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Positron annihilation lifetime spectroscopy was used to examine grown-in defects in Cd1–x Zn x Te mixed crystals as a function of Zn content (x = 0, 0.07, 0.11, 0.49, 0.9, 0.95, 1) and measuring temperature. All samples were prepared using the high-pressure modified vertical Bridgman–Stockbarger method. The crystal structure and material phase were characterized by X-ray diffraction. The positron lifetime spectra reveal the presence of both open volumes and shallow traps regardless of the sample composition. In particular, both average and bulk lifetimes are found to be much higher in ternary alloys (CdZnTe) than those in binary systems (CdTe and ZnTe). This originates from distinct differences in average electron densities and the nature of open-volume defects between binary and ternary samples. Competition in positron trapping with increasing Zn content is observed between defects characteristic for both structural systems. Moreover, a clear correlation is shown between defects and the lattice thermal conductivity of studied samples. The applicability of the positron trapping model to CdTe-based materials is discussed.

Hypothesis The negative pressure in liquids under the concave meniscus of nanometer size can be observed experimentally. This allows verification of the predictions of the macroscopic Young-Laplace law, which has so far been performed only on the basis of theoretical calculations. The deviation of the negative pressure from the Young-Laplace law allows to get information about the structure of the porous matrix. Experiments The properties of n-heptane confined in nanometer-sized spaces are monitored in situ due to the particular ability of positronium to form subnanometer bubbles in liquids. Positron annihilation lifetime spectroscopy allows to detect their sizes, which in turn are used to determine surface tension and negative pressure of the investigated liquid. These results are obtained by means of an improved quantum-mechanical model approximating the o-Ps bubble with a 1.3 eV finite potential well. Findings The dependence of the negative pressure on the curvature of the concave meniscus is found, which follows the Young-Laplace law with a good accuracy for model cylindrical pores. The differences between the pressure in the liquid confined in pores of various sizes and shapes in different materials allow inference about several phenomena (e.g. pore blocking in materials with a complex pore structure or swelling of the polymer).

The paper presents a novel simple and cost-effective approach to preparation of mixed-valence mesoporous manganese oxide in the form of easy to handle spheres. The synthesis relies on swelling of porous polymer templates (i.e. three selected resins Amberlite® XAD7 HP, XAD4 and XAD16) in a saturated Mn(NO3)2 solution and subsequent removal of the template via calcination in air. The products are porous with the specific surface area ( S B E T ) up to 100 m2 g−1. The detailed characteristic of the materials, thermogravimetric insight into its calcination in air, and the influence of porous polymer (template) on MnOx structure is provided. The final product can be of great significance for electrochemistry, catalysis and is of some importance to the environment protection.

The sorption of n-heptane in the SBA-3 silica was investigated using positron annihilation lifetime spectroscopy (PALS). The PALS technique allows to study in situ evolution of pore filling by the n-alkane. In the dry SBA-3, the free volumes attributed to the silica skeleton, micropores, mesopores as well as intergranular spaces can be distinguished by PALS as various ortho-positronium components. The liquid n-heptane appears as an additional component, which allows to monitor adsorption and desorption using the ortho-positronium parameters. Filling the SBA-3 silica with n-heptane leads to the rapid, already at p/p0 = 0.08, disappearance of the pore-related components. Simultaneously, a large increase in the intensity of the components attributed to liquid n-heptane is observed. The adsorption proceeds slightly faster than the desorption, which is most likely the consequence of the difference in the alkane–alkane and alkane-silica interaction forces. The pore size distributions calculated for n-heptane and water from the PALS results clearly indicate that the mechanism of sorption is different for both liquids. This can result from the different strength of the interactions between molecules of each liquid and between the liquid and the atoms of pore walls.

Nickel catalysts supported on silica microspheres were prepared by the application of porous resin beads (Amberlite XAD7HP) as hard template using different order of nickel nitrate and tetraethoxysilane (TEOS) introduction. Large nickel oxide nanoparticles distributed over silica microspheres were formed when nickel precursor was introduced directly to the polymer template prior to the silica framework development or added into the silica-polymer composites. On the other hand, an impregnation of as-prepared silica microspheres after template removal led to the formation of small nickel oxide nanoparticles. The catalysts showed hierarchical pore structure. Low-temperature nitrogen adsorption/desorption and photoacoustic Fourier-transform infrared spectroscopy studies revealed slight changes of porosity and surface properties of catalysts affected by the synthesis methods. X-ray diffraction, scanning and transmission electron microscopy, temperature-programmed reduction and hydrogen desorption studies were used for determination of the properties of metallic nickel nanoparticles. It was stated that the activity and selectivity of catalysts in the CO2 methanation reaction was related to the active surface area and the size of nickel nanoparticles. An increase in CO2 conversion and selectivity to methane at low temperatures (220–350 °C) with an increase in active surface area and decrease in nickel crystallite size was observed.

