Chemistry

a b s t r a c t SBA-15 ordered mesoporous material is an excellent carrier material for the poorly soluble drug molecule itraconazole. Immediate itraconazole release is obtained upon contacting the formulation with simulated biological fluid. The stability of the formulation upon storage was investigated. Samples were stored for 3, 6 and 12 months at 4 and 25°C and relative humidity of 0%, 52% and 97%. The original release behavior was maintained upon storage in dry conditions. Surprisingly, long-term storage at a relative humidity of 52% or 97% had a beneficial effect on the release. The surface chemical modification of the formulation upon storage in humid atmosphere was investigated using nitrogen adsorption, 29 Si MAS NMR, TGA-MS, XPS and DSC. Itraconazole phase analysis using DSC and analysis of the presence of itraconazole concentration gradients using XPS revealed that storage did not cause migration, aggregation nor crystallization of itraconazole. The surface of the pores of SBA-15 was found to undergo hydroxylation at high relative humidity. The enhanced hydrophilicity was responsible for the observed improvement of itraconazole release upon contact with water. These findings contribute to the understanding of drug delivery systems based on mesoporous silica carrier materials.

A fully extended description is given of an automated setup to monltor H,S continuously in a sensltlve, qualitative, and quantltatlve way. H,S Is led by a stream of N, Into an alkallne solution and is contlnuousty determlned as S2-by a potentiometric detectlon system. The H,S detection system has been applied to the temperature-programmed reduction (TPR) of fossil fuel samples. The TPR procedure conslsts of the non-Isothermal heating of a sample in a reducing atmosphere, In order to liberate the different sulfur functional groups as H,S at dlscrete temperature ranges. I n this way a better Insight can be provlded Into the structural characterlstics of organic sulfur In fossil fuels and related products.

The effect of the presence of limestone and dolomite in coal, and calcium in lignite, on atmospheric-pressure temperature-programmed reduction (AP-TPR) analysis was studied. AP-TPR experiments were carried out on a bituminous coal with added limestone and dolomite and on a demineralized lignite. The results showed that both calcium minerals captured the gaseous H2S formed under AP-TPR conditions and produced CaS. Consequently the sulfur recovery monitored was too low and the AP-TPR kinetograms were deformed. The study also showed that the influence of dolomite is greater than of limestone. AP-TPR analysis of lignite demineralized and then loaded with calcium ions again showed a clear lowering of sulfur comparable with that of dolomite, but starting at a higher temperature.

Ultrathin ͑Nb 1−x Ta x ͒ 2 O 5 films, with thicknesses from ϳ3 to ϳ 25 nm, were deposited by chemical solution deposition starting from aqueous precursor solutions. The film's dielectric properties were characterized by capacitance-voltage and current-voltage measurements. Permittivities ranged from 20 to 31 after annealing at 600°C, with the highest value obtained for pure Nb 2 O 5 . With increasing Nb content, increasing leakage currents were observed. The crystallization temperature was determined by in situ X-ray diffraction measurement for films with ϳ15 nm thickness: Nb 2 O 5 was crystalline as deposited ͑600°C͒, while the crystallization temperature of solid solutions increased with increasing Ta content, up to 875°C for pure Ta 2 O 5 . NbTaO 5 showed a marked increase in permittivity from 27 to 38 after crystallization anneal at 600 and 800°C, respectively. For Nb 2 O 5 , no significant difference in permittivity was observed between amorphous and crystalline layers.

Phase pure lanthanum substituted bismuth titanate was prepared by an aqueous solution-gel route. In this route aqueous precursors are synthesized by stabilization of the metal ion in the aqueous medium through complexation with strong electron donor ligands. The chemical structure of metal-less, monometal ion as well as multimetal ion precursorgels was studied by means of FTIR and FT-Raman spectrometry. The precursors were transformed to phase pure oxides by heat treatment in an appropriate dynamic atmosphere. The decomposition reactions of the gels were studied by means of several hyphenated thermal analysis techniques (thermogravimetry coupled on-line to FTIR or MS (TGA-MS, TGA-FTIR) and high temperature-diffuse reflectance infrared spectrometry by fourier transform (HT-DRIFT)) and reactions are proposed. The phase formation was studied by means of X-ray diffraction. Phase segregation during gel calcination was correlated to the oxygen partial pressure. An explanation for this phenomenon was suggested based on thermal analysis and on SEM and TEM studies.

