Adsorption properties of biochars obtained by KOH activation

Abstract

In this study four kinds of biochars were prepared from the KOH modified biomass. As the carbon precursors there was used the sawdust from the following trees: oak, hornbeam, apple and cherry. The physicochemical properties of the materials were characterized by the N2 adsorption, scanning electron microscopy, thermal analysis (TG, DTG and DTA), infrared spectroscopy, and the Boehm’s titration method. Moreover, pHpzc (the point of zero charge) was determined. The adsorption capacity and the temperature-programmed desorption of ammonia were also studied. The obtained activated biochars were characterized by the large specific surface area (672 to 912 m2/g) and the total pore volume (0.30 to 0.4 cm3/g) as well as the well-developed microporous structure (85–97%). These observations were also confirmed by the SEM analysis. The maximum NH3 adsorption capacity of the activated biochar was determined to be 3.05 mmol/g. These results prove that the sawdust of various origins is appropriate to prepare a cost-effective, environmentally friendly biochar.