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Proč a čím se namazat?
Kociánová, R. ; Šimková, Ludmila ; Boháčová, J.
Školní projekt Proč a čím se namazat?, seznamuje žáky aktivní formou s problematikou ubývání ozónové vrstvy, příčinami a důsledky této skuteč nosti. Projekt vede žáky k uvědomění si negativního vlivu činnosti lidí na životní prostředí a zodpovědnosti každého jedince za životní prostředí a své vlastní zdraví.
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DYE SENSITISED SOLAR CELLS: NEW CHALLENGES FROM GRAPHENE CATHODE AND IODINE-FREE ELECTROLYTE
Kavan, Ladislav
Graphene nanoplatelets (GNP) in the form of thin semitransparent film on F-doped SnO2 (FTO) exhibit high electrocatalytic activity for Co(L)2; where L is 6-(lH-pyrazol-l-yl)- 2,2‘-bipyridine. GNP films with optical transmission below 88% are outperforming the activity of platinized FTO for the Co2+/3+(L)2 redox reaction. Dye-sensitized solar cells with Y123 dye adsorbed on TiO2 photoanode achieved energy conversion efficiencies between 8 to 10 % for both GNP and Pt-based cathodes. However, the cell with GNP cathode is superior to that with Pt-FTO cathode in fill factors and in the efficiency at higher illumination intensities.
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Electrochemical and spectroelectrochemical study of nanocrystalline TiO2 anatase with exposed (001) faces
Lásková, Barbora ; Zukalová, Markéta ; Bouša, Milan ; Kavan, Ladislav ; Liska, P. ; Grätzel, M.
The electrochemical and spectroelectrochemical behavior ot TiO2 anatase with a predominant (001) face was studied and compared to a reference anatase material with dominating (101) face. The electrochemical measurements indicate that Li-ion insertion/extraction is facilitated for TiO2 anatase with (001) faces as compared to (101) one. The performance of both different crystal morphologies as a photoanode material in DSC (dye sensitized solar cell) was tested too. The (001) face adsorbed smaller amount of the used dye sensitizer (C101) but provides larger open circuit voltage (Uoc) of the solar cell. The different band energetics of both particular morphologies was suggested to be the reason for the voltage enhancement of the device employing (001) anatase. To prove our hypothesis and determine their flatband potential, a spectroelectrochemical study of transparent films of nanocrystalline (001) and (101) anatase on coaducting glass was carried out. UV/Vis spectra were measured at potentials between 0 and -1.4V vs SCE and confirmed the negative shift of flatband potential for (001) anatase as compared to (101) one.
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Modification of TiO2 electronic properties by means of chemical treatment (doping)
Zukalová, Markéta ; Lásková, Barbora ; Procházka, Jan ; Bastl, Zdeněk ; Havlíček, D. ; Kavan, Ladislav
The product of the reaction of nanofibrous anatase with ammonia in gas phase is nanofibrous cubic titanium oxynitride, c-TiO2N3. In contrary to the preparation of cubic titaniurn oxynitride from microcrystalline TiO2, requiring temperatures above 800°C, the conversion of nanofibrous TiO2 to TiO2N3 is completed at about 500°C due to its enhanced chemical reactivity. This conversion is fully reversible; the product of the back reaction is again nanofibrous Ti02. By the thermal treatment of nanofibrous anatase in H2 flow at 800°C for 2 hours the mixture of black disordered anatase, rutile and titanium suboxides was prepared. Evidently, particular phases can be synthesized simply by tuning the temperature of the treatment, which is a subject of the further research.
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GRAPHENE UNDER UNIAXIAL DEFORMATION: A RAMAN STUDY
Frank, Otakar ; Tsoukleri, G. ; Parthenios, J. ; Papagelis, K. ; Riaz, I. ; Jalil, R. ; Novoselov, K. S. ; Kalbáč, Martin ; Kavan, Ladislav ; Galiotis, C.
The presented work summarizes various aspects of uniaxial deformation in monolayer graphene studied by means of Raman spectroscopy. Graphene flakes were subjected to tension - compression uniaxial loading using the cantilever beam technique. The evolution of the Raman single-resonance (G) and double-resonance (2D) bands was monitored at strain levels < 1%. The position of all peaks redshifts under tension and blueshifts under compression. The G peak splitting into two sub-bands (G(-) and G(+)) which is caused by symmetry lowering, is observed in both strain directions. The sub-bands' intensities are used to calculate the crystal lattice orientation of the measured graphene flakes with respect to the strain axis. The nature and splitting of the 2D band even in the unstrained flakes, when excited by the 785 nm (1.58 eV) laser line, is interpreted as the interplay between two distinct double resonance scattering processes.
