İç ortam havasında bulunan uçucu organik bileşiklerin (UOB) farklı nanomalzeme katkılı polimerik nanolif filtreler ile giderilmesi
Removal of volatile organic compounds (VOC) in indoor air with polymeric nanofiber filters added to different nanoparticles
Yazar: DİLA AYDIN
Danışman: DOÇ. DR. DERYA YÜKSEL İMER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Şehirlerde yaşayan insanların çoğu zamanlarının yaklaşık olarak %80-90'ını evler, işyerleri, alışveriş merkezleri, ulaşım araçları (tren, otobüs, uçak, gemi vb.) gibi kapalı mekânlarda geçirmektedir. Bu durum zamanlarının çoğunu bu gibi kapalı ortamlarda geçiren insanların sağlıklarını, çalışma verimliliklerini etkilediği için son yıllarda yapılan çalışmalar da iç ortam hava kalitesine yoğunlaşmaktadır. Yapılan bu araştırmalar, iç ortam havasının havalandırma sistemindeki zayıflıklar nedeniyle dış ortamdaki seviyelerden daha yüksek kirletici madde bulundurabileceğini göstermektedir. Bu kirleticilerden uçucu organik bileşikler (UOB) miktarsal olarak büyük paya sahiptir ve özellikle "Hasta Bina Sendromu (HBS) " olarak isimlendirilen rahatsızlığın en temel nedenlerinden birisidir. UOB'lerin gideriminde farklı teknolojiler kullanılabilmektedir. Literatürdeki çalışmalara bakıldığında en ideal teknolojinin fotokatalitik oksidasyon olduğu fakat adsorpsiyonunda yardımcı mekanizma olarak kullanılması gerektiği sonucuna varılmaktadır. Bu iki mekanizmanın farklı malzemelerin kullanımıyla filtre malzemesinde gerçekleştirilmesi bu tezin ana fikridir. Heterojen fotokatalizörlerin havadaki organik kirleticilerin gideriminde verimli, ekonomik ve çevre dostu malzemeler olduğu literatürde belirtilmiştir. Özellikle titanyum dioksit (TiO2) ve çinko oksit (ZnO) katalizörleri sahip oldukları yüksek fotokatalitik aktivite, kimyasal ve biyolojik olarak parçalanamıyor olmaları ve yüksek fotokimyasal stabiliteleri nedeniyle organik maddelerin parçalanmasında kullanılan en verimli ve özellikleri en iyi bilinen fotokatalizörlerdir. Tezde önerilen temel mekanizma, bir nanolif ağ yapısı içerisine adsorpsiyonu arttırıcı nanokil ve fotokatalitik oksidasyon sağlayıcı TiO2 ve ZnO malzemelerin entengre edilmesi ve uzun süreli ortam havasından UOB'nin giderilmesidir. Bu mekanizmanın verimini etkileyen iki önemli faktör bulunmaktadır. Bu faktörler iç ortam havasında düşük konsantrasyonlarda bulunan UOB'lerin fotokatalizör ile temasının sağlanması için adsorpsiyonu arttıracak yüzey alanı ihtiyacı ve zamanla kirlenmeden dolayı verimi düşecek olan fotokatalizörlerin sürdürülebilir bir şekilde tekrar kullanılabilirliğinin sağlanmasıdır. Bu sebeple temel reaksiyonu sağlayacak fotokatalizörlerin bu iki faktör göz önünde bulundurularak uygun bir nanolif yapısı içerisinde kullanılması gerekmektedir. Bu yapıların oluşturulması için son yıllarda birçok alanda kullanılan yüksek yüzey alanı ve düşük filtrasyon dirençlerine sahip olan polimerik nanolif  filtreler incelenmiştir. Nanolif filtre üretiminde poliamit-6 (PA6) polimeri ve bu polimer ile nanoadsorbent olarak halloysit nanotüp-HNT ve nanokil-NK, katalizör olarak ise TiO2 ve ZnO yapıların kompozit olarak hazırlanması, karakterizasyon ve performans çalışmaları gerçekleştirilmiştir. Polimer ile elektroeğirme yönteminin optimizasyonu sonrası HNT ve NK adsorbentleri ve nanofotokatalizörler için (i) agloremasyon olmayacak şekilde konsantrasyon belirlenmesi (ii) uygun disperse etme koşullarının belirlenmesi (iii) elektroeğirme şartlarının belirlenmesi aşamaları uygulanmıştır. Üretim ardından nanoliflerin yapısal karakterizasyonu için fiber çapı (SEM ile), organik bağlar (FTIR ile), kristal yapısı (XRD ve SEM-EDS ile) ve akma/çekme dayanımı değerleri ile mekanik dayanım özelliği (DMA ile), performans değerlendirmesi için standart yöntemler ile hava geçirgenliği ve su buharı geçişi, model UOB olarak toluen adsorpsiyon ve oksidasyon döngülerinde giderim verimleri belirlenmiştir. Bu tezdeki özgün değer; iç ortam havasından UOB giderimi için hızlı kütle transferi sağlayacak, yüksek oksidasyon verimine ve kendi kendini temizleme özelliğine sahip ve yüksek mekanik dayanımı olan, eşzamanlı giderim mekanizmalarının (adsorpsiyon+oksidasyon) gerçekleşeceği verimli ve modüler filtre sistemlerine yerleştirilebilecek filtre malzemelerinin literatürden farklı yaklaşımlar ile gerçekleştirilmesidir. Güçlendirilmiş/fotokatalizör katkılı polimerik nanolif filtre malzemelerinin mühendislik yaklaşımıyla üretilmesi, karakterizasyonu, laboratuvar ölçekte denenmesi izlenen temel yöntemlerdir.

