Sol-gel Impregnation Research Articles

Alteration of pore size distribution by sol–gel impregnation for dynamic range and sensitivity adjustment in Kelvin condensation-based humidity sensors

It has been theoretically established that the dynamic range of sensitivity in porous dielectric ceramic-based resistive or capacitive humidity sensors is mainly determined by the open pore size distribution in their sensing pallets. Here, we directly apply the concept on ceramic resistive humidity sensors and utilize the results for the experimental verification of the theoretical model. The open pore size distribution in a number of identical titanium dioxide pallets, fabricated by the sintering of the slip-cast powder at 1073K, is modified in two different directions: (a) impregnation with titanium tetraisopropoxide, followed by a heat treatment at 773K increases the proportion of the finer pores and (b) re-sintering the original pallets at 1223K closes the finer pores and substantially shifts the distribution towards larger pore dimensions. Sensitivity measurement results are consistent with the theoretically established concept: increasing the population of larger pores heightens the sensitivity to high relative humidity (RH) levels and shifts the dynamic range of the pallets from the original 20–85% to 50–95% RH. On the contrary, increasing the proportion of the finer pores in the microstructure of the ceramic pallet enhances the sensitivity at the lower RH range, shifting the dynamic range of the sensor to the 2–25% RH range.

Photocatalytic degradation of methyl tert-butyl ether (MTBE) by Fe-TiO2 nanoparticles

Nowadays, since the underground waters are known as the main source for supplying the drinking water, their pollution to the organic contaminants such as methyl tert-butyl ether (MTBE) is a very significant issue. Therefore, in this study, photocatalytic degradation of MTBE was investigated in the aqueous soloution of Fe-TiO2 nanoparticale under UV irradiation (wavelenght 254nm) in a batch reactor. The Fe-TiO2 mixed oxides were prepared by sol–gel impregnation method. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and BET specfic surface area. Then, the effect of various operational parameters namely pH, catalyst loading, molar ratio of [H2O2]0/[MTBE]0 and UV light intensity on degradation of aqueous MTBE were evaluated in a batch reactor. The optimal condition to achieve the best degradation for the initial concentration of 75ppm MTBE was found at pH 7, catalyst concentration 2g/L, molar ratio of [H2O2]0/[MTBE]0 4, and UV irradiation 24W. Total degradation of MTBE with initial concentration of 75ppm was reached in optimal condition after 70min. In addition, investigations were also carried out to determine the appropriate kinetics of MTBE degradation using UV/Fe-TiO2/H2O2 process in optimal condition.

Preparation of Ru/Ba-ZrO2Catalyst and Its Performance for Ammonia Synthesis

分别采用柠檬酸络合法、改性共沉淀法和湿浸渍法制备了掺Ba纳米ZrO2材料,负载Ru后用于催化氨合成反应.采用X射线衍射、CO2程序升温脱附（CO2-TPD）、N2物理低温吸附、H2程序升温还原技术（H2-TPR）、扫描电镜（SEM）、透射电镜（TEM）、X射线光电子能谱（XPS）和CO化学吸附对载体材料和催化剂进行了表征.结果表明,不同方法制备载体的物相结构和织构性能均有明显差别,负载Ru后催化剂的氨合成性能差别也较大.其中,以柠檬酸络合法制备的载体材料中Ba以BaZrO3的形式存在,钙钛矿型BaZrO3具有较强的供电子能力,电子可以通过Ru与载体间强相互作用传递到Ru表面,有效地促进N≡N的断裂,使催化剂的低温活性显著提高.在425℃,3 MPa,空速为10000 h-1条件下,出口氨浓度为5.72%.其氨合成活性分别是改性共沉淀法和湿浸渍法制备催化剂的3.8倍和14.3倍.

