J. Fiber Sci. Technol., 72(11), 237-243 (2016) doi 10.2115/fiberst.2016-0035 © 2016 The Society of Fiber Science and Technology, Japan
【Transaction】
Adsorptive Removal of Phosphate from Water by Ammonia Gas Activated Polyacrylonitrile Fiber Yuki Yamazaki*1, Tanita Gettongsong*2, Masahiro Mikawa*3, Yoshimasa Amano*3,4, and Motoi Machida*3,4,# *1
Faculty of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan *2 Department of Marine Science, Chulalongkorn University, Bangkok 10330, Thailand *3 Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan *4 Safety and Health Organization, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Abstract: Commercially available oxidized black colored polyacrylonitrile (PAN) fiber was heat treated above 900 ̊C under helium or ammonia gas flow. Ammonia gas treatment made specific surface area of the oxidized PAN increase from 7 m2/g to 1000 m2/g or more, becoming activated carbon fiber (ACF), whereas helium treatment resulted in the maximum surface area of only 60 m2/g. Adsorption of phosphate improved from 0.022 mmol/g for oxidized PAN to 0.057 mmol/g for the helium treatments at pH range of 5-6. In case of ammonia treatment, the adsorption amount of phosphate attained 0.056 to 0.17 mmol/g in maximum, depending on the treating temperature ranging from 925 to 975 ̊C. The adsorption sites for negatively charged phosphate could be estimated to be positively charged quaternary nitrogen species generated on PAN fiber surface by the heat treatment. Langmuir adsorption affinity of PAN-ACF was derived from isotherms to be 0.6 L/mmol or more; moderate adsorption affinity was exhibited. (Received May 11, 2016; Accepted September 14, 2016)
1. Introduction
such as silica [5] and ferric sludge [6], respectively. However, there have been much less studies of
Phosphate-phosphorus and ammonium/nitrite/
phosphate removal by activated carbons [7] including
nitrate-nitrogen are essential for increasing food
in our previous study [8]. Phosphates in aqueous
production. However, excess amount of them has
solution are present as anionic species, thereby
been discharged to ecosystem as fertilizer and
positively charged surface has an advantage to
through livestock manure leading to red tide in closed
attract
and semi-closed water and sea area [1] and also
functional groups are oxygen such as carbonyl and
resulting in overgrowth of algae in lake [2]. Although
quinone as weak basic sites and nitrogen such as
nitrogen containing fertilizer come from industrial
quaternary and aliphatic amine as strong basic sites.
scale
In
ammonia
synthesis,
phosphorous
can
be
this
anionic
study,
substances.
introduction
Positively
of
basic
charged
nitrogen
obtained only from natural phosphate rock, which is
functionalities onto carbon surface was attempted
unevenly distributed to the limited area of Morocco in
with high temperature heat and ammonia treatments
the world [3]. Development of recovery technique of
of oxidized polyacrylonitrile (PAN) fiber which had
phosphate seems to be required in near future.
nitrogen and oxygen in the polymer structure. Using
Formation of hydroxyapatite from phosphate in
the
water is one of the promising techniques to recover
phosphate from aqueous solution was carried out to
phosphate. Adsorptive removal of phosphate is also a
inspect what kinds of species were estimated to be
candidate technique. A lot of adsorbents have been
generated and/or transformed on the PAN surface.
obtained
materials,
adsorptive
removal
examined to uptake phosphate from water [4] and most of them are ceramic and metal oxide materials # corresponding authors: Tel/fax: +81 43 290 3559
E-mail:
[email protected] (M. Machida)
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
237
of
2. Materials and methods
respectively, in which OG stands for outgassing so that surface oxygen of oxidized PAN (PYR) will be
All chemicals were reagent grade, purchased
principally
removed
by
the
helium
treatment.
from Kanto Chemical Co., Inc., and used without
Likewise ammonia treated PYR samples at 925-975 ̊C
further purification. Oxidized polyacrylonitrile (PAN)
are designated as PYR 925 AG, PYR 950 AG and PYR
fiber felt was obtained from Toho Tenax Co., Ltd.
