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1.
Stabilised titania sols were prepared using an additive free particulate sol-gel route, via electrostatic stabilisation mechanism, with various processing parameters. Peptisation temperature, 50°C and 70°C, and TiO2 concentration, 0.1, 0.2 and 0.4 molar, were chosen as processing parameters during sol preparation. Results from TiO2 particle size and zeta potential of sols revealed that the smallest titania hydrodynamic diameter (13 nm) and the highest zeta potential (47.7 mV) were obtained for the sol produced at the lower peptisation temperature of 50°C and lower TiO2 concentration of 0.1 M. On the other hand, between the sols prepared at 70°C, smaller titania particles (20 nm) and higher zeta potential (46.3 mV) were achieved with increasing TiO2 concentration up to 0.4 M. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) results of produced powders annealed at different temperatures showed that the 300°C annealed powder made from 0.1 M sol prepared at 50°C was a mixture of anatase and brookite, corresponding to a major phase of anatase (∼95% estimated), with the smallest average crystallite size of 1.3 nm and the highest specific surface area (SSA) of 193 m2/g. Furthermore, increasing TiO2 concentration up to 0.4 molar for the sols prepared at 70°C resulted in decreasing the average crystallite size (1.9 nm at 300°C) and increasing SSA (116 m2/g at 300°C) of the powders annealed at different temperatures. Anatase-to-rutile phase transformation temperature was increased with decreasing peptisation temperature down to 50°C, whereas TiO2 concentration had no effect on this transition. Anatase percentage increased with decreasing both peptisation temperature and TiO2 concentration. Such prepared powders can be used in many applications in areas from photo catalysts to gas sensors.  相似文献   

2.
Highly stable TiO2 sols were prepared by adjusting the water-to-titanium molar ratio to ~4 in the process of hydrolysis and condensation of titanium isopropoxide in ethanol with HNO3. Particularly, long-term stable TiO2 sols were prepared without adding any chemical additives. Anatase TiO2 nanocrystallites with sizes of 3–5 nm in diameter were uniformly dispersed in the stable sol. Crystallized TiO2 films were successfully deposited on Si (100) using the stable sol via a dip-coating process with low temperature curing at as low as 100 °C. The synthesized TiO2 sols and films are promising for use in flexible or dye-sensitized solar cells.  相似文献   

3.
In this research, TiO2 sols were synthesized via a sol?Cgel reaction at room temperature followed by heating under reflux. Hybrid thin films were prepared using the TiO2 sols and dipentaerythritol hexacrylate on poly(methyl methacrylate) substrates via spin coating followed by UV-curing. The images of transmission electron microscopy (TEM) and results of dynamic light scattering (DSL) showed that some originally synthesized TiO2 nanoparticles aggregated while many small-sized (~5?nm) TiO2 nanoparticles still existed after reflux heating. The synthesized TiO2 sols showed poor photocatalytic ability, which might avoid degradation of organic moieties in the hybrids. The refractive indices of the hybrid thin films were increased from 1.66 to 1.82 while the water contact angles on the thin films were increased from 70.2° to 87.7° with the increment of TiO2 content. Increasing the heating time of the TiO2 sol resulted in an increase in the refractive index and contact angle.  相似文献   

4.
The preparation of SiO2-TiO2 thin films by the sol-gel method using silicic acid and titanium tetrachloride as starting materials was studied. The homogeneous sols were obtained by the condensation reaction of silicic acid with titanium tetrachloride in methanol-tetrahydrofuran. The dipcoating of slide glasses and silicon wafers followed by heat treatment gave oxide thin films of 88–93% transmittance, 3000–4500 Å thickness, and 1.45–1.80 refractive index, depending on heat-treatment temperature and TiO2 content. FT-IR measurement showed that the Si-O-Ti bond is formed even in the sol and films. The variations of film thickness and refractive index on transformation from the gels into the oxides were found to be quite low.  相似文献   

