Carbonate hydroxyapatite (CHAP) was synthesized from domestic hen egg shells. The obtained CHAP was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy and investigated as metal adsorption for Pb 2+ from aqueous solutions. The effect of various parameters on the adsorption process such as contact time, solution pH, and temperature was studied to optimize the conditions for maximum adsorption. The results showed that the removal efficiency of Pb 2+ by carbonate hydroxyapatite calcined at 600°C (CHAPF) reached 99.78 %, with an initial Pb 2+ concentration of 200 mg · L -1 , pH ) 3, and a solid/liquid ratio of 1 g · L -1 . The equilibrium removal process of lead ions by CHAPF foam at pH ) 3 was well described by the Langmuir isotherm model, with a maximum adsorption capacity of 500 mg · g -1 at (25 and 35)°C. The removal mechanism of Pb 2+ by the CHAPF varies, depending on the initial concentration of lead in the aqueous solution: the dissolution of CHAPF and precipitation of hydropyromorphite (Pb 10 (PO 4 ) 6 (OH) 2 ) is dominant at low concentration [(20 to 200) mg · L -1 ], and the adsorption mechanism of Pb 2+ on the CHAPF surface and ion exchange reaction between Ca 2+ of hydroxyapatite and Pb 2+ in aqueous solution is dominant at high concentration [(500 to 700) mg · L -1 ]. The thermodynamics of the immobilization process indicates an exothermic sorption process of Pb 2+ .

International audienceIn order to reinforce the clinical applications of hydroxyapatite (HAP) sol–gel coatings deposited onto 316 L stainless steel, we suggest the introduction of an intermediate thin layer of titania (TiO2) on the substrate. The titania sub-layer is introduced in order to improve both the corrosion resistance and the mechanical properties of the HAP/316 L stainless steel coated system. The two coatings, HAP and TiO2, were studied separately and afterwards, compared with the bi-layered coating. A film without any cracks is obtained under the optimum conditions in terms of annealing temperature, dipping rate and aging effect. Microstructural, morphological and profilometry analysis revealed the non-stoichiometric carbonated porous nature of the hydroxyapatite coatings, which were obtained after annealing at 500 °C during 60 min in the atmosphere. The obtained TiO2 coatings exhibit a dense and uniform surface. Addition of TiO2 as sub-layer of the HAP coating tends to increase the homogeneity and the crystallinity rate as compared to the HAP one.The mechanical properties, i.e. hardness and elastic modulus, are determined by means of nanoindentation experiments and the adhesion between the coating and substrate is estimated by scratch tests. The corrosion behavior is evaluated by potentiodynamic cyclic voltammetry tests. As a main result, the values of the elastic modulus and hardness, respectively of 30 GPa and 2.5 GPa, are relatively high for the HAP–TiO2 bilayer coating. This result allows the use of such coated material as a replacement material for hard tissues. The adhesion strength increased from 2925 mN up to 6430 mN after the addition of the TiO2 intermediate film. According to the Tafel's analysis, the 316 L stainless steel specimens coated with both HAP and titania layers (ECorr = − 234 mV, lCorr = 0.089 μA cm− 2) present a better resistance than the HAP-coated specimens (ECorr = − 460 mV, lCorr = 0.860 μA cm− 2)

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Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca10‐xMgx(PO4)6OH2) were synthesized using sol‐gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg+2) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as‐prepared powders had a specific surface area ranged between 6.37 and 27.60 m2/g.

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