Abstract:
Most of the people living in cities spend approximately 80-90% of their time in closed places such as houses, workplaces, shopping malls, transportation vehicles (train, bus, plane, ship, etc.). Since this situation affects the health and working efficiency of people who spend most of their time in such indoor environments, recent studies focus on indoor air quality. These studies show that indoor air may contain higher pollutants than the outdoor levels due to weaknesses in the ventilation system. Volatile organic compounds (VOCs) from these pollutants have a large share in quantity and are one of the main causes of the disease called "Sick Building Syndrome" in particular. Different technologies can be used in the removal of VOCs. Considering the studies in the literature, it is concluded that the most ideal technology is photocatalytic oxidation but should be used as an auxiliary mechanism in its adsorption. The realization of these two mechanisms in filter material by using different materials is the main idea of this thesis. It is stated in the literature that heterogeneous photocatalysts are efficient, economical and environmentally friendly materials for the removal of organic pollutants in the air. In particular, titanium dioxide (TiO2) and zinc oxide (ZnO) catalysts are the most efficient and most well-known photocatalysts used in the decomposition of organic substances due to their high photocatalytic activity, chemical and biodegradability and high photochemical stability. In heterogeneous catalysts, since the catalyst and the pollutant are in different phases, the molecules that will react with the catalyst first adsorb on the catalyst surface and undergo oxidation in a very rapid time. In the aquatic environment, this process is fast, but in the indoor air, the catalyst shows a weak adsorption feature against apolar VOCs due to its polar structure. Low adsorption for air pollutants also affects the oxidation efficiency because VOCs, which are in very low concentrations in the air environment, need to contact the material for a certain period of time for efficient photocatalytic oxidation. While this contact time in the aquatic environment is adjusted by the reactor designs and the reaction occurs very quickly, it is more difficult to follow and control the reactions in the air environment. For this reason, the adsorption feature of the nanofiber filter system to be developed for VOC removal should be considered during the material development phase. In order to remove the pollutant, its certain concentration on the surface of the catalyst should be reached, the adsorption must be provided on the surface where the catalyst is located, especially in the air environment, due to the low mass transfer of the low concentration pollutants to the surface of the photocatalyst. The main mechanism proposed in the thesis is to introduce adsorption enhancing nanoclay and photocatalytic oxidants (TiO2 and ZnO) into a nanofiber network structure and remove the VOC from long-term indoor air. There are two important factors that affect the efficiency of this mechanism. These factors are the need for a surface area that will increase adsorption and the reusability of photocatalysts, whose efficiency will decrease due to contamination over time, to ensure that VOCs with low concentrations in indoor air are in contact with the photocatalyst. For this reason, the photocatalysts that will provide the basic reaction should be used in a suitable nanofiber structure considering these two factors. In the development of nanofiber materials to integrate TiO2 and ZnO photocatalysts, it is aimed to successfully apply the classical electrospinning technique. Electrospinning mechanisms consist of three basic parts. In the first part, it is a thin tube that can consist of a syringe-like structure in which the polymer solution is stored and sprayed. This section can be both passive (starting the motion of the solution with the effect of gravity) and active (spraying the solution with the help of a device such as a syringe pump). The second part consists of the electric field region formed along the jet trajectory by means of high voltage, and the last part consists of the assembly where the formed nanofiber structure is collected. The aim of this thesis is that photocatalysts with high performance do not lose their performance after being integrated into the nanofiber structure. Therefore, especially in the design of nanofiber filters produced by this method, it is thought that the high rate of adsorption of VOCs to the photocatalysts captured on the fibers at the first stage, the immediate occurrence of oxidation and the contact between the photocatalysts and the UV-LED light source during the photocatalytic reaction will be more. The reason for using UV-LED is less energy consumption and longer service life. Other UV sources emit a significant portion of their power as heat. At the same time, conventional UV lamps contain mercury and their use is harmful to nature. Both environmentally friendly and energy efficient oxidation can be achieved with UV-LEDs. In addition, UV-LEDs' average 60000 hour lifetime provides an advantage. Toluene was used as the model VOC in the system for the performance tests of nanofiber filters produced. The system consists of four basic parts. The first component is the CO2 and hydrocarbon-free dry air generator (air flow is kept constant at 1.5 L / min) providing a continuous and constant air flow, the second component is the gas mixing bottle in which the incoming fixed air enters the toluene vapor and is positioned in the water bath. The third component is the filtration cell where the measurement of adsorption and oxidation is provided together and the fourth component is the sampling