Adsorption of methylene blue and 2,4-diciilorophenol onto modified activated carbons prepared from agricultural waste
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Date
2010
Authors
Shaarani, Farra Wahida
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Abstract
The expensive cost of starting materials used to prepare commercial activated
carbon and the difficulties in regenerating the used activated carbon restricted the
activated carbon usage in wastewater treatment industries. Therefore, the objectives
of this study are to prepare and modified activated carbons from agricultural wastes
abundantly available in Malaysia, namely' oil palm fibre (OPF) and oil palm empty
fruit bunch (OPEFB). Activated carbons were prepared via chemical activation by
using phosphoric acid (H3P04) and modification of prepared activated carbons were
made via chemical treatment by using citric acid (CA) and ammonia (NH3) solution.
The potential feasibility of prepare'-' activated carbons were tested for the removal of
methylene blue (MB) and 2,4-dichlorophenol (2,4-DCP). All prepared activated
carbons possess high surface areas and total pores volumes whereas the average pore
diameters for all samples were greater than 2.2 nm. Scanning Electron Microscopy
(SEM) analyses confirmed that homogeneous pores were well developed on the
surface of activated carbons while Fourier Transform Infrared (FTIR) analyses
verified the presence of various functional groups on the surface of activated
carbons. The batch adsorption study was carried out at different initial concentrations
of adsorbate (MB: 50-500 mg/L, 2,4-DCP: 25-250 mg/L), contact time, solution
temperature (30-50 °C) and solution pH (2-12). The adsorption uptakes of MB and
2,4-DCP showed the same trend where with the increasing of initial concentration
the adsorption uptake will increase. MB removal were maximum at pH 12 while 2,4-
DCP removal were the highest at pH 2. All adsorbate-adsorbent systems were
showing the same trend where they were well described by Langmuir adsorption
isotherm model and the data fitted well pseudo-second-order kinetic model. Modified
activated carbons via chemical treatment were proven to enhance the uptake of
adsorbate. This work revealed that modification of activated carbons via acidic
treatment enhanced the adsorption uptake of MB between 26.32 to 46.43% while
basic treatment applied on activated carbons improved adsorption uptake of 2,4-DCP
between 22.86 to 39.13%. Thermodynamic parameters such as activation energy
(Ea}, enthalpy (M?), entropy (~S") and free energy (~G0) :were also evaluated. All
prepared activated carbons demonstrate the effectiveness and feasibility for the
removal ofMB and 2,4-DCP.
Description
Keywords
Methylene blue and 2,4-dichlorophenol , Activated carbons