TiO2-SiO2 Composites Research Articles

Green synthesis of submicron-sized Ti-rich MWW zeolite powders via a novel mechanochemical dry gel conversion in mixed steam environment

In this research, a novel green mechanochemical dry gel conversion method (MDGC) is reported to obtain submicron-sized Ti-rich MWW zeolite. First, titanium and silica sources were milled under milder conditions in a planetary ball mill to construct the uniform SiO2-TiO2 composite powders with higher Ti contents. Subsequently, submicron-sized Ti-rich MWW zeolite powder was prepared via dry gel conversion (DGC) route using the obtained composite under mixed steam environment consisting of water and piperidine. The physicochemical properties of the SiO2-TiO2 composites before and after calcination and corresponding Ti-MWW-MDGC were investigated by XRD, UV–Vis, FT-IR, SEM, XRF, and N2 absorption-desorption. Moreover, Ti-MWW (30)-MDGC exhibited a superior catalytic activity during epoxidation with H2O2 compared with the traditional DGC method, and the conversion of 1-hexene increased from 4.2% to 26.3%. The MDGC method is a promising approach for the green production of various zeolites with higher heteroatom contents, such as TS-1, Ti-Beta and Sn-MWW, etc.

SiO2@TiO2 Composite Synthesis and Its Hydrophobic Applications: A Review

Titanium dioxide is well known for its photocatalytic properties and low toxicity, meanwhile, silicone dioxide exhibits hydrophobic and hydrophilic properties and thermal stability. The union of these two materials offers a composite material with a wide range of applications that relate directly to the combined properties. The SiO2-TiO2 composite has been synthesized through physical methods and chemical methods and, with adequate conditions, morphology, crystallinity, boundaries between SiO2-TiO2, among other properties, can be controlled. Thus, the applications of this composite are wide for surface applications, being primarily used as powder or coating. However, the available research information on this kind of composite material is still novel, therefore research in this field is still needed in order to clarify all the physical and chemical properties of the material. This review aims to encompass the available methods of synthesis of SiO2-TiO2 composite with modifiers or dopants, the application and known chemical and physical properties in surfaces such as glass, mortar and textile, including aspects for the development of this material.

Efficient monolithic dye sensitized solar cells with eco-friendly silica-titania spacer layers

Monolithic assembly of dye-sensitized solar cells (M−DSSCs) is technologically attractive due to its ease of fabrication, compactness and lower production cost. However, combining cost-effective materials with high power conversion efficiency in M−DSSCs is still a challenging task. New silica–based spacer layers for M−DSSCs, derived from entirely water-based paste formulation were developed. A commercial aqueous suspension of SiO2 nanoparticles (LUDOX-40), modified with hydroxypropyl cellulose as a binder, were used for formulating the silica paste. The reflectance of the spacer layers was tuned by adding anatase nanoparticles; when 30 wt% of titania was added to the SiO2-TiO2 composite, a sharp increase of the reflectivity of the spacer layers was observed rendering a device with the highest to date reported power conversion efficiency of 8.3% and full stability. The effect of titania concentration in the SiO2 spacer layer on the photovoltaic performance, the spectral response of the photocurrent and recombination in M−DSSCs is discussed.

Fabrication of freestanding SiO2-TiO2 composite by a facile one pot method

ABSTRACTA freestanding SiO2–TiO2 monolith with bicontinuous structure was prepared via a one pot sol-gel reaction. This monolith was fully characterized by using field emission scanning electron microscopy (FE-SEM), nitrogen adsorption and X-Ray diffraction (XRD). Synthesized SiO2–TiO2 monolith possesses great mechanical strength and interconnected macropores (throughpores, textural pores) on the micrometer scale as well as skeleton pores in nanoscale, and also possesses an anatase TiO2 crystalline structure. Photo-catalytic breakdown of aqueous methylene blue (MB) with UV light was chosen to evaluate photocatalytic efficacy of the SiO2–TiO2 catalyst. These photodegradation activities indicated that MB decomposed completely within 180 min and the SiO2-TiO2 catalyst was readily separated from the reaction system and easily regenerated. Moreover, the photocatalytic activity of the monolithic catalyst remained unchanged after four catalytic cycles and the morphology was still intact.