The article presents a cost-effective approach to the preparation of polymer-hybrid silica composites in the form of spherical beads, a micrometer in size, which are easy to handle and comp...

This paper presents novel types of polysilsesquioxane (PSQ)–polymer composites formed through polycondensation of ethyltriethoxysilane in the spatially limited system of polymer pores in the presence of acid or base catalysts vapors. In addition, it gives an insight into the architecture of the PSQ network. It is shown that PSQ formed under acidic conditions is mainly composed of long ladder-like structures, whereas small three and four-membered rings are dominating structural units in the base set PSQ. Theoretical calculations extend the common interpretation of the 29 Si NMR spectra according to which signals at ca. −47, −55, and −65 ppm can be simply attributed to T 1 , T 2 , and T 3 Si atoms, respectively. Moreover, they indicate that T 1 and T 0 29 Si NMR signals should be easily distinguishable from T 2 , and T 3 (and among each other), since T 0 is placed upfield (−31.5 ppm) as compared to the other mentioned 29 Si signals.

The article demonstrates the series of silicas produced from various alkoxysilanes introduced into the Amberlite® XAD7HP and lyophilized agar, whose transformation took place in the presence of ammonia vapors as catalyst. The silicas have been investigated by the means of the up-to-date analytical methods for the full characterisation of produced solids including positronium annihilation lifetime spectroscopy. The morphology of the silica is the result of the specific conditions applied for precursors transformation. Usage of lyophilized agar as a template for the vapor-phase method does not lead to creation of highly porous silica. The same applies to SiO2 materials produced without any template, with one except for tetrapropoxysilane. On the contrary Amberlite® XAD7HP is a very effective template. This polymer used as a template allows to obtain porous silica (specific surface area > 300 m2 g−1) in a form of microspheres from each of the employed precursors.

Transport of fluids through channels and cavities of nano/mesoporous materials is of paramount importance in various fields of science and industry. The transport properties can be well derived from the adsorption–desorption behavior of fluids. Positron annihilation lifetime spectroscopy (PALS) allows probing adsorption–desorption of water from 2D mesopores of SBA-3. In situ study of the size of evolving water-free volumes during successive stages of adsorption and desorption is a sensitive way to elucidate the course of pore filling and emptying. The changes of positron annihilation parameters indicate that adsorption of water is mediated through the formation of isles on the surface of the pore walls, and these, in turn, develop into water plugs. Subsequently, these plugs grow and consecutively join together when the distance between them decreases to ca. 1 nm until the complete capillary condensation occurs. Akin to adsorption, desorption of water from the pores involves the formation of cavities cappe...

The purpose of this study was to investigate the thermal properties of polymeric microspheres and their modified with drug molecules and silica gel counterparts under oxidative atmosphere. Permanently porous polymeric microspheres of poly(TRIM) (trimethylolpropane trimethacrylate) and poly(HEMA-co-TRIM) (2-hydroxyethyl methacrylate) were synthesized via the suspension-emulsion polymerization method. The polymer-sodium ibuprofen (IBS) solid dispersions were prepared by the solvent diffusion method. The ternary polymer-sodium ibuprofen-silica gel composites were obtained by hydrolysis and condensation of silica precursor (tetraethoxysilane, TEOS) introduced into the solid dispersions. The acidic and basic environments of TEOS gellation were used, so the acid (A) and base (B) sets of ternary composites were produced. The conducted TG/DSC/FTIR analyses reveal that thermal decomposition of pure polymers starts at about 240 °C with degradation of methacrylate linear units in accordance with the depolymerization mechanism which is accompanied by the oxidation process of methacrylate ester bonds. The next maxima of degradation of pure organic matrices are observed at about 360 °C, 430 °C and 510 °C and are connected with oxidation processes. The thermal stability of solid dispersions of the drug within polymeric matrices as well as ternary composites is higher at about 90 °C in comparison with pure organic matrices. Drug molecules and silica spices act as a shield preserving both the transfer of air inside the structure of the studied materials and the evaporation of gases produced as a result of thermal decomposition of the organic phase.

