Mechanism for the formation of tin oxide nanoparticles and nanowires inside the mesopores of SBA-15

The formation of polycrystalline tin oxide nanoparticles (NP) and nanowires was investigated using nanocasting approach included solid-liquid strategy for insertion of SnCl₂ precursor and SBA-15 silica as a hard template. HR-TEM and XRD revealed that during the thermal treatment in air 5 nm tin oxide NP with well defined Cassiterite structure were formed inside the SBA-15 matrix mesopores at 250 °C. After air calcination at 700 °C the NP assembled inside the SBA-15 mesopores as polycrystalline nanorods with different orientation of atomic layers in jointed nanocrystals. It was found that the structure silanols of silica matrix play a vital role in creating the tin oxide NP at low temperature. The pure tin chloride heated in air at 250 °C did not react with oxygen to yield tin oxide. Tin oxide NP were also formed during the thermal treatment of the tin chloride loaded SBA-15 in helium atmosphere at 250 °C. Hence, it is well evident that silanols present in the silica matrix not only increase the wetting of tin chloride over the surface of SBA-15 favoring its penetration to the matrix pores, but also react with hydrated tin chloride according to the proposed scheme to give tin oxide inside the mesopores. It was confirmed by XRD, N₂-adsorption, TGA-DSC and FTIR spectra. This phenomenon was further corroborated by detecting the inhibition of SnO₂ NP formation at 250 °C after inserting the tin precursor to SBA-15 with reduced silanols concentration partially grafted with tin chloride.     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.     

The Effect of Thermal Treatment on the Structural and Electrokinetic Properties of Porous Glass Membranes

The properties of porous glass membranes prepared by acid leaching of sodium borosilicate glasses 8B and 8V and also 8B glass containing small amounts of fluorine and phosphorus (SFP) are comprehensively studied. The effect of the composition and conditions of thermal treatment of the original and porous glasses on their structural (specific surface area, structure resistance coefficient, average pore radius, volume porosity, and filtration factor) and electrokinetic characteristics (conductivity, counterion transport numbers, and electrokinetic potential) in KCl solutions at neutral pH values is studied. It is shown that an increase in thermal treatment temperature T _TT of the porous glasses from 120 to 750°C leads to a decrease in structure resistance coefficient β of 8B membranes. For membranes prepared from SFP glass, β values, efficiency coefficients, and counterion transport numbers are virtually independent of T _TT at 120–600°C and increase at T _TT = 750°C. Specific surface area and volume porosity decrease with a rise in T _TT for all studied membranes. The observed regularities of variations in the membrane characteristics are explained by the increasing fraction of large pores because of sintering of small pores with an increase in T _TT and by the different amounts of secondary silica in the pore space of porous glasses.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 299–307.Original Russian Text Copyright © 2005 by Volkova, Ermakova, Sidorova, Antropova, Drozdova.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.     

Synthesis and characterization of a novel crystalline AlPO4 molecular sieve,CFAP-7

The novel crystalline aluminophosphate CFAP-7, having a characteristic X-ray powder diffraction pattern, has been synthesized hydrothermally in a system consisting of di-n-butylamine-(NH₄)₂O–P₂O₅–Al₂O₃–H₂O at 120 to 140°C, the P₂O₅ and Al₂O₃ sources of which were provided by (NH₄)₃PO₄·3H₂O and Al₂(SO₄)₃ in aqueous solution, respectively. Investigations by DTA, TG, DTG, XRD, and IR indicate transformation of the original product (form A) into more stable crystal forms B and C on heating at about 180°C and 240°C, respectively, while liberating water and amine. Isotherms for the adsorption of water and methanol at 23°C show that both form B and form C are molecular sieves with a window dimension of 4.3–4.9 Å, and a methanol volume adsorbtion greater than that of water.     

Thermal stability of microencapsulated epoxy resins with poly(urea-formaldehyde)

A series of microcapsules filled with epoxy resins with poly(urea-formaldehyde) (PUF) shell were synthesized by in situ polymerization, and they were heat-treated for 2 h at 100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C. The effects of surface morphology, wall shell thickness and diameter on the thermal stability of microcapsules were investigated. The chemical structure and surface morphology of microcapsules were investigated using Fourier-transform infrared spectroscope (FTIR) and scanning electron microscope (SEM), respectively. The thermal properties of microcapsules were investigated by thermogravimetric analysis (TGA and DTA) and by differential scanning calorimetry (DSC). The thermal damage mechanisms of microcapsules at lower temperature (<251 °C) are the diffusion of the core material out of the wall shell or the breakage of the wall shell owing to the mismatch of the thermal expansion of core and shell materials of microcapsules. The thermal damage mechanisms of microcapsules at higher temperature (>251 °C) are the decomposition of shell material and core materials. Increasing the wall shell thickness and surface compactness can enhance significantly the weight loss temperatures (T_d) of microcapsules. The microcapsules with mean wall shell thickness of 30 ± 5 μm and smoother surface exhibit higher thermal stability and can maintain quite intact up to approximately 180 °C.     

