PDA@UiO-66-NH2-derived nitrogen and oxygen-doped hierarchical porous carbon for efficient adsorption of BPA and dyes

Abstract

MOF-derived carbon materials have garnered significant attention in the field of adsorption due to their abundant porosity, excellent stability, and structural diversity. In this study, nitrogen and oxygen-doped hierarchical porous carbon materials were obtained by carbonizing PDA@UiO-66-NH2 at various temperatures and subsequently etching with hydrofluoric acid for different times. The adsorption capacity of these materials towards bisphenol a (BPA), methyl orange (MO), and methylene blue (MB) was evaluated. The results suggest excessive carbonization temperature and etching time may cause the collapse of the pore structure. In addition, the introduction of a PDA carbon layer can reduce the nitrogen–oxygen ratio and modify the nitrogen species in the materials. Among these materials, UPCH800, which was carbonized at 800 °C followed by etching for 6 h, exhibits the best adsorption performance towards BPA and MO, with a maximum adsorbed amount of 350.51 and 417.34 mg/g respectively. For MB, the maximum adsorption amount is 227.53 mg/g. All adsorptions reach equilibrium within 1 h. Thermodynamic studies reveal that the adsorption of MO by UPCH800 is an entropy-driven adsorption process, while the adsorption of BPA and MB is an enthalpy-driven exothermic process. Based on experimental and characterization results, the primary adsorption mechanisms involve π-π interactions, n-π interactions, pore-filling, and hydrogen bonding between the pollutants and the material. Moreover, UPCH800 exhibits high removal efficiency after 5 adsorption cycles, making it a promising material for the adsorption of BPA and MO.