Non-hydrolytic Sol Gel Route Research Articles

Close Packing Existence of Short-Chain Ionic Liquid Confined in the Nanopore of Silica Ionogel

We used small/wide-angle X-ray scattering and nitrogen gas sorption to explore the structural confinement effects of confining hydrophobic ionic liquid (IL), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), in the hydrophilic nanopores of silica ionogels. A nonhydrolytic sol–gel route with tetraethyl orthosilicate (TEOS) as precursor and formic acid solvolysis was adopted to prepare the studied silica ionogels. The results revealed that all these ionogels had fractal silica frameworks, but three distinct nanopores (H2-type nanopores with various radiuses, H3-type board slit-shaped capillary nanopores, and H4-type narrow slit-like nanopores) would be respectively formed with increasing nIL/nTEOS molar ratios. Moreover, neat [C6mim][PF6] formed self-organized nanoscale segregation in the bulk. However, when [C6mim][PF6] was confined within nanopores, narrow H2 and H4 nanopores would destroy this nanoscale segregation; inversely, confined [C6mim][PF6] further formed a more close packing in the...

Study on the Preparation of BaTiO<sub>3</sub> Nano Powder via Non-Hydrolytic Sol-Gel Method

BaTiO3 (BT) nano powder was prepared via non-hydrolytic sol-gel (NHSG) method by using barium acetate, titanium tetrabutoxide as precursors, glycerol and ethanol as solvents. The samples were characterized by DTA-TG, XRD, FT-IR and TEM. The influences of heat treatment temperature on the morphology and the microstructure of powder were studied, and the mechanism of low temperature synthesis was discussed. In addition, the de-esterification action between the precursors was also described in detail. The results show that the formation of Ba-O-Ti bond in the xerogel via NHSG route is duo to the de-esterification polycondensation of barium acetate and titanium tetrabutoxide, which plays the key role in the low temperature synthesis of BT powder. With the temperature rising to 700 °C, BT nano powder with good dispersion and even size distribution can be acquired and the average particle diameter is about 25 nm. Overlow and overhigh heat treatment temperatures are both not beneficial to the preparation of BT nano powder.

WO3-based catalysts prepared by non-hydrolytic sol-gel for the production of propene by cross-metathesis of ethene and 2-butene

One-step non-hydrolytic sol-gel (NHSG) route is presented as a powerful method to prepare highly effective alkene metathesis catalysts. Tungsten-based catalysts are the industrially relevant system and are prepared for the first time using NHSG. The catalysts were characterized by N2-physisorption, XRD, NH3-TPD, NH3-chemisorption, XPS, TPR, ICP-AES and evaluated in the cross-metathesis of ethene and trans-2-butene to propene. These new catalysts are systematically compared with reference catalysts prepared by impregnation methods on 2 commercial supports (silica and silica-alumina). NHSG catalysts markedly outcompete reference impregnated catalysts in terms of conversion, selectivity and stability. Characterization results show that the texture, tungsten dispersion, reducibility and surface acidity of the NHSG catalysts depend strongly on their composition. This in turn can be correlated with the catalytic performance.

Formation and Characterization of TiO<sub>2</sub> Scattering Layer Deposited by Spray Pyrolysis for DSSC

In this paper the TiO2 nanoparticle for scattering layers were prepared using hydrolytic and non-hydrolytic sol gel route. The TiO2 nanoparticles by hydrolytic sol gel were prepare by adding 5 ml of titanium (IV) isopropanol (TTIP) with 15 ml isopropanol. Then this TTIP mixture was added dropwise into 250 ml water with adjusted pH to 3 using nitric acids. For non-hydrolytic sol gel route 12 gram of acetylacetone, 12 gram of TTIP and 16 gram of ethanol anhydrous were mixed in a beaker under vigorous stirring. Then the prepared TiO2 nanoparticles solutions were deposited onto TiO2 mesoporous layer via spray pyrolysis and assemble into complete solar cell. From the XRD (X-ray diffraction) results show that the phase of TiO2 nanoparticles formed by hydrolytic sol gel route was amorphous and for non-hydrolytic route the phase formed was mixture of anatase and rutile. The efficiency of the solar cell shows that scattering layer prepare by hydrolytic route give higher efficiency, 6.0 x 10-5 %, as compare to scattering layer prepare by non-hydrolytic route, 4.9 x 10-5 %.

