Single-step and two-step syntheses of magnetic carbons from coffee residue: elimination of sulfamethazine by adsorption

The magnetization process of activated carbons prepared from coffee residue was performed according to two protocols: The first one involved a chemical impregnation with a mixture of two salts: FeSO4·7H2O and FeCl3, followed by a treatment with NaOH (2 M). The second procedure required an impregnation with both salts mentioned above, taken alone or in mixture, followed by a pyrolysis at 600 °C during an hour. A commercial activated carbon treated in the same way was used as reference. Physicochemical analysis of all materials revealed that activated carbon treated with iron sulfate (FeSO4·7H2O) alone contains magnetite; activated carbon prepared with iron chloride (FeCl3) alone contains magnetite, while activated carbon prepared with a combination of both salts contains magnetite and maghemite. Adsorption tests for the sulfamethazine removal from the aqueous phase were carried out at pH = 6 and pH = 4. Magnetized carbon prepared with an impregnation ratio of 75% iron sulfate followed by pyrolysis gave the most effective performance with an elimination efficiency of 64.12% of sulfamethazine.