point. The temperature of the water bath was kept at 40oC in the adsorption and oxidation cycles and tests of all materials. The inlet flow was continuously controlled by the flow meter device in order to control any leakage problems in the drift of toluene to the filtration cell with the continuous air flow. The filtration cell used in preliminary tests has approximately 300 mL of void volume. In order to prevent toluene from condensing in all lines, the temperature was kept constant at 40oC with the heater. At the sampling point, gas analyses were carried out in GC-MS using both toluene in gas phase and methanol accumulation methods. In experiment setups, the method of accumulation in methanol was preferred due to the ease of sampling depending on time and high reproducibility. Here, by using vials with air gaps and providing the necessary sealing, the off-gas stream was collected in methanol for 1 min. It has been stated in the studies that the adsorption capacity of VOCs in the indoor air under dark conditions, ie. without photocatalytic oxidation, varies between 11-20% of the inlet VOC concentration. In this thesis, it was aimed that the total adsorption capacity of the fabricated filter materials reached at least 10% in the dark conditions, considering that two approaches including methods that have not been tried in this field. High adsorption efficiency increased the basic oxidation mechanism of the nanocomposite filter. It is possible that both the adsorption and oxidation capacities of the materials decreased after a certain period of time because of material properties. This will reduce the useful life of the materials. Thus, it is aimed to identify and evaluate these uncertainties and performance-reducing risks and to design nanofiber filters with a long service life. The final goal is to develop innovative materials for the removal of gas phase pollutants / characterization / performance tests and to construct all stages of filter development / production within an experimental systematic with disciplines and to finalize them using statistical methods. In order to create these structures, the polymeric nanofiber filters with high surface area and low filtration resistance, which have been used in many areas in recent years, have been studied. PA-6 polymers were used in the studies. PA-6 nanofibers were prepared by dissolving the polymer in formic acid (FA) and acetic acid (AA) solvents at the appropriate concentration (13% by mass, m/m). The optimum voltage for the preparation of nanofibers (25 kV), polymer feed rate (between 1, 1.5 and 2 ml / h), end-collector distance (15 cm) were determined by preliminary tests. Each parameter affecting the efficiency of the electrospinning process has been evaluated within itself and optimum conditions have been reached. After this stage, the conditions for each polymer have been determined and the effect of nanoparticles has been investigated. Halloysite nanotubes (HNT) and nanoclay (NK) are expressed as nanoclay to be used. It is stated that due to the increased conductivity of the solution with nanoclay additive, fiber diameters had more uniform and no bead formation, which can be named as production defects. Bentonite was used as the nanoclay addition and it is stated that it increased the mechanical strength of the fibers and caused to a more reticulated structure. The solutions were prepared by using nanoclay at the rate of 0.025%, 0.05, 0.1 and 0.5% by mass according to the polymer and the most suitable ratios were determined by making trials. TiO2 and ZnO are used as photocatalysts. TiO2 and ZnO materials were obtained commercially and their ratios to polymer were realized as 0.5% by mass of ZnO and 1% of TiO2. Nanoclay and HNT were dispersed in suitable solvents (AA and FA) and mixed with PA polymer solutions. Then, photocatalysts were dispersed in the mixture and used in the preparation of nanofibers by classical electrospinning method. Composite production, characterization and performance studies of polyamide-6 (PA6) polymer and nanoadsorbent as well as halloysite nanotube-HNT and nanoclay-NC as a catalyst, and characterization and performance studies were carried out in nanofibre filter production. PA can easily form fibers due to the short di-acid and di-amine functional groups in its structure. PA fibers can be used as effective materials in air filtration due to their properties such as small and narrow distribution of fiber diameters and large surface area. After optimization of the electrospinning method with polymer, the steps of (i) determining the concentration of no dispersion (ii) appropriate dispersing conditions for the HNT and NC adsorbents and nanofotocatalysts (iii) determining the electrospinning conditions were applied. Production, characterization and laboratory testing of reinforced / photocatalytic added polymeric nanofiber filter materials with engineering approach are the main methods. Following the production, fiber diameter (with SEM), organic bonds (with FTIR), crystal structure (with XRD and SEM-EDS) and mechanical strength properties (with DMA) were determined with standard methods for performance evaluation and structural characterization of nanofibers. With air permeability and water vapor transmission, the removal efficiency in toluene adsorption and oxidation cycles were determined using with test systems. The original value in this thesis, it is the realization of filter materials with different approaches from the literature that will provide rapid mass transfer from indoor air VOC removal, have high oxidation efficiency and selfcleaning properties, and have high mechanical strength, can be placed in efficient and modular filter systems where simultaneous removal mechanisms (adsorption + oxidation) will take place.