Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

The effect of nanosized titania-silica film composition on the photostability of adsorbed methylene blue dye

The effect of nanosized porous films (average density 10 g/m²) of TiO₂. TiO₂/SiO₂, and SiO₂ on the photostability of adsorbed methylene blue (MB) dye during UV irradiation in air was investigated by optical spectroscopy and laser-induced mass spectrometry. The effectiveness of the photodecomposition of MB decreases in the order TiO₂ > TiO₂/SiO₂ > SiO₂ with rate constants 1E-2, 0.6E-2, and 0.3E-2 min⁻¹ respectively. A mechanism including the participation of both excited states of the dye molecules and photoexcited titanium dioxide is proposed for the photodecolorization of MB adsorbed on the surface of the investigated films. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 220–225, July–August, 2007.     

Preparation of TiO<Subscript>2</Subscript>/activated carbon with Fe ions doping photocatalyst and its application to photocatalytic degradation of reactive brilliant red K2G

Titanium dioxide coated on activated carbon (AC) with Fe ions doping (Fe-TiO₂/AC) composite was prepared by an improved sol-gel method. The photocatalytic activities were tested by photocatalytic degradation of reactive brilliant red K2G in solution. The results show that in comparison with the agglomeration of pure TiO₂, the TiO₂ nanoparticles are well dispersed in the AC matrix, of which sizes are decreased with Fe ions doping. Additionally, the iron species on TiO₂ of composite are Fe₂O₃ and FeO, which do not affect the crystalline structures of TiO₂ nanoparticles. The AC matrix and iron doping content influence the fluorescence intensity of composite due to their effects on recombination probability of hole-electron pairs. Compared with TiO₂, 0.3% Fe-TiO₂, TiO₂/AC, 0.5% Fe-TiO₂/AC and 0.1% Fe-TiO₂/AC, the 0.3% Fe-TiO₂/AC shows the highest photoactivity with the complete mineralization of K2G for finite time due to the optimum Fe ions content and AC matrix. Furthermore, the kinetic constant (k = 0.0229 min⁻¹) of 0.3% Fe-TiO₂/AC composite is more than the sum of both TiO₂/AC (0.0154 min⁻¹) and 0.3% Fe-TiO₂ (0.0057 min⁻¹) because coexistence of the AC and Fe ions has an enlarging effect on improving the photoactivity of TiO₂. Supported by the Education Department Foundation of Hunan Province (Grant No. 08B063) and Science and Natural Science Foundation of Hunan Province (Grant No. 09JJ6101)     

Effect of silicon dioxide on the formation of the phase composition and pore structure of titanium dioxide with the anatase structure

The formation of the structure of titanium dioxide modified with silicon dioxide, which was introduced as tetraethyl orthosilicate, was studied. It was found that the formation of the nanocrystalline structure of TiO₂ occurred upon the modification of titanium dioxide with silicon dioxide. This nanocrystalline structure of TiO₂ was formed by highly dispersed anatase particles of size 6–10 nm stabilized by silicon oxide layers, which were formed upon the decomposition of tetraethyl orthosilicate. An increase in the modifier concentration resulted in a deceleration of the growth of anatase particles and an increase in the temperature of the phase transition of anatase to rutile. It was found that the anatase phase in the samples containing 5–15 wt % SiO₂ was stable up to 1000°C. The stabilization of highly dispersed anatase particles facilitated the retention of the developed fine-pore structure of xerogels with a pore diameter of 4 nm up to 900°C.     

Synthesis,characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins

Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH₃, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO₂–SiO₂, ZnPP–TiO₂–SiO₂ and ZnCP–TiO₂–SiO₂, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO₂–SiO₂ samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO₂–SiO₂ under visible light irradiation and follow the order of ZnMP–TiO₂–SiO₂ > ZnPP–TiO₂–SiO₂ > ZnCP–TiO₂–SiO₂.     

