Bioresource Technology 101 (2010) 426–429
Contents lists available at ScienceDirect
Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech
Short Communication
Influences of pyrolysis condition and acid treatment on properties of durian
peel-based activated carbon
Kamchai Nuithitikul, Sarawut Srikhun, Samorn Hirunpraditkoon *
Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand
a r t i c l e
i n f o
Article history:
Received 28 February 2009
Received in revised form 15 July 2009
Accepted 18 July 2009
Available online 19 August 2009
Keywords:
Durian peel
Activated carbon
Basic Green 4 dye
Vacuum pyrolysis
Adsorption kinetics
a b s t r a c t
Durian peel was used for the synthesis of activated carbon used for adsorption of Basic Green 4 dye. Activated carbon was synthesised under either nitrogen (N2) atmospheric or vacuum pyrolysis, followed by
carbon dioxide (CO2) activation. The synthesised activated carbon then was treated with hydrochloric
acid (HCl) solution. The results showed that activated carbon synthesised under vacuum pyrolysis exhibited better properties and adsorption capacities than that under nitrogen atmospheric pyrolysis. The HCl
treatment improved properties and adsorption capacities of activated carbons. Pseudo-second-order
kinetics well described the adsorption of Basic Green 4.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Adsorption by activated carbon is an effective method for dye
removal from wastewater (Chandra et al., 2007; Önal et al.,
2007; Hameed and Hakimi, 2008; Wang et al., 2008). Several agricultural wastes have been used for the production of activated carbon in order to reduce the raw material cost. These wastes are also
renewable, providing the environmental benefit.
Despite numerous studies in preparation of activated carbon
from several agricultural wastes, a limited number of studies have
reported the production of activated carbon from durian peel or
the direct use of dried durian peel as an adsorbent (Chandra
et al., 2007; Hameed and Hakimi, 2008). Chandra et al. (2007) prepared activated carbon from durian peel by chemical (KOH) activation, and used for the removal of basic dye (methylene blue) from
aqueous solution. Hameed and Hakimi (2008) used dried durian
peel without significant processing as a low cost adsorbent for
the removal of acid dye (Acid Green 25) from aqueous solution.
Since activated carbon synthesised from physical activation was
reported to give wider pore size distribution and more mesoporous
structure compared to that derived from chemical activation
(Azargohar and Dalai, 2008). This mesoporous character is expected to be favourable for the adsorption of large molecules of
adsorbates such as dye molecules. Therefore, in the present work
the activated carbon was prepared from durian peel with physical
(CO2) activation. Prior to activation, durian peel was carbonised
* Corresponding author. Tel.: +662 9132500x8231; fax: +662 5870024.
E-mail address: samornh@hotmail.com (S. Hirunpraditkoon).
0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2009.07.040
under either nitrogen (N2) atmospheric or vacuum pyrolysis in order to investigate the effect of pyrolysis condition. After the synthesis, the effect of HCl treatment on properties of activated
carbon was investigated. Finally the adsorption capacities of activated carbons synthesised from N2 atmospheric or vacuum pyrolysis were evaluated, using Basic Green 4 dye as a studied model.
2. Methods
2.1. Preparation and characterisation of activated carbon
Durian peel was obtained locally, washed, cut into small pieces
(1 1 cm2) and dried at 80 °C for 24 h. The dried durian peel (100 g
a batch) was carbonised in an electrical furnace (Model N7 Naber)
under either N2 atmospheric (150 mL min1) or vacuum (56 kPa)
pyrolysis with heating from room temperature to 900 °C at a heating rate of 5 °C min1. Once the final temperature was reached,
activation with 300 mL min1 of CO2 took place and lasted for
1 h. The activated product was cooled down to room temperature
under N2 flow. Activated carbons synthesised under N2 atmospheric and vacuum pyrolysis were assigned as ACN and ACV
respectively. Both ACN and ACV were then treated with 2 M HCl
or deionised water (H2O) for 24 h. The treated ACN and ACV were
washed with deionised water until pH of the washing water was
neutral. Finally they were dried at 110 °C for 3 h. Prior to use, they
were grounded to a desired mesh size of less than 0.18 mm.
Proximate and ultimate analyses of dried durian peel, ACN and
ACV treated with water were performed with thermal analyser
427
K. Nuithitikul et al. / Bioresource Technology 101 (2010) 426–429
(NETZSCH STA 409C) and elemental analyser (CHN analyser)
respectively. Yields of both ACN and ACV treated with water were
calculated based on the weight of dried durian peel initially put
into the furnace. The treated ACN and ACV were characterised with
N2 adsorption at 196 °C using Autosorb I (Quantachrome Corporation) and the Brunauer–Emmett–Teller (BET) model.
