Controlling ZIF-67 crystals formation through various cobalt sources in aqueous solution

Evaluation of phosphate removal from aqueous solution using metal organic framework; isotherm, kinetic and thermodynamic study

BACKGROUND

Phosphate (PO₄ ^3-) is the main etiological factor of eutrophication in surface waters. Metal organic frameworks (MOFs) are novel hybrid materials with amazing structural properties that make them a prominent material for adsorption.

METHODS

Zeolitic imidazolate framework 67 (ZIF-67), a water stable member of MOFs, with a truncated rhombic dodecahedron crystalline structure was synthesized in aqueous environment at room temperature and then characterized using XRD and SEM. PO₄ ^3- adsorption from synthetic solutions using ZIF-67 in batch mode were evaluated and a polynomial model (R²: 0.99, R² _adj: 0.98, LOF: 0.1433) developed using response surface methodology (RSM).

RESULTS

The highest PO₄ ^3- removal (99.2%) after model optimization obtained when ZIF-67 dose, pH and mixing time adjusted to 6.82, 832.4 mg/L and 39.95 min, respectively. The optimum PO₄ ^3- concentration in which highest PO₄ ^3- removal and lowest adsorbent utilization occurs, observed at 30 mg/L. PO₄ ^3- removal eclipsed significantly in the presence of carbonate. The equilibrium and kinetic models showed that PO₄ ^3- adsorbed in monolayer (q_max: 92.43 mg/g) and the sorption process controlled in the sorption stage. Adsorption was also more favorable at higher PO₄ ^3- concentration, according to the separation factor (K_R) graph. Thermodynamic parameters (minus signs of ∆G°, ∆H° of 0.179 KJ/mol and ∆S° of 44.91 KJ/mol.K) demonstrate the spontaneous, endothermic and physisorption nature of the process.

CONCLUSION

High adsorption capacity and adsorption rates, make ZIF-67 a promising adsorbent for PO₄ ^3- removal from aqueous environment.

Tetracycline removal from aqueous solutions using zeolitic imidazolate frameworks with different morphologies: A mathematical modeling

Concerns about environment pollution by antibiotics raised notable attention. In this context, metal-organic frameworks (MOFs) can produce an excellent platform for toxicant removal from water environments. In the current investigation, eight MOFs (ZIF-67-NO₃, ZIF-67-Cl, ZIF-67-SO₄, ZIF-67-OAC, ZIF-8-Octahedron, ZIF-8-Leaf, ZIF-8-Cuboid, and ZIF-8-Cube) with different chemical and textural compositions were synthesized, and furthermore, the adsorption of Tetracycline (TC) by them was evaluated. Also, the key experimental conditions were modeled using response surface methodology (RSM). Among the prepared MOFs, the highest tendency for TC removal was nominated to ZIF-67- Acetate (ZIF-67-OAC). By model optimization approach, the optimum system conditions as contact time, adsorbent dosage, pH and adsorbed antibiotic concentration were reported as 26.8 min, 0.63 g/L, 5.9, and 74.6 mg/L, respectively. The proposed equilibrium model showed that the TC accumulated on ZIF-67-OAC surface is reversible in multilayer with the highest monolayer capacity of 446.9 mg/g. Furthermore, based on separation factor (K_L), TC adsorption is more favorable at a higher amount of MOFs added. Moreover, according to the fitted kinetic model, the process was controlled by chemisorption. ZIF-67-OAC shows excellent structural stability during mechanical agitation in an aqueous environment, and the TC removal capacities of regenerated adsorbent did not change considerably at the end of cycle 4 compared to the first cycle. Considering the findings among the examined MOFs, the ZIF-67-OAC can be approached as a promising adsorbent for the removal of antibiotics from aqueous environments.

A 2D metal–organic framework/reduced graphene oxide heterostructure for supercapacitor application

Metal organic frameworks (MOFs) with two dimensional (2D) nanosheets have attracted special attention for supercapacitor application due to their exceptional large surface area and high surface-to-volume atom ratios. However, their electrochemical performance is greatly hindered by their poor electrical conductivity. Herein, we report a 2D nanosheet nickel cobalt based MOF (NiCo-MOF)/reduced graphene oxide heterostructure as an electrode material for supercapacitors. The NiCo-MOF 2D nanosheets are in situ grown on rGO surfaces by simple room temperature precipitation. In such hybrid structure the MOF ultrathin nanosheets provide large surface area with abundant channels for fast mass transport of ions while the rGO conductive and physical support provides rapid electron transport. Thus, using the synergistic advantage of rGO and NiCo-MOF nanosheets an excellent specific capacitance of 1553 F g⁻¹ at a current density of 1 A g⁻¹ is obtained. Additionally, the as synthesized hybrid material showed excellent cycling capacity of 83.6% after 5000 cycles of charge–discharge. Interestingly, the assembled asymmetric device showed an excellent energy density of 44 W h kg⁻¹ at a power density of 3168 W kg⁻¹. The electrochemical performance obtained in this report illustrates hybridization of MOF nanosheets with carbon materials is promising for next generation supercapacitors.

In this 2D NiCo-MOF/rGO hybrid, the MOF nanosheets provide abundant active sites while the conductive rGO provide rapid electron transport.

