Synthesis of COF-5 using microwave irradiation and conventional solvothermal routes

A covalent organic framework, COF-5, was synthesized by microwave heating and by conventional solvothermal synthesis. The highest apparent Brunauer–Emmett–Teller surface areas were obtained for materials produced by a combination of microwave heating and microwave extraction. The total surface area for the samples could be sub-divided into external and internal surface areas, arising from the macroscopic morphology and the molecular crystal structure, respectively. Variations in external surface area could be attributed to the different sample morphologies resulting from the various synthesis and purification methods. The experimental internal surface areas correlated well with the simulated Connolly and solvent-accessible surface area (2034 m2 g−1 and 1737 m2 g−1). Pore filling simulations can rationalize the stepped gas uptake behavior and identify a physisorbed monolayer followed by filling of the pore interior. This study suggests that microwave irradiation is a convenient alternative route for the synthesis of COF materials, and underlines the importance of considering sample morphology in evaluating surface area data.