The effect of cobalt content in Zn/Co-ZIF-8 on iodine capping properties

Enhanced Iodine Capture Using a Postsynthetically Modified Thione-Silver Zeolitic Imidazole Framework

Efficient management of radionuclides that are released from various processes in the nuclear fuel cycle is of significant importance. Among these nuclides, radioactive iodine (mainly 129I and 131I) is a major concern due to the risk it poses to the environment and to human health; thus, the development of materials that can capture and safely store radioactive iodine is crucial. Herein, a novel silver-thione-functionalized zeolitic imidazole framework (ZIF) was synthesized via postsynthetic modification and assessed for its iodine uptake capabilities alongside the parent ZIF-8 and intermediate materials. A solvent-assisted ligand exchange procedure was used to replace the 2-methylimidazole linkers in ZIF-8 with 2-mercaptoimidazole, forming intermediate compound ZIF-8 = S, which was reacted with AgNO3 to yield the ZIF-8 = S-Ag+ composite for iodine uptake. Despite possessing the lowest BET surface area of the derivatives, the Ag-functionalized material demonstrated superior I2 adsorption in terms of both maximum capacity (550 g I2/mol) and rapid kinetics (50% loading achieved in 5 h, saturation in 50 h) compared to that of our pristine ZIF-8, which reached 450 g I2/mol after 150 h and 50% loading in 25 h. This improvement is attributed to the presence of the Ag+ ions, which provide a strong chemical driving force to form a stable Ag-I species. The results of this study contribute to a broader understanding of the strategies that can be employed to engineer adsorbents with robust iodine uptake behavior.

Photoswitchable Zirconium MOF for Light-Driven Hydrogen Storage

Here, we report a new photosensitive metal–organic framework (MOF) that was constructed via the modification of UiO-66-NH₂ with diarylethene molecules (DAE, 4-(5-Methoxy-1,2-dimethyl-1H-indol-3-yl)-3-(2,5-dimethylthiophen-3-yl)-4-furan-2,5-dione). The material that was obtained was a highly crystalline porous compound. The photoresponse of the modified MOF was observed via UV–Vis and IR spectroscopy. Most of the DAE molecules inside of the UiO-66-pores had an open conformation after synthesis. However, the equilibrium was able to be shifted further toward an open conformation using visible light irradiation with a wavelength of 520 nm. Conversely, UV-light with a wavelength of 450 nm initiated the transformation of the photoresponsive moieties inside of the pores to a closed modification. We have shown that this transformation could be used to stimulate hydrogen adsorption–desorption processes. Specifically, visible light irradiation increased the H₂ capacity of modified MOF, while UV-light decreased it. A similar hybrid material with DAE moieties in the UiO-66 scaffold was applied for hydrogen storage for the first time. Additionally, the obtained results are promising for smart H₂ storage that is able to be managed via light stimuli.

Iodine Immobilized Metal-Organic Framework for NIR-Triggered Antibacterial Therapy on Orthopedic Implants

Iodine has been known as an effective disinfectant with broad-spectrum antimicrobial potency yet without drug resistance risk when used in clinic. However, the exploration of iodine for antibacterial therapy in orthopedics remains sparse due to its volatile nature and poor solubility. Herein, leveraging the superior absorption capability of metal-organic frameworks (MOFs) and their inherent photocatalytic properties, iodine-loaded MOF surface is presented to realize responsive iodine release along with intracellular reactive oxygen species(ROS) oxidation under near-infrared (NIR) exposure to achieve synergistic antibacterial effect. Iodine is successfully loaded using vapor deposition process onto zeolitic imidazolate framework-8(ZIF-8), which is immobilized onto micro arc oxidized titanium via a hydrothermal approach. The combination of NIR-triggered iodine release and ZIF-8 mediated ROS oxidative stress substantially augments the antibacterial efficacy of this approach both in vitro and in vivo. Furthermore, this composite coating also supported osteogenic differentiation of bone marrow stromal cells, as well as improved osseointegration of coated implants using an intramedullary rat model, suggesting improvement of antibacterial efficacy does not impair osteogenic potential of the implants. Altogether, immobilization of iodine via MOF on orthopedic implants with synergistic antibacterial effect can be a promising strategy to combat bacterial infections.