The porous structure of polymer-silica composites, based on three polymer templates, which differ in a porosity and hydrophobicity, was examined using positron annihilation lifetime spectroscopy. Additionally, the investigation of silicas obtained after removal of polymers during calcination of composite materials, was performed. In composites based on hydrophobic polymers, silica condensates only in larger free volumes, while SiO2 deeply penetrates spaces between polymer chains, when the template is polar. Moreover, the structure of the silica gel, obtained after polymer removal, depends on chemical character of the template, rather than its porosity.

The dynamics of n-heptane adsorption and desorption on two silicas (Si-A and SBA-15) with different porosity was studied using positron annihilation lifetime spectroscopy (PALS). Simplified method of spectra analysis consisting in the summation of counts in the long-lived part of PALS spectra was used. It allowed to observe changes occurring in the minute time scale. The dependence of the number of counts on time could be fairly well approximated by exponential functions. It was found that the time required for reaching equilibrium in long cylindrical pores is up to ten times longer than in bell-mouthed interconnected ones. The longest time constants (ca. 5 min in Si-A and ca. 60 min in SBA-15) were observed for desorption in both samples.

Highly porous (SBET > 160 m2/g) cerium oxide in the form of easy to handle microspheres and particles of micrometric size was produced by the low temperature (300 °C) calcination of Amberlite® XAD7HP microspheres saturated with cerium nitrate solution. The presented synthesis relies on both swelling ability and thermal stability of the polymer template. The final cerium oxide is characterized by SEM, TEM, XRD, XPS and the low temperature N2 sorption method. Additionally, the effect of temperature on the polymer microspheres saturated with cerium nitrate solution was assessed in synthetic air, in conditions resembling the calcination process in the furnace, by means of TG with the simultaneous QMS analysis of the gases evolved during their degradation and also of DSC analysis.

The adsorption and desorption of n-heptane on the mesoporous polymer resin Amberlite XAD4 were investigated in situ by positron annihilation lifetime spectroscopy (PALS). This technique allows the monitoring of porosity and subnanometer free volume changes as well as the amount of liquid adsorbate captured within an investigated sorbent, without causing any interference with the course of adsorption/desorption. In consequence, the conducted studies provide microscale insight into the sorption processes of n-heptane (which is a significant component of volatile organic compounds - VOCs) on the polymeric material. The total pore volume decreases parabolically with n-heptane pressure until it reaches zero just below the saturated vapor pressure. Simultaneously, the average pore size increases linearly until it has approximately doubled. However, much faster rates of change in both these parameters occur at relative pressures below 0.05. The PALS results can be properly explained only if the swelling of the polymer skeleton is taken into account during the alkane adsorption process. This is confirmed by long-term pumping, which was required to achieve stabilization of PAL spectra during the final phase of desorption. In addition, the evolution of subnanometer free volumes (located between polymer chains and formed in liquid n-heptane) support this interpretation of the results.

The present study concerns the preparation of ternary composites via the in situ encapsulation of solid dispersion of diclofenac sodium within the acrylic polymer beads. The encapsulating species were produced through the hydrolysis and condensation of the silica precursors (tetraethoxysilane or ethyltriethoxysilane) introduced into the solid dispersion. The transformation of precursors occurred in the vapor phase of ammonia. A great advantage of the presented vapor-phase method is preventing the desorption of the highly soluble drug during gelation of silica precursors, which stands in contrast to the conventional sol-gel processes occurring in the solution. The conducted studies, involving the low temperature N2 sorption together with spectroscopic techniques, provide insight into the structural differences of drug loaded particles. They reveal that the formation of silica gel accompanies the conversion of the drug into its amorphous form. Finally, the desorption profiles of diclofenac sodium demonstrate that the deposition of silica gel successfully diminishes the degree of the initial drug desorption while significantly modifying its release rate.

The research describes systematic approach to the novel synthesis and formation of a potential organic-inorganic drug carriers. The poly(trimethylolpropane trimethacrylate) and polymer-silica composites based on SBA-3 or SBA-15 mesoporous silica were fabricated by the suspension-emulsion polymerization method in the form of small micrometric porous beads (specific surface area approx. 500 m2/g). The type of organic templates filling silica pores has proved to be crucial in the synthesis of the composites. The introduction of diclofenac sodium via solvent diffusion method into the polymer and composites resulted in the solid drug dispersions. The composites have greater effectiveness in the drug desorption (90% of the release) in comparison with the pure polymer (20% of the release after 7 h). Both, however, suffer from the burst effect. This downside can be overcome by functionalization of the solid drug dispersions with (3-aminopropyl)triethoxysilane. The functionalized solid drug dispersions do not desorb the diclofenac sodium in an acidic medium (the desorption rate is less than 6% during 2 h contact), which makes them attractive for oral multiparticulate formulations of modified release. The presented solids were characterized with modern analytical methods and the relation between the material structure and desorption rate were discussed.

