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1.
Development of Advanced TiO2/SiO2 Photocatalyst for Indoor Air Cleaning
Andraž Šuligoj, 2015, doctoral dissertation

Abstract: TiO2 - SiO2 composites were synthesized by low-temperature sol-gel impregnation method, using four different titania sources (P-25 from Degussa, PC500 from Millennium, CCA 100 AS and CCA 100 BS from Cinkarna, later denoted as AS and BS, respectively) and deposited on aluminium and glass carriers. Ordered and disordered mesoporous silicas were impregnated with ce{TiO2} in powder or suspension form in the Ti : Si molar ratio 1 : 1. Structure, size, band gap, chemical composition and specific surface area of nanoparticles were determined by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DR-UV-vis), Fourier transform infrared spectroscopy (FT-IR) and ce{N2} physisorption. Additionally, quantity of surface hydroxyl groups, surface acidity and mechanical stability of the coatings were determined by temperature programmed Fourier transform infrared spectroscopy (TPD-IR) and Wolff-Wilborn method, respectively. The photocatalytic activity of TiO2 and TiO2 - SiO2 composites was evaluated in the photodegradation of toluene and formaldehyde, as model VOCs, under UVA light irradiation in lab-made photoreactor system with two different regimes; batch and plug-flow mode. These two VOCs are being considered as examples of two of the six major classes of indoor air contaminants. Adsorption properties of the samples with toluene, have shown that the addition of mesoporous silica was beneficial. The increase of the adsorption of the bare AS TiO2 (9.5 %) was higher in the case of ordered silica, SBA-15 (2.8 times for AS/SBA15 to 26.8 %) than disordered SiO2 KIL-2 (2.4 times for AS/KIL2 to 22.7 %) although it was significant in both types of mesoporous silica supports (over 20 %). Adsorption was found to be dependent mostly on the quantity of surface Si-OH groups. Regarding the photocatalytic activities towards toluene degradation, the results with pure TiO2 showed the fastest kinetics in case of sample AS followed by PC500 and P25. The observed behaviour was ascribed to smaller particle size, and consequently higher specific surface area. Grafting titania onto silica showed the importance of structural parameters. Most importantly, if the pore structure of bare TiO2 collapsed, this resulted in decreased activity. On the other hand, retainment of the pore structure improved the distribution of nanoparticles, crystallinity and optical properties, which resulted in improved photocatalytic activity. In the degradation of formaldehyde, it was found that adsorption and degradation abilities of the materials were much more dependent on the structural properties of the samples, i.e., the pore structure. This was explained as a consequence of the different degradation mechanisms of both pollutants. Toluene degradation is governed by the oxidation through photogenerated holes - direct oxidation, whereas in the degradation of formaldehyde, the major oxidative species are OH radicals. In addition, the same as in toluene oxidation, the activity was dependent mainly on the number of crystal defects and the band gap values, that is the oxidation and reduction potentials of the catalysts. The degradation efficiency was increased from 88 % in pure AS TiO2 to 97 % when this titania was grafted onto colloidal silica (7C). An important highlight of the thesis is synthesis of a novel photocatalyst, labelled AS7C, which comprises an acidic colloidal suspension AS as TiO2 source and colloidal silica, using a low-temperature sol-gel impregnation method. This sample used all the above mentioned properties that improve photocatalytic activity towards both pollutants. Mechanical stability of the samples was also tested. The tests showed that binder, in the form of colloidal SiO2 (in size of 25 nm) in combination with colloidal titania of appropriate size - 6 nm, produced the highest mechanical stability of the coatings, which also showed excellent photocatalytic activity. Stability of the coatings, using AS as titania source, was greatly improved. The Wolff-Wilborn test on AS coating showed no mechanical resistance, while with the optimal (in terms of photocatalytic performance) addition of 7C SiO2 binder stability was excellent (F, which is in the middle of 6B-6H hardness scale). This sample (AS7C) was also tested for release of aerosols, during operation of the reactor, which could be harmful for human health at longer exposure times. It was found that aerosols are formed, probably as a consequence of detachment of nanoparticles in the first period of photodegradation test. However, their formation in consecutive tests was greatly reduced. Last but not least, a pilot plug-flow reactor was constructed to test the photocatalyst's efficiency in one-pass degradation of toluene. Sample AS7C was able to degrade toluene at conditions applied (v= 400 mL/min, m(catalyst) = 1049 mg, C(0) = 1 ppmv), which means that the out-flow from reactor was clean of the pollutant and any possible intermediates, comprising only of humid air and CO2. Deactivation of the catalyst was found at higher air flow and higher initial concentration of the pollutant. However, the concentrations of pollutants in living conditions are few orders of magnitude lower, hence this is a promising result.
Found in: ključnih besedah
Keywords: Air remediation, TiO2 photocatalysis, Immobilization, Thin layers, TiO2/SiO2 composites
Published: 31.08.2015; Views: 4661; Downloads: 80
.pdf Fulltext (33,47 MB)

