Building a Greener Dye Trap: How Replacing <i>N</i> , <i>N</i> -Dimethylformamide with γ-Valerolactone Improves the Ultrasonic-Assisted Synthesis of the Copper-Based Metal–Organic Framework HKUST-1

Employing γ-valerolactone (GVL) as a cosolvent in the ultrasonic-assisted synthesis of the metal–organic framework (MOF) [Cu3(BTC)2·xH2O]n where [BTC]3– = 1,3,5-benzenetricarboxylate = 1,3,5-[C6H3(CO2)3]3– (HKUST-1) enables a “greener” approach than the current published experiment which uses hazardous N,N-dimethylformamide (DMF). Equally important, the revision of the oven-drying step to 200 °C for at least 15 h instead of 1 h at 130 °C removes sequestered solvent from the MOF pores and markedly improves the adsorption characteristics of the final material. A further small gain in adsorption capacity is realized by the inclusion of a second, short ultrasonic treatment during workup as a so-called “swelling step” to maximize the MOF’s pore size and thus its effective surface area. The overall student experience is enhanced by incorporating a nontoxic cosolvent derived from biomass and by augmenting the established test of HKUST-1 activity, namely removal of methylene blue from aqueous solution, with an operationally simple determination of water vapor adsorption capacity. A new perspective is suggested to help students understand the complex extended HKUST-1 structure by having them first appreciate the molecular structure of copper(II) acetate hydrate, which is best formulated as Cu2(O2CCH3)4·2H2O. The revised experiment is flexible and accommodates a variety of laboratory schedules, student skill levels, and pedagogic objectives.