Synergistic effects of N-containing heterocyclic and Ca ligand structures on the phosphorus adsorption of N/Ca co-doped biochar

Using modified biochar for phosphorus removal from water is widely recognized as an eco-friendly and viable alternative to conventional methods. Notably, biochar co-doped with metals and heteroatoms exhibits enhanced active sites and a greater affinity for pollutants compared to biochar doped solely with either metals or heteroatoms. This study involved synthesizing N/Ca single-doped and co-doped biochar through direct and active doping techniques, exploring their structural alterations and adsorption mechanisms. The findings reveal that doping with heteroatoms (N) and metals (Ca) primarily leads to a heterocyclic reconfiguration of the carbon framework. This reconfiguration facilitates the integration of metal ions into the carbon matrix via oxidative coordination. The maximum adsorption capacity of the Ca/N co-doped biochar for phosphorus was measured to be 145.47 mg/g. The interaction between N-containing heterocycles and Ca ligand structures on the biochar surface significantly boosts phosphorus removal, achieving synergistic adsorption effects (1 + 1>2). Key mechanisms driving this efficient adsorption include pore filling, hydrogen bonding, anion-π interactions, ligand exchange, and chemical precipitation. These insights provide a comprehensive understanding of the structural modifications necessary for optimizing phosphorus adsorption in biochar. [Display omitted] •N and Ca co-doped strategies are proposed for the modification of biochar structures.•Growth patterns of N-containing heterocyclic and Ca ligand structures on biochar are revealed.•Adsorption behaviors between N/Ca-doped structures and phosphate are discovered.•Pore filling, hydrogen bonding, anion-π interaction, ligand exchange, and chemical precipitation dominate adsorption.