The large-scale production of various synthetic dyes has contributed significantly to the release of large volumes of wastewater into the environment. It is estimated that approximately 14,000 tons of dyes from the textile industry are released directly into the environment annually, significantly compromising water quality [1]. The objective of this work was to prepare activated carbons (ACs) from agricultural waste from Mozambique for use in removing methylene blue (MB) dye. These ACs were simultaneously modified by impregnation with nitrogen-containing chemicals, such as urea, to increase their porosity and surface area. Three natural precursors were used in the preparation of the urea-modified ACs, with KOH as the activating agent in a 1:2:1 ratio (precursor–activating agent–urea). Kinetic studies, concerning methylene blue (MB) removal, from the aqueous phase, were performed at 298 K and pH 6 for 168 hours. Adsorption isotherms were obtained using 10 mg of the modified AC, in 25 mL of MB solution, with concentrations ranging from 0 to 250 mg L ^-1. The mixtures were stirred at 20 rpm and 298 K, for 24 hours. In general, ACs are efficient in removing MB dye. Modified ACs with the precursor–KOH–urea ratio of 1:2:1 presents better performance, while the ratio 1:2:0.5 resulted in lower adsorption capacity.

[1] Rendón-Castrillón, L., Ramírez-Carmona, M., Ocampo-López, C., González-López, F., Cuartas-Uribe, B., & Mendoza-Roca, J. A. (2023). Treatment of water from the textile industry contaminated with indigo dye: A hybrid approach combining bioremediation and nanofiltration for sustainable reuse. Case Studies in Chemical and Environmental Engineering, 8, 100498. doi.org/10.1016/j.cscee.2023.100498