Shape-controlled synthesis of F-substituted hydroxyapatite microcrystals in the presence of Na2EDTA and citric acid

We present a facile strategy for the shape-controlled synthesis of F-substituted hydroxyapatite (FHAp) microcrystals based upon using a combination of Na2EDTA and citric acid (CA). Novel, well-defined FHAp microcrystals of various shapes, such as hexagonal disks with predominant (0 0 0 1) faces, hexagonal shuttles, hexagonal prisms, icosahedrons, and hexagonal microrods with tunable aspect ratios, were fabricated. In particular, FHAp hollow microcrystals with tunable shapes were fabricated directly without using any additional template. The central features of our approach are the use of both Na2EDTA and CA as two distinct chelating reagents and the use of substitution ions (F−) itself as a growth inhibitor for the FHAp crystals. F− ions were found to play a critical role in the formation of hexagonally shaped FHAp microcrystals, and in the one-pot formation of hollow microcrystals, which relies on the addition order of F− ions in the synthesis.

Graphical abstractHigh-quality F-substituted hydroxyapatite solid and hollow microcrystals with various novel shapes were fabricated via a facile hydrothermal method based on the use of Na2EDTA, citric acid, and doping ions (F−) itself.Figure optionsDownload full-size imageDownload high-quality image (84 K)Download as PowerPoint slideResearch highlights► A combination of Na2EDTA and citric acid (CA) yields a series of high-quality FHAp microcrystals with tunable shapes. ► The double-chelating-agent system enables an investigation of the effect of individual calcium chelating agents on the growth of FHAp microcrystals. ► The double-chelating-agent system is capable of making FHAp hollow microcrystals with tunable shapes. ► F− ions were found to play multiple roles in shaping FHAp microcrystals.