<![CDATA[Textile wastewater containing persistent synthetic dyes poses significant environmental concerns due to the toxicity and low biodegradability of these dyes. This study developed a sustainable ZnO/hydroxyapatite (ZnO/HA) nanocomposite photocatalyst using shallot peel extract and seashell waste as renewable precursors for the visible-light-assisted degradation of Remazol Red RB (RRRB) dye. ZnO nanoparticles were synthesized through a phytochemical-mediated route using aqueous shallot peel extract, while hydroxyapatite was obtained from seashell waste. The resulting ZnO/HA nanocomposite, prepared at a mass ratio of 1:2.5, was characterized using XRD, FTIR, SEM-EDX, and point-of-zero-charge analysis. The effects of catalyst dosage, solution pH, initial dye concentration, and irradiation time on RRRB degradation were investigated under a 50 W visible-light source. XRD analysis confirmed the coexistence of crystalline ZnO and hydroxyapatite phases, with an average crystallite size of 24.80 nm and crystallinity of 80.20%. The highest degradation efficiency obtained in the investigated conditions was 95.85% for 10 mg/L RRRB in 250 mL solution at pH of 6 using 1.0 g of ZnO/HA after 150 min irradiation. Under identical conditions, pristine ZnO achieved 93.40% degradation. The modest improvement indicates that the contribution of hydroxyapatite was primarily associated with surface adsorption, dispersion of ZnO, and increased pollutant–catalyst interaction rather than a demonstrated modification of the ZnO band structure. Because UV–Vis diffuse reflectance and catalyst-reusability measurements were not performed, changes in optical bandgap and long-term catalyst stability could not be experimentally established. Nevertheless, the results demonstrate the feasibility of utilizing two locally available biowaste resources to prepare a ZnO/HA material for visible-light-assisted dye treatment. Copyright © 2026 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).]]>
