Activated carbon production from the Guadua amplexifolia using a combination of physical and chemical activation

Abstract

This paper presents the use of the Guadua amplexifolia bamboo specie as a precursor to obtain activated carbon using a combination of physical and chemical activation with H3PO4 or NaOH. The effect of different parameters such as carbonization temperature, activation temperature and activation time as well as chemical agent on the yield, functional groups and iodine number was analyzed using a full factorial experimental design and the response surface methodologies. From the analysis of variance, the most influence factor of each experimental design was identified. Moreover, the activated carbon was evaluated for the removal of non-biodegradable organic matter (COD) in leachates. The optimum conditions were obtained in the carbonized samples at 350 °C, impregnated by H3PO4 and thermal treatment at 500 °C during 120 min where a high surface area of ~1226.8 m2 g−1, a total pore volume of ~1.21 cm3 g−1 and an average pore diameter of ~3.83 nm were observed. Important differences were observed in the morphology and microporosity of the activated carbons as a function of the activating conditions. The results confirm the viability of G. amplexifolia bamboo specie as precursor for activated carbon production and promising absorbents for the elimination of COD in leachates.

Full text

Activated carbon production from the Guadua amplexifolia using
a combination of physical and chemical activation
B. G. Salas-Enrı
´quez
1
•A. M. Torres-Huerta
2
•E. Conde-Barajas
3
•
M. A. Domı
´nguez-Crespo
2
•L. Dı
´az-Garcı
´a
4
•Ma. de la Luz X. Negrete-Rodrı
´guez
3
Received: 13 February 2015 / Accepted: 6 January 2016
Akade
´miai Kiado
´, Budapest, Hungary 2016
Abstract This paper presents the use of the Guadua
amplexifolia bamboo specie as a precursor to obtain acti-
vated carbon using a combination of physical and chemical
activation with H
3
PO
4
or NaOH. The effect of different
parameters such as carbonization temperature, activation
temperature and activation time as well as chemical agent
on the yield, functional groups and iodine number was
analyzed using a full factorial experimental design and the
response surface methodologies. From the analysis of
variance, the most influence factor of each experimental
design was identified. Moreover, the activated carbon was
evaluated for the removal of non-biodegradable organic
matter (COD) in leachates. The optimum conditions were
obtained in the carbonized samples at 350 C, impregnated
by H
3
PO
4
and thermal treatment at 500 C during 120 min
where a high surface area of *1226.8 m
2
g
-1
, a total pore
volume of *1.21 cm
3
g
-1
and an average pore diameter of
*3.83 nm were observed. Important differences were
observed in the morphology and microporosity of the
activated carbons as a function of the activating conditions.
The results confirm the viability of G. amplexifolia bamboo
specie as precursor for activated carbon production and
promising absorbents for the elimination of COD in
leachates.
Keywords Bamboo Guadua amplexifolia Activated
carbon Chemical activation Response surface
methodology
Introduction
Bamboos are perennial plants of the grass family (Poaceae/
Gramineae) and include more than 1200 species worldwide
in more than 100 genera. They are widespread along the
subtropical and tropical regions worldwide, particularly in
South, Southeast and East Asia, as well as in tropical
Africa and South America [1]. Bamboos have two bio-
logical characteristics that make them extraordinary plants:
flowering and fast growth; even some species of bamboo
can grow 1.25 cm per day [2]. In addition, the bamboo has
the property of rapidly sequestering the atmospheric car-
bon; also, it presents excellent physical and mechanical
characteristics, which turn it a promising material [3]. The
common uses for bamboo are: forestry (erosion control,
environmental remediation); wood industry (beams, roof-
ing, flooring, and fencing); bioenergy industry (bamboo
charcoal, biofuel); pulp, paper and textile industry [4].
In terms of woody bamboos, Mexico has the second
place of bamboo diversity in Central America. At present, 8
genera and 37 species are reported with one genus, Olmeca,
and 14 species being endemic. The majority (47 %) of these
species belong to the genus Chusquea, and the remaining to
Arthrostylidium,Aulonemia,Guadua,Olmeca,Otatea and
&A. M. Torres-Huerta
atorresh@ipn.mx; atohuer@hotmail.com
1
Postgraduate student Instituto Polite
´cnico Nacional,
CICATA-Altamira, km 14.5 carretera Tampico-Puerto
Industrial Altamira, 89600 Altamira, Mexico
2
Instituto Polite
´cnico Nacional, CICATA-Altamira, km 14.5
carretera Tampico-Puerto Industrial Altamira,
89600 Altamira, Mexico
3
Laboratory of Environmental Biotechnology, Department
environmental engineering, Instituto Tecnolo
´gico de Celaya,
Av. Tecnolo
´gico y A. Garcı
´a Cubas 1200, Fovissste,
38010 Celaya, Guanajuato, Mexico
4
Instituto Mexicano del Petro
´leo, Avenida Eje Central La
´zaro
Ca
´rdenas No. 152, Col. San Bartolo Atepehuacan,
07730 Mexico, DF, Mexico
123
J Therm Anal Calorim
DOI 10.1007/s10973-016-5238-8

