Gümüş nanotanecik katkılı nanokompozit malzemelerin üretimi ve karakterizasyonu
Fabrication and characterization of silver doped nanocomposites
Yazar: ÖZLEM KABAK
Danışman: PROF. DR. SADRİYE OSKAY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı / Kimya Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Kimya Mühendisliği = Chemical Engineering

Özet:
Günümüzde endüstriyel uygulamaların artmasıyla birlikte, çevre problemleri önemli ölçüde artmıştır ve bu sorunlara çözüm arayışı hızla devam etmektedir. Önemli çevre problemlerinden biri olan su kirliliği, nüfus artışıyla da birlikte, temiz suya erişimi zorlaştırmaktadır. Var olan su kaynaklarının sınırlı olması ve temiz su talebinin artışı, araştırmacıları yeni çözümler bulmaya yöneltmiştir.  Nanoteknoloji ile elde edilen malzemeler birbirinden farklı özellikleriyle bu alanda uygulama alanı bulmuştur. 
Nanomalzemeler, büyüklüğü 1 ila 100 nm arasında değişen malzemelerdir ve elektronik, biyomedikal, ilaç, kozmetik, enerji, çevre ile tekstil gibi alanlarda kullanılmaktadır. Yüzey-hacim oranlarının yüksek oluşu birçok farklı alanda kullanılmalarına olanak tanımaktadır. Karbon nanotüpler, fullerenler, kuantum dotlar, metal ve metal oksit nanotanecikleri özgün özellikleri sayesinde sık kullanım alanı bulan nanomalzemelerdendirler.
Fotokatalitik malzemeler su arıtma sistemlerinde, antibakteriyel uygulamalarda ve kirlilik gidermede kullanım alanı bulmaktadırlar. Titanyum dioksit ise, yüksek oksidasyon gücü, toksik olmaması ve kararlı bir yapıda olması nedeniyle yaygın kullanılan fotokatalizörlerden biridir. Titanyum dioksit fotokatalizör olarak, güneş pillerinde ve su arıtma uygulamalarında kullanılmaktadır. Kendi kendini temizleyebilme özelliği sayesinde yüzeylerde ve kaplamalarda kullanılmaktadır.
Titanyum dioksit, gümüş gibi metalik nanotanecikler içeren nanokompozitmalzemelere katıldığında, fotokatalitik, kendi kendini temizleyebilme ve antibakteriyel özellikler kazandırmaktadır.
Nanomalzeme üretiminde kullanılan yöntemlerden olan sol-jel yöntemi, diğer yöntemlere göre yüksek saflıkta ve homojen yapılar üretilebilmesi, düşük sıcaklıkta prosesin gerçekleştirilebilmesi ile farklı yapılar oluşturulabilmesi sebebiyle tercih edilen bir yöntemdir. Nanolif üretim yöntemlerinden olan elektrospinning yöntemi ise, farklı özelliklerde malzemler kullanarak ince lif yapıları elde edilmesinden dolayı tercih edilmektedir. Bu temelden yola çıkılarak,bu çalışmada sol-jel ve elektrospinning yöntemiyle ve Ag+ nanotanecik katkılı TiO2/PAN polimer nanoliflerin üretilmesi amaçlanmıştır. 
Yapılan deneysel çalışmalarda, elektrospinning parametrelerinin nanolif çapına etkisi, üç değişkenli üç aşamalı Box-Benkhen deney tasarımı uygulanarak  belirlenmiştir. Değişkenler; uygulanan voltaj, kolektör-uç arasındaki uzaklık ve akış hızı olarak seçilmiştir. Elektrospinning çözeltisinin sol/pol oranı, elde edimesi hedeflenen nanoliflerin morfolojik özellikleri göz önüne alınarak belirlenmiştir. Sol-jel çözeltisine (TTIP, AA, PAN, DMF), gümüş nanotanecikleri eklenmeden önce elektrosinning çalışma koşulları optimize edilmiş. Daha sonra mikrodalga metodu ile üretilen Ag+ nanotanecikleri çözeltiye %1.5 , %2 ve %2.5 oranlarında eklenerek elektrospinning işlemi gerçekleştirilmiştir. Elde edilen nanoliflere 700 oC'de ısıl işlem uygulandıktan sonra  SEM, XRD, FTIR analizleri yapılmış, fotokatalitik aktivite ölçümü yapılmıştır.
