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3912. Effects of Different Copper Loadings on the Photocatalytic Activity of TiO2-SiO2 Prepared at a Low Temperature for the Oxidation of Organic Pollutants in WaterT. Čižmar, Iztok Arčon, Mattia Fanetti, Urška Lavrenčič Štangar, 2018, original scientific article Abstract: The objective of this research is to examine how Cu modification can improve the photocatalytic activity of TiO2-SiO2, to explainthe correlation between the Cu concentration and the chemical state of Cu cations in the TiO2-SiO2 matrix, and the photocatalytic activity under UV/solar irradiation. The Cu-modified TiO2-SiO2 photocatalysts were prepared by a low-temperature sol–gel method from organic Cu, Si and Ti precursors with various Cu concentrations (0.05–3 mol %). The sol–gels were dried at 150 8C to obtain the photocatalysts in a powder form. The photocatalytic activity was determined by using a fluorescence- based method of terephthalic acid decomposition. An up to three times increase in photocatalytic activity is obtained if the 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 the Cu-modified photocatalysts is lower than that of the un-modified reference TiO2-SiO2 photocatalyst. XRD was used to show that all Cu-modified TiO2-SiO2 composites with different Cu concentrations have the same crystalline structure as un-modified TiO2-SiO2 composites. The addition of Cu does not change the relative ratio between the anatase and brookite phases or unit cell parameters of the two TiO2 crystalline structures. We used Cu K-edge X-ray absorption near edge structure and extended X-ray absorption fine structure analyses to determine the valence state and local structure of Cu cations in the Cu-modified TiO2-SiO2 photocatalysts. The results elucidate the mechanism responsible for the improved photocatalytic activity. In samples with a low Cu content,
which exhibit the highest activity, Cu@O@Ti connections
are formed, which suggests that the activity enhancement is
caused by the attachment of CuII cations on the surface of the photocatalytically active TiO2 nanoparticles, so CuII cations may act as free-electron traps, which reduce the intensity of recombination between electrons and holes at the TiO2 photocatalyst surface. At higher Cu loadings no additional Cu@O@Ti connections are formed, instead only Cu@O@Cu connections are established. This indicates the formation of amorphous or nanocrystalline
copper oxide, which hinders the photocatalytic activity
of TiO2.
Keywords: Cu modified TiO2-SiO2 photocatalyst
Cu EXAFS, XANES, Organic pollutants
Published in RUNG: 30.08.2018; Views: 3593; Downloads: 0
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3913. The Topic of Mining in Secondary School Literature Textbooks from 1850 to 1950Zoran Božič, 2018, original scientific article Abstract: During the first century of secondary school literature textbook publishing (from the introduction of Slovenian language as a school subject after the March Revolution in the Austrian Empire to the first Five-Year Plan after World War II) over a hundred texts featuring the topic of mining and related activities were included. The first writings have a clearly affirmative attitude towards mining, perceived and presented as a way of promoting general prosperity. The first mentions of the negative aspects of mining and the deceptive folly of coveting precious mineral resources appear towards the end of the 19th century. Only during the interwar period, however, were there various texts which presented mining as an inhumane and dangerous activity. After World War II the approach was again optimistic: in central literature textbooks mining was depicted as the glorification of socialist progress. Relevant texts were published in eight series of textbooks, the first as early as in the Bleiweis series for lower secondary schools in 1850 and the last in the ethnic Slovenian Beličič series of textbooks in 1947. The discovery of mercury in the Idrija mine was described by Valvazor, Kastelic, Hrovat and Oblak.
Keywords: natural science, didactics, mineral resources, Idrija mine, mercury
Published in RUNG: 30.08.2018; Views: 3942; Downloads: 162
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