Mesoporous titanium phosphates and related molecular sieves: Synthesis, characterization and applications

Abstract

Titanium (IV) phosphates TCM-7 and -8 with mesoporous cationic framework topologies using both cationic and anionic surfactants have been synthesized. Experimental data suggest the stabilization of the tetrahedral state of Ti in TCM-7/8 (O-P-O-Ti-O-, at Ti/P = 1:1)vis-à-vis the most stable octahedral state of Ti in the rutile/anatase or pure mesoporous TiO₂. Mesoporous TCM-7 and-8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. Grafting the organic functionality in the surface or bridging the organic moiety in between the inorganic phosphorus precursors can enhance hydrophobicity of these materials similar to that of mesoporous silica materials. The high catalytic activity in the liquid phase partial oxidation of cyclohexene over such organically surface modified mesoporous titanium phosphate using a dilute H₂O₂ oxidant supports the tetrahedral coordination of Ti in these materials. These materials also show excellent photocatalytic activity in the production of H₂ by photo-reduction of water under UV light irradiation.