1. Bi2O3-BASED PYROCHLORE NANOSTRUCTURES AND THEIR CRYSTALLOGRAPHIC, OPTOELECTRONIC AND PHOTOCATALYTIC PROPERTIESMetka Benčina, 2015, doctoral dissertation Abstract: Bi2O3-based pyrochlore nanomaterials and their photocatalytic, optoelectronic and crystallographic properties are the research topics of this doctoral dissertation. We synthesized these materials at nanoscale, since they are expected to possess photoactivity in the visible-light spectrum, which is an important target for the high-performance photocatalysts. To prepare nanoparticles that are not agglomerated, different synthesis methods (coprecipitation, coprecipitation followed by the digestion, reverse micelle) and post-treatments (furnace or hydrothermal reactor) were examined. Micrometer size materials were prepared with the solid-state reaction and annealing at high temperature.
Bi2Ti2O7 nanoparticles were synthesized with the coprecipitation reaction, followed by annealing at 570 °C in the furnace or in the hydrothermal reactor at 230 °C for 18h in NH4OH medium. UV-Vis diffuse reflectance spectra of the Bi2Ti2O7 samples showed that they exhibit the maximum absorption edge at ~420-440 nm. The UV-Vis diffuse reflectance measurements of Bi2Ti2O7 loaded with 10 wt. % of Ag as a co-catalyst showed an enhanced absorbance in the visible region, presumably due to a contribution of Local Surface Plasmon Resonance. The Bi2Ti2O7 nanoparticles are not photocatalytically active under the visible light irradiation without assistance of a sacrificial reagent. The photocatalytic activity does not increase even with Ag as a co-catalyst under visible light irradiation. All samples are active under UV light irradiation, especially the sample with Ag that is able to decolourize 7 mg/L of metyl orange in just 3 min of exposure to UV light. However, H2O2 as a sacrificial reagent increases the photocatalytic activity of Bi2Ti2O7 under visible light irradiation.
Phase pure pyrochlore Bi1.647Nb1.118Fe1.157O7 (BNF) nanoparticles were synthesized with coprecipitation reaction and further annealing in the furnace at 570 °C for 7h or 15h and in the hydrothermal reactor at 160 °C for 18h in 3 M or 6 M NaOH medium. The BNF materials exhibit shift toward longer wavelengths in absorbance of visible light (up to ~550-650 nm). This result confirmed that incorporation of Fe in the pyrochlore structure decreases the band gap. The BNF nanoparticles annealed for 7h showed intense photoactivity under visible light irradiation in the presence of a sacrificial reagent. The improved photoactivity, much better than with BNF, was shown for the composite nanoparticles BiOCl/BNF. They decolourize 100 % of the 7 mg/L methyl orange within only 2h of the visible light irradiation in the presence of H2O2.
Phase pure pyrochlore Bi1.9Te0.58Fe1.52O6.87 (BTF) nanoparticles were synthesised by coprecipitation reaction and further annealing in the furnace at 570 °C for 7h. Although the BTF nanoparticles include higher amount of Fe than BNF nanoparticles and exhibit narrower band gap, the photoactivity of these nanoparticles is a bit lower than that of BNF nanoparticles. We assume that Fe at some critical concentration causes formation of mid-band states, which act as recombination centers. The same as BiOCl/BNF, the BiOCl/BTF composite is able to decolourize 100 % of the 7 mg/L MO within 2h of the visible light irradiation in the presence of H2O2.
Based on the band gap determination and estimation of valence and conduction band levels, the proposed photodecolourization mechanisms are discussed. The conduction band levels of all synthesized materials lie more positively than O2/O2● redox potential (vs. negative hydrogen electrode potential), but are more close to H2O2/●OH redox potential. Thus, we assume that the photogenerated electrons form ●OH radicals, the species that induce dye decolourization under visible light irradiation. We believe that better performance of composite materials (BiOCl/BNF, BiOCl/BTF) is due to the formation of heterojunction, which facilitates the electron transfer between semiconductors, and O2 vacancy states formation in the BiOCl material.
Found in: ključnih besedah
Summary of found: ...nanoparticles, pyrochlore structure, photocatalysis, visible light...
Keywords: nanoparticles, pyrochlore structure, photocatalysis, visible light
Published: 26.06.2015; Views: 7089; Downloads: 200
 Fulltext (7,29 MB) |
2. 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
Summary of found: ...Air remediation, TiO2 photocatalysis, Immobilization, Thin layers, TiO2/SiO2 composites...
