Cutting COF‐like C₄N to Give Colloidal Quantum Dots: Towards Optical Encryption and Bidirectional Sulfur Chemistry via Functional Group and Edge Effects

Abstract

Herein, we report the first synthesis of colloidal C4N quantum dots (QDs) and their functional composites and explore their optical activities and edge‐selective polysulfide adsorption‐catalysis. As‐obtained C4NQDs are rich in carbonyl groups and edges, allowing good solution processability and facile assembly with other moieties for creating functionalities. While C4NQDs show normal fluorescence (FL), the QD/poly(vinyl alcohol) (PVA) composites give FL/room‐temperature‐phosphorescence (RTP) dual‐mode emission, enabling the corresponding solution to be used as an encryption ink. The QDs anchored onto carbon nanotubes can be used as a barrier layer to decorate commercial separators, endowing a Li−S cell with excellent cycling stability, high rate capability, and large areal capacity. Computation and experiment studies show that edge sites in C4N favor polysulfide adsorption and catalysis and the enriched edges and carbonyl groups in QDs synergically promotecatalytic conversion of sulfur species.

C4N quantum dots/g-C3N4 nanosheets organic homogeneous structure self-assembly for efficient charge separation and photocatalytic hydrogen evolution

“…1a From HR-TEM testing (Fig. 1d), two different widths of lattice stripes, 0.330 nm and 0.325 nm, can be observed, 18,19 which belong to C 4 N quantum dots and the (002) crystal plane of g-C 3 N 4 nanosheets, respectively. 25,26 In addition, according to the quantum dot size statistics of the AFM image for C 4 NQDs (Fig.…”

“…Previous reports have shown that the C 4 N polymer synthesized by adjusting the N/C stoichiometry could effectively narrow the band gap and promote charge separation, which was a new low band gap carbon nitride polymer. [18][19][20][21] More importantly, C 4 N and g-C 3 N 4 are also composed of C and N, which is more conducive to close integration. [22][23][24] Therefore, the combination of C 4 N dots and g-C 3 N 4 maybe a promising strategy for improving the photoelectric performance.…”

Carbon-Nitride-Based Materials for Advanced Lithium–Sulfur Batteries

“…Yu et al reported a covalent organic framework (COF)-like C x N y material, C 4 N, with a C/N ratio of 4:1 connected with pyrazine, and subsequently prepared ultra-small colloidal C 4 N quantum dots (C 4 NQDs) with the average size of 2.2 nm (Fig. 10 a) [ 112 ]. Pyrazine N atoms and carbonyl groups at the edge of C 4 NQDs show preferential adsorption capability to LiPSs with significantly higher binding energy compared with that of the N sites in the C 4 NQDs plane (Fig.…”

“…10 a Schematic illustration of the structure of C 4 N. b Adsorption energies for Li 2 S, Li 2 S 2 , Li 2 S 4 , Li 2 S 6 , and Li 2 S 8 on various sites of C 4 N. c Potentiostatic discharge curves and d potentiostatic charge curves of Li 2 S precipitation on the CP, C 4 NNSs/CP and C 4 NQDs/CP. e Cycling performance of cells with CNT modified separator and C 4 NQDs@CNT modified separator at 1.0C [ 112 ]. Copyright 2021, Wiley–VCH …”

Fabricating Covalent–Organic Quantum Dots through Selective Disassembly of Hydrogen-Covalent Hybridized Organic Frameworks for Efficient and Sensitive Uranium Detection

“…14−16 However, the reported COFs usually exist in the form of insoluble polycrystalline powders, which hinder their processing and shaping, thereby limiting their practical applications to some extent. Notably, reducing the size of COFs is an effective approach to enhancing their solubility or dispersibility, and the common reported methods include solvent-assisted ultrasound treatment 17 and ball milling, 18 etc. However, due to the high bond energy of covalent bonds within the COF structure, it is challenging to achieve bond breaking at the atomic level through simple ultrasonic treatment or ball milling, leading to limited size reduction and heterogeneous size distribution.…”