İç ortam havasından biyoaerosol giderimi için enzim katkılı antibakteriyel nanolif filtrelerin geliştirilmesi
Development of enzyme-doped antibacterial nanofiber filters for bioaerosol removal from indoor air
Yazar: BURÇİN BAŞŞAHİNOĞLU
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, 2023
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Hava filtresi = Air filter

Özet:
Günümüzde insanlar vaktinin büyük bir kısmını iç mekanlarda geçirmektedirler. İşyerleri, okullar, toplu taşıma ulaşım araçları gibi iç mekanlarda taze hava sirkülasyonu azalmaktadır ve iç ortamda bulunan kirleticilerle temas oranı artmaktadır. İç ortam havasındaki biyoaerosollerin kolayca taşınması ve insanlarla temas etmesiyle birlikte iç ortam havasıyla alakalı astım, alerji, enfeksiyon gibi insan sağlığı üzerinde çeşitli rahatsızlıklar görülebilmektedir. Biyoaerosol, aerosol haline gelmiş hücrelere, virüslere, polenlere veya sporlara verilen genel isimdir. Biyoaerosollerin önemi, yaşanan COVID-19 pandemisiyle birlikte tüm dünyaca deneyimlenmiştir. İç ortamdaki partikül madde giderimi için yaygınlıkla filtrasyon sistemleri kullanılmış ve geliştirilmiştir fakat biyoaerosol giderimine özel filtre dizaynları, etki mekanizması ve filtre performansı arasındaki ilişkiler açısından uygulamalar ve çalışmalar kısıtlı kalmıştır. İç ortam hava kalitesi uygun filtre seçimi ile tasarlanmış sistemlerle iyileştirilebilir. 
Bu tez çalışmasının konusu, sürdürülebilir filtrasyon performansı için biyoaerosol giderimi sağlayan nanolif yapılı yenilikçi bir antibakteriyel hava filtresi geliştirmektir. Antibakteriyel nanolif hava filtresi üretiminde, iki temel metodoloji uygulanmıştır (i) Ticari poliakrilonitril (PAN) polimerinin, grafen nanoplatelet (GNP) katkısı ile elektroeğirme yöntemi ile üretimi ve (ii) Antibakteriyel özellik kazandırması hedeflenen glukoz oksidaz (GOx) enzimi için farklı immobilizasyon tekniklerinin uygulanması. Tez çalışması nanolif filtre üretimi, enzim immobilizasyonu, SEM, FTIR, CLSM, su buharı geçirgenlik değeri gibi karakterizasyon, yapısal analiz, doğrulama ve test faaliyetlerinin yanısıra antibakteriyel etkinlik testlerini içermektedir. 
Tez çalışmasının ana hedefleri (i) Nanolif üretim yöntemlerini uygulamak, (ii) Enzim immobilizasyon tekniklerini araştırmak ve uygulamak, (iii) Üretilen filtrelere karakterizasyon ve performans testlerinin yanı sıra antibakteriyel testleri de uygulayarak antibakteriyel hava filtrelerinin fizibilitesini araştırmak ve (iv) Biyoaerosol giderimi yaparak iç ortam hava kalitesini iyileştiren ve insan sağlığını koruyan yeni bir antibakteriyel hava filtresi ürünü oluşturmaktır.

Abstract:
Nowadays, people spend most of their time indoors. As fresh air circulation decreases in indoor environments such as workplaces, schools, and public transportation, the likelihood of contact with pollutants in the indoor environment increases. 
Indoor air pollutants such as particulate matter (PM2,5, PM10, etc.), volatile organic compounds (VOC), and microorganisms have significant adverse effects on human health such as sick-building syndrome (SBS), building-related illness (BRI), irritation, respiratory tract infections, and even cancer. Indoor air pollutants can be emitted from a variety of sources. These pollutant sources can be related to the fabric of the buildings, construction materials, activities of the building occupants, and heating systems.
Bioaerosols are airborne particles originating from biological sources and include living and dead organisms such as algae, archaea, bacteria, fungal spores, plant pollen, and fragments of plant debris. With the widespread recognition of the potential hazard of biological agents, interest in bioaerosol exposure has increased, and exposure to bioaerosols, especially in indoor environments, can have significant effects on human health. Indoor sources of bioaerosols can generally occur through human emissions such as coughing, sneezing, speaking, or breathing, direct particle scattering of exfoliated skin cells and hair, and these significantly affect airborne bacterial populations.
As the bioaerosols in the indoor air are easily transported and come into contact with people, various health problems such as asthma, allergies and infections related to indoor air can occur. Bioaerosol is the generic name given to aerosolized cells, viruses, pollen, or spores. The importance of bioaerosols has been experienced all over the world during the COVID-19 pandemic. 
