ORIGINAL PAPER
Pentachlorophenol (PCP) adsorption from aqueous solution
by activated carbons prepared from corn wastes
N. T. Abdel-Ghani
•
G. A. El-Chaghaby
•
E. M. Zahran
Received: 19 June 2013 / Revised: 30 September 2013 / Accepted: 17 November 2013 / Published online: 17 December 2013
Ó Islamic Azad University (IAU) 2013
Abstract Corn wastes generated from starch and glucose
production industry were used for the preparation of acti-
vated carbons. The prepared activated carbons and a
commercial activated carbon were evaluated for their
capability of adsorbing pentachlorophenol (PCP) from
aqueous solution. Batch adsorption experiments were per-
formed under different operating conditions including pH
(2–8), adsorbent dosage (0.5–4.0 g/l), initial PCP concen-
tration (10–100 mg/l), contact time (30–300 min), and
temperature (25–45 °C). The kinetics and equilibrium
models describing the adsorption of PCP by the prepared
adsorbents were obtained. The adsorption of PCP by corn
waste-based adsorbents was found to follow the second-
order kinetics and the Freundlich equilibrium models. The
intraparticle diffusion mechanism was successfully fitted to
the obtained experimental data. Thermodynamic studies
indicated that the adsorption process was exothermic. The
adsorbents surface characterization revealed the presence
of many functional groups capable of binding the adsorbate
molecules. The study results suggest the possible use of
corn wastes as a starting material for the production of
activated carbon, thus lowering the costs of wastewater
treatment processes.
Keywords Activated carbon Adsorption Corn waste
Isotherms Kinetics Pentachlorophenol
Thermodynamics
Introduction
Pentachlorophenol (PCP) is one of the seven chlor-
ophenols with industrial production (Estevinho et al.
2006). Although PCP does not belong to the primarily
elaborated list of 12 persistent organic pollutants (POPs),
it is considered a persistent compound in the environ-
ment (Bra
´
s et al. 2005). The United States Environ-
mental Protection Agency (US-EPA) fixed 1 lg/l as the
maximum limit of PCP in drinking water, while the
European Union limited the maximum PCP discharge
concentration in industrial effluents to 1–2 mg/l (Estev-
inho et al. 2006).
Aqueous effluents from industrial operations such as
polymeric resin production, oil refining, iron–steel, petro-
leum, pesticide, paint, solvent, pharmaceutics, wood-pre-
serving chemicals, coke-oven, and paper and pulp
industries contain chlorophenolic compounds (Jianlong
et al. 2000). PCP has been widely used as biocide mainly in
wood preservation industries and other pesticide applica-
tions (Mathialagan and Viraraghavan 2009).
Pentachlorophenol is acutely toxic to a variety of
microorganisms and mammals; as it is an inhibitor of
oxidative phosphorylation, it appears to accumulate within
the food chain and is thought to be mutagenic or at least
comutagenic (Mollah and Robinson 1996). PCP acts by
uncoupling oxidative phosphorylation via making cell
membranes permeable to protons, resulting in dissipation
of transmembrane proton gradients and consequential
electrical potentials (Law et al. 2003).
N. T. Abdel-Ghani
Chemistry Department, Faculty of Science, Cairo University,
Giza, Egypt
G. A. El-Chaghaby (&)
RCFF, Agricultural Research Center, Giza, Egypt
e-mail: ghadiraly@yahoo.com
E. M. Zahran
Holding Company for Water and Wastewater, Greater Cairo
Water Company, Cairo, Egypt
123
Int. J. Environ. Sci. Technol. (2015) 12:211–222
DOI 10.1007/s13762-013-0447-1
It is thus necessary to remove PCP from contaminated
water, and several methods have been used for this purpose.
