Abstract
Covalent organic frameworks (COFs) have emerged as a new class of crystalline porous materials prepared by integrating organic molecular building blocks into predetermined network structures entirely through strong covalent bonds. The consequently encountered “crystallization problem” has been conquered by dynamic covalent chemistry in syntheses and reticular chemistry in materials design. In this contribution, we have reviewed the progress in the crystallization of COF materials and their hydrogen, methane and carbon dioxide gas storage properties for clean energy applications.
Highlights
In recent decades interest in organic materials with permanent nanometer scale pores has grown very quickly due to their specific properties and broad applications in gas storage, gas separation, drug delivery, energy conversion, catalysis, and optoelectronics
In orderCovalent to achieve higher of reversibility for efficient error correction during crystallization, dynamic covalent chemistry (DCC)
The use of squaric acids and amines or hydrazines as building blocks has been developed for the synthesis of squaraine-linked covalent organic frameworks (COFs) that allow the integration of zwitterion structures into the skeletons
Summary
In recent decades interest in organic materials with permanent nanometer scale pores has grown very quickly due to their specific properties and broad applications in gas storage, gas separation, drug delivery, energy conversion, catalysis, and optoelectronics. The first synthetic challenge to make COFs, which was even thought impossible due to the difficulty of linking organic building blocks into crystalline extended structures entirely through strong covalent bonds, is the so-called “crystallization problem”, the lack of solubility and reversibility for correcting errors during crystallization. Such difficulties were first conquered by the judicious choice of reversible condensation reactions where water is the byproduct, whose retention can be further used to control the direction of reactions for good reversibility.
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