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In the present work, we report the effect of the addition of platinum (Pt loading 1 wt%) on photocatalysts based on TiO2 and its incorporation in a SiO2 matrix using the sol gel method. The photocatalyst/silica matrix ratio was w(TiO2)/w(SiO2) of 15/85. The characterization of the samples was carried out with X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), specific surface area by N2 physisorption (BET) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The photoactivity of the samples was evaluated in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The production of hydroxyl radicals (•OH) on the surface of the samples irradiated with UV light was detected by the fluorescence technique using terephthalic acid as a test molecule. The resulting supported catalyst showed enhanced photocatalytic activity towards 2,4-D degradation, almost 97% of the 2, 4-D was degraded with Pt/TiM–Si sample in 180 min compared to pure commercial TiO2 P25 under UV radiation. The increase in photoactivity can be attributed to the extended band gap energy, large surface area, and a better charge separation and more efficient transfer of the photogenerated charges (e−–h+) due to the presence of Pt ions on the surface of the photocatalyst. Finally, stability and reusability test of the samples was estimated using recycling experiments, indicating its remarkable efficiency in contaminated water treatment. more...

Hybrid Ag/CeO2/SBA-15 mesoporous nanocatalysts were prepared and their bactericidal activity was evaluated aiming at elimination of Escherichia coli (E. coli) in the potable water system. It was found that there existed electrons transferring from Ag0 to CeO2 to form Ag+/Ag0 and Ce4+/Ce3+ couples in the heterojunction structure, which resulted from strong interaction between Ag nanoparticles (AgNPs) and highly dispersed CeO2. By increasing the Ag content from 1wt% to 3 and 5 wt% in the catalysts, the bactericidal power of Ag/CeO2/SBA-15 materials significantly enhanced in the presence of both visible and UV light, which can be explained by the increasing electrons transferring function from Ag0 to CeO2 under UV-visible light irradiation. A combination mechanism of E. coli deactivation was proposed where E. coli body may be simultaneously attacked by both AgNPs and Ag+ ions promoted by CeO2. The former may attack the cell membrane, leading to its cleavage and disruption; and the latter may be ionized and released from AgNPs to enter inside the cell, modifying its permeability and respiration, finally resulting in complete deactivation and death. more...

Highly active Fe3+ doped TiO2 (xFe–TiO2 where x = 3 or 5 wt%) photocatalysts were synthesized by the sol–gel method and their structures were refined with the Rietveld method. Several important effects of calcination temperature on the crystalline structure, textural features, phase concentration, Fe3+ distribution, optical properties, and photocatalytic activity were determined. When Fe–TiO2 materials were calcined at 400 °C, most of Fe3+ were formed α-Fe2O3 and some of them were incorporated in the network of TiO2 anatase; as calcination temperature increased to 800 °C, α-Fe2O3 and FeTiO3 coexisted on the TiO2 rutile phase. High calcination temperature also led to surface area sharply diminishing and the surface oxygen reducibility significantly decreasing. The interatomic distances of Fe–TiO2 catalysts obtained from the method of radial distribution function (RDF) were: Ti…O = 1.93 A (anatase), Fe…O = 2.59 A, Ti…Ti = 3.08 A, Ti…Fe = 3.69 A, Ti…Ti = 3.79 A, Ti…O = 4.83 A (rutile). In the photooxidation of 2,4-dichlorophenoxyacetic acid (2,4-DA), the photocatalytic activity of Fe–TiO2 catalyst increased with increase of Fe3+ content in anatase phase. The 2,4-DA photooxidation followed the first-order kinetic reaction model and favored under acidic condition. Approximately 95% 2,4–DA were photooxidized with the best catalyst 5Fe–TiO2–400 after 120 min of reaction under UV irradiation. TiO2 phase transformation from anatase to rutile and FeTiO3 formation at 800 °C negatively impacted on the photocatalytic performance. The catalytic activity of the catalysts correlated well with variations of textural properties, phase concentration, and surface oxygen reducibility that were all controlled by the calcination temperature. more...

Ti-MCM-41 supported vanadia core–shell catalysts were prepared and their catalytic activity was evaluated in a biphasic reactor for simultaneous oxidation/separation of refractory organosulfur compounds (dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT)) in a model diesel fuel. Formation of core–shell structure in the catalyst nanoparticles resulted from the surface diffusion of the vanadium ion in semimelted state of vanadia during the calcination process. It was found that both the value of V5+/(V4+ + V5+) and the surface acidity of the catalysts generally increased as the content of V content increased to 15 wt % of vanadium and correlated well with variations in catalytic activity, indicating that the surface V5+ and surface acid sites were chiefly responsible for the oxidation of sulfur compounds. The reactivity of organosulfur compounds was influenced by their steric hindrance. Addition of carboxylic acid (acetic acid or formic acid) promoted the... more...

