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11.
Self-cleaning and photoactive TiO2 – ZrO2 – SiO2 films on thermosensitive and glass substrates
Nives Vodišek, Urška Lavrenčič Štangar, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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 [6]. 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. References [1] H. Schmidt, M. Naumann, T.S. Müller, M. Akarsu, Thin Solid Films (2006) 502, 132– 137. [2] W. A. Daoud, J.H. Xin, Y.H. Zhang, Surf. Sci. (2005) 599, 69–75. [3] Ž. Senić, S. Bauk, M. Vitorović-Todorović, N. Pajić, A. Samolov, D. Rajić, Sci. Tech. Rev. (2011) 61, 63–72. [4] T. Yuranova, R. Mosteo, J. Bandara, D. Laub, J. Kiwi, J. Mol. Catal. A: Chem. (2006) 244, 160–167. [5] T. Yuranova, D. Laub, J. Kiwi, Catal. Today (2007) 122, 109–117. [6] N. Vodišek, K. Ramanujachary, V. Brezová, U. Lavrenčič Štangar, Catal. Today (2017) 287, 142–147.
Ključne besede: Self-cleaning surface, photocatalysis, TiO2, ZrO2, SiO2, PVC, PMMA, thermosensitive substrates, glass
Objavljeno v RUNG: 05.03.2019; Ogledov: 4001; Prenosov: 0
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XAS studies of Sn modified TiO2 coatings
Ksenija Maver, Iztok Arčon, Urška Lavrenčič Štangar, 2018, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Coatings based on TiO2 are extensively investigated material for the preparation of surfaces which are referred as self-cleaning. Under solar illumination these coatings catalyze pollutants degradation and enhance their removal from the surface due to photoinduced superhydrophilicity [1]. There are two main drawbacks of using pure TiO2 (anatase) as a photocatalyst; i) its band gap lies in the UVA region so it can exploit only a part of the sunlight spectrum, and ii) it has a high degree of recombination between photo generated electrons and holes on the surface. There are various strategies to improve the photocatalytic efficiency of TiO2, one of them is the modification with transition metals. Based on our previous experiences with sol-gel synthesis of low-temperature TiO2 thin films [2], we prepared a series of Sn modified TiO2 photocatalysts. As a starting material only organic (Ti and Sn alkoxide) precursors were used. The loadings of Sn cations were varied in the range of 0.05 to 20 mol.%. The coatings, deposited on glass substrates by dip-coating technique, were dried at 150 oC. In addition, another set of photocatalyst coatings was prepared by further calcination at 500 °C in air. The comparison of photocatalytic activities of Sn modified TiO2 to unmodified TiO2 showed that Sn loadings in the range of 1-10 mol.% improved photocatalytic activity up to 8 times. At lower loadings of Sn, the photocatalytic activity was improved only by 30 %. After the coatings are calcined, their photocatalytic activity was significantly reduced. The objective of the research was to examine the mechanism responsible for photocatalytic properties of Sn modified TiO2 and to to clarify the role of Sn cations in the TiO2 photocatalytic process. For this purpose, Sn and Ti K-edge XANES and EXAFS analysis was used to precisely determine the local structure and the site of incorporation of Sn cations on titania nanoparticles in the coatings. We examined the hypothesis that the solid-solid interface was a crucial structural feature that facilitates charge separation and enhances photocatalytic efficiency of titania.
Ključne besede: Sn, EXAFS, TiO2 fotokatalizator
Objavljeno v RUNG: 12.09.2018; Ogledov: 3754; Prenosov: 0
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15.
The effect of Zr loading on photocatalytic activity of Cu modified TiO [sub] 2
Olena Pliekhova, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2018, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: Cu Zr modified TiO2, EXAFS, XANES
Objavljeno v RUNG: 12.09.2018; Ogledov: 3715; Prenosov: 0
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16.
The effect of Zr loading on photocatalytic activity of Cu modified TiO2
Olena Pliekhova, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2018, objavljeni znanstveni prispevek na konferenci

Ključne besede: Titanium diokside, acidic sites, surface titration, copper, zirconium
Objavljeno v RUNG: 10.09.2018; Ogledov: 4180; Prenosov: 0
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17.
Crystal phase controlled synthesis of TiO2 nanoparticles by solution combustion method
Olena Pliekhova, Urška Lavrenčič Štangar, 2018, objavljeni znanstveni prispevek na konferenci