Effects of hydrothermal post-treatment on microstructures and morphology of titanate nanoribbons

Titanate nanoribbons were prepared via a hydrothermal treatment of rutile-type TiO₂ powders in a 10 M NaOH solution at 200 °C for 48 h. The as-prepared titanate nanoribbons were then hydrothermally post-treated at 150 °C for 12-36 h. The titanate nanoribbons before and after hydrothermal post-treatment were characterized with FESEM, XRD, TEM, UV-VIS and nitrogen adsorption-desorption isotherms. The results showed that the hydrothermal post-treatment not only promoted the phase transformation from titanate to anatase TiO₂, but also was beneficial to the removal of Na⁺ ions remained in the titanate nanoribbons. After hydrothermal post-treatment, the TiO₂ samples retained the one-dimensional structure feature of the titanate nanoribbons and showed an obvious increase in the specific surface area and the pore volume.     

Hydrothermal,microwave and mechanochemical modification of amorphous zirconium phosphate structure

The influence of hydrothermal HTT, microwave MWT and mechanochemical MChT treatments on structure of precipitated amorphous zirconium phosphate has been studied. Using XRF, XRD and DTA-TG techniques, the formation of the low-crystalline zirconium hydrophosphate Zr(HPO₄)₂·H₂O after HTT and MWT has been established. All types of modification promote increase in specific surface area, pore volume and pore size as well as extend the limits of the porous structure parameters variation. MChT of wet gel allow to prepare the samples possessing simultaneously high values of specific surface area, volume and pore size. Total surface acidity significant increases as a result of modification. HTT and MWT as well as MChT of wet gel lead to increasing surface homogeneity as the decrease in fractal dimension for modified samples indicates.     

Study on the hydrothermal reaction of FeCl<Subscript>3</Subscript> solution in the presence of poly(vinyl alcohol)

A 0.5 dm³ aqueous solution of 0.1 M FeCl₃ dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T _h=110–200 °C). Highly ordered red corpuscle-like hematite particles around 2 m in diameter were produced after aging the solution at T _h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T _h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T _h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T _h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H₂O and N₂ adsorption experiments revealed that there are no ultramicropores in the particles. The H₂O and CCl₄ adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H₂O (diameter 0.253 nm) and N₂ (diameter 0.318 nm) molecules but not to CCl₄ (diameter 0.514 nm).     

Degradation of phenylarsonic acid and its derivatives into arsenate by hydrothermal treatment and photocatalytic reaction

The degradation of phenylarsonic acid (PA) and its derivatives by hydrothermal treatment (HTT) was examined, especially focusing on the effect of adding H₂O₂ upon the degradation efficiency. The degradation was assessed by the generation of arsenate resulting from the cleavage of As C bonds in the PA derivatives. When PA (without substituents) was subjected to an HTT with H₂O₂ (H₂O₂‐HTT; 0.5–1% H₂O₂) at 175–200 °C, PA was almost completely degraded into arsenate, whereas an HTT with NaOH (NaOH‐HTT; 3 M NaOH) at the temperatures provided almost no degradation. The H₂O₂‐HTT also worked well for the degradation of PA derivatives with hydroxy and/or nitro groups on the phenyl ring. However, the degradation of aminophenylarsonic acids was not favorably performed by the H₂O₂‐HTT. The effect of the structure of PA derivatives upon the degradation susceptibility was discussed. A photocatalytic reaction using TiO₂ was also attempted for the degradation of PA derivatives. Copyright © 2005 John Wiley & Sons, Ltd.     

Porous silicon oxycarbide glasses from organically modified silica gels of high surface area

High surface area alkyl-substituted silica aerogels and xerogels were successfully prepared by sol-gel processing and supercritical drying. The gels were further heat treated in inert atmosphere to temperatures as high as 1000°C. Surface areas and pore structure of the gels and gels pyrolyzed at high temperatures were determined by multipoint BET surface area measurement. The aerogels and xerogels exhibited surface areas of about 1100 m²/g. No significant effect of pH was found on the surface areas of gels in the two step sol-gel process, but gels of low pH showed smaller pore diameter and higher density. Xerogels showed smaller surface area, pore size, and pore volume compared to aerogels. Upon pyrolyzing in inert atmosphere, the surface areas of all the gels decreased with temperature as a result of collapse of micropores and shrinkage of mesopores. Unlike pure silica gel, which loses almost all surface area and densifies at 1000°C, the advantage of the alkyl-substituted gels is that they maintained a high surface area of 400 m²/g at 1000°C.Also with the Department of Agronomy.     

