Mesoporous TiO2-SiO2 Research Articles

Hydrothermal synthesis of mesoporous TiO2-SiO2 core-shell composites for dye-sensitized solar cells

It is challenging to utilize TiO2-based composites with high specific surface area to improve dye-sensitized solar cells (DSSCs) performance. Herein, we report efficient TiO2-SiO2 core-shell composites for DSSCs by optimizing the microstructure and crystalline structure. Mesoporous TiO2-SiO2 core-shell composites were synthesized by hydrolysis of TiOCl2 and Si(C2H5O)4 under hydrothermal condition. The shell thickness can be tuned through adjustment of the SiO2 addition content. Rutile phase of TiO2 formed without SiO2 addition, while anatase phase of TiO2 was stabilized by SiO2 loading. By addition of SiO2, the crystallite size decreased from 29nm of rutile to 15nm of anatase, and the specific surface area increased from 23 m2/g to 150 m2/g. The best transfer efficiency (5.9%) was obtained in TiO2-SiO2(0.10), which is much higher than that of commercial TiO2 powder (P25).

Visible-light-induced photocatalysis of 2D-hexagonal mesoporous SiO2-TiO2 deposited with Au nanoparticles.

Au nanoparticles (NPs) are deposited using a couple of methods onto a sol-gel-derived mesoporous SiO2-TiO2 template. A modification of the template with 3-aminopropyltriethoxysilane (APTES) before the deposition of Au leads to the formation of Au nanorods instead of Au nanospheres in the tubular mesopores. The modification also causes a deterioration of visible-light-induced photocatalytic activity. Heat treatment of this sample to remove APTES results in an amelioration of the photocatalytic activity. The detailed mechanism of the deterioration and amelioration of the activity is discussed on the accessibility of the reactant to the sample and the easiness of the charge carrier transfer between TiO2 and Au NPs.

Highly active mesoporous SiO2-TiO2 based nanocomposites for photocatalytic degradation of textile dyes and phenol

Titania-silica nanocomposites (20% SiO 2 -TiO 2 , 30% SiO 2 -TiO 2, 40% SiO 2 -TiO 2 and 50 % SiO 2 -TiO 2 ) with tailored morphology and tunable band energy have been synthesized successfully via micro emulsion method. The morphology, chemical composition, band gap energy and stability of prepared nanocomposites were investigated by XRD, SEM/EDX, FT-IR, DRS and TGA. While textural parameters such as surface area, pore volume, and pore diameter were evaluated by nitrogen adsorption-desorption isotherms. The prepared nanocomposites were employed for photocatalytic degradation of phenol and dyes (methyl yellow, auramine O, turquoise blue G) under visible light irradiations. The results of photocatalytic degradation and kinetic parameter (K app ) strongly suggest that 20% SiO 2 -TiO 2 showed remarkable photocatalytic efficiency in comparison to SiO 2 -TiO 2 nanocomposites with high silica contents. These findings proved significantly that 20% SiO 2 -TiO 2 have marked impact on the photocatalytic efficiency due to its high pore volume, more diameter, high availability of anatase TiO 2 in nanocomposite and reduced bandgap energy.

Synthesis of TiO2–SiO2 aerogel via ambient pressure drying: effects of sol pre-modification on the microstructure and pore characteristics

TiO2–SiO2 composite aerogels were prepared via ambient pressure drying by sol–gel and surface modification for both the sol and gel samples. The organosilane reagents of decamethyltetrasiloxane (DMTSO)/trimethylchlorosilane (TMCS) and hexamethyldisiloxane (HMDSO)/TMCS were introduced into the TiO2–SiO2 composite sol for pre-modification respectively, and subsequently the TMCS/hexane solution was used for surface modification of the obtained TiO2–SiO2 composite gel. The effects of sol pre-modification on the microstructure and pore characteristics of TiO2–SiO2 composite aerogels were investigated. The results indicate that HMDSO/TMCS coupling reagents is more appropriate for the pre-modification of TiO2–SiO2 composite sol than the DMTSO/TMCS reagents. The best volume ratio of HMDSO/TMCS/composite sol for preparing mesoporous TiO2–SiO2 composite aerogels is in the range of 1:0.33:10–1:1.0:10, with which the specific surface area and pore volume of the obtained TiO2–SiO2 composite aerogels are 492–645 m2/g and 2.63–2.85 m3/g, respectively. The results of adsorption and photocatalytic degradation of rhodamine B show that the as-prepared TiO2–SiO2 composite aerogels have higher adsorption/photocatalysis. Particularly, the as-prepared TiO2–SiO2 composite aerogels with HMDSO/TMCS showed prominent adsorption capability with the adsorption rate attaining to 89.4 % within 60 min.

