Phosphorus-zirconium co-doped walnut shell biochar prepared by pyrolysis for efficient Pb (II) captured from synthetic wastewater

In this research work, biochar-zirconium phosphate (BC-Zr-P) nanocomposites were utilized for the adsorption of Pb (II) in sewage through functionalization of zirconium and phosphate on the surface of biochar. A series of characterization analyses were conducted on BC-Zr-P nanocomposites to comprehend their morphology and functional groups. Furthermore, the adsorption performance of BC-Zr-P towards Pb (II) in aqueous solution was investigated and four crucial parameters including concentration, pH, adsorption time and temperature were optimized. The experimental results demonstrate that BC-Zr-P exhibits a high adsorption capacity for lead ions with a value of 82.04 mg g−1. Comparative analysis indicates that BC-Zr-P possesses excellent potential as an effective sorbent for lead removal. The adsorption capacity of the material for Pb (II) is highly pH-dependent, with optimal performance observed at pH 2.5, indicating that ion exchange plays a dominant role in the adsorption process and leading to significant changes in adsorption capacity. Rapid kinetic performance within 2 h suggests chemisorption of Pb (II) by BC-Zr-P. We observed a strong agreement between the pseudo-second-order kinetic model and the experimental data, while the adsorption isotherms at different temperatures were well described by the Langmuir model, which outperformed the Freundlich model. These results provide evidence for a monolayer chemisorption mechanism of BC-Zr-P. In addition, the impact of varying temperatures on the adsorption capacity of BC-Zr-P was examined within the range of 278.15–318.15 K, and the thermodynamic behavior of adsorption was analyzed by determining ΔSo and ΔHo through a linear relationship between lnKd and 1/T. The positive value obtained for ΔHo suggests that the process of adsorption is endothermic. BC-Zr-P had excellent selective adsorption capacity for Pb (II) ions in various metal ion solutions and had practical application value for the adsorption of Pb (II) ions in sewage.