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Towards efficient removal of contaminants from households grey waste water: Photocatalytic ozonation process
Marko Kete, Urška Lavrenčič Štangar, 2015, published scientific conference contribution abstract (invited lecture)

Keywords: compact reactor, immobilized TiO2, porous alumina monolith, LAS, PBIS, RB19
Published in RUNG: 01.02.2016; Views: 5686; Downloads: 0
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Alternativni nosilci za TiO2 v procesih fotokatalize
Rok Oblak, 2015, master's thesis

Abstract: Z naraščanjem populacije na Zemlji se povečuje potreba po čisti pitni vodi, hkrati pa, zaradi dvigovanja standarda življenja, močno narašča tudi količina odpadnih vod. Za čiščenje odpadnih vod se uporabljajo številni fizikalni, biološki in kemijski procesi, katerih učinkovitost je odvisna od prisotnih onesnaževal. Napredne oksidacijske metode (NOM) se uporabljajo za razgradnjo težje razgradljivih organskih onesnaževal. Pri tem gre za kemično obdelavo odpadnih vod z namenom razgradnje organskih snovi z oksidacijo preko hidroksilnih radikalov. Dve izmed naprednih oksidacijskih metod sta tudi fotokatalitska oksidacija in fotokatalitska ozonacija. Fotokataliza običajno poteka pod UV svetlobo v prisotnosti fotokatalizatorja (npr. TiO2). Fotokatalizator je lahko suspendiran v raztopini ali pa pritrjen na različne nosilce/substrate. Drug način uporabe je sicer manj učinkovit, vendar enostavnejši in zato bolj primeren za prenos tehnologije v prakso. V svoji magistrski nalogi sem se ukvarjal z iskanjem novih nosilcev za fotokatalizator in razvojem metod za nanos TiO2 na izbrane nosilce. Kot fotokatalizator sem po opravljenih poskusih z več katalizatorji uporabil Aeroxide® TiO2 P-90, proizvajalca Evonik. Preizkusil sem dva nosilca, in sicer pletena steklena vlakna in pa mrežico iz nerjavečega jekla. Izbrana sta bila, ker sta kemijsko inertna, poleg tega pa ju je enostavno prilagajati obliki reaktorske celice. Učinkovitost nosilcev sem preverjal z razgradnjo vodnih raztopin fenola in komercialnega tekstilnega barvila, Reactive Blue 19. Razgradnjo sem izvajal v pretočnem fotoreaktorju. Za analizo vzorcev sem uporabil visokotlačno tekočinsko kromatografijo (HPLC), analizo celokupnega ogljika (TOC) in pa UV-VIS spektrofotometer. Oba nosilca sta se izkazala za učinkovita, vendar pri različnih metodah. Steklena vlakna so bila najučinkovitejša pri fotokatalitski oksidaciji, mrežica iz nerjavečega jekla pa pri fotokatalitski ozonaciji. Za oba nosilca sta bili razviti tudi metodi nanašanja TiO2.
Keywords: TiO2 fotokataliza, P90, fenol, Reactive Blue 19, pretočni reaktor, steklena vlakna, mrežica iz nerjavečega jekla
Published in RUNG: 30.09.2015; Views: 8853; Downloads: 327
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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.
Keywords: Air remediation, TiO2 photocatalysis, Immobilization, Thin layers, TiO2/SiO2 composites
Published in RUNG: 31.08.2015; Views: 9014; Downloads: 208
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Novel applications of oxygenic photosynthetic organisms : dissertation
Danijel Stojković, 2015, doctoral dissertation

Abstract: Inspired by natural microorganisms that possess a rigid cell wall to protect them in harsh conditions, individual cells of Chlamydomonas reinhardtii were artificially encapsulated with different materials and hydrogen production was enhanced. The first attempt was to cover the cells with hydrated silicon dioxide, which is naturally formed by diatoms. The cells covered with silica were not able to produce hydrogen, but the improved TiO2-encapsualtion of Chlamydomonas reinhardtii was found to positively affect their hydrogen production under sulfur-deprived conditions. It was shown that incubation of the cells in the dark before exposure to light was necessary in order to overcome the toxic effects of the (RKK)4D8 catalytic peptide that is essential for TiO2 formation. The TiO2-encapsulated cells were able to produce H2 with about double efficiency during 5-day period compared to non-encapsulated cells. The light-to-H2 conversion efficiency of TiO2-encapsulated Chlamydomonas reinhardtii system was estimated to be more than 4 % under optimized conditions. The encapsulation with platinum led us to discover the bioreductive properties of Chlamydomonas reinhardtii. Beside the homogeneous Pt reduction carried out by the algae, the most surprising discovery was the possibility to use algae culture for targeted heterogeneous nucleation. An important discovery was that is possible to control the nucleation mechanism and redirect predominantly homogeneous into fully heterogeneous nucleation.
Keywords: photosynthesis, H2 production, TiO2, encapsulation, Chlamydomonas reinhardtii, platinum reduction
Published in RUNG: 01.04.2015; Views: 8674; Downloads: 304
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