Flexible ligand l-serine-directed synthesis of amino-functionalized MIL-101-Ser for enhanced greenhouse gas capture

Abstract

To address the global greenhouse effect, this study employed a hydrothermal method to synthesize a series of MIL-101-X%Ser samples (X = 0, 7, 10, 15, 20, 25, 30, 35) via a one-pot procedure in which L-serine partially replaced H₂BDC, targeting the capture of greenhouse gases. BET analysis revealed that MIL-101-25%Ser is the optimal sample, exhibiting a specific surface area of 2960 m² g⁻¹—substantially higher than the 1269 m² g⁻¹ of MIL-101-0%Ser. FTIR spectra further confirmed the successful incorporation of L-serine into the crystal framework. Pore size distribution, SEM and thermogravimetric analysis indicated that, as a flexible monocarboxylic ligand, L-serine introduces monocoordination defects that markedly increase the pore volume while preserving the intrinsic microporous structure and regular octahedral morphology, as well as maintaining excellent thermal stability. Concurrently, PXRD results demonstrated that the addition of L-serine enhances the crystallinity of the material. Static adsorption experiments revealed a significant improvement in greenhouse gas uptake for the modified samples. Notably, MIL-101-25%Ser achieved a CO₂ adsorption capacity of 24.28 mmol g⁻¹ at 5 MPa, approximately a 70% increase over MIL-101-0%Ser's 14.33 mmol g⁻¹ and exhibited enhanced adsorption for SF₆, NF₃, C₂F₆, CH₄, CF₄ and N₂ as well. Dynamic separation experiments further validated its superior performance, with MIL-101-25%Ser displaying separation factors of 33.1, 27.6, 21.5, 8.2, 7.9 and 4.5 for the SF₆/N₂, CO₂/N₂, C₂F₆/N₂, NF₃/N₂, CF₄/N₂ and CH₄/N₂ gas pairs, respectively. Consequently, materials modified via a monocoordination strategy not only exhibit exceptional greenhouse gas adsorption capacities but also demonstrate favorable selectivity in gas separation, holding promise as highly efficient candidates for greenhouse gas capture and separation applications.