Enhancing the synthetic routes to prepare MIL-96(Al) and their efficiency for CO2 capture

Abstract

Synthetic routes to produce metal–organic frameworks (MOFs) utilizing a sustainable method and the smallest amount of toxic organic solvents are desirable to avoid problems associated with chemical waste liquids. Herein, we report the synthesis of an aluminum trimesate-based MOF, MIL-96-(Al), under solvent-free conditions. Moreover, novel syntheses by reflux and solvothermal methods are described. All the synthetic routes yielded pure crystalline MIL-96-(Al). Solvent-free synthesis was achieved within 4 h, providing an improvement over current literature methods. Solvothermal synthesis prepared in mixed solvents allowed superior quality of hexagonal bifrustum MIL-96-(Al) crystals without surfactants or modulators, as those found in previous reports. Furthermore, reflux methodology was performed in attempts to scale up the yielding of solids. However, the scanning electron microscopy images exhibited variations in morphology, and at least three crystal shapes were observed. The carbon dioxide (CO2) adsorption properties of MIL-96(Al) samples were evaluated to determine the enthalpy of adsorption (ΔHads) of CO2. In the four synthetic routes explored, the CO2 adsorption behavior of MIL-96-(Al)-ST synthesized by the solvothermal route is the most promising, exhibiting a constant value of ΔHads of −30 kJ mol−1, suggesting that the chemical environment and well-defined bifrustum shape of MIL-96(Al) crystals, could play an important role in the diffusion of CO2.