2.
Vpliv dielektrika na delovanje organskega tankoplastnega tranzistorja: organski in anorganski dielektriki
Anže Peternel, 2015, undergraduate thesis

Abstract: Organski tankoplastni tranzistorji (OTFT) so polprevodniški elementi, ki opravljajo funkcijo stikal v elektronskih napravah. Med njihovo najpomembnejšo lastnost štejemo hitrost preklapljanja električnega toka. Hitrost preklapljanja je odvisna od mobilnosti nosilcev naboja, ta pa je odvisna predvsem od stične površine med plastjo dielektrika in polprevodnika. Preučili smo vpliv dielektrika na mobilnost vrzeli v OTFT-jih s polprevodnim polimerom poli(3-heksiltiofen) (P3HT). Primerjali smo dielektrike parilen C, termični oksid (SiO2) in oktadekiltriklorosilan (OTS). Ugotovili smo, da na mobilnost vrzeli močno vplivata hrapavost in polarnost dielektrika. Za najboljši dielektrik se je izkazal OTS, saj je bila mobilnost vrzeli najvišja glede na ostale preučene OTFT-je. Najvišja izmerjena mobilnost vrzeli je znašala 0.03 cm^2 V^−1 s^−1 . Pri OTFT-jih z dielektrikom OTS smo izmerili upor stika med elektrodama in plastjo polprevodnika. Upor je znašal 1 MΩ in predstavlja veliko oviro za tok, ki teče skozi OTFT. Iz pridobljenih rezultatov sklepamo, da so OTFT-ji z organskimi dielektriki boljši kot OTFT-ji z dielektrikom SiO2, če je njihova površina ravna in hidrofobna. Sklepamo da z optimizacijo upora stika med elektrodo in plastjo polprevodnika lahko pripravimo OTFT-je, ki so primerni za izdelavo fleksibilne organske elektronike.
Found in: ključnih besedah
Summary of found: ...(P3HT). Primerjali smo dielektrike parilen C, termični oksid ( SiO2) in oktadekiltriklorosilan (OTS). Ugotovili smo, da na mobilnost...
Keywords: konjugirani polimeri, P3HT, termični oksid SiO2, parilen C, OTS, tokovno-napetostna karakteristika, mobilnost nosilcev naboja, pragovna napetost, upor stika kovina – polprevodnik
Published: 28.09.2015; Views: 4217; Downloads: 112
.pdf Fulltext (10,50 MB)

3.
STRUCTURAL PROPERTIES OF MANGANESE-FUNCTIONALIZED SILICA AEROGELS
Tatjana Kobal, 2016, master's thesis

Abstract: Manganese-functionalized silica with interparticle mesoporosity and isolated Mn sites (Mn/Si = 0.01) is an excellent Fenton catalyst for water cleaning. However, there is a problem that needs to be solved, i.e., Mn leaching from the silica support during the reaction. The solution may lie in using aerogels as the silicate supports for the manganese. The goal of this master thesis is the synthesis and characterization of manganese-functionalized silica aerogels with different Mn/Si molar ratios and a determination of their structural properties. The emphasis is on the preparation of manganese-functionalized silica aerogels with isolated manganese sites. Firstly, manganese-functionalized microporous and mesoporous silicates with a molar ratio Mn/Si = 0.005–0.02 were synthesized according to the literature and characterized as reference materials for manganese-functionalized aerogels. Manganese silicalite-1 (MnS-1) as a microporous zeolite-type silicate and manganese-functionalized silica (MnKIL-2) as a mesoporous silicate were prepared by the sol-gel process with a hydrothermal and solvothermal treatment, respectively. MnS-1 and MnKIL-2 with a molar ratio of Mn/Si ≤ 0.01 contain manganese as isolated sites in the silica framework and with a molar ratio of Mn/Si > 0.01 contain manganese as manganese oxides. Secondly, manganese-functionalized aerogels (MnAEG) with a molar ratio Mn/Si = 0.005–0.02, were prepared according to the acid-base of the sol-gel polymerization of a tetraethylorthosilicate precursor, which is followed in combination with a supercritical drying using CO2. The prepared materials were characterized using the following techniques: X-ray powder diffraction (XRD), energy-dispersive X-ray elemental analysis (EDX), nitrogen physisorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characterization results on manganese-functionalized aerogels (MnAEG) showed Mn oxide nanoparticles incorporated into the aerogel already at a low Mn concentration (Mn/Si = 0.005), which means that Mn aerogels are not promising silica supports for Mn catalysts applied for water cleaning, because they do not contain isolated Mn sites.
Found in: ključnih besedah
Summary of found: ...: SiO2 aerogels, manganese-functionalized SiO2 aerogels, sol–gel process, CO2...
Keywords: : SiO2 aerogels, manganese-functionalized SiO2 aerogels, sol–gel process, CO2 supercritical drying
Published: 02.09.2016; Views: 2748; Downloads: 153
.pdf Fulltext (4,37 MB)

