Vesna Rakić

The adsorption of pharmaceutically active compounds from aqueous solutions onto activated carbons

In this study, the adsorption of pharmaceutically active compounds - salicylic acid, acetylsalicylic acid, atenolol and diclofenac-Na onto activated carbons has been studied. Three different commercial activated carbons, possessing ∼650, 900 or 1500m(2)g(-1) surface areas were used as solid adsorbents. These materials were fully characterized - their textural, surface features and points of zero charge have been determined. The adsorption was studied from aqueous solutions at 303K using batch adsorption experiments and titration microcalorimetry, which was employed in order to obtain the heats evolved as a result of adsorption. The maximal adsorption capacities of investigated solids for all target pharmaceuticals are in the range of 10(-4)molg(-1). The obtained maximal retention capacities are correlated with the textural properties of applied activated carbon. The roles of acid/base features of activated carbons and of molecular structures of adsorbate molecules have been discussed. The obtained results enabled to estimate the possibility to use the activated carbons in the removal of pharmaceuticals by adsorption.

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.

Microcalorimetry in the Identification and Characterization of the Most Reactive Active Sites of Heterogeneous Catalysts

The microcalorimetric technique has been applied to investigate the strongest active sites of zeolites, heteropolyacids and perovskites. The differential heats of adsorption of carbon monoxide, ammonia and oxygen were determined. The results imply that the method is very useful in the identification and characterization of the most reactive active sites of solid catalytic materials.

Thermal effects of the interactions of carbon monoxide with zeolites

Abstract The interactions of carbon monoxide with Lewis acid sites of zeolites were investigated using microcalorimetric and temperature programmed desorption (TPD) techniques. Carbon monoxide was adsorbed at 25°C on transition-metal ion-exchanged FAU (Y and X) and MOR type zeolites. The differential heats of adsorption ( Q dif ) indicate the heterogeneity of the acid sites, in all the investigated systems. The specific interactions of CO with the strongest acid sites were recognized. The results of TPD confirm that CO molecules were adsorbed on the sites of different strength.

Temperature-Programmed Desorption (TPD) Methods

This chapter presents the fundamentals, the experimental setups and the applications of temperature-programmed desorption (TPD), method used to investigate the events that take place at the surface of solid material while its temperature is changed in a controlled manner. At the beginning, fundamental principles of adsorption and desorption phenomena, as well as the data concerning first experimental setups are given. Further, important information related to the construction of nowadays used equipment and the organization of common experiments are underlined. The significance of data directly obtained from temperature-programmed experiment—TPD profile, which are the area under it and the position of peak maximum, are highlighted. Particular attention is given to the results that can be derived from these data—characterization of active sites that can be found on the surface of solid material and determination of kinetic and thermodynamic parameters of desorption process. In this regard, the influence of important experimental parameters on derived values is explained. Besides, the distinctions between TPD experiments performed in ultra-high vacuum and in the flow systems (differences in experimental setups and in the derivation of kinetic and thermodynamic parameters) are explained. Also, the modification of temperature-programmed techniques, known as temperature-programmed oxidation and temperature-programmed reduction are shortly explained and compared with temperature-programmed desorption method. In the end, a brief comparison of the TPD and adsorption calorimetry, two most widely used techniques for the study of acid/base properties of catalysts, is given.

Novel modified nanocellulose applicable as reinforcement in high-performance nanocomposites

The influence of modification and vacuum/supercritical CO2 (scCO2) drying methods on the surface properties, morphology and thermal stability of cellulose nanocrystals (NC) was presented in this study. Introduction of reactive vinyl groups on NC surface was performed by either direct esterification with oleic acid, linseed or sunflower oil fatty acids; or by amidation of maleic acid/ethylene diamine with methyl ester of fatty acid. Obtained modified NC (m-NC) were characterized using FTIR and Raman spectroscopy; and by determination of acid, iodine and ester values. Structural analysis of m-NC showed varieties of forms, from spongy to nanostructural non-uniform layered morphology with observable agglomeration, which confirmed morphology dependence on modification/processing methods Thermogravimetry-MS spectrometry showed different thermal stability and degradation pathways of NC/m-NC. Incorporation of 1 wt% of reactive m-NC in unsaturated polyester lead to high performance nanocomposites and contributed to increase of stress at break in the range from 76 to 93%.

High temperature transformations of NH4A zeolite

Abstract Transformations of various forms of NaNH4A zeolite were investigated in the paper. It was determined that the degree of ion exchange considerably influences the stability of the A framework and the formation of crystalline phases in the high temperature region. The sillimanite phase forms from NH4A zeolite, while in the case of mixed forms the carnegite phase is found only for small degrees of ion exchange.

The use of clinoptilolite as an ammonia adsorbent and a nitrogen carrier to be used in grass production

The clinoptilolite-rich tuff (NZ) from Zlatokop deposit (Vranjska Banja, Serbia) has been studied as a nitrogen carrier for grass production. Mechanism of binding ammonium cations present in water solutions by NZ has been examined as well as possibility of adsorption of ammonia released in fresh cattle manure during its fermentation. The NH 4 + binding from solutions proceeds via an ion-exchange process which follows the pseudo-second-order kinetics. Adsorption isotherms studied at 298-318 K follow the Freundlich isotherm equation. The NZ readily adsorbs ammonia liberated from manure and an addition of 10 wt.% of NZ to manure can preserve up to 90% of ammonia. The potential benefit of this effect has been examined in greenhouse pot experiments with the Italian ryegrass using three different types of soil (silty, clayey and sandy). The zeta potential measurements show that stability of their colloidal dispersions differs mutually and that addition of the NZ differently affects the stability and nitrogen cycling. All results indicate that NZ can be applied in grass production.

Study of consecutive mechanism of desorption with diffusion step under non-isothermal conditions

Abstract A mechanism of desorption consecutive with diffusion into the micropores of a solid phase is postulated. In the development of the consecutive model complex integrals were obtained; these are solved using the Gauss-Kronrod method of numerical integration. Theoretical temperature programmed desorption spectra (TDS) are calculated. The influence of diffusion parameters on the position and shape of the calculated TDS were investigated. Kinetic parameters calculated using methods based on the change of temperature of the peak maximum and those assumed in the calculation of theoretical spectra are compared.

The study of diffusion processes in the thermodesorption results

A consecutive model of surface reaction, consisting of two steps (desorption and diffusion) was applied. It was concluded that diffusion modifies the temperature programmed desorption spectra, although the single peak curves appear. The differential method for calculation of kinetic parameters based on thesTM shift give values close to predicted ones only in the cases when particular steps are rate limiting. Generally, the desorption process have to be considered as a complex reaction, with the overall kinetic parameters. As a consequence of diffusion influence, the overall kinetic parameters are smaller than those for desorption step was obtained.ZusammenfassungEin konsekutives Modell für Oberflächenreaktionen, bestehend aus zwei Schritten (Desorption und Diffusion) wird angewendet. Dabei zog man die Schlußfolgerung, daß das temperaturabhängige Desorptionsspektrum durch Diffusion modifiziert wird, wenn sich auch Single-Peak-Kurven ergeben. Die auf der Verschiebung von TM basierende Differentialmethode zur Berechnung der kinetischen Parameter liefert nur in denjenigen Fällen Werte, die mit den prognostisierten übereinstimmen, in denen Einzelschritte geschwindigkeitsbestimmend sind. Ganz allgemein ist der Desorptions-vorgang als komplexe Reaktion mit kinetischen Bruttoparametern zu berücksichtigen. Als Folge des Einflusses der Diffusion sind die kinetischen Bruttoparameter kleiner als die für den Desorptionsschritt.