Monolithic Covalent Organic Frameworks with Hierarchical Architecture: Attractive Platform for Contaminant Remediation

The insolubility in solvents and poor processability of powder covalent organic frameworks (COFs) considerably impede their practical application. To address these issues and bridge the gap between powder COFs and their practical application, the construction of monolithic COFs has emerged as a feasible and effective solution. Monolithic COFs (i.e., macroscopic three-dimensional architectures) with hierarchical structures have attracted tremendous interest for environmental remediation and exhibited good contaminant removal performances owing to their wide distribution of pore sizes ranging from micropores to macropores, large specific surface area, tailored chemical components, and excellent chemical stability. Monolithic COFs can be either pure COFs with self-supporting structures or composites of COFs with other materials. The resulting COF-based monoliths inherit the merits of the parent powder COFs (such as tunable pore size, tailored structure, and super chemical/thermal stability) and the intriguing features of monolithic materials, such as hierarchical structure, high porosity, and easy handling, endowing them with fast mass transfer and high adsorption capacity. This review provides a comprehensive summary of the recent advances in the synthesis of monolithic COF materials. Additionally, the recent progress of their application in environmental remediation is summarized, including metal-ion removal, organic-pollutant capture, and oil–water separation. Furthermore, this review discusses the current challenges and provides future perspectives. We sincerely hope that it will contribute to the further development of COF-based materials in other fields, especially environmental remediation.