This study describes the development of mesostructured TiO2 photocatalysts modified with PO43- to improve its specific surface area and reduce the recombination rate of the electron—hole pairs. The mesoporous photocatalyst was successfully incorporated into a high specific surface area silica matrix by the hydrolysis reaction of tetraethyl orthosilicate (TEOS). Pluronic 123 and phosphoric acid were used as the directing agent for the structure of the mesoporous TiO2 and as a source of phosphorus, respectively. TiO2, P/TiO2, TiO2-SiO2 and P/TiO2-SiO2 materials were characterized by BET, XRD, TEM-EDS, FTIR and UV-vis DRS measurements. The photoactivity of TiO2-SiO2 nanocomposites containing 15 wt.% photocatalyst/silica was evaluated in the degradation reaction of anionic dyes with UV radiation. The proposed nanomaterials showed high potential for applications in the remediation of wastewater, being able to reuse in several cycles of reaction, maintaining its photoactivity and stability. The separation and recovery time of the material is reduced between cycles since no centrifugation or filtration processes are required after the photooxidation reaction. more...

A series of FeOx/Ti-MCM-41 mesostructured catalysts were synthesized and characterized by the X-ray diffraction (XRD), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM), and Mossbauer spectroscopy. The surface reducibility and acidity of the catalysts were measured by temperature-programmed reduction of hydrogen (TPR-H2) and temperature-programmed desorption of ammonia (TPR-NH3) methods. Incorporating Ti4+ in the MCM-41 framework and loading Fe2O3 in the surface of the catalysts would create the acid sites and enhance the surface oxygen reducibility. Most of Fe3+ ions were highly dispersed on the surface and some were inserted into the framework of the support with different structural environments. The amount of the Fe3+ ions locating around the structural defects increased as the Fe content increased. In a biphasic reaction system (n-hexadecane/acetonitrile), the oxidation/elimination of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) could correlate perfectly with the surface acidity and the amount of iron ions around the structural defects of the catalysts. The reactivity of sulfur compounds decreased with increasing of the steric hindrance, showing an order as: DBT > 4-MDBT > 4,6-DMDBT. In the presence of catalyst and oxidant, the polar/non-polar biphasic reaction system developed herein could effectively oxidize the sterically hindered sulfur compounds and simultaneously extracted the produced sulfones from oil phase into polar phase. more...

Double modifications of TiO2 by doping with WO3 and by dispersing on a SiO2 support were made by the one-pot sol-gel method. Doping with W shifts the TiO2 band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO2/SiO2 material was significantly increased, by approximately 3 times, in comparison to the bare TiO2. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO2/SiO2 catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals such as O2- and ⋅OH, together with W6+/W5+ couples and e-/h+ pairs in the catalysts in the p-nitrophenol photodegradation. The one-pot sol-gel synthesis method was proven to be effective to obtain W-TiO2/SiO2 catalyst with large surface area and high photocatalytic activity, and it can be also used for the preparation of other heterogeneous catalysts. more...

Mesoporous silica materials (SBA-15) doped with calcium (Ca) at 1, 3 and 5% w/w were synthesized in order to immobilize candida rugosa lipase (CRL), through the adsorption method. It was found that calcium (Ca) is present as CaO, highly dispersed on the surface of SBA-15, the specific area of SBA-15 decreases on incrementing CaO content. The environmental pH influences the adsorption of CRL due to the polarization of positive charges below the isoelectric point (IEP) whereas the Ca-SBA-15 materials present negative charges. The adsorption model proposed for CRL is about the accessible surface of the material, as this has a size of 7 nm and the Ca-SBA-15 present pores at an interval of 3 nm. more...

A series of CuO supported on graphite carbon catalysts (noted as Cu/GC) was prepared with impregnation method and CuO loading varied from 1 wt% to 5, 10 and 15 wt%. Textural properties, crystalline structure, phase composition, copper oxidation states, and morphology of the Cu/GC catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. Surface acidity was measured by using temperature-programmed desorption of ammonia (TPD-NH3). Surface Cu2+ ions, H2O2 oxidant, acetic acid promoter, and acidic media were all crucial for oxidative desulfurization (ODS) of a model diesel fuel. Both XRD and XPS results confirmed that Cu2+ and Cu+ coexisted on the carbon surface and the Cu2+/(Cu2+ + Cu+) ratio increased with increasing of copper oxide loading. The copper speciation result is in good correlation with the catalytic activity, indicating that surface Cu2+ ions are the active catalytic sites. Acetic acid reacted with H2O2 to form surface peroxyacetic species that coordinated with Cu2+ on the Cu/GC catalysts in acidic media and promoted the ODS activity. Low pH condition favored significantly dibenzothiophene (DBT) oxidation. Under the optimal operation condition (pH = 0, reaction temperature 70 °C, and catalyst loading 0.3 g with H2O2-glacial acetic acid), DBT concentration in oil was reduced from an initial value of 300 ppm to 78 ppm, 9 ppm, 3 ppm and 0 ppm after ODS treatment using Cu/GC catalysts loading with 1, 5, 10, and 15 wt% of CuO, respectively. more...

