Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites

UiO-66 is an archetypal zirconium-based metal–organic framework (MOF) that is constructed from hexanuclear zirconium oxide clusters as secondary building units (SBUs) and 1,4-benzenedicarboxylate (bdc) linkers. For the first time, a room-temperature solution-based synthesis is reported for UiO-66 and several of its derivatives, UiO-66-X (X = NH2, OH, or NO2), resulting in materials that are as porous and crystalline as those made at elevated temperatures. In addition, via modulation of the temperature at which UiO-66 is synthesized, the number of defect sites can be varied. It was found through N2 sorption isotherm analysis and potentiometric acid–base titrations that increasing the synthesis temperature from 25 to 130 °C results in a systematic decrease in the number of defect sites in UiO-66. The results suggest that, with respect to this synthetic procedure, a maximal number of defect sites is achieved [∼1.3 missing linkers per Zr6O4(OH)4(bdc)6] at a temperature of 45 °C.