Investigation of the Structure of Microporous Ti-Si Mixed Oxides by X-ray, UV Reflectance, FT-Raman, and FT-IR Spectroscopies

Abstract

A series of high surface area, microporous, T i S i mixed oxides having a wide range of elemental compositions was prepared by a sol-gel method. Since the materials were noncrystalline, X-ray absorption spectroscopy a t the Ti K edge was used to probe the first-shell coordination environment around Ti. Incorporation of Si into the mixed oxide shortened the average Ti-0 bond distance derived from EXAFS and disrupted the normal octahedral coordination of pure titania. The shortest Ti-O bond distance was 1.82 A and was attributed to Ti primarily residing in tetrahedral sites, which was also indicated by a significant pre-edge peak present in Ti K edge XANES. Shifts in the U V absorption edges for the mixed oxides were attributed to titania domain sizes decreasing with increasing Si content in accord with the well-known quantum size effect. The smallest domain size was estimated as less than 1 nm for a sample with a Ti:Si atomic ratio of 1:8. Lattice vibrations in the materials were probed with FT-Raman and FT-IR absorption spectroscopies, and the results wereconsistent with a shortening of the Ti-0 bond and the formation of T i -O S i linkages in the mixed oxides. In situ experiments showed that adsorbed water profoundly affects the local environment around surface Ti atoms.

Synthesis of Titanium Dioxide Nanoparticles by Sol-Gel Technique

“…Among the various photocatalytic materials that have been used, most attention has focused on titanium dioxide (TiO 2 ) as a photocatalystin diverse areas ranging from water and air treatment to self-cleaning surfaces.Nanoparticles have been prepared by many methods such as Langmuir-Blodgett filmsYi et al [7], vesiclesYoun et al [8]and reverse microemulsionsFendler et al [8].The chemical and physical properties exhibited by these materials depend,amongothers,on both the composition and the degree of homogeneity.Therefore, different synthesis strategies have been developed Toba et al [9], Gao et al [10].such as co-precipitation,flame hydrolysis, impregnation,chemicalvapourdeposition,etc.The sol-gel route has demonstrated a high potential for controlling the bulk and surface properties of the oxides (Ward et al [11],Liu et al [12], Schraml-Marth et al [13]). Depending on the drying conditions the binary oxides could be obtained as aerogels, either by supercritical drying Pajonk et al [14], Dusi et al [15],or by silanization of the material previously to a conventional drying Sotelo et al [16].Additionally, non-hydrolytic sol-gel routes have been also reported in the literatureHay et al [17].…”

Using shell-tunable mesoporous Fe3O4@HMS and magnetic separation to remove DDT from aqueous media

“…The sharp peak at 964 cm −1 present in pristine HMS silica increases upon loading with Fe 3 O 4 . More evidence, in that a very similar band is observed in mixed oxides [30] or in mixed oxides grafted on silica [31], supports that the characteristic band is due to a modification of SiO 4 units indirectly related to the presence of heterometals. Therefore, the adsorption peak at 964 cm The hysteresis loops of the prepared samples were registered at 300 K. The field-dependent magnetization plots illustrate these samples are magnetic at room temperature (Fig.…”

Characteristics of Ti-MCM-41 Post-synthesized in Organic or Aqueous Solution using Organo-titanium Compounds as Ti Sources

“…Binding energy of the second component (460.1/465.8 eV) coincides with titanium in tetrahedral coordination, Ti (IV) [12,13], which means the incorporation of titanium atoms into the framework of the mesoporous Ti-MCM samples. Finally, the third component of the Ti 2p3/2/Ti 2p1,(at 456.9-457.4 / 462.6-463.1 eV) matches the binding energy of a cubic TiO with a NaC1 structure (octahedral Ti) and a long Ti-0 bond length of 0.209 nm [14,15], namely octahedrally coordinated Ti species, TiO (VI). The TiO (VI) species is probably located at surface of the pores as extraframework titanium oxide species, since no cubic TiO crystallites was detected in XRD profile for the Ti-MCM samples.…”