Biofunctionalization of porous titanium coatings through sol–gel impregnation with a bioactive glass–ceramic

In implant technology, open porous Ti coatings are applied as functional surface layers on prosthetic devices to improve osseointegration. Since a successful clinical performance strongly depends on the (initial) quality of bone ingrowth in the porous structure, surface functionalization of the porous Ti to incorporate an additional osteoconductive capacity is recommended. In this paper, a bioactive glass–ceramic coating is applied into the open porous network of Ti coatings with a pore throat size of 1–20μm through a sol–gel process. Using an all-alkoxide precursor route, homogeneous amorphous powders of three- (SiO2–CaO–P2O5) and four-component (SiO2–CaO–Na2O–P2O5) bioactive glass compositions are prepared. By sol impregnation followed by a heat treatment, it is possible to deposit a micrometer thin bioactive glass–ceramic layer on the walls of the internal pore surface, while the original porosity and the open pore structure of the Ti coatings are maintained. The tensile adhesion strength of the Ti/bioactive glass–ceramic composite coatings is 22 to 29MPa, suggesting a good mechanical adhesion.

Photocatalytic Degradation of p-Nitroaniline with Composite Photocatalyst H<sub>3</sub>P<sub>12</sub>W<sub>40</sub>/TiO <sub>2</sub>

The prepared composite photocatalyst H3PW12O40/TiO2 was synthesized by sol-gel impregnation method and characterized by scanning electron microscope(SEM), energy-dispersive X-ray spectroscopy(EDS), Fourier transform infrared(FT-IR), X-ray diffraction(XRD), UV-vis diffuse reflectance spectrum(DRS) to investigate its optical, physical and chemical properties. The results indicated that the modified catalyst was coated with P and W element, still have uniform anatase structure. Meanwhile, there is a chemical interaction exists between the Keggin unit and the surface of the titania matrix. Compared with original H4PW12O40 or TiO2 matrix, the adsorption threshold onset of the composite extended to the visible region. Effects of H3PW12O40/TiO2 dosage, pH value, initial p-NA concentration on the photocatalytic degradation of p-NA under 250W UV irradiation were investigated. The optimal H3PW12O40/TiO2 dosage and pH value for degradation of 10mg/L p-NA were o.6g/L and 3.0, respectively. The degradation rate of p-NA by H3PW12O40/TiO2 process could be fitted pseudo-first-order kinetics. Moreover, 66% degradation of p-NA was still observed in the 5th recycle experiment. Futhermore, 4-Aminophenol, Phenol, Hydroquinone, 4-Benzoquinone and other intermediate products were indentifieded by GC/MS and a possible reaction mechanism is proposed on the basis of all the information obtained from the analysis of FT-IR and the above intermediates.

Synthesis of TiO<sub>2</sub>/Al-MCM-41 Composites with Coal-Measure Kaolin and Performance in Its Photocatalysis

TiO2/Al-MCM-41 composites with various titania content were prepared by loading titania into the mesopores of Al-MCM-41 mesoporous molecular sieve from coal-measure kaolin as silicon and aluminum source via general sol-gel method and incipient wetness impregnation method. TiO2/Al-MCM-41 composites were characterized by XRD, FT-IR and SEM, and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the titania crystalline phase was anatase, and the particles size of TiO2 increase with TiO2 content. The photocatalytic degradation rates of all samples prepared by sol-gel method and incipient wetness impregnation have been become stable by visible light irradiation for 150 min, and the highest degradation rate was 83.7% and 76% respectively.

