Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

Enhanced photocatalysis using metal-organic framework MIL-101(Fe) for organophosphate degradation in water

Metal-organic frameworks (MOFs) are attractive novel classes of porous materials with diverse potentiality and easily tailored structures. It is desirable to evaluate the performance of MOFs as photocatalysts for organic contaminant removal in aqueous matrixes. In this study, iron-based MIL-101(Fe) was synthesized and a photo-Fenton reaction system (multiple wavelength light + MIL-101(Fe) + H₂O₂) was developed for elimination of tris(2-chloroethyl) phosphate (TCEP). Degradation pattern of TCEP followed an S-shape curve, which included a slow induction period and a rapid radical oxidation process. Transport of reactants into MIL-101(Fe) and the activation of electron transport within Fe-O clusters of MIL-101(Fe) may be the dominant mechanisms in the induction period, while a pseudo-first-order kinetics was observed in the hydroxyl radical oxidation process. Removal efficiencies in these two stages highly depended on the reaction conditions. Irradiation at 420 nm and acid condition were conductive, while high temperature and high [H₂O₂]:[MIL-101(Fe)] mass ratio accelerated the reaction. Before complete mineralization, eleven degradation products were generated, and the dominant degradation pathways included cleavage, hydroxylation, carbonylation, and carboxylation. Under acid condition (pH = 3), only 1% mass loss was observed after 60-min reaction, but the iron leakage was aggravated when pH increased. Furthermore, this MOF-photo-Fenton system demonstrated a robust performance on TCEP degradation in actual wastewater matrixes under acid condition. Generally, the MOF-photo-Fenton system is a potential technology for elimination of organic pollutants in aqueous solution.

Iron-Based Metal-Organic Frameworks as a Theranostic Carrier for Local Tuberculosis Therapy

PURPOSE

The purpose of the study was initial evaluation of applicability of metal organic framework (MOF) Fe-MIL-101-NH2 as a theranostic carrier of antituberculous drug in terms of its functionality, i.e. drug loading, drug dissolution, magnetic resonance imaging (MRI) contrast and cytotoxic safety.

METHODS

Fe-MIL-101-NH2 was characterized using X-ray powder diffraction, FTIR spectrometry and scanning electron microscopy. The particle size analysis was determined using laser diffraction. Magnetic resonance relaxometry and MRI were carried out on phantoms of the MOF system suspended in polymer solution. Drug dissolution studies were conducted using Franz cells. For MOF cytotoxicity, commercially available fibroblasts L929 were cultured in Eagle's Minimum Essential Medium supplemented with 10% fetal bovine serum.

RESULTS

MOF particles were loaded with 12% of isoniazid. The particle size (3.37-6.45 μm) depended on the micronization method used. The proposed drug delivery system can also serve as the MRI contrast agent. The drug dissolution showed extended release of isoniazid. MOF particles accumulated in the L929 fibroblast cytoplasmic area, suggesting MOF release the drug inside the cells. The cytotoxicity confirmed safety of MOF system.

CONCLUSIONS

The application of MOF for extended release inhalable system proposes the novel strategy for delivery of standard antimycobacterial agents combined with monitoring of their distribution within the lung tissue.

A recyclable hybrid manganese(III) porphyrin magnetic catalyst for selective olefin epoxidation using molecular oxygen

The synthesis and characterization of a hybrid Mn(III)-porphyrin magnetic nanocomposite is described. Moreover, a sustainable methodology for epoxidation of olefins is reported, using O[Formula: see text] as a green oxidant and the magnetic nanoparticle as a recyclable catalyst. High activity in alkene oxidation was observed, with full selectivity for epoxide formation. The magnetic catalyst presented high stability, being recovered and reused in five consecutive runs without loss of catalytic activity or selectivity in cyclooctene oxidation. Moreover, the catalytic system showed very good reactivity toward epoxidation of a range of terminal, substituted, cyclic or acyclic, aliphatic and aromatic olefins, including terpene and steroid derivatives, affording a range of biologically relevant epoxides in excellent yields. The isobutyric acid, formed as side-product, was recovered with high yield and purity, which provides the potential reutilization of this important industrial product.

Preparation of iron-based MIL-101 functionalized polydopamine@Fe3 O4 magnetic composites for extracting sulfonylurea herbicides from environmental water and vegetable samples

Here, we describe a simple one-pot solvothermal method for synthesizing MIL-101(Fe)@polydopamine@Fe₃ O₄ composites from polydopamine-modified Fe₃ O₄ particles. The composite was used as a magnetic adsorbent to rapidly extract sulfonylurea herbicides. The herbicides were then analyzed by high-performance liquid chromatography. The best possible extraction efficiencies were achieved by optimizing the most important extraction parameters, including desorption conditions, extraction time, adsorbent dose, salt concentration, and the pH of the solution. Good linearity was found (correlation coefficients >0.9991) over the herbicide concentration range 1-150 μg/L using the optimal conditions. The limits of detection (the concentrations giving signal/noise ratios of 3) were low, at 0.12-0.34 μg/L, and repeatability was good (the relative standard deviations were <4.8%, n = 6). The method was used successfully to determine four sulfonylurea herbicides in environmental water and vegetable samples, giving satisfactory recoveries of 87.1-108.9%. The extraction efficiency achieved using MIL-101(Fe)@polydopamine@Fe₃ O₄ was compared with the extraction efficiencies achieved using other magnetic composites (polydopamine@Fe₃ O₄ , Hong Kong University of Science and Technology (HKUST)-1@polydopamine@Fe₃ O₄ , and MIL-100(Fe)@polydopamine@Fe₃ O₄ ). The results showed that the magnetic MIL-101(Fe)@polydopamine@Fe₃ O₄ composites have great potential for the extraction of trace sulfonylurea herbicides from various sample types.

Facile synthesis of a Fe3O4/MIL-101(Fe) composite with enhanced catalytic performance

The as-prepared Fe₃O₄/MIL-101(Fe) shows enhanced catalytic performance for the dimerization reaction of o-phenylenediamine via synergistic peroxidase-like activity.