Submicron sized water-stable metal organic framework (bio-MOF-11) for catalytic degradation of pharmaceuticals and personal care products

Water-stable and active metal organic frameworks (MOFs) are important materials for mitigation of water contaminants via adsorption and catalytic reactions. In this study, a highly water-stable Co-based MOF, namely bio-MOF-11-Co, was synthesized by a simplified benign method. Moreover, it was used as a catalyst in successful activation of peroxymonsulfate for catalytic degradation of sulfachloropyradazine (SCP) and para-hydroxybenzoic acid (p-HBA) as representatives of pharmaceuticals and personal care products, respectively. The bio-MOF-11-Co showed rapid degradation of both p-HBA and SCP and could be reused multiple times without losing the activity by simply water washing. The effects of catalyst and PMS loadings as well as temperature were further studied, showing that high catalyst and PMS loadings as well as temperature produced faster kinetic degradation of p-HBA and SCP. The generation of highly reactive and HO radicals during the degradation was investigated by quenching tests and electron paramagnetic resonance. A plausible degradation mechanism was proposed based on the functionalities in the bio-MOF-11-Co. The availability of electron rich nucleobase adenine reinforced the reaction kinetics by electron donation along with cobalt atoms in the bio-MOF-11-Co structure.

Design and preparation of metal-organic framework papers with enhanced mechanical properties and good antibacterial capacity

In this study, a biodegradable paper-based composite with good mechanical and antibacterial properties was obtained by first reinforcing the cotton pulp-based paper with carboxylated cellulose nanofiber (CNF) via the Williamson reaction, followed by in situ generating zeolitic imidazolate framework-67 (ZIF-67) nanoparticles on the surface of the resulting cellulosic material. The mechanical properties and antibacterial activities of the resulting composite were investigated. The tensile testing demonstrated that the composites prepared with 2.5 wt% CNF exhibited outstanding mechanical performance under dry and wet conditions with the tensile strength values of 17.20 and 1.90 MPa, respectively, approximately 1.3 and 11 times higher compared to that of the original cellulose paper. Furthermore, the antibacterial experiments showed that the composites exhibited significant bacteriostasis, and the antibacterial properties increased significantly with increasing ZIF-67 loading in the composites. Consequently, this biodegradable composite could be potentially used in the field of medical and health security.

Strategies for Improving the Functionality of Zeolitic Imidazolate Frameworks: Tailoring Nanoarchitectures for Functional Applications

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs) built with tetrahedral metal ions and imidazolates, offer permanent porosity and high thermal and chemical stabilities. While ZIFs possess some attractive physical and chemical properties, it remains important to enhance their functionality for practical application. Here, an overview of the extensive strategies which have been developed to improve the functionality of ZIFs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species (such as metal and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations. Furthermore, the developed strategies for achieving size and shape control of ZIF nanocrystals are considered, which are important for optimizing the textural characteristics as well as the functional performance of ZIFs and their derived materials/hybrids. Moreover, the recent trends of using ZIFs as templates for the derivation of nanoporous hybrid materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/phosphide hybrids, are discussed. Finally, some perspectives on the potential future research directions and applications for ZIFs and ZIF-derived materials are offered.

Zinc Imidazolate Metal-Organic Frameworks (ZIF-8) for Electrochemical Reduction of CO2 to CO

Metal-organic frameworks (MOFs) are regarded as promising materials for CO₂ adsorption, which is an important step in CO₂ electrochemical reduction. In this work, zeolitic imidazolate framework (ZIF-8) nanomaterials were synthesized with various zinc sources and used as electrocatalysts for CO₂ reduction to CO. Among them, ZIF-8, prepared using ZnSO₄ , delivers the best catalytic activity towards CO₂ electroreduction, with 65 % CO yield. The main catalytic center can be attributed to the discrete Zn nodes in ZIF-8. Electrolytes are important in increasing the CO selectivity, and NaCl is the best suitable electrolyte due to facile anion exchange.

Extensive and selective adsorption of ZIF-67 towards organic dyes: Performance and mechanism

Zeolitic imidazolate frameworks-67 (ZIF-67) was prepared via electrochemical deposition, which was used to conduct adsorptive removal of various organic dyes. The results revealed that ZIF-67 displayed good adsorption performance towards some dyes due to its positive Zeta potential at wide pH range or some special functional groups like SO₃ of dyes. Also, ZIF-67 could separate some dyes from the matrix subjected to its preferential uptake towards certain dyes. The possible adsorption mechanism including electrostatic interactions, coordination interactions and hydrogen bonding interactions was proposed and tested.

MOF-Derived Hollow Cage Nix Co3-x O4 and Their Synergy with Graphene for Outstanding Supercapacitors

Highly optimized nickel cobalt mixed oxide has been derived from zeolite imidazole frameworks. While the pure cobalt oxide gives only 178.7 F g^-1 as the specific capacitance at a current density of 1 A g^-1 , the optimized Ni:Co 1:1 has given an extremely high and unprecedented specific capacitance of 1931 F g^-1 at a current density of 1 A g^-1 , with a capacitance retention of 69.5% after 5000 cycles in a three electrode test. This optimized Ni:Co 1:1 mixed oxide is further used to make a composite of nickel cobalt mixed oxide/graphene 3D hydrogel for enhancing the electrochemical performance by virtue of a continuous and porous graphene conductive network. The electrode made from GNi:Co 1:1 successfully achieves an even higher specific capacitance of 2870.8 F g^-1 at 1 A g^-1 and also shows a significant improvement in the cyclic stability with 81% capacitance retention after 5000 cycles. An asymmetric supercapacitor is also assembled using a pure graphene 3D hydrogel as the negative electrode and the GNi:Co 1:1 as the positive electrode. With a potential window of 1.5 V and binder free electrodes, the capacitor gives a high specific energy density of 50.2 Wh kg^-1 at a high power density of 750 W kg^-1 .