Sorption behavior of germanium(IV) on titanium dioxide nanoparticles

Titanium dioxide nanoparticles were employed for the sorption of Ge(IV) ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, and temperature. The sorption process was found to be fast, equilibrium was reached within 3 min. A maximum sorption could be achieved from solution when the pH ranges between 4.0 and 11.0. Sorbed Ge(IV) ions can be completely desorbed with 2 mL of 0.3 mol L⁻¹ K₃PO₄-1.0 mol L⁻¹ H₂SO₄ mixture solution. The kinetic experimental data properly correlate with the second-order kinetic model (k ₂ = 0.88 g mg⁻¹ min⁻¹ (25°C)), Reichenberg equation and Morris-Weber model. The estimated E _a for Ge(IV) adsorption on nano-TiO₂ was 19.66 kJ mol⁻¹. The overall rate process appears to be influenced by intra-particle diffusion. The sorption data could be well interpreted with the Langmuir and Dubinin-Radushkevich (D-R) type sorption isotherms. The D-R parameters were calculated to be K = −0.00321 mol₂ kJ⁻², q _m = 0.59 mmol g⁻¹ and E = 12.48 kJ mol⁻¹ at room temperature. Furthermore, the thermodynamic parameters were also determined, and the ΔH ⁰ and ΔG ⁰ values indicated a spontaneous exothermic behavior.     

Kinetic studies of the crystallization process of glass-ceramics based on basalt

The crystallization kinetic of the basalt glass ceramic of the oxide composition, (%): SiO₂ − 50.82; Al₂O₃ − 12.05; Fe₂O₃ − 9.28; CaO − 15.48; MgO − 11.08; Na₂O+K₂O − 1.14; TiO₂ − 0.15, with addition of 10% TiO₂ as nucleating agent has been studied using thermal analysis under non-isothermal conditions. In this order, the non-isothermal DTA curves were obtained at different heating rates between 4 and 20°C min⁻¹ in the temperature range of 25–1000°C using a Derivatograph-C (MOM, Hungary). The kinetic parameters of the crystallization process were calculated on the basis of Ozawa-Flynn-Wall, Friedman, Budrugeac-Segal and non-parametric kinetic methods.     

Ag and Cu loaded on TiO<Subscript>2</Subscript>/graphite as a catalyst for <Emphasis Type="Italic">Escherichia coli</Emphasis>-contaminated water disinfection

TiO₂ film was synthesized by means of the chemical bath deposition (CBD) method from TiCl₄ as a precursor and surfactant cetyl trimethyl ammonium bromide (CTAB) as a linking and assembling agent of the titanium hydroxide network on a graphite substrate. Ag and Cu were loaded on the TiO₂ film by means of electrodeposition at various applied currents. Photoelectrochemical testing on the composite of Ag-TiO₂/G and Cu-TiO₂/G was used to define the composite for Escherichia coli-contaminated water disinfection. Disinfection efficiency and the rate of disinfection of E. coli-contaminated water with Ag-TiO₂/G as a catalyst was higher than that observed for Cu-TiO₂/G in all disinfection methods including photocatalysis (PC), electrocatalysis (EC), and photoelectrocatalysis (PEC). The highest rate constant was achieved by the PEC method using Ag-TiO₂/G, k was 6.49 × 10⁻² CFU mL⁻¹ min⁻¹. Effective disinfection times of 24 h (EDT₂₄) and 48 h (EDT₄₈) were achieved in all methods except the EC method using Cu-TiO₂/G.     

Photo catalytic oxidation of TNT using TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> nano-composite aerogel catalyst prepared using sol–gel process