Rhipidocladum. In Mexico, there are 5 species of Guadua:
G. aculeata,G. amplexifolia,G. longifolia,G. paniculata
and G. velutina [5] which are utilized for numerous pur-
poses. Specifically, in south part of Tamaulipas (Mexico),
the specie Guadua amplexifolia is only used for domestic
applications due to there is not enough information to
determine other potential applications.
One of the most prominent applications of bamboo is the
preparation of activated carbon which can act as versatile
absorbents. Activated carbon (AC) is an amorphous form
of carbon, and it has a complex porous structure outcome
of the existence of disordered arrangements of carbon
atoms forming micropores with a radius minor than 2 nm,
mesopores with a radius of 2–50 nm and macropores with a
radius bigger than 50 nm [6]. Properties of AC are essen-
tially attributed to their high surface and chemical reac-
tivity [7]. The surface chemistry of carbon materials is
mainly determined by the acidic and basic character of
their surface, and this feature can be modified by treating
them with oxidizing agents either in gas phase or in solu-
tion [8]. The activation process can be divided into two
different procedures: physical activation and chemical
activation. Comparing both methods, chemical activation
has shown different advantages such as low energy and
operating cost, higher carbon yields and larger surface
areas when it is compared with physical activation [9].
Chemical activation can also provide a higher development
of the microporous structure [10], and it is usually a one-
step process at a temperature range around 450–900 C
[11]. According to Suarez-Garcia et al. [12], the optimum
pyrolysis temperature for manufacturing AC from ligno-
cellulosic materials is 500 C. The activation with H
3
PO
4
is eco-friendly as it is non-polluting, easy to recover by
simply solubilizing the H
3
PO
4
salts in water and can be
recycled back into the process [13]. On the other hand,
Tseng [14] reported that NaOH activation in comparison
with KOH activation has advantages such as: lower dosage
(mass measurement), cheaper, more environmentally
friendly and less corrosive. Authors such as Muı
´et al. [15]
reported that the surface area in the carbons could be
increased with the holding time, and Martinez et al. [16]
indicate that the use of an oxidant atmosphere instead of an
inert atmosphere produces AC with higher oxygen content,
larger surface areas and more negative surface charge.
The AC materials have practical advantages over other
kind of adsorbents [17], because they may be obtained
from a great variety of organic materials which are rich in
carbon content and have low amount of ashes (these
include by-products or wastes from industrial processes
such as: coconut shell, rice hull fruit waste, sugar industry
wastes, corncob, cherry stone, coffee bean, olive pit, cas-
sava peel, walnut shell, bamboo [18–20]). Particularly,
some of the objectives of using the agro-waste as raw
material for the AC production are its sustainability and the
potential reduction of the production cost [21].
Synthesis of activated carbon from bamboo has been
reported in several earlier studies. Huang and Zhang et al.
[22,23] synthesized highly microporous activated carbons
from different bamboos (Phyllostachys pubescens) using
physical (steam) and chemical (KOH) activations. The
authors found similar total surface areas (SBET) indepen-
dently of the bamboo species but agreed that a carbonization
in presence of a dehydrating agent is most efficient than
physical activation: 1135–1210 and 2527 m
2
g
-1
for phys-
ical and chemical routes, respectively. Lo et al. [24] also
prepared activated carbons by physical activation from
Moso (P. pubescens) and Ma (Dendrocalamus latiflorus)
bamboos, evaluate the adsorption kinetic and removal effi-
ciencies for different heavy metals such as: Pb(II), Cu(II),
Cr(III) and Cd(II), and found high efficiencies for their
removal ([95 %). Other kind of bamboo, Makino (Phyl-
lostachys makinoi Hayata) [25], has been also investigated
with removal efficiencies close to 100 % for Pb
2?
and Cu
2?
and in the range of 88–98 % for chromium ions. Finally,
Ahmad et al. [26] prepared AC from bamboo by chemical
activation highlighting the importance of finding an ade-
quate relationship between activation temperature, time and
H
3
PO
4
: precursor (mass%) to eliminate color (93.08 %) and
COD (73.98 %) of textile mill wastewater. Thus, due to the
extensive variety bamboo species, the need to investigate the
characteristics of new species that can be used as absorbent
materials is mandatory. Thus, systematic designs of car-
bonization and activation processes such as utilization of full
factorial experimental design (FFED) and the response
surface methodologies can provide engineering-oriented
solutions for optimizing the AC production process.
The goal of this study was to evaluate the feasibility of
developing activated carbons with very large microporosity
from the uncommon studied G. amplexifolia bamboo spe-
cie as precursor. The effect of different synthesis parame-
ters during the production of activated carbon on yield,
adsorption capacity, surface oxygenated acid groups
(SOAG) and surface area is also reported. For this purpose,
a FFED and the response surface methodologies were
applied. This design simplifies the process, reduces overall
costs of research and allows many levels of analysis [27].
Materials and methods
Bamboo characterization
The precursor used to obtain the activated carbon was the
G. amplexifolia bamboo specie older than 4 years. The raw
material was sliced into strips of 50 mm (length) 96mm
(width) 94–6 mm (thickness), and it was sun-dried. After
B. G. Salas-Enrı
´quez et al.
123

that, the samples were subjected to a proximate analysis
based on the ASTM standards: moisture [28], volatile
matter [29], ash content [30] and fixed carbon. The ligno-
cellulosic composition of the materials was determined
according to Van Soest method [31].
Thermal decomposition of the bamboo was observed in
terms of mass loss through LABSYS Evo TG thermo-
gravimetric analyzer. The bamboo was pulverized, and
11 mg was collocated in a sample holder. Before the
thermal decomposition analysis, a high purity argon stream
(flow rate of 60 mL min
-1
) was continuously passed into
the furnace in order to prevent any undesired oxidative
decomposition. In this analysis, the temperature was con-
trolled from room temperature to 700 C using a heating
rate of 10 C min
-1
.
Carbonization of bamboo and activation
of carbonized bamboo
The carbon activation was carried out using a combination
of physical and chemical methods; for this reason, the
experimental section was divided in two steps as follows:
In the first step, the bamboo was carbonized to evaluate the
effect of the carbonization temperature on yield. For this
purpose, 100 g of different samples of G. amplexifolia
bamboo was sintered in a Thermolyne furnace at different
temperatures (200, 250, 300, 350, 400, 500 and 600 C)
with a heating rate of 5 C min
-1
during 30 min (in air
atmosphere). From the initial analysis and yield of the
samples were selected two carbonization temperatures (300
and 350 C). In the second stage, the as-prepared samples
were milled and sieved to discrete sizes (400–500 lm), and
thereafter, 10 g of each sample was impregnated under
stirring at 80 C for 300 min, using a 2:1 ratio of a solution
containing a 20 mass% of H
3
PO
4
or NaOH (20 mass%
acid or basic solution: 10 g of sintered bamboo). After-
ward, the samples were dried at 110 C for 720 min to
remove the moisture followed by a thermal treatment 500
or 700 C using a heating rate of 5 C min
-1
, for 60 or
120 min, and air atmosphere. After thermal treatment, the
sample was washed with HCl or NaOH solutions depend-
ing on previous treatment and several times with distilled
water to remove H
3
PO
4
and NaOH traces until reached a
pH closed to 7. Finally, the washed product was dried in air
condition at 110 C for 600 min and completely milled
into small activated carbon particles.
Experimental design
The interactions among the parameters were obtained by a
full factorial experimental design (FFED) 2
4
where two
levels (low and high) and four factors were used (Table 1).
The factor A consists in the activation temperature (500
and 700 C); factor B, time (60 and 120 min); factor C,
bamboo carbonization temperature (300 and 350 C); and
factor D, the activating agent (H
3
PO
4
or NaOH). The sta-
tistical calculations (ANOVA analysis of variance) were
performed using the software packages STATGRAPHICS
Centurion XV.
Interaction effect values are easily calculated from the
results of the factorial design using Eq. 1[27].
Effect ¼
Rþ;i
R;ið1Þ
where 
Rþ;iand 
R;iare average values of yield, surface
oxygenated acid groups (SOAG) and iodine number for
the high (?) and low (-) levels of each factor. For the
effects, the above averages simply refer to the results at
the high (?) and low (-) levels of the factor whose effect
is being calculated independent of the levels of the other
factors. For binary interactions, 
Rþis the average result
for both factors at their high and low levels, whereas 
R
is the average result in which one of the factors involved
is at the high level and the other is at the low level. In
general, high-order interactions are calculated using the
above equation by applying signs obtained by multiplying
those for the factors involved (?) for high and (-) for
low levels. The matrix of signs of the experiments is
shown in Table 2.
Characterization of activated carbon
AC properties were assessed through adsorption capacity
(iodine number, ASTM D 4607-94) [32] and SOAG by
Boehm’s method [33], and the activated carbon yield was
obtained by the following Eq. 2.
Yield %ðÞ¼
W1
W0
100 ð2Þ
where W
0
is the mass of the carbonized bamboo and W
1
is
the mass of the carbon after the activation procedure.
Fourier transform infrared spectroscopy (FTIR) was
used to study the changes in the functional groups of the
raw material and the final product. This technique was
realized in a PerkinElmer Spectrum One apparatus with
attenuated total reflectance (ATR) from 4000 to 650 cm
-1
wavenumber. The structure of bamboo charcoal was ana-
lyzed by the X-ray diffraction technique (XRD) using an
X-ray diffractometer (Bruker D8, Advance) Cu Karadia-
tion (k=1.5406 A
˚), at 35 kV and 25 mA. The data were
collected at room temperature in the 2hrange 5–65with
a step size of 0.01and step time of 0.5 s using a Lynxeye
detector. Scanning electron microscopy (SEM) was real-
ized in a JEOL 6701F scanning electron microscope to
observe the changes in the specimens’ morphology. The
total surface area and micropore volume of the activated
carbon were calculated from the Brunauer–Emmett–Teller
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