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti 4+ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15-20 nm grains. At higher crystallization temperatures (600, 650 • C) also larger particles (40-70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450 • C. Crystallization temperatures equal to or higher than 600 • C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness ( ≤ 1.1 nm) measured by AFM.

This study aims at the deposition of PbTiO 3 (PT) islands prepared by a water-based chemical solution deposition (CSD). Two aqueous citrato-based PbTiO 3 precursor solutions, either with or without peroxide, are deposited by spin coating. The effect of different substrates on the formation of separated grains or islands is examined. It is observed that spin coating of a 0.6 M precursor solution on a Pt(1 1 1)/IrO 2 /Ir/SiO 2 /Si substrate gives the best results towards island formation. For this substrate, crystallizations are carried out between 600 • C and 900 • C. A final crystallization at 800 • C results in the highest degree of separation for the islands, while keeping the platinized substrate intact. The deposition of diluted precursors shows that it is possible to form islands from a precursor solution with a concentration down to 0.3 M. Solutions with a lower concentration result in irregularly shaped structures.

The synthesis of nanoparticulate ZnO via an aqueous carboxylate gelation route is presented. Starting from a solution of zinc acetate with citric acid as a complexing agent, a solid glassy gel is obtained after drying that is converted into a ®ne powder by calcination. It is found that a very homogeneous precursor is indispensable when preparing very ®ne particles with a narrow size distribution. Cryo-transmission electron microscopy (Cryo-TEM) investigation is used as a feedback tool to prevent early precipitation during gelation. Study of the thermal decomposition of the gel shows that ZnO is formed before the ®nal decomposition step takes place. After removing the organic backbone, very small oxide particles are found. The in¯uence of the thermal treatment parameters on the particle size is investigated and a particle growth process is found. By a proper adjustment of the ®nal calcination temperature in dry air, the mean particle size can be controlled between $11 and 175 nm. It was also seen that even in inert atmosphere, ZnO is formed and that particle morphology is greatly in¯uenced by the calcination atmosphere. #

Our research is focused on the preparation and characterization of promising multimetal oxide ceramic materials, such as superconducting cuprates and ferroelectric materials. Results of the sol-gel synthesis of two compounds are discussed: PbTiO 3 (PTO) and BaTiO 3 (BTO). These are important products in the study of ferroelectric materials, with interesting applications as non-volatile ferroelectric random access memories (NVFRAMs), such as PbZr 1Àx Ti x O 3 (PZT) and BTO-stabilized PbZn 1/3 Nb 2/3 O 3 (PZN).

Zirconia ultrathin films were deposited by aqueous chemical solution deposition, using citratoperoxo-Zr(IV) precursors with different citric acid content. The precursor synthesis, thermal decomposition and crystallization of oxide powders was studied. This showed an effect of the citric acid content in every stage. The precursors were applied for the deposition of uniform, ultrathin films (< 30 nm thickness) as well. Tetragonal ZrO 2 crystallized starting from 500°C for thin films with a thickness of 10 nm. This was independent of the citric acid content in the precursor. The topography after annealing at 600°C was also similar. However, annealing at higher temperatures led to coarser grain size. The dielectric constant was high (~21-22) and comparable to ZrO 2 deposited by atomic layer deposition.

The thermal decomposition of an aqueous chemical solution deposition Zn2+-precursor is studied by HT-DRIFT (high temperature diffuse reflectance infrared Fourier transform spectroscopy), on-line coupled TGA-EGA (thermogravimetric analysis - evolved gas analysis by Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS)), and HT-XRD (high temperature X-ray diffraction). Using these complementary techniques, it is found that the a-hydroxyl group of the