Ionic liquid template assisted synthesis of porous nano-silica nails

Our planned strategy to obtain porous materials was to synthesize porous silica at a fast gelation rate which can be attained by using non-hydrolytic sol–gel route with high ionic liquid (IL)-loading.

Synthesis and photoluminescent properties of yttrium vanadate phosphor prepared by the non-hydrolytic sol–gel process

We used the non-hydrolytic sol–gel route to synthesize YVO4 crystalline phases doped with europium III ion. We heat-treated the samples at 600, 800, and 1000°C and characterized the materials by thermal analysis, X-ray diffraction, small-angle X-ray scattering, and photoluminescence. Larger weight loss occurred until 500°C, ascribed to removal of residual precursor molecules. X-ray diffraction patterns evidenced YVO4 phase formation at 600°C. The crystallite size depended on the heat treatment temperature. SAXS showed that the nature of the system interfaces changed as a function of the thermal treatment. The excitation spectra of the samples displayed the charge transfer band. The photoluminescence data revealed the characteristic transition bands arising from the 5D0→5FJ (J=0, 1, 2, 3, and 4) manifolds under maximum excitation at the charge transfer band and the 5L6 level of the Eu3+ ion. The 5D0→7F2 transition dominated the emission spectra, indicating that the Eu3+ ion occupies a site without inversion center. The lifetime and quantum efficiency values were about 0.70ms and 50%, respectively, corroborating literature results.

EPDM rubber reinforced with titania generated by nonhydrolytic sol-gel process

EPDM rubber was reinforced with titania in situ generated by using a nonhydrolytic sol-gel (NHSG) process starting from TiCl4 as titania precursor and tert-butanol as oxygen donor. Titania particles in anatase form and with average diameter of 6 nm were synthesized via NHSG route and then the same procedure was adopted in presence of EPDM rubber to obtain composites containing up to 30 wt% of filler. Extraction and equilibrium swelling tests suggested an interfering effect of the NHSG reaction on the vulcanization process of the rubber resulting to a crosslink density which decreased in the presence of titania. Quasi-static and dynamic-mechanical characterizations indicated that the presence of titania as rigid filler in both the unvulcanized and vulcanized EPDM matrix led to a significant increase in stiffness and stress at break. The experimental values of modulus were systematically higher than the values predicted by classical equations suggesting an additional stiffening contribution deriving from the molecular interaction between the rubber and the filler. POLYM. ENG. SCI., 54:2544–2552, 2014. © 2013 Society of Plastics Engineers

Aluminate matrix doped with Tm3+/Tb3+/Eu3+ obtained by non-hydrolytic sol–gel route: White light emission

RGB represents the union of the colors red (R), green (G), and blue (B), the colors that are most often used in electronic displays. Several kinds of host can serve as phosphors, but the appropriate amount of dopant in tricolor white light with excitation at the same wavelength remains an issue. We used yttrium aluminum garnet (YAG) as host for the lanthanides europium, terbium, and thulium. We prepared the YAG host by the non-hydrolytic sol–gel methodology and doped it with the same amount of lanthanide ions − 1% in relation to the amount of yttrium. We have already reported the characterization of this sample previously. Here, we aimed to investigate the emission spectrum of the sample in the red, green, and blue regions when excited at a certain wavelength. The x and y coordination chromaticity − x=0.32 and y=0.35 − presented values close to those of the white color (x=y=0.33). In conclusion, the YAG host doped with lanthanides and prepared by the sol–gel methodology will help prepare efficient phosphors for several applications.