975 AG, in which AG means ammonia gas treatment.
Activated PAN fiber (FE 200) was purchased from
Additionally, commercial activated PAN fiber of FE
Toho Chemical Engineering & Construction Co., Ltd.
200 was employed as a reference material. FE 200
2.1 Oxidized PAN fiber and preparation of adsorbents
was also treated in helium flow ranging from 925 to
In order to produce carbon fiber from white
975 ̊C and ammonia gas flow at 950 ̊C as well as PYR
polyacrylonitrile (PAN) raw resin, PAN was oxidized
series. They are referred to as FE 925 OG, FE 950 OG,
at 200 ̊C or higher for 3-4 days to be stabilized for the
FE 975 OG and FE 950 AG, respectively.
first step. This step is extremely critical and special
2.2 Characterization of prepared adsorbents
attention has to be paid to prevent the fiber from
The pH of the point of zero charge (pHpzc) of the
melting and shrinking that will thoroughly change its
fiber samples was measured by the pH drift method
morphology as obtained in our previous study [9]. Liao
using NaCl solutions, for which pH was modified by
et al. also examined the air oxidation of PAN resin and
0.1 M HCl or 0.1 M NaOH [11]. Thirty milligram of
proposed the formation of ladder structure of pyridine
adsorbent was mixed with 15 mL acidic or basic
rings at this stabilized stage [10]. In this study,
solution in which pHpzc was determined when the
commercially available felt shaped oxidized black
initial solution pH without fiber sample is equal to the
PAN fiber was purchased from Toho Tenax Co., Ltd.
final pH after sufficient agitation of the mixture of
The commercial name of the oxidized PAN fiber was
solution and fiber sample to attain equilibrium state.
PYROMEX, hereafter referred to as PYR.
Elemental composition of C, H and N for the fiber
PYR was further treated in quarts tube at 925 ̊C,
samples was determined by elemental analyzer
950 ̊C and 975 ̊C under helium or ammonia gas flow.
(Perkin-Elmer, PE 2400 II). Textural properties of the
A 1.5 g portion of PYR was put into the quarts tube of
samples were obtained from N2 adsorption-desorption
25 mm inner diameter and heated up to the desired
isotherms at 196 ̊C observed by Beckman Coulter
temperatures using horizontal electric furnace with
Surface Analyzer (SA 3100). Specific surface area
the rate of increasing temperature of 10 ̊C/min at the
(SBET) was calculated using B.E.T. method and total
flow rate of 150 mL/min for helium, intending to
pore volume (Vtotal) was obtained from adsorbed N2
effectively remove ammonia formed on PAN surface
volume at relative pressure (Ps/P0) at 0.99. Pore width
in the heat treatments, and the flow rate of 100 mL/
(Wpore) was calculated from SBET and Vtotal assuming slit
min in case of ammonia gas. For the helium flow, the
shaped structure with Wpore = 2 Vtotal/SBET, because the
final temperature was held for 10 min, whereas the
obtained carbon fiber sample could be assumed to be
quarts tube was allowed to cool down immediately on
composed of incomplete graphene sheets.
attaining the final temperature for the ammonia
2.3 Adsorption of phosphate onto carbon fiber
treatment, because the decomposition of the obtained
derived from oxidized PAN
sample was progressed in our preliminary study in the ammonia flow.
