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11.
Correlations between photocatalytic activity and chemical structure of Cu-modified TiO2-SiO2 nanoparticle composites
T. Čižmar, doctoral dissertation

Abstract: The objective of this dissertation was to examine how copper modification can improve the photocatalytic activity of TiO2-SiO2 and to explain the correlation between Cu concentration and chemical state of Cu cations in the TiO2-SiO2 matrix, as well as the photocatalytic activity under the UV/solar irradiation. The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low temperature sol-gel method based on organic copper, silicon and titanium precursors with varied Cu concentrations (from 0.05 to 3 mol%). The sol-gels were dried at 150 °C to obtain the photocatalysts in the powder form. To test thermal stability, additional set of photocatalysts was obtained by calcinating dried samples in air at 500 °C for 1 h. The photocatalytic activity was determined by a fluorescence-based method of terephthalic acid decomposition. Up to three times increase in photocatalytic activity of air-dried samples is obtained when 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 Cu-modified photocatalyst is smaller than in the unmodified reference TiO2-SiO2 photocatalyst. Calcined samples showed significantly reduced photocatalytic activity compared to air-dried samples. XRD analysis showed that all Cu-modified TiO2-SiO2 nanocomposites with different Cu concentrations have the same crystalline structure as unmodified TiO2-SiO2 nanocomposites (air-dried or calcined). The addition of Cu does not change the relative ratio between the anatase and brookite phase or unit cell parameters of the two TiO2 crystalline structures. TEM analysis showed that the addition of Cu does not change the morphology of TiO2-SiO2 catalyst dried at 150 °C. The Cu K-edge XANES and EXAFS analysis were used to determine valence state and local structure of Cu cations in Cu-modified TiO2-SiO2 photocatalyst. The results elucidate the mechanism responsible for the improved or hindered photocatalytic activity. In the air-dried samples with low Cu content, which exhibit largest activity, Cu-O-Ti connections are formed, suggesting that the activity enhancement is due to Cu(II) cations attachment on the surface of the photocatalytically active TiO2 nanoparticles, so Cu(II) cations may act as free electron traps, reducing the intensity of recombination between electrons and holes at the TiO2 photocatalyst’s surface. At higher Cu loadings no additional Cu-O-Ti connections are formed, instead only Cu-O-Cu connections are established, indicating the formation of amorphous or nanocrystalline Cu(II) oxide, which hinders the photocatalytic activity of TiO2. Calcination of Cu-modified TiO2-SiO2 photocatalysts at 500 °C induces significant structural changes: Cu-O-Ti connections are lost, Cu partially incorporates into the SiO2 matrix and amorphous copper oxides, which again reduce the photocatalytic activity of the material, are formed.
Found in: ključnih besedah
Summary of found: ...method based on organic copper, silicon and titanium precursors with varied Cu concentrations (from 0.05... ...titanium dioxide, Cu-modified TiO2-SiO2 photocatalyst, photocatalytic activity, Cu K-edge...
Keywords: titanium dioxide, Cu-modified TiO2-SiO2 photocatalyst, photocatalytic activity, Cu K-edge XANES, EXAFS.
Published: 17.12.2018; Views: 704; Downloads: 38
.pdf Fulltext (3,05 MB)

12.
Cu and Zr surface sites in photocatalytic activity of TiO [sub] 2 nanoparticles
Olena Pliekhova, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2019, original scientific article

Abstract: The present work is focused on the role of ZrO2 modification in the performance of CuO modified TiO2. Zirconia loading leads to formation of more resistant photocatalytic layers compared to samples modified with only copper containing species. Surface modification of mixed phase TiO2 with CuO/ZrO2 improves the degradation of Reactive blue 19 dye under simulated solar irradiation. An in-depth investigation of the catalysts showed that in case of CuO/ZrO2 modification, the covering of the TiO2 surface with zirconium containing species prevents morphological and harmful energetic changes induced by copper species formed on the rutile TiO2 phase at a higher copper loading.
Found in: ključnih besedah
Summary of found: ... titanium dioxide, surface modification, XAS analysis, surface acidity,...
Keywords: titanium dioxide, surface modification, XAS analysis, surface acidity, Hammett indicators
Published: 26.03.2019; Views: 405; Downloads: 0
.pdf Fulltext (996,21 KB)

