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Title	Adsorption of phenol, 4-chlorophenol and 4-nitrophenol from aqueous solution by activated carbon prepared from Eucalyptus seed: Kinetics, equilibrium and thermodynamics
Paper ID	L3OW5
Author(s)	Nelson Giovanny Rincon-Silva, Juan C. Moreno-Pirajan, Liliana Giraldo
Abstract	Activated carbons were prepared from lignocellulosic waste material (shell of Eucalyptus globulus), by chemical activation by impregnation with sodium hydroxide solutions at different concentrations (10, 25, 40 and 60 % w/V), followed a process of carbonization was performed and finally the samples were washed until constant pH. For the characterization of samples different techniques were used; The apparent surface area and micropore volume using nitrogen physisorption was evaluated, the samples increased surface area provided were low activated NaOH concentrations which presents values of area of 765 and 654 m2 g-1 and also have greater micropore volume content with 1.690 and 1.883 cm3 g-1. The surface chemistry of the activated carbon was characterized by Boehm method, where it is evident that the values of concentrations of basic groups are high up to 1.805 meq g-1, which was confirmed by the high values in the pHpzc aspects relationship with the nature of the activating agent used. ACs were tested in the adsorption of phenol, 4-nitrophenol and 4-chlorophenol, where remarkably high phenols adsorption capacities were found for the ACs prepared at lower concentrations of NaOH with values up to 500.00 and 357.143 mg g-1 to remove nitrophenol and chlorophenol respectively on NaAC25. Thus, it is observed that the activated carbons at low concentrations of the base, the textural properties prevail on the adsorption capacity, but activated carbon at high concentrations, specifically NaAC60 have priority over surface the chemical properties for adsorption of phenols. Likewise, a kinetic study was carried out, showing that the phenol adsorption data may be correctly adjusted, for all the ACs tested, by an equation corresponding to a pseudo second-order. Freundlich, Langmuir and Tempkin equations were tested for modelling the adsorption isotherms at equilibrium, and it was concluded that Langmuir model fitted adequately the experimental data. Additionally, thermodynamic parameters i.e. Gibbs free energy change (?G°), enthalpy change (?H°) and entropy change (?S°) were also evaluated. The overall adsorption process was exothermic and spontaneous in nature. The values found in the thermodynamic study, confirm that the adsorption process corresponds to a clearly physical process. Finally, the importance of the pH of the solutions of phenols in the adsorption process is evidenced, which is favored at low pH values where the protonated species are present
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