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Information about new cesium-containing quartzoid glasses (QGs) obtained as a result of the heat treatment of high-silica porous glasses (PGs) impregnated with aqueous solutions of CsNO3 is presented. Quartzoid glasses have been studied by SEM, X-ray diffraction, flame photometry, and energy-dispersive X‑ray spectroscopy. It has been established that the total content of cesium in the synthesized QGs increases with an increase in the concentration of the impregnating solution of cesium nitrate and an increase in the impregnation time of PGs for the selected synthesis conditions. [ABSTRACT FROM AUTHOR]

The paper presents the results of acoustic studies of the melting and crystallization of Ag–Ga alloys with a silver content of 1.5 and 3 at % embedded into porous glasses with an average pore size of 13 nm. The temperature dependences of the velocity of longitudinal ultrasonic waves are measured by a modified pulse-phase method at a frequency of 7 MHz in the 200–325 K range for complete and partial cooling–heating cycles. The temperature dependences of the ultrasonic velocity showed regions corresponding to phase transitions. Significant changes in the phase diagram of the bulk alloy due to nanostructuring have been revealed. It is shown that segregates with different crystal structures are formed in the pores for alloy of different compositions. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of the optical properties of materials especially at a nanoscale, is considered as important tasks for the engineering of photonic devices and systems. In this paper we study the photoluminescence of new nanocomposite material consisting of arsenic sulfide doped in porous glasses and the effect of photoinduced structural transformations on it. The nanocomposite was obtained via chemical deposition method in which arsenic sulfide powder was dissolved in an amine solution and then clean pieces of porous glass were impregnated for 2 days in the solution. Strong photoluminescence signal was observed in the samples when excited with lasers with excitation wavelengths of 405 and 532 nm. Also, the effect of laser irradiation on the photoluminescence of the samples was studied using confocal microscope with two different operating lasers 405 and 514 nm. It was observed that laser irradiation influences photoluminescence differently depending on the irradiation wavelength.

The article presents the results of a study of the optical properties of cesium-containing quartzoid glasses (QG NFF-Cs) obtained as a result of the heat treatment of high-silica porous glasses (PGs) impregnated with aqueous solutions of CsNO3. It is established that the introduction of cesium into the composition of high-silica quartz glasses (QG NFF) led to the emergence of absorption bands at 332, 384, 388, 442, 492, 565, 567, 583, 586, 621, 635, 695, 696, and 703 nm, which are related to the absorption of cesium atoms. The introduction of cesium into the composition of the glass leads to a decrease in the absorbance QG NFF-Cs by 15–20% compared to the QG NFF and to the drag of the refractive index. The maximum increase in the refractive index of the synthesized quartzoid glasses containing cesium is 0.002 (QG NFF nD, 1.4605; QG NFF-Cs nD, 1.4625) for PG impregnation conditions with 0.6 mol/L CsNO3 within 3 days. [ABSTRACT FROM AUTHOR]

Dielectric properties and structure of pure and carbon-modified nanocomposites on the base of porous glasses with an average pore diameter of 6 nm (PG6) with embedded KNO3 have been studied at the temperature diapason of 300–430 K and at frequencies of 0.1–3 × 106 Hz on cooling. X-ray diffraction studies of these samples have shown, that in modified and unmodified composites there is a mixture of the low-temperature paraelectric phase (α -phase) and the ferroelectric γ -phase. In modified composites, a decrease in permittivity and conductivity is observed. Dielectric response has been analyzed in the framework of modern theoretical models. Two relaxation processes have been identified and their origin has been determined. It has been found that the main contribution to the dielectric response of nanocomposite material PG6+KNO3 is provided by charge polarization on interfaces, which can be governed by modifying the inner pore surfaces. DC-conductivity of both composites has been estimated and the activation energies have been determined. Activation energy change observed in a vicinity of 360 K is attributed to the phase transformation and the appearance of KNO3 α -phase. [ABSTRACT FROM AUTHOR]

The study of structure of nanocomposite material based on porous glass with 7 nm average pore diameter filled by sodium nitrate from the melt under pressure has been carried out by synchrotron radiation diffraction upon heating and cooling. The temperature evolution of the elastic peak lineshapes corresponding to the sodium nitrate structure has been analyzed, and it is shown, that in the "virgin" sample there are two types of nanoparticles with dendrite spatial organization and with fundamentally different characteristic sizes. The temperature dependences of the critical index β(T) for the structural transition in sodium nitrate have been obtained, and the crossover in this dependence for nanoparticles with a characteristic size of about 20 nm has been found at T∗ ∼ 445 K both upon heating and cooling. The temperatures of the structure and "melting – crystallization" phase transitions observed in this nanocomposite have been determined. [ABSTRACT FROM AUTHOR]

