ZIF-8. This improvement was attributed to the mutual interactions between the ILs and ZIF-8, which effectively fine-tuned CO2 adsorption within the composite structure. This understanding may act as a general guide for gaining more insight into the interfacial interactions between ILs and ZIFs structures and how these molecular-level interactions can help predict the selection of ILs for CO2 adsorption and separation, thereby addressing environmental challenges with greater precision and effectiveness.

Synthesis of Metal-Organic Framework-Based ZIF-8@ZIF-67 Nanocomposites for Antibiotic Decomposition and Antibacterial Activities.

Toxic antibiotic effluents and antibiotic-resistant bacteria constitute a threat to global health. So, scientists are investigating high-performance materials for antibiotic decomposition and antibacterial activities. In this novel research work, we have successfully designed ZIF-8@ZIF-67 nanocomposites via sol-gel and solvothermal approaches. The ZIF-8@ZIF-67 nanocomposite is characterized by various techniques that exhibit superior surface area enhancement, charge separation, and high light absorption performance. Yet, ZIF-8 has high adsorption rates and active sites, while ZIF-67 has larger pore volume and efficient adsorption and reaction capabilities, demonstrating that the ZIF-8@ZIF-67 nanocomposite outperforms pristine ZIF-8 and ZIF-67. Compared with pristine ZIF-8 and ZIF-67, the most active 6ZIF-67@ZIF-8 nanocomposite showed higher decomposition efficacy for ciprofloxacin (65%), levofloxacin (54%), and ofloxacin (48%). Scavenger experiments confirmed that •OH, •O2-, and h+ are the most active species for the decomposition of ciprofloxacin (CIP), levofloxacin (LF), and ofloxacin (OFX), respectively. In addition, the 6ZIF-67/ZIF-8 nanocomposite suggested its potential applications in Escherichia coli for growth inhibition zone, antibacterial activity, and decreased viability. Moreover, the stability test and decomposition pathway of CIP, LF, and OFX were also proposed. Finally, our study aims to enhance the efficiency and stability of ZIF-8@ZIF-67 nanocomposite and potentially enable its applications in antibiotic decomposition, antibacterial activities, and environmental remediation.

Fabrication of larger surface area of ZIF8@ZIF67 reverse core-shell nanostructures for energy storage applications

The construction of uniform nanostructure with larger surface area electrodes is a huge challenge for the high-value added energy storage application. Herein, we demonstrates ZIF67@ZIF8 (core-shell) and ZIF8@ZIF67 (reverse core-shell) nanostructures using a low-cost wet chemical route and used them as supercapacitors. Pristine ZIF-67 and ZIF-8 was used as reference electrodes. Benefiting from the synergistic effect between the ZIF8 and ZIF67, the ZIF8@ZIF67 exhibited the outstanding electrochemical consequences owing to its larger surface area with uniform hexagonal morphology. As optimized ZIF8@ZIF67 nanostructure displayed the high-capacity of 1521 F/g at 1 A/g of current density in a three-electrode assembly in 1 M KOH electrolyte compared with other as-fabricated electrodes. In addition, the ZIF8@ZIF67 nanostructure employed into the symmetric supercapacitors (SSCs) with 1 M KOH electrolyte in two-electrode setup and it exhibited still superior output including capacity (249.8 F/g at 1 A/g), remarkable repeatability (87 % over 10,000 GCD cycles) along with high energy and power density (61.2 Wh/kg & 1260 W/kg). The present study uncovers the relationship between the larger surface area and electrocatalyst performance, supporting an effective approach to prepare favorable materials for enhanced capacity, extended lifespan, and energy density.

Introducing Mn into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer for detection of organophosphorus pesticides.