(BET) technique using surface analyzer model ASAP-2020
of Micrometrics brand.
Batch adsorption experiments
Batch adsorption experiments were performed with 12 sets
containing 100 mL of raw leachate and 0.1 g of AC
21
(carbonized samples at 350 C, impregnated by H
3
PO
4
and
thermally treatment at 500 C during 60 min). It is
important to comment that all samples were filtered prior to
analysis in order to minimize the AC interference. Batch
adsorption experiments were conducted at room tempera-
ture selecting optimal conditions obtained from two perti-
nent factors, pH (2 and 8) and stirring time at 400 rpm (120
and 480 min). Then, 15 mL was taken from the solution
for pollutant uptake analysis of COD (mg L
-1
) a titration
method was applied. Organic and oxidizable inorganic
substances in the sample were oxidized by potassium
dichromate in 50 % sulfuric acid solution at reflux
temperature. Silver sulfate was used as a catalyst, and
mercuric sulfate was added to remove chloride interfer-
ence. The excess dichromate was titrated with standard
ferrous ammonium sulfate, using orthophenanthroline fer-
rous complex as an indicator. The experiments were
repeated at least three times. The pollutant removal per-
centages in the aqueous solutions were calculated by using
the following Eq. 3:
COD removal %ðÞ¼ððCoCeÞ=CoÞ100 ð3Þ
Results and discussion
Guadua amplexifolia bamboo characterization
The chemical composition of the G. amplexifolia bamboo
specie was obtained from proximate analysis based on the
ASTM standards: D2867-09 [28], D5832-98 [29] and
Table 1 Full factorial experimental design (FED) 2
4
used for the optimization of activated carbon
Activating agents factor: D Carbonization temperature factor: C Temperature/C factor: A
500 700
Time/min factor: B
1212
H
3
PO
4
300 CA
11
CA
12
CA
13
CA
14
350 CA
21
CA
22
CA
23
CA
24
NaOH 300 CA
31
CA
32
CA
33
CA
34
350 CA
41
CA
42
CA
43
CA
44
Table 2 Experimental matrix used for a full factorial experimental design 2
4
B A AB D BD AD ABD C BC AC ABC CD BCD ACD ABCD
(1) --? -? ? - -? ? - ? - - ?
B?-- -- ? ? -- ? ? ? ? - -
A-?- -? - ? -? - ? ? - ? -
ab ??? -- - - -- - - ? ? ? ?
d--? ?- - ? -? ? - - ? ? -
bd ?-- ?? - - -- ? ? - - ? ?
ad -?- ?- ? - -? - ? - ? - ?
abd ??? ?? ? ? -- - - - - - -
c--? -? ? - ?- - ? - ? ? -
bc ?-- -- ? ? ?? - - - - ? ?
ac -?- -? - ? ?- ? - - ? - ?
abc ??? -- - - ?? ? ? - - - -
cd --? ?- - ? ?- - ? ? - - ?
bcd ?-- ?? - - ?? - - ? ? - -
acd -?- ?- ? - ?- ? - ? - ? -
abcd ??? ?? ? ? ?? ? ? ? ? ? ?
B. G. Salas-Enrı
´quez et al.
123

