Catalytic activation preparation of nitrogen-doped hierarchical porous bio-char for efficient adsorption of dichloromethane and toluene

Volatile organic compounds (VOCs) adsorption by carbonaceous materials is one of the most promising technologies for their efficient abatement, which requires the construction of both suitable porous structures and functional groups. In this work, nitrogen-doped hierarchical porous bio-char (NHWC) was prepared via a facile catalytic activation process, in which NH₃·H₂O was used as activation agent to introduce nitrogen dopants and trace CaCl₂ acted as catalyst for hierarchical pore formation. VOCs dynamic adsorption experiments indicated that the prepared NHWC exhibits excellent dichloromethane and toluene adsorption properties. Particularly, the combined adsorption capacities of dichloromethane and toluene in NHWC are 54.9 and 308 mg g⁻¹, respectively, much higher than those in microporous bio-char, indicating the significant role of hierarchical porosity in multiple VOCs molecules combined adsorption. Control experiments using the prepared model carbon materials indicate that the excellent combined adsorption performance originates from both nitrogen dopants and hierarchical porous structure. Density functional theory calculations further reveal that the introduced nitrogen functional groups enhance the van der Waals interactions between VOCs molecules and carbon surface, thereby improving the combined adsorption of VOCs. This work provides a new strategy of optimizing the pore structure and surface chemistry of bio-char.