The degradation of nitro aromatics like trinitrotoluene (TNT) released in the waste water from explosive process plants is the serious problem due to toxic and explosive nature of TNT. The poor response of TNT to biodegradation enhanced the gravity of the problem. We have demonstrated that high specific surface area TiO₂–SiO₂ nano-composite aerogel is promising photo catalyst in successful treating of TNT contaminated aqueous solution. The TiO₂–SiO₂ composite aerogel with nominal content of 20 and 50% TiO₂, used as catalyst, were prepared by co-precursor sol–gel method using titanium isopropaxide and tetramethylorthosilicate as source of titania and silica, respectively. The XRD studies confirmed formation of anatase phase of crystalline TiO₂ with nano sized crystallites. The TiO₂–SiO₂ aerogel showed specific surface area of 1,107 and 485 m²/g for the aerogels containing 20 and 50% TiO₂, respectively. The 100 ppm TNT solution was treated, in 700 ml capacity reaction vessel, using H₂O₂ oxidizer and TiO₂–SiO₂ aerogel catalyst in presence of UV light (8 W UV lamp). Using TiO₂–SiO₂ (50/50) aerogel with surface area of 485 m²/g, we succeeded to reduce the TOC to 1 ppm within 3.5 h where as using TiO₂/SiO₂ (20/80) aerogel with surface area of 1,107 m²/g, the TOC was reduced to about only 7 ppm in the same time. It revealed that the combination of high TiO₂ content and high specific surface area is an important factor to achieve effective and faster degradation of TNT for complete mineralization.     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

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.     

Modeling the infrared and raman spectra of silicon dioxide clusters absorbing water

The effect of absorbed water on the dielectric properties of silicon dioxide nanoparticles is studied by the molecular dynamic method. It is demonstrated using the model of flexible molecules that increasing the number of water molecules in the (SiO₂)₅₀ cluster to 40 results in an enhancement of absorption of infrared radiation over the frequency range 0 cm⁻¹ ≤ ω ≤ 1000 cm⁻¹. It is ascertained that the absorption of water molecules by the (SiO₂)₅₀ cluster considerably alters the shape of Raman spectra of light, smoothing all the peaks after the first one, and that water molecules are concentrated near the cluster surface formed by SiO₂ structural units.     

Electrode modified with toluidine blue-doped silica nanoparticles, and its use for enhanced amperometric sensing of hemoglobin

Three-dimensionally structured, silica based, organic–inorganic hybrid nanoparticles (NPs) were prepared by a simple and feasible water-in-oil (W/O) microemulsion method and a promising platform for bioelectrochemical analysis was obtained. The commonly used phenathiazine organic compound, toluidine blue (TB) was readily captured in the three-dimensional cage of the inorganic SiO₂ network, which was considered to serve as a protective “shell” toward the embedded TB. A TEM image indicated the size of the thus prepared TB-doped SiO₂ (TB@SiO₂) NPs was 21 ± 3 nm. UV–visible and IR spectroscopy confirmed successful formation of the organic–inorganic composite and possible interaction between TB and SiO₂, which favored enhanced stability of the hybrid. A sensitive amperometric sensor for hemoglobin (Hb) biomolecules based on TB@SiO₂ NPs conjugated with a biopolymer chitosan (CHIT) membrane was then developed. The surface of the silica NPs was highly biocompatible and the TB captured inside maintained its high electron-transfer efficiency. Dye leakage of TB from the TB@SiO₂ hybrid was proved to be minimal, owing to the inorganic SiO₂ network and the force of interaction between TB and SiO₂. The amperometric sensor had a detection limit of 2.5 × 10⁻⁹ mol L⁻¹ (S/N = 3) with a linear range from 5.0 × 10⁻⁹ to 3.0 × 10⁻⁶ mol L⁻¹ for Hb. When it was applied to determine the concentration of a clinical blood sample, satisfactory results were obtained which were in good agreement with those obtained by the standard method.     

Adsorption and redox chemistry of cis-RuLL'(SCN)2 with L=4,4′-dicarboxylic acid-2,2′-bipyridine and L'=4,4′-dinonyl-2,2′-bipyridine (Z907) at FTO and TiO2 electrode surfaces

