Synthesis of UiO-66 in Supercritical CO2 and Its Application in Dye Adsorption

UiO-66 nanocrystals were synthesized by supercritical reaction crystallization with anhydrous zirconium chloride as the metal precursor, terephthalic acid as the ligand, and a small amount of N,N-dimethylformamide (DMF) and formic acid as cosolvents in supercritical CO2. In our work, the product UiO-66 obtained exhibits typical octahedral morphology with a specific surface area of 1092 m2/g and concentrated micropore diameters of 0.77, 1.05, and 1.73 nm. The thermal decomposition temperature of the product is 450 °C. It was found that the adsorption selectivity of UiO-66 for Congo red is much higher than those for methylene blue and methyl orange, which can reach up to over 1300 mg/g. The adsorption process conforms to the second-order adsorption kinetics curve, and the adsorption isotherm fits into the Langmuir model. Meanwhile, the adsorbent UiO-66 possesses good cycle stability and its adsorption performance remains excellent after seven cycles.