Postsynthetic Modification of Core–Shell Magnetic Covalent Organic Frameworks for the Selective Removal of Mercury

Abstract

Core–shell magnetic covalent organic framework (COF) materials were prepared, followed by shell material functionalization with different organic ligands, including thiosemicarbazide, through a postsynthetic modification approach. The structures of the prepared samples were characterized with various techniques, including powder X-ray diffraction (PXRD), Brunauer–Emmett–Teller (BET) method, thermogravimetric analysis (TGA), photoinduced force microscopy (PiFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and solid 13C NMR. PXRD and BET studies revealed that the crystalline and porous nature of the functionalized COFs was well maintained after three steps of postsynthetic modification. On the other hand, solid 13C NMR, TGA, and PiFM analyses confirmed the successful functionalization of COF materials with good covalent linkage connectivity. The use of the resulting functionalized magnetic COF for selective and ultrafast adsorption of Hg(II) has been investigated. The observations displayed rapid kinetics with adsorption dynamics conforming to the quasi-second-order kinetic model and the Langmuir adsorption model. Furthermore, this prepared crystalline magnetic material demonstrated a high Langmuir Hg(II) uptake capacity, reaching equilibrium in only 5 min. Thermodynamic calculations proved that the adsorption process is endothermic and spontaneous.

Rapid, Mild, and Catalytic Synthesis of 2D and 3D COFs with Promising Supercapacitor Applications

“…Therefore, at first, the effects of two different Keggin HPAs including phosphotungstic (PTA, H 3 PW 12 O 40 ) and phosphomolybdic acid (PMA, H 3 PMo 12 O 40 ) were investigated for the synthesis of TPT-PDA COF from the Schiff base polycondensation reaction between 2,4,6-tris­(4-formylphenoxy)-1,3,5-triazine (TPT) and p -pheneylenediamine (PDA) with the aid of PXRD analysis (Scheme S2). Similar to the acetic acid, HPAs as a Bronsted acid can produce a proton (H + ) to catalyze the Schiff base polycondensation reaction between aldehyde and amine (Scheme S3). Hence, at first, the aldehyde can be activated with a proton to be ready for an amine attack, and then, after loss of one H 2 O molecule, the final Schiff base product can be produced.…”

Emerging trends in membrane-based wastewater treatment: electrospun nanofibers and reticular porous adsorbents as key components

“…Most recently, Khojastehnezhad et al demonstrated the significance of PSM of a COF (covalent organic framework) in enhancing the heavy metal removal performance. 325 Initially, they synthesized an imine-linked TFPOT-PDA COF on the surface of spherical Fe 3 O 4 nanoparticles with a particle size of 200 nm. Subsequently, a three-step PSM was carried out to incorporate thiourea units into the COF structure.…”

Linkage Transformations in a Three-Dimensional Covalent Organic Framework for High-Capacity Adsorption of Perfluoroalkyl Substances

“…The need to functionalize monomers in the early stages of COF synthesis prevents chemists from rapidly establishing structure–property relationships and leads to costly and time-intensive synthetic routes. Alternatively, it has been shown that COFs can undergo chemical transformations, postsynthetically, to add additional functionality without altering the existing framework. − This strategy is particularly useful for three-dimensionally linked (3D) COFs, whose monomers draw from a limited selection of tetrahedral building blocks. We sought to expand the range of functionality in 3D COFs because these 3D networks show improved stability and crystallinity compared with their 2D counterparts.…”