Biogenic Hydroxyapatite/ZnO Heterostructures: Photocatalytic Degradation of Dye Mixtures and Antibacterial Activity

In this work, biogenic HAp/ZnO heterostructures were synthesized by a microwave-assisted hydrothermal method using marine shell waste as the calcium precursor for hydroxyapatite production. ZnO was incorporated at 20, 30, 40, and 50 wt %. XRD and FTIR confirmed the coexistence of HAp and ZnO phases, while UV–Vis/DRS indicated optical absorption suitable for photocatalytic activation. FE-SEM and TEM/HRTEM analyses revealed morphological changes and confirmed the nanostructured character of the heterostructures. BET showed a significant increase in the specific surface area of H40ZN, and PL and EIS analyses indicated improved charge separation and reduced electron–hole recombination. Photocatalytic activity was evaluated by degrading crystal violet, malachite green, and their mixture under UV–C irradiation, with the best sample also tested under solar light. H40ZN exhibited the highest performance, reaching 71% degradation for CV, 74% for MG, and 83% for MIX under solar irradiation. Reusability tests showed only a slight efficiency decrease after four cycles, with no structural changes detected by XRD. Scavenger tests and EPR analyses indicated that •O2–, h+, and •OH were the main reactive species. The heterostructures also showed antibacterial activity against Staphylococcus aureus. These results demonstrate the potential of biogenic HAp/ZnO heterostructures for environmental remediation and bacterial control.