The production of activated carbon was carried out by impregnating the sargassum with a 85% H3PO4 solution in a mass ratio of 1/3 sargassum/ H3PO4, with an impregnation time of 15 hours. The production of activated carbon from sargassum was carried out in a pyrolytic muffle furnace with a controlled nitrogen atmosphere. Sargassum samples were collected on the beaches of the Dominican Republic. Sargassum activated carbon has a specific surface area of 754 m2/g and the 2,4-D adsorption was pH dependent.