4.
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO [sub] 2-SiO [sub] 2 nanoparticle composites
T. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2016, published scientific conference contribution abstract

Found in: ključnih besedah
Summary of found: ...Cu-modified TiO2- SiO2, sol-gel, XANES, EXAFS...
Keywords: Cu-modified TiO2-SiO2, sol-gel, XANES, EXAFS
Published: 06.02.2017; Views: 1427; Downloads: 0
.pdf Fulltext (378,67 KB)

5.
Correlations between photocatalytic activity and Cu structure in Cu-modified TiO2-SiO2
T. Čižmar, published scientific conference contribution abstract

Found in: ključnih besedah
Keywords: Titanium dioxide, Cu-modified, TiO2-SiO2, photocatalysts, photocatalytic activity, Cu K-edge XANES, EXAFS
Published: 26.06.2017; Views: 1455; Downloads: 0
.pdf Fulltext (641,42 KB)

6.
Chemical structure in Cu-modified TiO2-SiO2 nanocomposites calcined at 500 °C for 1 h in air
T. Čižmar, Iztok Arčon, Urška Lavrenčič Štangar, 2017, published scientific conference contribution abstract

Found in: ključnih besedah
Keywords: Cu-modified TiO2-SiO2 photocatalysts, titanium dioxide, metal doping, Cu K-edge XANES, EXAFS, photocatalytic activity
Published: 22.08.2017; Views: 11090; Downloads: 0
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7.
Vibrational spectra of vitreous SiO2 and vitreous GeO2 from first principles
Alfredo Pasquarello, Luigi Giacomazzi, 2007, original scientific article

Found in: ključnih besedah
Keywords: SiO2, GeO2, glasses, ab-initio, vibrational spectra, Raman
Published: 16.10.2018; Views: 726; Downloads: 0
.pdf Fulltext (228,60 KB)

8.
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, original scientific article

Abstract: 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.
Found in: ključnih besedah
Keywords: Cu modified TiO2-SiO2 photocatalyst Cu EXAFS, XANES, Organic pollutants
Published: 30.08.2018; Views: 769; Downloads: 0
.pdf Fulltext (1,53 MB)

9.
Transparent Photocatalytic Thin Films on Flexible Polymer Substrates
Nives Vodišek, Andraž Šuligoj, Dorota Korte, Urška Lavrenčič Štangar, 2018, original scientific article

Found in: ključnih besedah
Summary of found: ...photocatalysis, self-cleaning surface, TiO2, ZrO2, SiO2, transparent films, thermosensitive substrates, PMMA, PVC, PES, PVDF...
Keywords: photocatalysis, self-cleaning surface, TiO2, ZrO2, SiO2, transparent films, thermosensitive substrates, PMMA, PVC, PES, PVDF
Published: 19.10.2018; Views: 713; Downloads: 69
.pdf Fulltext (4,37 MB)

10.
Generalized stacking fault energy surfaces and dislocation properties of coesite
Sandro Scandolo, Luigi Giacomazzi, 2009, published scientific conference contribution abstract

Found in: ključnih besedah
Keywords: coesite, first-principles, dislocations, sio2
Published: 02.11.2018; Views: 668; Downloads: 0
.pdf Fulltext (82,44 KB)

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