Fe TiO 2 catalysts were synthesized with the sol–gel method and were characterized by X-ray diffraction, N 2 adsorption measurement, Mossbauer spectroscopy, UV–vis spectroscopy, Raman spectroscopy, temperature programmed reduction, and temperature programmed desorption of NH 3 . The Fe TiO 2 catalysts chiefly consist of crystalline anatase. Fe 3+ ions are highly dispersed on the surface and distributed in octahedral-coordinate sites within different environments in TiO 2 . The Fe TiO 2 catalysts were then evaluated for oxidation desulfurization of dibenzothiophene in a biphasic reaction mixture consisting of an acidified polar phase and a hexadecane model fuel phase. Compared to control tests, the catalytic activity for dibenzothiophene (DBT) oxidation is markedly improved by addition of acetic acid, typically at least doubling DBT conversion compared to that observed under control conditions. Under optimal conditions (10 wt% Fe in the Fe TiO 2 catalyst and a pH adjusted to 0), 100% of the 300 ppm DBT initially present in the reaction mixture could be completely oxidized within 5 min. Oxidation of DBT formed sulfoxide/sulfones which were found to be enriched in the polar phase. The sol–gel Fe TiO 2 catalysts possess several attributes which may contribute to their activity for DBT oxidation: (1) their hydrophilic–hydrophobic character that facilitates DBT oxidation as a phase transfer catalyst; (2) coordination and activation of acetic acid and peroxyacetic acid with Fe 3+ and Ti 4+ present at the Fe TiO 2 surface, and (3) formation of superoxides at the Fe TiO 2 surface. more...

An experimental physisorption study on the adsorption of chloroalkenes (CXHYClZ), such as dichloroethylene, trichloroethylene and tetrachloroethylene, on SiO2 and Ag-doped SiO2 micro–mesoporous solids is performed. The existence of the adsorbed phase is assessed by observing the position of the incumbent FTIR chloroalkene vibration bands. The SiO2 substrates are prepared from the reaction of tetraethyl orthosilicate and water in the presence of ethanol. Adsorption of CXHYClZ compounds on the pristine and Ag-doped SiO2 samples is measured in the temperature range 408–523 K by a chromatographic method. The uptake degree of the chlorinated compounds results to be temperature dependent, and the Freundlich adsorption model is found to fit the CXHYClZ adsorption data. The degree of interaction between these molecules and the SiO2 samples is analyzed through evaluation of the isosteric heat of adsorption of C2H2Cl2 at different sorption loadings on the SiO2 and Ag/SiO2 substrates. This heat is found to fulfill the following decreasing order: SiO2 > Ag/SiO2 (2 wt.% Ag) > Ag/SiO2 (10 wt.% Ag) > Ag/SiO2 (5 wt.% Ag). more...

Fe–TiO2 sol–gel thin film photocatalysts were prepared by the spin-coating method. Precursory Fe–TiO2 films, containing 3 and 5 wt.% Fe, were thermally treated at 400 and 800 °C; the dominant crystalline phases of TiO2 were anatase and rutile, respectively. The thin films were characterized by X-ray diffraction, UV–vis spectroscopy, and scanning electron microscopy. The antimicrobial photocatalytic activity over colonies of Escherichia coli bacteria, deposited on the thin films and induced by the incidence of visible radiation was evaluated by the plate counting method. The thin film containing 5 wt.% Fe and treated at 800 °C had a microcrystalline texture and could eliminate E. coli bacteria completely after 60 min. In these materials the active phases are both anatase and rutile. more...

Adsorption isotherms of chlorobenzene, chloroform and carbon tetrachloride vapors on undoped SiO(2), and metal-doped Ag/SiO(2), Cu/SiO(2) and Fe/SiO(2) substrates were measured in the temperature range of 398-593K. These substrates were prepared from a typical sol-gel technique in the presence of metal dopants that rendered an assortment of microporous-mesoporous solids. The relevant characteristic of these materials was the different porosities and micropore to mesopore volume ratios that were displayed; this was due to the effect that the cationic metal valence exerts on the size of the sol-gel globules that compose the porous solid. The texture of these SiO(2) materials was analyzed by X-ray diffraction (XRD), FTIR, and diverse adsorption methods. The pore-size distributions of the adsorbents confirmed the existence of mesopores and supermicropores, while ultramicropores were absent. The Freundlich adsorption model approximately fitted the chlorinated compounds adsorption data on the silica substrates by reason of a heterogeneous energy distribution of adsorption sites. The intensity of the interaction between these organic vapors and the surface of the SiO(2) samples was analyzed through evaluation of the isosteric heat of adsorption and standard adsorption energy; from these last results it was evident that the presence of metal species within the silica structure greatly affected the values of both the amounts adsorbed as well as of the isosteric heats of adsorption. more...

