Production of poplar branch-derived activated carbon with acidic deep eutectic solvent pretreatment coupled with chemical activation

Abstract

The structural constituents of original biomass played a crucial role in determining the structural properties and performance of activated carbon (AC). As a green ionic liquid counterpart, deep eutectic solvent (DES) was recommended as an appropriate medium for effective biomass fractionation. Therefore, an innovative strategy was proposed for preparing carbonaceous materials through DES pretreatment followed by chemical activation. In this study, the poplar branch was treated with DES synthesized by choline chloride and oxalic acid, and then activated by phosphoric acid or zinc chloride to produce AC. The results indicated that DES pretreatment induced substantial dissolution of hemicellulose, followed by framework destruction of lignin and cellulose component. Furthermore, activation efficiency of phosphoric acid or zinc chloride on the biomass with modified structure was considerably enhanced, resulting in an increment of AC yield. The presence of ZnCl2 promoted the dehydration and aromatization of aliphatic structure, improved the carbon content and inhibited the generation of conjugated organics. The activation procedure produced more micropores and mesoporous, contributing to larger specific surface area of AC (1648 m2g−1). In terms of burning capability, DES treatment improved the combustion performance of AC, resulting in lower ignition and burnout temperatures. With respect to its well-developed pore structure, the resultant AC exhibited excellent adsorption ability (99 % removal rate) for methylene blue in aqueous solution. Life cycle assessment revealed that DES treatment could lessen the impact degree of subsequent activation technique on the energy consumption and environmental degradation. This study supports the ability of deep eutectic solvent pretreatment combined with chemical activation to be potential strategy for producing porous activated carbon with excellent removal capacity of methylene blue.