Carbonização hidrotérmica para a obtenção de sistemas inorgânicos-carbono: compósitos magnéticos e carbono hidrotérmico contendo nutrientes

Abstract

Inorganic-carbon systems, magnetic composites based on carbon and iron oxides and hydrothermal carbon (HC) containing nutrients were prepared through hydrothermal carbonization (HTC) in moderate conditions. Composites Fe2O3@C were prepared using glucose and iron nitrate (III) as reagents. Reaction parameters such as temperature (190 ºC) and time (9 h) were kept constant, while the nominal percentage of iron ranged from 11 to 46% relative to carbon content in the organic precursor. Once Fe2O3@C composite was prepared, it was submitted to thermal treatment at 500 ºC under nitrogen flow, transforming into Fe3O4@C composite. The morphological characterization revealed micrometric spherical particles surrounded by nanostructures. The magnetic composites have medium porosity and good magnetic response and can be applied to environmental remediation. Adsorption experiments for Cr(VI) using Fe3O4@C composites as adsorbent showed that maximum adsorption capacity increased with increasing of iron content and the values ranged between 826 and 1,508 μg/g. Also, magnetic composites (BCMH) were prepared from hydrothermal carbonization of sugarcane bagasse in presence of iron nitrate (III). Reaction parameters such as temperature (190 and 230 ºC), time (9, 24 and 48 h) and mass of iron nitrate (0.6, 1.2 and 2.4 g) relative to mass of bagasse (1.0 g) were studied. Structural characterization revealed a mixture of iron oxide phases in the composites. SEM images of the BCMH composites showed clusters of nanostructures. Magnetic measurements revealed blocking temperature (TB) characteristic of the -Fe2O3 phase. Finally, hydrothermal carbons (HC) containing nutrients were prepared using a mixture of vinasse and sugarcane bagasse as carbon precursor in the presence of phosphoric acid (H3PO4). Chemical composition, structure and morphology of these carbonaceous materials were studied. The yield of hydrothermal carbons increased as a result of phosphate precipitation. The hydrothermal carbons are amorphous and present composition similar to that of lignite. Hydrothermal treatment allowed the immobilization of macronutrients such as P, N, K, Ca and Mg in hydrothermal carbons, which could potentially be applied as organo-mineral fertilizers.