Ti-containing Mesoporous Silica Research Articles

Embedding an organic dye into Ti-MCM-48 for direct photocatalytic selective aerobic oxidation of sulfides driven by green light

Ti-containing mesoporous silica materials with a well-defined structure could give a clear picture of the elusive reaction pathways in photocatalysis. However, the dispersion of Ti sites usually results in their bandgaps being larger than that of TiO2, which makes the narrowing of bandgaps more challenging to construct visible light photocatalysis. Here, Ti-MCM-48 with an ordered cubic mesostructure and a homogeneous dispersion of Ti sites were successfully synthesized to embed an organic dye alizarin red S (ARS), affording a visible light photocatalyst ARS–Ti-MCM-48. The selective aerobic oxidation of sulfides into sulfoxides driven by green light over ARS–Ti-MCM-48 was accomplished directly. Notably, both electron transfer and energy transfer pathways were involved in the activation of O2, in which the Ti sites play a crucial role. Importantly, the photobleaching was effectively alleviated by embedding ARS into the mesopores of Ti-MCM-48. Moreover, high selectivities of desired sulfoxides were favorably achieved. In general, Ti-containing porous materials could be a unique scaffold for embedding photoactive molecules to carry out selective organic transformations driven by visible light.

Facile photoinduced pH-adjusting synthesis of high amount framework Ti-containing meso-silica catalyst for cyclohexane oxidation

Here, we report a facile photoinduced pH-adjusting method to prepare highly-active Ti-containing mesoporous silica catalysts (PIMTS) for cyclohexane oxidation, featuring high amounts of framework titanium species (Ti ca. 2.92 mol%) with uniform tetrahedral coordination state. Ordered meso-structure and framework substitutions of titanium are evidenced by a set of mutually complementary characterizations, catalytic tests and item-by-item comparisons with the hydrothermal crystallized counterparts (Ti-SBA-15). PIMTS acts as an efficient catalyst for cyclohexane oxidation, leading to the maximum KA oil TOF up to 393 min−1 when cyclohexane conversion is 49.9%.

Catalytic performance of surface-silylated and phenyl-bridged Ti-containing mesoporous silica for epoxidation of propylene

Titanium-doped phenyl-bridged ordered mesoporous organosilicon (Ti-PMO) was initially prepared by a one-step hydrothermal synthesis method under acidic conditions. Following silanization modification, a Ti-PMO-S sample was obtained with an improved surface hydrophobic characteristic. The environment of titanium within the samples was analyzed by Fourier-transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet-visible spectroscopy (UV-Vis-DR), ammonia temperature programmed desorption (NH3-TPD), and Raman spectroscopy. Furthermore, the textural and structural properties of corresponding materials were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms and transmission electron microscopy (TEM). The results showed that Ti-PMO-S has more active Ti centers than Ti-SBA-15 and Ti-PMO on the basis of maintaining the mesoporous structure of ordered channels, despite the presence of few TiO2 species. The catalytic performance of the synthesized samples was assessed in the epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as an oxidant. The prepared Ti-PMO-S materials showed the best epoxidation performance under optimized conditions, with conversion of TBHP up to 95.8% and selectivity of propylene epoxide and tert butyl alcohol reaching 78.8% and 95.9%, respectively.

Facile synthesis of efficient and selective Ti-containing mesoporous silica catalysts for toluene oxidation

We report a novel, facile, physical mixing synthetic method that leads to titanium silicate and copper titanium silicate materials or highly effective solid acid catalysts for toluene oxidation reaction. The synthesis involves simple physical mixing of tetraethyl orthosilicate and various titanium alkoxide (and also copper(II) chloride), and then calcination of the products. The effects of the types of precursors on the catalytic activity of the resulting materials are investigated. Notably, titanium(IV) n-butoxide, whose hydrolysis rate is close to that of tetraethyl orthosilicate, yields a material that exhibits strong acidic properties and excellent catalytic activity for toluene oxidation with hydrogen peroxide (H2O2) as oxidant, giving 98% conversion of toluene and ca. 100% selectivity to benzaldehyde product. The work demonstrates not only simplicity in terms of synthesis of the materials but also unprecedented solid-acid catalytic activity for titanium silicate materials, the catalytic properties of which can be easily tailored by varying the types of precursors. It is also noteworthy that the materials give among the best catalytic performance (in terms of both conversion and product selectivity) under mild reaction conditions that has been reported for toluene oxidation with H2O2 as oxidant for heterogeneous catalysts.

