The increase in industrial production and the use of synthetic dyes has become one of the main sources of water pollution in recent decades. The textile industry, in particular, is responsible for discharging large volumes of wastewater with a high pollutant load, with estimates indicating that around 14,000 tons of dyes are released annually into the environment without proper treatment. These compounds exhibit high chemical stability and resistance to biodegradation, allowing them to accumulate in aquatic organisms and affect the entire food chain. Furthermore, they alter the physicochemical properties of water, such as pH and turbidity, and may contain toxic, mutagenic, or carcinogenic substances.

In this context, the development of sustainable wastewater treatment technologies has become essential to minimize environmental risks and preserve water resources. This study aimed to produce activated carbons (ACs) from Mozambican agricultural waste through chemical activation with potassium hydroxide (KOH), evaluating their efficiency in removing crystal violet (CV) dye from aqueous solutions. To optimize their adsorptive properties, ACs were simultaneously activated with KOH and a nitrogenous compound (urea) to increase porosity and specific surface area.

Three natural precursors were used, with a ratio of 1:2:1 (precursor: activating agent: urea). Kinetic adsorption tests were carried out at 298 K and pH 6 for 168 hours. Adsorption isotherms were determined using 10 mg of modified ACs added to 25 mL of CV solution (0–250 mg/L) under constant stirring at 20 rpm for 24 hours, ensuring equilibrium between the liquid and solid phases. The results showed high efficiency in removing the dye, with the sample prepared at a 1:2:1 ratio displaying the best adsorptive performance, a more porous structure, and a larger surface area. In contrast, the 1:2:0.5 ratio presented a lower adsorption capacity, likely due to reduced incorporation of nitrogen functional groups in the material matrix.