Adsorptive Removal of Ciprofloxacin by Ferric Chloride Modified
Biochar
Huaxuan Zhao
1,2
, Zhengmei Cao
3
, Jin Li
1,2
, Yinhai Lang
1,2,*
1
College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China;
2
Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China,
Qingdao 266100, China;
3
Qingdao Environmental Monitoring Central Station, Qingdao 266071, China.
Email: yhlang@ouc.edu.cn.
Key words: Ciprofloxacin, magnetic biochar, adsorption, mechanism
Abstract: A magnetic biochar (MBC) was fabricated through pyrolysis of FeCl
3
impregnated reed stalk powder, and
used for ciprofloxacin (CIP) adsorption from aqueous solution. The structure and properties of the MBC
were characterized by elemental analyzer, BET, SEM and FTIR. Results showed that the prepared MBC
had a large specific surface area and pore volume, which was conducive to the CIP adsorption. Adsorption
of CIP on MBC was of strong pH dependence and demonstrated a bimodal curve. Ionic strength increasing
was advantageous to the CIP adsorption. The Langmuir model and the pseudo second-order model
presented better fittings for the adsorption equilibrium and kinetic data. Adsorption thermodynamic
parameters manifested that the adsorption behavior was a spontaneous, endothermic and entropy-increasing
process. Pore-filling effect, π-π EDA interaction, electrostatic interaction, hydrogen bonding formation and
hydrophobic interaction were important mechanisms for CIP adsorption on the MBC.
1 INTRODUCTION
Ciprofloxacin (CIP) is one of the quinolone
antibiotics used to treat human and veterinary
bacterial infection because of its strong,
broad-spectrum antibacterial property and high
mobility (Wang et al., 2016). Due to its incompletely
metabolized by humans and domestic animals and
released in effluent from drug manufacturing, CIP
has become a widely monitored and frequently
detected antibiotic in surface water, wastewater of
the effluent treatment plants and hospitals (He et al.,
2015; Giger et al., 2003; Rodriguez et al., 2015).
Moreover, CIP in the environment could increase the
antibiotic resistance of the living organisms and
threaten human health (Berhane et al., 2016).
Therefore, it is imperative to eliminate CIP from the
water environments.
Adsorption method shows a promising prospect
for the elimination of quinolone antibiotics.
Magnetic biochar is an ideal adsorbent due to its
abundant raw materials, versatility and particularly
higher adsorption capacity for that the magnetization
of carbonaceous material can create additional
adsorption sites in comparison with the
non-magnetic adsorbent (Reguyal et al., 2017).
Moreover, magnetic biochar has been found to
provide simple separation after treatment using a
magnet (Thines et al., 2017). Compared with the
other common separation technologies such as
centrifugation and filtration, the magnetic separation
method is more efficient and cost-effective (Shang et
al., 2016).
These synthesized magnetic biochars have been
used for adsorption removal of multiple
contaminants, such as heavy metals, hydrophobic
organic pollutants, dyestuffs, pharmaceuticals,
entrophication anions such as nitrate and phosphate,
from aqueous solutions (Mohan et al., 2014; Bastami
and Entezari, 2012; Ma et al., 2015; Wang et al.,
2017; Usman et al., 2016; Li et al., 2016). However,
very few researches have been conducted with
respect to the synthesis of magnetic biochar using
reed biomass as raw material. Furthermore, the
studies on the CIP adsorption behaviors were not
enough.
In this task, a magnetic biochar (MBC) was
prepared by one-step synthesis through pyrolysis of
FeCl
3
impregnated reed stalk powder, and used for
the CIP adsorption from aqueous solution. Batch
56
Zhao, H., Cao, Z., Li, J. and Lang, Y.
Adsorptive Removal of Ciprofloxacin by Ferric Chloride Modified Biochar.
In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 56-61
ISBN: 978-989-758-342-1
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
adsorption experiments were employed to delve into
the adsorption behaviors and mechanisms of CIP on
MBC. The MBC served as a practical and effective
adsorbent presented great potential in wastewater
treatment.
2 MATERIALS AND METHODS
2.1 Preparation and Characteristics of
MBC
The reed stalk powder (40 g) was immersed into the
prepared FeCl
3
solution (40 g FeCl
3
ˑ6H
2
O in 60 mL
of ultrapure water) for 2 h and then dried under air.
The obtained biomass was pyrolyzed at a
temperature of 873.15 K for two hours in an
oxygen-limited environment. After washed and dried
overnight, the obtained magnetic biochar, denoted as
MBC, was milled and sieved to pass through a
100-mesh sieve (<0.15 mm).