D2866-04 [30] (Table 3). The analysis indicates that the
bamboo contains about *8.1 mass% of moisture,
*47.8 mass% of cellulose, *26.3 mass% of hemicellu-
lose and *20.5 mass% of lignin. In addition, this specie
presents a high content of volatile matter and low amount
of ash. Comparing the obtained values with other bamboo
species such as G. angustifolia,Bambusa vulgaris striata,
Bambusa oldhamii,Moso phyllostachys edulis and Den-
drocalamus sp [34–37], it can be seen that the specie G.
amplexifolia shows lowest moisture and fixed carbon
content; however, the value of volatile matter is highest
which may cause more porosity in the activated carbon
resulting an increment of the surface area [38].
The average chemical composition of bamboo was
determined by an elemental analysis, and the results are
presented in Table 4. As expected for bamboo specimens,
the major elements are carbon (43.69 %) and oxygen
(48.44 %), and other elements including hydrogen
(6.23 %), nitrogen (0.82 %) and sulfur (0.81 %) were also
quantified. These analyses corroborate that bamboo from
G. amplexifolia specie is rich in carbon content and has low
amount of ashes (2.2 %), which is a condition to have an
efficient raw precursor for the synthesis of activated car-
bons [39].
The bamboo is a type of natural lignocellulose polymer,
and bamboo is mainly composed of cellulose, hemicellu-
loses, lignin and extractives. It is very known that thermal
stability of natural lignocellulose polymer depends on its
compositions. Cellulose is highly crystalline, which makes
it more thermally stable [40]. The TG spectrum, according
to Oyedun et al. [41], shows four stages which are identified
in Fig. 1a. The first stage occurs at temperatures below of
160 C where a mass loss of *5 % is observed. This loss is
correlated with the evaporation of moisture and volatile
matter as well as extra-cellulosic water from the bamboo
component [40,41]. The second stage occurs between 160
and 240 C detecting a mass loss of *3 %. This stage
includes the start of decomposition of lignin (160–900 C)
[42] or even partial decomposition of hemicellulose that
decomposes between 220 and 315 C[42]. The third stage
is observed between 240 and 350 C showing a mass loss of
*44 mass%. In this stage, in addition to the decomposition
of the lignin and hemicellulose which started at lower
temperatures, the cellulose decomposition happens from
315 up to 400 C[40,42]. The highest mass loss is gen-
erated in this stage. The last stage considers also the gradual
decomposition of lignin and the cellulose (350–700 C)
with a mass loss close to 12.2 %. This effect is attributed to
the presence of cellulose, hemicellulose and lignin in the
samples, because the carbonization stage happens with the
elimination of these bamboo components and according to
the TG spectrum their total decomposition occurs at higher
temperatures (Fig. 1a). On the other hand, Fig. 1b shows
that the carbonization of the samples augmented with the
increase in temperature; however, this condition provoked
an ash increment starting from 400 C, due to the removal
of absorbed water or degradation of small molecules (mass
loss) or both [43]. In addition, on this graph is possible to
observe a high yield at temperatures below 250 C; never-
theless, the carbonization of the specimens is quite poor.
Table 3 Proximate analysis and lignocellulosic composition of bamboo G. amplexifolia and comparison with other species
Proximate
analysis/%
Guadua
amplexifolia
Guadua
angustifolia
[34]
Bambusa vulgaris
striata [34]
Bambusa
oldhamii [34]
Moso Bamboo
Phyllostachys edulis [35,
36]
Bamboo
Dendrocalamus sp.
[37]
Moisture
a
8.1 ±0.01 9.1 9.1 9.1 9.28 n.a.
Fixed carbon
b
10.9 ±0.14 23.1 24.7 22.6 14.56 n.a.
Volatile matter
b
86.8 ±0.14 74.1 73.9 76.4 75.04 n.a.
Ashes
b
2.2 ±0.07 2.9 1.5 1.1 1.12 n.a.
Lignocellulosic analysis/%
Cellulose 47.8 ±0.02 47.12 43.12 46.44 48 46.68
Hemicellulose 26.3 ±0.05 18.21 31.54 22.76 23.6 16.43
Lignin 21.5 ±0.07 22.76 24.56 23.72 20.60 17.66
n.a. not available
a
Wet basis
b
Dry basis
Table 4 Elemental analysis of the bamboo and selected activated
carbons
C/% H/% N/% S/% O
a
/%
Bamboo 43.69 6.23 0.82 0.815 48.44
AC
21
54.67 3.17 1.12 0.353 30.68
AC
22
58.65 1.93 0.77 0.185 38.46
AC
24
35.85 2.11 2.21 0.22 59.61
AC
33
79.34 2.07 0.75 0.20 17.64
a
Balance
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

The samples that showed a complete carbonization were at
400, 500 and 600 C; however, (Fig. 1b) all of them had a
reduced yield (\10 mass%). In this sense, it is important to
mention that the specimens at 300 and 350 C were selected
to the FFED, since they presented a moderate carbonization
(*45 and 67 mass%, respectively) as well as an accept-
able yield (*43 and *30 mass%, respectively).
For the DSC, in the temperature range studied (up to
700 C) three peaks were observed (Fig. 1a). The
endothermic first peak at about 80–90 C is the evaporation
of free water in the samples. The second endothermic peak
(at around 230 C) is attributed to the degradation of lignin
and hemicellulose. The exothermic peak (at around
330 C) is correlated with the decomposition of cellulose.
The DSC results obtained from these studies are consistent
with those results obtained from TG analysis above.
The IR spectrum of the bamboo precursor shows the
presence of alkene, ester, aromatic, ketone, alcohol,
hydroxyl, and ether and carboxyl functional groups
(Fig. 2a). These kinds of vibrations are typical in the
lignocellulosic precursors. The water content in the raw
material is related to band at *3250 cm
-1
, which corre-
sponds to the –OH stretching vibration of the H
2
O[44].
Other bands observed at 1500–1650 cm
-1
are related to the
double bond (C=C) vibrations in an aromatic system and
the highly conjugated C–O stretching vibration bands,
respectively [45]. Additionally, in this spectrum the signals
at 1595, 1426, 1326, 1241 and 1000 cm
-1
are associated
with the hemicellulose which corresponds to the C–H, C–C
and C–O stretching vibrations [46]. On the other hand,
Fig. 2b, c shows the effect of the carbonization temperature
at 300 and 350 C on the functional groups, respectively.
Several bands disappeared with the increase in temperature
which indicates that the bonds were broken. It is important
to mention that the sample at 350 C shows the remnant
bands of the lignin and cellulose because they totally
decompose at higher temperatures.
XRD patterns were realized to determine changes in the
bamboo crystallinity depending on the experimental con-
ditions, and the results are shown in Fig. 3. From this
figure, it is observed that raw material presented three
peaks at *16,*22and *35using a Bragg–Brentano
configuration. The intensity peaks matched well with the
intensity peaks of cellulose (ICDD 03-0289 card), but these
signals diminished with the increment of carbonization
temperature up to disappeared at 350 C due to decom-
position of cellulose, which occurs at 315 C[42]. The CI
has been used to describe the relative amount of crystalline
material in cellulose because the traditional model
describes cellulose chains as containing both crystalline
(ordered) and amorphous (less ordered) regions [47,48];
besides, CI indicates changes in cellulose structure after
100 200 300 400 500 600 700
30
40
50
60
70
80
90
100
350 °C
300 °C
240 °C
Temperature/°C
Temperature/°C
TG
DSC
–0.030
–0.025
–0.020
–0.015
–0.010
–0.005
0.000
0.005
160 °C
330 °C
230 °C
Mass/%
mW
90 °C
200300400500600
0
20
40
60
80
100
Yield/
mass%
0
20
40
60
80
100
Carbonization/mass%
(a)
(b)
Fig. 1 a TG/DSC of the G. amplexifolia specie. bThe effect of
carbonization temperature on the yield for the raw material
4000 3500 3000 2500 2000 1500 1000
C–C
C=C
Wavenumber/cm–1
Transmittance/%
C–O–C
C–OC–C
C–H
C=O
c) Carbonized at 350 °C
b) Carbonized at 300 °C
a) Camboo raw
C=O
OH
Fig. 2 FTIR spectra of the a) bamboo raw, b) carbonized at 300 C
and c) carbonized at 350 C
B. G. Salas-Enrı
´quez et al.
123

