Ayben Kilislioglu

Thermodynamic and kinetic investigations of uranium adsorption on amberlite IR-118H resin

The adsorption behavior of uranium(VI) on a strongly acidic cation exchanger amberlite IR-118H has been studied as a function of the solution concentration and temperature. Results have been analyzed by Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. The mean energy of adsorption 7.14kJmol(-1) was calculated from the D-R adsorption isotherm. In order to understand the significance of the diffusion mechanisms and to accurately estimate the diffusivities inside the adsorbent particles, a model for uranium(VI) adsorption on amberlite IR-118H was used. The rate constants have been calculated for 293, 313 and 333K using Lagergren equation and the activation energy (E(a)) was derived using the Arhenius equation. The thermodynamic quantities for the process of adsorption have been estimated by plotting Ln K(D) versus 1/T. The DeltaH(o) and DeltaG(o) values of uranium(VI) adsorption on amberlite IR-118H show endothermic heat of adsorption; higher temperatures favor the process.

Adsorption of uranium on halloysite

Summary Adsorption of uranium (U(VI)) from aqueous solutions on halloysite type clay was studied as a function of amount of adsorbent, initial concentration and pH. The values of adsorption data were fitted to Freundlich, Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms. The mean energy of adsorption was calculated as 5.91 kJ/mol from D–R adsorption isotherm. Lagergren and Bangham equation has been used for dynamic modelling of process and the rate constants of adsorption of uranium on halloysite type clay were calculated at 293, 313 and 333 K. In order to explain the mechanism of adsorption reaction, the rate constants were calculated at high and low uranium concentrations. Adsorption reaction was studied at 293, 303, 313, 323 and 333 K for halloysite type clay and also thermodynamic constants have been calculated. The results show that the adsorption reaction was endothermic and more spontaneous at high temperature.

Adsorption of uranium from aqueous solution on heat and acid treated sepiolites.

In this work adsorption of uranium on natural, heat and acid treated sepiolite was studied. For acid treatment HCl and H(2)SO(4) were used separately. Heat and acid treatment caused some changes in sepiolite such as surface area, micropore volume (cm(3)/g) and average pore diameter (A). Different amounts of Mg ions were extracted from the lattice depending on the type of acid. After acid treatment with HCl, the amount of Mg left in the sepiolite changed a little. During H(2)SO(4) treatment the sepiolite structure was progressively transformed into amorphous silica. These heat and acid treatments changed adsorption capacity and mechanism of uranium on sepiolite. Data obtained from the adsorption experiments were applied to Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. Using these isotherms different adsorption capacities were found for natural and treated sepiolite samples. The capacity values were 3.58x10(-3), 3.14x10(-3), 2.78x10(-3) and 1.55x10(-3)mol/g for HCl treated, heat treated, natural and H(2)SO(4) treated sepiolite samples, respectively. In order to evaluate the adsorption mechanism adsorption energies were calculated by the D-R isotherm. According to the adsorption energy values uranium fixed to the natural and heat treated sepiolite surface with ion exchange (12.75 and 12.12 kJ/mol, respectively). Simple physical attractions were the driving force for adsorption on HCl and H(2)SO(4) treated ones (6.62 and 6.87 kJ/mol, respectively).

The effect of various cations and pH on the adsorption of U(VI) on Amberlite IR-118H resin.

The effects of various metal cations and pH on the adsorption of uranium(VI) on strongly acidic cation exchanger Amberlite IR-118H (AIR-118H) were studied. The metal cations suppress U(VI) adsorption differently depending on their ionic radii. Adsorption of U(VI) on AIR-118H peaks at pH 3.4, which was attributed to the occurrence of different forms of U(VI) at different pH values. The adsorption data were then processed using the Frumkin-Fowler-Guggenheim equation, and the standard free energy of adsorption was calculated.

Kinetics of isotopic exchange between strontium polymolybdate and strontium ions in aqueous solution.

A heterogeneous isotopic exchange reaction of strontium polymolybdate in strontium chloride solution was studied using 90Sr as a tracer. The effects of low and high strontium chloride concentration on the rate and mechanism of the isotopic exchange reaction were investigated. It was found that, at high concentrations, the rate is independent of strontium concentration, but, at low concentrations, the rate is proportional to the strontium concentration. These results support a hypothesis that, at low concentrations, the rate is controlled by film diffusion, whereas at high concentrations it is controlled by particle diffusion. Experiments were performed at 293, 303 and 313 K. Activation energy of isotopic exchange reaction and thermodynamic parameters deltaH*, deltaS*, and deltaG* were calculated using the Arrhenius and Eyring equations. The results also indicated that recrystallization is a predominant factor in the present exchange reaction.

