Functional lignocellulosic material for the remediation of copper(II) ions from water: Towards the design of a wood filter

In this study, the chemical modification of bulk beech wood is described along with its utilization as biosorbent for the remediation of copper from water. The material was prepared by esterification using anhydrides, and reaction conditions were optimized to propose a greener process, in particular by reducing the amount of solvent. This modification yields a lignocellulosic material whose native structure is preserved, with an increased amount of carboxylic groups (up to 3 mmol/g). We demonstrate that the material can remove up to 95% of copper from low concentration solutions (100– 500 ppm). The adsorption efficiency decreases with concentrated copper solutions, and we show that a limited number of −COOH groups participate in copper binding (ca. 0.1 Cu/−COOH). This result suggests a limited accessibility of −COOH groups in the wood scaffold. This was demonstrated by the characterization of −COOH and copper distributions inside wood. Raman and EDX imaging confirmed that most –COOH groups are located inside the wood cell walls, thereby limiting interactions with copper. According to this study, critical limitations of bulk wood as a biosorbent were identified, and the results will be used to improve the material and design an efficient wood filter for heavy metal remediation.