NaOH-activated carbon of high surface area produced from guava seeds as a high-efficiency adsorbent for amoxicillin removal: Kinetic, isotherm and thermodynamic studies

We report the preparation and characterization of NaOH-activated carbon of high surface area produced from guava seeds (AC-GS) and its application for amoxicillin (AMX) adsorption. The AC-GS was fully characterized from the N-2 adsorption and desorption isotherms, scanning electron microscopy (SEM), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), Boehm titration and pH(PZC). Additionally, the kinetics, equilibrium and thermodynamic parameters on the adsorption of AMX onto AC-GS were evaluated. The AC-GS showed BET surface area of 2573.6 m(2) g(-1) and microporous features (85%), presenting average pore diameter of 1.96 nm, which are suitable for AMX adsorption. The experimental adsorption data were modelled using several kinetic (pseudo-first order, pseudo-second order and Elovich) and isotherm (Freundlich, Langmuir, Redlich-Peterson and Dubinin-Radushkevich) models, which suggested that the adsorption of AMX onto AC-GS occurs predominantly by chemisorption showing a maximum monolayer adsorption capacity of 570.48 mg g(-1) (pH = 4.0; T= 25 degrees C), which stands out compared to various adsorbents found in literature. Additionally, the thermodynamic parameters revealed the spontaneity of AMX adsorption (Delta G degrees = -1.915 kJ mol(-1) at 298 K) and its endothermic characteristic (Delta H degrees = 21.33 kJ mol(-1)), evidencing the high-efficiency of AC-GS for AMX adsorption and its great potential for organic pollutants removal. (C) 2015 Elsevier B.V. All rights reserved.