5.
This paper discusses the physical-chemical properties of γ-Al2O3 and TiO2 ceramic membranes which have been prepared by sol-gel techniques from alkoxide starting materials. Mean pore size and pore size distributions are examined using N2 sorption analysis. Particle size of sols as measured by in situ quasi-elastic light scattering is compared with SEM analysis of sintered membranes. Crack-free unsupported monoliths with thicknesses up to 120 μm have been prepared of γ-Al2O3. Supported TiO2 membranes have been fabricated with thicknesses up to 0.5 μm. The γAl2O3 membranes are obtained from “particulate” sols, while for TiO2 both “particulate” and “polymeric” sols have been used to produce membranes.  相似文献   

6.
Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO2:LaPO4 ratios were applied as thin coating on glass substrates in order to be transparent, hydrophobic, photocatalytically active coatings. The phase compositions of the composite powders were identified by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The anatase phase of TiO2 in TiO2-LaPO4 composite precursors was found to be stable even on annealing at 800 °C. The glass substrates, coated with TL1 (TiO2-LaPO4 composition with 1 mol% LaPO4) and TL50 (composite precursor containing TiO2 and LaPO4 with molar ratio 1:1) sols and annealed at 400 °C, produced contact angles of 74° and 92°, respectively, though it is only 62° for pure TiO2 coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 °C, has shown the highest UV photoactivity with an apparent rate constant, kapp=24×10−3 min−1, which is over five times higher than that observed with standard Hombikat UV 100 (kapp=4×10−3 min−1). The photoactivity combined with a moderate contact angle (85.3°) shows that this material has a promise as an efficient self-cleaning precursor.  相似文献   

7.
In order to clarify the effects of diethanolamine (DEA) in the silver (Ag)/titanium dioxide (TiO2) sol–gel process, sols with and without DEA, and films derived from these sols were prepared. The samples were investigated by X-ray diffraction, transmission electron microscopy, electron diffraction and optical absorption spectra. The results showed that metallic Ag clusters were formed in the sol with DEA and was absent in the sol without DEA. This indicated that DEA worked not only as the stabilizer but also as the reduce agent in Ag/TiO2 sol–gel process. After annealed, Ag metallic nanoparticles were generated in the films derived from both the sols with and without DEA. The particles in the films derived from the sol with DEA were smaller than those from the sol without DEA. This can be ascribed to the limitation of the growth of Ag cluster formed in the sol with DEA during heat treatment. Mechanisms for the formation of metallic Ag in the Ag/TiO2 sols and films were discussed. The effects of DEA in the sols and films were studied in detail.  相似文献   

8.
Microporous SiO2 and SiO2/MO2 (M=Ti, Zr, Al; 10 mol% MOx) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO2 sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1<d f<2.04.  相似文献   

9.
Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.  相似文献   

10.
Photochromism of a WO3 aqueous sol has been investigated in a nitrogen atmosphere under controlled temperature. Effects of ageing of the WO3 sols, concentrations of WO3 sols or Cl ion and temperature on the coloring rate were examined. The coloring rate was the first-order with respect of the WO3 concentration. The coloring process was accelerated by an addition of TiO2 aqueous sols. Spectral changes were measured using the mixing sol with various molar ratios (γ) of WO3 and TiO2. The absorption spectra changed from those having the single peak at 775 nm to those with two peaks at 640 and 980 nm. Such spectral transformation was ascribed to the structural change of the WO3 nanoclusters, depending on the γ value and the concentration of Cl ion.  相似文献   

11.
A multilayer sol-gel process has been developed in order to make highly doped rare-earth planar waveguides on silica or silicon substrates.Starting with a small range of constituents, such as SiO2, TiO2, P2O5 and Al2O3, we show that a large variety of gel compositions, with different spectroscopic behaviour, can be made when doped with rare-earths.We have doped the sol-gel films with neodymium and we have optimized their compositions by measuring the neodymium fluorescence lifetime. For a composition with 10 atom% of phosphorous, the lifetime evolution with neodymium concentration was studied and a quenching concentration was found at 1% of neodymium. We have also shown the strong influence of phosphorous or aluminium in the sol composition on the fluorescence lifetime, for a given neodymium concentration. First results on similar planar waveguides, doped with erbium, are also presented.The stability of the fluorescence lifetime over a long period of time is an other important point to be checked for these new materials: the lifetime evolution over a 9 months measurement period is presented.  相似文献   