The elemental compositions (C, H, S, O and N)
of the MBC were determined using an elemental
analyzer. The microscopic features were
characterized by SEM. The BET surface area and
micropore volume were measured using a
Physisorption and Chemisorption Analyzer. The
amounts of the acidic oxygen-containing groups on
the MBC surface were measured by the Boehm’s
titration method (Boehm, 1994). The surface
functional groups of the MBC were determined by
FTIR spectra in the 4000 to 400 cm
-1
spectral range.
The measurement of point of zero charge (pH
pzc
)
was on the basis of a reported paper (Bastami and
Entezari, 2012).
2.2 Adsorption Experiments
All the adsorption experiments were conducted
under the darkness condition in 150 mL Erlenmeyer
flasks with 50 mL of CIP solutions and 50 mg of
MBC samples in a reciprocating shaker at 190
r·min
-1
and 298.15 K unless stated otherwise.
Separate sets of experiments were carried out to
examine the influences of pH and ionic strength on
CIP adsorption. The pH values of CIP solutions (10
mg·L
-1
) were adjusted in the range of 4-12 with
NaOH or HCl solutions. 10 mg·L
-1
CIP solutions
containing 0 to 1.0 mol·L
-1
NaCl were prepared to
investigate the effect of ionic strength. In the
adsorption kinetic experiment, 10 mg·L
-1
CIP
solutions were used with adsorption time ranging
from 0.5 to 24 h. The initial CIP concentrations were
set from 2 to 20 mg·L
-1
at 298.15, 308.15, 318.15 K
for the adsorption isotherms study. All batch
adsorption experiments were performed with three
replicates. The CIP concentrations were analysed
with a UV-visible spectrophotometer at 272 nm.
The adsorption capacity of the MBC was
calculated by the following equation:
=
(

)
 (1)
Where q
e
(mg·g
-1
) is the amount of adsorbed CIP, C
0
and C
e
(mg·L
-1
) are the initial and equilibrium CIP
concentrations, respectively, V (L) is the solution
volume, and m (g) is the MBC weight.
3 RESULTS AND DISCUSSION
3.1 Characterizations of MBC
The calculated weight percentage of iron accounted
for 17.56% in MBC, indicating a lot of iron was
successfully loaded on the surface of MBC. MBC
had a relatively high porosity with BET surface area
of 238.3 m
2
ˑg
-1
and total pore volume of 0.257
cm
3
ˑg
-1
. The pH
pzc
was 2.5 for MBC.
Figure 1: SEM image of the MBC.
Figure 2: FTIR analysis spectra of the MBC.
Adsorptive Removal of Ciprofloxacin by Ferric Chloride Modified Biochar
57
Details about the structures and morphologies of
the MBC were investigated using SEM analysis.
Figure 1 showed that the MBC possessed roughness
and pores within its structure. A good dispersion of
particles with different shapes has been observed on
the surface of the MBC, which clearly delineated the
presence of iron oxide particles attached and
dispersed onto the surface of MBC.
Figure 2 showed the FTIR spectra of MBC
before and after CIP adsorption. The FTIR spectra
indicated that the adsorption peak at 559 cm
-1
can be
corresponding to the Fe-O stretching vibration
(Bastami and Entezari, 2012). After adsorption, the
disappearance of this peak indicated that the Fe-O
bond can serve as adsorption sites for CIP. The peaks
of MBC at 3386, 1558, 1100 and 870 cm
-1
can be
attributed to the skeletal vibration of O-H, C=O or
C=C, and C-O bonds, respectively (Bastami and
Entezari, 2012 ; Zhou et al., 2017 ; Zhu et al., 2014 ).
The above results indicated that there were many
oxygen-contained functional groups on the MBC
surface. The Boehm’s test also indicated that many
acidic oxygen-containing groups (such as carboxyl,
lactone, phenolic hydroxyl and carbonyl) were on
the MBC surface and the total amount of these
groups was about 3.263 mmolˑg
-1
. The
oxygen-containing functional groups can provide
adsorption sites for CIP, so that CIP formed
hydrogen bonds with the groups on the MBC
surface.
3.2 Effect of pH
The influence of pH on CIP adsorption coefficient
[K
d
, calculated by equation (2)] presented a bimodal
curve in Figure 3. The K
d
values for the adsorption
of CIP on MBC reached its first maximum at pH 6.
A further increase of pH up to 7.2 led to a decrease
in K
d
values. The second sharp peak was observed at
pH 11 and then the K
d
values decreased gradually up
to pH 12.1.