Fabrication of Shape-Controlled Au Nanoparticles in a TiO2-Containing Mesoporous Template Using UV Irradiation and Their Shape-Dependent Photocatalysis

A SiO2–TiO2 template with ordered tubular mesochannels has been prepared by the sol–gel method. Au nanorods are deposited in the tubular mesochannels of the SiO2–TiO2 template, and the shape of Au is changed from nanorods to nanospheres by ultraviolet irradiation during thermal deposition. The photocatalytic activity of mesoporous SiO2–TiO2 with/without Au nanorods/nanospheres is evaluated. Deposition of Au in the mesoporous SiO2–TiO2 template enhances the photocatalysis of TiO2. Interestingly, the sample containing Au nanorods exhibits higher photocatalytic activity than that with Au nanospheres. Photocatalysis by exciting surface plasmon resonance is not detected in the composite samples regardless of the shape of the deposited Au nanoparticles.

Bragg Stack-Functionalized Counter Electrode for Solid-State Dye-Sensitized Solar Cells

A highly reflective counter electrode is prepared through the deposition of alternating layers of organized mesoporous TiO(2) (om-TiO(2)) and colloidal SiO(2) (col-SiO(2)) nanoparticles. We present the effects of introducing this counter electrode into dye-sensitized solar cells (DSSCs) for maximizing light harvesting properties. The om-TiO(2) layers with a high refractive index are prepared by using an atomic transfer radical polymerization and a sol-gel process, in which a polyvinyl chloride-g-poly(oxyethylene) methacrylate graft copolymer is used as a structure-directing agent. The col-SiO(2) layers with a low refractive index are prepared by spin-coating commercially available silica nanoparticles. The properties of the Bragg stack (BS)-functionalized counter electrode in DSSCs are analyzed by using a variety of techniques, including spectroscopic ellipsometry, SEM, UV/Vis spectroscopy, incident photon-to-electron conversion efficiency, electrochemical impedance spectroscopy, and intensity modulated photocurrent/voltage spectroscopy measurements, to understand the critical factors contributing to the cell performance. When incorporated into DSSCs that are used in conjunction with a polymerized ionic liquid as the solid electrolyte, the energy conversion efficiency of this solid-state DSSC (ssDSSC) approaches 6.6 %, which is one of the highest of the reported N719 dye-based ssDSSCs. Detailed optical and electrochemical analyses of the device performance show that this assembly yields enhanced light harvesting without the negative effects of charge recombination or electrolyte penetration, which thus, presents new possibilities for effective light management.

Leishmaniose cutanée au Mali : aspects anatomocliniques et distribution géographique

Atmospheric pollution has an evidently adverse impact on the esthetics of urban buildings and structures. Thus, the synthesis of photocatalysts capable of removing pollutants deposited on the surface of stone and other building materials is a challenge to researchers. By a simple and low cost process we have synthesized mesoporous TiO2–SiO2 photocatalytic coatings that meet the requirements of outdoor application. These are new materials designed to give to the building material long-term self-cleaning and strengthening properties.We have varied the loading and size of TiO2 nanoparticles in order to investigate their effect on the photocatalytic activity. We find that the integration of larger and sharper titania particles in a silica network with a titania content of around 4% (w/v) significantly improves self-cleaning effectiveness, due to the enhanced availability of surface photoactive sites. For a higher TiO2 content (10%, w/v), photocatalytic action decreases because the porous volume is drastically reduced and consequently, access to photoactive sites is more difficult.

Photocatalytic activity of TiO2–SiO2 nanocomposites applied to buildings: Influence of particle size and loading

Atmospheric pollution has an evidently adverse impact on the esthetics of urban buildings and structures. Thus, the synthesis of photocatalysts capable of removing pollutants deposited on the surface of stone and other building materials is a challenge to researchers. By a simple and low cost process we have synthesized mesoporous TiO2–SiO2 photocatalytic coatings that meet the requirements of outdoor application. These are new materials designed to give to the building material long-term self-cleaning and strengthening properties.We have varied the loading and size of TiO2 nanoparticles in order to investigate their effect on the photocatalytic activity. We find that the integration of larger and sharper titania particles in a silica network with a titania content of around 4% (w/v) significantly improves self-cleaning effectiveness, due to the enhanced availability of surface photoactive sites. For a higher TiO2 content (10%, w/v), photocatalytic action decreases because the porous volume is drastically reduced and consequently, access to photoactive sites is more difficult.

