H. YANG et al.: PREPARATION OF MAGNETIC Fe3O4/ACTIVATED CARBON FIBER ...
505–510
PREPARATION OF MAGNETIC Fe
3
O
4
/ACTIVATED CARBON
FIBER AND A STUDY OF THE TETRACYCLINE ADSORPTION
IN AQUACULTURE WASTEWATER
PRIPRAVA MAGNETNIH, S Fe
3
O
4
AKTIVIRANIH OGLJIKOVIH
VLAKEN IN [TUDIJA TETRACIKLINSKE ADSORPCIJE V
ODPADNIH VODAH ZA GOJENJE VODNIH ORGANIZMOV
Hang Yang, Xiaocai Yu
*
, Jinghua Liu, Liping Wang, Meichen Guo
State College of Marine Science and Environment, Dalian Ocean University, no. 52 Helishijiao Street, Shahekou District, Dalian 116000,
Dalian, China
Prejem rokopisa – received: 2018-10-31; sprejem za objavo – accepted for publication: 2019-01-17
doi:10.17222/mit.2018.234
Fe3O4/activated carbon fiber (F–ACF) was synthesized by a simple precipitation method and used as an adsorbent for
tetracycline (TC) removal in aquaculture wastewater. The structural and chemical properties of the F–ACF were characterized
by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometry (EDS) and
Brunauer–Emmett–Teller (BET) analyses. Effects of various parameters such as solution pH (2–10), reaction time (0–24 h) and
extra ion on TC adsorption onto F–ACF were investigated. The equilibrium result has shown that the adsorption was fitted well
with Langmuir models compared to Freundlich models. The maximum Langmuir adsorption capacity was found to be 58 mg/g.
The adsorption behavior of TC on F–ACF was best fitted with the pseudo-second-order kinetics model.
Keywords: activated carbon fiber, Fe3O4, composite, adsorption, antibiotic
Avtorji so s Fe3O4 aktivirana ogljikova vlakna (F–ACF) sintetizirali z enostavno precipitacijsko metodo in jih uporabili kot
adsorbent za odstranitev tetraciklina (TC) v odpadnih vodah za gojenje vodnih organizmov. Strukturne in kemi~ne lastnosti
F–ACF so okarakterizirali z vrsti~nim elektronskim mikroskopom (SEM), rentgensko difrakcijo (XRD), energijskim
disperzijskim spektrometrom (EDS) in analizo po Brunauer–Emmett–Tellerju (BET). Analizirali so vpliv razli~nih parametrov,
kot so pH raztopine (2–10), reakcijski ~as (0–24 h) in ekstra ion med TC adsorpcijo na F–ACF. Rezultati v reakcijskem
ravnote`ju so pokazali, da se je adsorpcija v primerjavi s Freundlichovimi modeli dobro ujemala z Langmuirjevimi modeli.
Ugotovili so, da je maksimalna Langmuirjeva adsorpcijska kapaciteta 58 mg/g. Obna{anje adsorpcije TC na F–ACF se je najbolj
ujemalo z pseudokineti~nim modelom drugega reda.
Klju~ne besede: aktivirana ogljikova vlakna, Fe3O4, kompozit, adsorpcija, antibiotik
1 INTRODUCTION
With the extensive use of antibiotics in veterinary
medicine and aquaculture for disease control and to
enhance growth,
1,2
the global environment concern has
focused on the emergent problems it posed. The bacterial
resistance to antibiotics has generated, and human and
animal health have been threatened due to the misuse of
antibiotics.
3
In recent years, massive antibiotics, which
are widely used in humans, animals and plants for pre-
venting bacterial or fungal infections, are found in
surface water and seawater.
4
Tetracycline (TC) is a kind
of important antibiotic used extensively in livestock feed.
In recent years, TC has been detected in aquaculture
wastewater (seawater) and represents an uptrend. How-
ever, there is little research on antibiotic and practical
application to remove antibiotics in aquaculture waste-
water. Therefore, the effective actions are needed to
remove the antibiotics from contaminated water.
The mainstream methods for the degradation of TC
including adsorption, Fenton oxidation, electrochemical
oxidation and photocatalysis oxidation have been used
for the degradation of antibiotics.