13.
Zr/Cu-TiO2 CATALYSTS FOR PHOTOCATALYTIC WATER TREATMENT
Olena Pliekhova, doctoral dissertation

Abstract: This work entitled «Zr/Cu-TiO2 catalysts for photocatalytic water treatment» tackles a problem of tons of dyes discharged everyday mainly from textile industries. This is a huge concern because of dyes persistence, toxicity and potential to the bioaccumulation in living organisms. Here, a small contribution to overall problem is presented. The research work consists of three main parts: Theoretical background, Experimental and Results and discussion. In the Theoretical background chapter the overall problem is identified and discussed. The main water treatment techniques are presented briefly with their advantages and drawbacks. Photocatalysis assisted with TiO2 is shown as an alternative additional technique with its own pros and cons. Further, a cursory overview of TiO2 modification techniques is made and advantages in using copper and zirconium oxides for TiO2 modification are presented. The reason and possible positive effect of using of two oxides simultaneously for TiO2 modification is indicated. Additionally, a positive impact of solar light for overall rate of dyes degradation assisted with TiO2 is discussed. Within the framework of photosensitization effect, the problem of using dyes for assessment of photocatalytic properties of materials under the visible light is touched on. Photothermal methods as possible beneficial techniques for this purpose are proposed. In the Experimental chapter, all experimental techniques used in current research work with the technical details specific for the research work are presented. There are methods of materials preparation, photocatalytic tests under different conditions and varying model pollutants, and physico-chemical characterization techniques. The Results and discussion chapter is divided by three subchapters. Each chapter is dedicated to one hypothesis, which was checked and confirmed or disproved. The first hypothesis is about beneficial loading of copper and zirconium oxides to TiO2. After numerous experiments held, it was concluded that the pair of copper and zirconium oxides is beneficial for simultaneous application on TiO2 surface to promote its performance. The second subchapter is about zirconium distribution and its impact on the activity of studied materials towards the antraquinone dye Reactive Blue 19. Different techniques such as XRD, TEM, EXAFS and many others were used in order to characterize the materials and to understand the details of the processes taking place. The existence of upper limit of copper oxide loading for its beneficial effect on TiO2 performance was demonstrated. It was observed that zirconium species loading leads to improvement in performance of materials with higher copper loading, which otherwise lowers activity of TiO2 – this is in case when copper only above its optimal level is present. It was concluded that zirconium oxide containing species occupy rutile surface sites in mixed phase TiO2 and this way beneficially influence the material performance towards the dye removal. The third subchapter is about the visible light TiO2 assisted dye degradation. It is well known that photosensitization mechanism of dye degradation appears under the visible and as a consequence under the solar light irradiation. This leads to the overall enhancement of dyes degradation, which is positive and may be used as a benefit for faster pollutant destruction. However, this fact leads to mishmash in the determination of real photocatalytic activity of materials towards the dye. It was hypothesized that the impact of photosensitization mechanism on the overall material performance against Reactive blue 19 dye (RB19) descends with the dye concentration lowering. Thermal lens spectrometry (TLS) which is sensitive to chemicals at low concentrations was used for hypothesis evaluation. To summarize the research work achievements, the conclusions of the thesis are given at the end.
Found in: ključnih besedah
Summary of found: ... titanium dioxide, photocatalysis, zirconium/copper, surface modification, water treatmen...
Keywords: titanium dioxide, photocatalysis, zirconium/copper, surface modification, water treatment, dyes
Published: 03.12.2019; Views: 170; Downloads: 5
.pdf Fulltext (3,18 MB)

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