Olefin metathesis with mesoporous rhenium–silicium–aluminum mixed oxides obtained via a one-step non-hydrolytic sol–gel route

Mesoporous Re–Si–Al, Re–Al, and Re–Si mixed oxides were obtained via a one-step non-hydrolytic sol–gel route followed by calcination. The texture and surface properties of the resulting catalysts were characterized by a combination of EDX, XRD, N2-physisorption, XPS, ToF-SIMS, and NH3-TPD. The loss of rhenium during calcination, the texture and the acidity of the catalysts depended on their composition. Migration of rhenium toward the surface occurred during the calcination treatment, as evidenced by XPS and ToF-SIMS. After calcination, ToF-SIMS showed the presence of well-dispersed ReOx surface species. The influence of the composition of Re–Si–Al catalysts on their performances in the cross-metathesis of ethene and butene to propene was investigated. The specific activity of the Re–Si–Al catalysts was much higher than that of Re–Al catalysts, whereas the Re–Si sample was not active. The best Re–Si–Al catalysts displayed excellent specific activities (up to 45mmolg−1h−1) and apparent TOF values (98×10−3s−1).

Direct production of ultra-high molecular weight polyethylene with oriented crystalline microstructures

Titanocene (Cp2TiCl2) was immobilized by entrapping within a silica matrix using a non-hydrolytic sol–gel route. The catalyst was evaluated in ethylene polymerization under different experimental conditions. The catalyst was able to produce fibers of ultra-high molecular weight (UHMWPE) directly from the polymerization process. The polymer showed a well-organized and dense microstructure with evidence of extended-chain crystal formation. This resulting microstructure improved some mechanical properties in comparison with a commercial UHMWPE.

Dual-target sensors: the effect of the encapsulation route on pH measurements and ammonia monitoring

Six different sensors were prepared using hydrolytic and non-hydrolytic sol–gel routes and three different pH indicators as receptor elements. These materials were employed as dual-target sensors for ammonia gas sensing and pH measurements in real samples. Ultraviolet–visible diffuse reflectance spectroscopy and a colorimetric analysis were used to evaluate the pH transitions and the color change that resulted from the ammonia that was employed as a probe for gas sensing. The colorimetric analysis was performed using the CIELAB color space model with the D65 standard illuminant. The resulting $$ \Updelta {\text{E}}_{\text{ab}}^{*} $$ values correlated with the response time for the observation of the first visible color change detected by the human eye (N = 50), and the average time values ranged from 48 to 117 s. In addition, the response times were evaluated as a function of sample characteristics, namely, the gender, age and eye color. Only groups of these characteristics exhibited relevance to the response time and could be associated with a specific range of time. The sensors were also employed for pH measurements of an aqueous solution, and a double-color scale could be established both with the sensors synthesized by the acid route and with the pH indicators alizarin red and brilliant yellow. From this color scale, it was possible to identify a shift in the turning point of the pH indicator from the free molecule to the encapsulated molecule. The double-color scale was applied to evaluate real samples from a galvanic industry using the synthesized encapsulated sensors.

ChemInform Abstract: Nonhydrolytic Sol—Gel Routes to Heterogeneous Catalysts

AbstractReview: 251 refs.

Prepartion of Stabilized Aluminum Titanate Film via Nonhydrolytic Sol-Gel Route

The stabilized aluminum titanate (Al2TiO5) film was coated on the silicon carbide (SiC) substrate via nonhydrolytic sol-gel method (NHSG), using anhydrous aluminum chloride and titanium tetrachloride as precursors, ethanol as oxygen donor, different iron sources as stabilizers, and dimethyl mixed dibasic acid (DBE) with the characteristic of environmental protection and high boiling point as solvent. The phase transformation of modified Al2TiO5 xerogel during heat treatment, the effect of different iron stabilizers on the stabilization of Al2TiO5 film, and the influence of the coating process parameters on film-forming quality were investigated by means of DTA/TG, XRD and SEM. The results indicate that ethanol iron as the stabilizer, Al2TiO5 crystal phase can be formed at 750°C. While the temperature is raised further to 1000°C, Al2TiO5 is stable without decomposition, and has better synthesis effect. Selecting iron chloride, iron sulfate and iron ethanol as stabilizers respectively, only iron ethanol is effective to thermal stability of Al2TiO5 film. The best optimal vertical sliding velocity is 3.75 mm/s.

