Selüloz nanokristal ve fotokatalizör katkısıyla üretilen nanolif hava filtreler ile iç ortam havasında bulunan uçucu organik bileşiklerin giderimi
Removal of volatile organic compounds from indoor air with nanofiber air filter produced with cellulose nanocrystal and photocatalyst additives
Yazar: ESRA BÜYÜKADA KESİCİ
Danışman: DOÇ. DR. DERYA YÜKSEL İMER
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Elektroeğirme yöntemi = Electrospinning method ; Fotokatalitik = Photocatalytic ; Metal nanopartiküller = Metal nanoparticles ; Uçucu organik bileşikler = Volatile organic compound

Özet:
İnsanlar günlük hayatın büyük çoğunluğunu (%80- 90'ını) konut, işyeri ve okul gibi binalar ve uzun yol taşıma araçları (otobüs, uçak, tren vb.) gibi kapalı iç ortam havasında geçirmektedir. Bu nedenle, iç ortam havası, en az dış hava kalitesi kadar, insan sağlığı üzerinde önemli bir etkiye sahiptir. İç ortam hava kalitesi, dış havanın girişinin kontrol edildiği ve iç hava sirkülasyonunun uygulandığı yapılardaki hava kalitesi olarak tanımlanabilmektedir. Sanayinin gelişmesi ile sıcaklık kayıplarını önlemek için yeni binalarda dış havaya karşı daha fazla izole edilmeye başlanmış, iç ortamdaki hava değişimindeki azalma iç havanın kalitesinin dış havadan daha kötü hale gelmesine yol açmıştır. Son yıllarda, iç ortam hava kalitesi ile ilgili yapılan çalışmalarda bazı parametrelerden kaynaklı olarak o hacimde zamanını geçiren insanlarda kısa ve uzun vadeli sağlık sorunlarının oluştuğu tespit edilmiştir. Özellikle kronikleşen bazı hastalık belirtilerinin iç ortam havası ile birebir bağlantılı olduğu belirlenmiş ve bu sağlık sorunları "Hasta Bina Sendromu" terimi altında toplanmıştır. Kötü iç hava kalitesi olan binalarda uzun süre kalan kişiler, kirletici kaynakların yoğunluğuna bağlı olarak etkilenebilmektedir. Çeşitli sağlık sorunlarına neden olan bu yapılara "hasta binalar" denir. Hasta bina sendromunun yaygın belirtileri; göz, burun ve boğazda tahriş, baş ağrısı, baş dönmesi, bulantı, kusma, fiziksel ve zihinsel yorgunluk, hafıza kaybı, konsantrasyon eksikliği, deride gözlenen tahriş, kızarıklık, ağrı, kaşıntı ve kuruluk olabilmektedir. Hasta bina sendromuna neden olan iç ortam kirleticilerinden biri olan Uçucu Organik Bileşikler (UOB) konsantrasyonları düşük olmasına rağmen (ppb değerlerinde) uzun süreli maruziyet kronik eğilime sebep olmaktadır. Tezin konusu; iç ortam havasında bulunan ve hasta bina sendromunun temel nedenlerinden olan UOB'lerin adsorpsiyon ve oksidasyon mekanizmalarıyla yenilikçi kompozit nanolif filtre malzemeleri ile gideriminin incelenmesidir. Kompozit nanolif filtrelerin üretiminde elektroeğirme yöntemi kullanılmış ve farklı polimerler (poliamid6-PA6 ve poliakrilonitril-PAN), adsorpsiyonu sağlayan nanoadsorbent olarak selüloz nanokristal (SNK) ve oksidasyonu gerçekleştiren farklı nanofotokatalizörler (TiO2 ve ZnO) kullanılarak farklı içerikte nanofil hava filtreleri geliştirilmiştir. Tez kapsamında, hazırlanan kompozit nanolif filtrelerin üretimi, karakterizasyonu, performans testleri ve filtre tasarımı çalışmaları gerçekleştirilmiştir. Tezin önemi, literatürde kısıtlı çalışma alanına sahip olmuş ve genelde izleme çalışmalarına rastlanılan ama insan sağlığı için çok fazla öneme sahip olan iç ortam kirleticilerinin giderilmesi için filtrasyon teknolojilerinin uygulanabilirliğinin ayrıntılı incelenmesi, filtre malzeme özelliklerinin belirlenmesi ve bu özelliklerin kirletici maddeye özel geliştirmesi, bu aşamaların bir deneysel sistematik içerisinde kurgulanması ve yönetilmesidir. Neticede adsorpsiyon+fotokatalitik oksidasyon mekanizmalarının eş zamanlı olarak filtrasyon teknolojisinde uygulanması, UOB gideriminin sağlanması ve filtre malzemesinin günlük hayatta kullanılabilecek düzeyde ticari bir ürüne dönüşme potansiyelinin incelenmesidir.

