Synthesis of a cleaner potassium hydroxide-activated carbon from baobab seeds hulls and investigation of adsorption mechanisms for diuron: Chemical activation as alternative route for preparation of activated carbon from baobab seeds hulls and adsorption of diuron

Abstract

Lignocellulosic agricultural residues are worldwide used for the production of activated carbons with purpose of eliminate a large range of pollutants such as diuron, a very persistent herbicide found in streams. This work studies the adsorption of diuron in aqueous solution on two different activated carbons, a commercial activated carbon and a prepared one. Activated carbon has been produced from seed hulls of baobab (Andansonia digitata), as a valorization pathway for this waste. Precursors have been impregnated with potassium hydroxide and then carbonized under nitrogen flow. The porous structure of the carbon has been determined by methylen blue adsorption, iodine adsorption and nitrogen adsorption-desorption. The BET surface areas of the produced carbon was 1086 m2·g‒1 with an iodine and methylene blue values of 1854.2 mg·g−1 and 26.66 mg·g−1 respectively. Batch removal kinetics of diuron has been studied at 5, 13 and 20 ppm initial concentrations on the two activated carbons in a reconstituate solution. The results showed that adsorption of diuron can be modelled by Langmuir isotherm with a maximal adsorption capacity of 65.7 mg·g−1 for baobab carbon and 151.8 mg·g−1 for commercial activated carbon at 120 min equilibrium time. Speudo-second order reaction fits well with data collected during adsorption of diuron on carbons studied. Thus, Baobab seed hulls can be considered as good precursors for preparation of activated carbon with high specific surface area.