Dielectric properties and structure of pure and carbon-modified nanocomposites on the base of porous glasses with an average pore diameter of 6 nm (PG6) with embedded KNO3 have been studied at the temperature diapason of 300–430 K and at frequencies of 0.1–3 × 106 Hz on cooling. X-ray diffraction studies of these samples have shown, that in modified and unmodified composites there is a mixture of the low-temperature paraelectric phase ([Formula: see text]-phase) and the ferroelectric [Formula: see text]-phase. In modified composites, a decrease in permittivity and conductivity is observed. Dielectric response has been analyzed in the framework of modern theoretical models. Two relaxation processes have been identified and their origin has been determined. It has been found that the main contribution to the dielectric response of nanocomposite material PG6+KNO3 is provided by charge polarization on interfaces, which can be governed by modifying the inner pore surfaces. DC-conductivity of both composites has been estimated and the activation energies have been determined. Activation energy change observed in a vicinity of 360 K is attributed to the phase transformation and the appearance of KNO3 [Formula: see text]-phase.

A mechanism of the ferroelectric phase transition in nanocomposite materials based on porous glasses with the average pore diameter of 7 nm with embedded sodium nitrite has been discussed. The results of analysis of temperature evolution of structure, thermal vibrations of ions, and interatomic distances are presented for these nanocomposites. It is shown that the thermal vibrations play the important role in a modification of ferroelectric phase transition from the first order, characterizing bulk compound, to the second order in ultra-dispersed sodium nitrite nanoparticles. [ABSTRACT FROM AUTHOR]

In the last three decades, considerable effort has been devoted to obtain both open and closed porosity ceramics & glasses in order to benefit from unique combination of properties such as mechanical strength, thermal and chemical stability at low‐relative density. Most of these investigations were directed to the production and the analysis of the properties for open porosity materials, and regrettably quite a few compositions and manufacturing methods were documented for closed porosity ceramics & glasses in the scientific literature so far. This review focuses on the processing strategies, the properties and the applications of closed porosity ceramics & glasses with total porosity higher than 25%. The ones below such level are intentionally left out and the paper is set out to demonstrate the porous components with deliberately generated closed pores/cells. The processing strategies are categorized into five different groups, namely sacrificial templating, high‐temperature bonding of hollow structures, casting, direct foaming, and emulsions. The principles underlying these methods are given, with particular emphasis on the critical issues that affect the pore characteristics, mechanical, thermal and electrical properties of the produced components. [ABSTRACT FROM AUTHOR]

The results of studying IR absorption spectra under the condition of frustrated total internal reflection of 1,2-dichloroethane and 1,1,2,2-tetrabromoethane in porous glasses with different pore radii are presented. Changes in the intensities of trans-conformation and gauche conformation in the studied systems for various pore radii of glass are found. The dependences of the differences in free energies of trans-conformation and gauche conformation for 1,2-dichloroethane and 1,1,2,2-tetrabromoethane on the pore radius of porous glass are obtained. At nm, the number of -conformers for 1,2-dichloroethane increases, while the number of -conformers for 1,1,2,2-terabromoethane increases. [ABSTRACT FROM AUTHOR]

The temperature evolution of the crystal structure and dielectric response of a nanocomposite based on porous glasses with an average pore diameter of 7 nm and embedded sodium nitrate in the temperature range of 300–600 K have been studied on heating. The temperature dependences of the amplitudes of thermal vibrations of ions in sodium nitrate nanoparticles are obtained, and the activation energies of sodium hopping conductivity in these nanocomposite materials are determined. The results obtained allow us to state that it is the sharp increase in thermal vibrations that leads to the appearance of the previously observed crossover in the temperature dependence of the order parameter of the structural transition in sodium nitrate nanoparticles at T* ∼455 K and to a decrease in the activation energy of sodium ions hopping conductivity on heating above T*. • Unusual order parameter temperature dependence in NaNO3 nanoparticles. • Appearance of a crossover in this dependence near T* ∼450 K. • A sharp growth of ion thermal vibrations above T*. • Increase of sodium hopping conductivity when approaching the crossover. • Significant reduction of the structural transition temperature compared to bulk NaNO3. [ABSTRACT FROM AUTHOR]