As a stock solution, potassium dihydrogen
After cooling down to room
phosphate (KH2PO4) was dissolved in pure water to
temperature, ammonia treated samples were heated
meet with 3.0 mmol/L. Thirty milligram of prepared
again to 300 ̊C under helium flow and held for 30 min
PAN fiber was dosed into the 15 mL KH2PO4 solution
to completely desorb ammonia remaining on the fiber
in Erlenmeyer flask. The flask was agitated at
samples, while the helium treated PYR was removed
100 rpm and 25 ̊C for 24 hours in order to reach a
from
room
state of adsorption equilibrium. The equilibrium
temperature. All treated samples were washed with
solution was pipetted out and diluted to desired ratio
warm water at 65-70 ̊C for 2 days or more using
with pure water and a molybdenum blue colorimetric
Soxhlet extractor until the pH of extraction water no
method with UV-Vis spectrometer (Shimadzu, UV-
longer changed and dried in oven at 110 ̊C. RYR
2550) was used for the determination of phosphate
treated in helium flow at 925 ̊C, 950 ̊C and 975 ̊C are
concentration. The adsorption amount of phosphate
named as PYR 925 OG, PYR 950 OG and PYR 975 OG,
was calculated by,
238
the
quarts
tube
after
cooling
to
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
Q e = (C0 − Ce ) ×
was also observed for ammonia gas treatment of
v , w
(1)
FE 200 at 950 ̊C; SBET was considerably increased from 680 m2/g to 1190 m2/g. These results clearly
where Qe was equilibrium amount of phosphate on
indicated
adsorbent, C0 and Ce were the initial and the
carbonaceous materials [12] as well as steam and CO2
equilibrium concentrations of phosphate, v and m
activation. Carbonization of oxidized PAN fiber (PYR)
were volume of solution and amount of adsorbent
forming graphene sheets seems to be progressed by
dosage, respectively.
heat treatment under both the helium and the
that
ammonia
gas
could
activate
Influence of solution pH on adsorption amount of
ammonia gas flow, because carbon composition was
phosphate was also examined. Both phosphate species
increased but hydrogen was decreased. In contrast,
and surface charge of adsorbents will be significantly
since FE 200 itself was already activated PAN fiber,
changed by altering solution pH resulting in great
carbon
changes in adsorption capacity [8]. By varying the
significantly vary. The pHpzc value was also increased
initial
with
concentration
of
phosphate,
adsorption
and
hydrogen
increasing
surface
compositions area
and
did
not
progressing
isotherms were drawn as well and adsorption
carbonization, revealing that π-electron density was
parameters were calculated assuming Freundlich and
gradually increasing as graphite sheets were growing,
Langmuir isotherms. Desorption of phosphate from
because π-electrons on graphite layers could attract
the adsorbent was investigated by adding 20 mL of
protons in aqueous solution leading to the rise in pHpzc.
0.1 M HCl solution in order to inspect the possibility
For the development of porosity with rise in surface
for reuse of the adsorbent. All these adsorption
area by ammonia gas treatments, detailed mechanism
experiments mentioned above was made by the same
for the ammonia gas activation is not clear for the
procedure described at the beginning in this section.
present. 3.2 Adsorption capacity of phosphate Fig. 1 shows adsorption amount of phosphate (Qe)
3. Results and discussion
and equilibrium solution pH (pHe) for prepared 3.1 Properties of prepared samples
samples,
all
of
them
were
derived
from
In Table 1 was shown textural and surface
polyacrylonitrile resin. The adsorption amount of PYR
properties of prepared polyacrylonitrile (PAN) fibers.
