Ag- and SiO2-doped porous TiO2 with enhanced thermal stability

TiO2-based materials doped with Ag and Si have been prepared in 2-methoxyethanol through the simultaneous hydrolysis and condensation of Ti(IV) isopropoxide with an alkoxysilane-functionalized ligand in the presence of silver. After drying, the xerogels have been either simply washed and dried again, or calcined at increasing temperatures. Samples were thoroughly characterized by X-ray diffraction, FT-IR, DR-UV/Vis and Raman spectroscopies, inductively coupled plasma–atomic emission spectroscopy (ICP–AES) and their texture has been examined by nitrogen adsorption–desorption at 77 K. Silver is present in the form of metallic nanoparticles and silicon is most probably homogeneously distributed in the TiO2 matrix and forms Si–O–Ti bonds. Before calcination, washed only samples display a high surface area around 200 m2/g. While present in small amount (around 1 wt.%), silica dramatically modifies the thermal stability of TiO2 xerogels. Indeed, it inhibits to various extents both the collapse of the porosity and the anatase-to-rutile phase transition when samples are heated at high temperatures. Results show that well crystallized anatase materials with a significant porosity and doped with Ag can be obtained through the synthesis method proposed here. Those properties make such materials good candidates for applications in photocatalysis that could furthermore take advantage of a high surface area without calcination.