The photocatalytic degradation of aqueous solutions of cephalexin (CEP) and rifampicin (RIF) antibiotics using strontium titanate nanoparticles (STO NPs) as a photocatalyst activated by 365-nm UV light was investigated. Experimental results demonstrated that the photocatalytic degradation of both antibiotics was efficient and influenced by operational parameters, including photocatalyst dosage, irradiation time, solution pH, initial antibiotic concentration, and the presence of hydrogen peroxide. The kinetics, rate limiting steps, and thermodynamic parameters of the degradation processes were analyzed by fitting the experimental data to the modified Langmuir–Hinshelwood, Weber–Morris intraparticle diffusion, Arrhenius, and Eyring models. The photocatalytic degradation rate constants were estimated to be 0.049 ± 0.005 and 0.012 ± 0.002 min‒1 for CEP and 0.301 ± 0.015 and 0.016 ± 0.002 min‒1 for RIF. The rate limiting steps involved a combination of external mass transfer and intraparticle diffusion onto the surfaces of STO NPs. Thermodynamic analysis indicated that the overall degradation reactions were spontaneous, endothermic, and accompanied by an increase in the surface entropy of the photocatalyst. Radical scavenging experiments confirmed that the degradation process is governed by oxidation reactions involving O2·‒ and OH· radicals generated on the photocatalyst surfaces. Based on the chemical structures of the detected intermediates and degradation products, plausible degradation pathways were proposed, involving fragmentation through ring opening, hydroxylation, deamination, decarboxylation, dealkylation, and demethylation. The environmental safety of the degradation products was preliminarily assessed through antibacterial screening tests, which confirmed a reduction in antibacterial activity compared to the parent antibiotics, suggesting a reduced ecological risk. © Akadémiai Kiadó Zrt 2025.