3.2. Characterization Methods

The structural characteristics of Ca_10−xZn_x(PO₄)₆(OH)₂ with 0.01 ≤ x_Zn ≤ 0.05 were investigated by X-ray diffraction (XRD), Fourier Transform-Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The crystal phase was determined by powder XRD) measurements using a Bruker D8 Advance diffractometer (Bruker, Karlsruhe, Germany), with nickel filtered Cu_Kα (λ = 1.5418 Å) radiation and a high efficiency one-dimensional detector (Lynx Eye type) operated in integration mode. The samples were scanned in the 2θ range 20°–80°, with a step of 0.02° and 34 s measuring time per step. The secondary device was useful for the identification of the elemental composition. In order to highlight the functional groups, present in the prepared samples, FTIR spectra have been acquired using a Spectrum BX Spectrometer (PerkinElmer, Waltham, MA, USA). For these measurements, 1% of the powder was mixed and ground with 99% KBr. The powder mixture was then pressed at a load of 5 tons for 2 min obtaining pellets of 10 mm diameter. The spectrum was recorded in the range of 400 to 4000 cm⁻¹ with a resolution of 4 and 128 times scanning. XPS measurements were carried out using a SPECS Multimethod Surface Analysis System (SPECS GmbH, Berlin, Germany) using monochromatic Al_Kα radiation (1486.6 eV). The vacuum in the analyzer chamber was p ~ 3 × 10⁻⁹ Torr. The X-rays are emitted by an anti-cathode of Al, U = 12.5 kV, with filament emission current I = 20 mA. For charge compensation, a FG40 flood gun had been used, providing an electron beam of 2 eV and 0.3 mA. The XPS recorded spectrum involved an energy window w = 20 eV with the resolution R = 20 eV, and with 400 recording channels. The XPS spectra were processed using Spectral Data Processor v2.3 (SDP) software. The colloidal properties of the Ca_10−xZn_x(PO₄)₆(OH)₂ with 0.01≤ x_Zn ≤0.05 nanocomposites were investigated by Dynamic Light Scattering (DLS) and zeta potential using dynamic light scattering (SZ-100 Nanoparticle Analyzer, HORIBA, Ltd., Kyoto, Japan) at 25 ± 1 °C. All the samples were diluted in distilled water before analysis. Before measuring of zeta potential, all samples were sonicated for 15 min. The pH of Zn:HAp suspension was equal to 7. For each sample analyzed, three determinations were recorded. The final value was determined by averaging the three measurements. The textural characteristics of synthesized nanocomposites were investigated by low temperature N₂ adsorption desorption using a Micromeritics ASAP 2020 Physisorption Analyzer (Micromeritics Instrument Corp., Norcross, GA, USA) Scanning electron microscopy (SEM) has been used to show the morphology of all the samples using a HITACHI S2600N-type microscope (Hitachi High Technologies America, Inc., Schaumburg, IL, USA) equipped with an energy dispersive X-ray attachment (EDAX/2001 device).