Engineering shaping of covalent organic framework

Abstract

Designing materials to achieve ordered structures is a chemistry and materials science target. In this context, covalent organic frameworks (COFs) offer a platform for tailoring organic materials with ordered structures, enabling topology-guided integration of organic units to form crystalline porous material. COFs are novel-type porous materials made of light elements joined by covalent bonds with a wide range of applications, from water purification to energy storage. However, the as-synthesized COF crystallites integrate through wild covalent self-assembly, leading to their precipitation as polycrystalline powders. As a result, their potential is hindered from being exploited. In this thesis, novel synthesis strategies have been designed to produce imine-based COFs' macroscopic objects in a more suitable way to reach their top potential application. The first introductory chapter of this work desires to provide a state-of-the-art overview of COFs, explaining their general aspects, possible processing methodologies and potential applications. The first work provides a high-yield "one-pot" green synthesis of imine-based COFs in water. Additionally, this aqueous synthesis can be achieved under microwave conditions, significantly reducing the reaction time. In the second work, we first report a simple three-step method to produce COFaerogels based on sol-gel transition. The resultant COF-aerogel have extremely low densities, high hierarchical porosity, and outstanding mechanical properties. Moreover, they show excellent water-contaminant capacity, with high removal efficiency. The third work describes a simple compression method to prepare large-scale, free-standing homogeneous and porous imine-based COF-membranes with dimensions in the centimetre range and excellent mechanical properties. COFmembranes fabricated upon compression show good performances for separating gas mixtures of industrial interest, N2/CO2 and CH4/CO2Finally, two-additional works have been carried out to show COFs' potential possibilities. The first study presented a new procedure for the post-synthetic functionalization of imine-based COFs using a heterogeneous solid-gas reaction without a copper catalyst. The second study describes a general process for the preparation of centimetre-scale, hierarchically porous, monolithic COFs. These two works elevate the possibility of these versatile organic porous materials to be applied in a wide variety of applications. To sum up, evolution of COFs chemistry from chemical design of non-scalable, non-processable structures to a bulk-scale processable form tries to promote COFs for practical/industrial applications. In this thesis, it will be discussed about novel synthetic strategies to reach imine-based COF in an eco-friendlier way and their processability into macroscopic objects on large-scale