Vera Dondur

FTIR spectroscopy of framework aluminosilicate structures: carnegieite and pure sodium nepheline

Abstract In this work the spectroscopic studies of polymorph transformation of framework silicates containing six-membered rings and different Si/Al ratio were carried out. Two model systems with different stoichiometries (Na-LTA, Si/Al=1 and Na-FAU, Si/Al=1.23) were investigated. Thermally induced phase transformations of initial zeolites resulted in forming of stuffed derivatives of cristobalite (carnegieite) and tridymite (nepheline). Powder XRD method was used for the recognition of new phases. All obtained phases have framework structures built by single six-membered rings. The changes of middle range order (rings symmetry), which take place during transformations of Na-LTA and Na-FAU into low-temperature carnegieite, low-temperature carnegieite into pure sodium (ps) nepheline as well as ps-nepheline into high-temperature carnegieite, were investigated by IR spectroscopy. The rings symmetry is found to be dependent on a phase stoichiometry as well as on polymorph type.

Properties of diclofenac sodium sorption onto natural zeolite modified with cetylpyridinium chloride.

In this study an investigation of a model drug sorption onto cationic surfactant-modified natural zeolites as a drug formulation excipient was performed. Natural zeolite was modified with cetylpyridinium chloride in amounts equivalent to 100, 200 and 300% of its external cation-exchange capacity. The starting material and obtained organozeolites were characterized by Fourier transform infrared spectroscopy, zeta potential measurements and thermal analysis. In vitro sorption of diclofenac sodium as a model drug was studied for all surfactant/zeolite composites by means of sorption isotherm measurements in aqueous solutions (pH 7.4). The modified zeolites with three levels of surfactant coverage within the short activation time were prepared. Zeta potential measurements and thermal analysis showed that when the surfactant loading level was equal to external cation-exchange value, almost monolayer of organic phase were present at the zeolitic surface while higher amounts of surfactant produced less extended bilayers, ordered bilayers or admicelles at the zeolitic surface. Modified zeolites, obtained in this manner, were effective in diclofenac sodium sorption and the organic phase derived from adsorbed cetylpyridinium chloride was the primary sorption phase for the model drug. The Langmuir isotherm was found to describe the equilibrium sorption data well over the entire concentration range. The separate contributions of the adsorption and partition to the total sorption of DS were analyzed mathematically. Results revealed that that adsorption and partitioning of the model drug take place simultaneously.

Synthesis and Characterization of Conducting Self-Assembled Polyaniline Nanotubes/Zeolite Nanocomposite

Self-assembled conducting, paramagnetic polyaniline nanotubes have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in aqueous medium in the presence of zeolite HZSM-5, without added acid. The influence of initial zeolite/aniline weight ratio on the conductivity, molecular and supramolecular structure, paramagnetic characteristics, thermal stability, and specific surface area of polyaniline/zeolite composites was studied. The conducting (approximately 10(-2) S cm(-1)), semiconducting (3 x 10(-5) S cm(-1)), and nonconducting (5 x 10(-9) S cm(-1)) composites are produced using the zeolite/aniline weight ratios 1, 5, and 10, respectively. The coexistence of polyaniline nanotubes, which have a typical outer diameter of 70-170 nm and an inner diameter of 5-50 nm, accompanied by nanorods with a diameter of 60-100 nm and polyaniline/zeolite mesoporous aggregates, distinct from the morphology of microporous zeolite HZSM-5, was proved in the conducting nanocomposite by scanning and transmission electron microscopies. FTIR spectroscopy confirmed the presence of polyaniline in the form of conducting emeraldine salt and suggested significant interaction of polyaniline with zeolite. The evolution of molecular and supramolecular structure of polyaniline in the presence of zeolite was discussed.