physicochemical treatment [47]. Thus, CI was calculated
from the XRD spectra according to Eq. 4. It this formula
I
002
is the overall intensity of the peak at h-2h*22and
I
AM
is the intensity of the baseline at h-2h*16[49].
The CI results indicated that the raw material showed a CI
of *43 % and this parameter diminished after carboniza-
tion at 300 Cupto*35 %.
CI ¼I002 IAM
I002
ð4Þ
Activated carbon characterization
Elemental analysis of selected activated carbons is also
shown in Table 4. The results show an increase in the
carbon content after activation processes compared to the
raw material. In general, as expected, the C and O
amounts vary in an important manner as a function of
the activation time, sintering temperature and activating
agent. Specifically, AC
21
and AC
22
samples activated at
500 C with H
3
PO
4
show the positive activation time
effect on the content of C and O. On the other hand,
comparison of samples AC
22
with AC
24
activated with
H
3
PO
4
at 500 and 700 C for 2 h shows an important
diminishing in the C, H and S content, which can be
attributable to the elimination of different volatile groups
containing them in the samples during the increase in
activation temperature. In agreement with previous works
[50], the largest oxygen fraction in the activated samples
AC
21
,AC
22
and AC
24
can be associated with the acid
character of the carbon surface. The last point to observe
is that the most relevant parameter is related to the kind
of activating agent, which can control the carbon amount
after activation, reducing other main components. Sample
AC
33
was activated with NaOH at 700 C, and the
highest carbon quantity (79.34 %) was displayed.
The surface changes that occurred during the activating
process in the acidic and basic media were determined by
Boehm’s method (Table 5). In general, ACs displayed
higher content of SOAG compared with commercial acti-
vated carbon such as: tetrahedron and Norit RA-3SL [51].
This analysis also indicates that the concentration of car-
boxyl group was significantly higher compared with lactone,
phenolic and carbonyl groups. These results also pointed out
that the surface interaction of these groups was directly
affected by the combination of the activation methods
(physical and chemical) followed in this study [52].
The mechanism proposed to explain the formation of
acidic surface groups on activated carbons considers that
there are three contributions: (1) acidic hydrolysis of raw
materials at low temperature, (2) reaction between pre-
cursor and air during activation at low impregnation ratio
and (3) reaction between the precursor or its acidic
hydrolysis products and H
3
PO
4
or other forms of phos-
phorus-containing acids (pyro- or polyphosphoric acids
formed at activation temperature) [53].
On the other hand, Table 5shows that the increment in
the activation temperature reduces the amount of acidic
functional groups. The increase in activation temperature
made that several functional groups were decomposed to
form CO and CO
2
. This phenomenon is due to the insta-
bility of acidic groups at high temperatures [54]. Similar
result was also obtained by Prahas et al. for jackfruit peel
activated with phosphoric acid [55]. The ANOVA for
response surface for the SOAG onto the AC is given in the
model of Pvalues 0.05, which implied that this model is
also significant (Table 4). In this case factor D, activating
agent H
3
PO
4
(-1) y NaOH (?1) was significant model
terms, whereas factor A, B and C were insignificant to the
response. The correlations between SOAG and the con-
trollable parameters are shown in Fig. 4. This graph shows
the response surface plots obtained for the analysis of the
AD interaction.
Thus, Boehm’s method corroborates and may explain
the composition differences of ACs samples during the
elemental analysis, which in turn is correlated with the total
quantity of SOAG formed during activation process.
The yield of the AC was calculated from Eq. 2, and the
results are shown in Table 5. All the yields of AC samples
diminished as the activation temperature was increased (up
to 700 C), due to dehydration of the carbonaceous structure
of the precursor. On the other hand, it can be observed that
the carbonized samples at 350 C obtained the higher yields
than at temperature of 300 C. This may be due to the crystal
structure of cellulose in that 300 C remains provoking that
during the activation stage exist a greater amount of
decomposed polymeric structures which in turn inhibited the
10 15 20 25 30 35 40
b)
a)
CI = 34.05 %
CI = 56.79 %
(040)
(002)
(–111)
Intensity/a.u.
c)
2
θ
/°
Fig. 3 X-ray diffraction patterns of a) bamboo raw G. amplexifolia at
two different sintering temperatures
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

activation process, and may explain the low yield observed
at this temperature; whereas at 350 C more amount of
cellulose is decomposed, in this stage the H
3
PO
4
reacts with
carbon and small amount of biomass, leading to higher yield.
Specifically, the yield for the as-prepared samples in
phosphoric acid was obtained in the following order
CA
21
[CA
22
[CA
11
[CA
23
[CA
12
[CA
13
[CA
14
[
CA
24
with 85, 77.4, 58.5, 49.9, 45.0, 41.5, 16.5 and
13.5 mass%, respectively. On the contrary, AC with NaOH
solution displayed the order CA
42
[CA
41
[CA
31
[
CA
32
[CA
43
[CA
33
[CA
34
[CA
44
, with 42, 38, 32,
28, 10, 8, 8 and 6 mass%, respectively. Thus, a greater
yield can be obtained in acid media than that observed
when NaOH is used as an activating agent. Similar ten-
dency has been reported when H
3
PO
4
used as an active
agent in date palm pits [56]. As a matter of fact, acid media
favors the production of AC due to its ability to retain
carbon material and to avoid the loss of otherwise volatile
materials, i.e., phosphoric acid acts in two ways: (1) as an
acidic catalyst in promoting bond cleavage reactions and
formation of crosslink; and (2) by being able to combine
with organic species to form phosphate linkages, such as
phosphate and polyphosphate esters Eq. 5, that can serve to
connect biopolymer fragments that retain carbon and avoid
the loss of volatile material [57].
C6H10O5
ðÞ
nþH3PO4
Cellulose
!C6H10O5H2PO4þH2O
Polyphosphate esters ð5Þ
On the other hand, high activation temperature increases
carbon consumption in reactions with sodium hydroxide
[58]. It is believed that while activation temperature is
increased, the sodium in the medium can be reduced to
metallic sodium during the carbonization process Eq. 6.
SOAG/meq/g
SOAG/meq/g
2.62
2.72
2.82
2.92
3.02
3.12
3.22
3.32
3.42
3.52
Temperature/°C Activating agent
500
700 –1
1
2.7
2.8
2.9
3
3.1
3.2
3.3
Fig. 4 Three-dimensional
response surface plots on yield
SOAG, the combined effect of
AD temperature and activating
agent H
3
PO
4
(-1) and NaOH (1)
Table 5 Physicochemical characterization of the activated carbon
Samples Carboxil/
meq g
-1
Lactone/
meq g
-1
Phenolic/
meq g
-1
Carbonyl/
meq g
-1
Total acid/
meq g
-1
Yield/
%
Iodine number/
mg g
-1
AC
S
BET-N2
/
m
2
g
-1
Pore
volume
Micropore
volume/cm
3
g
-1
AC
11
1.28 1.33 0.07 0.74 3.42 58.5 490 – – –
AC
12
1.24 1.17 0.09 0.66 3.16 45.07 680 – – –
AC
13
1.27 1.19 0.14 0.61 3.20 41.5 400 – – –
AC
14
1.25 1.21 0.17 0.63 3.27 16.5 580 – – –
AC
21
1.24 1.35 0.13 0.70 3.42 85.0 600 561.63 0.304 0.180
AC
22
1.41 1.17 0.06 0.45 3.09 77.40 860 1226.80 1.21 –
AC
23
1.37 1.25 0.09 0.43 3.14 49.94 507 237.12 0.13 0.025
AC
24
1.27 1.33 0.10 0.75 3.45 13.5 640 812.87 0.44 0.222
AC
31
1.29 1.33 0.17 0.16 2.94 32.0 17 11.19 0.014 –
AC
32
1.30 1.25 0.06 0.0 2.62 28.0 80 – – –
AC
33
1.31 1.28 0.09 0.02 2.69 8.0 430 371.39 0.24 0.12
AC
34
1.29 1.30 0.08 0.0 2.64 10.0 500 – – –
AC
41
1.24 1.26 0.10 0.25 2.85 38.5 120 – – –
AC
42
1.34 1.25 0.05 0.03 2.67 41.5 280 – – –
AC
43
1.29 1.30 0.10 0.04 2.74 8.35 320 – – –
AC
44
1.32 1.29 0.08 0.11 2.79 6.32 520 – – –
– Not detected
B. G. Salas-Enrı
´quez et al.
123