Amorphous TiO2–SiO2 composites as selective heterogeneous catalysts for the oxidation of styrene to 1, 2-epoxyethylbenzene

A series of amorphous TiO2–SiO2 composite oxides with different TiO2 contents were prepared by a one-step co-precipitation process as catalysts for selective oxidation of styrene to 1, 2-epoxyethylbenzene with aqueous hydrogen peroxide in acetonitrile. The amorphous TiO2–SiO2 composites are found to be much more catalytically active than the one with partially crystallized TiO2. The TiO2–SiO2 composite with 40 wt% TiO2 (TSCO-3) presents the best catalytic performance. Under the optimal reaction conditions, the styrene conversion can reach 61.0% with a high selectivity of 95.4% to 1, 2-epoxyethylbenzene upon 1 h reaction. Moreover, the TSCO-3 catalyst exhibits a good cycling stability. The excellent catalytic performance can be attributed to the numerous exposed active centers and the fast release of the product from the active centers.

Experimental investigation of thermal insulating aerogel composites of hydrothermal reactor for biomass-to-hydrogen conversion

The paper presents aerogel SiO2–TiO2 composites used for thermal insulation of hydrothermal reactor for biomass-to-hydrogen conversion and the method of their production. The technology of aerogel composites production includes the following stages: ion exchange of liquid Na-glass resulting in production of silica hydrosol; hydrosol concentration; hydrogel production and its maturing; SiO2–TiO2 alcogel production; modification of its surface; subcritical drying of alcogel resulting in production of SiO2–TiO2 ambigel; its thermal treatment, granulating and classification. The influences of infrared opacifier (titanium dioxide) and thermal treatment temperature of SiO2–TiO2 composite on its structural and thermal characteristics have been investigated. Possibilities of hydrogen yield increase by reduction of power waste by means of vacuumized thermal insulation for reactor walls have been examined.

Crown Ether–SiO2–TiO2 Composites in the Sorption of Metal Ions from Acidic Aqueous Solutions

Crown ether–SiO2–TiO2 composites were obtained by adding crown ethers (dibenzo-18-crown-6 or dibenzo-21-crown-7) during the sol–gel synthesis of SiO2–TiO2. The behavior of the composites in the sorption of several alkali, alkaline-earth, and rare-earth metal cations from acidic solutions was investigated. The crown ether–SiO2–TiO2 composites of the crown ethers showed higher efficiency and selectivity in the sorption of barium cations, as well as ytterbium cations in the presence of Sr(II), Ce(III), La(III), and Nd(III) compared to the parent crown ethers. It was established by FTIR spectroscopy that the crown ether molecule immobilized on the oxide surface has a distorted structure, which can explain the change in the selectivity of complex formation in going from crown ethers to their composites.

Influence of ZnO doping on structural, optical and pH-stimulus characteristics of silica-titania nanocomposite matrix

In-situ sol-gel procedure is used to synthesize the silica-titania nanocomposite (SiO2-TiO2) as host matrix which is doped with ZnO and heated at 300 °C for 1 h for homogeneous and stable matrix surface. The mixture of organic dyes i.e. cresol red, bromophenol blue, phenol red and phenolphthalein is encapsulated within ZnO:SiO2-TiO2 nanocomposite for the evaluation of sensing activity at dynamic pH range 1–12. Microscopic findings showed that the synthesized nanocomposites have homogeneous crack-free porous coating with low roughness value of 9.7–7.6 nm. XRD analysis shows the formation of new phase ZnSiO3 after ZnO doping and heat treatment along with anatase phase of titania and silica. TEM analysis confirmed the spherical nanoparticles. The heterogeneous bonding of synthesized Zn:SiO2-TiO2 composites is investigated by FTIR. Surface analysis confirmed that prepared nanocomposites have high surface area, large pore diameters and mesoporous nature, which is desirable for good sensing behavior. Optical studies show that low refractive index (1.33–1.39) transparent nanocomposites (92–62% transparency in the visible range) are promising for sensing applications. TGA analysis shows that SiO2-TiO2 nanocomposites after ZnO doping and heat treatment are thermally stable. The fast response 0.15 s of the ZnO:SiO2-TiO2 nanocomposite coated fiber optic sensor is optimized at pH 12. The observed sensitivity is of 15 counts/pH with repeatability of 93% at 440 nm.

