<p>The adoption of environmentally friendly technologies for treating textile dye-containing wastewater through advanced oxidation processes is critical for maintaining ecological and environmental health. Calcium peroxide (CaO₂) has emerged as a powerful oxidant with significant oxidizing potential. This study evaluates the performance of Direct-CaO₂, UV/CaO₂, Fe²⁺/CaO₂, and UV/ Fe²⁺/CaO₂ processes for the decolorization of RB222 in an aqueous solution. Optimal conditions were identified, with the CaO₂ dosage being the most influential independent variable. At a pH of 10 and a CaO₂ dosage of 1.0&#xa0;g, the Direct-CaO₂ and UV/CaO₂ processes achieved dye removal efficiencies of 79.80% and 90.40%, respectively, with removal rates of 0.665&#xa0;mg/L/min and 0.755&#xa0;mg/L/min for 100&#xa0;mg/L RB222. The Fe²⁺/CaO₂ and UV/Fe²⁺/CaO₂ processes required a pH of 2.50 and a Fe²⁺/CaO₂ ratio of 0.40 for optimum performance. Under these conditions, Fe²⁺/CaO₂ achieved complete RB222 removal in 40&#xa0;min, corresponding to a removal rate of 2.50&#xa0;mg/L/min with 0.125&#xa0;g CaO₂. UV/Fe²⁺/CaO₂ achieved the same in just 10&#xa0;min, with a removal rate of 10&#xa0;mg/L/min using 0.0625&#xa0;g CaO₂.The presence of Cl⁻ anions adversely affected the efficiency of RB222 decolorization. Thermodynamic analysis confirmed that the decolorization reactions in all processes are endothermic in nature. The findings highlight the high efficiency of CaO₂-based processes for RB222 removal, offering a promising approach for the treatment of dye-contaminated wastewater.</p>