Combination of EPR Measurements and DFT Calculations To Study Nitrate Impurities in the Carbonated Nanohydroxyapatite

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• 作者：Timur Biktagirov ; Marat Gafurov ; Georgy Mamin ; Elena Klimashina ; Valery Putlayev ; Sergei Orlinskii
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：February 27, 2014
• 年：2014
• 卷：118
• 期：8
• 页码：1519-1526
• 全文大小：339K
• 年卷期：v.118,no.8(February 27, 2014)
• ISSN：1520-5215

文摘

We demonstrate the application of the combined experimental鈥揷omputational approach for studying the anionic impurities in hydroxyapatite (HAp). Influence of the carbonation level (x) on the concentration of the NO₃^{2鈥?/sup> radicals in the HAp nanocrystals of Ca_10鈥?i>xNa_x(PO₄)_6鈥?i>x(CO₃)_x(OH)₂ with x in the range 0 < x < 2 and average sizes of 30 nm is investigated by different analytical methods including electron paramagnetic resonance (EPR). Stable NO₃2鈥?/sup> radicals are formed under X-ray irradiation of nano-HAp samples from NO₃鈥?/sup> ions incorporated in trace amounts during the wet synthesis process. Density functional theory (DFT) based calculations show energetic preference for the PO₄ group substitution by NO₃鈥?/sup> ions. Comparison of the calculated and experimental spectroscopic parameters (g and hyperfine tensors) reveals that EPR detects the NO₃2鈥?/sup> radicals located in the positions of the PO₄ group only. It is shown that with the increase in x, the carbonate ions substitute the NO₃2鈥?/sup>/NO₃鈥?/sup> ions. DFT calculations confirm that carbonate incorporation in HAp structure is energetically more favorable than the formation of the nitrate defect.}