A multifunctional octacalcium phosphate pentahydrate with dual environmental and biomedical functions: efficient dye...

Ca₈(HPO₄)₂(PO₄)₄·5H₂O, (OCP), has been successfully synthesized via a wet chemical precipitation method. The analysis of the structure and identification of the composition were performed using X-ray diffraction (XRD), and Rietveld refinement was applied to confirm phase purity. The refined results indicated the formation of highly crystalline octacalcium phosphate with no detectable secondary phases. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of characteristic phosphate functional groups and water molecules. TGA shows that the thermal decomposition of the synthesized OCP leads to the release of water molecules, while scanning electron microscopy (SEM) revealed a plate-like morphology and a homogeneous calcium-to-phosphorus distribution, supporting its suitability for antimicrobial applications. Hirshfeld surface analysis (HSA) indicates that the structural integrity of OCP pentahydrate is predominantly governed by extensive hydrogen bonding. The synthesized material showed a BET surface area of 87.80 m² g^-1 and favorable adsorption for methylene blue dye (MB) from aqueous solutions, with an adsorption capacity of 8.05 mg g^-1 for an initial concentration of 10 ppm. Thermodynamic studies show that the sorption of MB onto OCP is spontaneous and endothermic. The sorption kinetics of MB on OCP fit the pseudo-second-order model better than the pseudo-first-order model, resulting in a higher correlation coefficient (R ² > 0.99). OCP demonstrated potent bactericidal activity against all tested bacteria, with MIC and MBC values ranging from 0.14-0.28 mg mL^-1 and 0.29-0.56 mg mL^-1, respectively, exhibiting the highest efficacy against S. aureus, and B. cereus. Furthermore, the ionic concentrations in simulated body fluid (SBF) were monitored in the presence of the synthesized material to evaluate its bioactivity.