İç ortam havasından biyoaerosol giderimi için pilot ölçekte antimikrobiyal nanolif filtrelerin üretimi ve mobil hava sterilizasyon sisteminin geliştirilmesi
Production of pilot scale antimicrobial nanofiber filters for bioaerosol removal from indoor air and development of a mobile air sterilization system
Yazar: ABDURRAHMAN TANRIVERDİ
Danışman: DOÇ. DR. DERYA YÜKSEL İMER
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Biyoaerosol = Bioaerosol ; Filtreler = Filters ; Mobil sağlık = Mobile health ; Organik madde bileşikleri = Organic matter compounds ; Sterilizasyon = Sterilization

Özet:
Son yıllarda solunum yoluyla bulaşan hastalıklarda, özellikle insanların temas halinde olduğu iç ortam hava kalitesi oldukça önemli bir konu haline gelmiştir. Bu kapsamda, sosyal mesafenin sağlanamadığı ya da çok iyi kontrol edilemediği ortamlarda biyoaerosol (aerosol halindeki hücreler, virüsler, sporlar veya biyolojik hücre kalıntıları) olarak isimlendirilen ve COVID-19'u da içeren iç ortam hava kirleticilerinin giderimine yönelik filtre malzemelerinin ve uzun süreli hijyen sağlayacak mobil sterilizasyon sistemlerinin geliştirilmesi önemli bir araştırma konusu oluşturmaktadır. Kapalı ortamların (ofis, hastane, AVM, uçak, tren vb.) iç ortam havasını temizlemek amacıyla kullanılan havalandırma sistemlerindeki en önemli kısım kullanılan filtre malzemesidir. Tez kapsamında, yüzey alanı/hacim oranı, değiştirilebilir yüzey özellikleri ve üstün mekanik dayanım sağlamak gibi özellikleri bulunan ve filtre malzemesi olarak üretilen nanolifler elektroeğirme yöntemi ile üretilmiştir. Nanolif üretim teknolojisi birçok alanda uygulanabildiği gibi hava filtresi geliştirmede de gelecek vaat etmektedir. Nanolif filtrelerin en büyük avantajlarından biri farklı polimerler ve nanomalzemeler ile çalışmaya olanak sağlamasıdır. Bu tezin temel çıkış noktası; polimer-nanomalzeme yapılarının nanolif üretimine uyumluluğunu öncelikle laboratuvar ölçeğinde kanıtlayarak pilot ölçek filtre üretimine geçmek ve hava ortamından ana hedef olarak partikül madde (PM) ve biyoaerosollerin giderimi için mobil cihaz tasarlamaktır. Tez kapsamında, yüksek mekanik dayanım ve fiber oluşturma yeteneğine sahip olması nedeniyle poliakrilonitril (PAN) polimeri kullanılarak nanolifler üretilmiştir. Tez kapsamında, polimerik nanoliflerin hazırlanması için ilk olarak, PAN polimeri dimetilformamid (DMF) çözücüsü içerisinde kütlece %10 oranında çözünerek polimer çözeltisi hazırlanmıştır. Hazırlanan PAN çözeltisinden nanomalzeme katkılı nanoliflerin karakterizasyonunda referans olarak kullanmak amacıyla elektroeğirme yöntemi ile saf PAN nanolifleri hazırlanmıştır. PAN polimeri ile kompozit nanolifler üretmek amacıyla, antimikrobiyal özellik için kütlece %1-2 aralığında TiO2 ve adsorpsiyon içinde kütlece %2-4 aralığında selüloz nanokristal (SNK) eklentileri polimer çözeltilerine eklenerek nanoliflerin üretimleri gerçekleştirilmiştir.
Literatürde yer alan çalışmalardan ve piyasadaki mevcut cihazlardan farklı olarak, nanolif filtrelere kazandırılan iki temel mekanizma ile biyoaerosol giderimi gerçekleştirilmiştir. Bu mekanizmalar, (i) seçici tutunum: selüloz nanokristal (SNK) nanomalzemenin nanolif yapısına eklenmesiyle, havada sıvı zerrecikler içerisinde asıltı halinde kaldığı kanıtlanmış olan biyoaeorosollerin hızlı bir şekilde hava ortamından alınarak nanolif filtre üzerinde/içerisinde adsorbe edilmesini/tutunmasını sağlamak ve anında fotokatalitik etkiye maruz bırakmak, filtreden kaçışını engellemek için nanoliflerin gözenek çapını ayarlamak (ii) fotokatalitik aktivite: TiO2 nanomalzemenin nanolif yapısına eklenmesiyle fotokatalitik özellik kazandırarak, nanolifte tutunmuş ve belirli çoğunluğa ulaşmış mikroorganizmaların yüzeye verilecek UVA ışığı ile katalitik olarak tamamen giderimini sağlamak şeklindedir. Geliştirilmiş olan sistemde farkı eş zamanlı adsorpsiyon ve fotokatalitik oksidasyon ile tek bir malzeme üzerinde yüksek kalitede filtrasyon performansına ulaşması hedeflenmiştir.

Abstract:
In recent years, the quality of indoor air with which people come into contact has become a very important issue in respiratory diseases. In this context, filter materials are provided for the removal of indoor air pollutants, the so-called bioaerosols (cells in aerosol form, viruses, spores or biological cellular debris), including COVID-19, and for long-term hygiene in environments where social distance cannot be achieved or controlled very well. The development of mobile sterilization systems is an important starting point in the fight against this pandemic. The most important part of the ventilation systems used to clean the indoor air in closed environments (offices, hospitals, shopping malls, airplanes, trains, etc.) is the filter material used.
