Fenollerin sulu çözeltilerden orgono kil üzerinde adsorpsiyon ile zenginleştirilmesi ve kapiler elektroforez yöntemi ile tayini
Preconcentration of phenols from aqueous solutions by adsorption on organo-clay followed by capillary electrophoretic determination
- Tez No: 68901
- Danışmanlar: DOÇ. DR. F. BEDİA ERİM
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 53
Özet
ÖZET Bu çalışmada, toksik maddeler sınıfına giren fenol bileşiklerinin sulu çözeltiler den giderilmesinde ve su örneklerinde fenol tayinleri için ön zenginleştirme çalışmalarında kullanılabilecek ucuz ve kolay hazırlanabilen bir adsorban olarak bir organo kilin hazırlanması amaçlanmıştır. 3-kloro fenol, 4-kloro fenol, 3-nitro fenol ve 4-nitro fenol ' ün karışım çözeltilerinden, Kurşunlu yöresi montmorillonit tipi kilin setiltrimetilamonyum bromür ile modifikasyonu sonucu elde edilen organo kil üzerinde tutulma ve geri kazanma oranları incelenmiş ve fenollerin konsantrasyonları kapiler elektroforez yöntemi ile tayin edilmiştir. VII
Özet (Çeviri)
SUMMARY The presence of organic toxicants in the environment is a major concern due to their hazardous effect to many life forms. Treatment of wastewaters containing organic toxicants requires concentration of the organic subtances into a smaller volume followed by recovery or secure disposal. Organic toxicants can be removed by adsorption on solid carries. Activated carbons are among the most effective adsorbents known for the removal of organic toxicants from aqueous effluents and contaminated groundwater. Although these high surface area materials can be regenerated by thermally desorbing or combusting the toxicant in air, a substantial fraction of the carbon is lost with each oxidation cycle. This loss of adsorbent isa major economic consideration in any large-scale remediation application. In the past few years, there has been increasing interest in designing recyclable inorganic adsorbents, particularly smectite clay-based materials for the efficient removal of organic pollutants from aqueous solutions. In general the term clay implies a natural, earthy, fine-grained material which develops plasticity when mixed with a limited amount of water. By plasticity is meant the property of the moistened material to be deformed under the application of pressure, with the deformed shape being retained when the deforming pressure is removed. Chemical analyses of clays show them to be essentially silica, alumina and water, frequently with apreciable quantities of iron, alkalies, and alkaline earths. The term clay has no genetic significance. It is used for material that is the product of weathering, has formed by hydrothermal action, or has been deposited as a sediment. As a particle-size term, the clay fraction is that size fraction composed of the smallest particles. The maximum size of particles in the clay size grade is defined differently in different disciplines. In geology the clay-grade is defined as material finer than about 4 microns. In soil investigations, the tendency is to use 2 microns as the upper limit of the clay size grade. Although there is no sharpe universal boundary between the particle size of the clay minerals and nonclay minerals in argillaceous sediments, a large number of analyses have shown that there is a general tendency for the clay minerals to be concantrated in a size less than about 2 microns, or that naturally occuring larger clay-mineral particles break down easily to this size when the clay is slaked in water. Clays contain varying percentages of clay-grade material and therefore, varying relative amounts of nonclay-mineral and clay-mineral components. viaPredominant contents of“ clay-minerals ”are hydrated silicates of aluminum, iron, or magnesium, both crystalline and amorphous. These range from hydrothermally formed nacrite through the relatively stable kaolinite, and into members of the montmorillonite family, which vary widely within themselves in their base-exchange properties, expanding crystal lattice, and proxying of elements. The montmorillonite group of minerals is well known as the main component of bentonite clays. Montmorillonites are derived structurally from pyrophyllite, SisAl402o( OH )4, or tale, SigMgöOaoC OH )4, by substitutions mainly in the octahedral layer. When substitutions occur between elements ( ions ) of unlike charge, deficit or excess charge develops on corresponding parts of the structure. Deficit charges in montmorillonite are compensated by cations ( commonly Na, Ca, K ) sorbed between the three-layer ( two tetrahedral and one octahedral, hence 2:1 ) clay-mineral sandwiches. These are relatively loosely, and although stoichiometrically, held and give rise to major cation exchange properties of the montmorillonite. Typical formulas of montmorillonite minerals are [ Ali.67Mg0.33(Nao.33 ) ] Sİ4O10 ( OH )2. In each formula, Nao.33 or X0.33 refers to the exchangeable“ base ”( cation, or base exchange ) of which 0.33 equivalent is a typical value. Most of the adsorbent clays, bleaching clays, and many of the clay catalysts are from the montmorillonite family, although some are attapulgite. The clay minerals have the property of sorbing certain anions and cations and retaining these in an exchangeable state; i.e., these ions are exchangeable for other anions or cations by treatment with such ions in a water solution. Bentonitic clay, with a large of montmorillonite mineral, shows a colloidal structure because of its internal surface area structure and the small particle size. One unit cell of crystal structure of bentonite forms with a Al-O-OH octahedral alumina sheet which enters between two Si-0 tetrahedral silica sheets. These two sheets bound each other with ionic bonds. A bentonit mineral contains hundreds of unit cells. There are spaces which contain water molecules and various cations depending on the type of clay. The wide surface of this unit is negatively charged because of unsaturated bonds, its narrow surface is positively charged because of Al3+ ions. Organic anions are adsorbed at the edges of the clay particles. Organic cations, on the contrary, are adsorbed on the negative face surfaces of the clay. This fact is evident from the much larger adsorption capacity of the clay for these cations and also from the increase of the basal spacing of montmorillonite clays after treatment with organic cations. The clay minerals have the property of sorbing certain anions and cations and retaining these in exchangeable state; i.e., these ions are changeable for other ions or cations by treatment with such ions in a water solutions. Montmorillonite-type clays are often termed bentonites.The most frequent mode of formation is direct surface weathering of volkanic glasses, espeacially when these are rich in magnesium or iron. Today, bentonit which is used about hundred industries branch shows strong colloidal characteristics and is very high plasticity and adsorption power. Substitued phenols are of great environmental concern owing to their high toxicity. Some of these phenols, which originate from such diverse sources as pesticide application, industrial wastes, water supplies and automobile exhausts, are highly toxic even at low concentrations. IXThe present study describes the preparation of a modified clay using a cationic surfactant, cethyltrimethylammonium bromide ( CTAB ) and its application as an adsorbent for the preconcentration of phenols from aqueous solution, followed by a capillary electropherotic determination. An ideal preconcentration process should allow the isolation of the analyte from the matrix with an appropriate enrichment factor. An important step in a successful preconcentration method is the choice of the instrumental method for the determination of trace substances in aqueous solution. By using a chromatographic method, problems associated with chemical and matrix interferences can be eliminated. A widely used technique for the analysis of phenols is high-performance liquid chromatography ( HPLC ) with either reversed-phase isocratice or gradient elution. However, owing to the inherent limited resolving power of conventional HPLC techniques, optimization of the separation of the phenols often involves complicated procedures or a large number of experiments. In the last years, CE has become a suitable alternative to HPLC for the analysis of phenolic compounds due to high efficiency and short analysis time of techniques. Electrophoresis has been defined as the differential movement of charged species ( ions ) by attraction or repulsion in an electric field. Capillary electrophoresis ( CE ) is recognized as a powerful new separation technique, which employs the separation mechanisms of conventional electrophoresis in a capillary format. CE provides rapid analysis, very high resolution, minimal sample consumption and fully-automated operation. Biomolecules can be detected directly during the separation without the need for staining and destaining of gels. A variety of different separation modes are avaible, and resolving power is often higher than other separation techniques such as HPLC and conventional gel electrophoresis. A commercial CE system usually comprises a detector, dual high voltage power supplies, and an electrophoresis compartment containing a capillary connecting two buffer reservoirs with high voltage electrodes. In CE the separation compartment is a narrow capillary filled with an electrolyte solution. The electride field is applied with an external high-voltage source between two electrodes in small vials in contact with the solution at both ends of a separation compartment. The