Yapılan çalışmada sol-jel ve elektrospinning yöntemleriyle, su kirliliğinin giderilmesinde kullanılabilecek nanokompozitlerin üretimi gerçekleştirilmiştir.

Abstract:
Nowadays, with increasing industrial applications, the world is facing environmental pollution and seeking solutions to this issue continues in today's world. Despite the fact that water has a vital role in our world, the water shortage around the world is becoming a serious problem. Water pollution, which is an important issue, with increasing population growth, makes difficult to reach fresh water. Degradation of organic pollutants leading to water pollution is important to get a sustainable future for new generations. New solutions are being searched by researchers due to water scarcity and increasing demand for fresh water and its sustainability. Application of nanotechnology in water treatment is a growing area and nanoscaled materials are used in this area substantially. Nanomaterials have been searching by researchers to overcome negative effects of industrialization. Many kind of nanomaterial has been utilizing for remediation of heavy metals, organic and inorganic pollutants etc. through various treatments to enhance the quality of our ecosystem. 
Nanomaterials' ranges change from 1 to 100 nm and have a wide variety of application areas such as electronics, biomedical industry, the pharmaceutical industry, cosmetics, energy applications, environmental and textile industry. With the development of  nanotechnology, nanomaterials have been using in new industries and varied application areas. They all have different properties in terms of size, morphology, surface area, porosity, structure, and composition. Since the nanomaterials have a high surface-volume ratio, they can be used in different application areas. The surface area of a nanomaterial is important since the properties of nanoparticles change with the surface area of the nanoparticles. Carbon nanotubes, quantum dots, metal and metal oxide nanoparticles with unique attributes have different areas of applications. Nanoparticles can be produced by many synthesis methods such as microwave method, sol-gel method, chemical vapor deposition, physical vapor decomposition, high ball energy milling and so on. The production method is important for the application type and  further usage of nanomaterials.  The type of the nanomaterial and requested diameter size are significant factors for choosing the right synthesis method.
Photocatalytic materials have been using in water treatment plants, antibacterial applications, and degradation of organic pollutants and dyes. The band gap of the semiconductor has a crucial role in photocatalytic reactions (photocatalysis). Wide range of photocatalysts have been using in industrial processes. Titanium dioxide, a photocatalytic semiconductor nanomaterial with low-band gap, is used because of its high oxidation rate, chemical stability, low toxicity and availability at low cost. 
Titanium dioxide nanoparticle, as a photocatalyst is used in solar cell applications and in water treatment plants, in fact, it has been used in remediation of pollutants via photocatalytic reaction. Thanks to its self-cleaning property, it is used in self-cleaning surfaces and coatings. Titanium dioxide nanoparticles can be produced by the sol-gel method in a controlled way at ambient temperature. Silver nanoparticles has a wide range application and can be synthesized with microwave method which is an easy, rapid and clean method. And silver nanoparticles exhibit antibacterial properties and have long been to the high suicidal effect on microorganisms, thus it has been used in various antibacterial applications such as medical diagnosis, drug delivery systems, water treatment and wound-healing.
In the sol-gel method which is one of the nanoparticle synthesis methods, nanomaterials can be synthesized in a controlled way at low temperature and with low cost compared to conventional methods. Sol-gel method comprises hydrolysis and condensation reactions and three types of precursors (metal salts, metal oxide solutions and organic and inorganic precursor solutions) can be used. Other advantages of this method are the homogeneity of the composition and multi-component systems can be obtained smoothly. The properties of the nanoparticles, that synthesized with sol-gel method, change with the materials used in the process. 
Electrospinning method is a technique which can be applied to polymer solutions at a voltage between 10-40 kV to overcome high surface tension of the solution. This technique is preferred since thin nanofiber networks from different polymers which have different properties could be produced with this technique.The electrospinning solution transports into the metallic surface with the effect of the electric field. Surface tension plays an important role in the process. When the voltage that applied to the system overcomes the surface tension of the spinning solution, the jet formation begins.  During this process, the solvent of the solution evaporates and the polymer transforms into a nanofiber structure respectively. The parameters of the electrospinning process are polymer and solvent type, the voltage that is applied, the flow rate of the electrospinning solution, the distance between the tip and the collector, temperature and humidity. These are the major parameters that affect the morphological structure of the nanofibers and they effect the ability to fabricate nanofibers by electrospinnig process. In electrospinning process different polymers, such as polyacrylonitrile, polyvinylpyrrolidone, polymethyl methacrylate, polystyrene etc. could be used as a solution or melt and various morphologies could be obtained. 	