Photocatalytic selective oxidation of the terminal methyl group of dodecane with molecular oxygen over atomically dispersed Ti in a mesoporous SiO2 matrix

Extraordinarily high selectivity (80–93%) for the oxyfunctionalization of the terminal methyl group was discovered in the photocatalytic selective oxidation of dodecane with molecular oxygen in a continuous flow system under mild gas phase reaction conditions over mesoporous TiO2–SiO2 mixed oxide photocatalysts. The oxygenated hydrocarbon products were mainly aldehydes with carboxylic acids and ketones as minor products. By dispersing most of the Ti atomically in a tetrahedral coordination in a SiO2 matrix, the oxygenated products were stabilized by diluting contiguous Ti sites present on the surface of TiO2 particles. The preferential oxidation of the terminal methyl group was ascribed to the extensive C–C bond breaking by photogenerated holes prior to oxyfunctionalization.

Citral hydrogenation on high surface area mesoporous TiO2–SiO2 supported Pt nanocomposites: Effect of titanium loading and reduction temperature on the catalytic performances

Platinum-based catalysts supported on TiO2-modified mesostructured silica were prepared using the direct co-condensation of silica and titania precursors to synthesize the mixed-oxide support. The physico-chemical properties of the Pt/xTi-SBA15 samples with various xTi contents (in mol%) were further evaluated using several techniques, including elemental analysis, X-ray diffraction, N2-physisorption, H2-chemisorption, transmission electronic microscopy and the probe reaction of cyclohexane dehydrogenation to evaluate the metal–support interaction (SMSI effect). All the Pt/xTi-SBA15 samples display high specific surface areas (650–820 m2g−1) and high mesopore volumes (0.44–0.68cm3g−1), with the formation of TiO2 anatase nanoparticles since the low titanium content, i.e. 2mol%. The hexagonal organized pore structure of SBA silica is also strongly altered by the titanium adding, but mixed oxides so obtained present very particular morphology with maintaining of high surface areas.The catalytic performances of the Pt/xTi-SBA15 catalysts were estimated for the citral hydrogenation performed at 70°C under hydrogen pressure (7MPa), and discussed in terms of activity and unsaturated alcohols (UA: nerol and geraniol) selectivity. A synergetic effect on the UA selectivity was obtained on the Pt/xTi-SBA15 catalysts, compared to both Pt/SBA15 and Pt/TiO2 P25 reference samples (reduction temperature=300°C), and was explained by the specific role of the reducible TiO2 species, which under the nano-anatase form generate a strong metal–support interaction (SMSI effect) with platinum after reduction at 300°C. The formation of partially reduced support species was finally modulated by varying the reduction temperature of the catalysts. It is then possible to achieve high selectivity after reduction at 350°C, while maintaining high conversions.

Excellent photocatalytic degradation activities of ordered mesoporous anatase TiO2–SiO2 nanocomposites to various organic contaminants

Ordered 2-D hexagonal mesoporous TiO2–SiO2 nanocomposites consisted of anatase TiO2 nanocrystals and amorphous SiO2 nanoparticles, with large mesochannels and high specific surface areas, have been extensively and detailedly evaluated using various cationic dyes (methylene blue, safranin O, crystal violet, brilliant green, basic fuchsin and rhodamine-6G), anionic dyes (acid fuchsin, orange II, reactive brilliant red X3B and acid red 1) and microcystin-LR. We use mesoporous 80TiO2–20SiO2-900 for the degradation of cationic dyes and MC-LR, due to the dominant adsorption of SiOH groups and synergistic role of coupled adsorption and photocatalytic oxidation. For anionic dyes, due to the adsorption results predominantly from TiOH groups, our strategy realizes the enhanced photocatalytic oxidation by strong surface acids and larger available specific surface area. Based on this, we prepared 90TiO2–10SiO2-700 to degrade them. The results show that our samples exhibit excellent degradation activities to all the contaminants, which are much higher than that of P25 photocatalyst. The dyes are not only decolorized promptly but degraded readily as well. It is strongly indicated that our mesoporous nanocomposites are considerably stable and reusable. These results demonstrate that our mesoporous TiO2–SiO2 nanocomposites present extensive and promising application in the fast and highly efficient degradation of various organic pollutants.