Study on the Preparation of TiO2-SiO2 Composites from Rice Husk Ash

In this paper, TiO2-SiO2 composites with different SiO2 content s were prepared by coprecipitation method using rice husk ash as raw material. The effects of the concentration of alkaline leaching solution and reaction temperature on the extraction rate of SiO2 from rice husk ash were investigated. The optimum formation conditions of TiO2-SiO2 composites were explored, and the microstructure and properties of the composites were analyzed. The experiment al results showed that the extract ion rat e of SiO2 from rice husk ash reaches the maximum when the concentration of alkaline leaching solution is 1.5 mol/L and the reaction temperature is 90°C. When the pH value is 7, the TiO2-SiO2 composites can achieve the optimum formation condition. TiO2-SiO2 composites are composed of approximately spherical particles with obvious pore structure of the surface and piling up in fluffy state. The Si atoms enter the crystal structure of TiO2 with Ti-O-Si bonds connected to Ti atoms, which inhibits the growth of TiO2 grains and leads to the increase of the transition temperature of TiO2 from anatase to rutile.

Particularities of photocatalysis and formation of reactive oxygen species on insulators and semiconductors: cases of SiO2, TiO2and their composite SiO2–TiO2

Highly defected tubular SiO2outperforms the photocatalytic activity of TiO2-P25 and the SiO2–TiO2composite.

Synthesis and photocatalytic performance of hollow sphere particles of SiO2-TiO2 composite of mesocellular foam walls

Abstract Hollow Microspheres of SiO 2 -TiO 2 photocatalysts whose walls are made up of mesoporous cellular foams were synthesized with the aid of hexane as a swelling agent and P123 as a pore template by an emulsion templating method. Pore structure of materials and crystal phase of titanium oxide was tailored by hydrothermal and calcination temperature during synthesis of samples. The samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N 2 adsorption–desorption experiments, X-ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD) techniques. The effect of pore structure and titania phase on photoactivity were evaluated by methylene blue (MB) degradation test under UV light as well. Results showed that hydrothermal temperature during synthesis process has a significant effect on pore and window sizes of mesostructured cellular foam. Interestingly, for the sample hydrothermally treated at higher temperature (130 °C), anatase to rutile transformation was avoided after calcination treatment as high as 800 °C. The highest photocatalytic activity was detected from the sample hydrothermally treated at 130 °C and calcined at 800 °C for which the highest degree of crystallinity and anatase phase as well as enhanced pore connectivity was obtained.

Heterogeneous Ag-TiO2-SiO2 composite materials as novel catalytic systems for selective epoxidation of cyclohexene by H2O2.

TiO2-SiO2 composites were synthesized using cetyl trimethyl ammonium bromide (CTAB) as the structure directing template. Self-assembly hexadecyltrimethyl- ammonium bromide TiO2-SiO2/(CTAB) were soaked into silver nitrate (AgNO3) aqueous solution. The Ag-TiO2-SiO2(Ag-TS) composite were prepared via a precipitation of AgBr in soaking process and its decomposition at calcination stage. Structural characterization of the materials was carried out by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption and ultraviolet visible spectroscopy (UV-Vis). Characterization results revealed that Ag particles were incorporated into hierarchical TiO2-SiO2 without significantly affecting the structures of the supports. Further heating-treatment at 723 K was more favorable for enhancing the stability of the Ag-TS composite. The cyclohexene oxide was the major product in the epoxidation using H2O2 as the oxidant over the Ag-TS catalysts. Besides, the optimum catalytic activity and stability of Ag-TS catalysts were obtained under operational conditions of calcined at 723 K for 2 h, reaction time of 120 min, reaction temperature of 353 K, catalyst amount of 80 mg, aqueous H2O2 (30 wt.%) as oxidant and chloroform as solvent. High catalytic activity with conversion rate up to 99.2% of cyclohexene oxide could be obtainable in water-bathing. The catalyst was found to be stable and could be reused three times without significant loss of catalytic activity under the optimized reaction conditions.