The importance of aluminum alkoxides precursors (ethoxide, isopropoxide and sec-butoxide) in the tailoring of the structural and textural properties of γ-alumina was reported. It has been found that the specific surface areas (336–426 m2/g), as well as the mean pore size distribution are modified in function of the length and branching of the aluminium alkoxide used in the synthesis. A narrow pore size distribution was obtained with aluminum ethoxide (14.7 nm), meanwhile a broad pore size distribution was observed in samples prepared with aluminium sec-butoxide or aluminium isopropoxide precursors (18.2 and 19.4 nm). In fresh samples, Boehmite phase and AlVI octahedraly coordinated were identified by XRD and 27Al MAS-NMR spectroscopies. After annealing at 500°C, the samples showed the γ-alumina phase formation and a mixture of aluminium in tetrahedral AlIV and octahedral AlVI coordination in variable proportions. The acidity of the calcined samples, determined from the pyridine-FTIR spectra, showed Lewis and Bronsted type acidity. Activity in the 2-propanol dehydration reaction showed that the highest activity corresponds to the samples showing the highest Lewis acidity. more...

In this paper, we prepared by the sol–gel method alkaline titania catalysts, doped by gelling titanium alkoxide with aqueous solutions containing potassium, rubidium or cesium chlorides. XRD patterns showed that samples annealed at 400 and 600 °C contained a single crystalline phase, anastase. Specific surface areas were higher in samples annealed at 400 °C (>100 m2/g) than in those annealed at 600 °C (25 m2/g). The weight density of basic sites determined by CO2–TPD drastically diminished in samples treated at 600 °C. Catalysts were tested for the self-condensation of acetone at 300 °C; main reaction products were isomesityl oxide, mesityl oxide and mesitylene. Samples annealed at 600 °C showed lower acetone conversion rate and low formation of mesitylene than that obtained on samples annealed at 400 °C. It is proposed that the formation of mesitylene occurs via the Michael reaction over the titania support. more...

The vapor-phase condensation of acetone was studied over TiO2-doped with 1 wt% of alkaline metals (Li, Na, K and Cs). The reaction was catalyzed by basic sites and the main products were mesityl oxide (MO), isomesityl oxide (ISMO) and mesitylene (M); other compounds as isophorone (IP) and phorone (P) were also obtained. The basic properties of the samples were determined by chemisorption of carbon dioxide. It was found that the number of the basic sites of the TiO2-doped catalysts increased in the following order: Li/TiO2 > Na/TiO2 ∼ K/TiO2 > Cs/TiO2; in contrast, the trend of the basic strength and total activity was Cs/TiO2 > K/TiO2 ∼ Na/TiO2 Li/TiO2. On the other hand, the selectivity patterns showed that the higher formation of MO was obtained with the catalyst which showed the lowest basic force (Li/TiO2). A direct correlation between the activity and the alkaline metal atomic radius was found, while the inverse dependence for the selectivity to mesityl oxide was observed. more...

Microencapsulation is a versatile technology that allows controlling the release of different active molecules. Recently the sol–gel process has emerged like a promising method to immobilization and stabilization of biologically active compounds like enzymes, antigens, microorganisms and drugs. Porous silica and titanium dioxide materials made by low temperature sol–gel processes are promising host matrixes for encapsulation of biological molecules. The preparation of a low-temperature silica sol followed by gelation to neutral pH with water for injection containing the antiepileptic drug is reported here. The structure is very important so the analysis of the new developed material is also reported. Particularly interesting is the presence of nanotubes and microtubes, produced in the inorganic matrix in the presence of the sodium phenytoin. The use of transmission electron microscopy and quantum mechanics molecular simulation allows determining a micelle-like effect during the synthesis of these materials, which controls the size, structure and stability of them. more...