2.2. Adsorption study
Basic Green 4 dye, C50H52N4O8, at pH of 5 was used for adsorption study. A set of volumetric flasks containing 25 mL of Basic
Green 4 solutions with different initial concentrations (337, 562,
784 and 1000 mg L1) was prepared. HCl-treated ACN or HCl-treated ACV (0.05 g) was added into each flask. The flasks were placed
in an isothermal shaker in which the temperature was maintained
at 30 ± 1 °C with the stirring speed of 150 rpm. The flasks were taken out from the shaker at various time intervals and samples were
taken for analysis. The amount of dye adsorbed onto activated carbon per unit mass of activated carbon at any time t, qt (mg g1),
was calculated by:
qt ¼
ðC 0 C t ÞV
m
ð1Þ
where C 0 and C t (mg L1) are the liquid–phase concentrations of
dye at initial and time t, respectively. V is the volume of solution
(L), and m is the amount of activated carbon used (g).
To determine dye concentrations, samples after adsorption
were taken and centrifuged at 2500 rpm. The clarified supernatant
solutions were carefully decanted to be analysed with a double
beam UV/VIS spectrophotometer (UV500 model, UNICAM). The
optimum wavelength for Basic Green 4 was 617 nm. The final concentrations of the solutions were calculated from the calibration
curve.
3. Results and discussion
3.1. Characterisation of activated carbon and durian peel precursor
Proximate and ultimate analyses of dried durian peel and ACN
and ACV treated with H2O are shown in Table 1. Yield of ACN treated with H2O is higher than that of ACV treated with H2O. This is
due to vacuum pyrolysis gives higher volatilisation and CO2–carbon reaction. Typically the yield loss of activated carbon is due to
two main causes: volatilisation and reaction. It is likely that char
obtained from vacuum pyrolysis has a lower yield than that obtained from N2 atmospheric pyrolysis because substances are more
volatilised under reduced pressure compared to atmospheric pressure. As a result, the structure of char from vacuum pyrolysis is less
occupied by deposits (Cao et al., 2002). When this char is further
activated, it can react faster with CO2. As can be seen from Table
1, the carbon content of ACV is lower than ACN, suggesting higher
CO2–carbon reaction.
BET surface areas and pore volumes of ACN and ACV treated
with HCl and H2O solutions are reported in Table 1. The results
show that activated carbons synthesised under vacuum pyrolysis
have greater BET surface areas and pore volumes than those synthesised under N2 atmospheric pyrolysis. This is owing to the char
obtained from vacuum pyrolysis being more reactive to CO2 oxidation than that obtained from N2 atmospheric pyrolysis (Cao et al.,
2002). Moreover, char produced from N2 atmospheric pyrolysis
has higher concentration of carbonaceous deposits on the surface
and/or in the pores than that from vacuum pyrolysis (Cao et al.,
2002). These deposits inhibit the access of the oxidising gas (CO2).
For activated carbons synthesised under the same carbonisation
condition (either N2 atmospheric or vacuum pyrolysis), those treated with HCl solution had greater BET surface areas and pore volumes than those treated with H2O. An increase in these
properties of activated carbons treated with HCl solution is likely
to be due to the removal of impurities on the surface and/or in
the pores. Acid solution is generally used to purify activated carbon
after the synthesis (Berman, 2003). Activated carbon can contain
up to 20 wt.% of mineral matter occluded in the pores (PastorVillegas et al., 1999). These inorganic constituents could be removed from both activated carbon and its precursor with HCl,
H2SO4 or HF treatment reducing, consequently ash content (Davini,
2001; Kopac and Toprak, 2007; Wang and Zhu, 2007). The highest
BET surface area (1015 m2 g1) and pore volume (0.66 cm3 g1) of
durian-based activated carbon prepared by physical activation in
this work were higher than that prepared by chemical KOH activation in the study of Chandra et al. (2007). Their activated carbon
had BET surface area of 991.82 m2 g1 and pore volume of
0.471 cm3 g1.
Nitrogen adsorption isotherms of ACN and ACV treated with HCl
solution and H2O are similar and shown in Fig. 1. Activated carbons
synthesised under vacuum pyrolysis give higher adsorption
capacities than those synthesised under N2 atmospheric pyrolysis.