In order to design and establish a highly efficient and selective nanozyme-based sensing platform for the UV-vis detection of organophosphorus pesticides (OPs), Mn was introduced into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer. The Mn-doped ZIF-8 (Mn-ZIF-8) nanocomposites were synthesized with a very facile one-pot method by heating the mixture of ZnO, 2-methylimidazole (Hmin) and Mn(CH3COO)2·4H2O in a solvent-free system at 180°C for 8h. The Mn-ZIF-8 nanocomposite showed a higher peroxidase activity and an additional thiocholine (TCh)-degradable property compared to the pristine ZIF-8. OPs could inhibit acetylcholinesterase (AChE) to catalyze the hydrolysis of acetylthiocholine (ATCh) to produce TCh, thus blocking the degradation of Mn-ZIF-8 and protecting the catalysis of the oxidation of colorless 3,3',5,5'-tetramethylbenzydine (TMB) to blue oxidized TMB (ox-TMB). Accordingly, a detection method for OPs with high sensitivity and selectivity was designed and established on the basis of the Mn-ZIF-8 nanozyme with a linear range of 0.1-20nM and a limit of detection (LOD) as low as 54pM.

Zeolitic Imidazolate Framework-8 and redox-additive electrolyte based asymmetric supercapacitor: A synergetic combination for ultrahigh energy and power density

In the present work, the electrochemical study of the synthesized electrode (ZIF-8 at 300 °C named as Z1) material was done in a three- and two-electrode (device) assembly using non redox-additive (6 M NaOH) and redox-additive (0.35 M K4(Fe(CN)6).3H2O in 6 M NaOH) electrolyte (RAE). X-ray diffraction (XRD) of Z1 sample confirmed the cubic phase with I -43 m space group. The hexagonal-type morphology was revealed by high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) analysis. The formation of narrow mesopores with average pore diameter of 1.53 nm and a large specific surface area of 1272 m2/g was confirmed by Brunauer-Emmett-Teller (BET) examination. The thermal stability of pristine ZIF-8 is investigated by Thermogravimetric analysis (TGA). In the three-electrode system, the Z1 sample as electrode reveals the pseudocapacitive (in NaOH) and battery-like redox behavior (in RAE). The fabricated electrode provides the specific capacitance of 30.6 F/g (1 A/g) and 33.1 F/g (10 mV/s) in NaOH. Moreover, the Z1 electrode exhibited an excellent specific capacity of 500.0C/g (at 10 A/g) and 532.5C/g (at 10 mV/s) in RAE. Additionally, an asymmetric supercapacitor (ASSC) device was assembled via RAE with activated carbon (AC) as an anode and Z1 as a cathode to investigate the practical feasibility. The constructed device in 0.0–2.0 V voltage window provides a significant power density of 20,000 W/Kg (for an energy density of 38.89 Wh/kg at 40 A/g) and an outstanding energy density of 75 Wh/kg (for a power density of 10,000 W/kg at 20 A/g). It exhibits good capacitance retention (80 % at 20 A/g) after 1500 cycles. Furthermore, three ASSC devices are connected in series to illuminate green, yellow, white, and red Light Emitting Diodes, thus demonstrating the potential realistic advantage of the current research work in supercapacitive energy storage devices.

Interfacial permeation preparation of ZIF-8 in reactive deep eutectic for efficient adsorption and selective removal of Congo red

Metal-based deep eutectic solvents (MDES) were used as reactive DESs and structure directing agents to control the morphology and oriented growth of ZIF-8. A series of ZIF-8-DESs were prepared in three MDESs (ZnCl2-urea, ZnCl2-1,3-dimethylurea and ZnCl2-tetramethyl urea) by the interfacial synthesis and two-phase permeation. The results showed that MDES acts as multi roles to affect the morphology and adsorption performance of ZIF-8-DES. The growth mechanism of ZIF-8-DES was also proposed. ZIF-8-DES could effectively adsorb anionic Congo red with 99.98 % removal efficiency, 2454 mg·g−1 adsorption capacity and a wide pH tolerance. ZIF-8-DES possesses excellent selectivity for Congo red in the presence of methyl orange and outstanding reusability as compared with pristine ZIF-8 and most reported adsorbents. The thermodynamics and adsorption kinetics was well described by a Langmuir model and pseudo-second-order model, respectively. The adsorption mechanism including π-π interaction and hydrogen bonding interactions was proposed. This work provided a facile synthesis route for MOFs with different morphologies and surface properties as well as novel insights into the design of selective absorbent for organic dyes.