Analogs of D(+)-pantothenic acid. V. Synthesis and investigation of the structure of N-pantoyl derivatives of proline

The synthesis of pantothenic acid analogs is described. Boiling the Na salt of L-proline (L-I) with D-(–)-pantolactone (D-II) in MeONa Yielded 53.91% of N-D-pantoyl-L-proline (III), [] _D ² ° –52° (c 2; MeOH), and 19.18% of cyclo(N-D-pantoyl-L-proline) (IV), mp 119–121°C (ethanol), [] _D ² ° –68.9° (c 2; MeOH). The following were obtained similarly: N-L-pantoyl-L-proline, cyclo(N-L-pantoyl-L-proline), N-D-pantoyl-D-proline, cyclo(N-D-pantoyl-D-proline), N-L-pantoyl-D-proline, cyclo(N-D-pantoyl-hydroxyproline), and N--hydroxybutyryl-L-proline. By fusing D-II and DL-I at 140°C cyclo(N-D-pantoyl-DL-proline) and prolylproline anhydride (V) were obtained. Compound (V) with mp 136–138°C was synthesized from DL-1 by heating at 140°C. The PMR spectra of compounds (III-V) are given. The IR spectra of compounds (III and IV) are discussed.All-Union Scientific-Research Vitamin Institute, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 378–383, May–June, 1979.     

Defect microstructures of TiO2 rutile due to Zr dissolution and expulsion

Defect microstructure of Zr-dissolved TiO₂ polycrystals, homogenized as rutile structure at 1600 °C and then aged at 900 °C for 2-200 h in air, was characterized by analytical electron microscopy. Diffuse diffractions occurred at 1/2(211) as a result of Zr⁴⁺ substitution for Ti⁴⁺ with volume/charge compensating defect clusters. Upon annealing at 900 °C, plate-like Guinier and Preston (G.P.) zone appeared with the plate surface parallel to (100) and (010) and in association with dislocations. Commensurate superstructures with apparent triple {101} and {111} periodicity also occurred as metastable intermediates, which are presumably the precursor of the equilibrium ZrTi₂O₆ precipitate.     

Influences of Mesoporous Structure on the NO+H2+O2 Low Temperature Reaction over Pt/Si-MCM-41 Catalyst

It was found that Si-MCM-41 mesoporous molecular sieves as a support of noble metal Pt could be used for the selective catalytic reduction of NO by hydrogen (H₂-SCR) under lean-burn conditions. Pt/Si-MCM-41, together with Pt/Si-ZSM-5 and Pt/SiO₂, was characterized by X-ray diffraction analysis (XRD), nitrogen adsorption/desorption, hydrogen adsorption, and transmission electron microscopy (TEM). The results indicated that Pt/Si-MCM-41 had the best H₂-SCR activity in comparison with Pt/Si-ZSM-5 and Pt/SiO₂ catalysts and that the maximum conversion of NO was up to 60.1% at 100 °C and a gas hourly space velocity (GHSV) of 80000 h_-1 under lean-burn conditions. Characterization showed that the large surface area and pore volume of MCM-41 favored the dispersion of Pt. The maximum NO conversion of Pt/Si-MCM-41 catalyst decreased obviously to 15% at 120 °C when the pore structure of Si-MCM-41 support was destroyed. The reaction mechanism over Pt/Si-MCM-41 was investigated using in situ diffuse reflectance infrared spectroscopy (DRIFTS), which revealed that the main reaction intermediates should be nitrate species during NO reduction.     

Characterization of CoMCM-41 mesoporous molecular sieves obtained by the microwave irradiation method

CoMCM-41 mesoporous molecular sieves with different amounts of cobalt were synthesized via the microwave irradiation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and N₂ adsorption-desorption technique, and thermal and hydrothermal stabilities of synthesized CoMCM-41 samples were also investigated. Results show that these synthesized materials have typical mesoporous structure of MCM-41. Also, specific surface area and pore volume of synthesized CoMCM-41 decrease with increasing amount of cobalt added, and mesoporous ordering also decreases. When the molar ratio of SiO₂:CoO in the starting material is 1.0:0.05, mesoporous ordering of synthesized CoMCM-41 is the best among the four doping contents. On the other hand, results of thermal and hydrothermal tests show that CoMCM-41 after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 5 days still retains mesostructure. However, mesoporous framework is entirely damaged after calcination at 850 °C for 3 h.     

