Karbon Nanotüp Katkılı Nanokompozit Polimerik Membranların Üretimi, Karakterizasyonu Ve Uygulaması

Abstract

Son yıllarda membran konusunda yapılan çalışmalar organik- inorganik kompozit membranların potansiyel gelecek kuşak membran materyali olarak kullanılması noktasında büyük bir potansiyele sahip olduğunu göstermektedir. Bu tür membranlar için, inorganik maddelerin fizikokimyasal kararlılığının ve organik polimerlerin membran oluşturma potansiyeli özelliklerinin nanokompozit membran sentezi için olağanüstü bir fırsat olduğu düşünülmektedir. Özellikle, nano boyutlu inorganik maddelerin harmanlandığı kompozit membranların yüksek seçiciliğe, yüksek hidrofilikliğe ve yüksek membran tıkanma direncine sahip olmalarından dolayı, son yıllarda çevre mühendisliği alanındaki kullanımının çok cazip hale geldiği belirtilmektedir. Karbon nanotüplerin düşük yoğunluk, yüksek dayanım ve setlik özellikleri, bu nano yapılı taneciklerin polimerik malzemelerin içerisine potansiyel güçlendirici malzeme olarak ilave edilmelerine olanak tanıması sebebiyle karbon nanotüplerin yüksek bir potansiyele sahip oldukları geçmişte yapılan çalışmalarla gösterilmiştir. Bu çalışmada, çok katmanlı karbon nanotüp ve polietersülfon polimeri kullanılarak nanokompozit membranlar faz ayrımı metodu ile sentezlenmiştir. Deneysel çalışmada, % 0,5-1-2 ve 4 oranında çok katmanlı karbon nanotüp içeren membranlar; şahit numune olarak kullanılmak üzere karbon nanotüp içermeyen (% 0 CNT) membranlar sentezlenmiştir. Sentezlenen bu nanokompozit membranların karakterizasyon işlemleri taramalı elektron mikroskobu (SEM), temas açısı, porometre, Fourier dönüşümlü kızılötesi spektrometre (FTIR), optik profilometre, dinamik mekanik analiz (DMA), toplam organik karbon (TOK), UV254 spektrofotometre ve membran hücresi enstrümanları kullanılarak gerçekleştirilmiştir. Karakterizasyonu tamamlanan membranlar içerisinden, en uygun olanları seçilerek sentetik su süzümünde kullanılmıştır. Çalışmada, aromatik model bileşik olarak tanin ve alifatik model bileşik olarak glisin seçilmiştir. Her bir model organik bileşik için belirlenen parametrik değerleri sağlayacak miktarda gerekli kimyasallar ilave edilmiş ve her bir çözeltinin TOK değeri 5,0 mg/L olacak şekilde ayarlanmıştır. Hazırlanan sentetik su çözeltileri 300 ml hacminde olacak şekilde kullanılmıştır ve seçilen membranlardan filtrasyonu gerçekleştirilmiştir. Filtrasyon esnasında akı profili zamana bağlı olarak bilgisayar ortamına aktarılmıştır. Membranlardan süzülen organik bileşik numuneleri, TOK ve UV254 cihazı kullanılarak giderme verimi hesaplanması için alınmıştır. Bu çalışmaların sonunda, membran üretiminde kullanılan karbon nanotüpün, sentezlenen membranların performansına ve karakterine etkileri incelenmiş, model organik bileşik filtrasyon performansı ortaya çıkarılmıştır.Membrane filtration is an efficient technique for removing pollutants in drinking water. Membrane technology is rapidly growing sector which improvedpermeability, selectivity, and antifouling efficiency fortreating water, reuse and safe disposal. The most important goals for membrane technology are to control membrane structure and membrane performance (flux and rejection). Membranes are produced by several techniques and the production parameters involved are very complex. Membrane production is a very difficult and sensitive process, and its final performance strongly depends on the control of the operating conditions. In addition to the material selection and solution preparation, the environment and applied technique also contributes to the final membrane morphology It was reported that .phase inversion and rheological factors manupulation including polymer concentration, membrane thickness, evaporation time, gelling bath temperature, reaction time and shear rate, are among parameters that play an important role in the determination of its final performance. In various environmental processes for raw water treatment treatment such as lake and river, membrane separation technologies of ultrafiltration (UF), microfiltration (MF) and reverse osmosis (RO) are widely used. Recently, polymeric membranes are mostly used for this processes. Usually, polymeric membrane is synthesized with the phase inversion technique. Since PVP with water solubility created islands of PVP in membrane formation, and PVP increased pore size, polymeric membrane become porous by using a casting solution such as polyvinylpyrrolidone (PVP) as an additive. Membrane development studies have recently focused on the addition of inorganic nanomaterials into polymeric materials to increase membrane chemical reactivity and reduce fouling. The recent studies regarding membrane filtrations indicate that there has been a great deal of interest in the use of organic-inorganic hybrid membranes as a potential next generation membrane material. It was expected that such membranes will have the physicochemical stability of inorganic materials and the membrane forming properties of polymers. Especially, nano-sized inorganic material blended composite membranes are attractive in the field of Environmental Engineering because of their enhanced properties, such as high permselectivity, higher hydrophilicity, and enhanced fouling resistance. Previous studies have shown that there is a high potential for carbon nanotubes (CNTs) to improve the material properties of polymers. Since its discovery, CNTs have been in the spotlight because of their superior properties. They play critical role in the removal of synthetic organics of polycyclic hydrocarbons (PAHs), nitrobenzene and phenol and natural organic matter (NOM) in water. As a result, the relationships between natural and synthetic organics and CNTs help the implementation of those kinds of nanostructured adsorbents for water treatment applications. In this study, the potential usage of CNTs in water treatment was investigated