A solubility and surface complexation study of a non-stoichiometric hydroxyapatite
A solubility and surface complexation study of a non-stoichiometric hydroxyapatite
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DOI：
10.1016/j.gca.2008.09.034
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发表时间：
2009-01-15
影响因子：
5
通讯作者：
Sjoberg, Staffan
中科院分区：
文献类型：
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作者：
Bengtsson, Asa;Shchukarev, Andrei;Sjoberg, Staffan
研究了非化学计量羟基磷灰石（Ca-8.4（HPO 4）（1.6）（PO 4）（4.4）（OH）（0.4））（HAP）在pH范围3.5-10.5、25 ℃下在0.1M Na（Cl）中的溶解和表面络合。将平衡良好的批量实验、电位滴定和zeta电位测量的结果与衰减全反射傅里叶变换红外（ATR-FTIR）光谱和X射线光电子能谱（XPS）提供的信息相结合。从分析的信息被用来设计一个平衡模型，考虑到溶解，表面电位，溶液和表面络合，以及可能的相变。XPS测量的结果清楚地表明，矿物的表面具有与本体不同的组成，并且表面层的Ca/P比为1.4 +/-0.1。在低pH值下平衡的批次溶液中也发现了该比例，其中主要反应是溶解。然而，在接近中性pH值平衡的批次中，溶液中的Ca/P比达到高达25的值，这是由于磷酸根离子重新吸附到HAP表面。质子的总浓度以及溶液中溶解的钙和磷酸盐的总浓度被用来计算HAP的溶解和表面络合的模型。应用恒电容模型设计了如下表面络合模型：CaOH + H+可逆箭头CaOH 2 + log beta（intr.）= 8.41 +/- 0.16OPO3H2可逆箭头OPO 3 H- + H+ log β（内部）= -1.11 +/- 0.13CaOH + HPO 42- + H+可逆箭头CaOPO 3 H- + H2O log beta（intr.）= 11.63 +/-0.15OPO 3 H2 + Na+可逆箭头OPO 3 Na- +2 H（+）log β（内部）= 11.08 +/-0.12此外，还得到了log β = -23.27 +/- 0.29的溶度积：Ca-8.4（HPO 4）（1.6）（PO 4）（4.4）（OH）（0.4）（s）+4.8H（+）可逆箭头8.4Ca（2+）+6HPO（4）（2-）+0.4H（2）O此外，该模型预测pH（zpc）= 7.9，这与从zeta电位测量获得的pH（iep）= 8.1一致。该模型可用于预测HAP在不同水环境中的反应性。(C)2008爱思唯尔有限公司保留所有权利。
The dissolution and surface complexation of a non-stoichiometric hydroxyapatite (Ca-8.4(HPO4)(1.6)(PO4)(4.4)(OH)(0.4)), (HAP) was studied in the pH range 3.5-10.5, at 25 degrees C in 0.1 M Na(Cl). The results from well-equilibrated batch experiments, potentiometric titrations, and zeta-potential measurements were combined with information provided by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The information from the analyses was used to design an equilibration model that takes into account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. The results from the XPS measurements clearly show that the surface of the mineral has a different composition than the bulk and that the Ca/P ratio of the surface layer is 1.4 +/- 0.1. This ratio was also found in solution in the batches equilibrated at low pH where the dominating reaction is dissolution. In the batches equilibrated at near neutral pH values, however, the Ca/P ratio in solution attains values as high as 25, which is due to re-adsorption of phosphate ions to the HAP surface. The total concentration of protons as well as the total concentration of dissolved calcium and phosphate in solution were used to calculate a model for the dissolution and surface complexation of HAP. The constant capacitance model was applied in designing the following surface complexation model:CaOH + H+ reversible arrow CaOH2+ log beta(intr.) = 8.41 +/- 0.16OPO3H2 reversible arrow OPO3H- + H+ log beta(intr.) = -1.11 +/- 0.13CaOH + HPO42- + H+ reversible arrow CaOPO3H- + H2O log beta(intr.) = 11.63 +/- 0.15OPO3H2 + Na+ reversible arrow OPO3Na- + 2H(+) log beta(intr.) = 11.08 +/- 0.12In addition a solubility product with log beta = -23.27 +/- 0.29 was obtained:Ca-8.4(HPO4)(1.6) (PO4)(4.4)(OH)(0.4)(s) + 4.8H(+) reversible arrow 8.4Ca(2+) + 6HPO(4)(2-) + 0.4H(2)OFurthermore, this model predicts a pH(zpc) = 7.9, which is in agreement with pH(iep) = 8.1 obtained from zeta potential measurements. This model can be used as a helpful tool to predict the reactivity of HAP in different aquatic environments. (C) 2008 Elsevier Ltd. All rights reserved.