The adsorption of sulphate, hydrogenchromate and dihydrogenphosphate anions on surfactant-modified clinoptilolite

Abstract The adsorption of sulphate, hydrogenchromate and dihydrogenphosphate anions on surfactant-modified clinoptilolite (SMC) was investigated. The SMCs were prepared by the adsorption of cis -1-aminoctadecen-9 (oleylamine) on both modified and unmodified natural clinoptilolite tuff. The properties of the modified clinoptilolite samples, such as cation type, structure of the zeolite framework and ECEC value, determined the mechanism of oleylamine adsorption, and consequently anion adsorption on the external clinoptilolite surface. According to the strength of the anion adsorption, two groups of SMCs could be distinguished: strong and weak anion adsorbents. Strong anion adsorbents were obtained by oleylamine adsorption on H + -clinoptilolites by protonation of the –NH 2 groups. This mechanism of oleylamine adsorption resulted in the surface precipitation mechanism of anion adsorption being the dominant mechanism. The oleylamine derivatives of Ca- and Na-clinoptilolite were weak anion adsorbents. Oleylamine is adsorbed on Ca- and Na-clinoptilolite by hydrogen bonding, thus yielding insufficient adsorption sites for anions. Hydrogenchromate and dihydrogenphosphate anions were nevertheless adsorbed on these SMCs by interaction with oleylamine. The experiments of anion adsorption on various oleylamine loaded SMCs confirmed the existence of two types of anion adsorption sites and showed that excess oleylamine did not significantly influence the anion adsorption in the investigated concentration range. The kinetic results showed that SO 4 2− and H 2 PO 4 − adsorptions were slow processes while HCrO 4 − adsorption was completed in a few minutes.

Adsorption of ochratoxin A on octadecyldimethyl benzyl ammonium exchanged-clinoptilolite-heulandite tuff

The in vitro adsorption of ochratoxin A (OCHRA) by clinoptilolite-heulandite rich tuff modified with different amounts—20, 50 and 100 μmol M+/g of octadecyldimethyl benzyl ammonium (ODMBA) ion was investigated. The organo-zeolites were denoted as OZ-2, OZ-5 and OZ-10. The maximal amount of ODMBA in organo-zeolites 100 μmol M+/g was equal to external cation exchange capacity of starting material. Adsorption of OCHRA by unmodified zeolitic tuff was 40% at pH 3 and 3% at pH 7 and 9. OCHRA adsorption on organo-zeolites increased as the levels of ODMBA increased. At low coverage of zeolitic surface with ODMBA–organo-zeolite OZ-2, adsorption of OCHRA was lower at pH 7 and 9 than at pH 3. The decreased adsorption of OCHRA at pH 7 and 9 may be induced by the presence of anionic form of OCHRA which probably led to repulsion between the OCHRA and uncovered negative zeolitic surface. At higher coverage of the zeolitic surface, organo-zeolites OZ-5 and OZ-10, adsorption of OCHRA was pH independent. OCHRA adsorption on OZ-2 and OZ-10 showed non linear type of isotherm at pH 3, 7 and 9. Adsorption of OCHRA by OZ-5 followed a non linear type of isotherm at pH 7 and 9, while at pH 3 the adsorption was best represented by an S-shaped isotherm. Adsorption of OCHRA on organo-zeolites is dependent on the amount of organic cation at the surface, as well as on their surface concentration—arrangement of alkyl chains at the surface. At low surface concentration of ODMBA, adsorption of OCHRA may be dependent on the form of OCHRA in solution.

Thermally induced phase transformations of Ca-exchanged LTA and FAU zeolite frameworks: Rietveld refinement of the hexagonal CaAl2Si2O8 diphyllosilicate structure

Thermally induced phase transformations of Ca-exchanged LTA and FAU zeolites are followed in the range from room temperature to 1500°C. Both frameworks collapse into amorphous intermediate products after heating between 800 and 900°C. Prolonged heating of the intermediate product obtained from the Ca-LTA zeolite over 900°C induces recrystallization of CaAl 2 Si 2 O 8 phases (hexagonal CaAl 2 Si 2 O 8 phase and anorthite) into a mixture. The crystal structure of the hexagonal CaAl 2 Si 2 O 8 phase [ a 0 = 5.1154 (A), c 0 = 14.767(9) A] is refined by the Rietveld method from X-ray powder diffraction data to final agreement factors R p = 8.99%, R WP = 11.87%, and R B = 4.31%. The refined hexagonal Ca-diphyllosilicate phase is unstable in prolonged calcination, and at 1050°C it can be transformed polymorphously into an highly ordered anorthite LTA . Prolonged heating of the amorphous intermediate product obtained from Ca-FAU zeolite over 900°C results directly in formation of a less ordered anorthite FAU Ca 0.88 0.12 Al 1.77 Si 2.33 O 8.00 framework with vacant Ca 2+ sites.