by synthesis of CNT blended polyethersulfone (PES) membranes. Since its discovery, CNTs have been in the spotlight because of their superior properties. They play critical role in the removal of synthetic organics of polycyclic hydrocarbons (PAHs), nitrobenzene and phenol and natural organic matter (NOM) in water. As a result, the relationships between natural and synthetic organics and CNTs help the implementation of those kinds of nanostructured adsorbents for water treatment applications. In this study, the potential usage of CNTs in water treatment was investigated by synthesis of CNT blended polyethersulfone (PES) of MF membranes. In this study, carboxylic multi-walled carbon nanotubes/polyethersulfone (CNT/PES) blend membranes were synthesized by phase inversion method using N-methyl-2-pyrrolidinone (NMP) as a solvent and water as a coagulant. Polyvinylpyrrolidone (PVP) was also used in the membrane casting solution. In the experimental studies, four different concentration of carbon nanotubes used in the membrane production as 0,5-1-2 and 4 %. As pure sample without carbon nanotube, produced from polyethersulfone polymer. In the membrane production step, all parameters was set to a constant value. The investigation of pure water flux conducted. Then the characterization of these membranes were performed by using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), pore sizer, contact angle, optical surface profiler instruments. After this chracteraization procedure, all membranes were utilized to treat synthetic waters containing aromatic and aliphatic synthetic organics. The membrane flux, TOC and UV254 analysis were performed. According to SEM images, membranes have dense top layer and a porous sublayer which is a sign of typical asymmetric membranes structure. The top layer acts as a selective barrier film, and the porous sublayer which consists of macrovoids, pores and micropores, offers good mechanical strength. It can be seen that with increasing carbon nanotube amount, pore size of the membranes was increased. In additon, all membranes with carbon nanotubes has finger like structures. Powder carbon nanotubes, pristine membrane and carbon nanotube blend membranes were used to determine the spectrum lines. FTIR spectrum results showed that, membranes with carbon nanotube has a new peak in the spectrum which pristine membranes don’t have. Mechanical strength tests were completed by dynamic mechanical analyser. Young’s modulus, tensile strength ve elongation rates of membranes were found.. According to the results, all membranes with carbon nanotubes had better mechanical strength than pristine membranes. It can be said that, carbon nanotubes was caused to gain mechanical strength. From the data of water contact angle and it was seen that the contact angle of the blend membrane surface decreased except %1 CNT. This result showed that the hydrophilicities of the blend membranes increased with the amount of MWCNT which could induce an increase in pure water flux. Hydrophilic effect of MWCNT increased the exchange of phase inversion process and MWCNT was collocated regularly in membrane. It was found that the average pore size of the membranes increased with MWCNT content. But there is also decrease in the carbon nanotube membrane series which depens on carbon nanotube distribution in the membrane samples. The pure water flux was at maximum when the MWCNT content of the membranes was 1%. 0,5% CNT has the minimum pure water flux value. This can be explained by the effect of hydrophilic MWCNT in the phase separation process. When the MWCNT content of the blend membranes was 1%, hydrophilic MWCNTs enhanced the phase separation process which resulted in a bigger pore size and a higher pure water flux. When the MWCNT content of the membranes was above 1%, the viscosity of the casting solution increased and delayed the phase separation which created smaller pore size and lower pure water flux. This inceasing and decreasing in pure water flux might be explained by the enhanced exchange of solvent and non-solvent during phase inversion, which made the MWCNTs regularly collocate in the membrane. However, the steric hindrance and electrostatic interactions between the MWCNT or between the MWCNT and PES made some portion of the MWCNT irregularly collocate in the membrane. This irregular positioning might increase the pore size of the membrane. According to the optical surface profiler images, the surface of membrane was getting rougher. By adding MWCNTs in the membrane casting solution, the surface morphology of membrane changed greatly. This result can be explained by kinetic and termodynamic interactions. At low amount of MWCNTs addition, this nanomaterials regularly collocated in membrane and the surface of membrane become a little smooth. But at higher amount of MWCNT addition, because of increasing viscosity, decreasing pore average size and aggregation of carbon nanotubes surface of the membranes was getting more rougher. In tannin synthetic solution filtration, pristine membrane showed best flux,but also has lowest TOC removal efficiency value. All carbon nanotbe blend membranes showed higher TOC removal comparing the pristine membrane. This result show that, carbon nanotubes can remove tannin solution better because of the carboxylic interactions between carbon nanotubes and tannin structures. In glycine synthetic solution filtration 0,5% CNT has highest and 1%CNT has lowest flux values. 1% CNT has the highest and the 0% CNT has the lowest TOC removal efficiency values. This result showed that, carbon nanotube membranes has better TOC removal in glycine solution comparing the pristine membrane. However, glycine TOC removal efficiency is lower than tannin solution which might be the reason of weaker interactions between carbon nanotube carboxylic groups and glycine than tannin solution.