Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Abstract

Synthesized by the wet chemical precipitation technique hydroxyapatite powders (HAp) with the sizes of the crystallites of (20-10 50) nm and 1 m were analyzed by multi-frequency (9 and 95 GHz) electron paramagnetic resonance (EPR) methods. It is shown that during the synthesis process nitrate anions from the reagents (by-products) could incorporate into the HAp structure. The relaxation times and EPR parameters of the axially symmetric NO 3 2paramagnetic centers detected after X-ray irradiation of the product at room temperature are measured with high accuracy. Assignments of the observed EPR spectra as compared with that given in literature are discussed. Analyses of electron-nuclear double resonance (ENDOR) data from 1 H and 31 P nuclei and ab-15 initio density functional theory (DFT) calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO 3 2radicals preferably occupy PO 4 3site in the HAp structure. 65 110 Troullier-Martins pseudopotentials [27] with the plane-wave cutoff energy of 70 Ry.

The role of nanoparticle structure and morphology in the dissolution kinetics and nutrient release of nitrate-doped calcium phosphate nanofertilizers

“…The sharp band associated to the ν 3 NO 3 asymmetric stretching at 1,384 cm −1 in N 0.3 -ACP confirms the material functionalization. The relative intensities of the ν 3 NO 3 bands in N 0.3 -ACP and N 0.3 -nAp, and the nitrate content by elemental analysis (2.12 and 0.44 w%, respectively, Table S2 ) indicate that longer maturation times, favouring self-healing processes, limit nitrate functionalization, in line with previous reports 23 , 39 , 40 . This result, and plant tests presented elsewhere 23 , suggest that fully amorphous NPs are best candidates for application as N-based nanofertilizers.…”

“…ions, their incorporation in apatite has been demonstrated by previous experimental and computational studies 39,40 . However, specific effects on the crystal lattice have not been reported, likely due to experimental difficulties in detecting tiny shifts of broad Bragg peaks by conventional XRPD.…”

“…On the fundamental side, direct evidence of NO 3 – incorporation in highly defective apatite nanocrystals has never been given or properly discussed. Indirect EPR evidence of paramagnetic NO 3 2 – ions generated by X-ray irradiation was reported in 30 nm nanocrystals, demonstrating that replacement of phosphate ions takes place but only in trace amounts 39 . Density Functional Theory (DFT) modelling fixed that the substitution is energetically preferred in the B-type than in the A-type configuration 40 .…”

“…2ions generated by X-ray irradiation was reported in 30 nm nanocrystals, demonstrating that replacement of phosphate ions takes place but only in trace amounts 39 . Density Functional Theory (DFT) modelling fixed that the substitution is energetically preferred in the B-type than in the A-type configuration 40 .…”

Phonon Spectrum in Hydroxyapatite: Calculations and EPR Study at Low Temperatures

“…2 shows the ESE detected EPR spectrum of the NO 3 2radiation induced radicals due to the hyperfine interaction between the stable nitrogencontaining paramagnetic center with electronic spin with S = ½ and one nitrogen nuclear spin with I = 1 for 14 N isotope. From the previous EPR data analysis it was concluded that NO 3 2radiation induced radical substitutes PO 4 3position in the HAp structure while the carbonate ions could also replace OH group [15][16][17][18]. The T 1e measurements were done in the magnetic field B 0 = 343 mT (see Fig.…”