Selective preparation of zero- and one-dimensional gold nanostructures in a TiO2 nanocrystal-containing photoactive mesoporous template

Nanocrystallized SiO2-TiO2 with tubular mesopores was prepared via the sol-gel technique. Gold was deposited in the tubular mesopores of the nanocrystallized SiO2-TiO2. The shape of the gold was varied from one-dimensional [1-D] to zero-dimensional [0-D] nanostructures by an increase in TiO2 content and ultraviolet [UV] irradiation during gold deposition. 1-D gold nanostructures [GNSs] were mainly obtained in the mesopores when a small amount of TiO2-containing mesoporous SiO2-TiO2 was used as a template, whereas the use of a template containing a large amount of TiO2 led to the formation of shorter 1-D or 0-D GNSs. UV irradiation also resulted in the formation of 0-D GNSs.PACS: 06.60.Jn (sample preparation); 81.07.Gf (nanowires); 81.16.Be (chemical synthesis methods).

Hydrogenated mesoporous TiO2–SiO2 with increased moderate strong Brönsted acidic sites for Friedel–Crafts alkylation reaction

The acidic properties of mesoporous TiO2–SiO2 mixed oxides were evaluated by 31P magic-angle spinning NMR spectroscopy using trimethylphosphine oxide (TMPO) and trimethylphosphine (TMP) as probe molecules. It confirms that mesoporous TiO2–SiO2 has moderate strong Brönsted acid sites. The number of the Brönsted acidic sites can be increased via a high-temperature hydrogenation process, which subsequently improves their catalytic performance in the Friedel–Crafts reaction of anisole and benzyl alcohol.

Heterogeneous Photocatalytic Remediation of Phenol by Platinized Titania–Silica Mixed Oxides under Solar-Simulated Conditions

Aperiodic mesoporous TiO2–SiO2 mixed oxide materials were platinized by the incorporation of Pt0 by three different methods to understand the role of Pt on the photocatalytic activity of phenol under solar simulated conditions. The physicochemical properties of the resultant photocatalysts were examined by powder X-ray diffractometry, nitrogen adsorption, diffuse reflectance spectroscopy, and transmission electron microscopy. These characterization techniques illustrated the enhanced morphological properties of the mesostructure such as the presence of highly crystalline anatase TiO2, large pore geometries, and active Ti–O–Si linkages, respectively. CO chemisorption analysis and TEM images accentuated the role of small Pt crystallite sizes in the development of photocatalysts with high degradation efficiencies.

Immobilization of hemoglobin within channel of mesoporous TiO2-SiO2 composite

In this investigation, mesoporous TiO2-SiO2 composites with different Ti/Si molecular ratios were synthesized by one pot method. Apart from the characterization by small angle X-ray diffraction (SAXRD), transmission electron microscope (TEM) and N2 absorption-desorption isotherms, these mesoporous materials were used in the adsorption and enrich of biological molecules. The results demonstrate that TiO2-SiO2 composites possess the ordered mesoporous structure with uniform pore. Bovine hemoglobin (BHb) can be immobilized within the mesopore of the composite and the immobilization amount increases with the Ti/Si molecular ratio. It is speculated that the strong electrostatic interaction between biomolecule and the inner surface of mesoporous materials enhances the adsorption of BHb. Moreover, our investigation confirms that the absorbed BHb still effectively retains its bioactivity, which is very significant for the potential application of this hybrid material in biocatalysis.

Length control of Ag nanorods in mesoporous SiO2–TiO2 by light irradiation

The length of Ag nanorods is uniquely controlled by irradiation with visible light using anatase TiO2-containing tubular SiO2 mesoporous templates. Spherical Ag nanoparticles and Ag nanorods of controlled length were fabricated by irradiation with visible light of selected wavelengths.