These methods include oxidation, biological degradation,
membrane filtration, ion exchange, reverse osmosis, photo-
catalytical degradation, and adsorption (Domı
´
nguez-Vargas
et al. 2009). The water treatment costs of these technologies
range from 10 to 450 US$ per cubic meter of treated water,
except adsorption technology. The cost of water treatment
using adsorption is 5.0–200 US$ per cubic meter of water
(Gupta et al. 2012). Moreover, ability of adsorption to
remove toxic chemicals without disturbing the quality of
water or leaving behind any toxic degraded products has
augmented its usage in comparison with some other treat-
ment methods (Mittal 2006). Thus, among various water
purification and recycling technologies, adsorption is a fast,
inexpensive, and universal method (Ali and Gupta 2007).
Adsorption as a cost-effective technique has been
widely applied for the removal of PCP from aqueous
solutions. Various adsorbents were successfully used for
PCP removal, e.g., peat–bentonite mixture (Viraraghavan
and Slough 1999), activated sludge biomass (Jianlong et al.
2000), spent mushroom compost (Law et al. 2003), pine
bark (Bra
´
s et al. 2005), almond shell residues (Estevinho
et al. 2006), coal fly ash (Estevinho et al. 2007), and fungal
biomass (Mathialagan and Viraraghavan 2009).
According to Gupta et al. (2009), activated carbon is
considered as an effective adsorbent but the high cost of
activated carbon has stimulated interest in examining the
feasibility of using cheaper waste materials as potential
adsorbents. Recently, activated carbons prepared from
natural materials have captured the interest of many
researchers for their high adsorption capacities and low cost
compared to commercial activated carbons (CAC). In the
adsorption technique, the major concern is the selection of
adsorbent material (Mittal et al. 2009). In this respect, the
production of activated carbon from agricultural by-pro-
ducts has potential economic and environmental impacts as
it converts unwanted, low-value agricultural waste to a
useful high-value adsorbent (Ekpete and Harcourt 2011).
Generally, two types of activation methods are
employed in the production of activated carbon, namely
physical and chemical activation (Olorundare et al. 2012).
However, chemical activation is now widely applied for the
activation because of its lower activation temperature and
higher product yield compared with the physical one
(Tongpoothorn et al. 2011). According to Tongpoothorn
et al. (2011), it was found that alkaline hydroxides such as
KOH and NaOH can be used to prepare activated carbons
with high specific surface area. Although NaOH and KOH
are related compounds, the reaction mechanisms of these
two hydroxides are known to be different. KOH interca-
lates between carbon layers while NaOH reacts with the
most energetic sites of the surface, thus presenting a
reactivity that strongly depends on both rank and crystal-
linity of the carbonaceous precursor (Perrin et al. 2004),
and sodium hydroxide activation was shown to be partic-
ularly interesting because of its low cost, simple handling,
and low corroding action (Perrin et al. 2004).
The aims of this work were to utilize corn wastes for the
preparation of activated carbons and to investigate the
potential use of the prepared carbons for PCP adsorption
from aqueous solution at different optimizing conditions.
The present research was carried out during 2012–2013 in
the laboratories of the Holding Company for water and
Wastewater, Greater Cairo Water Company, Cairo, Egypt.
Materials and methods
Pentachlorophenol (PCP)
Pentachlorophenol used as an adsorbate in this study was
supplied by Supelco Park, Bellefonte, chemical reagents
Co. (USA), and was used without any further purification.
The molecular weight of PCP is 197.45 g/mol and it has a
chemical formula of C
6
H
3
Cl
3
O. Corn cobs and corn nodes
were obtained from the Egyptian Starch & Glucose Man-
ufacturing Company (ESGC); the company generates corn
waste of 247.042 tone/year. The CAC used in the present
study is coconut shell-based activated carbon with the
following specifications: ash (3 %), moisture (10 %), and
bulk density (0.4 g/cm
3
).
Activated carbon preparation and characterization
The activated carbons were prepared according to the
procedure described by Tongpoothorn et al. (2011) with
some modification. The starting materials (either corn
nodes or corn cobs) were cleaned with water and dried at
110 °C for 48 h. The dried samples were crushed with a
blender and sieved before they were carbonized at 400 °C
for 1 h in a muffle furnace in order to produce charcoal.