Filtration systems have been widely used and developed for the removal of particulate matter in the indoor environment, but applications and studies have been limited in terms of filter designs specifically for bioaerosol removal, the relationship between the mechanism of action, and filter performance. Indoor air quality can be improved with systems designed with appropriate filter selection.
There has been increased interest in electrospinning as an innovative technique to produce nanofiber assemblies in an easy and customizable manner. The electrospinning process is notable for its versatility and wide applicability, utilizing a wide variety of materials. Electrospun nanofibers draw attention to their extraordinary properties such as small fiber diameter, large specific surface area, high porosity, functionalization suitability to active interfaces, and the ability to add antibacterial agents at the nanoscale.
Natural polymers, synthetic polymers, and polymer blends, carbon and metal oxides are some of the most commonly studied materials in electrospinning. Polyacrylonitrile (PAN) is one of the widely used polymeric materials for filtration, thanks to its high mechanical properties, good solvent resistance, thermal stability, and easy fiber production by electrospinning.
Among nanomaterials, especially graphene-based nanomaterials are seen as promising fillers for the development of high-performance materials. Graphene-supported electrospun polymers have been the focus of attention in a variety of applications, such as energy storage, photocatalysis, tissue engineering, water purification, and antibacterial materials. Graphene is a two-dimensional (2D) honeycomb-like monolayer composed of tight carbon atoms with unique thermal, mechanical, and electronic properties. Graphene nanoplatelets (GNP) are composed of multiple layers of graphene and retain the excellent properties of graphene while also having a lower production cost than graphene. GNP can be used as a reinforcing filler without compromising the long-term performance of nanocomposites. The inclusion of GNPs improves the mechanical, thermal conductivity, thermal stability, gas permeability, and dielectric properties of polymers.
Enzymes are important as environmentally friendly agents to control biofilm formation without creating toxic or harmful effects on the surrounding environments. Some oxidoreductases, such as glucose oxidase, hexose oxidase, and xanthine oxidoreductase, can be used to produce hydrogen peroxide (H2O2) from natural substrates as a potent natural oxidant. H2O2 is a frequently used biocide in various applications and has no significant toxic effects due to its spontaneous action and subsequent complete decomposition into water and oxygen. Glucose oxidase (GOx), as one of the antibacterial enzymes, has a catalytic feature to oxidize β-D-glucose to gluconic acid and H2O2. Glucose oxidase enzyme is of great interest due to its wide applications in chemical, pharmaceutical, food, beverage, clinical chemistry, biotechnology, and other industries. Glucose oxidase enzyme reaction;
Glucose + O2 + H2O ->(Glucose Oxidase)-> Gluconic Acid + H2O2
For the immobilization of the GOx enzyme, which is intended to provide antibacterial properties, two different techniques were applied to filters i) cross-linking method and ii) modifications plus enzyme loading by diffusion method. These two techniques were applied in two ways i) chemical (with glutaraldehyde) and ii) physical (without glutaraldehyde). 
Escherichia coli DH10B, a representative bacterial strain of indoor air microorganisms, was selected to test the antibacterial properties of PAN and PAN-GNP nanofiber filters with immobilized GOx enzyme. In laboratory studies, attention was paid to the low risk of the selected species in terms of biosecurity. Moreover, the Escherichia coli DH10B strain is also highly efficient for DNA cloning.
The subject of this thesis is to develop an innovative antibacterial air filter with nanofibers that provides sustainable filtration performance by removing bioaerosols. Two basic methodologies have been applied in the production of antibacterial nanofiber air filters (i) fabrication of polyacrylonitrile polymer (PAN)/graphene nanoplatelet (GNP) nanofiber by electrospinning method and (ii) application of different enzyme immobilization techniques for glucose oxidase (GOx), which is aimed to provide antibacterial properties. The thesis study includes the production of nanofiber filters, enzyme immobilization, characterization, structural analysis, verification, and testing activities such as SEM, FTIR, CLSM, water vapor permeability value, as well as antibacterial activity tests. 
The main objectives of the thesis study are (i) to apply nanofiber fabrication methods, (ii) to research and apply enzyme immobilization techniques, (iii) to investigate the feasibility of antibacterial air filters by applying antibacterial tests as well as characterization and performance tests to the produced filters and (iv) to create a new antibacterial air filter product that improves indoor air quality and protects human health by removing bioaerosols.
The results of the study show that GNP addition to PAN polymer increased the antibacterial property and retention capability. Also, the GOx-doped PAN/GNP nanofiber filter has drawn attention to its antibacterial properties by successfully removing bioaerosols from the air. 
The findings of the study show that the GOx enzyme can be immobilized to electrospun nanofibers to remove bioaerosol from indoor air. 
The advantages of GOx-doped PAN/GNP nanofiber filters in antibacterial applications are that the GOx and glucose reaction can kill bacteria in an environmentally friendly way without causing toxic effects. On the other hand, different antibacterial tests applied to the produced nanofibers gave mutually supportive results and highlighted the success of the filters.