Air-Flow Impacting Synthesis of Metal Organic Frameworks: A Continuous, Highly Efficient, Large-Scale Mechanochemical Synthetic Method

In this work, a novel air-flow impacting (AFI) synthetic technique for mechanochemical synthesis of metal organic frameworks (MOFs) was reported for the first time, which is an alternative approach for conventional mechanochemical synthesis. The MOFs, Cd3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) and HKUST-1, were characterized by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The results indicated that the MOFs were successfully prepared after 10 min at a feeding rate of 60 kg h–1, which exhibit a slightly better Brunauer–Emmett–Teller surface area and pore sizes compared to that of materials produced by the conventional solvothermal method. The space time yields (STYs) for AFI of up to 1.44 × 106 kg m–3 d–1 are one order of magnitude greater than STYs for twin screw extrusion. Furthermore, the kinetic analysis of Cd3(BTC)2 was carried out to study the reaction mechanisms by measuring the XRD of the products at different reaction times. It was found that the preparation of Cd3(BTC)2 belonged to the two-dimensional diffusion model. In general, the AFI method clearly enables the preparation of MOFs under solvent-free conditions and may also be applied in synthesis more generally.