Abstract—A review of the authors' studies on the processes of metal nanoparticles (silver and gold) formation and of various type structures in polymer and porous materials based on the effects of self-assembly and self-organization in the continuous laser radiation field is presented. Most experiments were performed either with samples saturated with metal precursors in supercritical carbon dioxide or with those exposed to this medium. Structures of various types from metal nanoparticles in polymers and porous glasses: periodic structures of micron and submicron scale, layered structures from nanoparticles with an unusually short period (about 90 nm), filament, ring structures, and island nanoparticle films have been synthesized. Several regularities and mechanisms of the formation of both the nanoparticles and their structures depending on the wavelength of laser radiation have been established. New results on the method for producing composite porous foam materials based on silver nanoparticles and polymer matrices, which combines laser-induced "drawing" of porous structures, their impregnation with precursor molecules using supercritical fluid technology, and subsequent reduction of nanoparticles are presented. [ABSTRACT FROM AUTHOR]

Abstract The evolution of porous structure and local density, and associated changes of potential energy in binary glasses under oscillatory shear deformation, are investigated using molecular dynamics simulations. The porous glasses were initially prepared via a rapid thermal quench from the liquid state across the glass transition temperature and allowed to phase separate and solidify at constant volume, thus producing an extended porous network in an amorphous solid material. We find that under periodic shear, the potential energy decreases over consecutive cycles due to gradual rearrangement of the glassy material, and the minimum of the potential energy after thousands of shear cycles is lower at larger strain amplitudes. Moreover, with increasing cycle number, the pore size distributions become more skewed toward larger length scales, where a distinct peak is developed and the peak intensity is enhanced at larger strain amplitudes. The numerical analysis of the local density distribution functions demonstrates that cyclic loading leads to formation of higher density solid domains and homogenization of the regions with reduced density. Highlights • Temporal evolution of porous structure and local density is studied in glasses under periodic shear. • The potential energy after thousands of shear cycles becomes lower at larger strain amplitudes. • Cyclic loading leads to formation of higher density solid domains and larger pores and channels. [ABSTRACT FROM AUTHOR]

Temperature evolution of small angle neutron scattering on nanocomposites on base of porous alkali borosilicate glasses filled by sodium nitrite has been studied. The gyration radius (33-35 nm) of NaNO2 nanoparticles has been determined. It is shown that on heating and passing through the temperature of ferroelectric phase transitions the density of nanostructured sodium nitrite decreases. [ABSTRACT FROM AUTHOR]

Sets of silica gels: aerogels, xerogels and sintered aerogels, have been studied in the objective to understand the mechanical behavior of these highly porous solids. The mechanical behaviour of gels is described in terms of elastic and brittle materials, like glasses or ceramics. The magnitude of the elastic and rupture modulus is several orders of magnitude lower compared to dense glass. The mechanical behaviours (elastic and brittle) are related to the same kinds of gel characteristics: pore volume, silanol content and pore size. Elastic modulus depends strongly on the volume fraction of pores and on the condensation reaction between silanols. Concerning the brittleness features: rupture modulus and toughness, it is shown that pores size plays an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size is related to the pore size. Weibull’s theory is used to show the statistical nature of flaw. Moreover, stress corrosion behaviour is studied as a function of environmental conditions (water and alcoholic atmosphere) and temperature.

From the earliest days of heterogeneous catalysis, high surface area solids were extensively used for attaining largest possible densities of active sites and, correspondingly, for maximizing turnover. Since sites are active in the real sense of the word only if they are occupied by reactants, i. e. by molecules still to be converted, the relative fraction of pore volume occupied by reactants (the "effectiveness factor") is a key number for the efficiency of a catalyst in a given reaction. Its determination, so far generally based on reaction rate measurements with purposefully varied catalyst particles, remained to date a challenging task since it must be based on additional assumptions. The "one‐shot determination" of effectiveness factors by IR microimaging, here exemplified on considering the catalytic hydrogenation of benzene to cyclohexane by platinum dispersed on nanoporous glass, is shown to open up a promising route to overcome these limitations. You got one shot! IR microimaging is shown to allow the determination of the effectiveness factor η of a chemical reaction within a porous catalyst during a single experiment ("one‐shot" measurement), exemplified by considering the hydrogenation of benzene to cyclohexane within platinum‐containing nanoporous glass beads. [ABSTRACT FROM AUTHOR]