Mesoporous and microporous silica substrates, each of these kinds endowed with unique textural characteristics, have been prepared via sol–gel and micelle-templating techniques and characterized through N 2 sorption. Materials consisting of a lattice of cage-like monodisperse cavities interconnected by narrow throats (SBA-16), a set of individual cylindrical pores of about the same size (SBA-15), a network of long sinuous ganglion-like sequences of bulges and throats (mesoporous glass, MG), or microporous arrangements of globular nanoparticles (microporous SiO 2 ) have been developed. The N 2 sorption isotherms of microporous silica at 76 K correspond to International Union of Pure and Applied Chemistry (IUPAC) type I, while those of mesoporous SBA-16, SBA-15, and MG silica match a type IV with hysteresis loops of types H1 or H2 depending on the regularity and nature of the void elements constituting the substrate. A characteristic common to all kinds of porous SiO 2 solids herein synthesized is the rigidity of the arrangements, since the total pore volumes attain limiting values. Pore-size distributions of mesoporous SiO 2 materials can be calculated by density functional theory (DFT) and sometimes by Barrett–Joyner–Halenda (BJH) methods. The microporous SiO 2 adsorbent depicts a larger amount of big micropores (supermicropores) rather than small micropores (ultramicropores), this being a very useful characteristic for the entrapment and ulterior release of volatile compounds. MG substrates depict a percolation vapor threshold while the SBA-16 material shows a cavitation phenomenon during capillary evaporation. Additional properties of SBA-16, SBA-15, MG silica substrates are studied via primary desorption scanning curves. more...

The effect on titania of doping with lithium and rubidium titania gels has been studied in samples prepared with titanium (IV) tetra-n-butoxide co-gelling with the alkaline metal precursors. Titania and doped titania were characterized by X-Ray diffraction, which showed that the catalysts were nanostructured. In samples calcined at 400°C, the crystallite size of the anatase phase was 17 and 14 nm, and 78 and 38 nm for samples calcined at 600°C, for Li/TiO2 and Rb/TiO2, respectively. The specific surface areas of doped samples (400°C) are lower in Li/TiO2 (90 m2/g) than in Rb/TiO2(125 m2/g). Evaluation of their basic properties has been carried out in the acetone condensation reaction. It was found that the activity strongly depended on the Li and Rb ionic radii. more...

Adsorption isotherms of aromatic BTX (benzene, toluene, and p-xylene) hydrocarbons on pure and Ag-doped SiO2 microporous substrates synthesized by the sol−gel procedure have been measured by the gas chromatographic technique at several temperatures in the range between 423 and 573 K. Both Langmuir and Dubinin adsorption models can reasonably fit every set of BTX adsorption data at all temperatures. The uptake degree of these hydrocarbon adsorptives on both SiO2 and Ag/SiO2 microporous substrates is temperature-dependent. Additionally, the degrees of interaction of BTX molecules with SiO2 and Ag/SiO2 microporous walls have been investigated by evaluation of the corresponding isosteric heats of adsorption (qst) by means of a Clausius−Clapeyron-type equation. The isosteric heats of adsorption of BTX hydrocarbons at different adsorbate loadings have been inferred from the adsorption isotherms and found to follow the decreasing sequence qst(benzene) < qst(toluene) < qst(p-xylene). Isosteric heats of adsorption... more...

Microporous silica solids of Si0 2 and Ag/Si0 2 (a microporous Si0 2 substrate containing 5 wt % Ag) are synthesized by the sol-gel method and analyzed through several characterization techniques. The type I shapes of N 2 sorption isotherms at 76 K on these materials indicate large micropore contents as well as important cohesive interactions between adsorbed N 2 molecules, i.e., a gradual cooperative filling process becomes more and more evident as the concentration of , adsorbate within the porous structure increases. In addition, negative values of the BET constant are found thus indicating that the adsorption mechanism on these solids can be better described in terms of a volume filling process rather than in terms of a multilayer formation phenomenon. The microporosity existing in these substrata is studied through Sing's as-plots. The adsorption capacities of n-alkanes (i.e. n-hexane, n-heptane, n-octane, and n-nonane) on Si0 2 and Ag/Si0 2 substrata are measured by gas chromatography (GC) at different temperatures. The uptake of every hydrocarbon sorptive, on both Si0 2 and Ag/Si0 2 substrata, is found to be temperature-dependent. Additionally, the intensities of attractive interactions between hydrocarbon ad molecules and the surfaces of the above solids are evaluated for each adsorbate type from determinations of the isosteric heats of adsorption. more...

TG, FTIR-(CO absorption), and catalytic activity in the NO reduction by CO were used to characterize Cu/Al2O3-TiO2 catalysts prepared by co-gelling aluminum tri-sec-butoxide and titanium iso-propoxide at pH 9 and at pH 3 gelling conditions. Under nitrogen flow, copper oxide decomposition, oxygen storage capacity (OSC) and sample dehydroxylation (total mass loss) was followed by TG. The CuO decomposition forming Cu0, Cu+1 was observed by means of FTIR (CO absorption) spectra. In pH 9 sample the large amount of Cu0 was observed. At low total mass loss and high Cu0/Cu+1+Cu+2 ratio (pH 9 sample) a lowest light-off in the NO reduction by CO was observed. more...

