Synthesis of metal-doped nano-hydroxyapatite for enhanced adsorption of textile effluents

Nanosized hydroxyapatite (HAp) is regarded as a fundamental substance for artificial bone tissue engineering, and its applications continue to develop, including the photocatalytic degradation of environmentally hazardous pollutants. A conventional wet-chemical precipitation method was employed to synthesize HAp nanoparticles in their pure form and doped with Cu, Fe, Zn, and Na. The study examined the comparative adsorption of Congo Red dye and the improvement in adsorption performance achieved through metal doping. Additionally, the structural analysis and functional group characterization of the synthesized samples were performed using an X-ray Diffractometer (XRD), a Fourier Transform Infrared Spectrometer (FTIR), a Transmission Electron Microscope (TEM), and a Scanning Electron Microscope (SEM). Moreover, the XRD analysis enabled a detailed estimation of the crystallite size, facilitating the tailoring of increased photocatalytic activity. The crystallite size of the resultant crystals ranged from 33 to 58 nm and was doped with metals, as proved by EDX analysis. Among the samples, HAp doped with 0.25 mol% exhibited the highest adsorption efficiency, removing approximately 96 % of the dye from the solution, compared to 90 % removal achieved by pure HAp. The point of zero charge (pH_pzc) evaluation showed that the pH of the adsorbents during maximum dye removal was 7.03 and was less than the value of pH_pzc (8.0–8.5), and determined the band gap analyses 5.77–6.05 eV, further confirming the interaction mechanisms between the adsorbent and Congo Red dye. These results highlight the potential of metal-doped nano-HAp as an enhanced adsorbent for the remediation of textile dyes.