Photochromic quartz-like glasses were synthesized by an impregnation of the high-silica porous glasses with mixture of the Ag/Cu-Hal compounds (where Hal = Cl, Br, I; Cu 2+ is sensitizer) from water-salt solutions. UV/VIS/NIR optical density and visible luminescence spectra of synthesized glassy composites have been obtained. It was shown that UV radiation of these materials causes luminescence of the silver centers in a visible spectral region (450–620 nm). The assumption that the photochromic quartz-like glasses based on the matrixes from silicate nanoporous glasses are promising materials for solar engineering has been stated on the grounds of obtained results. [ABSTRACT FROM AUTHOR]

Micelle-templated silica (MTS)-composites with flexible macroscopic shape, monomodal or bimodal (hierarchical) pore structure, and high mechanical stability can be prepared by partial or complete pseudomorphic transformation of porous glasses (PG). The state of research concerning synthesis, transformation mechanism, characterization, and application of MTS/PG-composites is reviewed and the investigation of the transformation products by 129Xe NMR spectroscopy and the direct synthesis of Al-MCM-41/PG-composites are introduced. Finally, several approaches like a double-templating strategy for pore protection is shown. [ABSTRACT FROM AUTHOR]

• Simple chemical deposition method was used for Au- As 2 S 3 nanocomposite fabrication. • Mixing As 2 S 3 and AuNPs results in complex formations and in SPR suppression of AuNPs. • The nanocomposite exhibits a distinct and reversible photobleaching effect. • The bandgap energy of the nanocomposite can be tuned over a wide range 2 - 2.68 eV. This article investigates the photoinduced changes (PICs) in the optical properties of As 2 S 3 impregnated in porous glasses (PGs) and the influence of gold nanoparticles (AuNPs). The composite material was obtained via a simple chemical deposition method where As 2 S 3 powder was dissolved in an amine solution and impregnated into PG pieces, with and without the addition of AuNPs. Using Fourier-transform infrared spectroscopy, it was confirmed that, when mixing solutions of As 2 S 3 and AuNPs they interact and form complexes that result in the plasmonic resonance suppression of AuNPs. Upon irradiation using green laser (532 nm) a significant increase in the bandgap energies of the samples was observed. This effect was studied using Raman spectroscopy. Moreover, it was noticed that the change in the bandgap energy depends on the As 2 S 3 concentration and is reduced by the presence of AuNPs. [ABSTRACT FROM AUTHOR]

The thermal stability of porous sol-gel phosphosilicates was studied by comparing the textural features upon calcination between 400 and 550 °C. A significant loss of surface area and pore volume were observed; the first is due to thermal coarsening of the nanoparticles, and the pore volume reduction was ascribed to sintering of the most external nanoparticles producing less void volume. Lanthanum addition was investigated as thermal stabilizer. For the mesoporous phosphosilicate composition, lanthanum addition enhanced the surface area, showing a 45% and 50% improvement with respect to the La-free counterpart; the effect was much less visible for the macroporous composition. [ABSTRACT FROM AUTHOR]

The site selective distribution of pore sizes in pure porous glasses and glasses doped by a luminescent colorant is determined by luminescent spectroscopy, SEM, SAXS and PALS. The potential applications of the studied materials as environmental and biological sensors are outlined. We suggest how luminescent porous glasses doped by complexes of Gd can act as solid scintillators in tracing elementary particles like neutrino. [ABSTRACT FROM AUTHOR]

Post synthetic surface modification is performed in order to increase Al 2 O 3 content on the porous glass surface. The effect of Al 2 O 3 grafting on the properties of porous glasses is further investigated. Textural properties show no changes after surface modification whereas total acid sites density increases. The modified samples exhibit higher hydrothermal stability than zeolites with no changes in textural properties and composition after aqueous phase biomass conversion at 208 °C for 50 h. Evaluation of the prepared materials in catalytic dehydration of sorbitol shows high selectivity towards 1,4-sorbitan as compared to the industrial standard H-ZSM-5 and H-MFI-55. • Al 2 O 3 was enhanced on the porous glass surface by post synthetic surface modification. • Textural properties are preserved whereas surface acid site density increases. • The modified porous glass-based catalyst exhibits high hydrothermal stability. • High selectivity towards 1,4-sorbitan was achieved as compared to industrial zeolites. • The modified porous glass-based catalyst show less degree of coking as compared to zeolites. [ABSTRACT FROM AUTHOR]

Highlights: [•] Porous glasses were produced by leaching of two-phase alkali borosilicate glasses. [•] Porosity was studied by nitrogen adsorption–desorption equilibrium and kinetic methods. [•] The effect of acid and alkaline treatments and chemical composition was revealed. [•] Porous glasses are characterized by polymodal size distribution of micro- and mesopores. [•] The relationship between micro- and mesoporosity can be varied in a wide range. [Copyright &y& Elsevier]