Effect of silylation temperature on the physicochemical properties and catalytic performance of Ti-containing hexagonal mesoporous silica

Ti-HMS (hexagonal mesoporous silica, HMS) was vapor silylated at 150–450°C. The samples were characterized by Si29 CP/MAS NMR, FTIR, TG, XRD, and N2-adsorption, respectively, as well as evaluated by the continuous epoxidation of propylene with cumene hydroperoxide (CHP) as oxidant. There showed only a peak at 14 ppm assigned to (CH3)3Si*OSi(OSi)3 species in NMR spectra when silylated at low temperatures. The samples at higher temperatures (>250°C) gave an additional peak at 20 ppm, which was assigned to novel titanium species of (CH3)3Si*OTi(OSi)3. The intensity of peaks relevant to trimethyl groups increased with the silylation temperature at 150–350°C and decreased at 350–450°C due to decomposing of organic groups. The intensity reached the highest point at 350°C. The catalytic results showed that the propylene oxide yield also changed as the same trend and reached the longest life of 100% PO yield at 350°C silylation. In conclusion, 350°C is an optimal silylation temperature.

Preparation of surface-silylated and benzene-bridged Ti-containing mesoporous silica for cyclohexene epoxidation

Organic–inorganic hybrid Ti-containing mesostructured materials were directly synthesized from tetrabutyl titanate in acidic media by using a non-ionic surfactant P123 as a structure-directing agent, tetraethoxysilane as an inorganic silicon source and 1,4-bis-(triethoxysilyl)benzene as organicsilica. The benzene-bridged Ti-containing periodic mesoporous organosilica Ti-SBA-15-ben was further modified by surface silylation with trimethylchlorosilane. The products were characterized by various means. We find the materials maintained good mesoporous structure, their hydrophobic properties were significantly improved after silanization, and the organic silicon source in the pore walls was favorable for obtaining tetravalent active titanium ions. The catalysts were evaluated in cyclohexene epoxidation with tertbutyl hydroperoxide as an oxidant agent. With Ti-SBA-15-ben as the catalyst, the epoxide selectivity and cyclohexene conversion were improved to 59.9 and 34.7 % respectively. Moreover, surface hydrophobization by silylation treatments further increased the epoxide selectivity to 71.5 %.

Ti-containing mesoporous silica packed microcolumn separation/preconcentration combined with inductively coupled plasma-mass spectrometry for the determination of trace Cr, Cu, Cd and Pb in environmental samples

Solid phase extraction with Ti-containing mesoporous silica as adsorbent combined with ICP-MS for trace metal analysis in environmental samples.

Ti containing mesoporous silica submicrometer-sphere, with tunable particle size for styrene oxidation

Ti-containing mesoporous silica materials with size-tunable mesopores and isolated tetrahedrally coordinated Ti species have widely applications in bulk molecular catalysis. Herein, mesoporous titanium silica submicrometer-spheres (Ti-MSSs) with tunable outer particle diameter were synthesized based on developed Stober method using nonionic surfactant P123 as particle dispersing agent at room temperature. P123 molecular assembled structures will interact with silica species through interface hydrogen bond leading to the formation of tunable sized particles. The particle size was controlled ranging from 400 to 80nm by adjusting the P123 concentration. The influence of Ti-MSSs particle size on the oxidation of styrene with aqueous H2O2 as oxidant was investigated in detail. Ti-MSSs showed better catalytical performance compared to mesoporous titanium silica large particles. Moreover, the catalyst activity increased with decrease in particle size of Ti-MSSs. Nano-sized Ti-MSSs of about 80nm demonstrated the optimized performance for styrene oxidation with styrene conversion 44.7%, benzaldehyde selectivity 82.2% and styrene oxide 17.7% while the reaction time was 6h.