5–8
Overall, (chemical
or physical) adsorption has been considered as one of the
most effective and facile techniques for TC removal from
water.
9
Up to now, various kinds of adsorbents, such as
graphene oxide, natural zeolite and activated carbon have
been developed for this purpose.
10,11
Among these,
graphene oxide possesses the most excellent adsorption
capacity for antibiotics, but it is very expensive.
12
There-
fore, it is necessary to develop other economic and
efficient material.
Activated carbon fiber (ACF) is an economic and
efficient adsorbent. Compared with the traditional gra-
nular activated carbon, ACF has a large specific surface
area and rich micropores. It has been widely applied in
the chemical industry, environmental protection, cata-
lysis, medicine, the electronics industry, food hygiene
and other fields.
13
Studies have shown that the adsorption
capacity of activated carbon for certain heavy metals and
organics can be improved by loading a certain amount of
Materiali in tehnologije / Materials and technology 53 (2019) 4, 505–510 505
UDK 620.1:661.872’02:546.26:577.182.54 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(4)505(2019)
*Corresponding author's e-mail:
978404210@qq.com (Xiaocai Yu)

iron and its oxide particles on activated carbon through
iron salt modification.
14
In this paper, F–ACF was
investigated as an adsorbent for TC.
The aim of this study was to evaluate the removal of
TC in aquaculture wastewater (seawater) using F–ACF.
In the experiment, the effects of several factors were also
examined and the adsorption kinetics and isotherm were
also studied.
2 EXPERIMENTAL PART
2.1 Materials and instruments
Activated carbon fiber (ST–1300) was provided by
Jiangsu Nantong Fiber Industry Co. All the reagents
required include tetracycline, NaOH, HCl, FeSO
4
, FeCl
3
,
NaCl, (NH
4
)
2
SO
4
, NaNO
3
,KH
2
PO
4
. A stock solution of
TC was configured using seawater for the aquaculture
area.
The spectrophotometric measurements were made
with a UV–Vis spectrometer (SP–752). Specific surface
area analysis and the distribution of the pore size
analysis was performed on Quantachromem 3.0. The
SEM and EDS analyses were performed using SU 1510.
The FTIR analyses were performed using FTIR–650.
Furthermore, a shaker (XB SHA–CA), pH meter
(STARTER 3100, made in CHINA), electric drill (JJ–1)
and magnet were used.
2.2 Pre–treatment and preparation of ACF
Pre-treatment: Prior to the experiments, the activated
carbon fiber was sheared into fraction with 5 mm × 5
mm and boiled in pure water at 450 °C for1htoremove
the organics and soluble salts on the surface.
The preparation of F–ACF: FeCl
3
·6H
2
O, FeSO
4
·7H
2
O
and ACF, at a ratio (quantity) of 6:3:1, were added to the
beaker with a certain amount of ultrapure water and
stirred by electric drill at 80 °C. Then, NaOH was slowly
added as precipitant to generate precipitation until pH
reached 10, stirred for 1 h. Then, the precipitate was
placed, sucked out using the magnet, washed and dried at
105 °C.
2.3 Batch experiments
The batch experiments were carried out in a 250-mL
flask containing 50 mL of aqueous solution, and the pH
was adjusted with H
2
SO
4
and NaOH. The aqueous
samples were filtrated and the concentrations of TC in
the solution were analyzed after the reaction. The details
of the experimental conditions are presented in Table 1.
2.4 Adsorption kinetics
The kinetics data were fitted by pseudo-first-order
and pseudo-second-order kinetic rate equations for
modelling the kinetics of TC adsorption (Equations
(1–2)).
15,16
qqe
kt
te
=−
−
()
()
1
1
(1)
t
q kq
t
q
t e e
=+
1
2
2
(2)
Among the constants, q
e
and q
t
are the adsorption
capacity (mg·g
–1
)o fT Cf o rA C Fw h e ni tr e a c h e d
adsorption equilibrium and when time reached t,
respectively. k
1
and k
2
are the pseudo-first-order and
pseudo-second-order constants, respectively.