The main approach of this thesis; The main objective is to produce nanofiber filters with high adsorption and photocatalytic activity for the removal of bioaerosols, which are the SARS-CoV-2 virus as the main target, with the compatibility of polymer nanomaterial structures for nanofiber production. It also involves the development of mobile air sterilization systems to address the urgent need for indoor air hygiene.
In this work, nanofibers are produced as filter materials, i.e., fibers with a diameter of less than 1000 nm produced by electrospinning. Nanofibers can be produced in different pore sizes ranging from micrometers to nanometers, depending on the intended use. This feature gives the obtained filter a very large surface-to-volume ratio, interchangeable surface properties and excellent mechanical strength. Nanofiber fabrication technology can be used in many fields and is also promising for the development of air filters. One of the biggest advantages of nanofiber filters is that they allow working with different polymers and nanomaterials. In this work, nanofiber filters were fabricated using polyacrylonitrile (PAN) because it is a polymer produced in our country that has high mechanical strength and fiber forming ability. In this work, for the preparation of polymeric nanofibers, a polymer solution was first prepared by dissolving the polymer PAN at 10% by mass in the solvent dimethylformamide (DMF). Pure PAN nanofibers were prepared by electrospinning to serve as a reference for characterization of nanomaterial-doped nanofibers from the prepared PAN solution. To prepare composite nanofibers with PAN polymer, nanofibers were prepared by adding TiO2 in the order of 1-2 mass% for antimicrobial property and CNC nanomaterials in the order of 2-4 mass% for adsorption to polymer solutions.
In contrast to the studies in the literature and the devices currently on the market, there are two basic mechanisms conferred to the nanofiber filters. These mechanisms include (i) selective attachment: the bioaerosols, which have been shown to be suspended in liquid particles in the air, are rapidly removed from the air environment by the addition of cellulose nanocrystalline (CNC) nanomaterial to the nanofiber structure while they are in the droplet and adsorbed on/in the nanofiber filter. (ii)Photocatalytic activity: the addition of TiO2 nanomaterials to the nanofiber structure gives it a photocatalytic property and catalytically completely removes the microorganisms adhered to the nanofiber and reached a certain majority by UV-A (320-400 nm) light emitted to the surface form. At this point, the main difference of the developed system from devices with UV-integrated photocatalytic TiO2 filters and/or activated carbon + HEPA filters is that a high-quality filtration efficiency has been achieved on a single material with simultaneous adsorption and photocatalytic oxidation. The filtration efficiency attempted in existing systems, such as activated carbon and HEPA filter systems, with separate materials is achieved with a single material, operation is simple, and material supply/cost problems are avoided.
TiO2 is the nanomaterial that imparts antimicrobial properties to the nanofiber filters to be fabricated in this work. Cellulose nanocrystal (CNC) is the nanomaterial that provides integration and long-term activation of this nanomaterial on the filter surface and prevents viruses suspended in the air as droplets from attaching to the filter surface and escaping. The two most important factors affecting the efficiency of this mechanism are the need for surface area to increase adsorption of bioaerosols in indoor air and ensure contact with the photocatalyst, and the sustainable reusability of photocatalysts, whose efficiency decreases over time due to pollution.
This thesis tested the antimicrobial properties of nanofibers and their performance in removing bioaerosols, and developed a mobile device design that integrates these nanofibers. It is equipped with two simultaneous mechanisms to remove viruses from indoor air. First, it aims to allow bioaerosols in the indoor air to accumulate on the filter surface and reach a maximum fraction without affecting the pressure drop too much by using the high adsorption property of the CNC nanomaterial in the fabricated filters. Therefore, the aim of the studies conducted in this work is to use these two technologies together and provide long-term indoor hygiene with the mobile air disinfection system. With simultaneous adsorption and oxidation in the filter (i) applying the catalytic UV-TiO2 reaction to bioaerosols that have reached a certain majority, thus applying a high UV dose in a shorter time (ii) achieving continuous self-cleaning of the filters (iii) adsorption supporting photocatalytic oxidation. It is aimed to convert the continuous operation mode of UV-A lamps to intermittent operation to ensure energy efficient operation.
As part of this work, the performance of nanofibers for the removal of particulate matter and bioaerosols was tested and a mobile device was designed to integrate these nanofibers. The goal of the studies conducted as part of this work is to fabricate pilot-scale filters using these two mechanisms together and to develop and test the effectiveness of a mobile air sterilization system using this filter.
The objectives to be achieved with respect to the filter materials are: (i) By aiming particles in the range of 0.3-2.5 μm, including bioaerosols in ambient air, mass produce nanofiber filters to remove 99.95% of sub-0.3 micron particles according to EN 1822 (ii) the adsorption function of CNC (iii) the reduction of pressure drop leading to performance loss in filtration efficiency by utilizing the surface area increase of CNC (iv) the increase of long-term usability of nanofiber filters by exploiting the mechanical properties of CNC (v) the increase of long-term usability of TiO2. It is to provide long-term indoor hygiene by utilizing its property.
Objectives to be achieved by the developed mobile filtration device: (i) Successful use by providing on-site solutions in environments where sterilization is not possible and/or insufficient with the existing ventilation system and/or air conditioning systems with high risk level (ii) The filters can operate in a filtration area of about 6-10 m2 and an air flow of 100-250 m3/h and should operate for a long time according to the air exchange rates recommended in the WHO -2009 document.
In experimental studies, the electrospinning method was used to fabricate nanofiber filters using PAN, CNC and TiO2 materials as polymer nanomaterial structures, and the results of structural tests such as filter characterization, performance characteristics, and bioaerosol and particulate matter tests conducted under reactor and room conditions were evaluated. In addition to the characterization tests of the nanofiber filter, studies on the removal of particulate matter using the mobile device for indoor air purification were conducted, ranging from laboratory-scale production to pilot-scale large production.