High-yield, fluoride-free and large-scale synthesis of MIL-101(Cr)

Abstract

MIL-101(Cr), one of the most important prototypical MOFs, is well investigated and widely used in many scientific fields. With regard to MOF synthesis in general, the addition of a modifier is commonly used to improve the properties of the products. The effect of inorganic (mineral) and organic acid modifiers was thoroughly investigated in the synthesis of MIL-101(Cr) and HNO₃ could increase the yield to over 80% of a product with average S_BET > 3200 m² g⁻¹ in repeated experiments (from an average of 50% in most published syntheses) in small-scale laboratory synthesis. The large-scale synthesis could use the finding of HNO₃ addition and produce MIL-101(Cr) in >100 g quantities with yields near 70% and BET-surface areas near 4000 m² g⁻¹. The addition of acetic acid (CH₃COOH) together with seeding could decrease the reaction temperature, the lowest being 160 °C (from typically 220 °C in published procedures), with still relatively good yield and BET surface area of the product. The use of other strong inorganic or weak carboxylic acids as modulators typically caused a decrease in yield and porosity.