Effects of Solvents on Synthesis and Dispersion of Zircon Powder via Non-Hydrolytic Sol-Gel Route

Zircon nano–powder has been synthesized via the non-hydrolytic sol–gel route, using industral zirconium tetrachloride (ZrCl4) and tetraethoxysilane (TEOS) as precursors, lithium fluoride (LiF) as mineralizer, PEG1000 as dispersant. The effects of solvents on the synthesis and dispersion of zircon nano-powder were investigated by means of XRD and TEM. The results indicate that the aprotic solvent N, N-dimethyl formamide (DMF) is not conducive to the nucleophilic substitution reaction, which directly affect the zircon synthesis, and the particles are easy to agglomerate due to the large surface tension; the powder with size of 30nm and good dispersion can be obtained using dichloromethane (CH2Cl2) as solvent; different anhydrous alcohols as solvents influence zircon synthesis, the order of the synthesis ratio is listed as EtOH›propanol (PrOH)› isopropanol (PriOH). Powder particles are larger than 50nm with wide distribution and serious agglomeration when taking PrOH and PriOH as solvents. Nano-zircon with good dispersion and synthesis ratio up to 94.5% can be obtained via using ethanol as solvent.

Study of the annealing temperature effect on the structural and luminescent properties of SrWO4:Eu phosphors prepared by a non-hydrolytic sol–gel process

In this paper, we investigate the influence of temperature on the structural and luminescent properties of Eu3+-doped strontium tungstate oxide (SrWO4) prepared by the non-hydrolytic sol–gel route. X-ray diffraction (XRD) analyses showed that the SrWO4:Eu scheelite type structure was formed in a unique phase at 900 and 1000°C over 2h. Raman spectra indicated only one type of [WO4] tetrahedron. The optical properties were investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements at room and liquid N2 temperatures. PL study showed 5D0→7F2 electric dipole transition is dominant when Eu3+ occupies a non-centrosymmetric environment. The (FEG-SEM) images indicated that an increase in the annealing temperature contributed to the coalescence process which promoted the growth of aggregated particles of a polydisperse nature. A qualitative analysis of the powders obtained by dispersive X-ray detector (EDS) indicated that the samples are composed of Sr, W and O while Eu3+ ion was not observed due to it low concentration.

Non-hydrolytic sol–gel routes to heterogeneous catalysts

Oxides and mixed oxides have a tremendous importance in the field of heterogeneous catalysis, serving either as catalysts or as supports for active species. The performance of a catalyst depends directly on its composition, texture, structure and surface properties, which have to be precisely controlled and adapted to each application. In this context, the sol-gel process is a unique tool for the preparation and understanding of catalytic materials, owing to its exceptional versatility. In the last 10 years, the non-hydrolytic sol-gel (NHSG) or non-aqueous sol-gel process based on nonhydrolytic condensations in nonaqueous media has established itself as a simple and powerful method for the design of a wide range of oxide, mixed oxide and hybrid materials with controlled composition, morphology, texture and structure. NHSG proved particularly interesting for the preparation of catalytic materials, notably mesoporous xerogels, single site catalysts and highly crystalline nanoparticles. This critical review addresses the application of NHSG to the preparation of heterogeneous catalysts, emphasizing the specificities of this process, and giving a comprehensive overview of the literature (251 references).