The charcoals obtained were then subjected to impregna-
tion in NaOH solution by weight ratio (1 g charcoal/4 g
NaOH) at 70 °C for 24 h. The resulting samples were
further activated in a muffle furnace at 800 °C for 2 h.
After cooling, the activated carbons were washed succes-
sively several times with 1 M HCl followed by hot water
until the pH became neutral (= 7). Finally, the washed
samples were dried at 110 °C. The obtained activated
carbons prepared from corn cobs and corn nodes were
abbreviated as CCAC and CNAC, respectively.
The prepared activated carbons were characterized by
Fourier transformation infrared technique (FTIR) over the
range of 500–4,000 cm
-1
using Thermo Nicolet Avatar
370 FTIR Spectrometer, Thermo scientific co. The surface
212 Int. J. Environ. Sci. Technol. (2015) 12:211–222
123
characteristics of the adsorbents were also investigated by
scanning electron microscope (SEM) using JEOL, JSM-
6490LA SEM–JEOL USA, Inc.
The pH point of zero charge (pH
pzc
) was carried out by
taking 50 ml of 0.1 M NaCl solutions in different closed
Erlenmeyer flasks. The pH of the solution (pH
o
) in each flask
was adjusted to values of 2, 4, 6, 8, 10, and 12 by adding
0.1 M HCl or 0.1 M NaOH solutions. Then, 0.2 g of each of
the adsorbents was added and agitated in a shaker for 1 h and
allowed to stay for 48 h to reach equilibrium with intermit-
tent manual shaking. Then, the final pH value (pH
f
) of the
supernatant liquid was noted (Abdel Ghani et al. 2013). The
value of pH
pzc
is the pH at which pH
o
= pH
f
.
Pentachlorophenol (PCP) adsorption experiments
The effects of operation parameters on the adsorption of PCP
onto corn waste-derived activated carbons such as pH (2–8),
adsorbent dosage (0.5–4.0 g/l), initial PCP concentration
(10–100 mg/l), contact time (30–300 min), and temperature
(25–45 °C) were studied in a batch mode of operation. The
solution pH was adjusted with 0.1 mol/L NaOH and 0.1 mol/
L HCl solutions. In each batch experiment, a 250-ml stopper
conical flask containing 50 ml PCP of certain concentration
was mixed with a certain weight of each of the adsorbents
and agitated mechanically at the controlled temperature in a
shaking water bath at 200 rpm until equilibrium was
reached. The mixture was then filtered and the remaining
PCP concentration was determined at wavelength 305 nm
using a spectrophotometer Jenway 6715 UV/Vis spectro-
photometer, Bibby–Barloworld Scientific Ltd.
The amount of PCP adsorbed at equilibrium (adsorption
capacity), q
e
(mg/g) was calculated by the following
equation:
q
e
¼
c
i
c
e
w
hi
v
whereas the PCP removal percentage (R %) was
calculated by the following equation:
R% ¼
c
i
c
e
c
i
100
where C
i
and C
e
are the PCP concentrations at the initial time
and at equilibrium (mg/l), respectively. V is the volume of the
solution (l) and W is the mass of adsorbent used (g).
Results and discussion
Determination of equilibrium time
Equilibrium time is one of the most important parameters
for selecting a wastewater treatment system (Abdel Ghani
and El-Chaghaby 2007). The equilibrium time for the
adsorption of PCP onto (CNAC), (CCAC), and (CAC) was
determined over a period from 30 to 300 min. The exper-
iments were performed using an adsorbent dose of (2 g/l),
initial solution pH (6), PCP concentration (10–100 mg/l),
at room temperature (25 ± 2 °C), and 200 rpm shaking
speed. The results are presented in Fig. 1a–c for CNAC,
CCAC, and CAC, respectively. It can be observed that the
adsorption of PCP onto the studied adsorbents generally
increased by increasing the contact time until equilibrium
was reached after 210, 240, and 180 min. for CNAC,
CCAC, and CAC, respectively. The difference in the
equilibrium time between the studied adsorbents might be
due to the differences in the surface properties of the
adsorbents (Gupta et al. 2011a). This result is interesting
because equilibrium time is one of the important consid-
erations for economical wastewater treatment applications
(Mbadcam et al. 2011).
