Efficient solvothermal synthesis of highly porous UiO-66 nanocrystals in dimethylformamide-free media

The UiO-66 metal–organic framework has remarkable physicochemical characteristics which have positioned it as one of the Zr-MOFs with greater potential for application in diverse processes. However, it remains a challenge how to optimize the synthesis methods so as to obtain this material with high yield and good porous properties under more eco-compatible conditions. In this work, we report the solvothermal synthesis of UiO-66 nanocrystals with high surface area using acetone as the synthesis medium, replacing the traditional and toxic N,N-dimethylformamide. The effects of solvents, reactant concentration, temperature, synthesis time and mixture protocol on the material properties were characterized by XRD, SEM–EDS, FTIR, TGA-SDTA and N ₂ adsorption isotherms. The sample obtained in pure acetone employing the optimized protocol exhibited spherical nanoparticles 150 nm in size and presented the greatest relative crystallinity. The alternative protocol allowed obtaining UiO-66 with high yields (~ 91%) without employing DMF, under mild conditions (80 °C), in the form of nanocrystals with high specific surface area (1299 m² g⁻¹) that can be activated by simple drying at 130 °C and atmospheric pressure. The MOF obtained in acetone under optimum conditions showed reversible CO₂ uptake capacity at room temperature and low pressures as determined by both CO₂ isotherms and TGA-CO₂ tests.