Characteristics of Hydrochars Prepared from Cassava Residues Using Different Aqueous Media

Abstract

This study presents the synthesis and physicochemical characterization of functionalized carbon-based materials prepared from cassava residues (Manihot esculenta). Cassava residues were obtained from a local market, washed, dried and ground to small particle size. This powder was mixed with different aqueous media: diluted sulfuric acid (0.2 M), nejayote and deionized water. These mixtures were treated in an autoclave at 200 °C for 4 h. The physicochemical characteristics of samples were studied by SEM, TGA, FTIR, XPS and elemental analysis. The chemical composition of C:O was similar among groups, but TGA suggested that the hydrochar prepared with sulphuric acid presented a better thermal stability, with a decomposition peak at 435 °C, which was 80 °C higher than samples prepared with deionized water. The acid sample also had lower mass loss (47.3%). The SEM images showed that sulphuric acid promoted the formation of small needle-like structures, while samples prepared using nejayote and water showed agglomerates with a few spherical shapes. The proximate analysis indicated that there was a carbon enrichment from 41% from the original sample to 62% after the hydrothermal process.