Chemically Stable Multilayered Covalent Organic Nanosheets from Covalent Organic Frameworks via Mechanical Delamination

Abstract

A series of five thermally and chemically stable functionalized covalent organic frameworks (COFs), namely, TpPa-NO2, TpPa-F4, TpBD-(NO2)2, TpBD-Me2, and TpBD-(OMe)2 were synthesized by employing the solvothermal aldehyde-amine Schiff base condensation reaction. In order to complete the series, previously reported TpPa-1, TpPa-2, and TpBD have also been synthesized, and altogether, eight COFs were fully characterized through powder X-ray diffraction (PXRD), Fourier transform IR (FT-IR) spectroscopy, (13)C solid-state NMR spectroscopy, and thermogravimetric analysis. These COFs are crystalline, permanently porous, and stable in boiling water, acid (9 N HCl), and base (3 N NaOH). The synthesized COFs (all eight) were successfully delaminated using a simple, safe, and environmentally friendly mechanical grinding route to transform into covalent organic nanosheets (CONs) and were well characterized via transmission electron microscopy and atomic force microscopy. Further PXRD and FT-IR analyses confirm that these CONs retain their structural integrity throughout the delamination process and also remain stable in aqueous, acidic, and basic media like the parent COFs. These exfoliated CONs have graphene-like layered morphology (delaminated layers), unlike the COFs from which they were synthesized.

Self-templated chemically stable hollow spherical covalent organic framework

“…COFs are usually synthesized as microcrystalline powders and their long-range growth is limited in the nano/micro domain due to the internal defects [11][12][13] . COF crystallites have been reported to have adopted various shapes such as belts 6 , fibres 14 , sheets 15 , cubes 16 , rectangular prisms 17 , spheres and platelets 18 . However, the mechanisms of the formation and self-assembly of COF crystallites are still poorly understood.…”

Mercury nano-trap for effective and efficient removal of mercury(II) from aqueous solution

“…1) that features high surface area with densely populated yet highly accessible Hg(II) binding sites thereby affording high Hg(II) adsorption capacity; strong Hg(II) chelating groups that are well dispersed throughout the single-walled pore surface thus rendering high affinity for Hg(II) and efficient utilization of Hg(II) binding sites; large yet tunable pore size to enable fast yet controllable kinetics of Hg(II) adsorption; Hg(II) chelating groups that are covalently anchored to the backbone thus avoiding the leaching of binding sites; exceptional water/chemical stability facilitating regeneration/recyclability. Such mercury 'nano-trap' can be targeted by grafting desired Hg(II) chelating groups to the highly robust porous organic polymers (POPs) [35][36][37][38][39][40][41][42][43][44] that exhibit high surface areas, tunable pore sizes and high water/ chemical stabilities, via stepwise post-synthetic modification 45 of the phenyl rings of their structural components using various established organic reactions. Herein we demonstrate such a POP-based mercury 'nano-trap' that exhibits an exceptional mercury saturation uptake capacity of over 1,000 mg g À 1 and can effectively reduce Hg(II) concentration from 10 p.p.m.…”

Intensified synthesis and post-synthetic modification of covalent organic frameworks using a continuous flow of microdroplets technique

“…22,31 In a typical procedure, a solution containing 0.08 M Tp and 0.12 M the corresponding p-diamine in 2 ml of a N,N-DMA and water mixture (9:1, v/v) and 6 M aqueous acetic acid (Supplementary Table S1 and Supplementary Figure S1) was first fed into a T-micromixer through a 0.01 m straight capillary. Silicone/ FC-40 oil, utilized as a carrier fluid, enabled smooth microdroplet generation with a lateral diameter of~200 μm at the T-micromixer with judiciously optimized flow rates (dV/dt).…”

“…22 All other chemicals, including reagents and solvents were commercially available and procured either from Sigma-Aldrich (Seoul, Korea), Alfa-Aesar (Seoul, Korea) or TCI Chemicals (Tokyo, Japan). All reagents were used as received without any further purification.…”

“…2,17 Additional post-synthetic modification step(s) with time-consuming purifications and separations are often required. 18,19 Alternate synthetic approaches are scarce, except for microwave-assisted synthesis, 20,21 which has rather inconsistent synthetic control; mechanosynthesis, 22 which affords COFs with relatively low crystallinity; and a few flow-based approaches, which lack longterm scalability owing to potential channel blockage issues with time. In particular, there are no reports on performing serially intensified synthesis and post-synthetic modification of COFs.…”