ABSTRACT:The removal of tartrazine dye (A5) onto activated carbon produced from pecan nut shells (Carya illinoinensis) obtained under specific conditions and one step simultaneous carbonization/activation process was carried out in this work. First order, pseudo-second order and Elovich adsorption kinetic models were applied for the kinetic studies. The experimental equilibrium data were analysed using the isotherms of Langmuir, Freundlich and Temkin. Batch adsorption studies were performed for the removal of tartrazine azoic dye from aqueous solutions by two materials obtained at 600 °C (NAC-600) and 857 °C (NAC-857) and another two materials prepared at the same temperatures but simultaneously activated with steam (NAC-600-H 2 O and NAC-857-H 2 O). The zero point charge was between pH values of 9 to 11 and the maximum adsorption occurred when activated carbons were steam activated and were 4.47 and 13.66 mg g Ϫ1 for NAC-600-H 2 O and NAC-857-H 2 O respectively. The results clearly showed that the adsorption of A5 onto carbonaceous materials from nut shells (NAC) best fit to the pseudo secondorder model, and the rate constants were in the range from 489.3 to 509.4 g mg. Maximum uptake capacity of tartrazine was comparable to values encountered in the literature for other carbonaceous materials. The results show that under specific activation conditions, Mexican pecan nut shells, as agricultural residues, present high potential as a raw material to produce alternative adsorbent materials for dyes removal from aqueous solutions.

a b s t r a c tWater pollution by emerging pollutants, such as antibiotics like tetracycline (TC), is a worldwide environmental problem. To eliminate TC from water, the present study used an advanced water treatment technology (sorption) that has shown a very good relation between cost and effectiveness. To develop a sustainable and cheap activated carbon with acceptable sorption capacity for TC removal, it was proved a friendly environmental activation by using an agricultural waste like alternative precursor: pecan nut shells and water-like activating agent. Four different materials were used for the sorption test: pecan nut shell carbonised and water activated (NAC-850), commercial activated carbon as reference (GAC), and both materials were modified with citric acid (NAC-850-mod and GAC-mod). All the materials were characterised by S BET , scanning electron microscopy, energy-dispersive X-ray and Fourier transform infrared. It was calculated that the sorption equilibrium time for the TC, kinetic parameters for pseudo-first-order, pseudo-second-order and Elovich models; the sorption isotherms for Langmuir, Freundlich and Temkin and thermodynamic parameters (ΔH, ΔS, ΔG and Ea) also were applied. It evaluated the effect of pH and temperature and the presence of competitive ions in the aqueous media. The prepared activated carbons that showed the best sorption capacity were those that followed a citric acid activation. The kinetics experiments fitted to pseudo-second-order equation and to isotherm Freundlich model. The efficiency to remove the TC increased with the modification of the surface with citric acid between 5% and 11%. The activation/modification method applied is simple and economical and improves the TC sorption capacity that is equivalent to the removal efficiencies of commercial activated carbons.