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2. Novel applications of oxygenic photosynthetic organismsDanijel 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.
Found in: ključnih besedah
Keywords: photosynthesis, H2 production, TiO2, encapsulation, Chlamydomonas reinhardtii, platinum reduction
Published: 01.04.2015; Views: 7383; Downloads: 295
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3. Development of Advanced TiO2/SiO2 Photocatalyst for Indoor Air CleaningAndraž 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: 7650; Downloads: 183
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4. Alternativni nosilci za TiO2 v procesih fotokatalizeRok 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.
Found in: ključnih besedah
Keywords: TiO2 fotokataliza, P90, fenol, Reactive Blue 19, pretočni reaktor, steklena vlakna, mrežica iz nerjavečega jekla
Published: 30.09.2015; Views: 7431; Downloads: 310
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8. Diclofenac removal by simulated solar assisted photocatalysis using TiO2-based zeolite catalyst; mechanisms, pathways and environmental aspectsDionysios D. Dionysiou, Urška Lavrenčič Štangar, Sandra Babich, Hrvoje Kušić, Martina Biosic, Daria Juretic Perisic, Subhan Salaeh, Ana Lončarić Božić, 2016, original scientific article Abstract: The study explores the potential of immobilized TiO2-based zeolite composite photocatalyst (TiO2-FeZ)
made of commercial AEROXIDE TiO2 P25 and iron-exchanged zeolite of ZSM5 type (FeZ), for solar assisted
treatment of diclofenac (DCF), pharmaceutical included in the ‘‘watch list” during last prioritization in
water legislation by EU.
In this study the efficiency of applied photocatalytic treatment, solar/TiO2-FeZ/H2O2, of DCF water
solution was evaluated on basis of DCF removal and conversion kinetics, as well as the changes of
common parameters for assessing water quality. Hence, the changes in the removal and mineralization
of overall organic content, biodegradability, toxicity to Vibrio fischeri, dechlorination of DCF and
its formed by-products, were monitored during the treatment. The obtained data were correlated with
the evolution of DCF by-products, identified and monitored during the treatment by HPLC/MSMS
analysis. In order to estimate the influence of water matrix, all experiments were performed in the
presence of chloride or sulphate as counter ions. The obtained data revealed that degradation
mechanism of DCF by applied treatment process using immobilized TiO2-FeZ includes the adsorption
onto photocatalyst surface and consequent degradation. The contribution of homogeneous Fenton
reaction due to leached iron ions was found to be negligible. The adsorption and degradation pathway of DCF were influenced by the type of counter ions, which was reflected in the observed changes of
water quality parameters.
Found in: ključnih besedah
Keywords: Solar photocatalysis, TiO2-FeZ catalyst, Diclofenac, Degradation pathway, Biodegradability, Toxicity
Published: 21.07.2016; Views: 4681; Downloads: 0
Fulltext (2,10 MB) |
9. Efficient mineralization of aqueous organic pollutants by photocatalytic ozonationMarko Kete, Urška Lavrenčič Štangar, invited lecture at foreign university Abstract: Photocatalytic ozonation process using TiO2 photocatalyst (O3/TiO2/UV – PH-OZ) conducted in acidic water environment often leads to synergistic effect in terms of decomposition and mineralization of aqueous organic contaminants, which makes the process suitable for waste water treatment or pretreatment of drinking water. [1,2] The synergism is among other factors (pH, O3 dose, T,…) greatly influenced by photocatalyst physicochemical properties and pollutant type. In the first part of the study, five different commercial TiO2 photocatalysts (P25, PC500, PC100, PC10 and JRC-TiO-6) were used in O2/TiO2/UV, O3/TiO2 and O3/TiO2/UV advanced oxidation systems for degradation of two pollutants (dichloroacetic acid - DCAA and thiacloprid – neonicotinoid pesticide), simultaneously present in water solution. [3] Results of PH-OZ (O3/TiO2/UV) experiments showed that in contrast to DCAA which adsorbs on TiO2 surface, synergistic effect is much more expressed in the case of thiacloprid which doesn’t adsorb. The influence of BET surface area of the photocatalyst and its dispersivity will be discussed.