In this study, Ag+ doped TiO2 /PAN nanocomposite materials were fabricated through both sol-gel and electrospinning techniques. In the first part of the study, optimum solution-polymer mixture ratio (sol/pol) and electrospinning conditions  were determined with the preliminary experimental studies. In preliminary studies, the best mixing rates of the polymer solution  and appropriate electrospinning conditions were determined according to calcinated nanocomposite morphology. After that, the sol-gel mixture (TTIP, acetic acid) and  polymer solution (PAN, DMF) were mixed together. The best sol-pol mixing ratio was determined as 1:5. Then, Box- Benkhen design method which is a three level, three variable response surface methodology was used to find optimum electrospinning parameters of the electrospun nanofibers. 15 different runs were neccessary with the same sol/pol solution ratio in order to get optimum electrospinning parameters. The variables were chosen as voltage in the range of 22 kV and 26 kV, flow rate between 1 and 3 ml/h and the distance between the collector and the metallic tip (170 and 220 mm). With respect to these parameters, the second order model was obtained and the most crucial variables were determined which affects the morphological structure and the diameter of the nanofibers. With the new model of response-surface design, R-squared value was obtained as 0.8875. The results of Box-Benkhen design were searched by verification experiments. Three different runs were used to affirmate the new response-surface design model accuracy. The electrospinning parameters' variables which were not located in Box-Benkhen design matrix were used for verification. After electrospinning process, nanofiber diameters were measured. It was observed that the calculated diameters of these nanofibers were in the 95 % confidence interval.
Silver nanoparticles were synthesized with microwave method which is an environmentally-friendly, green synthesis method. To obtain solid form of the silver nanoparticles, the liquid mixture was kept in drying oven at 120 oC for 30 minutes. After that, silver nanoparticles, added to the sol-pol solution then it was agitated to obtain a homogeneous solution. Three different silver concentrations (%1.5, %2 and %2.5)  in sol-pol solution were used. The solutions were transformed into nanofibers by electrospinning method regarding conditions which were obtained by preliminary studies. 
The heat treatment process was carried out with a laboratory muffle furnace at 700 oC to decompose polymer from the nanofiber structure and to see the crystal phase formation. After calcination, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) techniques were utilized to characterize the morphology and composition of nanocomposite membranes. The photocatalytic ability of the nanofibers was measured according to the concentration change of aqueous solution of methylene blue under UV irradiation and then the absorbance rates of the degraded methylene blue solutions were measured by spectrophotometry at 664 nm. Studies have shown that the nanofiber network formation was occured, furthermore the nanofibers' diameter and morphology were influenced by experimental conditions. 
According to Box-Benkhen experimental design method, the nanofiber changes with diameter voltage, flow rate, distance between the collector and the tip and the square root of the distance. SEM results showed that the formation of the fiber networks for all samples has been proved even after calcination processes. It was observed that the fiber diameters decreased with the addition of silver nanoparticles. Before calcination process, the diameter size of the nanocomposites which was measured regarding SEM results changed between 192 to 290 nm. After calcination process, the nanocomposites' diameters varied between 73 nm to 126 nm. The calcination process which provides evaporation of the polymer from the nanocomposite structure has an effect of reducing nanocomposites' diameter size. From the XRD results, the formation of anatase was proved for the nanocomposite materials. The results also showed that nanocomposites contained silver nanoparticles in their structure. FTIR results indicated that the as-spun nanofibers had all organic bonds corresponded to PAN while the calcined samples didn't have them. According to these results, polymer bonds between fabricated nanocomposite  was broken by the heat of the muffle furnace and the polymer was evaporated from the structure. To measure the photocatalytic property of the fabricated nanocomposites methylene blue which has wide commercial applications in the textile industry, was used. Using a spectrophotometer, methylene blue degradation was measured with 10 ppm methylene blue solution containing silver-doped nanocomposite samples under UV light. Photocatalytic activity measurements of the fibers showed that the photodegradation of methylene blue solution of the nanofibers was achived with degradation rate of 94%. Overall results indicated that the nanocomposite materials can be feasible candidates for industrial applications to clean wastewater especially in dye applications.