Phenoxazine-based COFs for CO2/N2 separation and organic dye adsorption

Abstract

Environmental issues have always been a concern, and designing a material that can effectively combat both gaseous and liquid pollutants is a goal we are working toward. Herein, two examples of N-rich covalent organic frameworks (COFs), named YCOF1 and YCOF2, were synthesized using the solvothermal method. Their structure, stability and morphology were characterized using PXRD, FT-IR, XPS, TGA and SEM. According to the Brunauer–Emmett–Teller (BET) method, the specific surface areas of YCOF1 and YCOF2 were 559.096 and 741.261 m² g⁻¹, respectively. Under the volume percentage of simulated flue gases, YCOF1 exhibits excellent CO₂ IAST selectivities of 70.97 at 273 K and 30.05 at 298 K, while YCOF2 also exhibits excellent CO₂ IAST selectivity of 51.90 at 273 K. Moreover, their high specific surface area and abundant active sites provide excellent adsorption capacity for malachite green (MG), with maximum adsorption amounts of 650.14 mg g⁻¹ (YCOF1) and 572.95 mg g⁻¹ (YCOF2). Furthermore, the adsorption of the COFs for dyes followed the pseudo-second-order kinetic model and the Langmuir isothermal adsorption model. The dye removal efficiency of YCOF1 and YCOF2 showed less than 5% change after 5 adsorption cycles.