Theoretical and experimental investigation of the effects of Pr dopant on the electronic band structure, thermal, structural, in vitro biocompatibility of Er-based hydroxyapatites
Introduction
Hydroxyapatite (HAp) is a calcium apatite mineral with the formula Ca10(PO4)6(OH)2 [1]. The crystal system of HAp is hexagonal. When pure, it appears as white granules and comes in a variety of colors, including colorless, yellow, yellowish-green, and gray depending on the impurities present [2,3]. Natural sources of HAp include oyster shells, fish shells, chicken eggshells, coral, as well as cow and fish bones [4].
Owing to its non-toxicity, chemical stability, high biocompatibility and bioactivity, HAp is widely employed in biomedical applications (hard tissue repair, replacement, augmentation, and coating) [5], [6], [7], [8]. HAp is also employed as an adsorbent in environmental repair engineering barriers. It also has a lot of potential as a biomaterial for other things like catalysis and chromatographic adsorption [9]. It is also utilized as a bio-imaging agent and as a form of cancer hyperthermia [10].
Because of their superior stoichiometry and purity, HAp nanoparticles have sparked a lot of interest in biomedical applications. HAp nanoparticles have improved densification and sintering capabilities because of their high surface energy [11]. Owing to its high chemical stability, wear resistance, and chemical composition similar to natural bone, HAp is more advantageous in comparison to metals or polymers in bone-tissue applications [12]. Nevertheless, HAp has disadvantages in new bone development, such as a low capacity to bind to bone and resistance to bacterial activity. Some antimicrobial agents (Fe3O4, Ag+, Cu2+, Ti4+, etc.) can be substituted in HAp to prevent this problem [13], [14], [15], [16].
Some cations (Na+, K+, Mg2+, Zn2+, Sr2+, Fe2+, etc.) and anions (F−, Cl−, CO32−, etc.) can substitute at the HAp lattice in biological apatite. This lowers the Ca/P ratio, which may improve solubility and have an effect on crystal structure [6,17]. Cationic replacements are influenced by polarizability, electronegativity, valence, and ionic radii. Surface shape, size, and crystal structure all influence the physical and chemical properties of HAp [18,19]. Although some cationic substitutions are minor, considerable changes in HAp structural features such as lattice parameters, crystal structure, morphology, and key qualities like thermal stability, magnetic, and mechanical properties can be detected [1].
The synthesis route is a different technique to improve material characteristics [20]. Sol-gel, hydrothermal, microwave irradiation, solid-state reaction, hydrolysis, spray pyrolysis, chemical precipitation, emulsion, or sonochemical processes have all been utilized to make HAp [5,18,21].
There are few studies on Pr or Er-doped hydroxyapatites. Ibrahimzade et al. [22] investigated the theoretical and experimental characterization of Ce-doped HAps with varying amounts of Pr doping. They used Ce-doped HAp samples doped with Pr in varying levels (0.35, 0.70, 1.05, and 1.40 at.%) having a constant amount of Ce (0.35 at.%). The addition of Pr reduced the bandgap energy, according to the theoretical results. As the amount of Pr increased, the linear absorption coefficient (LAC) increased. Both theoretical density and lattice parameter c increased, but the lattice parameter a and unit cell volume V decreased. According to their findings, the thermal study validated the thermal stability of all of the samples, and Pr-content was observed to affect cell survival [23]. Agid et al. [24] studied the structural characteristics of Pr-doped HAps prepared by a wet chemical technique and noticed a gradual increase in the crystallite size, a and V, as well as a gradual decrease in crystallinity. They discovered that when Pr was added to HAp, the bandgap energy reduced continuously from 3.82 to 1.32 eV, and the DOS was also influenced [24].
As noted above, there are some publications on Pr- or Er-doped HAps, but there is no study in the literature on the impact of Pr/Er co-dopants on the HAp structure to our knowledge. For the first time, we give a more detailed theoretical and experimental study report on these samples.
Section snippets
Synthesis and characterization
Er-based HAp samples with a constant amount of Er (0.39 at.%) co-doped with Pr at various amounts of (0.13, 0.26, 0.39, 0.52, 0.65, and 0.78 at.%) were synthesized by using wet chemical synthesis. For each synthesis, distilled water was used as a solvent for the as-used chemicals of calcium nitrate tetrahydrate (Ca(NO3)2·4H2O, Carlo-Erba), erbium nitrate pentahydrate (Er(NO3)3·5H2O, Sigma-Aldrich), praseodymium (III) nitrate hexahydrate (Pr(NO3)3·6H2O, Alfa-Aesar). Table 1 gives a detail
Bandgap and density of states calculations
A detailed explanation on theoretical calculations of the density of states (DOS) and band structure (BS) has been displayed in our previous work [23]. A brief overview will be provided in this subsection.
The DOS as a function of energy can be calculated using this formula.here g, E, and εi are a Gaussian with a fixed FWHM, total energy, and energy of the ith molecular orbital, respectively.
The BS and DOS measurements are based on the interaction of atoms, which causes the atomic
Conclusions
HAp samples co-doped with Pr and Er were successfully synthesized, modeled, and characterized experimentally and theoretically. A progressive increase in the density and a continuous decrease in the bandgap and linear absorption coefficient were observed. There were significant differences in the crystallite size, crystallinity, and lattice parameters. Adding Pr to Er-based HAp resulted in lattice strain and stress formation. Pr content affected the thermal behavior of the Er-Based HAps. Raman
CRediT authorship contribution statement
Lana Omar Ahmed: Methodology, Validation, Investigation. Niyazi Bulut: Conceptualization, Writing – original draft, Writing – review & editing, Supervision. Fatih Osmanlıoğlu: Formal analysis, Investigation. Beyhan Tatar: Investigation. Hanifi Kebiroglu: Visualization. Tankut Ates: Formal analysis, Investigation. Suleyman Koytepe: Investigation. Burhan Ates: Investigation. Serhat Keser: Investigation. Omer Kaygili: Methodology, Validation, Formal analysis, Writing – original draft,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was derived from Lana Omar Ahmed's Ph.D. Thesis and supported financially by the Management Unit of Scientific Research Projects of Firat University (FUBAP) (Project Numbers: FF.20.22, FF.21.18, and FF.22.05).
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