Porosity and Pore Size Distribution of Native and Delignified Beech Wood Determined by Mercury Intrusion Porosimetry.

The complex hierarchical structures of biological materials in combination with outstanding property profiles are great sources of inspiration for material scientists. Based on these characteristic features, the structure of wood has been increasingly exploited to fabricate novel hierarchical and functional materials. With delignification treatments, the density and chemistry of wood can be altered, resulting in hierarchical cellulose scaffolds with enhanced porosity for the fabrication of novel hybrid materials. In the present study, focusing on acidic delignification of beech wood and its influence on porosity, we report on a structural characterization and qualitative assessment of the cellulose scaffolds using mercury intrusion porosimetry (MIP). To account for the effect of water removal from the hygroscopic structure, different drying methods-e.g., standard oven and freeze-drying-were applied. While native beech wood is characterized by the presence of macro, meso and micro pores, delignification altered the porosity, increasing the importance of the macropores in the pore size distribution. Furthermore, we showed that the final porosity obtained in the material is strongly dependent on the applied drying process. Samples delignified under harsh conditions at high temperature (mass loss of ~35%) show a 13% higher porosity after freeze-drying compared to oven-dried samples. The obtained results contribute to a better understanding of the impact of the delignification and drying processes on the porosity of cellulose scaffolds, which is of high relevance for subsequent modification and functionalization treatments.

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.