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Does oxidation make the organic aerosol coatings more hydrophilic? Insight from molecular dynamics study of oxidized surfactant monolayers
Roeselová, Martina ; Khabiri, Morteza ; Cwiklik, Lukasz
Organic compounds are ubiquitous in atmospheric aerosols. The morphology and structure of the organic phase affect the optical properties of the aerosols, their heterogeneous reactivity as well as their ability to nucleate cloud droplets and ice particles. It is commonly assumed that atmospheric oxidative ageing of the organic material, leading to the formation of polar groups such as carbonyl (=O), hydroxyl (-OH) and carboxylic acid (-COOH), will render the aerosol particle surfaces increasingly more hydrophilic, hence, able to take up more water. Field measurements have shown that a large fraction of the organic material found in aerosols are surface active compounds, such as fatty acids and lipids(Tervahattu, 2002 and 2005). An inverted micelle structure, with an aqueous core surrounded by an organic surfactant layer, has thus been proposed for aqueous aerosols, both marine and continental (Donaldson, 2006). While recent experiments suggest the existence of more complex structures, such as organic inclusions and surfactant lenses (Dennis-Smither, 2012), a monolayer (ML) of surface active organics on an aqueous subphase (the so called Langmuir monolayers) represents the basic model system used in laboratory studies aimed at elucidating the effect of oxidative processes on structural properties of organic coatings on aerosol particles. In our previous work, we used molecular dynamics computer simulations to study the structure and stability of oxidized phospholipid MLs (Khabiri, 2012). In this contribution, we employed the molecular dynamics simulation technique to investigate – with atomistic resolution – structural changes occuring in a fatty acid ML upon moderate degree of oxidation.
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16th International Symposium on Intercalation Compound - ISIC16. Abstracts Book
Zima, Vítězslav ; Kavan, Ladislav ; Čejka, Jiří ; Lang, Kamil ; Vlček, Milan ; Beneš, L. ; Svoboda, Jan ; Melánová, Klára ; Frumarová, Božena ; Knotek, P. ; Jůza, Josef ; Látalová, Petra
The topic of the papers published in this proceedings is chemistry, properties and applications of intercalation compounds and related materials.
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LC-NMR Analysis of Phenylsilane Polymers
Pinkas, Jiří ; Merna, J. ; Sýkora, Jan
We report the analysis of dehydrocoupling polymerization reactions of phenylsilane via on-flow LC-NMR experiment. The successful separation was achieved by isocratic elution of acetonitrile and aceton (80:20). The separation was solely monitored by 1H NMR detection. The properties of the polymeric product depend on the catalytical system. The products can differ in the molar weight distribution, degree of branching and amount of cyclic and rearranged products. In our particular cases, the weight average molar mass (Mw) varies from several silane units up to 4100 g.mol-1. The branching of polysilanes is monitored by 29Si{1H} INEPT experiment with the polarization transfer from the ortho hydrogen (J~7 Hz). The connectivity within branched unit was established via 1H à 29Si-29Si INEPT-INADEQUATE experiment.
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Catalytic and photocatalytic processes on 18O-labeled TiO2
Kavan, Ladislav ; Zukalová, Markéta ; Ferus, Martin ; Kürti, J. ; Koltai, J. ; Civiš, Svatopluk
18O-isotope labelled titania (anatase, rutile) was synthesized. The products were characterized by Raman spectra together with their quantum chemical modelling. The interaction with carbon dioxide was investigated using high-resolution FTIR spectroscopy, in dark and upon UV-excitation. The oxygen isotope exchange at the Ti18O2/C16O2 interface was elucidated. The C18O2 was formed as the dominating final product with a minor content of C16O18O. The rate of oxygen-isotope exchange is highly sensitive to the conditions of the titania pretreatment. The vacuum-annealed Ti18O2 at 450 C exhibited a very high spontaneous oxygen exchange activity with gaseous C16O2. A mechanism for the 18O/16O exchange process is discussed at the molecular level. The photocatalytic formation of methane, acetylene and C16O released from the Ti18O2 surface was triggered by an XeCl excimer laser irradiation.
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