Core–shell architecture based on bio-sourced porous carbon: the shape formation mechanism at the solid/liquid interface layer

The overall goal of this work was to activate agri-food wastes by microbial action, which makes it possible to produce bio-digestate and energy (methane). The resulting bio-digestate could be transformed to porous carbon (PC), which was used for the preparation of core–shell particles with alginate (bio-polymer) and a calcium ion layer. Furthermore, surface charge measurements showed electrostatic attractions occurring between the alginate, calcium (Ca(2+)) ions and the PC, hence leading to the formation of core (PC)–shell (alginate–calcium ions) particles. However, in the absence of calcium ions, no electrostatic attractions were observed between the PC and the alginate. In the dried state (using scanning electronic microscopy analysis (SEM)) and in the hydrate state (using numerical microscopy), the designed core–shell architecture was confirmed. Transmission electron microscopy (TEM) shows that the PC particles were graphitic and porous. In addition, both Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) showed the presence of several chemical functions, in particular hydroxyl (–O–H) and carboxylic groups (–COO–H). In aqueous media, the results showed that the PC was negatively charged and its surface charge and particle size were found to be very sensitive to the variation in pH. Finally, the core–shell particles were used as an adsorbent for the removal of methylene blue (MB), crystal violet (CV) and congo red (CR) molecules from wastewater. The overall data indicated efficient dye removal, without the occurrence of the solid/liquid separation problem.