Loading of the Model Amino Acid Leucine in UiO-66 and UiO-66-NH2: Optimization of Metal-Organic Framework Carriers and Evaluation of Host-Guest Interactions

Two metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH₂, were considered as containers for bioactive chemicals. We provide a synthesis technique, which allowed the production of these materials suitable for biomedical applications. Both MOFs were characterized as single-phase porous materials composed of nanoparticles (30-65 nm) with a ζ-potential of more than 40 mV in water suspension. D,L-Leucine was applied as a model molecule, which allowed us to trace the mechanism of the loading process. We showed that after synthesis, amino groups of UiO-66-NH₂ are coordinated with solvent residuals. It results in a similar route of leucine loading in UiO-66 and UiO-66-NH₂ samples. Using joint data of thermogravimetric analysis and calorimetry, infrared spectroscopy, and nitrogen adsorption, we revealed that methyl groups of leucine molecules are responsible for bonding of an MOF matrix. We proposed the formation of bonds between CH₃ groups and benzene rings of linkers via CH-π interaction. We also assessed the toxicity of the synthesized MOFs toward HeLa cells at 50 μg/mL after 24 h incubation and revealed no negative effects on the viability of the cells, prompting further biomedical research in the areas of small-molecule delivery and cell signaling and metabolism modulation.

Bi-metallic zeolite imidazole framework nanofibers for the selective determination of Cd2+ ions

Cobalt zinc-zeolite imidazole framework (Co/Zn-ZIF) nanofibers are made via an electrospinning (ES) approach and tested for the detection of heavy metal cadmium ions. Electrostatically attracted cobalt and zinc ions are bound regularly on the surface of the ZIF network. The cobalt and zinc ions are organized with the ZIF network, which provides the sturdily bonded tetrahedral structure of Co/Zn-ZIF, giving essential steadiness to the composite material. Cyclic voltammetry revealed that the observed profile is reversible, and the catalytic behavior of the electrodes provided evidence of interfacial electron transfer between the nanofiber-modified GCE surface and the metal ions. Interestingly, a careful determination of Cd2+ ions within the range of 100 nM to 1 mM with a low limit detection of 27.27 nM was undertaken. The established heavy metal ion detector shows excellent anti-interference abilities toward the observed electroactive species, and it was successfully employed using a tap water sample for Cd2+ ion detection, where good results were observed.

MW Synthesis of ZIF-7. The Effect of Solvent on Particle Size and Hydrogen Sorption Properties

We report here fast (15 min) microwave-assisted solvothermal synthesis of zeolitic imidazolate framework material (ZIF-7). We have optimized solvent composition to achieve high porosity and hydrogen capacity and narrow particle size distribution. It was shown that synthesis in N,N-diethylformamide (DEF) results in a layered ZIF-7 III phase, while N,N-dimethylformamide (DMF) as solvent leads to a pure ZIF-7 phase in microwave conditions. A mixture of toluene with DMF allows the production of pure ZIF-7 material only with the triethylamine additive. Obtained materials were comprehensively characterized. We have pointed out that both X-ray diffraction and infrared spectroscopy could be used for the identification of ZIF-7 or ZIF-7 III phases. Although samples obtained in DMF, and in a mixture of DMF, toluene, and triethylamine were assigned to the pure ZIF-7 phase, solvent composition significantly affected the size of particles in the material and nitrogen and hydrogen adsorption process.

