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Fotochemie v klastrech a nanočásticích: systémy relevantní v atmosférické chemii a v biologii
Fárník, Michal
Influence of solvation on photodissociation of molecules is investigated in clusters produced in a molecular beam experiment. Photochemistry in three different systems is compared: (i) HBrArn and (HBr)n clusters, where the fragment does not react with the solvent and an effect of the fragment caging is observed, (ii) HBr(H2O)n system where chemical reaction occurs and a reaction channel is closed by the electronic interaction with the solvent. The practical relevance of the studied processes ranges from atmospheric chemistry to biology.
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Strukturní vlastnosti nanometrických železných částic
David, Bohumil ; Schneeweiss, Oldřich ; Pizúrová, Naděžda ; Klementová, Mariana ; Morjan, I.
Fe-based nanoparticles were prepared by the laser pyrolysis method using a cross-flow reactor in which the laser orthogonally irradiates the gas mixture of Fe(CO)5, C2H2, and C2H4. Ethylene serves as the CO2 laser radiation absorber. The as-synthesized powder was characterised by HRTEM, XRD, Raman spectroscopy, Mössbauer spectroscopy, and magnetic measurements. As observed under TEM, the as-synthesized powder consisted of nanoparticles smaller then 10 nm embedded in a pyrolytic carbon matrix. The XRD pattern exhibited three broad peaks: the first peak is assigned to pyrolytic carbon, the second peak is assigned to maghemite/magnetite, and the third peak belongs to α-Fe particles. The particle size d 2 nm was obtained for α-Fe from the Scherrer formula. The presence of α-Fe and maghemite/magnetite phases was also observed in the Mössbauer spectrum measured at 4 K.
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α-Fe nanočástice připravené rozkladem pentakarbonylu železa v mikrovlnném výboji
David, Bohumil ; Pizúrová, Naděžda ; Schneeweiss, Oldřich ; Hoder, T. ; Kudrle, V. ; Janča, J.
The nanocrystalline iron powder has been prepared by the introducing of Fe(CO)5 vapor into the microwave induced argon discharge. A microwave 2.45 GHz source was operated at 430 W. The reaction was performed in a quartz tube passing through the microwave waveguide. The in-situ passivation using air was applied after synthesis. The powder was characterised by TEM, XRD, and Mössbauer spectroscopy. According to our TEM investigation, the produced passivated powder included aggregated core-shell nanoparticles. The cores consist of α-Fe and the shell is supposed to be iron oxide (indicated by TEM). The presence of α-Fe and iron oxides was confirmed by XRD and Mössbauer spectroscopy. The mean coherence domain size of α-Fe cores was estimated to be 30 nm. The synthesized nanopowder exhibits ferromagnetic behaviour.
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Použití mikrovlnného plazmatu pro syntézu alfa-Fe nanočástic
Hoder, T. ; Kudrle, V. ; Frgala, Z. ; Janča, J. ; David, Bohumil
Microwave induced plasma decomposition of iron pentacarbonyl has been used to prepare iron nanosized particles. Vapours of iron pantacarbonyl have been introduced into argon surfaguide discharge, optical mission spectra have been taken and rotational and vibrational temperatures obtained. The temperatures were plotted as a functions of axial and radial distance and of iron pentacarbonyl concentration. Iron nanoparticles have been produced, XRD results and TEM images were obtained. The core-shell nanoparticles were observed, with alpha phase iron as a core and Fe(x)O(y)/C shell.
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