<p>Water scarcity is emerging as one of the most critical global issues of the twenty-first century, driven by rapid population growth, climate change, pollution, and mismanagement of resources. In this study, a cost-effective, non-toxic, and magnetically recoverable Fe₃O₄/activated carbon (AC)/ZnS nanocomposite was successfully synthesized via a hydrothermal method for the treatment of dye-contaminated water and wastewater. The as-prepared nanocomposite was comprehensively characterized using XRD, VSM, FT-IR, Zeta potential, BET, PL, FESEM, EDS, elemental mapping, and TEM analyses. VSM results demonstrated that the Fe₃O₄/AC/ZnS nanocomposite exhibited a saturation magnetization of about 32 emu/g, confirming its superparamagnetic nature and enabling easy separation using an external magnetic field. Zeta potential analysis revealed a surface charge of approximately − 8.9 mV, indicating a negatively charged surface that may facilitate interaction with dye molecules. Catalytic experiments showed that the Fe₃O₄/AC/ZnS nanocomposite achieved complete degradation of methylene blue within 6 min. Moreover, the catalyst maintained high performance over a wide pH range, demonstrating effective dye removal under acidic, neutral, and alkaline conditions. In addition to MB, the prepared nanocomposite displayed excellent photocatalytic activity toward other organic dyes, including methyl orange and crystal violet, achieving 89% and 86% degradation, respectively, within 6 min. Overall, the obtained results highlight the Fe₃O₄/AC/ZnS nanocomposite as a promising, reusable, and environmentally benign photocatalyst for rapid purification of dye-polluted water.</p>