Photocatalytic oxidation of gaseous toluene on titania/mesoporous silica powders in a fluidized-bed reactor

The photocatalytic degradation of toluene was carried out on titania/mesoporous silica photocatalysts in a self-constructed gaseous fluidized-bed photoreactor equipped with UVA light source. The powder photocatalysts were synthesized by incorporation of aqueous titania sol (as a photoactive component), into silica mesoporous materials (as a high-surface-area support), via the sol–gel impregnation method. SBA-15 was used as an ordered and KIL-2 as a disordered mesoporous silica support. The Ti/Si nominal molar ratio was adjusted to 1/2, 1/1 and 2/1. The photocatalysts were characterized by X-ray diffraction (XRD), nitrogen sorption (BET), UV–vis–NIR diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM). The effects of Ti/Si molar ratio and of the mesoporous silica structure were investigated measuring adsorption capacity and photocatalytic degradation of toluene. The rates of photocatalytic degradation reactions were found to be similar for photocatalysts with the same Ti/Si molar ratio independently of the mesoporous structure of silica. The adsorption capacity was decreasing as a function of the increasing Ti/Si molar ratio in the case of both types of mesoporous silica support. However, the photocatalytic degradation proceeded faster for the Ti/Si molar ratio 1/1 while, in the case of the other investigated Ti/Si molar ratios 1/2 and 2/1, the degradation rates were lower. In general, the photocatalytic activity was considerably improved by using supported titania–silica catalyst compared to an unsupported titania powder prepared from the same nanocrystalline titania sol.

Titania-containing mesoporous silica powders: Structural properties and photocatalytic activity towards isopropanol degradation

Ordered (SBA-15) and disordered (KIL-2) mesoporous silica supports have been synthesized and used for incorporation of titania with different Ti/Si molar ratios (1/2, 1/1, 2/1) via sol–gel impregnation method. Titanium isopropoxide and aqueous titania sol prepared by low-temperature sol–gel processing were used as a source of titania. Characterization by powder X-ray diffraction (XRD), nitrogen sorption measurements, scanning electron microscopy (SEM) and UV–vis–NIR diffuse reflectance spectroscopy (DRS) has been carried out to investigate the chemical framework and morphology of powders. The photocatalytic degradation of isopropanol in the gaseous medium was selected as a probe reaction to test the photoactivity of powders and to verify the potential application of these materials for air remediation. It was found that the titania source, Ti/Si molar ratio and the type of silica support influenced the functional properties of the material, which were evaluated by adsorption capacity and photocatalytic activity in the gas–solid reactor. The adsorption capacity of isopropanol was the highest in the presence of the SBA-15-supported materials. The photoactivity results indicated that the powders which were prepared using SBA-15 as a silica support and a Ti/Si molar ratio of 1/1 were the most active towards isopropanol oxidation monitored in situ by FT-IR spectroscopy.

Preferential oxidation of CO in H2-rich stream over CuO/Ce1−xTixO2 catalysts

CuO/Ce1−xTixO2 prepared by sol–gel impregnation was used as catalysts for the preferential oxidation (PROX) of CO in H2-rich stream. The effects of support composition, catalyst calcination temperature as well as the presence of H2O and CO2 in the reaction stream on the catalytic performance of CuO/Ce1−xTixO2 were investigated. The results indicated that the catalyst CuO/Ce0.8Ti0.2O2 exhibits the highest activity and the optimal temperature for the catalyst calcination is 500°C. The presence of H2O and CO2 in the reaction stream has a negative effect on the catalytic activity and stability of CuO/Ce0.8Ti0.2O2. The negative effect of CO2 on the catalyst stability is stronger than that of H2O, suggesting that the accumulation of carbonate species may be the main reason for catalyst deactivation. The characterization by means of XRD, HRTEM, and H2-TPR indicated that the doping of TiO2 in CeO2 enhances the surface area of the composite oxide support, decreases its particle size, and promotes the dispersion of active copper species. The strong interaction between TiO2 and CeO2 in the support as well as the interfacial interaction between CuO and the support may also contribute to the high catalytic activity of CuO/Ce0.8Ti0.2O2.