=
=

(2)
CIP (pK
a1
=6.1, pK
a2
=8.7) can exist as cations
(CIP
+
), zwitterions (CIP
±
) and anions (CIP
) with the
change of solution pH values. In addition, the pH
pzc
of the MBC was at pH of 2.5. Therefore under the
experimental conditions, the MBC surface was
negatively charged. Accordingly, the first peak of the
K
d
value at pH 6 was due to the electrostatic
attraction interaction between CIP
+
and the
negatively charged MBC surface. When 6<pH<7.2,
the electrostatic attraction interaction decreased,
bringing about the decrease in CIP adsorption. The
second peak of the K
d
value at pH 11, where the final
CIP solution pH after adsorption shifted to 8.2
because of proton release from MBC surface, was
mainly attributed to the hydrophobic effect. The CIP
solubility is lower in neutral solutions than in acidic
or alkaline solutions (Jalil et al., 2015). A further
increase of pH up to 12.1, the adsorption of CIP
species declined on account of the electrostatic
repulsion between negatively charged MBC surface
and CIP
. The same phenomenon was described
when investigating sulfonamides adsorption on
acidic functionalized biochar (Ahmed et al., 2017)
Figure 3: Effect of pH on CIP adsorption on MBC.
Figure 4: Effect of ionic strength on CIP adsorption on
MBC.
3.3 Effect of Ionic Strength
As can be seen in Figure 4, the amounts of CIP
adsorbed on MBC increased by 71.4% when the
initial NaCl concentration increased from 0 to 1.0
mol·L
-1
. The salting out effect between CIP
IWEG 2018 - International Workshop on Environment and Geoscience
58
molecules and NaCl may result in the decrease of
CIP solubility in aqueous solution when NaCl was
added, which facilitating the diffusion of more CIP
molecules to the MBC surface and increasing the
CIP adsorption amount (Peng et al., 2016).
Figure 5: Adsorption kinetics of CIP on MBC.
Figure 6: Adsorption isotherms of CIP on MBC.
3.4 Adsorption Kinetics
As illustrated in Figure 5, the adsorption rate was
quite rapid in the first four hours and then slowed
down progressively, bringing about the equilibrium
state. There were plenty of active adsorption sites on
the MBC surface. The adsorption rate decreased
with the adsorption sites occupied (Mao et al., 2016).
The result indicated that the saturation of CIP
adsorption on MBC was obtained in approximately
24 h.
The plots of the pseudo first-order (PFO) and
pseudo second-order (PSO) kinetic models for CIP
adsorption onto the MBC were given in Figure 5.
The PSO model provided the better fitting for the
adsorption process compared with the PFO model.
The determination coefficient (R
2
) value of the PSO
model (0.955) was higher than that of the PFO
model (0.854). Futhermore, the value of q
e,exp
(4.11
mgˑg
-1
) was evidently closer to the predicted values
calculated theoretically by the PSO model (3.97
mgˑg
-1
), manifesting that PSO model was more
appropriate in describing the adsorption kinetic of
CIP on the MBC (Zhu et al., 2014). The results
manifested that chemisorption process was the
rate-limiting step in the elimination of CIP by MBC
(Jalil et al., 2015). This discovery was similar to the
adsorption kinetic of tetracycline on magnetic
porous biochar (Ahmed et al., 2017).
3.5 Adsorption Isotherms
In order to further investigate the adsorption
mechanisms of CIP onto the MBC, the experimental
data was fitted with Langmuir and Freundlich
models as illustrated in Figure 6. The Langmuir
models gave higher determination coefficient values
(R
2
=0.974, 0.985, 0.973) to describe the adsorption
equilibrium data for CIP on MBC at 288.15, 298.15
and 308.15 K compared to Freundlich models,
indicating the monolayer coverage of CIP on the
MBC. Maximum Langmuir adsorption capacity (q
e
)
were 5.34, 5.41 and 6.14 mg·g
-1
for CIP adsorption
on MBC at 288.15, 298.15, 308.15 K, respectively.
For Langmuir isotherms, the values of k
L
increased with increasing temperature, indicating the
combining capacity for CIP on MBC increased
gradually. When R
L
values are between 0 and 1, the
adsorption process is favorable. In this study, the R
L
values were in the range of 0.058-0.105, indicating
the favorability of CIP adsorption on MBC (Reguyal
et al., 2017).
3.6 Adsorption Thermodynamics
The thermodynamic parameters (ΔG
0
, ΔH
0
, ΔS
0
) for
the adsorption process were calculated from the
following equations and given in Table 1.

