Polisakkarit Kaplı Titanyum Nanopartiküller Kullanılarak Bazı Ağır Metallerin Giderilmesi

Abstract

Çevre, insan ve hayvan dokularında kilogram başına miligram veya daha az miktarda bulunan elementlere eser element adı verilir. Eser miktarda bile sakıncalı olan bu maddeler arasında en önemli grup ağır metallerdir. Bazı ağır metallerin yaygın kullanımları onların deniz suları, doğal sular veya atık sular içerisinde istenmeyen derişimlerde olmasına yol açar. Eser miktarda ağır metal tayini ve uzaklaştırılması, son zamanlarda giderek artan çevre kirliliği sonucu çeşitli örneklerde önem kazanmıştır. Doğal sularda, biyolojik ve gıda örneklerinde ağır metallerin tayini ancak aletli analiz metotları kullanılarak yapılabilir. Ancak, örnekler içindeki eser ağır metallerin doğrudan tayini, düşük derişimde olmaları ve matriks etkisi gösteren türlerden dolayı zor olabilmektedir. Bundan dolayı; örnek analiz edilmeden önce tayin edilecek türün matriksten ayrılması amacıyla bazı metotlar geliştirilmiştir. Son yıllarda ağır metalleri çeşitli tipteki sulardan uzaklaştırmak ve eser metalleri matriksten ayırmak için reçinelerin yanında serbest veya bir materyal üzerine bağlanmış nanomalzemelerden analitik çalışmalarda yararlanılmaktadır. Bu çalışmada, eser miktarda kurşun, kobalt, kadmiyum, bakır ve nikel metalleri, doğal bir organik madde olan nişasta kaplı nano titanyum dioksit (TiO2) sorbenti ile uzaklaştırılması, grafit fırınlı atomik absorpsiyon spektrometresi (GFAAS) kullanılarak incelenmiştir. Modifiye edilmiş titanyum dioksit nanopartikülleri, FT-IR Spektroskopisi, Dinamik Işık Saçılması (DLS) ve zeta potansiyeli ile karakterize edilmiştir. Pb, Cu, Co, Cd ve Ni elementlerinin nanomalzeme üzerine adsorpsiyonu, sorbent miktarı, pH ve numune hacmi etkisi ile araştırılmıştır. Batch tekniği kullanılarak elementlerin katı faza tutunması sağlanmıştır ve hem analitlerin uzaklaştırılması hem de tayin yönteminde kullanılabilmesi amacıyla deneysel parametreler optimize edilmiş ve metot validasyonu gerçekleştirilmiştir. Optimize edilen adsorpsiyon koşulları altında Pb, Cu, Co, Cd ve Ni > % 95 oranında spayk edilmiş musluk suyu örneklerinde geri kazanılmıştır. Deney koşullarının optimizasyonu sonrasında, musluk suyu gibi bir matrikste analit elementlerinin, nişasta kaplı nano titanyum dioksit partiküllerinin üzerine tutunabildiğini ve grafit fırınlı atomik absorpsiyon spektrometresi (GFAAS) ile başarılı bir şekilde tayin edilebildiğini göstermektedir. Sorpsiyona dayalı bu ayırma metodu hızlı, kolay uygulanabilir, düşük dedeksiyon limitlerine sahip ve çevre dostu olarak tanımlanabilir. Sorbent olarak kullanılan nişasta kaplı titanyum dioksit nanopartikülleri yeni, doğal ve kolay sentezlenebilir. Nanopartiküller diğer kompleksleyiciler ile de modifiye edilerek bu amaçla geniş bir şekilde kullanılabilmektedir.

