Activated biochars derived from wood biomass liquefaction residues for effective removal of hazardous hexavalent chromium from aquatic environments

Abstract Residues obtained after wood biomass liquefaction were used as precursors for the synthesis of two activated biochars. The source of biomass liquefaction constituted of industrial wood processing by‐products, including bark and wood sawdust. The liquefied residues were analyzed in terms of chemical components and structure. Carbonization under nitrogen atmosphere followed by physical CO2 activation allowed to obtain microporous activated carbons with specific surface areas of 741 and 522 m2 g−1, and micropore volumes of 0.38 and 0.27 cm3 g−1, respectively. The obtained activated carbons were used to remove toxic hexavalent chromium from the aquatic environment. The observed sorption capacities were 80.6 mg g−1 versus 36.7 mg g−1 for wood bark‐derived and wood sawdust‐derived carbon, respectively, indicating a key role of the wood residue source in the effectiveness of Cr(VI) removal by resulting carbons. Despite the dominant microporous structure, the adsorption kinetics was surprisingly fast, especially for the bark‐derived carbon, since the adsorption equilibrium was reached within 2 h. The sorption mechanism of chromium was based on the carbon surface‐mediated reduction of toxic hexavalent form to its non‐toxic trivalent form, as confirmed by the X‐ray photoelectron analysis. Therefore, the residues from wood liquefaction can be easily converted into porous activated biocarbons capable of adsorbing significant amounts of hazardous Cr(VI) while reducing them to non‐toxic Cr(III)