Pure CuO and CuO/SrSO4 nanocomposites were synthesized via the hydrothermal method to explore their catalytic efficacy in degrading methylene blue (MB). CuSO4\ub75H2O, NaOH, and SrCl2\ub76H2O were used as primary reagents. XRD characterization unveiled the monoclinic structure (C2/c) of pure CuO NPs, exhibiting well-defined crystallinity with crystallite sizes ranging from 9.64 to 26.08 nm. Notably, samples with Sr concentrations exceeding 2wt% exhibited a secondary SrSO4 phase with an orthorhombic structure (Pnma). Infrared and Raman spectroscopy confirmed Cu-O, S-O, and Sr-O bond vibrations, validating CuO and SrSO4 synthesis. SEM micrographs depicted irregular platelet-like morphology with a surface area of up to 0.061 μm2 and nanometric thickness for pure CuO NPs, while this morphology varied for CuO/SrSO4 nanocomposites. BET analysis revealed a relatively large specific surface area (9.04 to 15.12 m2 /g), potentially advantageous for catalytic activity. Catalytic degradation of MB in aqueous solution by pure CuO NPs exhibited limited efficiency (19.77% in 60 min), markedly enhanced to 100% in 40 min with the addition of H2O2. Despite H2O2 presence, CuO/SrSO4 nanocomposites showed lower MB degradation efficiency due to sulfate SO4 2- ion poisoning. Monitoring the formation of SrSO4 phase is a synthesis strategy to adjust the poisoning effect by sulfate ions. The sample with a Sr concentration of 6 wt% demonstrated the highest degradation rate (83.78% in 40 min), attributed to its larger specific surface area. Furthermore, synthesized materials displayed satisfactory catalytic stability upon recycling for MB degradation
