Contiguous layer based metal-organic framework with conjugated π-electron ligand for high iodine capture

Construction of Ketoenamine-Based Covalent Organic Frameworks with Electron-Rich Sites for Efficient and Rapid Removal of Iodine from Solution

Porous covalent organic frameworks (COFs) have been widely used for the efficient removal of iodine from solution due to their abundance of electron-rich sites. In this study, two kinds of ketoenamine-based COFs, TpBD-(OMe)2 and TpBD-Me2, are successfully synthesized via Schiff base reaction under solvothermal conditions using 1, 3, 5-triformylphoroglucinol as aldehyde monomer, o-tolidine and o-dianisidine as amino monomers. The ability of TpBD-(OMe)2 and TpBD-Me2 to adsorb iodine in cyclohexane or aqueous solutions has been quantitatively analyzed and interpreted in terms of adsorption sites. TpBD-Me2 possesses two adsorption sites, -NH- and -C=O, and exhibits an adsorption capacity of 681.67 mg/g in cyclohexane, with an initial adsorption rate of 0.6 g/mol/min with respect to COF unit cell. The adsorption capacity of TpBD-(OMe)2 can be as high as 728.77 mg/g, and the initial adsorption rate of TpBD-(OMe)2 can reach 1.2 g/mol/min in the presence of oxygen atoms between the methyl group and the benzene ring. Compared with TpBD-Me2, the higher adsorption capacity and adsorption rate of TpBD-(OMe)2 towards iodine are not only reflected in organic solvents, but also in aqueous solutions. It is proven through X-ray photoelectron spectroscopy and Raman spectroscopy that iodine exists in the form of I2, I3-, and I5- within TpBD-(OMe)2 and TpBD-Me2 after adsorption. This work not only expands the application of COFs in the field of iodine adsorption, but also provides research ideas and important an experimental basis for the optimization of iodine adsorption sites.

A bifunctionalised Pb-based MOF for iodine capture and dye removal

A 2-dimensional Pb(II) metal-organic framework, [Pb(bdc)_0.5(py-Phen)NO₃]_n (SM-3), was synthesized under solvothermal conditions using a mixed ligand approach. SM-3 was assembled using dinuclear SBUs [Pb₂(COO)₂]^2-, an oxygen donor H₂bdc = 1,4-benzene dicarboxylic acid, and nitrogen donor py-Phen = pyrazino[2,3-f][1,10]-phenanthroline linkers. SM-3 was characterized by elemental analysis, FT-IR, powder-X-ray diffraction, thermal gravimetric analysis, SEM, EDS, TEM, and single-crystal X-ray diffraction techniques. Crystallographic studies confirmed that SM-3 displays a 2D layered structure with unique anagostic (Pb⋯H) interactions. Interestingly, the presence of abundant π-electron-rich rings embellished with free -N donor sites in the framework makes SM-3 an excellent adsorbent that exhibits adsorption performance for iodine and dyes. The experimental results show that SM-3 reversibly adsorbs radioactive iodine in the solution and vapor phases and exhibits selective adsorption performance for hazardous cationic dyes, namely, methylene blue (MB) and rhodamine-B (Rh-B), from aqueous solution. Moreover, the possible mechanism of iodine and dye adsorption was also discussed in detail. Thus, this work is remarkable for coordination chemists to engineer layered MOFs for adsorption purposes and expands their potential characteristics by converting them into 2D MOF nanosheets to further enhance the adsorption of hazardous pollutants for environment protection.

Exploiting a Multi-Responsive Oxadiazole Moiety in One Three-Dimensional Metal-Organic Framework for Remedies to Three Environmental Issues

Multifunctional metal-organic frameworks (MOFs) rely on the properties of metal centers (nodes) and/or linkers (struts) for their diverse applications in the emerging field of research. Currently, there is a huge demand for MOF materials in the field of capture/fixation/sensing of air pollutants, harmful chemical effluents, and nuclear waste. However, it is a challenging task to utilize one MOF for providing remedies to all these issues. On the basis of our current research activities, we have identified that an oxadiazole moiety-a five-membered ring with two different heteroatoms (O and N)-in a carboxylate linker can be the key to generating such MOF materials for its (a) inherent polarizable nature and molecular docking ability and (b) photoluminescence properties. In this work, we report a 3D MOF {[Co₂(oxdz)₂(tpbn)(H₂O)₂]·4H₂O}_n (1), self-assembled at room temperature from a three-component reaction, with an oxadiazole moiety (where H₂oxdz = 4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoic acid and tpbn = N,N',N,"N″'-tetrakis(2-pyridylmethyl)-1,4-diaminobutane). The inherent polarizable nature of the oxadiazole moiety in 1 has been efficiently exploited for (i) multimedia iodine capture and (ii) fixation of CO₂ under solvent-free and ambient conditions. On the other hand, the luminescent nature of the framework is found to be an efficient, highly preferred turn-on sensor for the ultra-fast detection of ketones with a limit as low as parts-per-trillion (mesitylene oxide: 447 ppt; cycloheptanone: 4.7 ppb; cyclohexanone: 17.2 ppb; acetylacetone: 18 ppb).

A series of isostructural lanthanide metal-organic frameworks: effective fluorescence sensing for Fe3+, 2,4-DNP and 4-NP

Because of the fluorescence properties, lanthanide metal-organic frameworks (Ln-MOFs) materials have potential application in the detections of metal ions and nitro-aromatic explosives. Herein, a series of isostructural Ln-MOFs [Ln2(PIA)3(DMF)3(CH3OH)] (JLU-MOF201-Ln,...