Metal–organic framework MOF-5 prepared by microwave heating: Factors to be considered

Solvothermal synthesis of MOF-5 was conducted by microwave heating using 1-methyl-2-pyrrolidone as a solvent. The effects of microwave power level, irradiation time, temperature, solvent concentration, and substrate composition on the product crystallinity and morphology were investigated. Under an optimum set of synthesis conditions, uniform cubic crystals with average size of 20–25 μm and a Langmuir surface area of 3008 m ²/g were produced within 30 min. However, prolonged microwave irradiation resulted in sharp deterioration of the physicochemical properties. The CO ₂ adsorption capacity of the best MOF-5 sample obtained was ca. 812 mg/g at 298 K/40 bar, determined by a gravimetric method. For comparison, MOF-5 prepared by normal convection heating for 24 h showed cubic crystals in a 400–500 μm size range with a Langmuir surface area of ca. 3200 m ²/g. CO ₂ adsorption capacity was 823 mg/g at 298 K/40 bar. The heat of adsorption for CO ₂ under low pressure condition (<1 atm) for both samples was estimated to be in a range of 15.8–16.5 kJ/mol.