Zinc oxide nanoparticles (ZnO NPs) were synthesized using a simple and eco-friendly precipitation method, employing a capping agent derived from chia seeds (Salvia hispanica). X-ray diffraction (XRD) analysis confirmed the formation of ZnO with a hexagonal crystal structure and an average crystallite size of less than 30 nm. Scanning electron microscopy (SEM) revealed distinct quasi-spherical and nanorod-like morphologies, while energy-dispersive X-ray spectroscopy (EDX) verified the presence of zinc and oxygen. Diffuse reflectance spectroscopy (DRS) indicated significant activity in the UV region, with the nanoparticles exhibiting a band gap of 3.25 eV. The photocatalytic efficiency of the synthesized ZnO NPs was evaluated through their ability to degrade diclofenac sodium (DCF) and para-nitrophenol (4-nitrophenol, PNP) under UV-LED irradiation, achieving pollutant removal rates exceeding 98%. The degradation mechanism is clarified by a detailed characterization of the reaction intermediates. These findings highlight the potential of ZnO NPs synthesized from chia seed extract for effective environmental remediation of pharmaceutical and organic pollutants.