=−ln
(3)

=
−
(4)
Where T (K) is the absolute temperature, R (8.314
Jˑmol
-1
ˑK
-1
) is the universal gas constant.
Table 1: Thermodynamic parameters of CIP adsorption on
MBC.
Temperature
(K)
K
d
(L g
-1
)
ΔG
0
(kJ mol
-1
)
ΔH
0
(kJ mol
-1
)
ΔS
0
(J mol
-1
K)
288.15 0.402 -0.915
24.616 88.602
298.15 0.685 -1.801
308.15 1.070 -2.687
ΔH
0
was positive, suggesting that the adsorption
process was an endothermic process. The positive
Adsorptive Removal of Ciprofloxacin by Ferric Chloride Modified Biochar
59
value of ΔS
0
demonstrated the
randomness-increasing character of the adsorption of
CIP on MBC. The negative ΔG
0
indicated the
feasibility and spontaneous nature of the adsorption
of CIP onto the MBC surface. The adsorption
behavior was a spontaneous, endothermic and
entropy-increasing process. In addition, the
absolute values |ΔG
0
| were less than 20 kJ·mol
-1
,
revealing that a physical adsorption may be included
in the reaction processes (Feng et al., 2013). This
also suggested that pore-filling effect may be a
significant mechanism for the CIP adsorption on
account of the abundant pores within the MBC
structure (Deng et al., 2017).
3.7 Adsorption Mechanisms
The mechanisms of CIP adsorption on MBC may be
attributed to a combination of pore-filling effect, π-π
EDA interaction, hydrogen bonding formation,
electrostatic interaction and hydrophobic interaction.
The pore-filling effect played a significant role in
the adsorption of CIP on MBC. The rich porosity of
the MBC played a crucial role in the elimination of
CIP. Chun et al reported that the surface and pore
properties of biochars were the main factors
influencing the adsorption of hydrophobic organic
pollutants and concluded that the pore-filling effect
was a predominant mechanism (Chun et al., 2004).
Wang et al also found the pore-filling effect
promoted the norfloxacin adsorption on magnetic
biochars tremendously (Wang et al., 2017).
FTIR analysis indicated that the MBC surface
was enriched with –OH, –COOH and aromatic
groups. –OH and –COOH on the MBC surface could
form hydrogen bonding with N-containing and
F-containing groups on the CIP molecules. The
aromatic groups acting as strong electron donors can
interact with CIP molecules which had a strong
π-electron acceptor nature to form a π-π bond
according to the π-π EDA theory (Wang et al., 2017;
Ahmed et al., 2017).
Among interactions, electrostatic interaction was
also an important factor for CIP adsorption on the
MBC. It can be confirmed by the former discussion.
And the hydrophobicity significantly affected the
CIP adsorption due to the decreased solubility.
4 CONCLUSIONS
MBC with a relatively high porosity was prepared
for the elimination of CIP from aqueous solution.
Adsorption of CIP on MBC was of strong pH
dependence and presented a bimodal curve. Ionic
strength increasing was advantageous to the CIP
adsorption. The Langmuir model and the pseudo
second-order kinetic model presented better fittings
for the adsorption equilibrium and kinetic data,
respectively. The adsorption behavior was a
spontaneous, endothermic and entropy-increasing
process. The adsorption of CIP on MBC was
controlled by multiple mechanisms. MBC is a good
adsorbent for CIP adsorption.
ACKNOWLEDGMENT
This study was sponsored by the Natural Science
Fundation of Shandong Province (ZR2016EEM28).
REFERENCES
Ahmed M B, Zhou J L, Ngo H H, et al 2017 Single and
competitive sorption properties and mechanism of
functionalized biochar for removing sulfonamide
antibiotics from water[J] Chemical Engineering
Journal 311 348.
Bastami T R, Entezari M H 2012 Activated carbon from
carrot dross combined with magnetite nanoparticles
for the efficient removal of p-nitrophenol from
aqueous solution[J] Chemical engineering journal
210 510.
Berhane T M, Levy J, Krekeler M P S, et al 2016
Adsorption of bisphenol A and ciprofloxacin by
palygorskite-montmorillonite: Effect of granule size,
solution chemistry and temperature[J] Applied Clay
Science 132 518.
Boehm H P 1994 Some aspects of the surface chemistry of
carbon blacks and other carbons[J] Carbon 32(5)
759.