Preparation of single-site Ti-containing mesoporous silica with a nanotube architecture and its enhanced catalytic activities

Single-site Ti-containing mesoporous silica with a nanotube architecture (Ti–MST) was successfully prepared by a solvent evaporation method through the combination of a precursor solution for the synthesis of Ti-containing mesoporous silica (Ti–MS) and carbon nanofibers (CNF) as a hard template. The nanotube architecture of the Ti–MST consisting of quite thin mesoporous silica walls was obtained by controllably coating a precursor solution on the CNF surface and then calcining to completely remove the templates, i.e., CNF and organic surfactant for the construction of the nanotube architecture and the mesoporous structure, respectively. Tetrahedrally coordinated Ti moieties (single-site Ti moieties) were also successfully incorporated within this unique mesoporous silica matrix. The construction of the nanotube architecture resulted in a significant enhancement of the catalytic activity for the epoxidation of alkenes and unsaturated fatty acid methyl ester, having relatively large molecular sizes. Such an enhancement was achieved by the advantageous structure of the nanotube architecture with mesoporous frameworks for the diffusion of substances to the catalytically active single-site Ti moieties.

A novel route for preparation of Ti-containing mesoporous silica with high catalytic performance by using a molecular precursor tetrakis(tris-tert-butoxysiloxy)titanium

Mesoporous silica containing isolated Ti with variable Si/Ti ratios was prepared by pyrolysis of a mixture of tetrakis(tris-tert-butoxysiloxy)titanium (TS4) and tetraethoxysilane (TEOS) through a hard template method. TEOS plays two roles as a silica source and solvent. TS4 works as a catalyst for the hydrolysis of TEOS. Titanium species are found to be isolated in the silica frameworks, supported by DR-UV-vis, FT-IR, ESR, and XPS. The mesoporous structure was verified by XRD, N2 adsorption, and SEM. The results of the catalytic performance for the oxidation reaction of cyclohexene using tert-butoxy hydrogen peroxide (TBHP) as oxidant show that high conversion (29%) of cyclohexene and selectivity (98%) of cyclohexene oxide are realized for the Ti-containing mesoporous silica with Si/Ti ratios of 28 and 51.

Structural Design of Pd/SiO2@Ti-Containing Mesoporous Silica Core–Shell Catalyst for Efficient One-Pot Oxidation Using in Situ Produced H2O2

This study reports the importance of the structural design of heterogeneous catalysts for one-pot reaction. A series of core–shell catalysts were synthesized that consisted of SiO2 core, Pd nanoparticles (NPs), and Ti-containing mesoporous silica (Ti-MS) shell with precise control of the Pd NPs positions, the mesopore diameter, and the thickness of the Ti-MS shell. The catalytic potentials were evaluated for one-pot oxidation reactions involving the direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 gases by the Pd NPs and the subsequent oxidation reaction of sulfide by the isolated TiIV species using in situ produced H2O2 in the mesoporous silica. The precise architecture of the core–shell catalyst significantly enhanced the catalytic performance by a factor of 20, and the catalyst exhibited excellent activity and selectivity toward sulfoxide as compared to the commonly employed Pd-supported/Ti-zeolite (Pd/TS-1) catalyst. This result provides a new perspective of heterogeneous catalysts aimed at...

Enhanced hydrogenation activity of nano-sized Pd–Ni bimetal particles on Ti-containing mesoporous silica prepared by a photo-assisted deposition method

A facile photo-assisted deposition (PAD) for the synthesis of highly dispersed and small Pd–Ni bimetal nanoparticles with a narrow size distribution has been developed by combining mesoporous silica materials including a single-site Ti-oxide moiety (Ti-HMS) as a promising photo-responsive catalyst support. Under UV-light irradiation, both Pd and Ni precursors can be deposited directly on the photo-excited tetrahedrally coordinated Ti-oxide moiety within the silica frameworks, and subsequently reduced with H2 to generate the nano-sized Pd–Ni bimetal particles. Compared with individual Pd or Ni-loaded Ti-HMS (Pd or Ni/Ti-HMS) prepared by PAD and PdNi/Ti-HMS prepared by the conventional impregnation (Imp) technique, the PdNi/Ti-HMS prepared by PAD showed a strong synergistic effect in the catalytic hydrogenation of nitrobenzene (NB) to aminobenzene (AB). It was also found that the hydrogenation activity reached a maximum at the molar ratio of Ni/Pd = 1.5, while further increases in Ni loading amount gradually decreased the catalytic activity.