Elements available in environment, human and/or animal tissues in miligram per kilogram or less are called as trace elements. Heavy metals are the most important group among the substances damaging even though in trace quantity. Some heavy metals used commonly causes being in undesired concentration in the sea waters, the natural waters and the waste waters. Determination of trace metal ions in various samples has gained importance due to growing environmental pollution recently. Heavy metal determination in natural water, biological and food samples can be implemented using instrumental analysis methods. It is difficult to determine trace heavy metals in their samples directly due to their low concentration and coexistence of matrix species. Thus, some methods have developed for separation of analyte. The toxicity and the effect of trace elements on human health and the environment are receiving increasing attention in pollution studies recently. Exposure to heavy metals, even at trace level, believed to be a risk for human beings. Thus, effectively and deeply remove undesirable metals from water systems is still a very important and challenging. Nowadays, various methods have proposed for efficient heavy metal removal from waters, including but not limited to chemical precipitation, adsorption, ion exchange, electrochemical technologies and membrane filtration. Among these techniques, adsorption offers flexibility in design and operation and in many cases; it will generate high quality treated effluent. Also, owing to the reversible nature of most adsorption processes, the adsorbents can be regenerated by convenient desorption processes for multiple use, and many desorption processes are of low maintenance cost, ease of operation and high efficiency. Therefore, the adsorption process has come to the forefront as one of the major techniques for heavy metal removal from water/wastewater. On the other hand, a nanometer material is a new functional material, which has gained importance owing to its special properties. Nanoparticles are defined as clusters of atoms or molecules of metal and oxide, ranging in size from 1 nm to 100 nm, falling between single atoms or molecules and bulk materials. One of their properties is that most of the atoms of a nanoparticle are on the surface. The surface atoms are unsaturated and can easily bind with other atoms, thus possessing high chemical activity. In conclusion, nanometer materials can selectively adsorb metal ions, and have a very high adsorption capacity. In recent years, free or coated nanomaterials are used for removing heavy metals from the various types of the waters and for separating the trace elements from the matrix in the analytical studies beside resins. Nano-sized metal oxides, including nano-sized ferric oxides, manganese oxides, aluminum oxides, titanium oxides, magnesium oxides and cerium oxides provide high surface area and specific affinity for heavy metal adsorption from aqueous systems. It has become a hot topic to develop new technologies to synthesize nano metal oxides, to evaluate their removal of heavy metals under varying experimental conditions so far. Titanium dioxide is the most commonly investigated metal oxide because of its nontoxicity, high stability, high photocatalytic activity and excellent dielectric properties. Changes in sized and shapes of nano materials affect physicochemical and physiological structures. Therefore, some parameters such as size, zeta potential and surface function properties generally investigated for the characterization of nanomaterials. Dynamic light scattering (DLS) method is preferred for particle size while zeta potential used for particle charge. In this study, removal of lead, cobalt, cadmium, copper and nickel metals in trace quantities using nano titanium dioxide (TiO2) coated with starch as a sorbent which is a natural organic substance were investigated with graphite furnace atomic absorption spectrometry (GFAAS). Modified nanoparticles characterized by Fourier Transform Infrared (FT-IR) Spectroscopy, Dynamic Light Scattering (DLS) and zeta potential. In Fourier Transform Infrared (FT-IR) Spectroscopy, maximum absorption was not available for colloidal titanium dioxide nanoparticles while there were some absorptions due to the availability of functional groups for titanium dioxide coated starch nanoparticles. Absorptions at approximately 1000 cm-1, 3000 cm-1 and 3350 cm-1 showed that the functional groups in TiO2@starch. According to the results of dynamic light scattering, the size of titanium dioxide nanoparticles was about 10 nm while the size of titanium dioxide coated with starch was between 15-20 nm. In addition to, the zeta potential of titanium dioxide nanoparticles was positive (18.9±0.8 mV) while the zeta potential of titanium dioxide coated with starch nanoparticules was negative (-20.7±0.6 mV). This result showed that coating of titanium dioxide nanoparticul surface with other functional groups and accordingly coating with negative charge. All of the results above such as increase in size of nanoparticules and other physicochemical parameters evidenced that coating of titanium dioxide nanoparticules with starch. To show that new sorbent can be used for removal of the heavy metals with high recovery, sensitivity and accuracy, base factors affected sorption should be investigated. In scope of this, the adsorption–desorption of metals can be affected by factors such as pH, adsorbent and sample properties. Therefore, in order to find the effects of adsorption of 0,1 mg L-1 analyte elements such as lead, cobalt, cadmium, copper and nickel elements on modified nanomaterial, amount of sorbent, pH and sample volume were investigated. The pH value has a very important effect on the adsorption of different ions on modified metal oxide surfaces. The pH of the solution influences the distribution of active sites on the surface of TiO2@starch and the –OH on the surface provides the ability to bind cations. Therefore, the hydroxyl groups are important in controlling the adsorption and desorption of metals from TiO2@starch surface. The pH affects the surface hydroxyl groups on the sorbent. Most of sorbents used in cation exchange adjusted to a neutral pH for adsorbing metal ions in matrix. In order to determine the optimum pH at which heavy metals adsorbed at the maximum level by sorbent, the pH values of sample solutions were adjusted within the range 3-9 and then the experiment procedure was followed. Under these conditions, while 60-70 % of metal ions in the aqueous solution were retained by the acidic and alkaline pH, the retention was obtained almost 100 % at pH 7. At these conditions, it evidenced that all metals can be adsorbed by the sorbent without adding any chelating agent at pH 7. Therefore, the optimum pH was set at pH 7. In case of low sorbent amount, metal ions could not adsorbed by sorbent and efficiency decreases. Therefore, optimum sorbent amount should be determined. In order to optimize the sorbent amount, the effect of different amounts of TiO2@starch on the sorption of analyte element within the range of 0,01-0,1 g was investigated. From a series of experiments, the optimum sorbent amount was selected as 0,01 g while a sorption is observed between 0,01-0,05 g. Finally, the effects of sample volume on the sorption investigated using different sample volumes. To optimize the sorbent volume for quantitative retention of analyte elements, 0,01 g TiO2@starch nanoparticles at pH 7 were added with sample volume between 2-50 mL. When the sample volume was above 10 mL, sorption decreased. However, the sample volume was between 2-10 mL, sorption of analyte elements was obtained above 90%. As a result, 5 mL of sorbent volume used at pH 7 for quantitative sorption of the analyte ions. Thus, easy applicability, easy preparation and easy sampling obtained with maximum sorption using minimum sample volume. All the optimum values mentioned above used throughout the study. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were calculated according to 3σ and 10σ of a blank solution (N=10), subjected to the presented procedure, respectively. Supernatant treated with titanium dioxide coated with starch nanoparticles used as blank solution. The elements adsorbed to solid phase using batch technique and analyzed to remove and determine the analytes. With the aim of investigating adsorption of metal ions to sorbent, distilled water, 2 M HCl and 2 M HNO3 were examined for recovery. The recovery ratio was obtained in level of > 95 %, except distilled water. The highest ratios obtained in 2 M HCl. Under the optimized adsorption conditions, lead, cobalt, cadmium, copper and nickel were recovered in the spiked tap waters samples taken from the laboratories in Istanbul in the ratio of > % 95. The amounts of direct and standard addition water samples were recovered between the ratio of 81-102 % (N=5). It shows that after the optimization of the test conditions, analyte elements be adsorbed on nano titanium dioxide particles coated with starch even in a matrix like tap water and they can be determined with graphite furnace atomic absorption spectrometry (GFAAS) successfully. In conclusion of this study, this separation method based on sorption can be defined as fast, easy applicable, having low dedection limits and environmentally friendly. Titanium dioxide coated with starch nanoparticles used as sorbent in the study are new, natural and easy synthesizable. Nanoparticles can be commonly used for this purpose modifying other complexing agents.