was increased from 0.02 mmol/g to 0.06-0.17 mmol/g
Specific surface area (SBET) of oxidized PAN fiber
by ammonia gas treatment as displayed for PRY 925-
2
2
(PYR) rose from just 7 m /g to over 1000 m /g by
975 AG, whereas only 0-0.06 mmol/g could be attained
ammonia gas treatment having only micropore of the
for helium gas treatment as PYR 925-975 OG. The
uniform pore width of 1.1 nm, whereas only a slight
difference between AG and OG series for PYR could
increase could be achieved by outgassing. Activation
be attributed to the difference in the specific surface
Table 1
Sample
BET specific surface area (SBET ), 2
Textural and surface properties of polyacrylonitrile (PAN) fibers
Total pore volume (Vtotal),
Pore width (Wpore),
pHpzc
Elemental composition, wt-%
mL/g nm C RYR 7 5.0 59.6 PYR925OG 49 0.036 1.5 6.1 82.1 PYR950OG 12 6.0 84.7 PYR975OG 60 0.043 1.4 6.0 83.5 PYR925AG 1260 0.711 1.1 7.5 79.2 PYR950AG 1030 0.576 1.1 7.8 77.9 PYR975AG 1210 0.685 1.1 7.5 81.9 FE200 680 0.362 1.1 6.9 76.0 FE925OG 460 0.250 1.1 7.4 76.6 FE950OG 490 0.270 1.1 7.6 74.7 FE975OG 330 0.210 1.3 7.4 76.6 FE950AG 1190 0.656 1.1 8.8 71.2 * calculated by balance, Pore width; calculated from S BET and Vtotal assuming slit shaped pore m /g
H 3.6 0.4 0.5 0.4 0.6 0.5 0.4 0.6 0.5 0.7 0.7 0.7
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
N 20.9 10.7 10.1 10.6 9.1 8.9 6.4 5.6 4.4 5.7 5.9 7.3
O* 15.9 6.8 4.7 5.5 11.1 12.7 11.3 17.8 18.5 18.9 16.8 20.8
239
positively charged carbon surface is required and at the same time negatively charged sites should be avoided to effectively attract phosphate on the carbon surface. Carboxy groups can be easily introduced onto carbon surface [13] and always negatively charged at pH above 4 resulting in no phosphate adsorption even if positively charged lactone groups are present in the same surface [8]. For the attractive sites in the carbon surface, π-electrons on graphene sheet itself can attract protons forming slightly positively
charged
surface
that
may
attract
phosphate [14]. Heteroatoms such as oxygen and nitrogen play an important role on the carbon surface Fig. 1 Adsorption amount of phosphate on each prepared adsorbent and equilibrium solution pH (pHe). Adsorbent dosage is 30 mg in 15 mL solution at the initial KH2PO4 concentration of 3.0 mmol/L.
to form positively charged sites to capture phosphate. As oxygen functional groups, lactone groups belong to positively charged Lewis acids and carbonyl groups are Lewis bases that may accommodate protons also resulting in becoming positively charged sites. As for nitrogen on the carbon surface,
area (SBET) of 12-60 m2/g for OG series but 1030-1260 m2/g
quaternary nitrogen (N-Q) probably formed inside and
for AG series. In case of OG and AG treatments of FE
peripheral of the graphene sheet is obviously
200, adsorption amount of phosphate was also
positively charged sites [15] and must attract
increased from 0.01 mmol/g for no treatment to 0.07-
negatively charged phosphate, but pyridine-N-oxide
0.16 mmol/g for FE 925-975 OG and FE 950 AG.
(N-X) may not be preferential because oxygen atom
Although the results imply that specific surface area
next to quaternary nitrogen is negatively charged in
may be one of the essential parameters for the
N-X that will generate repulsive force to phosphate
enhancement of adsorption amount of phosphate onto
anion. The other candidate for nitrogen element on
the
the
carbon surface is aliphatic amines, because their pKa
adsorption amounts are not always proportional to
polyacrylonitrile
(PAN)
carbon
fiber,
values are greater than 9.0 [16] that accommodate
specific surface areas of the PAN fibers. For example,
protons
the specific surface areas of FE 925-975 OG were
Hamoudi et al. examined the aliphatic amine grafted
smaller than that of FE 200, whereas the adsorption
to silica materials and achieved to 0.78-1.21 mmol/g of
amount of phosphate of them was much greater than
phosphate
FE 200 as clearly represented in Fig. 1. Particularly
quaternary nitrogen (N-Q) together unpreferably with
FE 975 OG exhibited 2.9 times greater adsorption
pyridine-N-oxide (N-X) could be generated on PAN
amount of phosphate than PYR 925 AG even though
fiber surface by the transformation from pyrrole (N-5)
2
forming
positively
adsorption.
