Chemically treated kola nut pod as low-cost natural adsorbent for the removal of 2,4-dinitrophenol from synthetic wastewater: batch equilibrium, kinetic, and thermodynamic modelling studies

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The feasibility of using chemically treated kola nut pod to remove 2,4-dinitrophenol from its aqueous solutions under batch mode was investigated. The results showed that biosorption of 2,4-dinitrophenol was dependent on initial concentration, contact time, pH, biosorbent particle size, biosorbent dosage, and temperature. The batch equilibrium biosorption data were analyzed by 2 two-parameter (Langmuir and Freundlich) and 2 three-parameter (Redlich--Peterson and Sips) adsorption isotherm models using linear and nonlinear regression methods. The Sips isotherm equation employing the parameter sets derived using the HYBRID/MPSD/ARE errors provided the overall best model to describe the biosorption data of the 2,4-dinitrophenol-kola nut pod system. The maximum monolayer biosorption capacity (Q\max) was obtained to be 32.26 mg/g with linear regression and 30.10 mg/g with nonlinear regression. The biosorption kinetic data were fitted to 6 biosorption kinetic models using the linear regression method. The 6 kinetic models fitted well to the biosorption kinetic data; however, the pseudo-first-order kinetic model gave the best fit and the biosorption mechanism was controlled by film diffusion. The thermodynamic analysis indicates that the biosorption process was spontaneous, feasible, exothermic, and physical in nature. Thus, chemically modified kola nut pod has potential for application as an effective bioadsorbent for 2,4-dinitrophenol removal from wastewater.