12.
Anatase TiO2 sols (RS) were synthesized by peptizing the hydrolysis of titanyl sulfate in abundant hydrogen peroxide solution and subsequent reflux to enhance crystallization. The influences of various reflux time on crystallinity, morphology, and size of the obtained TiO2 sol and dried TiO2 film particles were investigated. At room temperature, crystalline TiO2 thin film was deposited on glass silde from the as prepared TiO2 sol by dip-coating method. No further thermal posttreatment was required to eliminate organics from the film or to induce titania crystallization. TiO2 thin film on substrates could be thickened by means of consecutive dip-coating process. Titania film thus obtained was transparent and showed proper adherence. The photocatalytic activities of the TiO2 thin film was assessed by the degradation of methyl orange in aqueous solution. The preparation process of photocatalytic TiO2 thin film was quite simple and a low-temperature route.  相似文献   

13.
Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO3, TiO2/MoO3 or Mo-doped TiO2 have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO3.  相似文献   

14.
An original, halide-free non-hydrolytic sol–gel route to mesoporous anatase TiO2 with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non-hydrolytic and aprotic route to TiO2. Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO2 materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron-sized particles with high specific surface area (240 m2 g−1 before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non-calcined sample with the highest specific surface area favouring pseudo-capacitive storage: 253 mAh g−1 at 0.1 C and 218 mAh g−1 at 1 C (C=336 mA g−1). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g−1) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO2 nanomaterials.  相似文献   

15.
The sol-gel process, starting from tetraethylorthosilicate precursor, is a suitable technique for the preparation of silica thin films. The use of specific organic additives, like non ionic surface-active agents, drastically modifies the gelation process and allows the preparation of microporous materials with a high microporous volume. The effects of additives on the sol, gel and material characteristics have been investigated by several methods such as 29Si NMR, QELS, SAXS (for sols and gels), and N2 adsorption, FESEM (for fired materials). It appears that the interactions of surface active agents with TEOS derived species limit condensation reactions and particle growing. A brittle gel structure is generated which leads to highly porous microporous silica after the elimination of organic chains by thermal treatment at 450°C. The material porous texture (specific surface area, pore size distribution and porous volume) can be varied especially by varying the surface active agent chain length and quantity. This kind of sol-gel system is suitable to prepare microporous silica membranes candidate for gas separation or catalytic reactor applications.  相似文献   

16.
All solid state electrochromic devices have potential applications in architectural and automotive fields to regulate the transmission and reflection of radiant energy. We present the optical and electrochemical characteristics of two solid state windows having the configuration glass/ITO/TiO2-CeO2/TiO2/TiO2-CeO2/ITO/glass and glass/ITO/WO3/TiO2/TiO2-CeO2/ITO/glass where the three internal layers have been prepared by sol gel methods. The preparation of the individual sols and some physical properties of the different sol gel coatings are reported.  相似文献   

17.
Polyethylene (PE) composites with titanium oxide (TiO2) nanoparticles were produced via in situ polymerization representing a novel route to obtain antimicrobial polymeric materials. The TiO2 nanoparticles synthesized by the sol–gel method were used either as‐synthesized or modified organically with hexadecyltrimethoxysilane (Mod‐TiO2). These particles were added, together with the catalytic system (formed by a metallocenic catalyst and methylaluminoxane as cocatalyst), directly to the reactor, yielding in situ PE composites with 2 and 8 wt % content of nanofiller. The catalytic polymerization activity presented a slight decrease with the incorporation of the TiO2 and Mod‐TiO2 nanoparticles compared to polymerization without filler. Regarding the properties of the composites, crystallinity increased slightly when the different nanofillers were added, and the elastic modulus increased around 15% compared to neat PE. PE/TiO2 nanocomposites containing 8 wt % of TiO2 exposed to UVA irradiations presented antimicrobial activity against Escherichia coli. The PE/Mod‐TiO2 nanocomposite with 8 wt % filler killed 99.99% of E. coli, regardless of light and time irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   

