Ultrasound-Assisted Solvothermal Synthesis of M-BDC (M = Cu, Ni, Zn, Mg) Metal-Organic Frameworks

Metal-Organic Frameworks (MOFs) have attracted significant research interest owing to their high porosity, tuneable pore characteristics and broad applicability as an adsorbent. Conventional solvothermal synthesis, while effective, requires prolonged reaction time and high temperatures, which deliver higher yields and larger formations but, as a result, is more expensive. Ultrasound-assisted synthesis has emerged as a promising alternative to allow lower reaction times and lower synthesis temperatures. This study investigates the ultrasound-assisted solvothermal synthesis of a series of benzenedicarboxylate-based MOFs with varying metal nodes. Specifically, copper-, nickel-, zinc- and magnesium-based MOFs. As a source of metal nodes, metal nitrates were used along with benzenedicarboxylic acid as the source of lignan, with ethanol as a solvent. These were tested in varying ratios and at varying temperatures near the boiling point of the solvent for a range of reaction times in closed self-pressurising reactors. Conventional solvothermal would be at pressures much higher than the boiling point of the solvent and for much longer periods; as such, if this method delivers comparable results, it would be far more economical. The resulting precipitate was then removed from solution using a centrifuge and washed with methanol to replace the remaining adsorbed ethanol. This was again removed from solution using a centrifuge and then dried to give the final MOF. The resulting MOFs were assessed in terms of yield, size, and morphology.