The electrochemical and spectroelectrochemical properties of the sensitizer dye Z907 (cis-RuLL'(SCN)₂ with L=4,4′-dicarboxylic acid-2,2′-bipyridine and L'=4,4′-dinonyl-2,2′-bipyridine) adsorbed on fluorine-doped tin oxide (FTO) and TiO₂ surfaces have been investigated. Langmuirian binding constants for FTO and TiO₂ are estimated to be 3 × 10⁶ M⁻¹ and 4 × 10⁴ M⁻¹, respectively. The Ru(III/II) redox process is monitored by voltammetry and by spectroelectrochemistry. For Z907 adsorbed onto FTO, a slow EC-type electrochemical reaction is observed with a chemical rate constant of ca. k = 10⁻² s⁻¹ leading to Z907 dye degradation of a fraction of the FTO-adsorbed dye. The Z907 adsorption conditions affect the degradation process. No significant degradation was observed for TiO₂-adsorbed dye. Degradation of the Z907 dye affects the electron hopping conduction at the FTO–TiO₂ interface.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Sol–gel immobilization of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> on hydrophobic clay and its removal of methyl orange from water

In this study, SiO₂/TiO₂–organoclay hybrids with high adsorption capability and high photocatalytic activity were synthesized by immobilizing mixed silica and titanium dioxide nanoparticles on organically modified clay via a hydrothermal sol–gel method. Addition of negatively charged silica particles enhanced the uniform dispersion of titanium dioxide nanoparticles on organoclay layers by decreasing the system tension, which resulted in high photocatalytic activity of SiO₂/TiO₂–organoclay hybrids. The high adsorption capability endowed by organically modified clay enriched the organic compounds around the photoactive sites, and thus greatly improved the photodegradation efficiency. Combining the high adsorption capability of organoclay with the high photocatalytic activity of TiO₂ nanoparticles, SiO₂/TiO₂–organoclay hybrids were promising and cost-effective photocatalysts in removal of pollutants from wastewater.     

Synthesis and photocatalytic activity of mesoporous SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>

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.     

Reduction of water-soluble colloidal manganese dioxide by thiourea: a kinetic and mechanistic study

Kinetic data for the colloidal MnO₂–thiourea redox system are reported for the first time. The reduction of water-soluble colloidal MnO₂ by thiourea (sulfur containing reductant) in aqueous perchloric acid medium has shown that it proceeds in two stages, i.e., a fast stage followed by a relatively slow second stage. The log (absorbance) versus time plot deviates from linearity. The kinetics of both the stages was investigated spectrophotometrically. The first-order kinetics with respect to [thiourea] at low concentration shifts to zero-order at higher concentration. The reaction rate increases with [HClO₄] and the kinetics reveals complex order dependence in [HClO₄]. Addition of P₂O ₇ ⁴⁻ and F⁻ in the form of Na₄P₂O₇ and NaF, respectively, has inhibitory effect on the reaction rate. The reaction proceeds through the fast adsorption of thiourea on the surface of the colloidal MnO₂. A mechanism involving the protonated thiourea as the reactive reductant species is proposed. The observed results are discussed in terms of Michaelis–Menten/Langmuir–Hinshelwood model. From the observed kinetic data, colloidal MnO₂–thiourea adsorption constant (K _ad1) and rate constant (k ₁) were calculated to be 1.25×10¹⁰ mol⁻¹ dm³ and 3.1×10⁻⁴ s⁻¹, respectively. The variation of temperature does not have any effect on the reaction rate.     

Determination of the rate constants for the reaction Fe + O<Subscript>2</Subscript> = FeO + O in the forward and reverse directions

The results of our experimental studies and an analysis of the published data on the rate constant for the reaction Fe + O₂ = FeO + O in the forward (I) and reverse (−I) direction are reported. The data obtained in this work are described by the expressions k ₁ = 6.2 × 10¹⁴exp(−11100 K/T) cm³ mol⁻¹ s⁻¹ and k ₋₁ = 6.0 × 10¹³exp(−588 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K). The generalized expressions for the temperature dependences of these rate constants derived by combining our results with the literature data can be presented as k ₁ = 9.4 × 10¹⁴(T/1000)^0.022exp(−11224 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K) and k ₋₁ = 1.8 × 10¹⁴(1000/T)^0.37exp(−367 K/T) cm³ mol⁻¹ s⁻¹ (T = 200–2500 K).