Engineered biochar prepared using a self-template coupled with physicochemical activation for highly efficient adsorption of crystal violet

In this study, engineered biochar (EBC) was prepared from rice husk biochar to achieve highly efficient crystal violet (CV) removal. EBCs have critically controlled the structures through the use of three strategies of con-ventional chemical activation, self-templating coupled with chemical activation and self-templating coupled with physicochemical activation. EBCs are characterized by SEM, EDS, BET, and FTIR. The batch adsorption exper-iments using kinetic and isotherm studies are applied to investigate CV adsorption. The hierarchical porous structure is only observed in samples prepared by the self-template method using naturally available SiO2 templates inside rice husk. By using the self-template coupled with physicochemical activation, EBC-3 is pre-pared with an excellent SSA and mesoporosity of 2344 m2 g-1 and 0.70, respectively. As a result, EBC-3 achieves a remarkably high maximum CV adsorption capacity (564.42 mg g-1) and rapid CV adsorption rate (0.035 g mg-1 h-1). The obtained results are due to the formation of a hierarchical porous structure with high mesoporosity, facilitating the transport of CV molecules. The large SSA and rich functional groups provide abundant active sites for CV adsorption. The CV adsorption on EBC was governed by pore filling, electrostatic attraction, pi-pi inter-action and hydrogen bonding mechanisms.