Insight into the Transimination Process in the Fabrication of Surface Schiff-Based Covalent Organic Frameworks

Cu2O/2D COFs Core/Shell Nanocubes with Antiphotocorrosion Ability for Efficient Photocatalytic Hydrogen Evolution

Photocorrosion of highly active photocatalysts is an urgent problem to be solved in the field of photocatalysis; however, searching for effective strategies for inhibiting photocorrosion of photocatalysts is still a grand challenge. Herein, we design and construct a class of Cu₂O/2D PyTTA-TPA COFs (PyTTA: 1,3,6,8-Tetrakis(4-aminophenyl)pyrene, TPA: p-benzaldehyde) core/shell nanocubes to greatly boost the performance of photocatalytic hydrogen evolution and significantly inhibit the photocorrosion. The optimal Cu₂O/PyTTA-TPA COFs core/shell nanocubes exhibit an excellent photocatalytic H₂ evolution rate of 12.5 mmol h^-1 g^-1, which is ∼8.0-fold and ∼20.0-fold higher than those of PyTTA-TPA COFs and Cu₂O nanocube, respectively, and also is the best in all the reported metal oxides catalytic materials. The mechanism studies demonstrate that the appropriate matching band gaps and tight integration of PyTTA-TPA COFs and Cu₂O nanocubes can significantly facilitate the separation of photogenerated electron-hole pairs in the Cu₂O/PyTTA-TPA COFs core/shell nanocube during the photocatalytic process, which ameliorates the photocatalytic H₂ evolution activity. Most importantly, the 2D PyTTA-TPA COFs shell with outstanding intrinsic stability protects Cu₂O nanocubes core from photocorrosion by showing no morphology and crystal structure change after 1000 times of photoexcitation.

Insights into the Polymerization Reactions on Solid Surfaces Provided by Scanning Tunneling Microscopy

Understanding the polymerization process at the molecular level is essential for the rational design and synthesis of polymers with controllable structures and properties. Scanning tunneling microscopy (STM) is one of the most important techniques to investigate the structures and reactions on conductive solid surfaces, and it has successfully been used to reveal the polymerization process on the surface at the molecular level in recent years. In this Perspective, after a brief introduction of on-surface polymerization reactions and STM, we focus on the applications of STM in the study of the processes and mechanism of on-surface polymerization, from one-dimensional to two-dimensional polymerization reactions. We conclude by a discussion of the challenges and perspectives on this topic.

Two-dimensional covalent organic framework films prepared on various substrates through vapor induced conversion

Covalent organic frameworks (COFs) can exhibit high specific surface area and catalytic activity, but traditional solution-based synthesis methods often lead to insoluble and infusible powders or fragile films on solution surface. Herein we report large-area –C=N– linked two-dimensional (2D) COF films with controllable thicknesses via vapor induced conversion in a chemical vapor deposition (CVD) system. The assembly process is achieved by reversible Schiff base polycondensation between PyTTA film and TPA vapor, which results in a uniform organic framework film directly on growth substrate, and is driven by π‐π stacking interactions with the aid of water and acetic acid. Wafer-scale 2D COF films with different structures have been successfully synthesized by adjusting their building blocks, suggesting its generic applicability. The carrier mobility of PyTTA-TPA COF films can reach 1.89 × 10⁻³ cm² V⁻¹ s⁻¹. When employed as catalysts in hydrogen evolution reaction (HER), they show high electrocatalytic activity compared with metal-free COFs or even some metallic catalysts. Our results represent a versatile route for the direct construction of large-area uniform 2D COF films on substrates towards multi-functional applications of 2D π‐conjugated systems.

Solution-based synthesis of covalent organic frameworks (COFs) often leads to insoluble powders or fragile films on solution surfaces. Here, the authors report large-area two-dimensional (2D) COF films with controllable thicknesses via vapour induced conversion.

On-Surface Self-Assembled Structural Transformation Induced by Schiff Base Reaction and Hydrogen bonds

By utilizing scanning tunneling microscopy (STM), the self-assembled nanostructures of three characteristic aldehydes have been examined at the solution-solid interface. By introducing the active reactant 5-aminoisophthalic acid (5-AIPA), we succeeded in changing the self-assembled molecular structures through the condensation reaction and obtained the information on structural transformation in real time. The corresponding carboxyl conjugated derivatives were formed in situ and developed into the closely packed and ordered molecular architectures via hydrogen bonds at the solution-solid surface. The relevant simulations have been utilized to interpret the mechanisms of forming the nanostructures. The corresponding theoretical calculation is used to explain the reaction mechanism. Compared with the traditional ways, the on-surface condensation reaction in situ could not only provide a more convenient method for regulating the self-assembled architectures but also offer a promising strategy for building functional nanostructures and devices.

Covalent Organic Frameworks: Emerging Organic Solid Materials for Energy and Electrochemical Applications

Covalent organic frameworks (COFs), materials constructed from organic building blocks joined by robust covalent bonds, have emerged as attractive materials in the context of electrochemical applications because of their high, intrinsic porosities and crystalline frameworks, as well as their ability to be tuned across two- and three-dimensions by the judicious selection of building blocks. Because of the recent and rapid development of this field, we have summarized COFs employed for electrochemical applications, such as batteries and capacitors, water splitting, solar cells, and sensors, with an emphasis on the structural design and resulting performance of the targeted electrochemical system. Overall, we anticipate this review will stimulate the design and synthesis of the next generation of COFs for use in electrochemical applications and beyond.

Confined growth of ordered organic frameworks at an interface

This tutorial review covers the recent design, synthesis, characterization, and property study of COF thin films and covalent monolayers through interfacial polymerization.

Bulk COFs and COF nanosheets for electrochemical energy storage and conversion

The current advances, structure-property relationship and future perspectives in covalent organic frameworks (COFs) and their nanosheets for electrochemical energy storage (EES) and conversion (EEC) are summarized.