Co(II), Ni(II), Cr(III) ve Cr(IV) elementlerinin adsorbsiyonla zenginleştirilmesi ve grafit fırınlı AAS ile tayini /
Yazar: ÖZGÜL GÖÇER
Danışman: PROF.DR. ÜNEL KÖKLÜ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Yüksek Lisans, 1995
Konu: Kimya = Chemistry
Dizin: Amino = Amino ; Atomik soğurma spektrofotometri = Atomic absorption spectrophotometry ; Elementler = Elements ; Grafit fırınlar = Graphite furnaces ; Silis = Silica

Özet:
ÖZET : Bu çalışmada, amino ve tiyol modifiye silikalarm özellikleri ve hazırlanışları, ön zenginleştirme ve ayırma uygulamaları ile grafit fırınlı atomik absorpsiyon spektrofotometresi (GFAAS) kullanılarak eser miktarlardaki kobalt (II), nikel (II), krom (III) ve krom (VI) elementlerinin tayinleri anlatılmıştır. Modifiye silikalar hazırlanırken silikajel derişik hidroklorik asitle muamele edilip yıkama suyunda klor iyonu kalmaymcaya kadar deiyonize suyla yıkandı ve 150°Cfde bir gün kurutuldu. Kuru silikajel metanol içine kondu ve amino modifiye silika eldesi için (C2H5O) 3Sİ (CH2) 3NH2 (3-amino propiltrietoksisilan), tiyol modifiye silika eldesi için de (CH3O) 3Sİ (CH2) 3SH (3-Merkapto propiltrimetoksisilan) ilave edildi. Metanol vakum altında uzaklaştırıldıktan sonra, modifiye silika yıkama suyu berraklaşmcaya kadar deiyonize suyla yıkandı. Bütün adsorpsiyon deneylerinde "Batch ( çalkalama) " ve " Kolon" yöntemleri kullanılmıştır. Batch yönteminde pH'ın, çalkalama süresinin, kullanılan modifiye silika miktarının, kolon yönteminde ise sodyum klorürün ve çeşitli, akış hızlarının adsorbsiyon ve geri kazanma üzerindeki etkileri incelenmiştir.

Abstract:
SÜÜMMÖf DETEKÜimTION OF C©(II), Mi (II), CrflIIJ, Gr(VX) IH GlSâS JIFTER C0HCEKTBAT20H BY MODIFIED SILIG&S In this study, the preparation and characteristics of amino and thiol modified silicas and their applications to the preconcentration and determination of trace amounts of cobalt (II), Nickel (II), Chromium (III) and Chromium (VI) by Graphite Furnace Atomik Absorption Spectrometry are described. In the determination of trace elements, the use of separation and preconcentration technique is a necessity when the concentration of the analyte is too low to be determinated directly as well as interferences due to matrix can not be eliminated. Various analytical techniques, such as extraction, ion exchange, coprecipitation etc. with numerous materials have been widely applied for this purpose. Various chelating agents are recommended as the appropriate collectors for the preconcentration and separation of analyte elements prior to their determination by instrumental methods. The properties of different chelating agents have been investigated with respect to recoveries at different pH values, the choice of appropriate eluent, t rat e of retention and elution, capacity, the case of the preconcentration and separation procedure, reproducibility, blank values and the effect of different matrices on recoveries. One of the most extensively studied and widely used techniques of separation and preconcentration is solvent extraction using immiscible liquids, an aqueous and an organic solvent, according to the distribution law: VI[Al] D=(1) [A] Where D is the distrubutions coefficent and [Al], [A] are the concentrations in the organic and aqueous phase respectively. Ion exchange techniques are well suited for both separation of ions of opposite charge (cation-anion separation) and the separation ion like charge (for matrix-trace separations and for separating mixtures of trace ions). In an ion exchanger functional groups are immobilized on some type of solid substrate, thus providing the potential to either batch extract ions from solution or to use the ion exchange material in a packed column. Being covered with hydroxyl groups (silanol groups) t the surface of silica gel can be modified in many ways and a large number of different groups can be attacthed to its surface. Silica gel can be considered to be an amorphous condensation polymer of silicic acid. Conventionally, it is made by mixing aqueous solutions of sodium silicate and sulphuric acid. Molecules of silicic, disilicic and trisilicic acid are formed and condense with one another. Silicic acid first condenses with itself to form disilicic acid and water, the disilicic acid condenses with silicic acid to form trisilicic acid, and so on. Condensation between two molecules of disilicic acid is also possible. This stage leads to a colloidal solution of spheroidal particles of polysilicic acids which have a diameter of about 10 nm and contain roughly ten