Ru/SiO 2 , Cu/SiO 2 and Cu–Ru/SiO 2 catalysts containing 1% wt. of the active metal on the silica support were prepared in various ways and characterized by appropriate spectroscopic techniques. FTIR results show that the hydroxyl ions of the support is stable up at 800°C. Thermal treatment of samples does not modify BET areas, in the range of 600 m 2 /g, nor the values of the average size of the metallic particles. The study of the catalytic activity using the phenylacetylene hydrogenation test reaction shows that the Ru/SiO 2 catalysts have high activity and selectivity to styrene. However, when Cu is additionally impregnated into these solids, no activity is observed in the test reaction of hydrogenolysis of n -heptane. Finally, all catalysts show good activity in the reduction of NO x by CO. more...

Silica samples were prepared by the sol–gel process varying the hydrolysis catalyst. The samples were characterized by X-ray diffraction and the radial distribution function was determined (R.D.F.). Fourier transform infrared spectroscopy and thermal analysis were also used. It was found that OH-retention capacity as well as order in the material may be modified with hydrolysis catalysts. When the hydrolysis catalyst was NH 4 OH the sample did not dehydroxylate even at 1000°C. more...

The enzyme papain was adsorbed on mesoporous silica at 4°C and pH values between 3 and 11. From the adsorption kinetic data, the rate constant for the process was evaluated. The concentration of the enzyme in solution was calculated by monitoring the absorbance at 280 nm, and the quantity of papain bound to the solid was evaluated from the initial and residual soluble enzyme concentrations. The best results were observed for papain adsorption at pH 5.0; under these conditions, the desorption of the enzyme was more...

This paper reports the results of studies of the thermal behavior during sol-gel synthesis of SiO 2 , starting from a mixture of tetraethoxysilane (TEOS), ethanol and water at pH 3, 7 and 9. A heat flow calorimeter was used to study the thermal behavior of mixtures, from the initial stage of mixing to the formation of gel. When the TEOS gelation reaction takes place at pH 7, it behaves in unexpected ways; it can be observed that the hydrolysis reaction takes place in an oscillatory manner, with a frequency of 6.5 h, after which an increase in the heat capacity of the reacting mixture is noted. more...

In the sol−gel Cu/TiO2 system, nanocrystalline brookite, which was stable even after annealing the sample at 400 °C, was generated in high concentrations. This was achieved with copper chloride as copper precursor. The respective samples had a light absorption band at 562 nm that corresponded to an energy bandgap of 2.30 eV, which is smaller than the values reported for titania. When copper sulfate was the precursor, brookite was absent, but nanocrystalline anatase, the main phase, was stabilized even at 800 °C by sulfate ions. After annealing the samples at low temperatures, copper was well dispersed for 1 wt % copper, but part of it segregated forming copper compounds when the copper concentration was 10 wt %. By annealing the samples at 800 °C, copper oxidized to CuO; except in the 10 wt %-copper sample prepared with copper sulfate, where it formed antlerite. more...

Aluminosilicates were prepared by the sol−gel method using tetraethoxysilane as silica source and aluminum ethoxide, aluminum iso-propoxide, or aluminum sec-butoxide as alumina sources. An importan... more...

Borovanadate glasses (1−x)[B2O3–yLi2O]–xV2O5 with 0≤x≤1 and 0≤y≤1 have been prepared and systematically studied by Raman spectroscopy. The results have been compared with glass transition temperature measurements. The Raman spectra exhibit a characteristic band at about 900 cm−1 whose shape and frequency are dependent on both V2O5 and Li2O concentration. The study of the line shape has shown that vanadium–oxygen structural units formed in the glasses are VO4 tetrahedra and VO5 pyramids according to the Li2O content. It is also observed that V2O5 behaves as modifier or as glass former in regard to the boron–oxygen network. more...

The combination of a DuPont 942 thermomechanical analyzer with a CBM computer allowed the establishment of thermodynamic properties such as isobars, isobaric volumetric expansions, isothermal compressibilities, and the equation of stateV=V(p, T) in a limited region ofpVT space. more...

Platinum SiO 2 sonogel has been compared with the corresponding xerogel and an impregnated catalyst. The thermal behavior, the FTIR spectra and the pyridine adsorption show that Lewis acidity is present in the impregnated sample. In the sonogel, Lewis acidity turns to be very low and insensitive to desorption temperature. In the xerogel, both Lewis and Bronsted acidity was observed. In each sample, reduction in situ (without hydrogen flow) of the metal phase is determined by the OH content. Platinum is highly reduced in the sonogel, partially reduced in the xerogel and very slightly reduced in the impregnated sample. more...

