Fig. 2. Schematic illustration and structural and morphological characterizations for the tetravalent metallic MOFs: (a) scheme of the synthesis for hcp-UiO-66(Zr). It should be noted that NaI and GdmHCl are recommended because of the low efficiency of NaNO3 and NaClO4, while NaSCN decomposes into toxic species in acidic condition. The middle is the three-dimensional crystal structure of the hcp-UiO-66. Structural view of the Zr12(μ3-O)8(μ3-OH)8(μ2-OH)6 is shown on the right. Zr, O, C and H are shown in blue, red, grey and white, respectively. (b) XRD patterns of hcp-UiO-66-NaI and hcp-UiO-66-Gdm and a comparison with simulated one of hcp-UiO-66. (c) N2 adsorption (filled circles) and desorption (open circles) isotherms at 77 K for hcp-UiO-66-NaI and hcp-UiO-66-Gdm. (d) A typical SEM image of the hcp-UiO-66(Zr)–NaI. (e) A typical TEM image of the hcp-UiO-66(Zr)–NaI. (f) XRD pattern of UiO-66(Zr)-arg and a comparison with that of simulated fcu-UiO-66. The crystal model on the right is the structural view of the UiO-66(Zr) structures adopted an fcu topology. Zr, O, C and H are shown in blue, red, grey and white, respectively. (g) Scheme of synthesis of Hf- and Ce-based UiO-66 MOFs. Hf, Ce, O, C and H are shown in pink, orange, red, grey and white, respectively.
