Adsorptive removal of 4-nitrophenol from aqueous solution by activated carbon prepared from waste orange peels

The present paper deals with the adsorptive removal of 4-nitrophenol (4-NP) by activated carbon prepared from waste orange peels (ACOP). A batch adsorption study has been performed to study equilibrium, kinetics, and thermodynamics of the adsorption process along with a desorption study. The ACOP characteristics, namely the Brunauer, Emmett, and Teller (BET) surface area and iodine number, were found to be 540.61 m2/g and 420.14 mg/g, respectively. The optimum adsorbent dose was found to be 5 g/L with a liquid-to-solid ratio of 107:1 (v:v). The equilibrium time was found to be 90 min with the maximum percentage removal of 94.40%. The maximum adsorption capacity of the adsorbent was found to be 73.35 mg/g. The equilibrium study showed Radke-Prausnitz as the best-fitted isotherm. A kinetic study revealed that the pseudo second-order kinetic model best represents the adsorption process. In the thermodynamic study, the value of ΔG (-21.10 kJ/mol), ΔS (0.095 kJ/mol), and ΔH (7.78 kJ/mol) at 303 K show the spontaneous, randomness, and endothermic nature of the overall adsorption process. The isosteric heat of adsorption (ΔHst,a) increases with qe, indicating that ACOP has energetically a nonheterogeneous surface. The batch model design shows the field applicability of the ACOP adsorbent for 4-NP sorption as per industrial need. © 2016 American Society of Civil Engineers.