The kinetics of phenol adsorption from aqueous solution on activated carbons (ACs) obtained from coffee husk by potassium Hydroxide (KOH) activation at 650 and 750<sup>o</sup>C have been studied in the range of 100-250 mg L<sup>-1</sup> initial phenol concentrations and at the temperatures range of 10 – 40<sup>o</sup>C. Kinetic models for phenol adsorption were evaluated using pseudo-first-order, pseudo-second-order, and Elovich models. The adsorption mechanism was investigated using Reichenberg, Boyd, and Weber and Morris models. The adsorption on coffee husk activated carbon was found to be a fast or speedy process with the adsorption rate, k<sub>2</sub>q<sub>e</sub>, in the range of 0.130 to 0.977 min<sup>-1</sup>. The adsorption process was mainly physical and promoted by chemical sorption and controlled not only by intra-particle diffusion but also by pore diffusion throughout the entire adsorption period.
Activated carbons (ACs) obtained from coffee husk by KOH activation at 650 (ACK-650) and 750 o C (ACK-750), were used as an adsorbent for the adsorption of phenol from aqueous solution. The ACs was characterized by SEM, EDX, BET, and Boehm titration techniques. The experimental equilibrium data of phenol adsorption was analyzed by eight isotherm models, which are four two-parameter equations (Langmuir, Freundlich, Elovich, and Temkin) and four three-parameter equations (Redlich-Peterson, Sips, Radke-Prausnitz, and Tóth). The results reveal that in general, three-parameter isotherms can provide better prediction than two-parameter isotherms. The best fit for ACK-650 sample is Sips isotherm, while for ACK-750 sample is Redlich-Peterson isotherm. Isosteric heat and thermodynamic parameters ΔG o , ΔH o , and ΔS o of the adsorption were determined, and the results showed that the adsorption of phenol was exothermic and physical in nature. A scale-up of a batch system is designed for 2 to 10 L phenol with an initial concentration of 100 mg L -1 .
Activated carbons are prepared from coffee husks by chemical activation with ZnCl2 and are characterized by employing Brunauer, Emmett and Teller, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Boehm titrations. The effects of ZnCl2/coffee husks, activation temperature, and activation time are studied, and the results show that the sample ACZ3-600-2 has a high surface area of 1383 m2 g−1, a high pore volume of 1.6482 cm3 g−1, and numerous surface functional groups. The adsorption of reactive red 195 onto the prepared coffee husk activated carbon can be well-described by the pseudo-second-order kinetic model and is found to be controlled by film diffusion followed by intra-particle diffusion. The adsorption isotherm data obtained at 10–40 °C are analyzed and found to follow the Sips model at lower temperatures (10 and 20 °C) and the Redlich–Peterson model at higher temperatures (30 and 40 °C). The obtained thermodynamic parameters (Δ G° < 0, Δ H° = 33.487 kJ mol−1, and Δ S° = 202.30 J K−1 mol−1) suggest that the adsorption of reactive red 195 onto the prepared activated carbon is spontaneous, endothermic, and demonstrates an increasing of randomness at the adsorbate–adsorbent interface. The investigated results show that coffee husk activated carbon is an efficient adsorbent for the removal of reactive red 195 from aqueous solutions.
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