<p>This study aimed to assess the adsorption properties of activated carbon derived from formaldehyde resin to remove cationic dye, specifically methylene blue. The influence of different activating agents on the activated carbon’s structural characteristics and adsorption performance was systematically investigated. Various characterization techniques were employed to analyze the textural properties, surface morphology, and functional groups on the carbon surface. The specific surface area of the activated carbon ranged from 26.4 to 939.6 m²/g. Batch adsorption experiments were performed under different dye concentrations, contact times, and temperatures. The findings revealed that KOH activation produced activated carbon with an exceptional maximum adsorption capacity of 444&#xa0;mg/g for methylene blue. The adsorption behavior strongly complies with the Langmuir isotherm and pseudo-second-order kinetic models. Furthermore, both intraparticle and film diffusion played significant roles in the adsorption mechanism. The process was determined to be endothermic and spontaneous at elevated temperatures. These results highlight the potential of formaldehyde resin-based activated carbon as a promising waste-derived adsorbent for pollution mitigation, reinforcing its role in sustainable wastewater treatment strategies. This study contributes to SDG 6 (Clean Water and Sanitation) by providing an effective solution for removing hazardous dyes from wastewater, ensuring cleaner water resources. Additionally, using waste-derived materials for activated carbon production aligns with SDG 12 (Responsible Consumption and Production) by promoting resource efficiency and minimizing environmental waste. Furthermore, sustainable adsorption techniques support SDG 13 (Climate Action) by reducing chemical pollution and advancing eco-friendly approaches to industrial wastewater treatment.</p>