Tetrabutoxysilane (TBOS) transition introduced into the preformed porous polymer was found as an effective method in the preparation of highly porous silica adsorbents. The swelling of the acrylic polymer XAD7HP in TBOS causes the total infiltration of polymer beads by the silica precursor. Transformation of TBOS in aqueous solution at presence of the surfactant (hexadecyltrimethylammonium bromide, CTAB) produces two composite phases: silica-polymer beads and fine silica-CTAB particles. After their calcination, two pure silica phases exhibiting extremely high porosity were obtained. The paper presents the structural properties of the composites and silica materials. All materials were characterized by scanning and transmission electron microscopy (SEM and TEM), the low temperature nitrogen adsorption, X-ray diffraction (XRD) and 29Si NMR spectroscopy.

This study describes a newly synthesized crosslinked polymer poly(TRIM) (trimethylolpropane trimethacrylate, TRIM) and copolymers poly(HEMA-co-TRIM) (2-hydroxyethyl methacrylate, HEMA) as well as polymer–drug conjugates based on them. The resins were produced in the form of permanently porous beads via suspension-emulsion polymerization. The set of polymer–drug conjugates was prepared by loading ibuprofen sodium salt (IBNa) into polymer matrices by their swelling. Our study involves the characterization of polymers and polymer–drug conjugates, studies on the swelling of resins in the selected solvents as well as characteristics of drug release from conjugates. The conducted analyses reveal that the internal structure, total porosity and swelling characteristics of resins strongly depend on the presence of 2-hydroxyethyl methacrylate. The release profiles of ibuprofen sodium salt from the polymer−drug conjugates demonstrate that there are differences in the rate and efficiency of drug desorption from conjugates.

Highly porous polymer–silica nanocomposites and silica gels were prepared using cross-linked copolymer resins of various chemical character as organic templates. Tetraethyl orthosilicate (TEOS) was successfully introduced into the template by the swelling of the preformed polymer particles. The silica source introduced into the resins was transferred into the silica gel by the means of the sol–gel method. After the organic component had been removed during a high temperature treatment of the polymer–silica nanocomposites, the spherically shaped silica particles were obtained. The pore structure of nanocomposites and calcined pellets was investigated through the conventional adsorption method so as to study the evolution of the porosity in the polymer templates of various character. The analysis of the porosity parameters characterizing the investigated materials within micro- and mesopores indicates a varying extent of the penetration of silica component into polymer templates, depending on their geometrical structure and hydrophobicity.

The study describes the thermal properties of a series of porous microspheres synthesized with 2-hydroxyethyl methacrylate (HEMA) and trimethylolpropane trimethacrylate (TRIM), their conjugates with ibuprofen sodium salt (IBS) and finally the polymer-drug-silica composites based on them. The poly(HEMA-co-TRIM) and pure poly(TRIM) permanently porous microspheres were synthesized via suspension-emulsion polymerization. The polymer-drug conjugates were produced by introduction of the IBS into the polymer beads by their swelling. The polymer–drug–silica composites were synthesized by the hydrolysis and condensation of silica precursor (tetraethoxysilane, TEOS) introduced into the conjugates. The transformation of TEOS was performed in the vapor phase of the acidic (A) or basic (B) catalyst. The conducted TG/FTIR/MS studies reveal that the initial decomposition temperature for organic matrices was dependent on the amount of HEMA monomer. Moreover, the thermal properties of the composites differ significantly from the pure polymer matrices. After the introduction of the drug and silica gel into the polymeric beads, the thermal stability of the composite materials was enhanced in comparison with the parent matrices, even at about 40 °C. This result was attributed to the shielding effect of IBS molecules and silica particles. FTIR and QMS analysis of the gases evolved during degradation indicates that the depolymerization, α- and β-hydrogen bond scission reactions went probably in parallel during the samples’ thermal degradation.