This attributes to the higher BET surface area and pore volume of
the former. For activated carbons synthesised under the same
Table 1
Properties of activated carbons synthesised under nitrogen atmospheric and vacuum pyrolysis and treated with various solutions.
Properties
ACN treated with
ACV treated with
Durian peel
HCl
H2O
HCl
H2O
precursor
BET surface area (m2 g1)
Pore volume (cm3 g1)
Average pore diameter (nm)
Yield (wt.%)
748
0.46
2.488
–
659
0.40
2.411
21.32
1015
0.66
2.602
–
951
0.61
2.570
18.74
–
–
–
–
Proximate analysis (%)
Moisture content
Volatile matter
Ash
Fixed carbonb
–
–
–
–
–
23.05a
16.19a
60.76a
–
–
–
–
–
25.35a
19.91a
54.74a
4.54
69.82
4.22
21.42
Ultimate analysis (%)
Carbon
Hydrogen
Nitrogen
Oxygen, sulfur and othersb
–
–
–
–
64.36
1.25
0.00
34.39
–
–
–
–
55.77
0.96
0.06
43.21
42.86
5.71
0.18
51.25
Note: ACN, ACV mean activated carbon synthesised under nitrogen atmospheric and vacuum pyrolysis respectively.
a
Dry basis.
b
By difference.
428
K. Nuithitikul et al. / Bioresource Technology 101 (2010) 426–429
300
ACN - HCl
ACV - HCl
ACN - H 2O
ACV - H 2O
Commercial AC (Coconut shell based)
450
400
250
200
-1
qt (mg g )
3
-1
Volume adsorbed (cm g STP)
500
350
300
150
100
200
250
-1
150
100
50
50
200
a
0
0
15
30
45
60
337 mg L
-1
562 mg L
-1
784 mg L
-1
1000 mg L
0
150
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0
1.0
1000
2000
3000
4000
5000
t (min)
Relative pressure, p/p o
300
Fig. 1. Nitrogen adsorption isotherms of ACN and ACV treated with H2O and HCl
solution.
250
3.2. Adsorption kinetics
The influences of initial dye concentration and contact time on
adsorption capacities of HCl-treated ACN and HCl-treated ACV are
shown in Fig. 2. The adsorption can be described by two-stage kinetic behaviour for all the initial concentrations of Basic Green 4.
During the first 1 min, the rapid initial adsorption rates are observed. After that the adsorption capacities begin to level off indicating much slower rates. The plateaus are finally obtained
implying no more dye is removed from the solution. At this state,
equilibrium is reached. The amount of dye adsorbed at the equilibrium time indicates the maximum adsorption capacity of the activated carbon under that condition. When the initial dye
concentrations are increased, the maximum adsorption capacities
200
-1
qt (mg g )
carbonisation condition, those treated with HCl solution have
better nitrogen adsorption capacities than those treated with
H2O solution. Activated carbons synthesised under vacuum pyrolysis and treated with HCl solution or H2O give higher adsorption
capacities than a commercial activated carbon (C. Gigantic Carbon
derived from coconut shell), suggesting a potential use of the
durian peel-based activated carbon as a commercial grade.
According to the IUPAC classification for adsorption isotherm,
the isotherms in this study showed characteristics between those
of Type I and II. Volume of adsorbed nitrogen considerably increased with the relative pressure from 0 to 0.05. Moreover microporous solids are typically associated with Type-1 adsorption
isotherm. However, nitrogen could be adsorbed, but to a lesser degree, with the relative pressure higher than 0.05, particularly for
activated carbons synthesised under vacuum pyrolysis. This indicated a presence of mesopores. The average pore diameters between 2.411 and 2.602 nm principally denoted mesoporous
characteristics. Within the relative pressures range of 0.2–1.0, isotherms of activated carbons synthesised under vacuum pyrolysis
were steeper than those synthesised under N2 atmospheric pyrolysis. In other words, the former deviated more from Type-1 isotherm. This suggests that mesopores are more generated with
activated carbons synthesised under vacuum pyrolysis. Therefore
it can be concluded that the nature of the activated carbon derived
from durian peel is a combination of microporous and mesoporous.
This is in agreement with the study of Chandra et al. (2007). The
presence of mesopores in combination with micropores is expected to play a significant role in the adsorption of large molecules of adsorbates including dye molecules.