6NaOH þ2C !2Na þ3H2þ2Na2CO3ð6Þ
The reduction in the yield for AC in NaOH solution occurs
via elimination and dehydration reactions, i.e., breaking the
bonds C–O–C and C–C of the precursor material [59].
To prove the degree interaction of the experimental
conditions on the efficiency of the activating process, the
results have been statically analyzed. The ANOVA of the
yield (Table 6) and values of Prob [Fof \0.05 indicate
that the model terms were significant. In this case, the four
factors A, B, C and D having Pvalues \0.05 were sig-
nificant model terms; this means that the four factors have
the significant influence on yield of the AC. We considered
that the R
2
for these interactions (0.98) is consistent with
the proposed model and the experimental data of yield. The
correlations between yield (%) and the controllable
parameters are shown in Fig. 5. These graphs show the
Table 6 Analysis of variance for yield, SOAG and iodine number
Source Sum of squares Df Mean square Fratio Pvalue
SOAG
A:Temperature 6.25 910
-6
1 6.25 910
-6
0.74 0.4297
B:Time 6.2 910
-6
1 6.2 910
-6
5.95 0.0587
C:Temperature of carbonization 6.25 910
-6
1 0.00275625 0.52 0.5030
D:Activating agent 1.10776 1 1.10776 209.16 0.0000
AB 1.35 910
-1
1 1.35 910
-1
25.50 0.0039
AC 6.3 910
-6
1 6.3 910
-6
2.18 0.1997
AD 6.25 910
-6
1 6.25 910
-6
0.43 0.5428
BC 6.2 910
-6
1 6.2 910
-6
1.98 0.2180
BD 6.25 910
-6
1 6.25 910
-6
0.99 0.3649
CD 6.25 910
-6
1 6.25 910
-6
0.14 0.7210
Total error 1.3 910
-6
5 6.25 910
-6
Total/corr. 1.33779 15
Yield
A: Temperature 3964.59 1 3964.59 89.87 0.0002
B: Time 435.766 1 435.766 9.88 0.0256
C: Temperature of carbonization 409.455 1 409.455 9.28 0.0285
D: Activating agent 2882.08 1 2882.08 65.33 0.0005
AB 97.2196 1 97.2196 2.20 0.1978
AC 86.49 1 86.49 1.96 0.2204
AD 367.872 1 367.872 8.34 0.0343
BC 414.53 1 414.53 9.40 0.0279
BD 0.4356 1 0.4356 0.01 0.9247
CD 141.61 1 141.61 3.21 0.1332
Total error 220.584 5 44.1169
Total/corr. 9020.63 15
Iodine number
A: Temperature 37056.3 1 37,056.3 16.66 0.0095
B: Time 98,596.0 1 98,596.0 44.33 0.0012
C: Temperature of carbonization 28,056.3 1 28,056.3 12.61 0.0164
D: Activating agent 387506 1 387506. 174.23 0.0000
AB 506.25 1 506.25 0.23 0.6534
AC 16641.0 1 16,641.0 7.48 0.0410
AD 197136 1 197136. 88.64 0.0002
BC 3906.25 1 3906.25 1.76 0.2424
BD 4556.25 1 4556.25 2.05 0.2118
CD 3721.0 1 3721.0 1.67 0.2524
Total error 11120.5 5 2224.1
Total/corr. 788802. 15
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

response surface plots obtained for the analysis of the AD
interaction and BC interaction.
The adsorption capacity from ACs showed a wide range
of adsorption capacities, as can be seen in Table 5, varying
from 17 to 860 mg of iodine g
-1
of AC. According to the
results, those ACs with higher adsorption capacity are
impregnated with phosphoric acid; this acid has the capa-
bility of producing mesoporous carbon with high surface
area [60]. This result suggests that AC impregnated with
H
3
PO
4
promotes the development of porosity, resulting in a
higher adsorption capacity which is in agreement with
previous results [61]. The porosity developed is due to the
formation of phosphate linkages such as phosphate and
polyphosphate esters that can serve to connect and cross-
link biopolymers. However, this behavior is not observed
for the AC impregnated with NaOH because they showed
low adsorption capacity. The effect of temperature on the
iodine number could be explained because an increase in
the carbonization temperature enhance the release of
volatile matter from the precursor, causing a growth in the
dimensions of the pores and therefore causing an intensi-
fication in the iodine number [62].
The ANOVA for the response surface for the adsorption
capacity (Iodine number) onto the AC is listed in Table 6.
The Prob [Fof \0.05 implied that this model was also
significant. In this case, the four factors A, B, C and D were
significant model terms. The R
2
for the iodine number is
very close to 1 (0.9859), indicating a good correlation
between the predicted responses and experimental data.
The correlations between adsorption capacity and the
controllable parameters are shown in Fig. 6. These graphs
show the response surface plots obtained for the analysis of
the (a) AB and (b) CD interaction.
The surface modification of the activated carbon in acid
media (AC
22
) was similarly followed by FTIR spectra.
Figure 7shows FTIR spectra of the obtained samples,
which also presents the spectrums of bamboo charcoal at
350 C and AC
42
sample, which was activated with NaOH,
under the same experimental conditions. The FTIR of ACs
synthesized in both activating media displayed some
important differences: The transmittance was lower when
NaOH is used as activating agent, and the process also
provoked that some bands were missed at two wavenum-
bers, 3620 cm
-1
assigned to O–H bonds stretching of
phenolic groups and at 2995 cm
-1
assigned to alkyl (–
CH
n
). The other bands that appear in spectra AC
22
between
900 and 1200 cm
-1
are attributed to the presence of
phosphorus species (P-O-P) [63]. The peak at 1175 cm
-1
can be assigned to C–O stretching vibrations in a C–O–P
linkage. In addition, the bands that appear at 1011 and
696 cm
-1
are strong and weak P-O-P stretching, respec-
tively. Finally, at 1004 cm
-1
C–OH stretching of phenolic
groups appeared, whereas the band observed at 1580 cm
-1
was attributed to C=O of carboxylic groups [64]. Thus,
Yield/%
Temperature/°C
Yield/%
0.0
8.0
16.0
24.0
32.0
40.0
48.0
56.0
64.0
72.0
80.0
88.0
Activating agent
500
700 –1
1
0
20
40
60
80
Yield/%
Time/h
Yield/%
0.0
8.0
16.0
24.0
32.0
40.0
48.0
56.0
64.0
72.0
80.0
88.0
Carbonization temperature/°C
1
2300
350
30
40
50
60
70
(a)
(b)
Fig. 5 Three-dimensional
response surface plots on yield
of AC, athe combined effect of
AD activation temperature and
activating agent, bthe
combined effect of BC (time
and carbonization temperature)
B. G. Salas-Enrı
´quez et al.
123