thousand silicon atoms each. The colloidal solution eventually forms a hydrogel that is washed and dried to produced silica gel. Further condensation, inter and intra particules, occurs during these stages. During, the surface tension forces of water collapse the original, very open, texture until irxxthe mechanical strength of the agglomeration of particles becomes sufficient to resist further collaps. The remaining water than evaporates leaving a material of large area and substantial pore volume whose texture must rather resemble that of a loosely packed gravel bed. Silica gels of differing textures can be prepared by variations in the techniques of preparation and by aging of the gel subsequent to its formation. Most commercial silica gels are either of the narrow pore type (avarage pore diameter about 2.5 nm, specific area about 700 m2 per g and pore volume about 0.4 ml per g) or of the wide pore type (avarage pore diameter about 14nm specific area about 300 m2 per g, and pore volume about 1.1 ml per g). This study has employed mostly the narrow pore silica gel. The silanol group is a weak acid with a pKa in the vicinity of 9. It forms strong hydrogen bonds to water, alcohols, ethers etc. Since the protons of the silanol groups are weakly acidic, they can be replaced by cations. In this sense silica gel can be classified as a highly cross-linked, non-swellable, weak acidic ion exchanger. The rose complex Co (III) (en)2ClH2C>2+ can be ion exchanged onto silica gel. If the gel is treated immediately with dilute acid, the complex is rapidly liberated but, if the treatment is postponed for some hours extraction becomes very slow. The following reaction has occured and it is reversed by acid only slowly. Such complexes -rSi-cr - SiO-Co ( en ) 2C1+ Co (en) 2C1H202+ - *> X \ - Si-CT - Si-O- / y may become rather unstable if gel is dried. Thus silica gel ion exchanged by the coordinatively inert complex vxaxCr(NH3)6^+ decomposes on drying to give highly dispersed chromium on silica gel. The silanol group is the only functional group observed on the silica surface under normal conditions. The hydrogen ions appeared by the level to interest in chemical applications. The most potential uses of modified surfaces: 1) Catalysis: An important method of making metal based catalyst is by anchoring catalytically active species to a surface. 2 ) Enviromental Chemistry: Such modified silica gel could perhaps be used as selective metal adsorbents i.e. pollution of heavy metals. 3) Analytical Chemistry: Potential application as liquid chromatographic column material for separation and dedection. 4) Polymer Chemistry: Interactions between fillers and polymers in plastic materials. Polivalent ions react with those silanol groups in a complicated way to form complexes in some extent. Thus, for the application of silics surfaces in special processes, the surface should be modified by some groups. One of the common procedures is the chemical reaction of the surface silanol groups with an organoalkoxysilane. For the preparation of modified silicas, the silica was first stirred with hydrochloric acid, washed and dried at 150 °C for 24 hours. Typically 1 g was taken from dried sample and mixed with 1 mmol (3- Aminopropyltriethoxysilane) and 3-Merkaptopropyl trimethoxysilane to obtain amino and thiol modified silicas, respectively and the methanol was evaporated under vacuum at 100 °C. The residual silica was dried at 150°C and washed with distilled water until washing water contains no dissolved matter. xss.In the experimental study; both batch and column methods were used. In batch method, the effects of pH, shaking time and retention of Co (II), Ni(II), Cr(III) and Cr(VI) were investigated. The maximum loading capacity of the amino and thiol were determinated using the batch procedure. Metal ions were quantitatively adsorbed on both amino and thiol modified silicas. The shaking time for the completation of the quantitative retention and for the quantitative elution was thirty minutes. The sample was passed through the column, then the elements collected on the modified silica gels were eluted with 25 ml 2M eluent and determinated by GFAAS. In the column procedure, the effect of NaCl on the recovery was also investigated. A quantitative separation could be achived in the samples containing even 1% NaCl as the matrix. As a result, it can be concluded that amino and thiol modified silica gels are appropriated colectors for the preconcentration and separation of Co (II), Ni(II), Cr(III) and Cr(VI). 3S