New insights into temperature-induced mechanisms of copper adsorption enhancement on hydroxyapatite-in situ self-doped fluffy bread-like biochar

The utilization of kitchen bones as a renewable resource for biochar production holds significant promise. In this study, three distinct pig-bone-based biochars (PBCs) were synthesized at varying pyrolysis temperatures to investigate the influences of Hydroxyapatite (HAP) self-doped on crystal morphology, formation of functional active sites, and Cu2+ efficient adsorption. The results showed that low-temperature-induced alterations in HAP crystal morphology led to the formation of a highly active “fluffy bread-like” structure (FBS) in PBC-500, exhibiting exceptional Cu2+ adsorption capacity (71.60 mg·L−1) with an 86% adsorption achieved within 15 min. Notably, PBC-500 demonstrated a unit-specific surface area adsorption capacity for Cu2+, which was 1.52 and 1.19 times higher than the nano-wire-like PBC-700 and the nano-spherical-like PBC-900, respectively. Modern Spectroscopic analyses established the presence of a range of active centers (–OH, –CONH2, -PO43-) on PBC-500′s FBS carrier along with its highly efficient adsorption mechanism for Cu2+. These findings were strongly supported by electrostatic potentials and the frontier orbital theory of Quantum DFT methods, providing insights into the crucial chemical mechanisms by which active sites, such as phosphorus, nitrogen, and oxygen centers, enhance Cu2+ adsorption. Furthermore, PBC-500 exhibited superior adsorption binding energy and chemical reactivity, retaining high activity across a range of pH levels, inorganic ions, and organic matter. This study establishes empirical and theoretical foundations for the efficient utilization of kitchen pig bones as a sustainable resource and the eco-friendly synthesis of high-performance self-doped biochar, contributing to sustainable material innovation.