1. Tailoring the crystalline and amorphous phase ratios of TiO2 through the use of organic additives during hydrothermal synthesisNejc Rozman, Andrijana Sever Škapin, David Maria Tobaldi, Goran Dražić, Peter Nadrah, 2024, original scientific article Abstract: The photocatalytic properties of TiO2 are primarily determined by its crystallinity and crystalline phase ratios. To improve the photocatalytic properties of TiO2, greater control over the formation of crystalline and amorphous phases during synthesis is therefore required. In this study, we demonstrate how the addition of minute amounts of three organic compounds (isopropanol, acetone and acetic acid) during hydrothermal treatment affects the amorphous and crystalline phase ratios: the addition of isopropanol or acetone accelerates the phase transition from anatase and brookite to rutile, whereas the addition of acetic acid inhibits the transformation of anatase to rutile, increasing the content of amorphous phase compared to samples where no organic compound was added. We show that the combination of the organic compound added, along with the duration of the hydrothermal treatment, can be used to tailor the phase composition of TiO2, so as to obtain either: i) TiO2 with a high content of both rutile and amorphous phase, ii) TiO2 with a high rutile content and iii) TiO2 with different ratios of all four phases, when the duration of synthesis is short (2–4 h). The materials synthesized exhibited high photocatalytic activity (in most cases higher than P25), which is attributed to the beneficial phase composition and high specific surface area.
Keywords: sol-gel processes, X-ray methods, chemical properties, TiO2, photocatalysis
Published in DiRROS: 14.08.2024; Views: 43; Downloads: 87
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2. Photocatalytic CO2 reduction over mesoporous TiO2 photocatalystsMartin Reli, Peter Nadrah, Miroslava Filip Edelmannová, Rudolf Ricka, Andrijana Sever Škapin, Urška Lavrenčič Štangar, Kamila Kočí, 2024, original scientific article Abstract: In this study, we investigated different synthesis methods (template-free and template-based) using copolymers of poly(ethylene oxide) and poly(propylene oxide) to enhance the CO2 reduction activity of mesoporous TiO2. Our main goal was to identify key factors affecting photocatalyst efficiency and selectivity. We compared the newly synthesized TiO2 photocatalysts with the commercial photocatalyst P25. Among the materials studied, TiO2-P123 in its pure anatase form demonstrated the highest photoreduction efficiency and CO2 selectivity. In contrast, TiO2-EG, TiO2-F127, and P25, which contained both rutile and anatase phases, exhibited decreased photoactivity due to the formation of a type II heterojunction between the phases and higher oxygen adsorption on rutile's surface. Additionally, we observed that the choice of chemicals for photocatalyst preparation significantly influenced the specific surface area. TiO2-P123, the most active photocatalyst, had the highest specific surface area, providing more reactive sites for improved light absorption efficiency and prolonged electron-hole pair lifetimes, resulting in enhanced photocatalytic activity. We also calculated apparent quantum yields to support our findings.
Keywords: CO2 reduction, TiO2, photocatalysis, mesoporous material, Sol-gel method
Published in DiRROS: 14.11.2023; Views: 578; Downloads: 77
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3. Colorimetric cutoff indication of relative humidity based on selectively functionalized mesoporous silicaErika Švara Fabjan, Peter Nadrah, Anja Ajdovec, Matija Tomšič, Goran Dražić, Matjaž Mazaj, Nataša Zabukovec Logar, Andrijana Sever Škapin, 2020, original scientific article Abstract: We present a novel % cutoff concept of colorimetric indication of relative humidity based on dye dissolution in condensed water in capillaries of selectively functionalized mesoporours host SiO2 material. Consistently high levels of indoor air humidity induces mold and algae growth which represent a potential risks for human health and have deteriorating effect on walls as well. Simple localized humidity detection of high humidity with naked eye especially at places with low air circulation, where growth of mold usually starts first, is therefore highly desirable. The reporting dye was integrated in the non-functionalized mesoporous silica matrix with different pore diameters and selective-functionalized mesoporous silica material. After exposure to the environment of different air humidities the dye dissolved in water causing color change of adsorbent. With the use of adsorbents with different mesopore diameters high ability to tune the value of relative humidity when complete capillary condensation occurred was achieved. Materials with pore diameters of 3.0%nm, 3.5%nm and 7.0%nm exhibit gradual color change when reaching relative humidity up to 55, 79 and 88 RH% respectively. After selective methylation of the material with 7.0%nm pore diameter, non-gradual cutoff color change was achieved. Sample exhibited color change at narrow range of relative humidity (cutoff color change). Due to selective functionalized outer surface the dye dissolution occur only in condensed water in pores and therefore provide colorimetric indication only in this range. Selectively modified silica material has a great potential for a straightforward detection of high humid environment.
Keywords: turn-on colorimetric probe, selective functionalization, mesoporous silica, relative humidity, capillary condensation
Published in DiRROS: 05.09.2023; Views: 502; Downloads: 374
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