2.5 Adsorption isotherm
The equilibrium data were fitted by Langmuir and
Freundlich (Equations (3–4)).
17–19
c
qk q
c
q
e
em
e
m
=+
1
1
(3)
qk c
n
ee e
= (4)
Among the constants, q
m
and c
e
are the maximum of
the adsorption quantity (mg/g) and the residual solution
concentration (mg/L), respectively. The other constants,
including k
l
and k
f
, were calculated from the intercept
and the slope of the plots obtained from Equations (3–4).
2.6 Characterization of ACF and determination of TC
ACF and F–ACF were characterized by SEM, BET
and XRD analyses. The concentration of TC was
determined by ultraviolet spectrometer at  max
value of
TC (357 nm wavelength) and the amount of TC adsorbed
(mg/g) was calculated based on a mass-balance equation
as given in Equation (5). The degradation rate of TC was
calculated as given in Equation (6):
q
ccV
W
e
e
=
− ()
0
(5)
Degradation rate =
() cc
c
0
−
e
e
(6)
H. YANG et al.: PREPARATION OF MAGNETIC Fe3O4/ACTIVATED CARBON FIBER ...
506 Materiali in tehnologije / Materials and technology 53 (2019) 4, 505–510
Table 1: Experimental conditions
Set Aim of experiment
TC concentration
(mg/L)
Adsorbent
dosage (g/L)
Reaction time
(min)
pH
Temperature
(K)
1 Effect of pH 10 0.06 180 2–10 298
2
Effects of presence of Na
+
,
NH
4
+
,NO
3
–
,and H
2
PO
4
–
10 0.06 180 8 298
3 Isotherm 10–400 0.06 1440 8 298
4 Kinetics 10–30 0.06 10–1440 8 298

q
e
is the equilibrium adsorption capacity (mg/g); c
o
is
the initial concentration of TC in the solution (mg/L); c
e
is
the final or equilibrium concentration of TC in the solu-
tion (mg/L); V is the volume of the solution (L),
and W is the weight of the ACF (g).
3 RESULTS AND DISCUSSION
3.1 Characterization
Morphology analysis
Table 2: Surface properties of ACF and F–ACF
Samples S
BET
(m
2
/g) V
micro
(cc/g) D
average
(nm)
ACF 848.012 0.347 3.829
F–ACF 779.484 0.283 3.407
The surface morphology of ACF and F–ACF ob-
tained by SEM is given in Figure 1. The surface feature
of the origin ACF was relatively smooth and flat. Fe
3
O
4
particles with 10 nm in diameter were evenly distributed
on the surface of the F–ACF.
The XRD and EDS patterns of ACF and F–ACF
obtained are given in Figure 2. One intense peak at 23.5°
is observed in both patterns of XRD, which suggests that
the Fe
3
O
4
particles on ACF do not result in any evident
change in the ACF structure. The signature Fe
3
O
4
peaks
are obviously observed in the XRD pattern of F–ACF at
30.12°, 35.47°, 43.11°and 57.02°, which are assigned to
the (220), (311), (400) and (511) plane (JCPDS card no.
26–1136), respectively. The sizes of the Fe
3
O
4
crystallites were estimated with XRD peak analysis as
2.5 nm. It can be seen from the EDS pattern that, apart
from the signature peak of C and O, the signature peak
of Fe in F–ACF clearly appears, whose percent reaches
4.8 %. Besides, the signature peak of P in original ACF
appears, whose percent reaches 2.7 %. The appearance
of P is due to the phosphoric acid that was used to
activate the ACF during the preparation of ACF, and P
disappeared after the pretreatment of ACF.
The BET surface area, micropore volume and ave-
rage diameter of samples were summarized in Table 2.
Compared with the origin ACF, the surface area, micro-
pore volume and diameter of F–ACF were reduced.
These changes were probably due to the fact that Fe
3
O
4
particles were loaded on the surface of activated carbon
fiber, contributing to clogged partial pores and a reduced
surface area.
