Elektro Döndürme Yöntemi İle Elde Edilen Karbon Nanolif Ve Karbon Nanotüplerin Karakterizasyonu Ve İşlevselleştirilmesi

Abstract

Nanoteknoloji son yıllarda sıklıkla araştırılan bir konudur. Gelişmiş ülkelerde bu araştırmalar için nanoteknolojiye büyük bütçeler ayrılmaktadır. Ülkemizde de nanoteknolojinin öncelikli alan olarak belirlenip desteklenmesi ile nanoteknoloji ile ilgili araştırmaların artacağı beklenmektedir. Nanoteknolojinin disiplinler arası bir bilim olması, önümüzdeki yıllarda nanoteknolojik uygulamalar ile geliştirilmiş çeşitli ürünlerin günlük hayatımıza girmesini sağlayacaktır. Özellikle sağlık, savunma, tekstil, enerji ve elektronik gibi alanlarda elde edilecek katma değeri yüksek ürünlerin insanoğlunun hayatını kolaylaştırması beklenmektedir. Nanoteknolojinin gıda alanında da uygulanması konusunda araştırlmalar mevcut olsa da henüz sınırlı sayıdadır. Tarımdan gıda üretimine, besin takviyelerinden gıda ambalajlama sistemlerine kadar nanoteknolojiden faydalanılabilir. Gıda bileşenlerinden oluşan nano emülsiyonlar, nanoparçacıklar, nanokompozitler, nanolifler, nanotüpler ve nanosensörler çeşitli amaçlarla gıda uygulamalarında kullanılabilme özelliğine sahiptirler. 100 nm’den küçük boyuttaki iplikçikler olarak tanımlanan nanoliflerin gıda kaynaklı bileşenlerden elde edilmesi ve bunların gıda sanayinde kullanımı ile ilgili çalışmalar mevcuttur. Elektro döndürme yöntemi ile etkin ve basit bir şekilde elde edilebilen nanolifler, geniş yüzey alanları ile dikkat çekmektedir. Nanotüpler ise mikro ve nano boyuttaki liflerin içi boş, tüp şeklindeki yapılar olarak düşünülebilir. Nanotüpler, yüksek yüzey alanına sahip olmakla beraber farklı materyallerle işlevselleştirilebilir olması ve başlı başına nanotüp yapısının üstün özelikleri nedeniyle birçok alanda olduğu gibi gıda araştırma ve uygulamalarında da yer edinmiştir. Karbon kaynağı olarak kullanılan bir materyalin çeşitli metotlarla nanotüp şekline dönüştürülmesi ile elde edilen yapı karbon nanotüp (KNT) olarak adlandırılmaktadır. KNT’ler üstün mekanik, elektriksel ve optik özellikleri nedeni ile son yılların en çok araştırılan konularından birisidir. Gıda alanında da KNT’ler ile geliştirilen sensörler ilgi çekmekte ve araştırılmaktadır. Çeşitli bileşiklere karşı seçicilik kabiliyeti olan maddeler, KNT’leri işlevselleştirmek için kullanılmakta ve böylece hassas bir algılama sağlanabileceği belirtilmektedir. KNT ile geliştirilen sensörlerin gıda ambalajlama ve depolama sistemleri ile birlikte gıda analizlerinde ve gıda tağşişlerinin belirlenmesinde kullanılabileceği düşünülmektedir. Bu tez çalışmasında elektro döndürme yöntemi ile karbon nanolif ve karbon nanotüp eldesi amaçlanmıştır. İlk aşamada, nanolif eldesinde yaygın bir