Turning Redundant Ligands into Treasure: A New Strategy for Constructing MIL-53(Al)@Nanoscale TiO2 Layers

A strategy for in situ fabrication of nanoscale-thin layers of anatase TiO2 coated on the metal-organic framework (MOF) material, MIL-53(Al), is developed. The preparation conditions for crystallized TiO2 are normally incompatible with the thermal and chemical stability of MOFs. Based on our strategy, we found that the redundant organic ligands (1,4-benzenedicarboxylic acid, H2 BDC) within the pores of the as-synthesized MOF play a key function in the protection and support of the framework during hydrothermal loading of the TiO2 precursor, as well as in preventing the infiltration of the precursor into the pores. After annealing, a nanoscale-thin layer of highly crystalline anatase TiO2 , with a thickness of 6-10 nm, was successfully attached to the external surface of the MIL-53(Al) crystals, while the porous framework remains intact. The core-shell structure of the MOF@TiO2 nanocomposite endows the resulting materials with additional optical response and enhanced moisture and chemical stability.