<p>This study investigates the performance of pH-responsive microgel@nanoceria composites under harsh environmental conditions. Nanoceria (CeO₂) was selected for its superior biocompatibility, thermal stability, resistance to sintering, and unique redox properties, which enable it to switch between Ce⁴⁺ and Ce³⁺ oxidation states. These characteristics, along with its cost-effectiveness, make nanoceria highly suitable for catalytic reduction in coarse environments compared to other metal oxide nanoparticles. Polymeric microgels were synthesized through free radical emulsion polymerization using monomers: styrene, dimethyl acrylamide, 2-acrylamido-2-methyl-1-propane sulfonic acid, and 2-hydroxyethyl methacrylate (HEMA) monomer as a crosslinker. Nanoceria was successfully incorporated into polymeric microgels through hydrothermal methods to enhance catalytic performance. The synthesized microgel and microgel@nanoceria composites were characterized using several techniques, including Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The catalytic efficiency of the microgel@nanoceria composite was evaluated using ultraviolet–visible (UV–Vis) spectroscopy to monitor the reduction of methylene blue (MB) organic dye in all ranges of pH, i.e., 4, 7, and 11. The rate of dye reduction, analyzed as a function of concentration versus time, indicated the composite's ability to efficiently reduce organic dye pollutants in water, demonstrating potential for environmental remediation applications. The maximum K_app observed for the catalytic reduction reaction was determined to be 0.78 × 10^–2&#xa0;s^–1, achieved using the MGC2 catalyst at a dosage of 750 µL at pH 11.</p> Graphical abstract <p></p>