Abstract:
People spend most of their daily life (80-90%) in buildings such as houses, workplaces and schools, and long-distance transport vehicles (buses, planes, trains, etc.). Therefore, indoor air has an important impact on human health as much as outdoor air quality. Indoor air quality can be defined as the air quality in buildings where the intake of external air is controlled and where internal air circulation is applied. With the development of the industry, new buildings are more isolated against the outside air in order to prevent heat losses, and  the decrease in indoor air exchange causes deterioration of indoor air quality. In recent studies on indoor air quality, it has been determined that people who spend their time in that volume have short and long-term health problems due to some parameters. It has been determined that some chronic disease symptoms are directly related to indoor air and these health problems are gathered under the term "Sick Building Syndrome". People staying in buildings with poor indoor air quality for a long time may be affected depending on the intensity of the pollutant sources. These structures, which cause various health problems, are called "sick buildings". Common symptoms of sick building syndrome can be observed; irritation of the eyes, nose and throat, headache, dizziness, nausea, vomiting, physical and mental fatigue, memory loss, lack of concentration, skin irritation, redness, pain, itching and dryness. 
Although volatile organic compounds (VOC) concentrations, one of the indoor pollutants, are low (in ppb values), it causes a chronic tendency in long-term exposure. In general, three methods are recommended for removing VOC and similar pollutants; these are source control, ventilation and the use of air cleaners (Lee et al., 2002; Li et al., 2001); however, these methods have some disadvantages. Source control is difficult to achieve in many places. Increasing ventilation can carry more pollutants from the outside environment (Jones, 1999). VOCs are different from each other in terms of size and volatility. These unique physical and chemical properties of the compounds gain importance in the selection of the removal method (Kadam et al., 2018). 

The subject of the thesis is to examine the removal of VOCs in the indoor air with innovative composite nanofiber filter materials by simultaneous  adsorption and oxidation mechanisms. Adsorption takes place by physically capturing the VOC vapor in the air with adsorbents. Therefore, the specific surface area and pore volume of the adsorbent are crucial properties for a smooth and sustainable adsorption process. In the studies, VOCs in indoor environment are given as total volatile organic compounds (TVOC) values. As a result of the measurements made in 179 houses, it was observed that TVOC values ranged between 200-500 μg/m3 (Berry et al., 1996). The concentration of VOCs is very low in indoor air, so it is difficult to adsorb indoor air pollutants in the air stream on conventional adsorbents. As examined in recent studies, contaminated air can exit the system without interacting with the adsorbent in the commonly used fixed bed column adsorption, and polymer nanofiber materials can be used instead to prevent this situation (Khajeh et al., 2013). Nanofiber materials having irregular pores, fiber structure, and high surface area increase the possibility of interaction with VOCs. In order to increase the interaction between low-concentration pollutants and the adsorbent, adsorption processes are carried out with nano-sized materials instead of micro-sized adsorbents. Cellulose nanocrystals (CNCs) were used to increase surface area and improve adsorption in nanofiber materials produced within the scope of this thesis.
Cellulose nanocrystals (CNCs) are rigid rod-like particles composed of crystalline cellulose chain segments. Compared to cellulose with larger amorphous fractions, these nanocrystals exhibit high specific strength, high surface area and unique liquid crystal properties (George & Sabapathi, 2015; Lu et al., 2014). Since CNCs increase the adsorption performance with their high active surface area that interacts with pollutants, they enable to produce low cost and energy efficient composite filters. In some studies, CNC is used as a nano adsorbent for VOC adsorption in nanofiber structures.
Photocatalytic oxidation is a process used for air purification in recent years and it is an oxidation method in which organic pollutants are effectively removed in the presence of UV light and semiconductor photocatalyst. Some metal oxide semiconductors such as titanium dioxide (TiO2), zinc oxide (ZnO), tungsten trioxide (WO3) and cadmium sulfide (CdS) are used as photocatalysts in the photocatalytic oxidation reaction. The most commonly used are TiO2 and ZnO. In a study in which the photocatalytic activity of many metal oxides in the gas phase was measured, it was stated that the order of efficiency in the degradation of hydrocarbons was TiO2 (anatase)> ZnO> WO3 (Ollis, 2000). Among these, TiO2 is widely used due to its many advantageous properties; it is cheap, reliable, has high stability and photocatalytic efficiency and can provide the oxidation of indoor pollutants even at normal ambient temperature and does not require chemical additives (Yu & Brouwers, 2009).
Electrospinnig method is used to produce nanofiber filters with different content. Nanofiber air filters with different content have been developed by using different polymers (polyamide6-PA6 and polyacrylonitrile-PAN), cellulose nanocrystal (CNC) as the nanoadsorbent providing adsorption, and different nanophotocatalysts (TiO2 and ZnO) that perform the oxidation. 
Within the scope of the thesis, the production, characterization, performance tests and filter design studies of the prepared composite nanofiber filters were carried out. The importance of the thesis is the detailed examination of the applicability of filtration technologies for the removal of indoor pollutants, determination of filter material properties and the development of these properties specific to indoor pollutants which are very important for human health and have limited field of study in the literature. As a result, the simultaneous application of adsorption + photocatalytic oxidation mechanisms in filtration technology, providing VOC removal and examining the potential of the filter material to turn into a commercial product that can be used in daily life.
The results of the structural analysis and performance test applied to nanofiber filters produced within the scope of the thesis are shown in Table 5.1. Structural analysis results of nanofiber filters produced with different polymers and different nano additive rates are compatible with the literature. Results of performance tests are also compatible with the literature. The adsorption efficiency of nanofiber filters varies 20 - 50%. Generally, nanofiber filters produced with PAN polymer have higher efficiency than nanofiber filters produced with PA6 polymer. Considering all the results, innovative nanofiber filter materials that are produced with sustainable materials have an important potential in improving indoor air quality.