Metal-Organic Nanosheets (MONs): Exfoliation by Mechanical Grinding and Iodine Capture

An electron-rich pi-conjugated organic linker H4BPDP (BPDP = biphenyl dipyrrole tetracarboxylic acid) is designed and subjected to metal-assisted self-assembly to afford a layered metal-organic framework (MOF), i.e., Cd-BPDP. Single crystal X-ray structure determination and analysis show that two corrugated layers of the MOF are intertwined to yield thick strands of porous 2D metal-organic nanosheets (MONs). It is shown that the latter can be delaminated by ultrasonication-induced liquid-phase exfoliation and mechanical grinding techniques, as evidenced by Tyndall light scattering and comprehensive microscopy investigations that include field emission scanning electron microscopy (FESEM), atomic force microscopy, and high-resolution transmission electron microscopy. The MONs accessed by grinding permit notable capture of iodine when compared to the bulk layered MOF, i.e., Cd-BPDP; the extent of iodine capture can be correlated with the magnitude exfoliation, which is essentially determined by the duration of grinding. The observed notable iodine capture is attributed to i) a large increase in surface area with exfoliation, ii) ability of the e-rich pi-conjugated organic linker to form a charge-transfer complex with iodine, and iii) the presence of free and uncoordinated carboxylic acids of the linker that reinforce binding of iodine through charge transfer. Thus, a notable capture of iodine by 2D MONs generated by mechanical exfoliation of a layered MOF constructed from an e-rich pi-extended organic linker is compellingly demonstrated.

Automated summary

A layered metal-organic framework (MOF), Cd-BPDP, was synthesized using a metal-assisted self-assembly method. The MOF was then exfoliated into porous 2D metal-organic nanosheets (MONs) through ultrasonication and mechanical grinding techniques. The resulting MONs showed significant iodine capture ability, attributed to the increased surface area, charge-transfer complex formation, and reinforced binding of iodine through charge transfer.