şekilde kullanılan elektro döndürme metodu ile karbon kaynağı poliakrilonitril (PAN)’dan nanolif üretimi gerçekleştirilmiştir. Eş eksenli elektro döndürme metodu ile iç ve dış olmak üzere iki tabakadan oluşan nanolifler üretilebilmektedir. Kaplama (dış) tabakası olarak PAN, iç tabaka olarak (çekirdek) yağ kullanılarak PAN/yağ nanoliflerinin üretimi gerçekleştirilmiştir. İkinci aşama, nanoliflerin ısıl işlemlerle kontrollü atmosferde yakılmasını (piroliz) oluşturmaktadır. Piroliz işlemi stabilizasyon ve karbonizasyon olarak iki aşamayı içermektedir. Stabilizasyon, nanoliflerin 280 ºC’ye ısıtılması ve böylece nanolif yapısının kararlı hale gelmesidir. Karbonizasyon ise bir gaz atmosferi ortamında nanoliflerin 1000 ºC’ye ısıtılmasını içermektedir. Bu işlemle, PAN nanolif yapısında bulunan karbon olmayan elementlerin uzaklaştırılması sağlanmaktadır. Eş eksenli metodla elde edilen PAN/yağ nanolifleri karbonize edildiğinde çekirdek tabakada bulunan yağ yanıp uzaklaşmakta ve böylece içi boş nanotüp yapısı elde edilmektedir. Üçüncü aşama, elde edilen nanolif ve KNT’lerin karakterizasyonunun yapılmasıdır. Bu amaçla KNT ve nanoliflerin taramalı elektron mikroskopu (SEM) ile görüntüleri alınmış, BET yüzey alanı hesaplaması yapılmış ve X-ışını kırınım (XRD) analizi ile kristal yapıları incelenmiştir. İşlevselleştirilen KNT’lerin karakterizasyonu ise XRD’ye ek olarak FTIR (Fourier dönüşümlü kızılötesi spektroskopisi) ile gerçekleştirilmiştir. Ortalama 600 nm çapında PAN nanolifleri ve 400 nm çapında KNT’ler elde edilebilmiştir. SEM görüntülerinde içi boşluklu nanotüp yapısı açıkça gözlenebilmektedir. Ayrıca değişen çaplarda gözeneklere de rastlanmıştır. XRD analizinde nanoliflerin düzensiz amorf yapıda oldukları görülmektedir. KNT’lerin ise mükemmel grafitik yapıdan uzak olduğu görülse de nanoliflere göre daha düzenli bir kristal yapıya sahip oldukları söylenebilir. BET ölçümlerinde, nanoliflerin yüzey alanı 82,23 m2/g olarak bulunurken KNT’ün 207,86 m2/g olarak bulunmuştur. Son olarak, elde edilen KNT’ler yağ ile işlevselleştirilmiş ve bu işlemin başarı ölçütü olarak XRD ve FTIR analizi ile karakterizasyonu yapılmıştır. Elde edilen sonuca göre, KNT’ler işlevselleştirildiğinde daha düzenli bir kristal yapıya sahip olmaktadır. FTIR analizi ile XRD deseninde ortaya çıkan kararlı yapıyı sağlayan bağlanmalar gözlenebilmiştir. Elektro döndürme yöntemi ile KNT eldesi ve işlevselleştirilmesinde en önemli aşamalar elektro döndürme parametreleri ve piroliz işlemidir. Burada uygun koşullar sağlandığında, mükemmel yapıda KNT’lerin elde edilebileceği düşünülmektedir. Bu tez çalışması ile KNT’lerin işlevselleştirmede kullanılan materyale bağlı olarak sensör uygulamalarında kullanılabileceği öngörülmektedir.