Effects of I and F codoped TiO 2 on the photocatalytic degradation of methylene blue

Nanocrystalline I–F-codoped TiO 2 was prepared by a sol–gel-impregnation method, using tetrabutylorthotitanate in a mixed NH 4I–NH 4F aqueous solution. The as-prepared TiO 2 was characterized with UV–vis diffuse reflectance spectra, X-ray diffraction and nitrogen adsorption. The degradation of methylene blue (MB) over as-prepared TiO 2 in aqueous solution under simulated sunlight irradiation was remarkably enhanced by codoping with I and F. The effects of codoping and calcination temperature on the photocatalytic activity and microstructures were investigated. The photocatalytic activity of as-prepared I–F-codoped TiO 2 was remarkably higher than that of pure, I-doped, and F-doped TiO 2 when the molar ratios of I and F to Ti were kept in the value of 10. The influence of I–F-modification on the photocatalytic activity was discussed by considering the higher surface area, entire anatase phase, effective dopant content, and stronger absorbance of sunlight, corresponding to the higher quantum efficiency. In addition to a complete removal of color, the as-prepared TiO 2 was simultaneously able to oxidize MB and small amounts of intermediates such as formic acid and phenol were detected. After prolonged sunlight irradiation some intermediates almost vanished, and MB appeared to be eventually mineralized to NH 4 +, NO 3 − and SO 4 2−.

The Role of Catalyst Properties on Methanol Oxidation over V2O5–TiO2 Using Ozone

Oxidation of methanol over V2O5 catalysts supported on anatase TiO2 that were prepared using sol-gel formation and impregnation procedures were investigated. The effects of incorporating Mg in sol-gel to influence the properties of the catalyst were also studied. The process provides an alternative low temperature reaction pathway for reducing emissions of hazardous air pollutant (HAPs) such as methanol and total reduced sulfur compounds (TRS) from pulp and paper mills. The bulk and surface composition of the catalysts were determined by XRD and SEM-EDAX, respectively. The X-ray diffraction patterns of the vanadia–titania catalysts showed mainly the anatase phase of TiO2. Temperature programmed desorption of methanol from the different catalyst showed that the α and β peaks differ significantly with V content and addition of Mg. The combination of gas phase and surface reactions on the V/TiO2 catalysts reduced the amount of ozone required for high degradation of methanol to mainly COx with small quantities of methyl formate. In the absence of ozone the catalysts showed very low activity. It is hypothesized that the ozone is directly influencing the V4+ and V5+ redox cycle of the catalyst. Oxidation of methanol is influenced by the operation variables and catalyst properties. The results of this study revealed that the V content has significant influence on the catalyst activity, and the optimum vanadia loading of about 6 wt%. Higher turnover frequencies were observed over sol-gel catalysts than with catalysts prepared by the impregnation method.

EXAFS study and photocatalytic properties of un-doped and iron-doped ZrO 2-TiO 2 (photo-) catalysts

The local zirconium and iron arrangements of the iron-doped ZrO 2-TiO 2 system, prepared by sol–gel impregnation method, were studied by EXAFS spectroscopy. Only a tetragonal ZrO 2 structure is located on TiO 2 surface. For the iron-doped ZrO 2-TiO 2 system, the presence of the Fe-O-Fe species as well as and Fe-O-Zr species located on the surface/pre-surface region are shown; it seems that iron is heterogeneously distributed, forming small iron oxide nanoclusters and Fe x /ZrO 2 (tetragonal) spots at the catalyst surface. The photocatalytic activity of the un-doped and iron-doped binary system ZrO 2-TiO 2 was investigated in two kind of photoreactions: the salicylic acid photooxidation and the photocatalytic reduction of Cr(VI). Different photocatalytic behaviour has been found for the un-doped and iron-doped ZrO 2-TiO 2 systems which have been explained in terms of the EXAFS study. This study represents an example of attempt to prepare a new potential photoactive mixed oxide system, containing two ions (Ti 4+ and Zr 4+) with good photocatalytic activity if it is compared with commercial TiO 2 (Degusssa P25) calcined at 600 °C.