Thermal Treatment of Sol-Gel Derived Nickel Oxide Xerogels

Very fine nickel hydroxide and oxide xerogel powders were prepared using a new sol-gel synthesis procedure in which nickel ethoxide was produced through the reaction of nickel chloride, as a precursor, with sodium ethoxide in dehydrated ethanol, followed by the hydrolysis of nickel ethoxide with ammonia and drying the resulting hydrogel under subcritical pressures to form the xerogel. The effects of thermal treatment on the surface area, pore volume, crystallinity and particle structure of the resulting xerogels were investigated and found to have significant effects on all of these properties. Overall, the xerogel remained amorphous as Ni(OH)₂ space up to 200°C, with little change in the surface area and pore volume. At 250°C, the Ni(OH)₂ began to decompose and form crystalline NiO with the uniformity of the crystals increasing with an increase in temperature. The surface area and pore volume decreased sharply when increasingthe temperature beyond 250°C; this was the temperature where maximums of about 270 m²/g and 0.33 cm³/g were exhibited by this composite amorphous Ni(OH)₂ and crystalline NiO xerogel powders. At the higher calcination temperatures, very uniform NiO crystals with average crystallite sizes of 1.7 nm and 14.5 nm were obtained at 400 and 600°C, respectively.     

Syntheses of TiO2(B) nanowires and TiO2 anatase nanowires by hydrothermal and post-heat treatments

TiO₂(B) nanowires and TiO₂ anatase nanowires were synthesized by the hydrothermal processing in 10 M NaOH aq. at 150 °C followed by the post-heat treatment at 300-800 °C. As-synthesized Na-free titanate nanowires (prepared by the hydrothermal treatment and repeated ion exchanging by HCl (aq.) were transformed into TiO₂(B) structure with maintaining 1-D morphology at 300-500 °C, and further transformed into anatase structure at 600-800 °C with keeping 1-D shape. At 900 °C, they transformed into rod-shaped rutile grains. Microstructure of these 1-D TiO₂ nanomaterials is reported.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

The determination of oxygen in sulphur-containing organic compounds

Summary The reactions of anhydroiodic acid with CS₂, H₂S, and COS have been quantitatively investigated at 120° C and 170° C. The iodine formed was titrated and the gaseous reaction products determined by gas chromatography. At 170° C, CS₂ and COS are quantitatively oxidized to CO₂ and SO₂, and H₂S is oxidized to water and partially to SO₂ while a stoicheiometric fraction of the sulphur is obtained as elemental S. At 120° C the reactions are the same although in no case is the oxidation completely quantitative at this temperature.

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Zusammenfassung Die Reaktionen der Anhydrojodsäure mit CS₂, H₂S und COS wurden bei 120 und 170° C quantitativ untersucht. Das freigesetzte Jod wurde titriert und die gasförmigen Reaktionsprodukte gaschromatographisch bestimmt. Bei 170° C werden CS₂ und COS quantitativ zu CO₂ und SO₂ oxydiert, H₂S zu Wasser und teilweise zu SO₂, während ein stöhiometrischer Anteil des Schwefels in elementare Form übergeht. Bei 120° C laufen die gleichen Reaktionen ab, aber keinesfalls quantitativ.

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Résumé On a fait l'étude quantitative des réactions de l'acide anhydroiodique avec CS₂, H₃S et COS à 120° C et 170° C. On a titré l'iode formé et réalisé le dosage des produits gazeux de la réaction par Chromatographie en phase gazeuse. A 170° C, CS₂ et COS sont oxydés quantitativement en CO₂ et SO₂; H₂S est oxydé en eau et partiellement en SO₂ et il se forme une fraction stoechiométrique de soufre à l'état élémentaire. A 120° C, les réactions sont les mêmes bien que l'oxydation ne soit jamais quantitative à cette température.

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This work was supported by grants from the Statens Tekniska Forskningsrad (Swedish Technical Research Council).     

Microwave-assisted synthesis of 2-aminonicotinic acids by reacting 2-chloronicotinic acid with amines

2-(Methylamino)nicotinic acid was readily prepared in high yield by reacting 2-chloronicotinic acid with 40% aq MeNH₂ under microwave irradiation either at 120 °C for 2 h or at 140 °C for 1.5 h. Subsequently, we found that a range of 2-aminonicotinic acids could be obtained under microwave heating. The optimal reaction conditions involved the use of 3 equiv of amine, water as the solvent and heating at 200 °C for 2 h in the presence of diisopropylethylamine (3 equiv).