Investigation of the effects of quercetin on the structure and properties of zinc-modified hydroxyapatites

In this study, hydroxyapatite (HAp) samples, co-doped with 0.44 at.% of zinc and different amount of quercetin (Zn/Que-HAp), were synthesised using a wet-chemical method and calcined at 900°C. XRD shows HAp as the primary phase with minor β-TCP. Compared to the Zn-doped sample without quercetin (Q1), quercetin co-doping induces clear structural changes (shifts of lattice parameters a from −0.0017 to +0.0006 nm and c from −0.0026 to −0.0005 nm), accompanied by changes in crystallinity (from −3.6% to +2.5%) and crystallite size (from −3.5 to +0.6 nm), evidencing a distinct co-doping effect. DTA/TGA reveal reduced total mass loss for the Que-containing compositions relative to the Zn-doped sample, indicating enhanced thermal stability of the co-doped lattice. SEM reveals granular morphologies with interconnected porosity, while EDX yields (Ca+Zn)/P ratios greater than 1.67, consistent with Ca-sufficient apatite and modified defect chemistry. DFT calculations resolve the site-specific effects of Zn substitution and predict a preference for perturbation at Ca2 sites. The electronic density of states retains a wide-gap, insulating character, with localised states sensitive to the dopant configuration. By correlating experiment and theory, we demonstrate that the organic-inorganic co-dopant pair offers an effective means to tune lattice metrics, phase balance, and thermal response without compromising the intrinsic insulating nature of HAp.