Enhanced the hydrophobic surface and the photo-activity of TiO2-SiO2 composites

The aim of this research is to develop nanomaterials for coating applications. This research studied the effect of various TiO2-SiO2 composites in acrylic paint to enhance the hydrophobic properties of the substrate. Titanium dioxide containing silica in the range 20–35 mol% has been synthesized using sol–gel route. The XRD’s spectra show that increasing SiO2 content in the composite, decreasing its crystalline properties but increasing the surface area. TiO2-SiO2 composite was dispersed in acrylic paint in 2% composition by weight. The largest contact angle was 70, which produced by the substrate coated with TS-35-modified acrylic paint. This study also investigated the enhanced photo-activity of TiO2-SiO2 modified with poly-aniline. The XRD spectra show that the treatment does not change the crystal structure of TiO2. The photo-activity of the composite was evaluated by degradation of Rhodamine-B with visible light. The best performance of the degradation process was handled by the composite treated with 0.1mL anilines per gram of TiO2-SiO2 composite (TSP-A). On the other side, the contact angle 70 has not shown an excellent hydrophobic activity. However, the AFM spectra showed that nanoroughness has started to form on the surface of acrylic paint modified with TiO2-SiO2 than acrylic alone.

TiO<sub>2</sub>-SiO<sub>2</sub> Gel Photocatalytic Degradation of Methylene Blue and Composite Energy Gap Calculation

The objectives of this study were to mix TiO2 and SiO2 gel for photo catalyzing in methylene blue and calculated energy gap of TiO2- SiO2 gel composite. Nanoparticles of TiO2-doped SiO2 gels have been synthesized for use as composites in photodegradation of methylene blue. SiO2 gel was synthesized by a sol-gel method from rice husk ash. TiO2 was synthesized by microwave method from TiOSO4. The composite of TiO2-SiO2 was prepared by mixing of 25% wt TiO2 and 75% wt SiO2 gel and SiO2 gel bead. This work can be dived into two kinds of TiO­2 sources were TiO2 from microwave synthesis (MW) and TiO2 from P25. The UV absorption values of methylene blue after used TiO2-SiO2 composite were measured. Wavelengths of composites were measured by Uv-vis reflectometer and energy gap were calculated.

Economic Hydrophobicity Triggering of CO2 Photoreduction for Selective CH4 Generation on Noble-Metal-Free TiO2–SiO2

On the basis of the fact that the competitive adsorption between CO2 and H2O on the catalyst plays an important role in the CO2 photoreduction process, here we develop an economic NH4F-induced hydrophobic modification strategy to enhance the CO2 competitive adsorption on the mesoporous TiO2-SiO2 composite surface via a simple solvothermal method. After the hydrophobic modification, the CO2 photoreduction for the selective generation of CH4 over the noble-metal-free TiO2-SiO2 composite can be greatly enhanced (2.42 vs 0.10 μmol/g in 4h). The enhanced CO2 photoreduction efficiency is assigned to the rational hydrophobic modification on TiO2-SiO2 surface by replacing Si-OH to hydrophobic Si-F bonds, which will improve the CO2 competitive adsorption and trigger the eight-electron CO2 photoreduction on the reaction kinetics.

EXPERIMENTAL RESEARCH OF AEROGEL INSULATION COMPOSITES OF THE HYDROTHERMAL REACTOR FOR BIOMASS-TO-HYDROGEN CONVERSION

This paper presents aerogel SiO2–TiO2composites used for thermal protection of biomass-to-hydrogen hydrothermal reactor and the method of their production. The technology of aerogel composites production includes the following stages: ion exchange of liquid Na-glass leading to formation of hydrosol silica; hydrosol concentration; formation and maturing of hydrogel; production of SiO2-TiO2alcogel; modification of its surface; subcritical drying of alcogel leading to formation ofSiO2-TiO2 ambigel; its heat treatment, granulating and classification. The influence of the infrared opacifier (titania) and the heat treatment temperature of SiO2-TiO2composite on its structural and thermal characteristics is investigated. Possibilities of increasing the hydrogen yield by reduction of energy losses using vacuum thermal insulation for reactor walls are examined.

