Desenvolvimento de sistemas adsortivos de nanofibras de Sílica/Carbono-N pela técnica de Solution Blow Spinning.

Abstract

Nanofibers have specific characteristics for use as adsorbents of various dyes, for example the high specific surface area. Among the techniques of nanofiber production, solution blow spinning (SBS) has shown promising results in the synthesis of nanofibers of various materials. In this thesis, it was proposed to synthesize silica nanofibers and silica/carbon-N hybrid nanofibers via SBS based on polyvinylpyrrolidone (PVP), which was used as the auxiliary spinning polymer of silica nanofibers precursor as well as source of carbon (C) and nitrogen (N) for hybrid nanofibers. The precursor nanofibers constituted of PVP and tetraethylorthosilicate were submitted to calcination with high oxygen concentration at 550 °C for conversion to pure silica and submitted to calcination with low oxygen concentration for the carbonization of the polymer and the production of hybrid nanofibers. The effect of the PVP molar weight and the effect of the addition of Kolliphor 188 surfactant and sunflower oil emulsion on the morphology and surface area of the nanofibers after the heat treatment were evaluated. The samples were characterized in terms of their morphology, surface area, surface charge, chemical composition, thermal behavior and adsorptive capacity of methylene blue (AM) and rhodamine R (RB). The weight mass of PVP did not influence the morphology of nanofibers and the formation of internal pores was observed in the samples in which surfactants and emulsion were added. The obtained fibers presented average diameters in the range of nanometers and high surface area. The hybrid nanofibers presented better performance in the adsorption of both dyes. The experimental data of the AM and RB adsorption were better fitted to the Langmuir and Freundlich models, respectively. The kinetic data were adjusted to the pseudo-second order model for AM adsorption, whereas the intraparticle diffusion model was better adjusted to represent the adsorption mechanism of the RB. The thermodynamic parameter ∆H° indicated that the adsorption of both dyes on the silica nanofibers and the hybrid nanofibers are exothermic and endothermic, respectively.