Methyl orange and tartrazine yellow adsorption on activated carbon prepared from boiler residue: Kinetics, isotherms, thermodynamics studies and material characterization

Activated carbon (AC) obtained from boiler residue of sugarcane mills and prepared by NaOH activation in proportions equal to 1:1 and 1:3 (AC:NaOH) were studied as alternative adsorbent for removal of the Methyl Orange (MO) and Tartrazine Yellow (TY) dyes from aqueous media using electrochemical detection by square wave voltammetry (SWV). The materials were characterized by FT-IR, SEM, TGA analysis and textural data, including surface area, pore volume and pore diameter from N-2 adsorption isotherms in which was found that all materials are essentially mesoporous with surface area in order of 653.79 m(2) g(-1), 355.03 m(2) g(-1) and 1072.51 m(2) g(-1) for commercial activated carbon (COMAC), 1:1 AC:NaOH and 1:3 AC:NaOH, respectively. The kinetic and adsorption isotherm studies were performed for both dyes in the following materials: COMAC, 1:1 and 1:3 AC:NaOH. For MO dye, experimental data showed good fit to the Langmuir model with adsorptive capacities equal to 161.8123, 36.9004, and 77.1010 mg g(-1) onto 1:3 AC:NaOH, 1:1 AC:NaOH and for commercially-activated carbon (COMAC), respectively, while for TY experimental data also showed good fit to the Langmuir model with adsorptive capacities equal to 106.3830, 44.9438, and 67.7966 mg g(-1) onto 1:3 AC:NaOH, 1:1 AC:NaOH and COMAC, respectively. The kinetic studies shown that experimental data for both dyes in the three materials follow pseudo-second-order model, revealing chemical nature of adsorption process. The thermodynamic parameters such as change in free energy, enthalpy and entropy were determined and negative values of free energy indicated that the process of removal MO and TY was spontaneous process. The pH study also was carried out by batch adsorption experiments employing 10 mg of adsorbents and 10 mL of dyes solution (150.0 mg L-1) in Britton-Robinson buffer and all measurements conducted by SWV. Maximum adsorption of dyes was achieved at pH 5.