Enhanced selectivity of CO2 over CH4 in sulphonate-, carboxylate- and iodo-functionalized UiO-66 frameworksElectronic supplementary information (ESI) available: Additional ambient and temperature-dependent XRPD patterns, DRIFT spectra, TG curves, tables containing results of TG, DRIFT and elemental analyses. See DOI: 10.1039/c3dt32288b

Three new functionalized UiO-66-X (X = -SO 3 H, 1 ; -CO 2 H, 2 ; -I; 3 ) frameworks incorporating BDC-X (BDC: 1,4-benzenedicarboxylate) linkers have been synthesized by a solvothermal method using conventional electric heating. The as-synthesized (AS) as well as the thermally activated compounds were characterized by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric (TG), and elemental analysis. The occluded H 2 BDC-X molecules can be removed by exchange with polar solvent molecules followed by thermal treatment under vacuum leading to the empty-pore forms of the title compounds. Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that 1 , 2 and 3 are stable up to 260, 340 and 360 °C, respectively. The 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 , CO 2 and CH 4 sorption analyses, all of the thermally activated compounds exhibit significant microporosity ( S Langmuir : 769-842 m 2 g −1 ), which are comparable to that of the parent UiO-66 compound. Compared to the unfunctionalized UiO-66 compound, all the three functionalized solids possess higher ideal selectivity in adsorption of CO 2 over CH 4 at 33 °C. Three functionalized Zr-based metal-organic frameworks UiO-66-X (X = -SO 3 H, -CO 2 H, -I) having improved CO 2 /CH 4 adsorption selectivity are presented.