The adsorption of nicotine from aqueous solutions on different zeolite structures

The present work is focused on the adsorption of nicotine from aqueous solutions. Based on the data available in the literature, serious concern is claimed regarding the appearance of nicotine in ground, surface and municipal wastewaters. In order to investigate the possibility of abatement by adsorption, three different types of zeolites (BEA, MFI and HEU) have been applied as adsorbents. In addition, the adsorption was performed on activated carbon, a solid customarily used for removal of pollutants from water. The adsorption of nicotine was studied by isothermal microcalorimetry, which provided the heats evolved as a result of adsorption. The values of these heats revealed that the investigated solids are energetically heterogeneous for the adsorption of nicotine from aqueous solution. Additionally, the amounts of adsorbed pollutant were determined and presented in the form of adsorption isotherms. The obtained adsorption isotherms were interpreted using Langmuir, Freundlich, and Sips equations; the latter was found to express high level of agreement with experimental data of nicotine adsorption on the investigated solids. The possibilities to regenerate the adsorbents were examined by means of thermogravimetry coupled with mass spectrometry. From all obtained results, it was possible to distinguish zeolite BEA as a material which possesses the capacity for adsorption of nicotine comparable to that of activated carbon.

The thermal transformation of Na LiA zeolites. A new polymorph in the system Li2OAl2O3SiO2

Abstract High-temperature phase transformations of A zeolite with various degrees of exchange of Na + with Li + ions were investigated. An increase in the number of Li + ions per unit cell accelerates the thermal transformation of the zeolite framework to the amorphous state. Above 730°C, four phases (carnegieite, nepheline, β-eucryptite, and a new phase—γ-eucryptite) were identified. Only γ- and β-eucryptite phases were obtained from pure LiA zeolite. γ-eucryptite is a new metastable polymorph in the system Li 2 OAl 2 O 3 SiO 2 . γ-eucryptite a 0 = 7.231(3)A, b 0 = 10.270(6) A, c 0 = 12.054(7) A) is transformed to β-eucryptite ( a 0 = 10.533(5) A, c 0 = 11.148(5) A) above 840°C.

An approach to the kinetics of water desorption from A-zeolites. Part I. Isothermal and non-isothermal desorption

Abstract Desorption of water from zeolites: NaA, LiA, KA, CdA, ZnA, MgA and CaA were examined. Isothermal and non-isothermal kinetic analyses were carried out. It was found that the process of desorption can be presented as a first-order reaction. Due to the existence of several water—zeolite complexes, neither isothermal nor non-isothermal kinetic methods may be applied directly.

Cationic surfactants-modified natural zeolites: improvement of the excipients functionality

Context: In this study an investigation of cationic surfactants-modified natural zeolites as drug formulation excipient was performed. Objective: The aim of this work was to carry out a study of the purified natural zeolitic tuff with high amount of clinoptilolite as a potential carrier for molecules of pharmaceutical interest. Materials and methods: Two cationic surfactants (benzalkonium chloride and hexadecyltrimethylammonium bromide) were used for modification of the zeolitic surface in two levels (equal to and twice as external cation-exchange capacity of the zeolitic tuff). Prepared samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric, high-performance liquid chromatography analysis, and powder flow determination. Different surfactant/zeolite composites were used for additional investigation of three model drugs: diclofenac diethylamine, diclofenac sodium, and ibuprofen by means of adsorption isotherm measurements in aqueous solutions. Results: The modified zeolites with two levels of surfactant coverage within the short activation time were prepared. Determination of flow properties showed that modification of zeolitic surface reflected on powder flow characteristics. Investigation of the model drugs adsorption on the obtained composites revealed that a variation between adsorption levels was influenced by the surfactant type and the amount present at the surface of the composites. Discussion and conclusion: In vitro release profiles of the drugs from the zeolite-surfactant-drug composites revealed that sustained drug release could be attained over a period of 8 hours. The presented results for drug uptake by surfactant-zeolite composites and the afterward drug release demonstrated the potential use of investigated modified natural zeolite as excipients for advanced excipients in drug formulations.