H3PO4–activated carbon fibers of high surface area from banana tree pseudo-stem fibers: Adsorption studies of methylene blue dye in batch and fixed bed systems

Abstract The present work reports the preparation and characterization of activated carbon fibers (ACF) from banana tree pseudo-stem. ACF were prepared via slow pyrolysis from two methodologies: (i) direct impregnation of the raw material with H3PO4 and pyrolysis (ACFI), and (ii) previous hydrothermal carbonization (HTC) of the raw material followed by impregnation with H3PO4 and pyrolysis (ACFII). The characterization of materials showed ACFII has the higher BET surface area (SBET) value (1975 m2 g−1) than ACFI (1436 m2 g−1), greater uniformity of microfibers and more acidy surface. The ACFII was applied on adsorption of methylene blue (MB) dye using the bath and fixed bed systems. The kinetic models of pseudo first-order, pseudo second-order and Elovich, equilibrium models of Langmuir, Freundlich and Dubinin-Radushkevich, as well as fixed bed adsorption models of Thomas and Yoon-Nelson were fitted to the experimental data. The results indicated high monolayer adsorption capacity of MB onto ACFII (Qm = 728.9 mg g−1), being the process spontaneous and exothermic. The fixed bed study gave a maximum adsorption capacity (qs) of 714.0 mg g−1, exhaust time 512.4 and R2 values higher than 0.99 for models of Thomas and Yoon-Nelson.