ZIF-8 based porous liquids with high hydrothermal stability for carbon capture

Porous liquids (PLs), a novel material that combines both permanent porosity and fluidity, show enormous potential in gas capture and separation applications. However, MOF nanoparticles, as permanent porosity providers in PLs, have poor hydrothermal stability limiting their use in industries with the presence of water. In this study, the shell-ligand exchange reaction (SLER) was employed to replace the 2-methylimidazole on the surface of ZIF-8 crystals with 5,6-dimethylbenzimidazole, which improved the hydrothermal stability of ZIF-8 efficiently. The adsorption kinetic results showed that first-order kinetics could better predict the behavior of ZIF-8-based PLs in CO2 capture. Compared with ZIF-8-PLs, the CO2 capture capacity of ZIF-8-SLER-PLs was increased 30 % at 40 °C. When exposed to water at 80 °C for 20 days, ZIF-8-SLER retains its intact crystal morphology, high surface area and hydrothermal stability. Meanwhile, the 83 % CO2 adsorption capacity of ZIF-8-SLER (20 days) was retained. However, the pore structure of pristine ZIF-8 was collapsed seriously after hydrothermal experiment, and the CO2 adsorption capacity of ZIF-8 (20 days) was decreased by 40.6 % due to the lack of protection by hydrophobic ligands. This study opens a new pathway to use MOFs-based porous liquids for CO2 capture in industrial applications with the presence of water.

Addition of graphene oxide to ZIF-8/HKUST-1 composite for enhanced adsorptive and photocatalytic removal of congo red in wastewater

Ternary composites comprised of graphene oxide (GO), ZIF-8, and HKUST-1 with varying amounts of GO were successfully synthesized via the solvothermal method. Based on the photoluminescence characterization, the GO/ZIF-8/HKUST-1 composite presents a more efficient charge carrier separation and transfer compared to pristine HKUST-1 and ZIF-8. As a result, electron-hole recombination was hindered due to the presence of GO as an electron mediator in the heterojunction. The dark adsorption kinetics data for the removal of Congo Red (CR) dye fit well with the pseudo-second order model. The photocatalytic degradation performance of the GO/ZIF-8/HKUST-1 composite was investigated by means of degrading CR dye under UV-LED irradiation. The photodegradation efficiency of the GO(10)/ZIF-8/HKUST-1 composite for the removal of CR dye was 91.81% within 60 min of irradiation. The trapping experiments showed that hydroxyl and superoxide radicals are the main reactive species. The results of this study indicate that ternary composites comprised of MOFs as photocatalysts have great potential for degrading pollutants in aquatic environments.

Enhancing methyl orange adsorption capacity via functionalizing ZIF-8 with amphiphilic cetylpyridinium bromide

BackgroundThe precise design or functionalization of metal organic frameworks (MOFs) based on the properties of organic dyes is a promising direction in environment remediation. MethodsHerein, using methyl orange (MO) as the target dye, cetylpyridinium bromide (CPB) functionalized ZIF-8 (CPB@ZIF-8) was fabricated by the post-synthetic modification strategy. Significant findingsThe surface area and the pore volume of CPB@ZIF-8 are greatly reduced compared with pure ZIF-8. However, the introduction of amphiphilic CPB molecules into ZIF-8 can significantly enhance the adsorption performance of MO. This enhanced MO adsorption capacity can be attributed to the incorporation of more positively charged sites, hydrophobic sites and aromatic rings in the CPB-modified ZIF-8 frameworks, which provides the electrostatic attractions, the hydrophobic and π-π interactions that mainly govern the adsorption of MO on CPB@ZIF-8. The pseudo-second-order kinetic model and the Langmuir isotherm model can well represent the adsorption process of MO. The maximum adsorption capacity (195.54 mg/g) has been obtained at 30 °C, outperforming pristine ZIF-8 and various reported absorbents. The prepared CPB@ZIF-8 composite is a superior example of the tunable adsorption affinity of MOFs for anionic dyes.