The use of Y zeolite and erionite to remove UO2 2+ ions from aqueous solutions has been investigated. The effect of temperature, the concentration of UO2 2+ uptake, the diffusion coefficients, and the ion-exchange isotherms were also studied. X-ray diffraction, thermal analyses, and transmission electron microsocopy were used to characterize the solids. The UO2 2+ content was determined by neutron activation analysis. The diffusion coefficients are not clearly affected by temperature or concentration. They definitely depend on the structure of each zeolite. The UO2 2+ exchange capacities were 0.2037 and 0.7345 meq UO2 2+/g for erionite and Y zeolite, respectively. It was found that UO2 2+ is exchanged with the cations of the large cavity in Y zeolite. In the case of erionite, UO2 2+ is exchanged with the cations localized in sites where the charge densities are very high. more...

Alumina supported platinum-tin catalysts were synthesized using the sol-gel method. The solids were characterized by TGA and DTA analyses. It was found that the catalysts remain hydroxylated after having been thermally stabilized. Moreover, when under a hydrogen flux, Pt reduces producing an intense exothermic peak at room temperature. more...

Pt-Sn supported catalysts were prepared by the sol-gel method. The solids were characterized by FTIR and UV-VIS spectroscopy and N2 adsorption analysis. The platinum showed a deformed octahedral symmetry, tending to come to the surface as metallic platinum and forming small particles anchored to the support. more...

B2O3-xLi2O3 (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B2O3 glass obtained by melting and quenching. more...

Silica-zirconia materials were synthesized by the sol-gel process at pH 3 and 9. The synthesis precursors were tetraethoxysilane and zirconium acetate. The zirconia concentrations were 1.3%, 4.0% and 6.7%. The results obtained show that at pH 3 the tetragonal phase is present; at pH 9, the monoclinic phase is more stable. Thus, when the zirconia concentration is lower, the more stable crystalline phase is obtained in a number of steps. more...

Insium-dopod zinc thin films were grown using the chemical spray deposition technique and different doping compounds in the solution. The partucular, indium chloride, indium sulfate and indium acetate were used as indium sources. The films show a high degree of preferential crystalline orientation which depends mainly on the type of doping compound and the substrate temperature. The lowest value o the resistivity is 2 × 10 −3 ω cm and and the transmittance is on average higher than 90%. It was found that the texture of the films could be change quite easily making it possible to grow films for different applications. more...

Silica doped with Fe(II) has been prepared using the sol-gel technique. The reactions were hydrolysis and condensation yielding Si-O-Fe-O-Si. The compounds obtained were characterized by thermal analysis (TGA and DTA) which indicates the changes that occur in the gel. more...

Impregnation and sol-gel preparation methods are compared. Only when prepared by sol-gel synthesis, ruthenium is incorporated in the silica network; RuO2 particles are observed, but most Ru is occluded in the silica network. The ruthenium migrates to the surface with thermal treatments and small particles are formed. In the case of impregnated catalysts only RuO2 particles are observed. Their diameter is larger when the catalyst is treated at high temperatures, ortho-Xylene hydrogenation was performed on these two kinds of catalysts. The deactivation and selectivity values are attributed to the structural differences of the catalysts. © 1992 Academic Press, Inc. more...

Platinum on silica catalysts have been prepared by adding [PtCl 6 ] -2 to tetraethoxysilane (TEOS). After hydrolysis and condensation a gel is formed. The addition of platinum into the gel has an important effect on the surface area of the solid (up to 1,100 m 2 m/g). The catalysts with a low metal concentration (≤0.5 wt%) are active for the hydrogenation of alkenes but not for the hydrogenation of aromatics. A support effect can be proposed to explain the low activity for benzene and ortho-xylene hydrogenation more...

Adsorption isotherms of BTX aromatic hydrocarbons (benzene, toluene, and p-xylene) on pristine (SiO2) and metal-doped (Ag-SiO2, Cu-SiO2 and Fe-SiO2) mesoporous and microporous substrates were measured and interpreted. These adsorbents were synthesized by the sol-gel procedure and their BTX sorption isotherms were obtained by the gas chromatographic technique (GC) at several temperatures in the range 423-593 K. The uptake amount of these hydrocarbon adsorptives on SiO2, Ag-SiO2, Cu-SiO2 and Fe-SiO2 mesoporous and microporous substrates was temperature-dependent. Additionally, the interaction of BTX molecules with the pore walls was evaluated by means of the corresponding isosteric heat of adsorption (qst), which was found to follow the next increasing sequence: qst (benzene)qst (toluene)qst (p-xylene). In general, the isosteric heat of adsorption of aromatic BTX compounds on microporous silica depicted an increasing tendency when the amount adsorbed was raised. This was a consequence of the existence of cohesive interactions (adsorbate-adsorbate) besides of the adhesive ones (adsorbate-adsorbent). The inclusion of silver or iron atoms within the SiO2 structure leads to an increased adsorbed amount of BTX molecules on the solid surface if compared with the Cu-SiO2 adsorbent. The adsorption of benzene, but not of toluene and p-xylene, molecules on pristine SiO2 is facilitated by the pore size of this substrate since this is the highest of all materials. more...