In
charged
the
sites
present
[17].
study,
specific surface area of FE 975 OG (330 m /g) is 3.8
and pyridine (N-6). The N-Q sites are expected to
times smaller than PYR 925 AG (1260 m2/g) with
attract phosphate anions. From the reports of thermal
similar pore width (1.1-1.3 nm) of them. These results
treatments
indicated that surface chemical environment should
materials, the N-Q formation will be enhanced at
be considered to determine the difference in
higher
adsorption capacities of phosphate as long as some
transformations were reported for PAN fiber in
300 m2/g or higher specific surface area could be
which
obtained. In our previous study for the removal of
occurred at higher temperature than that of N-Q [15,
phosphate, adsorption capacity of 0.16 mmol/g could
21]. Based on the earlier studies in the literature, the
be achieved as well by wood-based activated carbon
increase in adsorption amount of phosphate with
outgassed in helium flow at 1000 ̊C [8]. Phosphate ions
increasing heating temperature could be attributed to
in aqueous solution are negatively charged in the
the transformation of quaternary nitrogen (N-Q) from
solution pH above 4.5, irrespective of total phosphate
N-5 and N-6 in the prepared activated PAN fiber
concentration examined in this study. Thereby
structures. Similar results were also obtained in our
240
of
nitrogen-containing
temperature the
formation
[ 18, of
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
19,
carbonaceous 20 ] .
pyridine-N-oxide
Similar (N-X)
previous study using FE 400 activated PAN fiber in
specific surface area and total pore volume of PYR
which the maximum adsorption amount of phosphate
975 are greater than PYR 950. The difference also
could be observed at 950 ̊C outgassing [22]. Decrease
indicated that surface chemistry could play an
in adsorption amount of phosphate for PYR 975 AG
important role for the phosphate adsorption and
compared to PYR 950 AG might be caused by
around 950 ̊C might be the optimum temperature to
eliminating total N-Q species as nitrogen containing
maximize the attractive species as quaternary
gas from PAN fiber, because nitrogen content was
nitrogen (N-Q). Table 2 represented Freundlich and
decreased from 8.9 wt-% to 6.4 wt-% by increasing
Langmuir
ammonia treatment temperature from 950 ̊C to
regression data analysis. The dotted and solid lines in
975 ̊C. The estimation was supported by the fact that
Fig. 2 were drawn with Freundlich and Langmuir
decrease in adsorption of phosphate could be
equations represented in Eqs. (2) and (3), respectively,
observed for another activated PAN fiber (FE 400) as
using the parameters in Table 2,
parameters
obtained
by
the
linear
well by increasing outgassing temperature from Q e = K F Ce1/n ,
950 ̊C to 1000 ̊C [22]. On the other hand, adsorption
(2)
amount of phosphate on FE 975 OG was a little larger than that of FE 950 OG possibly corresponding to a
where Qe and Ce are equilibrium adsorption amount
slight increase in nitrogen content from 5.7 wt-% to
and equilibrium concentration of phosphate in mmol/
5.9 wt-% by outgassing in this case.
g and mmol/L, respectively. KF in mmol/g and n
3.3 Adsorption isotherms of ammonia treated PAN
(dimensionless) are Freundlich constants [23].
fiber Qe =
Fig. 2 represented adsorption isotherms of phosphate for PYR 950 AG and PYR 975 AG. The
K eC e Qmax , 1 + K eC e
(3)
adsorption amounts of phosphate (Qe) on PYR 950 are
where Qmax is the maximum adsorption amount of
always larger than those of PYR 975 at any
phosphate in mmol/g, and Ke is adsorption affinity of
equilibrium phosphate concentration (Ce), besides both
phosphate in L/mmol. For both PYR 950 AG and PYR 975 AG, the R2 values of coefficient of correlation are a little better for Freundlich isotherms than Langmuir isotherms as can be seen in Table 2, implying that heterogeneity of surface adsorption sites of phosphate. However as drawn in Fig. 2, Langmuir isotherms approaching saturation amounts are more realistic to represent
the
concentrations
experimental than
plots
Freundlich
at
higher
isotherms.