18.
Stable sols of TiO2 were synthesized by a non-aqueous sol–gel process using titanium (IV) isopropoxide as precursor. The microstructure, optical and morphological properties of the films obtained by spin-coating from the sol, and annealed at different temperatures, were investigated using scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy and ellipsometry. The crystalline structure of the films was characterized by X-ray diffraction and their photocatalytic activity was evaluated for the oxidation of ethanol in air. The influence of the calcination temperature, pre-heat treatment and the number of layers was studied. Simultaneous thermo-gravimetric and differential thermal analysis measurements were carried out to ascertain the thermal decomposition behavior of the precursors. In order to obtain a higher photoresponse in the visible region, a series of vanadium-, niobium- and tantalum-doped TiO2 catalysts was synthesized by the same sol–gel method. For V doping two different precursors, a vanadium alkoxide and V2O5, were used. The effect on the crystallization and photocatalytic activity of the doped TiO2 films was investigated. Furthermore, to identify the effective composition of the samples, they were characterized by X-ray photoelectron spectroscopy and the surface area of the powders was measured by N2 adsorption. The 10 wt.% doped catalysts exhibit high photocatalytic activity under visible light and among them the best performance was obtained for the sample containing Ta as dopant. The crystallite sizes are closely related to the photocatalytic activity.  相似文献   

19.
《Comptes Rendus Chimie》2019,22(5):393-405
In this study, TiO2–ZnO nanostructured films prepared from different Ti/water mole ratios were deposited on glass plates by a sol–gel dip-coating method. The structural and surface properties, adherence, and photoactivity of synthesized TiO2–ZnO coatings in methylene blue degradation were investigated. Among the as-prepared TiO2–ZnO coatings from sols with different Ti/water mole ratios (1, 0.66, 0.5, and 0.4), the highest sol concentration (Ti/water mole ratio of 1) showed the highest methylene blue photodegradation of almost 80% after 400 min of UV irradiation. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray (EDX), and UV-vis diffuse reflectance spectra (DRS) confirmed that at high sol concentrations (Ti/water mole ratios of 1 and 0.66), a mixed phase of anatase and rutile is formed, whereas at a Ti/water mole ratio of 0.5, just pure rutile is formed. In detail, decreasing the sol concentration increases the cracks, degree of agglomeration, and the thickness of coatings. UV-vis DRS studies also confirm that decreasing the sol concentration in synthesized TiO2–ZnO films leads to a shift in the absorption region of the coating to the UV region. Moreover, decreasing the sol concentration declines the coating adherence onto glass plates. TEM images of the TiO2–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 revealed the formation of ZnO nanorods around a spherical TiO2, which indicates the presence of strong interaction between TiO2 and ZnO nanoparticles. The TiO2–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 was then evaluated at different methylene blue concentrations, pH values, and number of coatings. After five consecutive runs, no significant decrease in the photodegradation efficiency was observed. Scanning electron microscopy (SEM) picture of used coating showed a smooth and stable layer without any detachment. Thermogravimetric analysis (TG) and sonication test confirmed thermal and mechanical stabilities of this coating as well.  相似文献   

20.
Nanoparticulate TiO2/Rh3+ sols have been synthesized by the colloidal sol?Cgel route. The combination of the data measured with optical techniques such as laser diffraction, dynamic light scattering and multiple light scattering with a near-infrared light allows us to follow up the evolution of the peptization process and to establish the effect of the presence of Rh3+ on it. It is observed that the presence of rhodium ions retards the peptization step (t2) and decreases both the average particle size of the nanoparticles and the viscosity of the nanoparticulate sols. In addition, when Rh3+ is present the isoelectric point shifts up to higher pH, which suggests that chemical adsorption of the rhodium (III) cations onto the surface of the TiO2 nanoparticles is produced. The xerogels and cryogels obtained from the sols are constituted by anatase as major phase and traces of brookite. The phase transition is observed at lower temperatures for the xerogels containing rhodium (III) and at higher temperatures in the case of the cryogels. Finally, photocatalytic activity is higher in the case of the TiO2/Rh3+ sols due to the rhodium (III) effect on the electronic transitions from the valence band to the conduction band.  相似文献   

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