Thus, further experiments were conducted at 270 min to
ensure maximum PCP adsorption by the studied adsor-
bents. Figure 1 also indicate that the total adsorption
capacities increased with increasing the initial PCP con-
centrations from 10 to 100 mg/l, which may be attributed
to the finding that the initial sorbate concentration provides
an important driving force to overcome all mass transfer
resistance (Cherifi et al. 2009).
pHpzc and effect of solution pH on PCP adsorption
The solution pH is largely related to the surface chemistry
of the adsorbent and on the chemistry of the adsorbate in
solution. The surface chemistry of the three investigated
adsorbents (CNAC, CCAC, and CAC) has been studied by
determining their point of zero charge pH (pH
pzc
). The
point of zero charge pH is the pH at which the surface
charge of the solid phase is zero (Mubarik et al. 2012).
Figure 2 shows the final against initial pH plots for the
studied activated carbons. The intersection of each of these
plots with the y = x function is considered to be the pHpzc.
The pHpzc was found to be around 3, 6, and 7 for the CAC,
corn nodes activated carbon, and corn cobs activated car-
bons, respectively.
The higher pH
pzc
values obtained for CCAC and
CNAC as compared to the highly acidic pH
pzc
value of
CAC could be attributed to the preparation method of both
CCAC and CNAC, which involved an alkali activation
step. The acidic or basic pretreatments of the adsorbents
caused a change in their surface acidity. According to
Kang et al. (2008), acidic pretreatment produces many
acidic surface groups, which increased the acidic value. In
contrast, basic pretreatment of ACF and GAC decreases
the number of acidic groups and increases the number of
basic groups on the surface.
Int. J. Environ. Sci. Technol. (2015) 12:211–222 213
123
In order to find the optimum pH for maximum PCP
removal onto CNAC, CCAC, and CAC, batch experiments
were performed in the pH range from 2 to 8 using an
adsorbent dose of 2 g/l and PCP solutions of 25 mg/l at
room temperature. The results are presented graphically in
Fig. 3.
The effect of pH on PCP removal by the three studied
adsorbents can be explained as previously mentioned in
terms of both the surface chemistry of the adsorbents and
the chemistry of PCP in solution. The carbon surface is
positively charged at pH \ pHpzc and negatively charged
at pH [ pHpzc (Liu et al. 2010). It is also important to
mention the chemical characteristics of PCP while dis-
cussing the effect of solution pH on biosorption. PCP, the
strongest acid of the phenol family, has a pKa value of 4.75
(Schellenberg et al. 1984). Thus, PCP will be mainly in
protonated form at pH \ pKa and in deprotonated form at
pH [ pKa (Liu et al. 2010).
As can be seen from Fig. 3, the maximum uptake of
PCP by CNAC and CCAC was achieved at pH = 6. At this
pH value, the surface of CNAC will be neutral
(pH = pHpzc) and the surface of CCAC will be positively
charged (pH \ pHpzc). It has also to be noted that at
pH = 6, the PCP is mainly in its deprotonated form. Thus,
attraction between PCP ions and the adsorbent’s surface
will take place. According to (Ould-Idriss et al. 2011)atpH
values in the vicinity of neutrality, the adsorbents will tend
to adsorb preferably cations, due to the cooperative effect
of the net negative surface charge.
At pH values lower than the adsorbents pHpzc, the
removal of PCP by CNAC and CCAC was minimal
because of the repulsive forces existing between the
0
10
20
30
40
50
60
0 30 60 90 120 150 180 210 240
Adsorption capacity (mg/g)
Time (min.)