Distinction between molecular constitutions of differently made silica gels succeeded only recently. This paper seeks relationship between the different molecular structures of acid and base set gels and their morphology and pore structure. Gels were fabricated from both tetraethyl orthosilicate, TEOS, in organic solvent environment and from an economically more desirable, commercial, aqueous Na-silicate solution. When their gelling was performed in the pores of an organic resin, Amberlite, further molecular differences were observed, along with associated morphology and porosity differences. We present here unprecedented atomically resolved TEM pictures that visually prove that the molecular structures of gels deduced from their 29 Si NMR and Raman spectra are real, which could also be demonstrated by computer models. Copyright © 2015

The present paper describes the preparation of a new type of ternary composite where pure silica gel or polysilsesquioxane was deposited on a polymer carrier loaded with a high dose of diclofenac sodium. The silica species were prepared by in situ gelation of the precursors, tetraethoxysilane (TEOS) or ethyltriethoxysilane (ETEOS), in the presence of an acidic catalyst in the vapour phase. The conducted studies (low temperature nitrogen sorption, XRD, SEM, EDX) reveal that the introduction of drug molecules, as well as silica species, significantly changes the internal structure of the host material. The total porosity of the ternary composites strongly depends on the type of applied silica precursor. Additionally, it is shown that the exposure of the TEOS-saturated or ETEOS-saturated solid dispersion of drug within the polymer to acid vapors is sufficient to cause the irreversible transformation of diclofenac sodium into sodium chloride and a derivative of phenylacetic acid. Furthermore, TEOS prevents the transformation of the drug into its acidic form more effectively than the ETEOS precursor. Finally, the in vitro release of the drug is demonstrated, which clearly indicates that after the embedding both of the silica species, the rate of drug release is modified and the degree of initial drug delivery is successfully diminished. The obtained data are analyzed using different kinetics models to give insight into the possibility of prolonged release of a drug and the probable mechanism of drug release from the investigated samples.

This study presents an interesting and promising strategy for producing an oral multiparticulate formulation of the sustained-release of diclofenac sodium (DS) consisting of subunits closed inside hard gelatin capsules (each capsule contains ~50mg of diclofenac sodium). The subunits in the form of beads were produced through the encapsulation of diclofenac sodium dispersed within a nondisintegrating polymer carrier by a silica gel functionalized with the 3-aminopropyl groups. The hybrid silica gel, which plays the role of enteric coating, was fabricated by the gelation of the liquid silica precursors mixture (i.e. tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES)) in the vapor phase of ammonia. The conducted studies reveal that the introduction of the hybrid silica gel into the solid DS dispersion facilitates prolonged release in the neutral environment of the intestine. Since the ability of the multiparticulate formulation to control the release of the drug depends on the properties of its subunits, studies involving the low temperature N2 sorption, DSC analysis together with spectroscopic techniques (XRD, SEM, 29Si MAS NMR) were conducted.

The study discusses the synthesis of polymer-silica composites comprising water soluble drug (ibuprofen sodium, IBS). The polymers selected for this study were poly(TRIM) and poly(HEMA-co-TRIM) produced in the form of permanently porous beads via the suspension-emulsion polymerization method. The acid and base set ternary composites were prepared by the saturation of the solid dispersions of drug (poly(TRIM)-IBS and/or poly(HEMA-co-TRIM)-IBS) with TEOS, and followed by their exposition to the vapour mixture of water and ammonia, or water and hydrochloric acid, at autogenous pressure. The conducted analyses reveal that the internal structure and total porosity of the resulting composites strongly depend on the catalyst which was used for silica precursor gelation. The parameters characterizing the porosity of both of the acid set composites are much lower than the parameters of the base set composites. Moreover, the basic catalyst supplied in the vapour phase does not affect the ibuprofen sodium molecules, whereas the acid one causes transformation of the ibuprofen sodium into the sodium chloride and a derivative of propanoic acid, which is poorly water soluble. The release profiles of ibuprofen sodium from composites demonstrate that there are differences in the rate and efficiency of drug desorption from them. They are mainly affected by the chemical character of the polymeric carrier but are also associated with the restricted swelling of the composites in the buffer solution after precipitation of silica gel.

This study describes a novel approach to the synthesis of polymer-drug-silica nanocomposites via encapsulation/isolation of drug molecules, introduced into the polymer matrix by the silica gel. For the first time, tetraethoxysilane (TEOS) gelation in the vapor phase of the acidic catalyst is presented as an efficient method to enter the silica gel nanoparticles into the polymer-aspirin conjugate. The conducted studies reveal that the internal structure of the polymer carrier is significantly reorganized after the embedding of aspirin molecules and the silica gel. The total porosity of the polymer-drug-silica nanocomposites and the molecular structure of the silica gel embedded in the system strongly depend on the conditions of the silica source transformation. Additionally, the release of the drug was fine-tuned by adapting the conditions of hydrolysis and condensation of the silica gel precursor. Finally, to prove the usefulness of the proposed synthesis, the controlled release of aspirin from the polymer-drug-silica nanocomposites is demonstrated.

