Removal of chlorophenolic compounds from aqueous solution by adsorption onto various activated carbons produced from oil palm shell
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Date
2011
Authors
Kakil Hamad, Bakhtiar
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Abstract
This study seeks to explore the possibility of prepanng mesoporous
activated carbons from the oil palm shell agricultural by-product abundantly
available in Malaysia. Physiochemical activation processes using sodium hydroxide,
potassium hydroxide and potassium carbonate and impregnated with nitrogen and
carbon dioxide gases were used to prepare the activated carbons. The experimental
results showed that the activation temperature and time and the impregnation ratio of the
chemical agents were significant factors affecting the yield of the activated carbons and
adsorption efficiency for chlorophenolic compounds. All the activated carbons derived
from oil palm shell were mesoporous with higfi surface areas (1571-2247 m2/g) and
with the average pore diameters 2.2 - 2. 7 nm. SEM micrographs demonstrated many
orderly and developed homogeneous pores of the activated carbons. FTIR analyses
illustrated the presence of different functional groups on the activated carbon surfaces.
The adsorption rates of the chlorophenols increased with increasing contact time and
initial concentrations (30-225 mg/L). The highest removal efficiency of the
chlorophenols {CPs) onto the activated carbons was at pH 2 while the lowest removal
efficiency was at pH 12. Adsorption of 4-chloro-2-methoxyphenol on all activated
carbons was best fitted by the Langmuir isotherm model while adsorption of 2-
chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were better fitted by the
Freundlich &'1d Temkin models. Adsorption of all chlorophenols was best described by
the pseudo-second-order kinetic model. In general, the values of the activation energies
were lower than 40 kJ /mol of all the adsorption processes, which represented
physisorption mechanism. The negative values of ~Go (0.01-5.29 kJ/mol) and ~Ho
(0.77-12.14 kJ/mol) were obtained in all cases for all chlorophenols, indicating the
spontaneous and exothennic nature of the adsorption process whereas the positive
values of L1S 0 (0.03-17 .44 J/mol K) obtained demonstrated the affinity of the activated
carbon for CPs and the enhancement of randomness at the solid-solution interface.
Ethanol desorption was a feasible technique for regenerating the exhausted activated
carbons.
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Keywords
Adsorption onto various , Carbons produced