sample is introduced as a narrow band or zone at one end, and detection takes place near the other end of the capillary. Molecules are separeted as electrical force drives them at different rates through a segment of the capillary, and the detector signal is displaced as peaks on an electro- pherogram. The sample can be introduced into the capillary by hydrodinamic, electrokinetic, or displacement injection. During electrokinetic injection, high voltage is applied while the capillary inlet is immersed in the sample solution. Sample ions migrate into the capillary in proportion to their electrophoretic mobilities. In hydrodinamic injec tion, sample components are introduced into the capillary by applying pressure or by applying vacuum to the outlet of the capillary. Displacement injection can be achieved by changing the relative heights of the sample and outlet buffer vials (gravity injection). Virtually CE separations are performed using fused silica capillaries which are externally coated with a polymer such as polyamide to improve their mechanicalstrength. Capillary internal diameters may range from 25 to 200 micrometers, and capillary lengths up to 1 meter are used, depending upon the application. Although a variety of detection modes have been demonstrated for CE ( including fluorescence, electrochemical, and conductivity ) most commercial system UV or UV- Visible detectors. Capillary electrophoresis has been applied to the separation of a wide variety of compound types, including peptides, proteins, PCR products, oligonucleotides, carbohydrates, vitamins, organic acids, drugs, amino acids, inorganic ions, and industrial polymers. At pH values above 3, the fused silica capillary has negative surface charges due to ionization of silanol groups. Positive ions in the buffer will be attracted to these fixed anionic sites, forming an electrical double layer. When high voltage is applied, migration of hydrated cations in this double layer causes movement of bulk fluid in the direction of the cathode. This phenomenon is called electroendosmosis. The magnitude of electroendosmatic flow ( EOF ) increases as function of pH and under alkaline conditions the velocity of EOF is much greater than the migration speed of sample ions. This can be an advantage when analyzing mixtures of anionic and cationic species, since all analytes will be eventually swept past the detection point ofEOF. Resolution of sample components can be achieved based on differences in mass to charge ratio, isoelectric point, molecular size, hydrophobic character, and streochemistry. Capillary zone electrophoresis ( CZE ) is the most common CE separation method and employs a single buffer system in free solution. Separations are based on differences in mass-to-charge rations of sample components. In capillary isoelectric focusing ( CIEF ) the three basic steps are sample injection, focusing and mobilization. Separation of molecules based on their isoelectric points can be achieved using isoelectric focusing. In capillary gel electrophoresis ( CGE ) the sieving effect of the gel is used for the separation of large ions. Micellar electrokinetic chromotograpy ( MEKC ) is, as the name implies, a chromatographic separation technique performed using CE instrumentation. The separation medium is a buffer containing a surfactant at a concentration higher than the critical micelle concentration. The clay used for this study is Kurşunlu ( Turkey ) montmorillonite and an unit cell formula of Kurşunlu clay is given below: ( Sİ7.I8I Alo.819 ) O2O ( AI1.10I6 Feo.2664 Mgo.3227 Tİo.2850 ) ( Caı.0686 Ku684 Nao.6494) (OH )a Fractions having a particle size 40-75 jim were initially treated with 50 mM acetic acid at pH 5 and at 50°C to dissolve carbonates. After the washing step by water, the clay was dried at 90°C. The clay was then treated with CTAB. After washing, the modified clay was dried at 90°C prior to use. In the experiments, the adsorption isoterms of phenols were obtained employing a batch equilibrium technique. Table 1 shows the adsorption ratios of phenols from an aqueous solution at pH=7, on organo-clay and on treated clay. XIRecovery of the adsorbed phenols from modified clay was also studied in a batch experimental set-up using ethyl alcohol as eluent. Table 2 demonstrates the recovery ratios and uptake ratios of the second adsorption cycle. Both the adsorption and the recovery ratios were very high for all phenols. The work presented here demonstrates the effective use of the modified clay for the preconcentration of phenols from aqueous solution. Although the used montmorillonite did not adsorb substantial quantial quantities of phenols, after its modification the prepared organo-clay was very effective in removing phenols from water. XII
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