2,4-Dichlorophenoxyacetic acid adsorption onto coconut shell-activated carbon: isotherm and kinetic modeling

Abstract

The removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution by coconut shell-activated carbon (CSAC) was studied adopting batch adsorption techniques. The effect of contact time, initial concentration of 2,4-D, and pH was investigated. From the kinetic data, 8 h was considered as the equilibrium time for determining adsorption isotherms. Adsorption data were fitted to the Langmuir, Freundlich, Temkin, and the new Brouers–Sotolongo (BS) adsorption isotherms. Results showed that the BS isotherm model best described the adsorption process and the BS maximum adsorption capacity determined was 368.0 mg/g at 30°C. The Lagergren pseudo-first-order, Ho pseudo-second-order, Elovich, and the new Avrami models were applied to fit the kinetic results and it was found that the Avrami model was most suitable. The adsorption decreased with increasing pH, in the pH range 3–9, due to increased repulsion between 2,4-D molecules and CSAC surface. The results suggest that CSAC is effective as adsorbent for 2,4-D removal from water.

Keywords:

• 2,4-D
• Adsorption isotherms
• Kinetic modeling
• Pesticides
• Water treatment

Acknowledgments

The first author acknowledges the award of USM-TWAS postdoctoral fellowship in aid for research. Support of Deanship of Scientific Research grant for Research Groups RGP-VPP-292 at King Saud University is appreciated by M. Asif.