Properties of Cobalt- and Nickel-Doped Zif-8 Framework Materials and Their Application in Heavy-Metal Removal from Wastewater

Heterometallic zeolite imidazole framework materials (ZIF) exhibit highly attractive properties and have drawn increased attention. In this study, a petal-like zinc based ZIF-8 crystal and materials doped with cobalt and nickel ions were efficiently prepared in an aqueous solution at room temperature. It was observed that doped cobalt and nickel had obviously different effects on the morphology of ZIF-8. Cobalt ions were beneficial for the formation of ZIF-8, while addition of nickel ions tended to destroy the original configuration. Then we compared the absorption ability for metal ions between petal-like ZIF-8 and its doped derivatives with anion dichromate ions (Cr₂O₇^2-) and cation copper ions (Cu²⁺) as the absorbates. Results indicated that saturated adsorption capacities of Co@ZIF-8 and Ni@ZIF-8 for Cr₂O₇^2- reach 43.00 and 51.60 mg/g, while they are 1191.67 and 1066.67 mg/g for Cu²⁺, respectively, which are much higher than the original ZIF-8 materials. Furthermore, both the heterometallic ZIF-8 materials show fast adsorption kinetics to reach adsorption equilibrium. Therefore, petal-like ZIF-8 with doped ions can be produced through a facile method and can be an excellent candidate for further applications in heavy-metal treatment.

Synthesis of ZnO Nanoparticles Doped with Cobalt Using Bimetallic ZIFs as Sacrificial Agents

We report here a simple two-stage synthesis of zinc–cobalt oxide nanoparticles. We used Zn/Co-zeolite imidazolate framework (ZIF)-8 materials as precursors for annealing and optional impregnation with a silicon source for the formation of a protective layer on the surface of oxide nanoparticles. Using bimetallic ZIFs allowed us to trace the phase transition of the obtained oxide nanoparticles from wurtzite ZnO to spinel Co₃O₄ structures. Using (X-ray diffraction) XRD and (X-ray Absorption Near Edge Structure) XANES techniques, we confirmed the incorporation of cobalt ions into the ZnO structure up to 5 mol.% of Co. Simple annealing of Zn/Co-ZIF-8 materials in the air led to the formation of oxide nanoparticles of about 20–30 nm, while additional treatment of ZIFs with silicon source resulted in nanoparticles of about 5–10 nm covered with protective silica layer. We revealed the incorporation of oxygen vacancies in the obtained ZnO nanoparticles using FTIR analysis. All obtained samples were comprehensively characterized, including analysis with a synchrotron radiation source.

Reversible MOF-Based Sensors for the Electrical Detection of Iodine Gas

Iodine detection is crucial for nuclear waste clean-up and first responder activities. For ease of use and durability of response, robust active materials that enable the direct electrical detection of I2 are needed. Herein, a large reversible electrical response is demonstrated as I2 is controllably and repeatedly adsorbed and desorbed from a series of metal-organic frameworks (MOFs) MFM-300(X), each possessing a different metal center (X = Al, Fe, In, or Sc) bridged by biphenyl-3,3',5,5'-tetracarboxylate linkers. Impedance spectroscopy is used to evaluate how the different metal centers influence the electrical response upon cycling of I2 gas, ranging from 10× to 106× decrease in resistance upon I2 adsorption in air. This large variation in electrical response is attributed not only to the differing structural characteristics of the MOFs but also to the differing MOF morphologies and how this influences the degree of reversibility of I2 adsorption. Interestingly, MFM-300(Al) and MFM-300(In) displayed the largest changes in resistance (up to 106×) yet lost much of their adsorption capacity after five I2 adsorption cycles in air. On the other hand, MFM-300(Fe) and MFM-300(Sc) revealed more moderate changes in resistance (10-100×), maintaining most of their original adsorption capacity after five cycles. This work demonstrates how changes in MOFs can profoundly affect the magnitude and reversibility of the electrical response of sensor materials. Tuning both the intrinsic (resistivity and adsorption capacity) and extrinsic (surface area and particle morphology) properties is necessary to develop highly reversible, large signal-generating MOF materials for direct electrical readout for I2 sensing.