Removal of recalcitrant metronidazole from aqueous solution onto ZIF-8 & copper doped ZIF-8, process modelling and optimisation

ABSTRACT The challenges by release of pharmaceuticals into the environment have motivated scientists to study the removal of these substances. Metronidazole is particularly a pharmaceutical in the environment due to its extensive usage, high solubility in water and non-biodegradability. Herein, metronidazole removal was explored by materials of Metal – Organic Frameworks (MOFs), namely C8H10N4Zn(ZIF-8) and C8H10N4ZnCu(Cu-ZIF-8). The studied MOFs synthesised through an environmentally friendly approach and their structures and morphologies are fully characterised. The effects of the solution pH, contact time, adsorbent dose, and antibiotic concentration on the process were modelled and optimised by performing the experiments based on the Box – Behnken design (BBD). Cu-ZIF-8 exhibited an enhanced antibiotic adsorption potential compared to pristine ZIF-8. The optimal removal (94.09%) for antibiotic removal occurred in 0.69 g Cu-ZIF-8/L, mixing time 51 min and pH 6.6. A 93.7% removal also predicted for ZIF-8 when adsorbent dose, mixing time and pH are adjusted to 0.92 g/L, 54 min and 6.5. The environmental condition for antibiotic removal by two adsorbent materials was optimised based on the process models. In addition, isotherm and kinetic models predicted the antibiotic removal well. The metal leaching analysis indicated that zinc and copper concentrations for ZIF-8 and Cu-ZIF-8 complied with the maximum limit levels.

ZIF-8@Zn-MOF-74 core–shell metal–organic framework (MOF) with open metal sites: Synthesis, characterization, and gas adsorption performance

In this paper, an efficient hierarchical metal–organic framework (MOF), namely ZIF-8@Zn-MOF-74 with core–shell structure and coordinately open/unsaturated metal sites (OMS) was successfully synthesized. For this purpose, the facile post-synthetic ligand exchange (PSE) method at ambient temperature was applied. In the fabricated core–shell porous structure, the SOD-type ZIF-8 acts as the core, providing molecular sieving features, resulting in greater adsorption selectivity values. On the other hand, Zn-MOF-74 as the shell part, owing to the larger pore size, makes entrance and diffusion of the guest gas molecules more convenient. In addition, due to the presence of OMS in the Zn-MOF-74 structure, a greater adsorption capacity would be achieved. The prepared MOFs were characterized by FESEM, EDS, HRTEM, FTIR, XRD, BET, and TGA analyses, and formation of the core–shell structure was confirmed. The FESEM and HRTEM images demonstrated rather smooth coverage of the core (ZIF-8) with a layer of the shell (Zn-MOF-74). The rather high BET surface area (633.2 m2/g) and total pore volume (0.671 cm3 g−1) of the core–shell structure, make it promising for gas adsorption applications. The gas adsorption measurements were conducted for CO2, N2, H2, O2, CH4, C2H6, C3H8, C2H4, and C3H6 pure gases at 308 K and equilibrium pressures up to 4 bar. It was found that the CO2 adsorption capacity of ZIF-8@Zn-MOF-74 nanoparticles (3.27 mmol g−1) has enhanced ∼63.5 % compared to the pristine ZIF-8 (∼2 mmol/g). The CO2/N2 and CO2/CH4 selectivity values were also increased by 85.4 % and 74.4 %, respectively, that indicates overcoming the trade-off between adsorption capacity and selectivity.

Enhanced specific surface area of ZIF-8 derived ZnO induced by sulfuric acid modification for high-performance acetone gas sensor

Zeolitic imidazolate framework (ZIF)-8-derived zinc oxide (ZnO) is considered one of the most promising acetone sensing candidate materials for the diagnosis of type-I diabetes. However, very few studies focus on the effect of acidic conditions induced shape change of ZIF-8 derived ZnO on the diffusion and adsorption of acetone gas on the material surface. Here, novel ZIF-8-derived hierarchical ZnO micro-dodecahedra/flower structures (ZnO-DFs) were designed by using sulfuric acid modification. Interestingly, enhanced acetone sensing performance was achieved for the hierarchical ZnO-DFs-2.5 (derived from 2.5 μL sulfuric acid-modified ZIF-8) with a distinguished acetone response (∼120.6 to 100 ppm at 350 °C), which was ∼30 times higher than that of pristine ZnO-DFs. Moreover, the sensors exhibited fast response time (∼0.95 s), low detection limit (∼50 ppb), and superior selectivity. The enhanced performance in hierarchical ZnO-DFs could be ascribed to the improved specific surface area and gas transport channels resulted from the damage of Zn–N bonds in pristine ZIF-8 under acidic conditions. This finding represents an alternative strategy for highly efficient acetone gas sensors and structural-functionalism of MOF-derived metal oxide catalysts.