Ključne besede: Solution combustion, titanium dioxide, carbohydrazide, chloride ion, fluoride ion
Objavljeno v RUNG: 10.09.2018; Ogledov: 3701; Prenosov: 0
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18.
Effects of Different Copper Loadings on the Photocatalytic Activity of TiO2-SiO2 Prepared at a Low Temperature for the Oxidation of Organic Pollutants in Water
T. Čižmar, Iztok Arčon, Mattia Fanetti, Urška Lavrenčič Štangar, 2018, izvirni znanstveni članek

Opis: The objective of this research is to examine how Cu modification can improve the photocatalytic activity of TiO2-SiO2, to explainthe correlation between the Cu concentration and the chemical state of Cu cations in the TiO2-SiO2 matrix, and the photocatalytic activity under UV/solar irradiation. The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low-temperature sol–gel method from organic Cu, Si and Ti precursors with various Cu concentrations (0.05–3 mol %). The sol–gels were dried at 150 8C to obtain the photocatalysts in a powder form. The photocatalytic activity was determined by using a fluorescence- based method of terephthalic acid decomposition. An up to three times increase in photocatalytic activity is obtained if the TiO2-SiO2 matrix is modified with Cu in a narrow concentration range from 0.05 to 0.1 mol%. At higher Cu loadings, the photocatalytic activity of the Cu-modified photocatalysts is lower than that of the un-modified reference TiO2-SiO2 photocatalyst. XRD was used to show that all Cu-modified TiO2-SiO2 composites with different Cu concentrations have the same crystalline structure as un-modified TiO2-SiO2 composites. The addition of Cu does not change the relative ratio between the anatase and brookite phases or unit cell parameters of the two TiO2 crystalline structures. We used Cu K-edge X-ray absorption near edge structure and extended X-ray absorption fine structure analyses to determine the valence state and local structure of Cu cations in the Cu-modified TiO2-SiO2 photocatalysts. The results elucidate the mechanism responsible for the improved photocatalytic activity. In samples with a low Cu content, which exhibit the highest activity, Cu@O@Ti connections are formed, which suggests that the activity enhancement is caused by the attachment of CuII cations on the surface of the photocatalytically active TiO2 nanoparticles, so CuII cations may act as free-electron traps, which reduce the intensity of recombination between electrons and holes at the TiO2 photocatalyst surface. At higher Cu loadings no additional Cu@O@Ti connections are formed, instead only Cu@O@Cu connections are established. This indicates the formation of amorphous or nanocrystalline copper oxide, which hinders the photocatalytic activity of TiO2.
Ključne besede: Cu modified TiO2-SiO2 photocatalyst Cu EXAFS, XANES, Organic pollutants
Objavljeno v RUNG: 30.08.2018; Ogledov: 3865; Prenosov: 0
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19.
Surface modified titanium dioxide using transition metals : nickel as a winning transition metal for solar light photocatalysis
Andraž Šuligoj, Iztok Arčon, Matjaž Mazaj, Goran Dražić, Denis Arčon, Pegie Cool, Urška Lavrenčič Štangar, Nataša Novak Tušar, 2018, izvirni znanstveni članek

Opis: Titanium dioxide has been widely used as an antimicrobial agent, UV-filter and catalyst for pollution abatement. Herein, surface modifications with selected transition metals (Me) over colloidal TiO2 nanoparticles and immobilization with a colloidal SiO2 binder as composite films (MeTiO2/SiO2) on a glass carrier were used to enhance solar-light photoactivity. Colloidal TiO2 nanoparticles were modified by loading selected transition metals (Me ¼ Mn, Fe, Co, Ni, Cu, and Zn) in the form of chlorides on their surface. They were present primarily as oxo-nanoclusters and a portion as metal oxides. The structural characteristics of bare TiO2 were preserved up to an optimal metal loading of 0.5 wt%. We have shown in situ that metal-oxo-nanoclusters with a redox potential close to that of O2/O2 were able to function as co-catalysts on the TiO2 surface which was excited by solar-light irradiation. The materials were tested for photocatalytic activity by two opposite methods; one detecting O2 (reduction, Rz ink test) while the other detecting OH (oxidation, terephthalic acid test). It was shown that the enhancement of the solar-light activity of TiO2 by the deposition of transition metal oxo-nanoclusters on the surface depends strongly on the combination of the reduction potential of such species and appropriate band positions of their oxides. The latter prevented excessive self-recombination of the photogenerated charge carriers by the nanoclusters in Ni and Zn modification, which was probably the case in other metal modifications. Overall, only Ni modification had a positive effect on solar photoactivity in both oxidation and reduction reactions.
Ključne besede: surface modified TiO2, XANES, EXAFS, Nickel, solar light photocatalyst
Objavljeno v RUNG: 01.06.2018; Ogledov: 3823; Prenosov: 0
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