Controlled Synthesis and Surface Hydrophilic Properties of Ti-Containing Mesoporous Silica Thin Films Using Various Structure-Directing Agents

Transparent Ti-containing mesoporous silica thin films (Ti-MSTFs) have been successfully prepared on quartz substrates by a sol–gel/spin-coating method using various structure-directing agents (SDAs) with different chain lengths. Characterizations of their porous structures and local environments of Ti-oxide moieties in the silica framework were performed by XRD, XAFS, and FT-IR measurements, which revealed that all Ti-MSTFs had mesoporous structures and tetrahedrally coordinated Ti-oxide moieties. Their surface wetting properties were investigated by water contact angle measurements. Interestingly, water contact angles of Ti-MSTFs change depending on the length of the hydrophilic domains of the employed SDA, indicating that the surface wettability can be precisely controlled by varying the types of the SDA. Moreover, Ti-MSTFs act as a photocatalyst for the degradation of organics, such as methylene blue dyes and oleic acid, in which photocatalytic activities were influenced by the porous structure and su...

Preparation of hydrophobically modified single-site Ti-containing mesoporous silica (TiSBA-15) and their enhanced catalytic performances

Hydrophobic modification of single-site Ti-oxide moieties containing mesoporous silica (TiSBA-15) surfaces was performed by using triethoxyfluorosilane (TEFS) as a silylation reagent. The pore structure as well as the high surface area of TiSBA-15 was retained even after modification of these surfaces. TiSBA-15 modified with suitable amount of TEFS exhibited higher catalytic performance for the selective oxidation of cyclooctene to 1,2-epoxy cyclooctane using aqueous H 2O 2 as an oxidant than the unmodified TiSBA-15. The improvement of surface hydrophilic–hydrophobic properties of TiSBA-15 is quite effective for the enhancement of catalytic activity.

Synthesis and Unique Catalytic Performance of Single-Site Ti-Containing Hierarchical Macroporous Silica with Mesoporous Frameworks

Single-site Ti-containing hierarchical macroporous silica with mesoporous frameworks (Ti-MMS) was successfully prepared by a solvent evaporation method using organic surfactant and poly(methyl methacrylate) (PMMA) colloidal crystals as the template. The formation of a well-defined macroporous structure composed of mesoporous silica walls was characterized by SEM and TEM observations. The successful incorporation of tetrahedrally coordinated Ti oxide moieties within their frameworks was also confirmed by spectroscopic techniques such as UV-vis and XAFS measurements. Comparative studies revealed that Ti-MMS exhibited higher catalytic activities for the epoxidation of linear α-olefin compared to Ti-containing mesoporous silica without macropores (Ti-MS). The reaction rate was significantly enhanced on Ti-MMS depending on increases in the alkyl chain length of linear α-olefins. It was also found that Ti-MMS showed good catalytic performance in the selective epoxidation of methyl oleate, which is a kind of unsaturated fatty acid methyl ester (FAME), under acid-free reaction conditions with tert-butylhydroperoxide (TBHP) because of the advantages of the combination of hierarchical macroporous and mesoporous structures.

Low-temperature synthesis of highly hydrophilic Ti-containing mesoporous silica thin films on polymer substrates by photocatalytic removal of structure-directing agents

Download options Please wait... Article information DOI https://doi.org/10.1039/C0JM01404D Article type Paper Submitted 11 May 2010 Accepted 29 Sep 2010 First published 20 Oct 2010 Download Citation J. Mater. Chem., 2011,21, 236-241 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Low-temperature synthesis of highly hydrophilic Ti-containing mesoporous silica thin films on polymer substrates by photocatalytic removal of structure-directing agents Y. Horiuchi, H. Ura, T. Kamegawa, K. Mori and H. Yamashita, J. Mater. Chem., 2011, 21, 236 DOI: 10.1039/C0JM01404D To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Yu Horiuchi Haruhisa Ura Takashi Kamegawa Kohsuke Mori Hiromi Yamashita

Design of superhydrophobic surfaces by synthesis of carbon nanotubes over Co–Mo nanocatalysts deposited under microwave irradiation on Ti-containing mesoporous silica thin films