Nanotechnology is become a fequently reasearched topic in recent years. Nanotechnology involves the characterization, fabrication and/or manipulation of structures, devices or materials that have at least one dimension that is approximately 1–100 nm in length. When particle size is reduced below this threshold, the resulting material exhibits physical and chemical properties that are significantly different from the properties of macroscale materials composed of the same substance. Research in the nanotechnology field has skyrocketed over the last decade, and already there are numerous companies specializing in the fabrication of new forms of nanosized matter, with applications that include medical therapeutics and diagnostics, energy production, molecular computing and structural materials. In developed countries, the large amount of budgets have been allocated for nanotechnology. In our country, nanotechnological studies are expected to increase by which nanotechnology is identified as priority areas and supported by the government. Nanotechnology is an interdisciplinary science which provides entering a variety of products enhanced by nanotechnological applications into everyday life in the years ahead. High value added products especially in health, defense, textiles, energy and electronics, are expected to easy to life of humans. Although there are some studies about implementation of nanotechnology in the food area, it is limited yet. Scientists and industry stakeholders have already identified potential uses of nanotechnology in virtually every segment of the food industry, from agriculture (e.g., pesticide, fertilizer or vaccine delivery; animal and plant pathogen detection; and targeted genetic engineering) to food processing (e.g., encapsulation of flavor or odor enhancers; food textural or quality improvement; new gelation or viscosifying agents) to food packaging (e.g., pathogen, gas or abuse sensors; anticounterfeiting devices and stronger, more impermeable polymer films) to nutrient supplements (e.g., nutraceuticals with higher stability and bioavailability). Nanoemulsions, nanoparticals, nanocomposits, nanofibers, nanotubes or nanosensors consisted of fod components are capable of being used in food applications for various purposes. Nanofibers defined as fibrils having an average diameter of less than 100 nm. Research on the potential applications of nanofibers increased in recent years. Nanofibers, take interest with their large surface area, aspect ratio and porosity. There are several methods used in the production of nanofibers such as drawing, template synthesis, phase separation, self assembly, meltblown, electrospining and bicomponent technique. The simplest and most efficient method is electrospinning. Electrospinning method is carried on after dissolving the polymer in a suitable solvent such as water, asetic acid, formic acid etc. Polymer solution is placed in the syringe and finally, uniform nanofibers are obtained by applying high voltage between the tip and collector plate. Continuous nanofibers can be fabricated by electrospinning technique which is an application of high voltage to sprayed solution from a capillary tube. Electrospinnning is easiest and more economical method comparing to other methods for obtaining nanofibers. Nanotubes can be considered as tubular structure of micro/nano sized hollow fibers. Basicly, a carbon source material is formed nanotube structure by the various methods which is called carbon nanotube (CNT). A CNT is a hexagonal network of carbon atoms rolled up into a seamless, hollow cylinder, with each end capped with half of a fullerene molecule. Although chemical composition of CNTs is similar to graphite, CNTs are highly isotropic, and it is this topology that distinguishes nanotubes from other carbon structures and gives them their unique properties. There are several methods used in producing CNTs which are classified according to the phase of used materials as solid or gaseous. Solid methods are arc discharge, laser vaporization and solar furnace technique while there are several types of chemical vapor deposition (CVD) techniques in gaseous methods such as atmospheric pressure, low-pressure or ultrahigh vacuum CVD. Besides, CNTs can also be produced by diffusion flame synthesis, electrolysis and electrospining method. The electrospining method is used in this study to obtain CNT following by pyrolysis of electrospun carbon nanotubes. There are two main kinds of nanotubes: single walled nanotubes (SWNTs), individual cylinders of 1-2 nm in diameter, which are actually a single molecule; and multi-walled nanotubes (MWNTs), which are a collection of several concentric graphene cylinders. CNTs used as electrically conductive fillers in plastics firstly. In the automotive industry, conductive CNT plastics have enabled electrostatic-assisted painting of mirror housings, as well as fuel lines and filters that dissipate electrostatic charge. Other products include electromagnetic interference-shielding packages and wafer carriers for the microelectronics industry. For load-bearing applications, CNT powders mixed with polymers or precursor resins can increase stiffness, strength, and toughness. Besides, MWNTs are widely used in