Synthesis and thermoanalytical study of SiO2–TiO2 composites modified with macrocyclic endoreceptors

We have developed processes for the fabrication of SiO2–TiO2 composites containing crown ethers (CEs) with composite: CE weight ratios from 1: 0.06 to 1: 1. As oxide sources, we used titania and silica sols. The composites were characterized by differential thermal analysis, X-ray diffraction, and adsorption gravimetry. The results demonstrate that most of the water and the solvent are bound into a complex with the CE, which decomposes at temperatures from 170 to 230°C. The temperature range of CE removal depends on the SiO2: TiO2 and oxide: CE ratios in the composite. Our results demonstrate effectiveness of strontium cation imprint formation in an adsorbent in the sol–gel processing step, which ensures an increase in the amount of strontium cation adsorption by 20%. We have identified conditions for quantitative lanthanum, strontium, and barium adsorption on the synthesized composites.

Influence of the porous texture of SBA-15 mesoporous silica on the anatase formation in TiO2–SiO2 nanocomposites

TiO2–SiO2 composites with 44 wt% of anatase exhibit a better MO degradation rate than those with fully crystallized anatase.

TiO2–SiO2 films from organic-free colloidal TiO2 anatase nanoparticles as photocatalyst for removal of volatile organic compounds from indoor air

Different types of TiO2–SiO2 composites in the form of powder or films have been reported as efficient photocatalysts for decomposition of organic compounds in liquid and gas phase. Herein, we report for the first time on the formation of efficient TiO2–SiO2 films made from acidic organic-free colloidal solution of TiO2 anatase nanoparticles (AS) and mesoporous SiO2 (SBA-15) with 100% loading (TiO2: SiO2 molar ratio 1:1) under simple and low cost procedure. AS was prepared from metatitanic acid precursor using a novel, environmentally friendly approach of TiO2 nanoparticles precipitation with NaOH and peptization with HCl. These AS/SBA-15 films, immobilized by brush deposition on glass carriers, showed total decomposition of toluene and 91% decomposition of formaldehyde as model VOCs in gas phase, at room temperature under UVA irradiation in lab-made batch photoreactor. The trend of photocatalytic efficiency for decomposition of formaldehyde was AS/SBA-15>P25>PC500>AS. The adsorption capability of the AS/SBA-15 was higher in comparison to its pure TiO2 analogues (AS, P25, PC500) in case of toluene. Turnover frequency (TOF) of the AS/SBA-15 was approximately six times higher in comparison to its pure TiO2 analogue AS for toluene and formaldehyde. The potential of AS/SBA-15 for the use in air cleaning devices is finally discussed.

Robust Superhydrophobic and Photocatalytic Cotton Fabrics Based on TiO<sub>2</sub>-SiO<sub>2</sub>-PDMS Composite Coating <sup></sup>

In this work, self-cleaning cotton fabrics were prepared based on the TiO2-SiO2-Polydimethylsiloxane (PDMS) composites. TiO2-SiO2 composites were synthesized by depositing TiO2 nanocrystals onto preformed porous SiO2 and PDMS was used to enhance the linkage between TiO2-SiO2 composites and cotton fabrics. The TiO2-SiO2-PDMS composites coated cotton fabrics show superhydrophobicity with a water contact angle of 157°because of the abundant of methyl groups and hierarchical roughness features of the coated cotton fabrics. Meanwhile, the TiO2-SiO2-PDMS composites coated cotton fabrics display photocatalytic property, which were analyzed based on the removal and degradation of rhodamine B (RhB) under ultraviolet light. Abrasion resistance test indicates that the coating possesses a good mechanically durability.