Keywords: Air remediation, TiO2 photocatalysis, Immobilization, Thin layers, TiO2/SiO2 composites
Published: 31.08.2015; Views: 7487; Downloads: 179
Fulltext (33,47 MB) |
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4. Hydroxyl radical scavenging-based method for evaluation of TiO[sub]2 photocatalytic activityUrška Lavrenčič Štangar, Matija Strlič, Romana Cerc Korošec, Danijela Pucko, 2013, original scientific article Abstract: Hydroxyl radical scavenging-based method for evaluation of TiO[sub]2 photocatalytic activity
Found in: ključnih besedah
Summary of found: ...titanium dioxide, photocatalysis, N,N-(5-nitro-1,3-phenylene)bisglutaramide, radical scavenger, HPLC, ...
Keywords: titanium dioxide, photocatalysis, N, N-(5-nitro-1, 3-phenylene)bisglutaramide, radical scavenger, HPLC
Published: 05.01.2016; Views: 4305; Downloads: 27
 Fulltext (0,00 KB) |
5. Low‐temperature TiO2/ZrO2/SiO2 photoactive thin films on glassUrška Lavrenčič Štangar, Nives Vodišek, 2015, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ... photocatalysis, self-cleaning, methyl stearate, terephthalic acid...
Keywords: photocatalysis, self-cleaning, methyl stearate, terephthalic acid
Published: 01.02.2016; Views: 4522; Downloads: 2
Fulltext (6,39 MB) |
6. Development and characterization of improved materials for antifouling applicationsUrška Lavrenčič Štangar, Iztok Arčon, Tihana Čižmar, 2015, published scientific conference contribution abstract Found in: ključnih besedah
Summary of found: ...sol-gel method, photocatalysis, hybrid materials, Cu K-edge XANES, photocatalytic activity...
Keywords: sol-gel method, photocatalysis, hybrid materials, Cu K-edge XANES, photocatalytic activity
Published: 15.02.2016; Views: 4220; Downloads: 0
Fulltext (131,22 KB) |
7. 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: 4560; Downloads: 0
Fulltext (2,10 MB) |
8. Comparative analysis of UV-C/H2O2 and UV-A/TiO2 processes for the degradation of diclofenac in waterUrška Lavrenčič Štangar, Hrvoje Kušić, Marin Kovacic, Daria Juretic Perisic, Vedrana Marin, Ana Lončarić Božić, 2016, original scientific article Abstract: The study investigates the treatment of diclofenac (DCF), a pharmaceutical
included in the first watch list of the European Water Framework Directive
as a new potential priority substance in water. Since the conventional wastewater
treatment technologies do not efficiently remove DCF, advanced treatment technologies
capable of its complete removal or destruction of its biological activity,
need to be evaluated and eventually employed. For that purpose, typical representatives
of photooxidative and photocatalytic advanced oxidation processes were
applied. The effectiveness of UV-C/H2O2 and UV-A/TiO2 were compared regarding
DCF conversion and mineralization kinetics, water quality parameters for
assessing biodegradability and toxicity. In spite of similar biodegradability profiles,
the obtained results indicate different DCF degradation pathways, which are
reflected in different profiles of toxicity towards Vibrio fischeri. The observed DCF
conversion and mineralization kinetics revealed the benefits of UV-C/H2O2 process.
However, lower toxicity favored the application of photocatalytic over photooxidative
treatment for DCF removal.
Found in: ključnih besedah
Summary of found: ...Diclofenac, Photooxidation, Photocatalysis, Biodegradability, Toxicity...
Keywords: Diclofenac, Photooxidation, Photocatalysis, Biodegradability, Toxicity
Published: 21.07.2016; Views: 4104; Downloads: 0
Fulltext (496,03 KB) |
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
Summary of found: ...contaminants in water from household appliances by TiO2- photocatalysis: design, optimization and performance studies of the...
Keywords: photocatalysis, ozonation, TiO2, dichloroacetic acid, thiacloprid, mechanisms, LAS+PBIS, Reactive blue 19, phenol
Published: 21.07.2016; Views: 5901; 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
Summary of found: ... Photocatalysis, Thin films, TiO2-FeZ, Solar irradiation, Diclofenac, Water...
Keywords: Photocatalysis, Thin films, TiO2-FeZ, Solar irradiation, Diclofenac, Water Treatment
Published: 22.07.2016; Views: 5173; Downloads: 0
Fulltext (2,88 MB) |
