Novel green synthesis of hydroxyapatite uniform nanorods via microwave-hydrothermal route using licorice root extract as template

Hydroxyapatite (HAp) nanorods were synthesized in the presence of licorice root extract (LE) as a green organic template (or biotemplate) at 125 degrees C through a microwave-hydrothermal synthesis route. The products were characterized for shape, size, crystallinity, and phase purity. For the sample prepared in the presence of LE (denoted as HAp_L, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed a uniform hexagonal phase nanorod product with average dimensions of 105 nm length and 25 nm width. The control sample, prepared in the absence of LE (denoted as HAp_W), showed less crystallinity and poorer morphology. Thermogravimetric analyses (TGA) and differential thermal analyses (DTA) indicated minor moisture contents in both samples. Fourier transform infrared spectroscopy (FT-IR) indicated carbonate-free samples. Raman spectroscopy confirmed the phase purity of the products. Energy-dispersive X-ray spectroscopy (EDX) analysis showed that product HAp_L has a Ca/P atomic ratio close to the theoretical value of HAp. Compared to HAp_W, zeta-potential measurements have shown that suspensions of sample HAp_L were more stable in different aqueous salt solutions. Particle size distribution analysis (PSA) showed a narrow size distribution for sample HAp_L with an average particle size of 105 nm which is advantageous over the apparently multi-disperse sample HAp_W. Nitrogen adsorption/desorption isotherms for both samples showed type III trends, having H-3 hysteresis loops in the P/P-o range between 0.9 and 1.