In the second part of this study, selected catalysts were immobilized on a proper support to avoid post-filtration step in the process of greywater treatment. A good adhesion of a catalyst on various supports was successfully achieved by immobilization of commercial TiO2 powders (P25, P90, PC500) with the help of a sol-gel silica-titania binder [4]. For the purpose of simulated greywater treatment, special compact reactor was designed and developed, utilizing Al2O3 porous reticulated monolith foams as TiO2 carriers and UVA-lamps inside (Fig. 1). [5] With degradation of LAS+PBIS and Reactive blue 19 (RB 19) as representatives of surfactants and textile dyes respectively, commonly found in household greywater, and phenol as trace contaminant, an evaluation of PH-OZ and photocatalytic oxidation has been performed (an example in Fig. 2). Synergistic effect of PH-OZ was generally much more expressed in mineralization reactions, showing TOC half lives of less than one hour for the mixture of pollutants in compact reactor. [5] Due to its superior cleaning capacity, PH-OZ process employing efficient photocatalysts is suitable for treating wastewaters also with higher loading of organic pollutants.
1. U. Černigoj, U.Lavrenčič Štangar, J. Jirkovsky, J. Hazard. Mater. (2010) 177:399–406.
2. U. Černigoj, U.Lavrenčič Štangar, P. Trebše, Appl. Catal. B Environ. (2007) 75:229–238.
3. M. Kete, U. Černigoj, U. Lavrenčič Štangar: Photocatalytic ozonation – study of reaction parameters and mechanism, article under submission
4. M. Kete, E. Pavlica, F. Fresno, G. Bratina, U. Lavrenčič Štangar, Environ. Sci. Pollut. Res. (2014) 21:11238–11249.
5. M. Kete: Towards efficient removal of contaminants in water from household appliances by TiO2-photocatalysis: design, optimization and performance studies of the photoreactor with immobilized catalysts, Doctoral dissertation (2015), University of Nova Gorica, Nova Gorica.
Found in: ključnih besedah
Keywords: photocatalysis, ozonation, TiO2, dichloroacetic acid, thiacloprid, mechanisms, LAS+PBIS, Reactive blue 19, phenol
Published: 21.07.2016; Views: 6037; Downloads: 0
Fulltext (4,10 MB) |
10. Solar-driven photocatalytic treatment of diclofenac using immobilized TiO2-based zeolite compositesUrška Lavrenčič Štangar, Mattia Fanetti, Marko Kete, Andraz Suligoj, Hrvoje Kušić, Subhan Salaeh, Marin Kovacic, Dionysios D. Dionysiou, Ana Lončarić Božić, 2016, original scientific article Abstract: The study is aimed at evaluating the potential of
immobilized TiO2-based zeolite composite for solar-driven
photocatalytic water treatment. In that purpose, TiO2-iron-exchanged
zeolite (FeZ) composite was prepared using commercial
Aeroxide TiO2 P25 and iron-exchanged zeolite of ZSM5
type, FeZ. The activity of TiO2-FeZ, immobilized on glass
support, was evaluated under solar irradiation for removal of
diclofenac (DCF) in water. TiO2-FeZ immobilized in a form
of thin film was characterized for its morphology, structure,
and composition using scanning electron microscopy/energydispersive
x-ray spectroscopy (SEM/EDX). Diffuse reflectance
spectroscopy (DRS) was used to determine potential
changes in band gaps of prepared TiO2-FeZ in comparison
to pure TiO2. The influence of pH, concentration of hydrogen
peroxide, FeZ wt% within the composite, and photocatalyst
dosage on DCF removal and conversion efficiency by solar/
TiO2-FeZ/H2O2 process was investigated. TiO2-FeZ demonstrated
higher photocatalytic activity than pure TiO2 under
solar irradiation in acidic conditions and presence of H2O2.
Found in: ključnih besedah
Keywords: Photocatalysis, Thin films, TiO2-FeZ, Solar irradiation, Diclofenac, Water Treatment
Published: 22.07.2016; Views: 5306; Downloads: 0
Fulltext (2,88 MB) |