Batch experiments
Figure 3a indicates the effect of pH when the pH
value was from 2 to 10. As a result, the degradation rate
and unit adsorption quantity increased with the increase
of pH value, and reached peak, 100 % and 16.6 mg/g,
when the pH was no more than 4. TC possesses multiple
ionizable functional groups, mainly corresponding to
three acid dissociation constants (pK a = 3.3, 7.7, and
9.6), respectively. Therefore, TC exists as a cationic,
zwitterionic, and anionic species under various pH
values. In addition, many studies indicate the surface of
F–ACF may carry a negative charge, which increases
with the increase of the pH value. Therefore, the ad-
sorption of TC on F–ACF was driven by electrostatic
attraction at low pH value and driven by electrostatic
repulsion at high pH value.
20
In practice, the removal rate
H. YANG et al.: PREPARATION OF MAGNETIC Fe3O4/ACTIVATED CARBON FIBER ...
Materiali in tehnologije / Materials and technology 53 (2019) 4, 505–510 507
Figure 1: SEM of a), b) ACF and c), d) F–ACF
Figure 2: a) XRD and b) EDS patterns of ACF and F–ACF

of TC could still reach about 90 % under the condition of
weak alkalinity and neutral, which is common pH value
in aquaculture wastewater (seawater).
Figure 3b indicates the effect of interfering ions
under the existence of extra Na
+
,N H
4
+
,N O
3
–
,H
2
PO
4
–
ions (100 mg/L) that are common in aquaculture waste-
water. As a result, these interfering ions generally had
little effect on adsorption apart from Na
+
. The metal ions
maybe have a certain competition with the adsorption of
TC on F–ACF. In addition, TC may form complexion
with metal ions, which might cause the decreased ad-
sorption. In practice, the solution of TC was configured
by the seawater in which many extra ions exist;
therefore, the overall the effects of interfering ions is
neglected.
Adsorption kinetics
The adsorption kinetic analysis was studied to anal-
yse the adsorption mechanism, including the adsorption
rate and possible rate-limiting steps of the reaction
process. Figure 4 shows the pseudo-first-order a) and
pseudo-second-order b) plots. Table 3 provides the eva-
luated parameters of two kinetics models. The experi-
mental data fitted well with the pseudo-second-order
model.
As shown in Table 3, the fitting correlation
coefficients R
2
were between 0.82 and 0.92, which
indicated that the Lagergren first-order kinetic equation
is not suitable for describing the F–ACF adsorption
characteristics of TC.
21
Figure 4b shows the pseudo-second-order kinetic
fitting line of the adsorption of TC by F–ACF. The
experimental data was consistent with the fitting line.
The correlation coefficients R
2
of the pseudo-second-
order fitting were all greater than 0.993, as shown in
Table 3. Moreover, the theoretical equilibrium adsorp-
tion capacity q
e
obtained by the equation fitting was very
close to the actual measured equilibrium adsorption
H. YANG et al.: PREPARATION OF MAGNETIC Fe3O4/ACTIVATED CARBON FIBER ...
508 Materiali in tehnologije / Materials and technology 53 (2019) 4, 505–510
Figure 4: a) Pseudo-first-order and b) pseudo-second-order equation
plots for TC (10, 20, 30 mg/L) adsorption onto F–ACF
Table 3: Kinetic model parameters for TC adsorption onto F–ACF
Kinetic
parameters
10mg/L 20mg/L 30mg/L
Pseudo-first-order
k1
(min
-1
) 0.029 0.15 0.11
qm
(mg/g) 16.15 22.58 27.28
R
2
0.9260 0.8440 0.8206
Pseudo-second-order
qe
(mg/g) 16.90 28.83 36.14
k2 (g/mg/min) 3.9*10
–3
1.2*10
–3
8*10
–4
R
2
0.9993 0.9963 0.9934
Figure 3: The effects of: a) pH, b) extra ions on the adsorption of TC

capacity, which was basically consistent with the kinetic
adsorption mechanism of other adsorbents on anti-
biotics.
10
Isotherms
Table 4: Isotherms constants for the adsorption of F–ACF.
