Çetin Güler

β-Carotene adsorption on acid-activated montmorillonite

The adsorption of β-carotene from solution in benzene on acid-activated Canakkale montmorillonite of Turkey has been investigated. The adsorption isotherm had two steps. The first step was of the Langmuir type, and the isosteric heat of adsorption corresponding to this step was equal to −193.514 kJ/mol. The decrease in the total number of acid sites of the clay surface was determined to be 0.45×10−4 mol/g clay by nonaqueous titration with diethylamine. The phenomenon seems to be mainly a chemisorption stemming from the interaction of β-carotene with acid sites. Also, the activated clay acts as an oxidation catalyst on the β-carotene left in the solution.

Amine-intercalated montmorillonite matrices for enzyme immobilization and biosensing applications

Clay based biosensors were developed using montmorillonite (Mont) modified with methyl (M) and dimethylamine (DM). X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements were used to characterize the modified clays. After immobilization of glucose oxidase (GOx) via clay on the glassy carbon electrode, its application as a glucose biosensor was investigated in detail. The best response characteristics were obtained by DM-Mont and optimization of enzyme amount, reproducibility of biosensor fabrication, repeatability of measurements and operational stability were all evaluated. The optimized biosensor showed a very good linearity between 0.05 mM and 1.0 mM, a 7 s response time and a limit of detection to glucose of 0.038 mM. Also, kinetic parameters and stabilities were determined. Apparent Km and Imax values were found as 0.73 mM and 2.955 μA, respectively. As well as batch configuration, the DM-Mont/GOx biosensor was successfully applied in the flow injection analysis mode. Finally, the performance of the DM-Mont/GOx biosensor to analyze glucose in a wine sample was compared with HPLC.

The mechanism of β- Carotene adsorption on activated montmorillonite

AbstractsThe variations in the structure of mineral during adsorption have been examined comparing the results of X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetry (TG) and infrared (IR) spectroscopy of the acid activated montmorillonite clay mineral before and after adsorption of β-carotene. Based on the results, it was concluded that β-carotene attaches to the clay surface in the form of carbonium ions either by forming hydrogen bonds with Brönsted sites or by forming coordination bonds with Lewis sites of the activated clay mineral.

Kinetics of the thermal dehydration of acid-activated montmorillonite by the rising temperature technique

Abstract The activation energies of dehydration and combustion of organic materials in a clay sample, and of dehydration of natural and acid-activated montmorillonite have been determined using a rising temperature programme technique. The effect of acid activation of the montmorillonite on the dehydroxylation is discussed.

Investigation of the thermal decomposition kinetics of polyacrylamide using a dynamic TG technique

In this study, the kinetic parameters for the thermal decomposition of polyacrylamide are established with the use of a dynamic TG technique. Kinetic parameters which involve activation energy, reaction order and pre-exponential factor are found to be 157.48 ± 1.66 kJ mol−1,1 and 6.46 ×1011 respectively.

Chlorophyll adsorption on acid-activated clay

An acid-activated clay (Çanakkale montmorillonite from Turkey) was used to adsorb chlorophyll from hexane solutions. The phenomenon seems to be mainly driven by the interaction of chlorophyll with acid sites. The adsorption of chlorophyll on Brönsted acid sites was indicated by a characteristic infrared band for the -OH group at 3671 cm−1. The variations in the structure of clay mineral and chlorophyll during adsorption have been examined by differential thermal analysis, thermogravimetry and infrared spectroscopy of the activated clay before and after adsorption of chlorophyll. Oxidation of adsorbed chlorophyll was completed at quite a high temperature.

Synthesis of poly-2-hydroxyethyl methacrylate-montmorillonite nanocomposite via in situ atom transfer radical polymerization

The poly-2-hyroxyethyl methacrylate (PHEMA)/clay nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. To produce organically modified montmorillonite (MMT) that has ATRP initiator moiety, a new catalyst that consists of quaternary ammonium salt moiety and an initiator moiety was synthesized. This initiator was intercalated into the interlayer spacing of the MMT. The polymerization reaction was carried out in a mixed solvent system consisting of methyl ethyl ketone and 1-propanol at 50 °C, using the initiator that has been already synthesized with a copper bromide catalyst. The 2, 2′-bipyridyl (bpy) complex was used as ligand. The products were characterized via Fourier transform infrared, nuclear magnetic resonance ( 1 H NMR, 12 C NMR), transmission electron microscopy, x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry.

Electrokinetic Properties of Acid-Activated Montmorillonite Dispersions

In this study, the influence of pH, electrolyte concentration, and type of ionic species on the electrokinetic properties (zeta potential and electrokinetic charge density) of the acid-activated montmorillonite mineral have been investigated using the microelectrophoresis method. The electrokinetic properties of acid-activated montmorillonite dispersions have been determined in aqueous solutions of mono-, di-, and trivalent salts and divalent heavy metal salts. Zeta potential experiments have been performed to determine the point of zero charge (pzc) and potential determining ions (pdi). The zeta potential values of the acid-activated montmorillonite particles were negative and did not vary significantly within the pH range studied. Acid-activated montmorillonite dispersions do not have point of zero charge (pzc). The valence of the electrolytes has a great influence on the electrokinetic behavior of the suspension. A gradual decrease in the zeta potential (from −25 mV to −5 mV) occurs with the monovalent electrolytes when concentration increased. Divalent and heavy metal electrolytes have less negative z-potentials due to the higher valence of ions. A sign reversal of z-potential has been observed at AlCl3, FeCl3, and CrCl3 electrolytes (potential determining ions) and zeta potential values have had a positive sign at high electrolyte concentrations. The electrokinetic charge density of acid-activated montmorillonite has shown similar trends for variation in mono- and divalent electrolyte solutions. Up to concentrations of ca. 10−3 M, it has remained practically constant at approximately 0.5 × 10−3 C m−2 For higher concentrations of monovalent electrolytes more negative values (−16 × 10−3 C m−2) were observed. It has less negative values in divalent electrolyte concentrations according to monovalent electrolytes (−5 × 10−3 C m−2). For low concentrations of trivalent electrolytes, the electrokinetic charge density of montmorillonite particles is constant, but at certain concentrations it rapidly increased and changed its sign to positive.

Dielectric properties and electric conductivity of talc and doped talc

The dielectric properties of a MgO and Mg(NO3)2 doped and undoped talc are measured as a function of the frequency range 260 kHz-40 MHz. The ´, tan and ac values are given as a function of the firing temperature for a 5.0 MHz constant frequency. In this study the effects of an impurity and the firing temperature on the dielectric properties are also discussed.

Thermal investigation of acid-activated clay minerals

Abstract Samples of the clay mineral from the Canakkale reserve in Turkey were activated with sulphuric acid under three different sets of conditions. DTA and TG curves of both natural and activated samples were then obtained and compared with one other.