The adsorption behavior of natural sand in contact with uranium contaminated seawater.

ABSTRACT This study was undertaken to investigate the interaction between uranium contaminated seawater and the sand in contact with this seawater. Adsorption data have been evaluated from column experiments of seawater from Marmara, Black Sea and Mediterranean contaminated with 10−7 M uranium. The uranium uptake on the fractionated and non-fractionated sand of these sea have been measured as a function of time. The adsorption proceeds via a rather fast stage followed by a slower one. Results could be correlated with particle size and porosity of the sand. Adsorption isotherms are also derived from amount of adsorbed uranium vs. time plots and the results have been analyzed by the Langmuir, Freundlich and Dubinin–Radushckevich (D–R) isotherm equations over the entire range of uranium concentrations. By fitting the data to D–R isotherm, we have calculated the adsorption energy and decided to type of the adsorption.

Photocatalytic Degradation of Azo Dyes and Organic Contaminants in Wastewater Using Magnetically Recyclable Fe 3 O 4 @UA-Cu Nano-catalyst

In this study, we delineated the structural properties and catalytic behavior of nanocrystalline Fe3O4@Urocanic acid(UA)–Cu magnetically recyclable nanocatalyst (MRCs) which was produced via hydrothermal route. Here, Urocanic acid (UA) used as a linker to attach Cu nanoparticles and stabilized the iron oxide. Structural properties were examined through Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDX). Moreover, thermal and magnetic properties of MRCs were completed using thermal gravimetry (TG) and vibrating sample magnetometry (VSM) respectively. Moreover, the catalytic studies of product were recorded by UV–Vis absorption spectrophotometer for azo dyes and aromatic nitro compounds. The synthesized MRCs was found as an efficient nanocatalyst and magnetically recyclable from the reaction medium without significantly loss in its catalytic activity. Fe3O4@UA-Cu MRCs can be considered for the treatment of industrial dyes pollutants and organic contaminants from wastewater.Graphical AbstractProposed mechanism of photocatalysis degradation of dye by Fe3O4@UA-Cu MRCs.

Formation and distribution of ZnO nanoparticles and its effect on E. coli in the presence of sepiolite and silica within the chitosan matrix via sonochemistry

In this study, a new bio-nanocomposite was prepared and characterized with a focus on the formation of hexagonal ZnO and orthorhombic zinc silicate (Zn2SiO3(OH)2) phases under ultrasonic irradiation. Chitosan/sepiolite/ZnO and chitosan/silica/ZnO bio-nanocomposites were synthesized using a simple solution method in which extreme physical and chemical conditions created by cavitation within the chitosan solution allowed for the transformation of aqueous Zn(OH)2 to crystallized ZnO and Zn2SiO3(OH)2 in room temperature. Both the loading of sepiolite and silica with the zinc precursor significantly influenced the morphology and crystalline structure of the product, however, different zinc compounds were observed. Sepiolite was exfoliated, resulting in a fine, even colloidal solution through ultrasonic dispersion. Exfoliation of sepiolite nanofibers led to the homogeneous dispersion of Zinc in the form of Zn(OH)2 in chitosan matrix. When the same procedure was conducted using the silica component, a formation of ZnO and Zn2SiO3(OH)2 was observed, components that were not observed when the procedure was conducted using sepiolite. The average crystalline size of ZnO was calculated as 36nm for ZnO. In addition, the quantities of crystalline and the ZnO phase volume was determined as 15%. Through zone of inhibition, the silica nanocomposite was discovered to have antibacterial activity. In contrast, the sepiolite compound did not exhibit these properties. We thus hypothesize that HO radicals, formed during ultrasonic irradiation trigger the formation of a silicate ion (SiO32-) and formation of ZnO and Zn2SiO3(OH)2 species in chitosan/silica/ZnO bio-nanocomposite, which causes to exhibit these antibacterial properties against Gram-negative E. coli. Chemical characterization and dispersion of the structure of the ZnO and Zn2SiO3(OH)2 phases were done using X-ray diffraction (XRD) and scanning electron microscopy techniques (SEM) with EDAX and X-ray photoelectron spectroscopy (XPS).