Development of CO2 activated biochar from solid wastes of a beer industry and its application for methylene blue adsorption

An alternative activated biochar was developed from barley malt bagasse (BMB) through pyrolysis followed by CO2 activation. The materials BMB, biochar and activated biochar (CO2-biochar) were characterized and tested as adsorbents for the removal of methylene blue (MB) from aqueous solutions. Adsorption kinetics, equilibrium and thermodynamics were studied. It was found that BMB and biochar presented surface area values lower than 1 m2 g−1, while CO2-biochar was a typical mesoporous material with surface area around 80 m2 g−1. As consequence, the adsorption potential for methylene blue was in the following order CO2-biochar ≫ biochar > BMB. Adsorption kinetics of MB on CO2-biochar followed the pseudo-second order model. Langmuir presented the best fit with the equilibrium adsorption isotherms. The maximum adsorption capacity was 161 mg g−1. MB adsorption on CO2-biochar was spontaneous, favorable and exothermic. Pyrolysis followed by CO2 activation was a suitable route to produce an alternative mesoporous adsorbent from barley malt bagasse.