Hemoglobin immobilized within mesoporous TiO2–SiO2 material with high loading and enhanced catalytic activity

Hemoglobin (Hb) is immobilized within the channels of mesoporous TiO2–SiO2 materials. It was found that mesoporous TiO2–SiO2 material can immobilize more Hb than mesoporous SiO2 and the greatest loading is achieved on the sample with an optimized Ti/Si molar ratio of 4 : 6. The high loading of Hb in mesoporous TiO2–SiO2 material is attributed to the increased electrostatic interaction between Hb and the pore wall which possesses enhanced electron donating capacity after the lower electronegative Ti substitutes Si in the framework of mesoporous SiO2. Unlike its easy leaching from the pore of mesoporous SiO2, Hb can hardly be released once immobilized within mesoporous TiO2–SiO2 material. The immobilized Hb retains not only its structure like that of the native one in the aqueous solution, but also the catalytic activity. Specifically, Hb has a higher catalytic activity when immobilized within mesoporous TiO2–SiO2 material than that when immobilized within mesoporous SiO2. Furthermore, the catalytic activity of Hb increases when the Ti/Si molar ratio of mesoporous TiO2–SiO2 material changes from 2 : 4 to 4 : 6, which stems from the increasing Hb density in the pore of mesoporous TiO2–SiO2 material. However, the catalytic activity decreased when the Ti/Si molar ratio became 6 : 4 due to the low occupational volume of Hb.

Functional Assessment of Metal Oxide Nanoparticle Toxicity in Immune Cells

Understanding the nanoparticle-cell interaction is critical for the safe development of nanomaterials. Herein, we explore the impact of three metal oxide nanoparticles, nonporous Stober SiO(2), mesoporous SiO(2), and nonporous anatase TiO(2) nanoparticles, on primary culture mast cells. Using transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy, we demonstrate that each class of nanoparticle is internalized by the mast cells, localizing primarily in the secretory granules, with uptake efficiency increasing in the following order: nonporous SiO(2) < porous SiO(2) < nonporous TiO(2) nanoparticles. The influence of nanoparticle-laden granules was assessed using carbon-fiber microelectrode amperometry measurements that reveal functional changes in chemical messenger secretion from mast cell granules. Both nonporous and porous SiO(2) nanoparticles cause a decrease in the number of molecules released per granule, with nonporous SiO(2) also inducing a decrease in the amperometric spike frequency and, therefore, having a larger impact on cell function. As the two classes of SiO(2) nanoparticles vary only in their porosity, these results suggest that, while the mesoporous SiO(2) has a drastically larger total surface area due to the pores, the cell-contactable surface area, which is higher for the nonporous SiO(2), is more important in determining a nanoparticles' cellular impact. In comparison, exposure to nonporous TiO(2) slows the kinetics of secretion without altering the number of molecules released from the average granule. The varying immune cell response following exposure to nonporous SiO(2) and nonporous TiO(2) indicates that the nanoparticle-cell interactions are also modulated by surface chemistry.

Mild oxidation of bulky organic compounds with hydrogen peroxide over mesoporous TiO2-SiO2 xerogels prepared by non-hydrolytic sol–gel

The oxidation of bulky organic compounds with aqueous H2O2 over a TiO2-SiO2 xerogel catalyst prepared by a simple non-hydrolytic sol–gel route is described for the first time. Anthracene, cyclooctene, styrene, α-naphtol, diphenyl sulfide, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were oxidized with high activity, selectivity and H2O2 efficiency at moderate temperatures (40–60°C). Moreover, a similar catalytic behavior was observed when tert-butyl hydroperoxide (TBHP) was used as an oxidizing agent. These excellent catalytic performances were ascribed to the unique texture of the catalyst (specific surface area 1200m2g−1, pore volume 2.4cm3g−1, average pore diameter 15nm) and to the stability of Ti sites after exposure to aqueous H2O2 or TBHP.

Synthesis and photocatalytic activity of mesoporous SiO2–TiO2

Mesoporous SiO2–TiO2 was synthesized by the sol–gel method using Si(OC2H5)4, Ti(OC2H5)4, and stearyltrimethylammonium chloride. By using acetylacetone as the capping agent of Ti(OC2H5)4, homogeneous SiO2–TiO2 composite was obtained. Spherical mesoporous SiO2–TiO2 was also synthesized by the sol–gel method using W/O emulsion under microwave irradiation. The specific surface area of these mesoporous SiO2–TiO2 materials decreased when the Ti/Si molar ratio was higher than 0.1, which indicated that Ti was homogeneously distributed in mesoporous SiO2 matrix at Ti/Si ≦ 0.1. The photocatalytic activity of mesoporous SiO2–TiO2 materials was investigated by the degradation of methylene-blue in water under UV light irradiation. Mesoporous SiO2–TiO2 was effective for the adsorption–decomposition of methylene-blue.