Synthesis of Mixed-Metal MIL-68 under Mild Conditions by Controlling Nucleation Using a Microfluidic System

Metal–organic frameworks that contain trivalent metal ions as nodes (M3+–MOFs) exhibit potential for various applications due to their exceptional thermal and chemical stability; however, M3+–MOF synthesis requires extreme reaction conditions such as high temperatures, long reaction times, and hydrogen fluoride (HF) addition. Here, we rapidly synthesized MIL-68 containing trivalent metal ions without any HF addition by controlling nucleation using microfluidic synthesis and metal mixing. Al3+ addition during the initial reaction between Fe3+ and the ligand yielded 1D chain-based secondary building units, consequently forming MIL-68. Compared to the products obtained using bulk and microwave-assisted syntheses, the product obtained via microfluidic synthesis exhibited high crystallinity. Thus, the combination of microfluidic systems and metal mixing is a novel approach in synthesizing industrially applicable M3+–MOFs.