Equilibrium parameters
Freundlich Langmuir
kf
21.68 kl (L/mg) 0.074
n 0.16 qm (mg/g) 58.58
R
2
0.8214 R
2
0.9923
The adsorption isotherm showed the relationship
between the adsorbate concentration and the degree of
accumulation on the adsorbent surface. Figure 5 shows
the equilibrium isotherm equation plots for the adsorp-
tion of TC onto F–ACF. The adsorption isotherm para-
meters obtained from all the models were given in
Table 4. The experimental data fitted well with the
Langmuir model.
The fitting correlation coefficients (R
2
) of the Freund-
lich model was no more than 0.90. It could not be
employed to describe well the adsorption behaviour of
TC by F–ACF. The Langmuir model assumes that each
adsorption site can only adsorb a solute molecule, and
the adsorbed solute molecules form a monolayer on the
surface of the adsorbent. When all the adsorption sites
have adsorbed solute molecules, it will reach saturation.
Figure 5 a shows the fitting line of the Langmuir
equation of F–ACF to TC. In Table 4, the coefficient k
L
in the Langmuir model was less than 1, which indicated
that the adsorption of TC by F–ACF belongs to favour-
able adsorption. Besides, the theoretical equilibrium
adsorption capacity q
e
, 58.5 mg/g, obtained by the
equation fitting was very close to the actual measured
equilibrium adsorption capacity.
Comparison with other adsorbents
A comparison presented in Table 5 has been
employed for the adsorption capacities of different
adsorbents for TC. Table 5 shows the q
m
obtained
F–ACF was not very high compared with graphene oxide
adsorbents. This is due to the configured solution of TC
in this paper that was derived directly from aquaculture
wastewater, in which many interfering ions exist and the
pH value was close to 8. From the former conclusions,
the pH value and certain interference ions have a very
negative effect on the adsorption of TC. Therefore, under
the same conditions as in reference 10, an independent
experiment was carried out using F–ACF as adsorbent
and the maximum adsorption capacity q
m
, 192.1 mg/g
was obtained. The adsorption capacity was closed to
pure graphene oxide. In addition, graphene oxide
possesses higher surface area (>1500 m
2
/g) than F–ACF,
resulting in a higher adsorption capacity. However, the
price of graphene oxide is dozens of times more
expensive than ACF. So, in terms of cost and efficiency,
F–ACF is a promising and economic adsorbent for TC
removal from aquaculture wastewater.
Table 5: Maximum adsorption capacity (q
m
) of various adsorbents for
TC
Adsorbent q
m
(mg/g)Reference
F–ACF
58
This
study
Fe3O4 Nanoparticles@graphene Oxide 603
22
Pumice stone 20
23
Graphene oxide 212
10
Kaolinite 4.3
24
Activated sludge 72
25
4 CONCLUSIONS
Fe
3
O
4
/activated carbon fiber (F–ACF) was success-
fully prepared using a simple precipitation method. The
SEM, XRD and EDS characterizations of F–ACF and
ACF show the Fe was loaded on the surface of ACF in
the form of Fe
3
O
4
. The analysis of BET of F–ACF and
ACF indicates F–ACF has a lower surface area, which is
due to the introduction of Fe
3
O
4
over the surface of
F–ACF. The increase in pH has a negative effect on the
removal rate of TC. In addition, interfering metal ions
have a certain effect on the removal of TC. The adsorp-
H. YANG et al.: PREPARATION OF MAGNETIC Fe3O4/ACTIVATED CARBON FIBER ...
Materiali in tehnologije / Materials and technology 53 (2019) 4, 505–510 509
Figure 5: Langmuir and b) Freundlich equation plots for TC adsorp-
tion onto F–ACF

tion behavior of TC on F–ACF was fitted best with the
pseudo-second-order kinetics model. The equilibrium of
TC on F–ACF agrees well with the Langmuir models.
The maximum Langmuir adsorption capacity was found
to be 58 mg/g. The results of this paper show that
F–ACF is a practical and economical adsorbent for TC in
agriculture wastewater.
Acknowledgements
The authors sincerely thank the funds for State
Oceanic Administration marine nonprofit industry
research and special project (No. 20130500), the
Liaoning science public welfare research fund projects
(No. 20170002), the Liaoning Provincial Oceanic and
Fishery Department research projects (No. 201733) for
the financial support of this work.
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