Mesoporous glasses - the leaching products of phase-separated alkali borosilicate glasses - are widely used in fundamental research and practical applications. In this work, the option to control their internal mesopore structure by varying the conditions of microphase separation has been studied. Structure and transport characterization of a family of nanoporous glasses obtained under different conditions has been performed using a combination of several experimental techniques, including gas adsorption, nuclear magnetic resonance cryoporometry and diffusometry. [ABSTRACT FROM AUTHOR]

Porous glass can be widely applied due to favorable chemical and physical properties and the possibility to modify the surface. This work describes the synthesis and optimization of porous glass beads for recovering chiral anesthetics and the separation of the enantiomers. Besides a characterization by nitrogen adsorption and mercury intrusion, the retention behavior of desflurane is investigated in chromatographic experiments with the native support and after immobilization of a chiral selector. [ABSTRACT FROM AUTHOR]

An influence of the size effect on the phase transition temperature in potassium dihydrogen phosphate (KDP)-porous glass nanocomposites was studied in this work. Results of the dielectric measurements in a wide temperature range for KDP crystals embedded in porous glasses are presented. The phase transition temperature shift toward higher temperatures was observed for KDP embedded in porous glasses with the mean value of the pore size of 312 and 160 nm, whereas for smaller pore sizes (71 and 23 nm) the phase transition temperature decreased. The phase transition temperature dependence of the mean values of the pores dimensions of KDP-porous glass nanocomposites is the experimental evidence showing the non-monotonical character of the size effect on the phase transition temperature in ferroelectrics particles. It was found that the dielectric permittivity of KDP embedded into the porous glasses with the mean values of pore sizes of 160 nm and 312 nm practically did not depend on frequency, whereas for KDP embedded into the pores with dimensions of 71 nm and 23 nm a dispersion of the dielectric permittivity is observed in bothpara- and ferro-electric phases. [ABSTRACT FROM AUTHOR]

Abstract: The spectra and kinetics of fluorescence decay of 1,2-benzanthracene (1,2-BA) molecular clusters adsorbed in nanoporous borosilicate glasses were investigated. It has been shown that the type of the decay kinetics of delayed fluorescence is determined by the annihilation of triplet excitons in crystalline and percolation clusters. The influence of an external magnetic field on the annihilation rate constant of triplet excitons in the adsorbed 1,2-BA molecules has been studied. The response of the molecular clusters to the magnetic field strongly depends on temperature, pore size and time scale of the observation. Clusters with the crystal structure dominate in the decay kinetics of triplet–triplet annihilation (TTA) and delayed fluorescence in the initial microsecond period of time after excitation. Amorphous clusters determine the form of decay kinetics of delayed fluorescence in the millisecond range. The increase in the pore size and concentration of the adsorbate lead to the dominance of crystalline components. The results presented here can be used to develop techniques for probing the structure of the adsorbed layer in nanoporous systems examining the effect of an external magnetic field on the annihilation delayed fluorescence (ADF) kinetics. [Copyright &y& Elsevier]

Abstract: Macroporous alkali resistant glass has been developed by making additions of zirconia (ZrO2) and zircon (ZrSiO4) to the sodium borosilicate glass system SiO2–B2O3–Na2O. The glass was made using a traditional high temperature fusion process. Differential thermal analysis (DTA) was carried out to identify the glass transition temperature (T g) and crystallisation temperature (T x). Based on these findings, controlled heat-treatments were implemented to separate the glass into two-phases; a silica-rich phase, and an alkali-rich borate phase. X-ray diffraction (XRD) was used to identify any crystal phases present in the as-quenched and heat-treated glasses. Fourier transform infrared (FTIR) spectroscopy also proved effective in investigating phase separation and crystallisation behaviour. After leaching, a silica-rich skeleton with an interconnected pore structure and a uniform pore distribution was observed. Pore characterisation was carried out using mercury porosimetry. The size and shape of the pores largely depended on the heat-treatment temperature and time. ZrO2/ZrSiO4 additions increased the alkali resistance of the porous glass 3–4 times. [Copyright &y& Elsevier]