Boehm’s and FTIR results agreed that the acid treatment
increased the amount of oxygen functional groups in
comparison with the alkaline treatment [65].
Figure 8displays the XRD pattern of the (a) AC in
acidic medium (AC
22
) and (b) AC
42
in basic medium. The
patterns show two wide signals at *26.4and *44.4in
2hrange that matched the (002) and (101) planes (ICDD
50-0926). Similar result was also obtained by Danish et al.
[66], for Phoenix dactylifera L. activated with phosphoric
acid. It cannot observe discrepancies between the reaction
media (acid or base). The (002) and (101) reflections are
very wide probably due to the following factors: (1) AC
was not well structured, (2) AC had a high degree of dis-
order, and (3) crystals were very small with low degree of
graphitization.
The SEM micrographs of selected samples before and
after activation in acid and basic media are shown in
Fig. 9a–c. The G. amplexifolia bamboo specie showed the
Adsorption capacity/mg of iodine/g AC
Temperature/°C
Time/h
Iodine number/mg/g AC
440.0
480.0
520.0
560.0
600.0
640.0
680.0
720.0
760.0
800.0
840.0
880.0
500
700 1
2
440
540
640
740
840
A
dsorption capacity/mg of iodine/g AC
Carbonization temperature/°C Activating agent
Iodine number/mg/g AC
440.0
480.0
520.0
560.0
600.0
640.0
680.0
720.0
760.0
800.0
840.0
880.0
300
350 –1
1
250
350
450
550
650
750
(a)
(b)
Fig. 6 Three-dimensional
response surface plots on
adsorption capacity of AC, athe
combined effect of AB
temperature and time, bthe
combined effect of CD
carbonization temperature and
activating agent
3500 3000 2500 2000 1500 1000
c) AC42 NaOH
b) AC22 H3PO4
a) Bamboo charcoal at 350 °C
CH
P–O–P
Transmittance/%
C–C
C=O
OH
C–OH
O–H
Wavenumber/cm–1
Fig. 7 FTIR spectra of the activated carbons and its comparison a)
bamboo charcoal 350 C, b)AC
22
(H
3
PO
4
, 120 min, 500 C) and c)
AC
42
(NaOH, 120 min, 500 C)
10 20 30 40 50
b) AC42 NaOH
AC22 H3PO4
a)
(101)
(002)
Intensity/a.u.
2
θ
/°
Fig. 8 X-ray Diffraction patterns of a) activated carbons in acid
medium AC
22
and b)AC
42
in basic medium
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

typical porous vascular morphology, and similar results
were shown by Xu et al. [67]. The vascular bundle mor-
phology of the original G. amplexifolia bamboo cross
section is more regular in comparison with ACs, where it
has been obtained a highly distorted surface. It is clear that
the activation in both media damaged the primary cell wall
of bamboo, weakening or destroying the connection
between the cell wall outer layer of lignin and carbohy-
drates or connections between each other of carbohydrates
provoking fibers separation, which in turn increases the
accessible surface area and porosity of AC. As a conse-
quence, the activated carbon is full of cavities with pores or
mesopores of different sizes and shapes. To determinate the
surface area and pore volume, BET analysis was realized.
Figure 10a, b correlates surface area versus yield and
pore volume versus pore diameter of selected activated
carbon, respectively. All samples showed a relation
between the BET surface area and the pore volume, as the
BET surface area was increased or decreased and also did
the pore volume (Table 5). The BET analysis corroborates
that the highest surface area *1226.8 m
2
g
-1
was
obtained for the sample CA
22
activated at 500 C for
120 min, which seems to be in agreement with other source
to obtain activate carbons [68]. It can be mentioned that
increasing the holding time of 60–120 min produces a
great enhancement of nitrogen absorption capacity
(Fig. 10c, d), indicating the increase in the specific surface
area and pore volume, this may be due to the removal of
carbons atoms by the effect of time and temperature, dur-
ing the activation step leading to the creation of new pores
and enlargement of existing pores [69]. Also, AC
21
and
AC
22
samples increase the pore sizes. However, the pore
size in AC
23
and AC
24
samples activated at 700 C did not
increase by the effect of the holding time and temperature,
since above 450 C the phosphate and polyphosphate
bridges that formed during the activation are thermally
unstable, leading to a diminishing in porosity by contrac-
tion of the char which reduces the pore size [57].
Figure 10c shows the N
2
adsorption/desorption isotherm
at 77 K for the AC
21
,AC
22
,AC
23
samples; the isotherms
show a sharp increase in the adsorption volume up to a PP
o
-1
of 0.1 a typical behavior of the adsorption isotherm type I
(IUPAC classification) where the plateau showed nearly
parallel to the PP
o
-1
-axis, confirming that after activation the
formed pores are predominantly considered as micropores
[70]. On the contrary, the adsorption capacity of the AC
22
sample continues increasing with the relative pressure value
up to a PP
o
-1
value of 1 (Fig. 10d). The trend of the
adsorption isotherm belongs to type II isotherm under the
IUPAC classification of isotherms (Fig. 10d), based on the
progressive increase in the adsorption capacity beyond the
relative pressure of 0.1 [71]; moreover, this isotherm does
not present any significant hysteresis loop, meaning that the
mesopore volume is very low [72]. The average pore
diameter of the AC
21
,AC
23
, and AC
24
samples were found to
be about 1.97 nm, indicating that the activated carbon pre-
pared was in the micropores region, whereas the AC
22
samples show values close to 3.8 nm [6].
On the other hand, AC
31
and AC
33
samples in basic media
show a behavior where the pore volume increases by the
(a)
10 μm 1 μm
1 μm
(b)
(c)
Fig. 9 SEM observations of
selected samples before and
after activation abamboo raw,
bactivated carbon in basic
media and cactivated carbon in
acid media
B. G. Salas-Enrı
´quez et al.
123

