A General Strategy for the Synthesis of Functionalised UiO-66 Frameworks: Characterisation, Stability and CO2 Adsorption Properties

A general synthetic strategy has been developed, which can be used for the preparation of all the known as well as five new functionalised UiO-66-X compounds [X = H, F, F-2, Cl, Cl-2, Br, Br-2, I, CH3, (CH3)(2), CF3, (CF3)(2), NO2, NH2, OH, (OH)(2), OCH3, (CO2H)(2), SO3H, C6H4]. Starting from a reaction mixture of ZrOCl2 center dot 8H(2)O, H2BDC-X (BDC: 1,4-benzenedicarboxylate), formic acid and N,N-dimethylacetamide (DMA) having a molar ratio of 1:1:100:104.44, all the UiO-66-X compounds, except UiO-66-CO2H, were obtained under solvothermal conditions (150 degrees C, 24 h). The phase purity of all the compounds was ascertained by X-ray powder diffraction (XRPD) analysis, DRIFT spectroscopy and elemental analysis. Determination of lattice parameters from the XRPD patterns of the new thermally activated UiO-66-X {X = CF3 (1-CF3), (CO2H)(2) [2-(CO2H)(2)], F-2 (3-F-2), Cl-2 (4-Cl-2), Br-2 (5-Br-2)} compounds revealed their structural similarity with the unfunctionalised UiO-66. Thermogravimetric analyses (TGA) indicate that the five new compounds are stable in the range 290-390 degrees C in air. Except for 3-F-2, the new compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N-2 and CO2 sorption analyses, all of the new thermally activated compounds exhibit significant microporosity values (S-Langmuir = 217-836 m(2)g(-1)), which are lower than that of the parent UiO-66. Comparative CO2 sorption studies reveal that the UiO-66-X compounds with X = NO2, NH2, OH, CH3 and (CH3)(2) show enhanced CO2 uptake compared to that of the parent compound at 1 bar and 0 degrees C.