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Metal-Organic Frameworks (MOFs): Multi-Functionality within Order
Published in Esteban A. Franceschini, Nanostructured Multifunctional Materials Synthesis, Characterization, Applications and Computational Simulation, 2021
The organic struts (also called linkers) employed in the construction of MOFs are polyfunctional organic molecules, generally featuring a certain rigidity (shape persistent molecules) and high symmetry. Different functional groups have been used so far in these organic struts for binding the SBUs and holding the structure together. Among them, N-heterocycles were extensively used during the early development of MOFs. For instance, bipyridyl organic struts with different length were employed for the synthesis of a variety of high-dimensionality coordination structures including MOFs. Recently, bipyridyl struts have been mostly used in the construction of 3D pillared-layer structures, where 2D coordination layers are extended to 3D frameworks by the introduction of these N-heterocycle ‘bridges’ (Seo et al. 2009). Although these pyridyl struts can add interesting features to MOFs such as structure flexibility and a dynamic adsorption behavior, compared to other bridging coordination modes, they possess a relatively weak donor-ability, which translates to instability in the MOFs structures (Lu et al. 2014). Due to this reason, other N-heterocycles such as azolate-derivatives were more attractive for researchers in the construction of MOF. Imidazolate rings were used in the preparation of metal–imidazolate frameworks called Zeolitic Imidazolate Frameworks (ZIFs) due to their similarity to zeolite topologies. In ZIFs, imidazole derivatives used as organic struts (called HIM) deprotonate to form IM- anions (or simply IM) that bind tetrahedral metal centres with M-IM-M bond angles close to 145°, which resemble Si-O-Si linkage in zeolites (Park et al. 2006, Hayashi et al. 2007, Eddaoudi et al. 2015). The strong bonds between IM and the divalent metal cations (e.g., Zn2+, Fe2+, Co2+), along with the hydrophobicity of the formed cavities, provided ZIFs with excellent thermal and chemical stability, as well as gas separation properties (Nguyen et al. 2014). A few years ago the scope of this chemistry reported that ZIFs with cavities up to 4.6 nm and BET surface areas above 1400 m2.g−1 ( ZIF-414, Zn(nbIM)0.91(mIM)0.62(IM)0.4) . In the case of the reported ZIF-414, the steric effects provided by the chosen combination imidazolate-derivatives (nbIM: 6-nitrobenzimidazolate, mIM: 2-methylimidazolate and IM: imidazolate) led to the crystallization of structures with extra-large pore openings (Yang et al. 2017).
Preparation of a novel CSM@ZIF-67 composite microsphere to facilitate Congo red adsorption from dyeing wastewater
Published in Environmental Technology, 2023
Yan Zhao, Ning Yuan, Di Bian, Jianjun Sun, Guangsheng Qian
The zeolitic imidazolate framework-67 (ZIF-67) is a class of metal-organic frameworks (MOFs) composed of tetrahedrally coordinated transition metals. It possesses the structural advantages of conventional MOFs, such as high crystallinity and small specific surface area; additionally, it overcomes their disadvantages of poor thermal and chemical stability. According to the HSAB theory, ZIFs are borderline divalent metals with strong metal-ligand bonds with soft N-donor ligands (e.g. azo dyes). ZIFs are characterized with high crystallinity, small specific surface area, and excellent chemical stability [12]. They have been reported to selectively remove 60–70% of anionic dyes, and most of their synthetic composites have been found to remove more than 90% of anionic dyes [13, 14]. Lin et al. found that the maximum adsorption capacity of ZIF-67 for the oxidized amaranth dye at room temperature was 121 mg/g [15]. Yang et al. reported a magnetic ZIF-67 composite material prepared using the hot solvent method, and the experimental results revealed that its adsorption efficiency for methyl orange was as high as 92% after 800 min of operation at a pH of 8 [13]. However, the small particle size of ZIF-67 makes it prone to agglomeration during the adsorption process; further, it is readily decomposed under acidic and alkaline conditions, and has unsatisfactory recovery performance when used exclusively, all of which limit its application in the adsorption field [16, 17].
Green synthesis of SiO2 from Equisetnm arvense plant for synthesis of SiO2/ZIF-8 MOF nanocomposite as photocatalyst
Published in Journal of Coordination Chemistry, 2023
Babak Azari, Afshin Pourahmad, Babak Sadeghi, Masoud Mokhtary
A SiO2/ZIF-8 has photocatalytic activity and high stability with respect to pure SiO2 and ZIF-8. The SiO2 was extracted from Equisetnm arvense plant. The SiO2/zeolitic imidazolate framework-8 was synthesized by solvothermal method and used for removal of crystal violet as cationic dye. The nanocomposite had 98% removal of dye under UV irradiation. Important advantages of SiO2/ZIF-8 in degradation of dye over other photocatalysts is the low degradation time (15 min) and small amount of catalyst dose (0.07 g/L). The DRS result indicated ZIF-8 is an UV-light driven photocatalyst, so the photocatalytic activity of SiO2/ZIF-8 is mainly derived from ZIF-8. The SiO2 as support played important roles in the photodegradation mechanism, such as maximum interfacial contact ZIF-8 with the SiO2 surface without aggregation, preventing the accumulation of ZIF-8 and SiO2, accelerating the separation and transfer of electron-hole pairs of ZIF-8.
Metal organic frameworks: an effective application in drug delivery systems
Published in Inorganic and Nano-Metal Chemistry, 2022
Christine Jeyaseelan, Priyansh Jain, Deeya Soin, Deepshikha Gupta
In sono-chemical synthesis, ultra-sound radiations are used. According to Suslick et al.,[35] this method arises from acoustic cavitation during which implosion of bubbles takes place. This, consequently, creates hot spots having temperature ∼ 5000 K and pressure about 1800 atmosphere with the rate of cooling exceeding 109 Ks−1. Unlike solvothermal synthesis it is a solvent free method that can be carried out at room temperature. It is also considered to be a green synthetic method for synthesis of MOFs.[36]Figure 3 represents the sonochemical synthesis of Lipase-MOF. Nadar and Rathod[37] studied that when Lipase enzyme shows enhanced activity when it is treated with low intensity ultrasonic radiation. This highly activated lipase is then encapsulated with Zeolitic imidazolate framework-8 or ZIF-8 (Figure 1b) by biomineralization to form Lipase-MOF.