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• CO 2 helps to modify properties of biochar made via pyrolysis. • Porosity of biochar can be improved when CO 2 is used in the pyrolysis. • The modification approach can be applied to precisely engineer biochar for various applications. Biochar is widely used for various environmental remediation strategies such as soil amendment because of its intrinsic carbon negativity and porosity. Biochar is a charcoal-like material produced via pyrolysis of biomass. To determine an effective method for modification of the porosity and morphology of biochar and establishment of a more sustainable pyrolysis platform for biomass valorization, this study used CO 2 as a reactive gas medium in the biomass pyrolysis process. This study placed emphasis on elucidating the role of CO 2 in the production of biochar from different types of biomass, such as cellulose, xylan, lignin, grass, and oak wood. The surface area and porosity of biochar were strongly related to the type of biomass. Under comparable pyrolysis conditions, the surface area of biochar decreased in the following order: cellulose > xylan > lignin ∼ oak wood > grass. The use of CO 2 as the gas medium in biomass pyrolysis affected the surface area and porosity of biochar samples derived from biomass feedstock. For instance, the surface area and total pore volume of the oak-wood-derived biochar produced in the CO 2 environment were twice those produced in the N 2 environment. Given that the increases in the biochar surface area and porosity were attributed to the enhanced release of volatile organic compounds (VOCs) from biomass, CO 2 may have enhanced VOC release (removal) during pyrolysis. Therefore, the use of CO 2 in a pyrolysis platform is expected to be a strategic approach for biomass valorization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Application of Fe-impregnated bentonite as a catalyst in pyrolysis of grass cut. • CO 2 gas was employed as a pyrolysis gas medium. • Fe-impregnated bentonite enhanced syngas production. • Fe-impregnated bentonite induced formation of methyl 1,1-methyl-dodecanoate (C 14 H 28 O 2). • Obtained biochar had good As(V) adsorption capability. Fe-impregnated bentonite was employed in CO 2 -assisted pyrolysis of grass cut as a catalyst to improve syngas production, bio-oil quality, and biochar sorptive property. The gas analysis revealed that H 2 and CO production was enhanced by 332 and 7,110%, respectively, by applying Fe-impregnated bentonite in pyrolysis of grass cut while untreated bentonite had a limited influence on syngas production. Bio-oil produced from Fe-impregnated bentonite and grass cut (Fe-BG) had more homogenized chemical species in bio-oil as compared to that produced from pyrolysis of grass cut, and contained methyl 1,1-methyl-dodecanoate (C 14 H 28 O 2), one of the major components in biodiesel. The produced biochar had high surface area (69.2 m2 g−1) and possessed Fe0 and graphitic carbon structure, which was deemed to arise from reduction of Fe-oxides by syngas. Biochar also showed high As(V) adsorption capacity. The overall results of this work demonstrated the beneficial utility of Fe-impregnated bentonite in pyrolysis of biomass to improve syngas production as well as the quality of pyrogenic products. [ABSTRACT FROM AUTHOR]