Electrochemical Testing of Solid Oxide Fuel Cells with Sol Gel Impregnated Plasma Sprayed Electrolytes

Solid Oxide Fuel Cells (SOFCs) have been fabricated on tape cast anode substrates with plasma sprayed (PS) electrolytes and screen printed cathodes. To reduce the porosity in the PS electrolyte layers, spin coating was used to impregnate the as-sprayed electrolytes with yttria stabilized zirconia (YSZ) sols and YSZ composite sol powder suspensions. Fuel cells with electrolytes impregnated with different techniques were electrochemically tested and compared to fuel cells with no sol gel coatings to correlate the sol gel processing parameters with the resulting electrochemical performance changes. The sol gel impregnation significantly increased the open circuit voltage, slightly decreased the series resistance, and substantially decreased the polarization resistance compared to the cells with as-sprayed electrolytes. Impregnation of electrolytes offers the possibility of producing thinner electrolytes in simpler low-energy plasmas (100% nitrogen, no hydrogen) while lowering gas permeability through the electrolyte and improving fuel cell performance.

Effect of the hybrid catalysts preparation method upon direct synthesis of dimethyl ether from synthesis gas

Direct synthesis of DME from synthesis gas attains more attention recently due to higher conversion and lower cost in comparison to dehydration of the methanol. In this work Synthesis gas To Dimethylether (STD) conversion was examined on various hybrid catalysts prepared by seven different methods. These catalysts had the same general form as CuO/ZnO/Al2O3 with theoretical weight ratio 31/16/53, respectively. A novel preparation method for hybrid catalyst namely sol–gel impregnation has also been developed which showed better performance in comparison with the other methods. Also, in order to find out the effect of various alumina contents at a fixed CuO/ZnO ratio on the performance of the hybrid catalyst, a series of catalysts with different contents of alumina have been prepared by sol–gel impregnation method. The optimum weight ratio for CuO/ZnO/Al2O3 catalyst has been found to be about 2:1:5, respectively. These catalysts characterized by TPR, XRD, XRF, BET, TGA, N2O absorption. The catalysts performance were tested at 240°C, 40bar and space velocity 1000ml/gcat.h, with the inlet gas composition H2/CO/N2=64/32/4 in a micro slurry reactor.

Characterization of Modified Thick Thermal Barrier Coatings

In gas turbines and diesel engines, there is a demand for thick thermal barrier coatings (TTBCs) due to the increased process combustion temperatures. Unfortunately, the increased thickness of plasma-sprayed thermal barrier coatings (TBCs) normally leads to a reduced coating lifetime. For that reason, the coating structures have to be modified. When modifying the structure of TTBCs, the focus is normally on elastic modulus reduction of the thick coating to improve the coating strain tolerance. On the other hand, coating structural modification procedures, such as sealing treatments, can be performed when increased hot-corrosion resistance or better mechanical properties are needed. In this article, several modified zirconia-based TTBC structures with specific microstructural properties are discussed. Coating surface sealing procedures such as phosphate sealing, laser glazing, and sol-gel impregnation were studied as potential methods for increasing the hot-corrosion and erosion resistance of TTBCs. Some microstructural modifications also were made by introducing segmentation cracks into the coating structures by laser glazing and by using special spraying parameters. These last two methods were studied to increase the strain tolerance of TTBCs. The coating microstructures were characterized by optical microscopy, a scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The effect of sealing procedures on the basic thermal and mechanical properties of the coatings was studied. In addition, some correlations between the coating properties and microstructures are also presented, and the advantages and drawbacks of each modification procedure are discussed.