The present study reports the results obtained by UV-VIS spectroscopy, FT-IR (Fourier transform infrared) spectroscopy, and BET area measurements of Pd/SiO2 catalysts synthesized by the sol-gel process. This preparation technique results in the hydrolysis and polycondensation of a silicon alkoxide, which contains the metal halide salt PdCl2 in the initial solution. The reaction takes place at pH 9, forming intermediates which correspond most probably to surface species [SiO2]-[PdClxOHy]-OH The interaction between the silica gel and the palladium precursor has important effects on the specific surface area. The products are solids with BET specific areas up to 800 m2/g. Catalytic tests (hydrogenation of 1-hexene and phenylacetylene) show that sol-gel catalysts exhibit high selectivity in the formation of 2-methylpentane and styrene. To explain the high selectivities shown by the Pd sol-gel catalysts a geometric effect induced by the support is proposed on the structure of the ca. 1-nm-size Pd metal particles. more...

Impregnation and sol-gel preparation methods are compared. Only when prepared by sol-gel synthesis, ruthenium is incorporated in the silica network; RuO2 particles are observed, but most Ru is occluded in the silica network. The ruthenium migrates to the surface with thermal treatments and small particles are formed. In the case of impregnated catalysts only RuO2 particles are observed. Their diameter is larger when the catalyst is treated at high temperatures, ortho-Xylene hydrogenation was performed on these two kinds of catalysts. The deactivation and selectivity values are attributed to the structural differences of the catalysts. © 1992 Academic Press, Inc. more...

Silico-aluminates were synthesized from aluminum and silicon alkoxides by the sol-gel method and characterized by FTIR spectroscopy. The water and alumina concentration effects in specific BET areas and activity in isopropanol dehydration were studied. High specific BET areas were found and a correlation between the tetrahedral coordination and selectivity as well as deactivation is proposed. more...

"Calores isostéricos de adsorción de n-alcanos (n-hexano, n-heptano, n-octano y n-nonano) sobre substratos microporosos (zeolitas erionita, clinoptilolita y SiO2) fueron estudiados por el método de cromatografía gas-solido (CGS) a grados de cobertura nulos. Previamente los sólidos porosos fueron caracterizados por difracción de rayos X (XDR), microscopía de fuerza atómica (AFM), adsorción de N2 a 77 K y análisis químico. La adsorción de las parafinas ligeras ha sidoinvestigada en el intervalo de temperaturas 423-623 K, usando un detector de conductividad térmica y helio como gas portador. Los calores isostéricos de adsorción st q de las parafinas ligeras fueron obtenidos mediante la aplicación de la ecuación de Clausius-Clapeyron. Se observa que en todo el intervalo de temperaturas estudiado se lleva a cabo una adsorción selectiva de estos hidrocarburos en función del número de carbones que conforman la cadena de los n-alcanos. De los resultados obtenidos la zeolita ERIN presenta los mayores valores en los st q atribuida al efecto de tipo activado mostrado por esta zeolita." more...

We report results obtained from the study of the superconducting properties of the 110 K phase of the BiSrCaCuO high-Tc superconductor in different oxygen environments. Results of TGA analysis and electrical conductivity at high temperatures of samples with about 50% of the 110 K phase, with closed electrical paths of only the 110 K phase between the electrodes, induced us to anneal them in air and vaccum at 430°C. After this heat treatment the zero resistivity of the samples changes in the temperature interval between 70 K and 108 K. The transition temperature decreases by increasing the oxygen defienciency of the sample. more...

The clays of the ex-lake of Texcoco (Valley of Mexico) have a variable content of Na2CO3 and NaCl, which are usually evaluated by means of chemical methods. The experimental method presented in this article for the evaluation of these salts is thermogravimetric analysis. more...

Silicoaluminates were synthesized from aluminum and silicon alkoxides with varying water content. The obtained solids were studied by infrared spectroscopy (IR), Thermal Differential Analysis (DTA) and Thermogravimetric Analysis (TGA). The results show a positive water effect in the rate of polymerization and in the number of Si tetrahedral functional groups (OR) substituted by the aluminum. This type of material has high surface area, suitable to act as a catalyst support. more...