Chun Y, Sheng G, Chiou C T, et al 2004 Compositions and
sorptive properties of crop residue-derived chars[J]
Environmental science & technology 38(17) 4649.
Deng H, Feng D, He J, et al 2017 Influence of biochar
amendments to soil on the mobility of atrazine using
sorption-desorption and soil thin-layer
chromatography[J] Ecological Engineering 99 381.
Feng Y, Dionysiou D D, Wu Y, et al 2013 Adsorption of
dyestuff from aqueous solutions through oxalic
acid-modified swede rape straw: adsorption process
and disposal methodology of depleted
bioadsorbents[J] Bioresource technology 138 191.
Giger W, Alder A C, Golet E M, et al 2003 Occurrence and
fate of antibiotics as trace contaminants in
wastewaters, sewage sludges, and surface waters[J]
CHIMIA International Journal for Chemistry 57(9)
485.
IWEG 2018 - International Workshop on Environment and Geoscience
60
He K, Soares A D, Adejumo H, et al 2015 Detection of a
wide variety of human and veterinary fluoroquinolone
antibiotics in municipal wastewater and
wastewater-impacted surface water[J] Journal of
pharmaceutical and biomedical analysis 106 136.
Jalil M E R, Baschini M, Sapag K 2015 Influence of pH
and antibiotic solubility on the removal of
ciprofloxacin from aqueous media using
montmorillonite[J] Applied Clay Science 114 69.
Li R, Wang J J, Zhou B, et al 2016 Recovery of phosphate
from aqueous solution by magnesium oxide
decorated magnetic biochar and its potential as
phosphate-based fertilizer substitute[J] Bioresource
technology 215 209.
Ma H, Li J B, Liu W W, et al 2015 Novel synthesis of a
versatile magnetic adsorbent derived from corncob
for dye removal[J] Bioresource technology 190 13.
Mao H, Wang S, Lin J Y, et al 2016 Modification of a
magnetic carbon composite for ciprofloxacin
adsorption[J] Journal of Environmental Sciences 49
179.
Mohan D, Kumar H, Sarswat A, et al 2014 Cadmium and
lead remediation using magnetic oak wood and oak
bark fast pyrolysis bio-chars[J] Chemical
Engineering Journal 236 513.
Peng P, Lang Y H, Wang X M 2016 Adsorption behavior
and mechanism of pentachlorophenol on reed
biochars: pH effect, pyrolysis temperature,
hydrochloric acid treatment and isotherms[J]
Ecological Engineering 90 225.
Reguyal F, Sarmah A K, Gao W 2017 Synthesis of
magnetic biochar from pine sawdust via oxidative
hydrolysis of FeCl2 for the removal
sulfamethoxazole from aqueous solution[J] Journal
of Hazardous Materials 321 868.
Rodriguez-Mozaz S, Chamorro S, Marti E, et al 2015
Occurrence of antibiotics and antibiotic resistance
genes in hospital and urban wastewaters and their
impact on the receiving river[J] Water research 69
234.
Shang J, Pi J, Zong M, et al 2016 Chromium removal
using magnetic biochar derived from herb-residue[J]
Journal of the Taiwan Institute of Chemical
Engineers 68 289.
Thines K R, Abdullah E C, Mubarak N M, et al 2017
Synthesis of magnetic biochar from agricultural
waste biomass to enhancing route for waste water and
polymer application: A review[J] Renewable and
Sustainable Energy Reviews 67 257.
Usman A R A, Ahmad M, El-Mahrouky M, et al 2016
Chemically modified biochar produced from
conocarpus waste increases NO3 removal from
aqueous solutions[J] Environmental geochemistry
and health 38(2) 511.
Wang B, Jiang Y, Li F, et al 2017 Preparation of biochar
by simultaneous carbonization, magnetization and
activation for norfloxacin removal in water[J]
Bioresource Technology 233 159.
Wang F, Yang B, Wang H, et al 2016 Removal of
ciprofloxacin from aqueous solution by a magnetic
chitosan grafted graphene oxide composite[J] Journal
of Molecular Liquids 222 188
Zhou Z, Liu Y, Liu S, et al 2017 Sorption performance and
mechanisms of arsenic (V) removal by magnetic
gelatin-modified biochar[J] Chemical Engineering
Journal 314 223.
Zhu X, Liu Y, Qian F, et al 2014 Preparation of magnetic
porous carbon from waste hydrochar by simultaneous
activation and magnetization for tetracycline
removal[J] Bioresource technology 154 209.
Adsorptive Removal of Ciprofloxacin by Ferric Chloride Modified Biochar
61