Browsing by Author "Avansi Junior, Waldir"

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    Evidence of defect-mediated magnetic coupling on hydrogenated Co-doped ZnO.
    (2013) Godoy, Marcio Peron Franco de; Mesquita, Alexandre; Avansi Junior, Waldir; Neves, P. P.; Chitta, Valmir Antônio; Ferraz, Wilmar Barbosa; Boselli, Marco Aurélio; Sabioni, Antônio Claret Soares; Carvalho, Hugo Bonette de
    Hydrogenated bulk Zn1_xCoxO samples were synthesized via standard solid-state reaction route with Co molar concentrations up to 15 at.%. Magnetic characterization demonstrates a room temperature ferromagnetic behavior associated to a paramagnetic Curie–Weiss component. Detailed microstructural analysis was carried out to exclude the presence of extrinsic sources of ferromagnetism. The magnetization increases linearly as a function of Co concentration. Hall measurements reveal an insulating character for the whole set of samples. In this context, the defect mediated magnetic coupling between the Co atoms under the scope of the bound magnetic polarons model is used to interpret the observed room temperature ferromagnetism.
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    Microwave hydrothermal synthesis, characterisation, and catalytic performance of Zn1−xMnxO in cellulose conversion.
    (2014) Bernardi, Maria Inês Basso; Araújo, Vinicius D.; Ribeiro, Caue; Avansi Junior, Waldir; Longo, Elson; Albuquerque, Nilson J. A. de; Meneghetti, Simoni Margareti Plentz; Almeida, Rusiene Monteiro de; Fajardo, Humberto Vieira
    Wurtzite-type Zn1−xMnxO (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn0.97Mn0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn0.95Mn0.05O and Zn0.93Mn0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reaction