Hydroxyapatite as a bifunctional nanocatalyst for solventless Henry reaction: a demonstration of morphology-dependent catalysis

In the current investigation, HA nanorods and nanoplates with a high surface area have been synthesized using the chemical precipitation method via alcogel formation employing l-arginine as a crystal growth modifier. The prepared HA particles have been characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), High resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray analysis (EDXA) and nitrogen adsorption-desorption analysis. A representative morphology-dependent catalysis of the synthesized HA particles has been attempted using the Henry reaction under solventless conditions. The HA nanorods have been found to catalyze the Henry reaction with 100% conversion and 84.1% yield while the nanoplates were found to be catalytically inactive. A plausible mechanism supported by DFT studies has been proposed for the observed morphology-dependent catalysis of Henry reaction signifying the importance of surface Ca2+ ions in lowering the LUMO levels of the substrate besides assembling the reactants to proximity.

Automated summary

In this study, HA nanorods and nanoplates with high surface area were synthesized using the chemical precipitation method. The synthesized particles were characterized using various techniques. It was found that the HA nanorods exhibited excellent catalytic activity, while the nanoplates were catalytically inactive. The importance of surface Ca2+ ions in the catalysis was also discussed.