The present article describes the synthesis of a novel type of a composite which has potential application in controlled drug release. The system comprises of the porous polymer matrix with embedded active agent and the silica gel. The silica is introduced into the polymer beads with encapsulated drug by swelling in tetraethoxysilane as the silica precursor. After the condensation of the silica source, the silica membrane is formed inside the core of pores. Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX) allow for the assumption that the examined polymer–drug–silica composite is rich in silica, homogeneously dispersed within the polymer matrix. What is more, the introduction of the siliceous membrane significantly changes the porosity, which affects drug diffusion. The purpose of this study was to investigate the drug release process from the pure polymer and polymer–silica composite with regard to their structural parameters. The drug desorption was examined in a NaCl solution and in a simulated body fluid (SBF) at different temperatures.

The development and testing of positron annihilation lifetime spectroscopy (PALS) – the method used for the characterization of a model pore system, is presented. The PALS technique is used to study in situ the porosity changes during n-heptane adsorption and desorption in the periodic mesoporous silica SBA-15. The results are analyzed in terms of PALS spectra as well as nitrogen and n-heptane conventional adsorption/desorption experiment. The PALS results allow to monitor character of a n-heptane multilayer at p/p0 < 0.45. The multilayer made of “isles” is formed during adsorption, while a much smoother layer of adsorbed n-heptane remains during desorption. In the pressure range where n-heptane capillary condensation occur (p/p0 = 0.45–0.55) a hysteresis of the ortho-positronium intensities is observed. A similar phenomenon is commonly registered during the nitrogen conventional adsorption and desorption isotherm for mesoporous solids. Above p/p0 = 0.55, when the regular pores in the SBA-15 are filled with n-heptane, a small amount of pores blocked by condensate plugs remains empty.

The condensation and evaporation of n-heptane at 298 K in mesopores of silica material obtained by the polymer templating method have been studied by PALS measurements. It is demonstrated that the ortho-positronium lifetimes and intensities provide valuable information on pore filling and emptying which are not accessible from a conventional adsorption experiment. The results confirm the specific adsorption mechanism of n-heptane in pores with narrow openings (ink-bottle shape) which is different from that known for other pore geometries. The results from PALS experiment are compared to those derived from the conventional n-heptane and nitrogen adsorption data.

Polymer (XAD7HP)/Ti4+ nanocomposites were prepared through the swelling of polymer in titanium (IV) ethoxide as a titanium dioxide precursor. The nanocomposite beads exhibit relatively high porosity different than the porosity of the initial polymer. Thermal treatment of composite particles up to 200 °C in vacuum causes the change of their internal structure. At higher temperature, the components of composite become more tightly packed. Calcination at 600 °C and total removal of polymer produce spherically shaped TiO2 condensed phase as determined by XRD. Thermally treated composites show the substantial change of pore dimensions within micro- and mesopores. The presence of micropores and their transformation during thermal processing was studied successfully by positron annihilation lifetime spectroscopy (PALS). The results derived from PALS experiment were compared with those obtaining from low-temperature nitrogen adsorption data.

Temperature dependence of ortho-positronium lifetime in the mesopores of solids provides information about the electron density of the pore walls. This feature was used to determine the difference in electron density between the porous polymer XAD7HP and two kinds of porous polymer-silica composites prepared by swelling XAD7HP in a silica source and condensing it in both basic and acidic solutions. A higher amount of silica on the pore surface was found for the material prepared in basic conditions as compared to the one synthesized in the acidic solution. Taking into account the results of SEM, nitrogen sorption and 29Si MAS NMR, one can say that in acidic conditions silica penetrates the polymer micropores and condensates mostly between the polymer chains, while in basic conditions the penetration inside the pores is more shallow.

Many papers are devoted to interpretation of adsorption of gases on solids. A complete understanding of the mechanism of pore filling and emptying by adsorbate molecules is a fundamental meaning for obtaining the accurate parameters characterizing the pore structure. The present article deals with application of positron annihilation lifetime spectroscopy (PALS) for determination of free volumes dimensions in pores upon adsorption process. On the basis of PALS spectra a comprehensive insight into adsorption mechanism of n -heptane in silica gel is presented.

