Photoactive nanocomposite thin films on glass and thermosensitive substratesNives Vodišek
, 2019, doctoral dissertation
Abstract: Photocatalysis is a well-known process for the last few decades; it is predominantly used for water and air purification, but also for self-cleaning and antibacterial surfaces. The photocatalytic process is one of the advanced oxidation processes, where semiconductors are mainly used as photocatalysts. The most known and used semiconductor is nanosized titania, which can non-selectively decompose organic matters. One of the side effects of nano TiO2 under UV irradiation is photoinduced hydrophilicity, which furthermore improves the self-cleaning effect. The main drawback of TiO2 is that for its activation UV light is needed, which represents only 5 percent of the solar spectrum. Consequently, actinic irradiance power is low and the response of photocatalyst is limited. Novel approaches are being introduced to improve TiO2 response to visible light such as doping, coupling, modification of surface morphology and others.
The thesis consists of five principal chapters. The first chapter is focused on a short literature review and explanation of some basic terms and principles that are related to this thesis.
The aim of the research was to prepare transparent photocatalytically active thin films on glass and thermosensitive substrates. Four thermosensitive substrates were used: polyvinyl chloride (PVC) foil, polymethyl methacrylate (PMMA) sheet and polyester (PES) fabric coated with a polyvinyl and acrylic coating, with (D1) or without (D2) an additional polyvinylidene fluoride topcoat. The synthesis of films was modified with the introduction of zirconium aiming at improving the photocatalytic activity of the TiO2 films, and the final films had a SiO2 phase present for increased mechanical robustness.
The third chapter is dedicated to the experimental part of the thesis. The detailed process of synthesis is described. The sol-gel process was used to prepare initial Ti-Zr sols, colloidal aqueous solutions with TiO2 and ZrO2 nanoparticles derived from titanium and zirconium alkoxides. The four different Ti-Zr sols were prepared with 0, 5, 10 and 20 molar % of Zr according to Ti. The depositing solution was prepared by mixing Ti-Zr sol, SiO2 sol binder, 1-propanol and 2-propoxyethanol, and then thin films were deposited by dip-coating technique. After the deposition, samples did not require high-temperature calcination since the photocatalytic anatase phase was present already after drying the deposited layers. Coated glass slides were put into a furnace at 150 °C, while samples on thermosensitive substrates were just treated by a heat gun. Samples in powder and thin film form were characterized by UV-Vis, FTIR-ATR and laser beam deflection spectroscopy, X-ray diffraction, scanning electron microscopy and thermal analysis. One of the main aspects of the photocatalyst is its activity. Photocatalytic activity of the thin films was determined, either quantitatively by the formation of fluorescent hydroxyterephthalic acid, one of the first degradation products of terephthalic acid deposit, or qualitatively by a visual-based method where degradation of resazurin ink was observed. Two additional methods were used on glass samples, electron paramagnetic resonance, and degradation of methyl stearate by observing the change in water contact angle under UVA irradiation. Mechanical stability of films on various substrates is an essential factor, describing how successful was immobilization of the photocatalytic materials on the substrate. It was determined by the pencil hardness test, i.e., Wolff-Wilborn method.
In the fourth chapter, titled “Results and Discussion,” the most important part of the thesis is placed. Materials characterization and associated discussion of the results are divided into three major parts: i) powder samples characterization; ii) characterization of thin films on a glass substrate, and iii) characterization of films on thermosensitive substrates.
In the conclusions, the main findings of the Ph.D. research work are summarized. One of our initial hypotheses was disapproved, thin films were not more active with a higher content of zirconium. However, they were more durable. All the obtained films were transparent and photoactive, despite the low-temperature synthesis procedure. Besides commonly used glass substrate, immobilization on thermosensitive substrates was also successful.
Keywords: glass substrate, immobilization, nanocomposite, nanomaterials, PES, photocatalysis, PMMA, PVC, self-cleaning surfaces, silica, plastic substrates, thin films, titania, zirconia
Published in RUNG: 14.10.2019; Views: 3510; Downloads: 179
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Self-cleaning and photoactive TiO2 – ZrO2 – SiO2 films on thermosensitive and glass substratesNives Vodišek
, Urška Lavrenčič Štangar
, 2017, published scientific conference contribution abstract
Abstract: Nanosized TiO2 is well-known for its photocatalytic property. From the combination of photocatalysis and photoinduced hydrophilicity properties, thin films of this material have also anti-fogging, self-cleaning and antimicrobial properties. There are numerous deposition techniques e.g. spin-coating, dip-coating, spraying, the most suitable one is chosen based on substrate or solution characteristics. Thin films are often required to be transparent for visible light, especially if we use them on transparent substrates, or they should not affect the color of the substrate. Radicals that are produced during photosensitizing process are able to destroy structure of a substrate and substrate can lose mechanical stability [1,2]. Some studies show that adding a SiO2 protective layer can prevent the damage of the substrate [3–5]. Ti-Zr containing sols were prepared with sol-gel process, where titanium(IV) isopropoxide, zirconium(IV) butoxide and ethanol were hydrolyzed with aqueous solution of perchloric acid. Solution was then refluxed for 48 hours. During that time crystallization and deaggregation took place and that resulted in a stable final solution . To prepare suitable solution for production of durable films silica binder was added. On glass and plastic substrates, thin films were deposited with the dip-coating method and dried with a heat-gun. Thin films were characterized by measurements of photocatalytic activity with terephthalic acid as model organic pollutant subjected to oxidation via fluorescent degradation product, photoinduced superhydrophilicity phenomena, UV-Vis and ATR-FTIR spectroscopy, SEM images, as well as mechanical properties measurements.
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Keywords: Self-cleaning surface, photocatalysis, TiO2, ZrO2, SiO2, PVC, PMMA, thermosensitive substrates, glass
Published in RUNG: 05.03.2019; Views: 3249; Downloads: 0
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Transparent Photocatalytic Thin Films on Flexible Polymer SubstratesNives Vodišek
, Andraž Šuligoj
, Dorota Korte
, Urška Lavrenčič Štangar
, 2018, original scientific article
Keywords: photocatalysis, self-cleaning surface, TiO2, ZrO2, SiO2, transparent films, thermosensitive
substrates, PMMA, PVC, PES, PVDF
Published in RUNG: 19.10.2018; Views: 3267; Downloads: 147
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Transparent titania-zirconia thin films for self-cleaning and photocatalytic applicationNives Vodišek
, Kandalam Ramanujachary
, Vlasta Brezová
, Urška Lavrenčič Štangar
, 2016, published scientific conference contribution abstract
Abstract: Thin films were prepared by sol-gel process, where different amount of zirconia were added to titania.
Photocatalytic activity of thin films was measured by two methods i) determination of degradation ration of methyl stearate with measuring the contact angle and ii) formation of hydroxyterephthalic acid was measured by spectrofluorometer.
Prepared samples were characterized by UV-Vis spectrophotometer, SEM, XRD, FT-IR ATR, and BET.
The result of measurements of photocatalytic activity shows that the highest activity has a sample without addition of zirconia, but mechanical stability of that sample is worse.
Keywords: photocatalysis, ZrO2/ TiO2, thin films, self-cleaning, low-temperature, sol-gel process
Published in RUNG: 14.03.2017; Views: 4793; Downloads: 200
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