Synthesis of activated carbons from water hyacinth biomass and its application as adsorbents in water pollution control

The water hyacinth biomass was used for the synthesis of activated carbons in a process of chemical activation with ZnCl2, followed by controlled pyrolysis. The applied impregnation weight ratios ZnCl2 and dry hyacinth biomass were in the range of 0.5-3.5. The carbonization was conducted at four different temperatures (400-700 degrees C) under an inert atmosphere. The highest yield of activated carbon was obtained for the impregnation ratio of 0.5 and carbonization temperature of 400 degrees C. The samples were characterized using elemental analysis, adsorption-desorption isotherms of nitrogen and SEM analysis. The activated carbon obtained with an impregnation ratio 2.0 and carbonization temperature of 500 degrees C (2.0AC500) showed the highest values of specific surface area and total pore volume of 1317 m2 g-1 and 0.697 cm3 g-1, respectively. The adsorption of glyphosate, pesticide with a strong negative environmental impact, was a fast process, with the equilibrium time of 120 min. The adsorption isotherms were fitted with Langmuir and Freundlich model. The Langmuir adsorption capacity of qmax = 240.8 mg g-1 for 2.0AC500 classified the selected adsorbent as a very efficient one. The tested adsorption process followed the kinetics of the pseudo-second-order model.