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

Core-shellmagnetic covalent organic framework (COF) materialswere prepared, followed by shell material functionalization with differentorganic ligands, including thiosemicarbazide, through a postsyntheticmodification approach. The structures of the prepared samples werecharacterized with various techniques, including powder X-ray diffraction(PXRD), Brunauer-Emmett-Teller (BET) method, thermogravimetricanalysis (TGA), photoinduced force microscopy (PiFM), transmissionelectron microscopy (TEM), scanning electron microscopy (SEM), X-rayphotoelectron spectroscopy (XPS), and solid C-13 NMR. PXRDand BET studies revealed that the crystalline and porous nature ofthe functionalized COFs was well maintained after three steps of postsyntheticmodification. On the other hand, solid C-13 NMR, TGA, andPiFM analyses confirmed the successful functionalization of COF materialswith good covalent linkage connectivity. The use of the resultingfunctionalized magnetic COF for selective and ultrafast adsorptionof Hg-(II) has been investigated. The observations displayed rapidkinetics with adsorption dynamics conforming to the quasi-second-orderkinetic model and the Langmuir adsorption model. Furthermore, thisprepared crystalline magnetic material demonstrated a high LangmuirHg-(II) uptake capacity, reaching equilibrium in only 5 min. Thermodynamiccalculations proved that the adsorption process is endothermic andspontaneous.