Carbonização hidrotérmica de celulose e nanocelulose e preparação de compósitos magnéticos em única etapa

Abstract

Hydrochars and magnetic composites were prepared by hydrothermal carbonization (HTC) of nanocellulose, cellulose and ferric salt. The study of the hydrochar (HC) developed from the cellulose HTC was performed by analysing different reaction parameters. The Van Krevelen diagram of these HC showed that the degree of carbonization is directly proportional to the initial mass, the temperature and the reaction time. Infrared spectroscopy analyses revealed that the initial mass increase, temperature and reaction time increase the intensity of the bands ranging from 700 to 900 cm-1 assigned to C-H and C =C bonds of aromatic rings. The diffraction pattern of the hydrochar is typical of amorphous carbon. The morphology of the HC is irregular and presents some spherical particles of a micrometric size, embedded in the carbonaceous matrix. A systematic study of the preparation of hydrochar obtained from HTC of nanocellulose (HN) was carried out, evaluating the reaction parameters: temperature (200 to 260 °C) and initial pH (3.3 and 12 ). CHN compositional analysis of this carbon revealed that the reaction medium acts as a catalyst (acidic pH) or retarder (basic pH) of the carbonization reactions. Also, they showed that the increase in temperature raised the carbon content in the hydrochar, consequently increasing the heating energy value (HHV). Infrared spectroscopy (FTIR) results showed that reactions occurring at temperatures from 230 °C showed products with different functional groups hydroxyl, carboxylic acid, alcohol, among others. Besides, the presence of the C =C bond was identified at around 1580 cm-1 assigned to aromatic domains. The X-ray diffraction pattern for the carbonized samples showed an amorphous halo close to 20° (2θ), indicating that the structure of the carbon HN is similar to amorphous carbon. The adsorption-desorption isotherms of the HN coals were type II and III with type III hysteresis and revealed that they have relatively low specific surface areas (between 19 and 35 % m2g-1). Magnetic compounds (HM) prepared in a single step by the hydrothermal carbonization of cellulose in the presence of iron (III) nitrate. The TGA curves showed that the amounts of iron oxide in HM range between 48 and 82 %. FTIR spectra revealed the presence of typical Fe-O binding bands ranging from 220 to 470 cm-1. The diffraction pattern of the composites showed that the magnetic composites are formed by hematite and maghemite, results confirmed by electronic paramagnetic resonance spectroscopy (EPR). The results of the vibrating sample magnetometry (VSM) indicated a good magnetic response. Hystereses are characteristic of ferrimagnetic particles. The mechanism of composite formation was suggested and discussed. The set of results presented in this thesis showed that the HTC process is promising in the generation of carbonaceous or composite materials, it allows to add value to the biomass and to increase its potential of applications.