The
estimated Langmuir maximum adsorption capacities exhibited the same value of 0.28 mmol/g for the two adsorbents in Table 2, but adsorption affinity of PYR 950 AG is 1.6 times larger than PYR 975 AG, also implying that the amount of attractive surface species
Fig. 2 Adsorption isotherms of phosphate on PYR 950 AG (circle) and PYR 975 AG (triangle). Adsorbent dosage is 30 mg in 15 mL KH2PO4 solution. Dotted and Solid lines are respectively Freundlich and Langmuir model fitting using parameters given in Table 2. Table 2
on PYR 950 AG toward phosphate could be more than that of PYR 975 AG. 3.4 Influence
of
solution
pH
on
phosphate
adsorption Fig. 3 (a), (b) and (c) represents influence of
Freundlich and Langmuir parameters of ammonia activated PAN fibers
Freundlich isotherms Adsorbent PYR950AG PYR975AG
Langmuir isotherms 2
KF
n
R
0.10 0.075
1.7 1.4
0.9774 0.9534
Qmax, mmol/g
Ke, L/mmol
R
0.28 0.28
0.63 0.39
0.9429 0.8994
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
2
241
dramatically switched from HPO42 to H2PO4 around pHe 7.2 with decrease in pHe value also accompanied by more positive charged surface at lower pHe. Based on the experimental results, H2PO4 species would be preferable to adsorb onto PYR 925-975 AG series, but decrease in adsorption amount for lower pHe solution could
also
be
observed,
probably
caused
by
-
competitive adsorption with Cl anion increased when solution pHe shifted to acidic side by the modification with hydrochloric acid [24, 25]. 3.5 Regeneration of adsorbent for repeated use The result of repeated use performance of PYR 950 AG was displayed in Fig. 4. As displayed in desorption for the first-step, most of phosphate could be removed from adsorbents. The adsorption amount of the second-step was obviously declined compared to the first-step, implying that relatively strong adsorption sites for chloride ion compared to those for phosphate could be present on PYR 950 AG as well as competitive adsorption with high concentration of chloride ion remaining on the surface [24], because regeneration was attempted with 0.1 M HCl (pH 1.0) solution. In principle, not all chloride anion on the surface of PYR 950 AG cannot be replaced with phosphate ion, when excess amount of chloride anion are still present on the surface just after the treatment of 0.1 M HCl solution. Evidently the adsorption amount of third-step was as much as that
Fig. 3 Adsorption amounts of phosphate on PYR 925 AG (a), PYR 950 AG (b) and PYR 975 AG (c) as a function of equilibrium solution pH (pHe) together with speciation diagram of phosphate at total phosphate concentration of 3.0 mmol/L. equilibrium solution pH (pHe) on adsorption amounts of phosphate on PYR 925 AG, PYR 950 AG and PYR 975 AG,
respectively,
together
with
speciation
diagrams of phosphate. Although adsorption amounts of phosphate were significantly altered with varying equilibrium solution pH (pHe) for each fiber adsorbent, the maximum adsorption amount was observed for PYR 950 AG. The significant difference in adsorption amount for each fiber could be principally caused by changing phosphate species in the pHe range examined in this study; phosphate species would be
242
Fig. 4 Adsorption amount of phosphate on PYR950AG adsorbent as a function of the number of recycle times. Adsorption was carried out using mixture of 15 mL KH2PO4 solution at initial concentration of 3.0 mmol/L and 30 mg PYR 950 AG. Desorption was conducted by 0.1 M HCl solution to replace phosphate anion trapped on PYR 950 AG with chloride anion.
Journal of Fiber Science and Technology (JFST), Vol.72, No. 11 (2016)
of the second step, although limited to 75% of the first adsorption
amount.
Consequently
the
prepared
samples can be expected to be repeatedly applicable as phosphate adsorbents from the practical point of view.