lithium ion batteries for notebook computers and mobile phones, marking a major commercial success. These CNTs provide increased electrical connectivity and mechanical integrity, which enhances rate capability and cycle life. Ongoing interest in CNTs as components of biosensors and medical devices is motivated by the dimensional and chemical compatibility of CNTs with biomolecules, such as DNA and proteins. At the same time, CNTs enable fluorescent and photoacoustic imaging, as well as localized heating using near-infrared radiation. Especially, their unique elec-trochemical, electronic and optical properties provide a unique platform for the development of chemo- and biosensors based onelectrochemical, electrical or optical signal outputs. Although CNTs can act as asignal transduction substrate, they have no intrinsic recognitionability for selective binding and sensing. Thus, CNTs are usually needed to hybrid with a component having specific recognition unitto prepare composite probe to address this issue. Substances capable of selectivity to various compounds are used to functionalize CNTs and sensitive detection can be achieved in this way is indicated. Nanotubes appeared in food research and applications as in many fields, due to the large surface area, superior features of themselves and enabling to functionalized by different materials. The CNT based sensors are of interest and investigated in food science. CNT based nanosensors considered to be use of determination of food adulteration, food analysis, beside food packaging and storage areas. In this thesis, it was aimed to obtain carbon nanofiber and carbon nanotube by electrospining method. Firstly, nanofiber is produced from polyacrylonitryle (PAN) as a carbon source, by electrospining method which is widely used to obtain nanofiber. PAN, a well-known polymer with good stability and mechanical properties, has been widely used in producing carbon nanofibers (CNFs) as these have attracted much recent attention due to their excellent characteristics, such as spinnability, environmentally benign nature and commercial viability. The core/shell electrospun nanofibers can be produced by coaxial electrospining method. PAN/oil nanofibers produced whereby PAN was used as shell and oil was used as core. Second step is heating of nanofibers (pyrolysis) under atmosphere controlled conditions. Pyrolysis is comprised of two steps as stabilization and carbonization. Stabilization is a heating process about 250 ºC by which nanofibers become stable. Stabilization involves heating PAN fibers in an oxygen-containing atmosphere, inducing cyclization of nitrile groups and crosslinking of the chain molecules, a process that prevents melting during subsequent carbonization. When the PAN fiber is subjected to the stabilization temperature, dense ladder-polymer structure begins to form by reacting with oxygen that prevents melting during subsequent carbonization. In the second step, carbonizing the stabilized PAN fibers in an inert atmosphere removes non-carbonized components selectively in the form of gases, to give carbon fibers with a yield of about 50–57% of the mass of the original PAN. After carbonization, denitrogenation takes place, resulting in the formation of a network structure. Briefly, carbonization is carried out by which nanofibers are heated in an atmosphere controlled furnace about 1000 ºC. The non-carbon elements are removed by carbization process. When PAN/oil nanofibers carbonized, the core is evaporated and the hollow nanotube structure is obtained. Characterization of obtained nanofibers and CNTs are in the third stage. For this purpose, SEM images of obtained nanofibers and CNTs were taken, surface area and crystal structure of them measured by BET and X-Ray diffraction method, respectively. We obtained PAN nanofibers in diameter of 600 nm and CNTs about 400 nm. The hollow nanotube structure could be seen clearly at SEM images. In addition, pores were found in varying diameters. According to XRD patterns, it was observed that nanofibers were disordered amorphous structure. Althoug, CNTs were far away from perfect graphitized structure, it can be said that CNTs have ordered crystalline structure in comparsion with nanofibers. BET results show that the surface area of nanofibers were 82,23 m2/g, while surface area of CNTs were 207,86 m2/g. Lastly, the obtained CNTs were functionalized by treatment with oil olive. For this purpose, 0.1 g of CNT was treated with 100 mL of oil olive. The flask was stirred in a magnetic stirrer for 10 min and ultrasonically vibrated at room temperature for 15 min. After that, the functionalized MWCNTs was collected via filtered method under vacuum and then washed thoroughly chloroform to remove oil from sample. Success of the functionalization process was stated by XRD and FTIR analyses. Results indicates that, functionalization of CNTs become more ordered crystal structure and FTIR results supported that idea. The oil could be successfully bound on the CNT surface covalently. We state that, electrospinning parameters and pyrolysis are the most important stages to obtain perfect structured CNTs. This study provides that according to the choosen selective material, CNTs may be used in sensor applications.