Photocatalytic degradation of o-cresol sensitized by iron–titania binary photocatalysts

The degradation of ortho-cresol ( o-cresol) assisted by Fe/TiO 2 photocatalysts was investigated in oxygenated aqueous suspension in a spiral glass flow reactor. Iron–titania (1–10 wt.% Fe) mixed catalysts have been prepared by sol–gel impregnation method using metal alkoxide precursors. The surface structure of Fe/TiO 2 catalyst was studied by surface analysis with XPS and TEM techniques. Characterization of these catalysts, fired at different temperatures (in the range 500–900°C) using X-ray diffraction (XRD) showed that the sintering temperature and incorporation of iron ions mediate the phase transformation and growth of pseudobrookite (Fe 2TiO 5) phase at higher temperatures. The rate of degradation of o-cresol decreases with the increasing sintering temperature and iron content of the catalysts and the initial pH of the aqueous solution of o-cresol changes with the illumination time due to the formation of various acidic intermediate photoproducts.

Highly hydrogen selective ceramic membranes: application to the transformation of greenhouse gases

This paper reports the preparation of modified Vycor glass membranes by several methods: polymerization, dip coating, sol–gel impregnation, and chemical vapor deposition (CVD). It was found that a membrane (here called Nanosil) formed by the high-temperature CVD of tetraethylorthosilicate (TEOS) in inert gas exhibited hydrogen selectivities of 100% with respect to CH 4, CO, CO 2 and H 2O. The transport of hydrogen was not through Knudsen diffusion, but was activated, and probably involved atomic hydrogen species. The membrane was also stable to hydrothermal stresses (10% H 2O at 873 K and 1 bar) for over 150 h of operation. The membrane was employed in a catalytic reactor for the dry reforming of methane, CH 4+CO 2⇌2CO+2H 2, using a 1% Rh/Al 2O 3 catalyst. As a result of simultaneous reaction and separation, conversions were higher than those obtained in a packed-bed reactor operated at the same conditions, and exceeded equilibrium levels.

Preparation and characterization of TiO 2/Fe 2O 3 binary mixed oxides and its photocatalytic properties

Binary mixed oxide of Fe/Ti (1 : 1 composition) with homogeneous distribution of iron into the TiO 2 has been prepared by sol–gel impregnation using metal alkoxide precursors. The structural features of Fe/Ti mixed oxide fired at different temperatures (500, 700 and 900°C) have been investigated by XRD, Mössbauer effect, FTIR, SEM, and TEM studies. Phase composition and crystallinity changes with increasing sintering temperature of the specimens. The mixed oxide exhibits excellence absorption (570–600 nm) in the visible spectral region. Photocatalytic activity of Fe/Ti oxide reduces to large extent at high sintering temperature of the sample due to the presence of increasing amount of inactive (Fe 2TiO 5) pseudobrookite phase. The sample sintered at 500°C shows highest activity for the degradation of aqueous solution of O-Cresol.

Differentiation between the Green and Turkish Blue Solid Solutions of Vanadium in a Zircon Lattice Obtained by the Sol-Gel Process

In this communication, zircon containing vanadium samples which gradually turn greenish have been prepared by controlling the composition (fluoride addition) and the method of preparation (sol-gel, ceramic and solid impregnation) in order to investigate how to affect the shape and size of the vanadium particles, and their location, clustering and distribution. The level of green color, and consequently the amount of V5+ in the sample, could be associated with the development of an Si-O-Si network in the zircon lattice, bonding with the highly reactive zirconium precursors.

Preparation of Layer Structure-Controlled Ru-Sn-Al2O3 Catalysts and Their Reactivity

In order to achieve functional group selective hydrogenation, the layer structure of Ru-Sn-Al2O3 catalysts was controlled by using sol-gel, powder impregnation and combined sol-gel impregnation methods. The properties of the catalysts and effectiveness in hydrogenation of dimethyl terephthalate were examined. The surface Sn contents of the catalysts characterized by X-ray photoelectron spectroscopy depended on the preparation method, in spite of almost the same bulk Ru and Sn compositions measured by X-ray fluorescence analyses. TPR and CO adsorption of the catalysts also depended on the preparation method. With regard to the conversion rate of dimethyl terephthalate and the rate of product conversion from methyl 4-hydroxy methylbenzoate to p-xylene via methyl p-toluate, Ru impregnation catalysts had higher rates than the other catalysts.