Fractal mesoporosity and proton transport in WO3 xerogels

Mesoporous WO3 xerogels with mixed proton–electron conductance were prepared by a non-hydrolytic sol–gel route based on alcoholysis of WCl6 solutions. By varying the alkyl-chain length and carbocation stability of the alcohol reagent, oxides with a widely varying mesoporous structure were obtained. These materials were systematically analysed in terms of their surface fractal dimension as derived from nitrogen-adsorption isotherms according to the Frenkel–Halsey–Hill equation. The fractal dimension is shown to be a key parameter in controlling and tailoring the mesoporous properties of these xerogels: specific surface area (56–184 m2 g−1), pore volume (0.06–0.35 cm3 g−1) and average pore diameter (3.2–8.6 nm). Resistance of the mesoporous structure to thermal conditions was also found to be correlated with the fractal dimension. Using electrical-impedance spectroscopy, d.c. proton conductivities as high as 4.7 × 10−2 S cm−1 were measured at 25 °C and 100% relative humidity. Proton-dynamics relaxation times and Cole–Cole exponents, as determined by fitting impedance data to a proper model circuit, are shown to be related to the fractal dimension. Importantly, a sharp transition from a fast- to a slow-transport regime was observed as this parameter increases beyond a critical threshold. It is discussed how the fractal dimension is crucial to understand proton transport as it relates to the porous structure.

A non-hydrolytic sol–gel route to highly active MoO3–SiO2–Al2O3 metathesis catalysts

MoO3-based materials are known to be appropriate catalysts for the heterogeneous metathesis of light olefins. Classical preparation methods involve the deposition of a Mo oxide phase on the surface of preformed support via impregnation, grafting or thermal spreading. An alternative sol–gel approach for the elaboration of Mo-based catalysts is presented in this article. Mesoporous ternary Si–Al–Mo mixed oxides are prepared in one step, via non-hydrolytic condensation of chloride precursors in non-aqueous media. After calcination, effective catalysts with very good textures and highly dispersed surface molybdenum species are obtained. The Si/Al ratio influences both the texture and the acidity of the materials, which significantly affects the propene self-metathesis activity. The activity also increases with the MoO3 content. The best catalysts with optimized composition significantly outperform the catalysts prepared by other methods.

Synthesis of ZrTiO<sub>4</sub> and MgAl<sub>2</sub>O<sub>4</sub> Powders via Non-Hydrolytic Sol-Gel Route Using Alcohol as Oxygen Donor

Zirconium titanate and magnesium aluminate spinel precursors were prepared by non-hydrolytic sol-gel method using ethanol as oxygen donor. The gels and calcined powders were investigated by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD). The results show that the ZrTiO4 and MgAl2O4 crystallized at low temperature of 550 °C and 700 °C, respectively. It indicated that the highly homogeneous zirconium titanate and magnesium aluminate gels were aslo obtained by nonhydrolytic sol-gel process using ethanol as oxygen donor. The particle size distribution measured by laser scattering exhibit that ZrTiO4 and MgAl2O4 powders were large soft agglomerates which could be broken through milling process.

Synthesis and luminescent properties of gadolinium aluminates phosphors

In this work, aluminum–gadolinium oxides with different phases were prepared by the non-hydrolytic sol–gel route, using lower temperatures than those employed in methods such as solid-state reaction and Pechini method. The influence of heating treatment on sample structure was investigated. The formation process and the local structure of the samples are discussed on the basis of thermal, X-ray diffraction, photoluminescence (PL) spectroscopy, and infrared spectroscopy analyses. The quantum efficiency of Eu3+ in the different phases obtained in this studied was evaluated. Initial crystallization and the GdAlO3 phase were observed at temperatures around 400°C. PL data of all the samples revealed the characteristic transition bands arising from the 5D0→5FJ (J=0, 1, 2, 3, and 4) manifolds under maximum excitation at 275, 393, and 467nm in all cases. The 5D0→7F2 transition often dominates the emission spectra, indicating that the Eu3+ ion occupies a site without inversion center.