0 200 400 600 800 1000 1200 1400
0
10
20
30
40
50
60
70
80
90
(a) (b)
(c)
(e)
(d)
BET-N2Diameter/A°
/m2 g–1
Yield/%
AC21/1 h,500 °C
H3PO4
AC22 /2 h,500 °C
H3PO4
AC23 /1 h,700 °C
H3PO4
AC24 /2 h,700 °C
H3PO4
AC31 /1 h,500 °C
NaOH
AC33 /1 h,700 °C
NaOH
20 25 30 35 40 45 50 55
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Pore volume/cm3g–1
AC21 /1 h,500 °C
H3PO4
AC22
/2 h,500 °C
H3PO4
AC23 /1 h,700 °C
H3PO4
AC24
/2 h,700 °C
H3PO4
AC31
/1 h,500 °C
NaOH
AC33
/1 h,700 °C
NaOH
3
6
9
12
3
6
9
12
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
3
6
9
12
AC21
AC24
AC23
0.0 0.2 0.4 0.6 0.8 1.0
5
10
15
20
25
30
35
Quantity adsorbed/mmol g–1
Quantity adsorbed/mmol g–1
Quantity adsorbed/mmol g–1
Relative pressure/PP –1
o
Relative pressure/PP –1
o
Relative pressure/PP –1
o
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.0 0.2 0.4 0.6 0.8 1.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
AC33
AC31
Fig. 10 Surface area and pore structure arelationship between the
surface area and yield, brelationship between pore volume versus
pore diameter, cadsorption/desorption isotherms of N
2
at 77 K for the
AC
21
,AC
23
and AC
24
samples, dadsorption/desorption isotherms of
N
2
at 77 K for the AC
22
and eAdsorption/desorption isotherms of N
2
at 77 K for the AC
31
and AC
33
specimens
Activated carbon production from the Guadua amplexifolia using a combination of physical and…
123

effect of temperature (Fig. 10e); the activation temperature
has remarkable effects on the surface area, since volatile
compounds are released at higher temperature, letting a high
surface area. The shape of adsorption isotherm in these
samples was classified as a combination of classification
type I at low pressure and IV at intermediate and high PP
o
-1
ratio. In the initial part, they are type I, with an important
uptake at low relative pressures, the characteristic of
microporous materials. However, the open knee is pre-
sented, no clear plateau is attained, and certain slope was
observed at intermediate and high relative pressures. All
these facts indicate the transition from microporosity to
mesoporosity (type IV) [72]. The pore diameter for these
samples was about 5.2 and 2.5 nm, for samples AC
31
and
AC
33
, respectively. The two materials show a hysteresis loop
which enlarges according to the sequence AC
31
[AC
33
,
indicating a high mesopore volume. It may also be observed
that the AC
31
displays higher mesopore volume than AC
33
(as it can be seen by the height of the hysteresis loop); on the
other hand, AC
31
exhibits lower micropore volume than
AC
33
(as it can be seen by the amount of adsorbed N
2
at low
relative pressures) [73].
From the above results, it is seen that the BET surface
area and iodine number at 500 C of the samples CA
22
activated at 500 C for 120 min reached a maximum of
*1226.80 and *860 mg g
-1
, respectively, it is also clear
that the activation time has a significant effect on the
activated carbon. Increasing the activation duration from
60 to 120 min caused the BET surface area and iodine
number to increase.
Finally, the surface area obtained by BET isotherms
range from *371.39 to *1226.8 m
2
g
-1
and is compa-
rable to that of commercial activated carbon (CACs), such
as DCL320 (wood base, activated with phosphoric acid)
and DCL200 (coal base, steam activated) which have
SBET values of 1350 and 850 m
2
g
-1
[74] higher than
other materials such as Pica Chem 150 (671 m
2
g
-1
), Pica
Chem 120P (517 m
2
g
-1
), Pica Chem 120PN Ceca
(634 m
2
g
-1
) and CXA (606 m
2
g
-1
)[75].
To evaluate possible variations in the COD removal at
120 and 480 min, pH 2 and 8, adsorption experiments were
carried out (Fig. 11). COD concentration reduced from 560
to 80 mg O
2
L
-1
at pH 8. The COD reduction was
81 mass%. The pH does not significantly affect COD
removal; the more the time of adsorption, the more the
COD removal. The activated carbon prepared in this work
showed relatively great percentage removal of COD, as
compared to some previous works reported in the literature.
For example, Ahmad, et al. [26] found that maximum
reduction in COD of 75.21 mass%.
Conclusions
In this study, diverse synthesis conditions were used for the
preparation of the activated carbon using the G. amplexi-
folia bamboo specie as precursor and the following con-
clusions can be withdrawn: The activation with H
3
PO
4
favors a high surface area and more functional groups
(SOAG). Another important fact is that using two stages
during the activation process (carbonization–activation)
porosity values can be obtained similar to those reported in
the literature. The FFED methodology allowed to identify
the experimental factor influence over the final character-
istic of the AC; more important factors were activation
temperature, activation time and activating agent, being the
last one the most influent on activated carbon properties. In
addition, according to FFED results, the optimum condi-
tions for the preparation of the activated carbon were found
to be activation temperature of 600 C, activation time of
120 min, carbonization temperature of 325 C and acti-
vating agent H
3
PO
4
. Finally, G. amplexifolia bamboo
specie can be potentially used as an efficient raw precursor
for the synthesis of activated carbons and has shown to be
an effective adsorbent in the removal of DQO in leachates.
Acknowledgements B.G. Salas-Enrı
´quez is grateful for her post-
graduate fellowship through SIP-IPN and COFAA-IPN. The authors
are also grateful for the financial support through SIP2015-0202,
SIP2015-0227 Projects, COFAA and CONACYT through 132660,
133618 Projects and SNI. To Centro de Investigacio
´n en Micro y
Nanotecnologı
´a (Microna) for their facilities, Ph.D., L. Garcı
´a-Gon-
za
´lez and Ph.D., P.G. Gonza
´lez for their technical support. To
CICATA-Legaria IPN for their facilities, Ph.D., E. Reguera and Eng.
Neil Torres Figueredo for their technical support. And finally thanks
to, Q.F.B. Sandra Luz Suastes Acosta and Adela E. Rodrı
´guez-Sal-
azar for her technical support during the revision of the manuscript.
02468
0
20
40
60
80
100
Removal/%
Removal/%
pH 2
pH 8
Time/h
0
20
40
60
80
100
Fig. 11 Removal COD from leachates
B. G. Salas-Enrı
´quez et al.
123

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