Removal of sodium diclofenac from aqueous solution by adsorbents derived from cocoa pod husks

The presence of sodium diclofenac (SD) in wastewater effluent, surface water and even in drinking water has prompted worldwide concerns due to the harmful effects of this pollutant to terrestrial and aquatic organisms. This study investigated the potential of activated carbon from cocoa pod husk (CPHAC) as a low-cost adsorbent for the removal of SD from aqueous solution. Characteristics of the unmodified and the CPHAC were evaluated using SEM, EDX, and FTIR analyses. The effects of pH, initial SD concentration, CPHAC dosage, and contact time in removing SD via adsorption were investigated using central composite design (CCD) of the response surface methodology (RSM) from Design Expert 7.0 software. The SD removal efficiency was observed to increase from 76.0% to 93.6% at decreasing pH and CPHAC dosage and increasing initial concentration. The optimum conditions to maximize SD removal were at pH 7, 30 mg L−1 initial SD concentration, 0.25 g CPHAC dosage, and 15 min contact time. From batch experiments, the equilibrium time was achieved at 45 min. Kinetic studies showed that the adsorption followed pseudo-second order reaction (R2 = 0.99998) and the analysis of the equilibrium data revealed that SD adsorption using CPHAC best fitted the Freundlich isotherm (R2 = 0.99707, n value of 4.34) compared to the Langmuir and Temkin models. The study demonstrated that activated carbon from CPH efficiently removed the SD in aqueous solution with adsorption capacity of 5.53 mg g−1 at equilibrium.