Tryptophan-incorporated metal-organic framework MIL-101 for adsorptive capture of greenhouse gases

Abstract

To address the environmental challenges posed by the global greenhouse effect, this study synthesizes a series of l-tryptophan-functionalized MOFs (X %Trp-MIL-101, X = 0, 3, 5, 7, 9, 11, 13), and systematically investigates their pore structure, crystal morphology, as well as gas adsorption and separation performance. The results indicate that 9 %Trp-MIL-101 exhibits the most favorable porosity characteristics, with a BET surface area of 3087 m²/g, significantly surpassing the unmodified sample (1269 m²/g), and displaying a more diverse micropore distribution. FTIR, SEM, PXRD and TGA characterizations confirm that l-tryptophan has been successfully incorporated into the framework, enhancing both the crystal morphology and crystallinity, while imparting superior thermal stability to the material. Gas adsorption experiments reveal that the modified samples exhibit significantly improved adsorption capacities for CO₂, SF₆, C₂F₆, NF₃, CF₄, CH₄ and N₂, with 9 %Trp-MIL-101 achieving a CO₂ uptake of 24.20 mmol/g at 298 K and 5 MPa and 11.31 mmol/g for SF₆ at 298 K and 2 MPa, reflecting increases of approximately 70 % and 80 %, respectively. Dynamic separation tests further demonstrate that 9 %Trp-MIL-101 shows exceptional selectivity for greenhouse gases and N₂, with separation factors of 32.0 for SF₆/N₂, 30.0 for CO₂/N₂, 24.1 for C₂F₆/N₂, 8.1 for NF₃/N₂, 7.5 for CF₄/N₂ and 4.8 for CH₄/N₂. In conclusion, l-tryptophan modification significantly enhances the gas adsorption and separation performance of MIL-101, providing crucial theoretical and experimental insights for the functional modification of MOFs in greenhouse gas capture and related industrial applications.