Müşerref Önal

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: SPECIFIC SURFACE AREA BY THE BRUNAUER EMMETT TELLER (BET) METHOD

Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

THE EFFECT OF THERMAL TREATMENT ON SOME OF THE PHYSICOCHEMICAL PROPERTIES OF A BENTONITE

A white calcium bentonite (CaB) from the Kütahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. 9c Ca-rich montmorillonite (CaM). Samples were heated at various temperatures between 100–1300°C for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtained. The change in the <i(001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol−1, respectively. The average deformation enthalpies, in the respective temperature intervals between 200–700°C and 700–900°C, were estimated to be 25 and 205 kJ mol−1 using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a “zig zag” variation with increasing temperature to 700°C, but decrease rapidly above this temperature. The S and V values were 43 m2 g−1 and 0.107 cm3 g−1, respectively, for untreated bentonite. They reach a maximum at 500°C and are 89 m2 g−1 and 0.149 cm3 g−1 respectively. The XRD data clearly show that, at 500°C, where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.

The effect of heating on the surface area, porosity and surface acidity of a bentonite

The Hançılı bentonite from Turkey shows significant changes in surface area, micro- and mesoporosity, surface acidity and acid strength with heating from 100 to 900°C for 2 h. The specific surface area (S) and specific micro-mesopore volume (V) of the original and heated samples were evaluated from N2 adsorption and desorption data, respectively, by standard methods. The adsorption of n-butylamine from the solution in cyclohexane on the samples was used to determine the total surface acidity (nm) and the adsorption equilibrium constant (K) was taken as a measure of the acid strength. S, V and nm having initial values of 98 m2g−1, 0.080 cm3g−1 and 4.8 × 10−4 mol g−1, respectively, stayed approximately constant as the temperature increased to 450°C and then decreased almost in parallel with each other, reaching their minimum or zero at 900°C. The total surface acidity, in general, declines with increasing temperature. The most acidic sites, however, increase with heating, and especially at dehydration and dehydroxylation. Acid strength reaches its maximum during the dehydroxylation phase at ∼600°C. It was concluded that the total surface acidity does not necessarily parallel the strength of the most acid sites.

SOME PHYSICOCHEMICAL PROPERTIES OF THE WHITE SEPIOLITE KNOWN AS PIPESTONE FROM ESKIŞEHİR, TURKEY

Various physicochemical characteristics of a sepiolite sample from the Eskişehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N2-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m2g−1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m2g−1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N2-AD results were 0.16, 0.21, 0.45, and 0.82 cm3g−1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N2-AD data) tobe 35 and 2.4 nm, respectively.

Synthesis, characterization, and properties of conducting polypyrrole/Na-montmorillonite nanocomposites

Polypyrrole/Na-montmorillonite nanocomposites were prepared by oxidative polymerization of pyrrole in aqueous medium using ammonium peroxydisulfate as the oxidant. The synthesized nanocomposites were confirmed by a series of characterization techniques including Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermal analysis. X-ray diffraction and transmission electron microscopy images showed that the polypyrrole was intercalated into the clay layers. The thermogravimetric analysis and differential thermal analysis revealed the improved thermal stability of nanocomposites with respect to pure polypyrrole due to modification of the incorporated Na-montmorillonite. Furthermore; adsorptive properties, the moisture retains, and water uptake values of nanocomposites were investigated. Conductivity behaviour of nanocomposites was also studied. The nanocomposites exhibit the room temperature conductivities varied from 1.2 × 10−8 S cm−1 to 8.7 × 10−8 S cm−1 range, depending on the amount of polypyrrole.

Study on the synthesis and properties of polyacrylamide/Na-montmorillonite nanocomposites

A series polyacrylamide/Na-montmorillonite nanocomposites was prepared by in situ free radical polymerization in aqueous medium using benzoyl peroxide (Bz2O2) as a radical initiator. To characterize the resultant nanocomposites, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis techniques were used. The moisture retain, water uptake, antibacterial properties, BET specific surface area and specific nanopore volume of nanocomposites were determined. The X-ray diffraction pattern showed that the polyacrylamide was intercalated up to 60.0 mass% acrylamide concentration, and then montmorillonite layers exfoliated into the polyacrylamide matrix. The interlayer spacing (d001) of the montmorillonite increased from 1.19 to 1.90 nm by intercalation. Transmission electron microscopy views showed that the Na-montmorillonite partially exfoliated in polyacrylamide. The nanocomposites exhibited better thermal stability than the pure polyacrylamide.

Preparation and characterization of intercalated polymethacrylamide/na-montmorillonite nanocomposites

Polymethacrylamide/Na‐montmorillonite nanocomposites have been prepared by free‐radical polymerization. All the nanocomposites were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and differential thermal analysis. The thermal properties of nanocomposites are notably improved by the presence of the montmorillonite layers in comparison with pure polymethacrylamide. X‐ray diffraction and scanning electron microscopy confirmed that polymethacrylamide could be easily inserted between the layers of Na‐montmorillonite to form intercalated nanocomposites, and significantly large d‐spacing expansions from 1.19 to 2.93 nm of the nanocomposites. Adsorptive properties of nanocomposites were also investigated.

Polythiophene/Na-montmorillonite composites via intercalative polymerization:

Conducting polythiophene (PTP)/Na-montmorillonite (Na-MMT) composites have been prepared by intercalative polymerization. The synthesized composites are characterized by Fourier transform infrared spectroscopy, x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), and thermal analysis. XRD and TEM images showed that the PTP was intercalated into the clay layers. The thermogravimetric analysis and the differential thermal analysis revealed the introduction of Na-MMT results in thermal stability of composites with respect to pure PTP. Furthermore, adsorptive properties, the moisture retention, and water uptake values of composites were investigated. Conductivity behavior of composites was also studied.

Preparation and characterization of poly(2-hydroxyethyl methacrylate)/ Na-montmorillonite intercalated nanocomposites

Abstract A series of intercalated nanocomposites were prepared via in situ polymerization of 2-hydroxyethyl methacrylate (HEMA) between the interlayer spacing of hydrous Na-montmorillonite (Na-MMT) using benzoyl peroxide (Bz2O2) as a radical initiator. X-ray diffraction patterns showed the absence of any intercalation up to 61.7 mass% of HEMA, but anhydrous Na-MMT formed by the hydrophilic effect of HEMA. The interlayer spacing (d001) values of hydrous and anhydrous Na-MMT were calculated as 1.19 and 1.03 nm, respectively. At higher monomer contents, the increase in the value of d001 from 1.19 to 2.01 nm indicated intercalation of polymer in the interlayer spacing of Na-MMT. Besides, transmission electron microscopy results supported the formation of the intercalated nanocomposites. Thermogravimetric analysis showed that the thermal stability of the nanocomposites increased considerably by intercalation of pure poly-HEMA. Specific surface area and specific nanopore volume of the nanocomposites decreased with the increasing of the monomer content taken by the preparations. The decrease is due to the nonporous nature of the polymer matrix.