Search

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]

• Activated carbons were synthesized from coffee waste by chemical activation method. • The activated carbons were successfully tested for amoxicillin adsorption. • The adsorption capacity of our adsorbent was compared to a commercial activated carbon. • The reusability of the prepared activated carbons has been tested at three cycles by a chemical method. • Adsorption was found to be thermodynamically spontaneous and endothermic. In the present study, we describe the synthesis of coffee waste activated carbon (SAC) as potential material for the amoxicillin (AMOX) removal from aqueous solution. The conditions for synthesizing SAC were an impregnation weight ratio of raw biomass to KOH equal to 1:2 followed by activation at 800 °C for 1 h. The FTIR analysis and Boehm titration showed that SAC has 1.7627 and 1.5414 m eq / g, respectively for acidic groups and of basic groups. The operating experimental parameters that govern the adsorption namely the temperature (288–318.16 K), intial pH (2.0–12.0), initial AMOX concentration C o (50–450 mg/L) and ionic strength were optimized. The adsorption isotherms were analyzed by various models. The experimental data were suitably matched to the Sips and Langmuir equations (R2 = 0.998). A Langmuir sorption capacity of 370 mg g−1 was determined, a value higher than that obtained on commercial activated carbon (CAC) employed for similarity purposes. The nature of the electrolyte was also examined with non-buffered AMOX solutions at different NaCl concentrations. The experimental results showed that AMOX adsorption is favored above pH 10. Otherwise, the absorption capacity is not influenced by the ionic strength of the electrolyte. The AMOX adsorption onto SAC was found to be exothermic and spontaneous under the operating parameters. The reusability of the adsorbent was tested by using appropriate chemical solvents and the results showed also that the sorption capacity decreases from 370 mg/g to 250 mg/g after four consecutive cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, new activated carbons (ACs) from coffee grounds were synthesized using different impregnation ratios of KOH. The obtained materials were characterized by the Fourier Transform Infrared Spectroscopy (FTIR), Boehm titration, N 2 adsorption-desorption isotherms and Scanning Electron Microscopy (SEM). The results of the FTIR and Boehm titrations indicate the presence of many functional groups on the ACs surface. Basic groups determined from the Boehm titration show a strong dependence on the impregnation ratio. N 2 adsorption-desorption isotherms show an augmentation of the adsorbed volume for high impregnation ratios. This is due to the well-developed microporosity which increases with increasing the impregnation ratio. The maximal specific surface area obtained from the BET measurement was found to be 1778 m 2 g −1 for an impregnation ratio of 36 mmol of KOH/g of precursor. The prepared ACs were tested for their removal efficiency for the phenol (Ph) and methylene blue (MB) molecules. Batch adsorption tests were performed and the effects of contact time, initial concentration and temperature were investigated. The adsorption kinetic parameters were determined by fitting with the pseudo-first and pseudo-second order models to the experimental data. An evaluation of both the correlation coefficients (R 2 ) and the adsorbed amount per unit mass of adsorbent (Q e ) at equilibrium indicates that Ph and MB adsorption by ACs are satisfactorily described by the pseudo-second order model. The experimental adsorption equilibrium data were fitted to the Langmuir and Freundlich models. The effect of temperature on the adsorption was studied and the thermodynamic parameters: enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were determined for each molecule. The adsorption for Ph and MB was found to be thermodynamically spontaneous (ΔG° < 0), although it was exothermic (ΔH° < 0) for Ph and endothermic (ΔH° > 0) for MB. [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]