Abstract Well-organized hollow hierarchical hydroxyapatite microspheres were prepared hydrothermally via a template free process. Citrate was used as chelating or morphology regulating agent in this study. In the presence of regulating agent two-dimensional monetite phase evolved into three-dimensional hollow hydroxyapatite microspheres with an average diameter of 4 μm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed the importance of Citrate/Calcium (Cit/Ca) ratio in regulating the particle morphology. The results indicate that the surface morphology of microspheres can be engineered from nanosheets to nanorods by regulating agent concentration. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirmed crystallinity and purity in the synthesized powders. Brunauer-Emmett-Teller (BET) indicated an increase in the specific surface area with the change from hydroxyapatite microspheres with nanosheets (HAMNS) to hydroxyapatite microspheres with nanorods (HAMNR) on the surface. Thermodynamic and kinetic theories are proposed to account for the observed changes in the surface morphology and crystal growth.

中文翻译：

---

表面工程空心羟基磷灰石微球：水热合成和生长机制

摘要 通过无模板工艺水热制备了组织良好的空心分级羟基磷灰石微球。本研究中柠檬酸盐用作螯合剂或形态调节剂。在调节剂的存在下，二维三磷灰石相演化为平均直径为 4 μm 的三维空心羟基磷灰石微球。扫描电子显微镜 (SEM) 和透射电子显微镜 (TEM) 研究揭示了柠檬酸盐/钙 (Cit/Ca) 比率在调节颗粒形态方面的重要性。结果表明，通过调节试剂浓度，可以将微球的表面形态从纳米片设计为纳米棒。X 射线衍射 (XRD) 和傅里叶变换红外 (FTIR) 光谱证实了合成粉末的结晶度和纯度。Brunauer-Emmett-Teller (BET) 表明，随着从具有纳米片的羟基磷灰石微球 (HAMNS) 变为表面具有纳米棒 (HAMNR) 的羟基磷灰石微球，比表面积增加。提出了热力学和动力学理论来解释观察到的表面形态和晶体生长的变化。