Microwave-assisted preparation of pumpkin seed hull activated carbon and its application for the adsorptive removal of 2,4-dichlorophenoxyacetic acid

This study explores the feasibility of pumpkin seed hull as a potential raw precursor for preparation of mesoporous activated carbon by microwave induced KOH activation. The pumpkin seed hull activated carbon (PSHAC) was characterized by pore structural analysis, zero-point-of-charge, Fourier transform infra-red spectroscopy and scanning electron microscopy. The adsorptive performance of PSHAC was quantified using pesticide, 2,4-dichlorophenoxyacetic acid (2,4-D) as model adsorbate. The effects of contact time, initial concentration, and solution pH on the adsorption process were evaluated. Results indicated high percent of removal, with the adsorptive removal of 98.28%, 97.57%, 96.03%, 93.40%, 78.11% and 65.07% at the initial concentration 50, 100, 150, 200, 300 and 400 mg/L, respectively. Kinetic studies showed that the adsorption process was well described by the pseudo-second-order kinetic model. The adsorption isotherm was analyzed using the nonlinear Langmuir, Freundlich and Temkin isotherm models. The best fit was obtained with the Temkin isotherm model, predicting a uniform distribution of binding energy over the heterogeneous surface binding sites. The maximum monolayer adsorption capacity of 2,4-D for PSHAC was identified to be 260.79 mg/g. (C) 2012 Elsevier B.V. All rights reserved.