Novel BHMTP-Modified Hydroxyapatite for the Efficient Removal of Cu ²⁺ and Zn ²⁺ Ions from Water

This study developed a novel Bis(1,6-hexamethylenetriamine penta(methylenephosphonic acid)) (BHMTP)-modified hydroxyapatite (30BH-HAP) composite for efficient removal of heavy metal ions. The material was synthesized via coprecipitation and characterized by BET, FTIR, XRD, and SEM. BHMTP incorporation increased the specific surface area from 88.38 to 140.3 m2/g (a 58.7% enhancement) and total pore volume from 0.27 to 0.35 cm3/g. In separate batch adsorption experiments, the optimized 30BH-HAP exhibited exceptional adsorption capacities of 239.5 mg/g for Cu2+ and 268.3 mg/g for Zn2+ at pH 6.0, which are 6.12 and 5.38 times higher than commercial HAP, respectively, and surpass most previously reported adsorbents. Mechanistic studies combining Density Functional Theory (DFT) calculations, Independent Gradient Model (IGM), and Hirshfeld surface analysis revealed that BHMTP’s phosphonic acid groups form stable coordination complexes (P═O···M2+) with metal ions. The material maintained >80% regeneration efficiency after 5 cycles and demonstrated strong interference resistance (>84% capacity retention in the presence of 10 mM Ca2+). This work provides a sustainable strategy for heavy metal ion remediation through the functional reuse of industrial phosphonates, offering novelty in material design and application.