Titanium dioxide nanoparticles (NP) and nanofibers (NF) were incorporated from polymeric gels into porous glasses. Two types of glasses A and B with different porosity were chosen for measurements. Optical absorbance and photoluminescence spectra of the samples were measured at the range of 200-1100 nm and 370-800 nm correspondently before and after TiO2 incorporation. The enhancement of TiO2 photoluminescence (PL) and short-wave shift of peaks for samples A and B was found. The obtained results are explained by quantum confinement effects. [ABSTRACT FROM AUTHOR]

Positronium annihilation lifetime spectroscopy (PALS) is an alternative method for the determination of pore sizes and pore size distributions. It is a measuring methodology which shows no limitations in the lower nanometer region and works, besides, without destruction of the sample material. It can be used for the characterization of open and closed pores. Additionally, this technology offers the possibility to obtain pore filling ratios of gases, liquids and solids precisely. Polymorphous medicaments, like acetaminophen, show different crystallization behavior within a pore system, depending on the pore size. This property can be used to control the crystalline state of the medicament and to optimize therefore the pharmaceutical use of the active substance. In this study, acetaminophen (C8H9NO2), also known as Paracetamol, is incorporated into different porous systems. The filling of the pores is realized by an acetaminophen melt at 453 K. The silica membranes are dipped into the melt, subsequently removed and cooled. Information concerning the filling ratio of the pores with the pharmaceutical was received with the help of PALS. The extended Tao--Eldrup model forms the theoretical base, takin [ABSTRACT FROM AUTHOR]

The influence of a hybrid thermal processing on the spinodal decomposition of sodium borosilicate glasses was investigated. The pore diameter of the resulting porous glasses is a function of the parameters of the thermal treatment. One result of this study was the inversion of the phase separation under preservation of the external shape of glass monoliths. Furthermore by using microwaves in addition to thermal radiation it was possible to generate temperature gradients in the samples and so gradients in pore size too. The glass templates were heated with microwaves in a tube furnace consisting of a resonant rectangular waveguide (TE103). Additionally the tube wall was heated by thermal radiation. The heating control was realized by steering the input power and the frequency of a 200 W semiconductor source. The regulation was performed with a HOMER 3-stub tuner, which simultaneously measured the impedance by reflected wave analysis and the actual template temperature with an IR-sensor. Various temperature-time courses of the hybrid furnace led to different pore size gradients. This was discussed by analyzing specific properties like mean pore diameter, surface area and pore volume. Further effects like the pore orientation and properties of the pore walls were determined by scanning electron microscopy and focused ion beam (FIB). [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure and dielectric response of nanocomposite materials on base of porous glasses with average pore diameters of 320, 46 and 7nm with embedding sodium nitrate have been studied by neutron diffraction and dielectric spectroscopy in low and high temperature phases up to melting. In porous glasses with 46 and 7nm pores NaNO3 forms dendrite nanoclusters with "diffraction" sizes of 50(2.5) and 20(2) nm. Decreasing of particle sizes results in decreasing of Tc (temperature of order–disorder orientational transition) and Tmelt and in smearing of structure phase transition. The values of critical exponent β for orientational transition are estimated from temperature dependences of intensities of superstructure elastic peaks for these three types of nanocomposite materials. [Copyright &y& Elsevier]

Abstract: The aim of this study is to compare water vapour sorption isotherms on various mesoporous materials in their pristine state and after silanisation. Commonly the pristine state is regarded as hydrophilic and the silanised one as hydrophobic. Water vapour sorption experiments are discussed for a highly ordered nanoporous aluminium oxide with straight cylindrical channels of ca. 25nm diameter and for various controlled porous glasses (CPGs) with disordered pores in the range of 13nm diameter. The water sorption isotherms exhibit in both cases a hysteresis over the entire humidity range. At higher humidities the pristine materials show capillary condensation whereas for the silanised samples this phase transition does not occur or even a loss of water is recorded as for the silanised Al2O3. Surprisingly, for the silanised Al2O higher water uptake is observed in the low humidity region. Application of the excess surface work (ESW) method delivers a reduced structural component in the long range interaction of the water molecules with a hydrophobic surface. Inverse gas chromatography studies of the silanised CPGs result in an increased short range dispersive part of the surface energy with the increasing degree of silanisation. [Copyright &y& Elsevier]

