SYNTHESIS AND CHARACTERIZATION OF MESOPOROUS NIOBIUM-DOPED SILICA MOLECULAR-SIEVES

Hexagonally-packed mesoporous Nb-doped silica molecular silica were hy drothermally synthesized with various siliceous sources and dopant con centration levels. The microstructure of mesoporous materials was char acterized by a variety of physico-chemical methods. The pore packing o rder of the Nb-doped material depended strongly on the synthesis condi tions such as aging temperature, pH of reaction mixture, surfactant-to -Si ratio and dopant concentration. Different silica precursors gave r ise to different reactivity with the Nb dopants and interactions with the surfactants. The pore size and surface area of the materials can b e systematically varied. The chemical environment of the Nb dopants in the silica framework was studied by XPS, EPR, PA-FTIR, UV-Vis, and Si -29 MAS NMR. The results indicated that the Nb5+ ions were well disper sed in the framework of the mesoporous silica. The diffuse-reflectance UV-Vis spectrum of the mesoporous Nb-doped silica is red-shifted with respect to pure mesoporous silica. The Si-29 MAS NMR spectrum contain ed a broad component at about - 105 ppm, which may have been attribute d to the presence of Nb-O-Si bonding in the mesostructure.