Versatile, Aqueous Soluble C₂N Quantum Dots with Enriched Active Edges and Oxygenated Groups

Abstract

C2N has emerged as a new family of promising two-dimensional (2D) layered frameworks in both fundamental studies and potential applications. Transforming bulk C2N into zero-dimensional quantum dots (QDs) could induce unique quantum confinement and edge effects that produce improved or new properties. Despite their appealing potential, C2NQDs remain unexplored, and their intriguing properties and a fundamental understanding of their prominent edge effects are still not well understood. Here, we report the first synthesis of water-soluble C2NQDs via a top-down approach without any foreign stabilizer and exploit their linear/nonlinear optical properties and unique edge-preferential electrocatalytic activity toward polysulfides for versatile applications. The resultant dispersant-free C2NQDs with an average size of less than 5 nm feature rich oxygen-carrying groups and active edges, not only enabling excellent dispersion in water but also creating interesting multifunctionality. They can emit not only blue one-photon luminescence (OPL) under ultraviolet (UV) excitation but also green two-photon luminescence (TPL) with a wide near-infrared (NIR) excitation range of 750-900 nm, enabling their use as a new fluorescent ink. Interestingly, when C2NQDs are introduced to modify commercial separators, they can function as new metal-free catalysts to boost polysulfide redox kinetics and endow Li-S batteries with excellent cycling stability, high rate capability, and large areal capacity (7.0 mA h cm–2) at a high sulfur loading of 8.0 mg cm–2. Detailed theoretical and experimental results indicate that the edge of C2N is more favorable for trapping and catalyzing the polysulfide conversion than the terrace and that the synergy between the active edges and oxygenated groups enriched in C2NQDs remarkably improves polysulfide immobilization and catalytic conversion.

C2N: A Class of Covalent Frameworks with Unique Properties

“…These results indicated that the oxygenated edges enriched in the C 2 NQDs significantly improved the polysulfide immobilization and catalytic conversion. [ 111 ]…”

Macroporous Multichannel Carbon Nanofibers Embedded with Co/Fe‐N Electrocatalyst as the Sulfur Host for Boosting Polysulfides Conversion in Lithium‐Sulfur Batteries

“…Notably, the binding energy of Co/FeÀ N increases from 398.92 to 399.72 eV, implying that the nitrogen in Co/FeÀ N serving as electron-rich donors can interact with lithium atoms in LiPSs molecules to form LiÀ N bond. [45] In the Li 1s spectrum (Figure 3d), the peak located at 55.48 eV is ascribed to the LiÀ S bond of Li 2 S 6 and a new characteristic peak at 56.34 eV is belonged to the LiÀ N bond. The XPS analysis suggests that Co/FeÀ N/MCFs have double-end binding sites towards LiPSs, which improve LiPSs trapping capacity.…”

“…Additionally, the N 1s peaks of Co/Fe−N/MCFs upshift to higher binding energies after treating with Li 2 S 6 solution (Figure 3c). Notably, the binding energy of Co/Fe−N increases from 398.92 to 399.72 eV, implying that the nitrogen in Co/Fe−N serving as electron‐rich donors can interact with lithium atoms in LiPSs molecules to form Li−N bond [45] . In the Li 1s spectrum (Figure 3d), the peak located at 55.48 eV is ascribed to the Li−S bond of Li 2 S 6 and a new characteristic peak at 56.34 eV is belonged to the Li−N bond.…”

Effect of Oxygen-Containing Group on the Catalytic Performance of Zn/C Catalyst for Acetylene Acetoxylation

“…All the samples demonstrated that more OCGs, especially –COOH, were introduced to the surface of AC. To further reveal the changes in OCGs on the supports before and after the ozone treatment, the Boehm titration method ( Appendix A ) [ 27 ] and XPS [ 28 , 29 ] analysis were exploited to investigate the property of the AC surface.…”