The photoluminescence of AgBr nanoparticles formed by a two stage liquid-gas microsynthesis technology in two types of porous glass with different sizes of pores was investigated. Polyvinyl alcohol (Polinol) was used as a binder. It has been found that AgBr nanoparticles in the glasses with smaller pores luminesce more intensively, and we attribute this phenomenon to the differences in pore size distributions. The luminescence spectra were shown to have two maxima corresponding to AgBr nanoparticles formed within the nanopores of two different sizes characteristic of each of the matrices. In both cases, the spectra excited by xenon lamp irradiation are more intensive than those stimulated by a 337-nm nitrogen laser. Comparing the maxima shifts in the phosphorescence excitation spectra with ones in phosphorescence spectra we can conclude that the luminescence and phosphorescence centers in AgBr nanoparticles are of identical nature in the matrices of both types. The investigation results fit neatly into the inherently consistent quantum confinement model and are well correlated with the poroscopic spectra of both types of glass. [ABSTRACT FROM AUTHOR]

Abstract: Inverse gas chromatography (IGC) is a modern technique for the characterization of porous materials, which provides thermodynamic parameters of the solids. Porous glass beads, silica gels and ordered mesoporous materials were used as model systems to study correlations between the dispersive part of the surface energy and the surface chemistry of porous materials. The surface chemistry of silica was controlled via thermal treatment and reaction with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) or 3-amino-propyltriethoxysilane (3-APTS). The dependency of the surface energy on the various modifications was investigated in this study. Furthermore, the impact of microstructure on the dispersive surface energy was determined by a comparative study of the ordered mesoporous materials MCM-41, SBA-15 and SBA-16. [Copyright &y& Elsevier]

The dielectric response of K0,26(NH4)0.74H2PO4-SiO2 composite prepared by embedding of corresponded salts into porous SiO2 glass with 320 nm average pore diameter has been studied at the temperature range of 10-300 K. The transition from paraelectric to antiferroelectric (AFE) phase in implanted particles is detected at TN ≈ 45 K. Below ≈ 20 K the specific dispersion of dielectric response indicates a transition into proton glass (PG) state. It was found that the average time of dielectric relaxation follows the empirical Vogel—Fulcher law. Obtained results speak in favor of the coexistence of AFE and PG phases at low temperatures. [ABSTRACT FROM AUTHOR]

Silver-containing nanocomposites were prepared by impregnating Vycor glass (a pore diameter of 4 nm) and synthesized opal matrices (an interstitial void size of 40 nm) with cyclooctadiene complex of silver hexafluoroacetylacetonate (Ag(hfac)COD), a silver precursor, dissolved in supercritical carbon dioxide and were examined by optical absorption spectroscopy, atomic force microscopy, and electron spin-resonance spectroscopy. It was demonstrated that the absorption spectra of Vycor glass and opal matrices impregnated with Ag(hfac)COD molecules and subjected to thermal treatment in air at temperatures above 50°C exhibit plasmon resonances characteristic of Ag nanoparticles at 420–430 nm. The peculiarities of the plasmon resonance band for both types of samples were attributed to the morphology of the pore space in which silver particles are formed. Paramagnetic Cu(hfac)2 molecules (copper hexafluoroacetylacetonate) were used as a spectroscopic probe for estimating the distribution of the precursor in the pores of Vycor glass and opal matrices during supercritical fluid impregnation. [ABSTRACT FROM AUTHOR]

Nowadays a perspective appears of applying porous glasses in microanalytical devices. The opportunity of application of porous glasses as optical sensors has been shown in the present paper. Preliminary results of studying the electroosmotic flows through porous glasses are discussed. [ABSTRACT FROM AUTHOR]

Frequency dependences of imaginary part of the dielectric response ε"(f) of SiO2-NaNO2 nanocomposite, prepared by embedding of sodium nitrite into porous glasses with 7 nm average pore diameter, have been studied within a temperature range of 360-520 K. It has been found that the spectrum S(ω) = ε"( f )/f contains the component ~1/fα, where α is a coefficient indicating the dynamical heterogeneity of dipoles. Peculiarities of the temperature dependence of α are discussed. [ABSTRACT FROM AUTHOR]

We are proposing Rubpy complex incorporated in a number of porous sol-gel thin films as a sensor for oxygen. The principle is based on the following fact: triplet oxygen reacts with the excited states of Rubpy resulting in decay of luminescence of the complex due to triplet quenching. The decrease of fluorescence is proportional to the amount of absorbed oxygen. We discuss here several sol-gel matrices with doped by Ru(bpy)3+2 deposited as thin films on ITO conducting glass. The absorption and emission spectra of the complex, and electrical conductivity of the doped films show how the fluorescence can be excited either by optical or electronic means. The decrease of fluorescence indicates the concentration of oxygen. [ABSTRACT FROM AUTHOR]

