the system increase and these functional groups were
protonated, and the surface of the adsorbent acquiring
a positive charge, as confirmed by zeta potential
measurement (Fig. 3). As previously explained, humic
acid is the main components of peat water, which
consist of many phenolic and carboxylic functional
groups. As known, the phenolic and carbonyl functional
group can be ionized in aqueous medium and may
acquire a negative charge in aqueous medium. On the
other hand, the humic acid molecules became more
negatively charged as pH value increased due to
ionization of carboxylic and phenolic groups of humic
acid (Fig. 3). This ionization would lead to an increase
of negative charge of humic acid molecules, thus the
humic acid ion will be attracted to the surface of the
adsorbent by electrostatic interaction. Meanwhile at
high pH, more hydroxyl ions are present in the bulk
solution and the functional groups on the CSC surface
were deprotonated are, so the surface charge is negative
(Fig. 3). These will reduce the electrostatic attraction
between the CSC surface and humic acid compound
because the less positive or more negative surface
charges. This decreases the adsorption rate of humic
acid. To further understand the adsorption mechanism,
Langmuir, Freundlich and Sips isotherm models were
used to analyze the experimental results. The Langmuir
isotherm model assumes that the forces of interaction
between the adsorbed adsorbate molecules are
negligible and once the adsorbate molecule occupies
the adsorption site no further adsorption will take place.
The non-linear form of Langmuir isotherm is expressed
as:
the system increase and these functional groups were
protonated, and the surface of the adsorbent acquiring
a positive charge, as confirmed by zeta potential
measurement (Fig. 3). As previously explained, humic
acid is the main components of peat water, which
consist of many phenolic and carboxylic functional
groups. As known, the phenolic and carbonyl functional
group can be ionized in aqueous medium and may
acquire a negative charge in aqueous medium. On the
other hand, the humic acid molecules became more
negatively charged as pH value increased due to
ionization of carboxylic and phenolic groups of humic
acid (Fig. 3). This ionization would lead to an increase
of negative charge of humic acid molecules, thus the
humic acid ion will be attracted to the surface of the
adsorbent by electrostatic interaction. Meanwhile at
high pH, more hydroxyl ions are present in the bulk
solution and the functional groups on the CSC surface
were deprotonated are, so the surface charge is negative
(Fig. 3). These will reduce the electrostatic attraction
between the CSC surface and humic acid compound
because the less positive or more negative surface
charges. This decreases the adsorption rate of humic
acid. To further understand the adsorption mechanism,
Langmuir, Freundlich and Sips isotherm models were
used to analyze the experimental results. The Langmuir
isotherm model assumes that the forces of interaction
between the adsorbed adsorbate molecules are
negligible and once the adsorbate molecule occupies
the adsorption site no further adsorption will take place.
The non-linear form of Langmuir isotherm is expressed
as:
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