Direct Growth on Si(100) of Isolated Octahedral Mil-101(Fe) Crystals for the Separation of Aromatic Vapors

Octahedral crystals of Fe(III)-based Mil-101 and amino-functionalized Mil-101 are directly grown on Si(100) using easy solution routes under mild conditions. Images from microscopy analyses show that samples consist of a layer of isolated octahedral crystals in which the [111]-direction develops vertically with respect to the Si(100) substrate. Structural and chemical characterizations indicate that crystals consist of Mil-101(Fe) with the following stoichiometry: Fe3(O)Cl-(DMF)2(Terepht)3 (DMF = dimethylformamide and Terepht = terephthalate or aminoterephthalate). Both Si-grown Mil-101(Fe) and NH2-Mil-101(Fe) layers are capable of adsorbing two aromatic gases with different polarities, toluene and nitrobenzene. Their characteristic thermal desorption profiles depend on the amino-functionalization of the terephthalate ligand as well as on the mutual interactions between the two guests when adsorbed from a mixture. It is also shown that, by adapting suitable experimental conditions, Mil-101(Fe) layers are ...