Insights into performances of magnetic and bio-based doped-nanohydroxyapatites as water decontamination agents

Hydroxyapatite, a mineral from the apatite group, is widely distributed in living organisms and largely studied because of its many properties, including the adsorption of many different substances. In this work, two functionalized nanohydroxyapatites were synthesized starting from their precursors (calcium hydroxide and phosphoric acid) in the presence of Fe(II)/(III) ions and bio-based substances (BBS) isolated from green compost. The products were characterized with different techniques (nitrogen adsorption/desorption, ATR-FTIR, XRD, TGA and ζ-potential measurements) and compared to nanohydroxyapatite obtained without further functionalization. The ability of these materials to remove different water pollutants by adsorption was tested using two organic dyes (crystal violet and methyl orange) and four inorganic ions, Al(III), Cr(III), Ni(II) and As(V), characterized by different ionic charges, dimensions and nature. Moreover, for the same purpose, the antibacterial properties of iron- and iron/BBS-added materials were also tested. The result showed the effective adsorption capability of the materials, in particular with respect to crystal violet, Al(III) and Cr(III), and an enhancement of adsorption capacity with respect to all the adsorbates after functionalization. Finally, the tests towards Staphylococcus aureus and Escherichia coli showed high antimicrobial activity for the bare nanohydroxyapatite samples, whereas the doping with iron and BBS or the high-temperature treatment remarkably impacted this capacity depending on the bacterial strain to eliminate.