<![CDATA[This study aims to synthesize and characterize a limestone-based ZnO-hydroxyapatite (HA/ZnO) composite and evaluate its performance in the photocatalytic degradation of Rhodamine B under UV irradiation. Hydroxyapatite was synthesized by reacting calcined CaO from limestone with orthophosphoric acid and subsequently combined with ZnO via a co-precipitation–hydrothermal method. The materials were characterized using X-ray Diffraction (XRD) and Fourier Transform Infra Red (FTIR) to determine their crystal structure and functional groups. The HA/ZnO composite exhibited the smallest crystallite size (14.86 nm), indicating enhanced surface area and strong interfacial interaction. Photodegradation tests revealed optimal conditions at pH of 9, Rhodamine B concentration of 20 mg/L, and catalyst dosage of 1.5 g, achieving a maximum degradation efficiency of 99.81%. Toxicity assessment using a corn seed germination test showed a significant increase in germination rate from 16% (untreated) to 92% (after photocatalytic treatment). These findings suggest that the limestone-derived HA/ZnO composite is a promising, environmentally friendly, and efficient photocatalyst for textile dye wastewater treatment. Copyright © 2025 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).]]>
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