Abstract: Porous glasses in shape of beads and flat membranes with controlled mesoporosity in the range between 2 and 20nm were used as model system to study the correlation between the texture properties and the transport characteristics in the primary pore system of catalyst supports. The beads and membranes were distinguished by comparable texture parameters. The tortuosity factors of the pore structure were obtained from measurements of the permeability of nitrogen of the porous glass membranes. The tortuosity factors vary in the range between 1.5 and 40 depending on the pore diameter and the porosity of the membranes. The hydrogenation of benzene over nickel catalysts based on the porous glass beads was used as test reaction. Here, the effective mesopore diffusivities were obtained from the Arrhenius plots. Furthermore, the pore diffusion coefficients of benzene were determined. The values are in the range between 1×10−6 and 2×10−5 cm2 s−1. A systematic correlation between the texture properties (mean pore size) and transport characteristics (pore diffusion coefficient) was observed. [Copyright &y& Elsevier]

Abstract: In this work we present the utilization of the heterometallic alkoxide [FeCl{Ti2(OPr i )9}] as the first sol–gel single-source precursor to achieve nanocomposites made of iron and titanium oxides incorporated into Porous Vycor Glass (PVG). The nanocomposites were prepared by the impregnation of the precursor in a PVG plate followed by hydrolysis reactions. Different samples were obtained by further thermal treatment of the hydrolyzed sample. The nanocomposites were characterized by UV–vis-NIR, Raman and EPR spectroscopies, XRD and TEM. The results indicate that the room-temperature hydrolyzed samples are formed by nanoparticles of FeOOH and brookite-TiO2 embedded on a glassy matrix. After the heat treatment at temperatures above 900 °C, a pseudobrookite Fe2TiO5 was formed. All samples present high transparency and homogeneity. The results showed here indicate that the sol–gel process using the single-source precursor [FeCl{Ti2(OPr i )9}] should be a novel and efficient approach to the preparation of nanometric Fe/Ti oxides incorporated into a glassy matrix. [Copyright &y& Elsevier]

The porous structure of glasses incorporated by ruthenium tris bipyridyl chloride (further Rubpy) and adsorbed by Rubpy is studied by positron annihilation lifetime spectroscopy and liquid nitrogen adsorption method. The first method provides the radius of the pores in the range of 0.6-4 nm and their distribution. The second method provides the radius of the pores in the range of 1-150 nm, their total volumes, size distribution and specific surface area. In the first method both closed and opened pores can be seen when the measurements are made on bulk samples as in this work. When thin films are measured, one has to use a capping material to prevent backscattering. The dimension of the pores can be controlled by the catalyst used for sol-gel formation. When Rubpy is prepared by adding its salt to precursor solution catalyzed by HCl, the pore size increases because of stress exhibited by large molecules. The pore size decreases with adding of Rubpy in precursor solution, catalyzed by HF and HNO3. Glass doped by Rubpy is less sensitive to the type of catalyst, than undoped glasses. A comparative study was performed on undoped glasses prepared by the identical method. We shall discuss the similarities and differences of the two methods. [ABSTRACT FROM AUTHOR]

Periodic mesoporous organosilica (PMO) have been prepared from bis(triethoxysilyl)methane (BTM) and cetyltrimethylammonium chloride (C16TAC). A large range of synthesis conditions (pH, C16TAC/BTM ratio, post-treatment and concentration) were used to study their effects on the structure of the as-prepared meso-structured samples. The sample obtained with the optimised composition presents a 2D-hexagonal structure with a large surface area of about 950m2/g. This material has been pyrolysed under Argon up to 1000°C. Conversion into a silicon oxycarbide glass has been followed by X-ray diffraction. The organised structure can be retained until 800°C. Further characterisations were performed by 29Si MAS NMR, 13C CP MAS NMR and N2 adsorption–desorption experiments to follow the structural changes occurring during the pyrolysis. [Copyright &y& Elsevier]

Porous glasses prepared by the sol–gel technique have a variety of applications when incorporated by photonic materials: tunable lasers, sensors, luminescence solar concentrators, semiconductor quantum dots, biological markers. The known methods of pore size determinations, the nitrogen adsorption and mercury porosimetry allow to determine the sizes of open pores. Positron annihilation lifetime spectroscopy (PALS) allows to determine pore sizes also of closed pores. As an example we have performed measurements of non-doped zirconia–silica–polyurethane (ZSUR) ormocer glasses and the same glasses doped with lead sulfide quantum dots. The pore radii range between 0.25–0.38 nm, total surface area 15.5–23.8 m2/g. [Copyright &y& Elsevier]