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Abstract This work is devoted to the study of the adsorption properties of a food waste "coffee grounds" activated carbon (AC) for the uptake of acid dye orange G (OG). ACs were previously prepared from chemical activation of pyrolysed coffee ground by KOH (1 g of KOH/1 g of biomass). The AC characterization shows that it has essentially microporous structure with a specific surface area of 1455 m2 g−1 and acid-basic functional surface character. Many aspects of the kinetics and isotherms for the dye removal indicate that the equilibriums were achieved in 3 h. Three models are attempted to fit the kinetic data i.e. pseudo-first order, pseudo-second order and intra-particle diffusion models. An evaluation of the correlation coefficients (R2) and adsorbed amount per mass unit of adsorbent (Q e) at equilibrium indicates that orange G adsorption on AC is well fitted by the pseudo-second order model (R2 = 0.998). The experimental adsorption equilibrium data are described by the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Redlich-Peterson isotherm models. The Langmuir and Redlich-Peterson models are judged to be the closest for the description of the experimental data based on the coefficients (R2 ≈ 0.999). Non-linear regression was also used to evaluate the isotherms models. The thermal effect on the adsorption is studied and the thermodynamic parameters: enthalpy (∆H°), entropy (∆S°) and free energy (∆G°) are determined. The adsorption of orange G is thermodynamically spontaneous (∆G° < 0) and endothermic (∆H° > 0). Highlights • Prepared activated carbon were used as adsorbent for the removal of orange G from aqueous solution. • Adsorption kinetics and equilibrium were studied using different models. • The adsorption were found to be spontaneous and endothermic in nature. [ABSTRACT FROM AUTHOR]

The objective of this work is to examine the effectiveness of low cost material as adsorbent for the removal of free amino acid l-tryptophan from aqueous solutions in order to avoid the formation of undesirable disinfection by-products, trihalomethanes and iodinated trihalomethanes, during the water chlorination. The adsorbent was prepared from date pits and activated with H 3 PO 4 (DPH). The textural properties of DPH were characterized by FT-IR spectroscopy, SEM analysis and N 2 adsorption-desorption isotherms. DPH possesses a large specific surface area (1040 m2 g−1) and a high total pore volume (1.089 cm3 g−1). Batch adsorption experiments were investigated to examine the effects of contact time, initial concentration, temperature, ionic strength and pH on the l-tryptophan adsorption. Among three isotherm models, the Langmuir model gave a perfect fit for the experimental data of l-tryptophan with a maximum monolayer adsorption capacity of 144.93 mg g−1 on DPH. The functional groups on the DPH surface can attract the l-tryptophan via π–π hydrophobic interactions, dipole-dipole hydrogen bonding and n–π interactions. The thermodynamic parameters suggested that the l-tryptophan adsorption is spontaneous and exothermic with a physisorption process. After four cycles, the regeneration efficiency of the used DPH was about 59.9%. Image 1 • Low cost activated carbon from date pits for the adsorption of l-tryptophan. • The initial pH has a greater effect on the removal of free amino acid l-tryptophan. • The maximum adsorption capacity was achieved 144.93 mg g−1 over DPH. • The thermodynamic analysis of l-tryptophan adsorption exhibits a physisorption. [ABSTRACT FROM AUTHOR]