The molecular structures of various silica gels are compared using 29Si NMR and laser Raman spectroscopy. When gels are deposited onto a porous organic resin from tetra ethyl orthosilicate, TEOS, at acidic or basic conditions, their appearance and physical properties show dramatic differences. It is demonstrated that these differences are associated with distinct Q3/Q4 Si–O–Si connectivity ratios in the two materials although both are mainly constructed from 3 and 5 member siloxane rings (3R and 5R). Comparative NMR and Raman spectroscopic experiments on these gels and related model calculations indicate that Raman is disproportionally more sensitive for Q1 and Q2 connectivities than for Q3 and Q4. This is an important new aspect to consider in the Raman identification of Qn connectivities in amorphous silicates. It is also shown that the molecular structures of TEOS based gels differ when made in the presence or absence of the porous organic substrate. Hence the substrate seems to exert structure directi...

The simple and effective approach for preparation of highly porous poly(TRIM)/MCM-41 composite material has been presented. The structural properties of the spherically shaped particles of the composite were investigated by positron annihilation lifetime spectroscopy (PALS) and low temperature adsorption of nitrogen. The parameters characterizing the porosity of investigated materials derived from two different techniques have been compared. PALS provides a convenient tool for characterization of polymer-based composite materials.

The mechanism of n -heptane evaporation from mesoporous MCM-41 silica was investigated by positron annihilation lifetime spectroscopy (PALS). Experiments were performed in situ during desorption of hydrocarbon under stepwise lowered pressure. Desorption is a quasicontinuous process that corresponds to emptying various types of free volumes in the silica/ n -heptane system, including mesopores. Insight into the kinetics of desorption was derived from the changes of PALS spectra associated with succeeding stages of pore emptying. For the investigated system emptying of pores and formation of bubbles in the n -heptane condensate present in regular pores were found to take place at various bulk saturating vapour pressure of the fluid.

The synthesis of mesoporous MCM-41 silica materials was investigated at various conditions. A series of ordered mesopores MCM-41 silica materials was synthesized in concentrated reaction mixtures. The influence of water concentration at the constant ratio of the remaining reagents on the morphology and structural parameters of MCM-41 was studied. Hexadecyltrimethylammonium bromide CTAB was used as a structure-directing agent. The pore size, the wall thickness and cylindrical pores array were characterized by powder X-ray diffraction and nitrogen adsorption. The presented results show that in concentrated reaction mixtures, the pore size and the thickness of the pore walls remain practically constant. However, the dimensions of silica particles depend strongly on the water concentration. A high regularity of pore structure for large MCM-41 particles synthesized in concentrated solution was supported by independent AFM technique.

Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal surfactant degradation outside and inside pores were identified at various temperatures using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and 13C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41 synthesis on molecular level.

FT-IR spectroscopy with photoacoustic detector has been applied to investigate organic template transformations during thermal treatment of silica and silica-alumina MCM-41 molecular sieve. The role of surfactant degradation and type of organic deposits on silica surface remaining after surfactant elimination depends on the presence of alumina in MCM-41 pore network.

Positron Annihilation Lifetime Spectroscopy (PALS) results for ordered mesoporous silica sieves (MCM-41 and its fibre form MSF) are used to verify predictions of the Extended Tao-Eldrup (ETE) model. Cylindrical pores (R ∼ 1–2 nm) in these materials have well defined geometry and size, thus the structure of MCM-41 and MSF reproduces the model assumptions. Positron lifetimes were measured in the range 100-500K. In MCM-41, due to low intensity of pore related ortho-positronium component, it is difficult to determine the component's lifetime precisely. Accuracy of the lifetime fitting is better for MSF, where temperature dependence is in a good agreement with the ETE model results. For comparison, the ETE model predictions fit the lifetime of the pore related component in the Vycor sample only for T > 200 K. Below this value the lifetime exceeds the model predictions by over 30%. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal evacuation of template surfactant from MCM-41 in hydrogen atmosphere was investigated. Micelle templated silica was prepared using hexadecyltrimethylammonium bromide. The mechanism of template removal appears to be completely different in hydrogen as compared to calcination in air. It seems that moderate heating of as-synthesized MCM-41 (up to about 250 °C) in hydrogen stream for about 15 h is effective and simple method of template removal leaving no pure carbon residues on silica surface. Adsorption properties of partially evacuated MCM-41 samples were tested using gas chromatography. Products of template degradation were analyzed using GC–MS technique. The main products of template degradation at 250 °C in hydrogen flow are hexadecene and hexadecane- N , N -dimethylamine. Concentration of surface silanols for MCM-41 calcined and thermally treated in hydrogen flow was investigated by NMR technique.

Mesoporous materials MCM-41 with the hexagonal arrangement of pores were obtained using dodecyltrimethylammonium bromide and octadecyltrimethylammonium bromide as templating surfactants. Adsorption of toluene and propan-1-ol on the as-synthesized MCM-41 silica samples was investigated using the TG-DTG, DTA and DSC techniques. The sorption mechanism of used adsorptives is discussed in terms of hydrophobicity of pore interior filled with template as well as pore dimensions.

