Adsorption of 2,4-dichlorophenoxyacetic acid onto oil palm trunk-derived activated carbon: Isotherm and kinetic studies at acidic, ambient condition

Abstract

Adsorption represents an attractive method to remove pesticide from contaminated water given its relatively low cost and simple process. This work evaluates the adsorption isotherms and kinetics of 2,4-dichlorophenoxyacetic acid (2,4-D) onto oil palm trunk-derived activated carbon (OPT-AC). Batch adsorption was performed to determine the effects of pH, temperature, initial adsorbate concentration, and contact time. The highest removal efficiency was obtained at pH 2 due to the absence of electrostatic repulsion between the adsorbent and the adsorbate as indicated by the point of zero charge (pHpzc) of 4.8 for OPT-AC and a pKa of 2.73 for 2,4-D. The adsorption isotherm data at 25, 35, and 45 °C and pH of 2 can be fitted better by the non-linear Langmuir model relative to the non-linear Freundlich model. Langmuir monolayer maximum adsorption capacity was found to be 420.43 mg g−1, which lies among the highest reported values for activated carbon materials used for 2,4-D removal. Adsorption kinetic data at 35 °C and pH of 2, on the other hand, can be better correlated by pseudo-second order (PSO) kinetic model compared to pseudo-first order (PFO) model, which implies the more dominant presence of chemisorption relative to physisorption. The high adsorption uptake of 2,4-D by OPT-AC highlights its potential as an attractive alternative to commercial AC particularly for medium to large scale 2,4-D removal from acidic wastewater.