Covalent-Frameworked 2D Crown Ether with Chemical Multifunctionality

Abstract

Here, we present the synthesis and characterization of a novel 2D crystalline framework, named C 2 O, which mainly consists of carbon and oxygen in a 2:1 molar ratio and features crown ether holes in its skeletal structure. The covalentframeworked 2D crown ether can be synthesized on a gram-scale and exhibits fine chemical stability in various environments, including acid, base, and different organic solvents. The C 2 O efficiently activates KI through the strong coordination of K + with crown ether holes in a rigid framework, which enhances the nucleophilicity of I − and significantly improves its catalytic activity for CO 2 fixation with epoxides. The presence of C 2 O with KI results in remarkable increases in CO 2 conversion from 5.7% to 99.9% and from 2.9% to 74.2% for epichlorohydrin and allyl glycidyl ether, respectively. Moreover, C 2 O possesses both electrophilic and nucleophilic sites at the edge of its framework, allowing for the customization of physicochemical properties by a diverse range of chemical modifications. Specifically, incorporating allyl glycidyl ether (AGE) as an electrophile or ethoxyethylamine (EEA) as a nucleophile into C 2 O enables the synthesis of C 2 O-AGE or C 2 O-EEA, respectively. These modified frameworks exhibit improved conversions of 97.2% and 99.9% for CO 2 fixation with allyl glycidyl ether, outperforming unmodified C 2 O showing a conversion of 74.2%. This newly developed scalable, durable, and customizable covalent framework holds tremendous potential for the design and preparation of outstanding materials with versatile functionalities, rendering them highly attractive for a wide range of applications.

Remarkably high tensile strength and lattice thermal conductivity in wide band gap oxidized holey graphene C2O nanosheet

“…Shifting our focus to the structural properties of the two monolayers, the optimized lattice constants for the C 2 O and C 2 N monolayers are 8.24 and 8.33 Å, respectively. The calculated lattice constant for the C 2 N is in good agreement with previous theoretical reports (8.325 Å [ 52 ] and 8.33 Å [ 53 ]), and that of the C 2 O monolayer is also very close to the experimentally determined value of 8.25 Å [ 27 ]. Examination of bond lengths in both C 2 O and C 2 N monolayers reveal that despite of the slightly longer lattice constant in the C 2 N lattice, C–C bond lengths in C 2 N (1.43 and 1.47 Å) are slightly more elongated than their counterparts in the C 2 O lattice (1.39 and 1.40 Å).…”

“…In order to investigate the comparative synthesis favorability of the C 2 O and C 2 N monolayers, we calculated their polymerization energy. According to an experimental report [ 27 ], the C 2 O lattice was simply synthesized by the self-condensation reaction of trichlorophloroglucinol: 2C 6 O 3 Cl 3 H 3 → 6C 2 O + 6HCl. While there are several synthesis routes for the synthesis of C 2 N [ 50 , 51 ], we adopted the condensation reaction between hexaaminobenzene and hexaketocyclohexane, resulting in: C 6 N 6 H 12 + C 6 O 6 → 6C 2 N + 6H 2 O.…”

“…In Fig. 5 b the MTP-based NEMD predictions for the length effects on the room temperature phononic thermal conductivity of the C 2 O nanosheet is plotted, assuming a thickness of 3.5 Å according to the experimental report [ 27 ]. In the NEMD simulations, after the initial equilibration with the NPT method, a few rows of atoms at both ends were fixed and then the remaining of the system was then divided into 22 sections along the heat transport direction, with a 20 K temperature difference applied between the two ends using the NVT method.…”

“…VESTA [ 43 ] and OVITO [ 44 ] free packages were employed to illustrate the atomic structures.We utilized the LAMMPS package [ 45 ] to examine thermal and mechanical properties based on the trained MTP, with a time step of 0.5 fs. We assumed a fixed thickness of 3.5 Å for the C 2 N and C 2 O monolayers, according to the experimental report [ 27 ]. Non-equilibrium molecular dynamics (NEMD) simulations on the basis of the trained MTP were carried out to evaluate the length-dependent lattice thermal conductivity of the C 2 O monolayer, using the same approach as that discussed in our previous studies [ 46 – 48 ].…”

“…In a latest breakthrough in the synthesis of nanoporous carbon-based nanomembranes, an oxidized holey graphene with a chemical formula of C 2 O, was fabricated through an irreversible nucleophilic aromatic substitution reaction [ 27 ]. From a practical standpoint, assessing the various physical properties of the C 2 O nanosheets is crucial to determine their suitability across diverse applications.…”