Solvothermal Shaping of Imine-Linked Covalent Organic Frameworks by a Two-Step Solvent Feeding Process

Abstract

Solvothermal synthesis is the predominant method for creating new structured covalent organic frameworks (COFs), yet it grapples with challenges in controlling shape and morphology. This issue is attributed to the unregulated solvent-feeding process, which results in rapid polymerization and uncontrolled phase separation. Consequently, a two-step solvent-feeding process is reported for the solvothermal shaping of imine-linked COF monoliths with hierarchical porosity. The synthesis conditions for COF powders reported in existing literature are directly utilized without extensive optimization; however, solvents are divided into two segments prior to feeding. A minor segment of solvents is employed to dissolve monomers, which polymerize in situ to form amorphous monoliths. Subsequently, the remaining organic solvent, along with an acetic acid aqueous solution, is added for crystallization. The versatility of this two-step feeding process in producing COF monoliths is illustrated. The high-quality COF monoliths demonstrate benzene uptakes ranging from 6.0 to 16.8 mmol g−1 at 298 K. This study confirms that the two-step solvent feeding process can be effectively integrated with the conventional solvothermal method to enhance the solution-processability of COFs. It is anticipated that this modified solvothermal approach can readily shape COFs to meet practical application requirements.