5. S. Hamoudi, A. El-Nemr, M. Bouguerra, K. Belkacemi, Can. J. Chem. Eng., 90, 34‒40 (2012). 6. X. Song, Y. Pan, Q. Wu, Z. Cheng, W. Ma, Desalination, 280, 384‒390 (2011). 7. B. Keito, S. Tanada, T. Miyoshi, R. Yamasaki, N. Ohtani, T. Tamura, Jpn. J. Hyg., 42(3), 710‒720
4. Conclusions
(1987). 8. Y. Amano, Y. Misugi, M. Machida, Sep. Sci.
Based on the experimental result, summary of this study can be itemized below.
Technol., 47, 2348‒2357 (2012). 9. M. A. A. Zaini, Y. Amano, M. Machida, J. Hazard.
1)Ammonia treatment of oxidized PAN fiber at the temperature 925−975 ̊C results in the formation
Mater., 180, 552‒560 (2010). 10. X. Liao, Y. Ding, L. Chen, W. Ye, J. Zhu, H. Fang, H. Hou, Chem. Commun., 51, 10127‒10130 (2015).
of activated carbon fiber (ACF). 2)Combined with earlier reports in the literature,
11. M. V. Lopez-Ramon, F. Stoeckli, C. Moreno-
ammonia treatment at 950 ̊C maximizes quater-
Castilla, F. Carrasco-Marin, Carbon, 37, 1215‒1221
nary nitrogen (N-Q) on the surface of PAN ACF adsorbing the maximum amount of phosphate
(1999). 12. R. Wang, Y. Amano, M. Machida, J. Anal. Appl. Pyrolysis, 104, 667‒674 (2013).
ions. 3)Adsorption of phosphate on PAN ACF is governed by surface charge, phosphate species and concentration of co-existing ions such as
13. M. Machida, S. Chensun, Y. Amano, F. Imazeki, Bull. Chem. Soc. Jpn., 88(1), 127‒132 (2015). 14. S. Sato, K. Yoshihara, K. Moriyama, M. Machida, H. Tatsumoto, Appl. Surf. Sci., 253(20), 8554‒8559
chloride and sulfate ions. 4)Repeated use of PAN ACF would be possible with hydrochloric acid to remove phosphate
(2007). 15. J. R. Pels, F. Kapteijn, J. A. Moulijn, Q. Zhu, K. M. Thomas, Carbon, 33(11), 1641‒1653 (1995).
trapped on the adsorbent.
16. J. H. Bitter, S. van Dommele, K. P. de Jong, Catal. Today, 150(1–2), 61‒66 (2010).
Acknowledgements
17. T. Iida, Y. Amano, M. Aikawa, M. Machida, J. This study was funded in part by the Japan
Environ. Chem., 23(2), 91‒94 (2013).
Society for the Promotion of Science (JSPS) under
18. S. R. Kelemen, M. L. Gorbaty, P. J. Kwiatek, T. H.
Grants-in-aid for Scientific Research (C) (No. 26340058).
Fletcher, M. Watt, M. S. Solum, R. J. Pugmire,
Gratitude is greatly extended to Ms. Shizuka
Energy Fuels, 12(1), 159‒173 (1998).
Ishibashi, Safety and Health Organization, Chiba University,
for
her
dedicated
support
in
the
19. T. N. Huan, T. Van Khai, Y. Kang, K. B. Shim, J. Mater. Chem., 22(29), 14756‒14762 (2012).
experiments. We also thank Prof. Dr. Fumio Imazeki,
20. G. Wu, N. H. Mack, W. Gao, S. Ma, R. Zhong, J. Han,
the head of Safety and Health Organization, Chiba
J. K. Baldwin, P. Zelenay, ACS Nano, 6(11), 9764‒
University, for his financial support on our study.
9776 (2012). ! 21. K. Stanczyk, R. Dziembaj, Z. Piwowarska, S.
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