(a)
Ci= 100 mg/l
Ci =50 mg/l
Ci =25 mg/l
Ci=10 mg/l
0
20
40
60
80
100
0 30 60 90 120 150 180 210 240 270
Adsorption Capacity(mg/g)
Time(min.)
(b)
Ci= 100mg/l
Ci= 50mg/l
Ci =25mg/l
Ci=10mg/l
0
10
20
30
40
50
60
0 30 60 90 120 150 180 210 240 270
Adsorption Capacity (mg/g)
Time (min.)
(c)
Ci = 100mg/l
Ci = 50mg/l
Ci = 25mg/l
Ci = 10mg/l
Fig. 1 Effect of contact time on
PCP adsorption by a CNAC,
b CCAC, and c CAC, adsorbent
dosage = 2 g/l, pH:6.0, shaking
speed: 200 rpm,
Temp = 25 ± 2 °C
214 Int. J. Environ. Sci. Technol. (2015) 12:211–222
123
positively charged activated carbon surface and the PCP
present in its protonated form.
The removal of PCP by CNAC and CCAC decreased
sharply after pH 6. This observation was attributed to the
fact that at pH values higher than pHpzc, the adsorbent
surface will be negatively charged. At the same time, PCP
exists entirely in the anionic form at neutral and basic pH
(Mathialagan and Viraraghavan 2009). Therefore, electro-
static repulsion between the negatively charged adsorbent
surface and the anionic PCP will take place leading to
lower adsorption.
Regarding the effect of pH on the removal of PCP by
CAC, it can be seen from Fig. 3 that the percentage
removal of PCP was maximum at pH = 4 and declined by
increasing the pH above this value with a sharp decrease at
pH [ 8. Similar results were obtained by (Lu
¨
et al. 2011)
for the adsorption of phenol by lignite activated carbon.
According to these authors, at very low pH values, there
are many positive charges on the surface of activated car-
bon, which gives a large static repulsion force. As pH
increases, the static repulsion force decreases and the
phenol adsorption increases. At pH [ 8, the decrease in
phenol adsorption may be resulted from three reasons.
First, the negative charges on the surface of activated
carbon increases with pH and phenol changes from
molecular state to ionic state, which makes the repulsion
force between phenol ions and the activated carbon sig-
nificant. Second, the phenol ions adsorbed by the activated
carbon also have a repulsion force between themselves.
Third, the negative charges on the surface of activated
carbon are repulsive that represses the disgregation of
phenol ions and phenol adsorption.
Kinetic studies
Kinetic studies were conducted at the optimum pH prede-
termined for each of the investigated adsorbents using an
adsorbent dose of 0.1 g; with 50 ml of PCP solution at
different concentrations (10, 25, 50, and 100 mg/l). The
pseudo-first-order and pseudo-second-order kinetic models
were applied to the experimental data in order to predict
the adsorption kinetics.
The pseudo-first-order equation can be written as fol-
lows (Lagergren, 1898): ln(q
e
- q
t
) = lnq
e
- k
1
t, where
pHpzc
0
1
2
3
4
5
6
7
8
9
10
012345678910111213
pH initial
pH final
CAC
CCAC
CNAC
Fig. 2 The final against initial
pH plots for the studied
activated carbons
0
2
4
6
8
10
12
2345678
pH
adsorption capacity (mg/g)
CNAC
CCAC
9.8
10
10.2
10.4
10.6
10.8
11
11.2
11.4
11.6
11.8
012345678
pH
adsorption capacity (mg/g)
CAC
(a)
(b)
Fig. 3 Effect of pH on the adsorption of PCP by a CNAC, CCAC,
and b CAC at PCP initial concentration = 25 mg/l, adsorbent
dosage = 0.1 g/50 ml, contact time 270 min
Int. J. Environ. Sci. Technol. (2015) 12:211–222 215
123