The superhydrophobic surface has been designed by the synthesis of carbon nanotubes (CNTs) on Ti-containing mesoporous silica thin films (Ti-MSTFs) with Co-Mo binary nanocatalysts. The active Co-Mo catalysts have been successfully deposited on Ti-MSTFs under microwave irradiation. SEM and TEM observations after CNT synthesis revealed that surfaces of Ti-MSTFs were densely covered with CNTs having a diameter of 15 nm. Raman spectra indicated that the undesired structural defects in the carbon network of the synthesized CNTs, which would lead to the formation of hydroxyl groups, were scarce. Interestingly, hydrophobic properties of samples after CNT synthesis were enhanced with increasing titanium concentration of Ti-MSTF, and the water contact angle reached up to 165° on Ti-MSTF with a titanium concentration of 10 at%. The combination of dispersed titanium oxide moieties within the silica frameworks and the microwave irradiation made a great contribution to deposit active Co-Mo catalysts responsible for the formation of well-dense CNTs.

Ti-containing mesoporous silica for methylene blue photodegradation

Photodegradation of methylene blue (MB) on Ti-containing mesoporous silica prepared by microwave-assisted irradiation as a function of Si/Ti molar ratio was studied. The materials were characterized by N 2 adsorption, XRD, UV–vis/DR, and TEM. All solids showed mesoporous textures with high surface areas, relatively small pore size diameters and large pore volume. XRD showed that framework of solids consists of amorphous silica. It was found that the lower the Si/Ti ratio the higher the photocatalytic activity. Under irradiation with a lamp with more photons from visible light the sample with a Si/Ti ratio equal to 10 showed a higher photoactivity than that of a commercial TiO 2 photocatalyst. This result was in agreement with the UV–vis/DR spectra which showed that material with a Si/Ti = 10 has slightly higher energy band gap than that of commercial TiO 2 suggesting that these materials behave as a photoactive semiconductor.

Characterization and application of Ti-containing mesoporous silica for dye removal with synergistic effect of coupled adsorption and photocatalytic oxidation

Highly ordered mesoporous silica, Santa Barbara Amorphous-15 (SBA-15), and titanium-substituted mesoporous silica (TiSBA-15) materials were successfully synthesized, characterized, and evaluated. The textual and structural properties of the prepared materials with various titanium contents were characterized by inductively coupled plasma-mass spectrometer (ICP-MS), powder X-ray diffraction (XRD) patterns, nitrogen physisorption isotherms, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A limited content of titanium could be effectively substituted into the framework of SBA-15 without provoking structure change. The adsorptive performance was examined by methylene blue (MB) adsorbed on prepared materials. The isotherm models were analyzed to describe the adsorption behavior of prepared materials. The adsorption isotherms were well-fitted with Langmuir and Freundlich models in the simulation of the adsorption behavior of dyes. The SBA-15 and TiSBA-15 materials were found to be effective adsorbents for MB from aqueous solutions. The photodegradation of MB and total organic carbon (TOC) analysis on solid composites were used to evaluate the catalytical performance of Ti-containing mesoporous silica. The synergistic effect of adsorptive and photocatalytical ability of prepared TiSBA-15 was identified. The regeneration and cyclic performance were also proved. These results revealed that TiSBA-15 could be one effective alternative material for dye removal.

Design of superhydrophilic surfaces on metallic substrates by the fabrication of Ti-containing mesoporous silica thin film

Ti-containing mesoporous silica thin films (Ti-MSTFs) have been prepared on Al and Al–Mg alloy substrates via a sol–gel/spin-coating method including two different processes for removal of a structure directing agent (SDA). One is calcination and the other is photocatalytic removal under UV-light irradiation utilizing photocatalysis of tetrahedrally coordinated titanium oxide moieties within the silica framework. Characterizations of mesoporous structures and local structures of titanium oxide moieties were performed by FT-IR, XRD, and UV–vis measurements. Water contact angle measurements revealed that highly hydrophilic surfaces were successfully formed on both metallic substrates by coating with Ti-MSTFs. These surfaces also exhibited photoinduced superhydrophilic properties under UV-light irradiation.