Ultrasound and microwave assisted-synthesis of ZIF-8 from zinc oxide for the adsorption of phosphate

The conversion of solid matters into metal-organic frameworks has emerged as a new alternative for the synthesis of MOFs. Various synthesis methods have been applied for this transformation using wet-chemistry and solid-state methods to result in the formation of a mixture of MOF and oxide@MOF. Thus, it is highly desired to develop other methods to increase the MOF yield from oxide and accelerate the conversion rate. In this context, the use of ultrasound and microwave methods, known in the preparation of MOFs from metallic salts with an accelerated reaction time and enhanced yield, have surprisingly never been used in the transformation of oxides into MOFs. Herein we describe the conversion of zinc oxide to ZIF-8 in different solvent mixtures (DMF/water, methanol/water and water) under microwave (MW) and ultrasonic (US) irradiation. The results revealed different morphologies and particle sizes in different synthesis conditions and solvents with higher conversion rate using US over MW. The synthesized MOFs demonstrated excellent phosphate adsorption capacity, thereby giving them the potential to be used as effective adsorbent materials for wastewater treatment. This work opens up a new avenue toward the development of MOFs from other inorganic sustainable solid resources using US and MW.