Mesoporous silica material of MCM-41 type was synthesized by co-condensation of highly concentrated octyltriethoxysilane (OTEOS), octadecyltriethoxysilane (ODTEOS) and tetraethoxysilane (TEOS). The obtained hybrid materials were characterized using XRD, TG-DSC and low temperature adsorption/desorption of nitrogen. It was shown that the applied method of synthesis allows to obtain silica of MCM-41 type with a high degree of hydrocarbon saturation.

The temperature resistance of chemically bonded phases on commercial silica gel. LiChrosorb RP 2, RP 8, RP 18 and unmodified Si 60 were tested at different temperatures by photoacoustic FT-IR spectroscopy. The surface characteristics and possible degradation of hydrocarbon phase at higher temperatures were investigated by means of FT-IR/PAS technique. For a series of investigated samples heated up to 423K, the FT-IR/PAS spectra are similar to those for initial silica samples. The most characteristic band for alkyl modified silica gel, i.e., RP 2, RP 8, and RP 18 was observed between 3200 cm-1 to 2800 cm-1 corresponding to various hydrocarbon species. The bands at 3745 cm-1, 3650 cm-1, and 3430 cm-1 observed in the photoacoustic FT-IR spectra may be ascribed to isolated silanol groups (Si-OH), geminal groups (si-(OH) 2 ) and hydrogen-bonded Si-OH groups, respectively. For all samples the intensity of the broad band in the region 3800 cm-1 to 3200 cm-1 decreases with the increasing temperature. The additional peak at 3745 cm-1 for chemically bonded long hydrocarbon chain, i.e., C18 and C8 after thermal treatment at 573 K is observed.

Using a new synthesis technique, in which mesoporous Amberlite XAD7HP resin beads swollen with TEOS were exposed to vapors of either (H2O+HCl) or (H2O+NH3), we obtained smooth, porous, mechanically stable silica gel spheres after burning out the sacrificial organic template. Combined N2 sorption, SEM, TEM, (29)Si NMR, and Raman measurements were used to characterize the physical properties and molecular structures of the intermediate and final gels. Our atomically resolved TEM pictures provide the first visual demonstration of the presence of 3 to 6 member siloxane rings predicted by our Raman studies and other indirect methods. It is demonstrated that the physical appearance, morphology and porosity of the acid and base set gels are different from each other and also from those silica gels that were earlier polymerized from TEOS or Na-silicate saturated Amberlite XAD7HP with aqueous NH4OH or HCl solutions in liquid phase. We show that the different physical properties of the vapor-phase set gels are associated with different gelling rates at acidic and basic conditions, which generates molecular differences both in the intermediate and the final products.

The swelling of poly(TRIM) spherical particles in TEOS is assessed as a potential way for obtaining polymer–silica nanocomposite materials. Silica deposition was achieved by simply stirring of swollen polymer particles in acidic hydrochloric-water solution. This procedure leads to spherical composite particles with dispersed silica gel within the polymer matrix. The resulting material exhibits the same morphology as the initial polymer. Nanocomposite particles are silica rich (about 17 wt.%). Characterization of the nanocomposites was performed using scanning electron microscopy, FT-IR spectroscopy, 29Si CP MAS NMR spectroscopy and thermogravimetry. Moreover, the use of positron annihilation lifetime spectroscopy PALS to characterize the structural properties of the nanocomposites is presented. This technique gave more realistic pieces of information about the pore structure of the investigated samples in contrast to nitrogen adsorption studies.

Monodisperse polymer/silica composite material with a polymer as the core and hydrophilic silica gel as the shell was prepared by a two-stage procedure. In the first stage, the swelling of Amberlite XAD7HP particles in tetraethoxysilane (TEOS) was performed. Subsequently a portion of the XAD7HP particles impregnated with TEOS were transferred to acidic aqueous solution to facilitate a sol-gel process of the silica precursor. This procedure is assessed as a potential route to a composite material with a core-shell morphology. Scanning electron microscopy and (29)Si MAS NMR indicated the formation of silica microfibers on polymer beads. The silica microfibers were anchored in the polymer matrix. In consequence, the silica shell exhibited relatively high mechanical stability. The swelling of the polymer and the formation of the silica phase substantially changed the porosity of the initial polymer material. The final composite surprisingly exhibited very homogeneous porosity. The textural characteristics of the investigated materials were defined by nitrogen adsorption-desorption at 77K.