150
250
200
150
100
50
0
100
50
b
0
0
-1
0
1000
2000
15
30
45
60
3000
337 mg L
-1
562 mg L
-1
784 mg L
-1
1000 mg L
4000
5000
t (min)
Fig. 2. Influences of initial dye concentration and contact time on adsorption
capacities of: (a) HCl-treated ACN; (b) HCl-treated ACV.
of both HCl-treated ACN and HCl-treated ACV increase due to the
increase in the driving force (concentration gradient).
The equilibrium time for adsorption of Basic Green 4 with initial
concentrations of 337 and 562 mg L1 was 24 h. However for dye
with higher initial concentrations of 784 and 1000 mg L1, longer
equilibrium time of 48 h was noticed. The long equilibrium time
indicates that adsorption of Basic Green 4 from aqueous solution
onto durian peel-based activated carbon is a gradual process. This
corresponds to the fact that activated carbon typically consists of a
porous structure with large internal surface area, and the adsorption process consists of three consecutive steps. First molecules
of dye diffuse through the film surrounding the surface of the activated carbon (film diffusion). Next the molecules move from the
external surface into the pores of the activated carbon (pore diffusion). Finally the molecules are adsorbed onto the active sites at
the internal surface within the pores of the activated carbon. Long
contact time is required for this phenomenon. Moreover, HCl-treated ACV had higher maximum adsorption capacities than those
HCl-treated ACN. With an increase in the initial dye concentrations
from 337 to 1000 mg L1, the maximum adsorption capacities for
HCl-treated ACN and HCl-treated ACV increased from 122.4 to
243.8 mg g1 (Fig. 2a) and 147.6 to 284.0 mg g1 for (Fig. 2b),
respectively.
To determine adsorption kinetics, pseudo-first-order and pseudo-second-order kinetic models (Lagergren, 1898; Ho and McKay,
1999) were used and compared with the adsorption data. The results indicated that pseudo-second-order kinetics better represented the adsorption of Basic Green 4 on activated carbons both
synthesised under N2 atmospheric and vacuum pyrolysis. As
429
K. Nuithitikul et al. / Bioresource Technology 101 (2010) 426–429
Table 2
Rate constants, correlation coefficients and parameters of pseudo-first-order and pseudo-second-order kinetics models.
C0
(mg L
qe;exp
1
)
HCl-treated ACN
337
562
784
1000
HCl-treated ACV
337
562
784
1000
(mg g
Pseudo-first-order
1
)
3
1
k1 10 (min
)
Pseudo-second-order
qe;cal (mg g
1
)
2
R
k2 104 (g mg1 min1)
qe;cal (mg g1)
R2
122.4
155.5
226.8
243.8
6.45
3.22
2.30
3.46
54.8
74.6
129.5
119.9
0.948
0.906
0.963
0.893
9.05
8.82
5.76
5.74
113.6
125.0
186.3
226.1
0.996
0.995
0.990
0.996
147.6
217.8
259.6
284.0
5.53
5.07
5.52
4.14
42.4
74.2
88.1
91.1
0.938
0.935
0.907
0.828
14.48
7.65
6.97
8.12
137.0
200.0
238.1
250.0
0.998
0.998
0.998
0.998
shown in Table 2, pseudo-second-order model gives very high
values of correlation coefficients (R2) of more than 0.99 for both
HCl-treated ACN and HCl-treated ACV. Moreover the calculated
qe values from the pseudo-second-order kinetic model are better
closed to the experimental data than those from the pseudofirst-order kinetic model. Similar finding was reported by Wang
et al. (2008) who found the pseudo-second-order equation better
predicted the adsorption of Basic Green 4 on wheat bran-based
activated carbon. However Chandra et al. (2007) who produced
activated carbon from durian peel with chemical activation found
that pseudo-first-order kinetics model was better described the
adsorption kinetics of methylene blue than pseudo-second-order
kinetics model. This difference is attributed to a difference in the
adsorption system (e.g. adsorbate).
4. Conclusions
BET surface area and pore volume of durian peel-based activated carbon synthesised from vacuum pyrolysis and CO2 activation at 900 °C in this study were comparable to those
synthesised from chemical activation using KOH (Chandra et al.,
2007). Vacuum pyrolysis provided activated carbon with superior
properties (higher BET surface area, pore volume and adsorption
capacities for Basic Green 4 dye) than N2 atmospheric pyrolysis.
Post-treatment of activated carbon with HCl solution improved
BET surface area and pore volume in comparison to H2O treatment.
Acknowledgements
This research was financially supported by Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, Thai-
land. The authors would like to thank C. Gigantic Carbon Co., Ltd.
for the provision of the commercial activated carbon.
References
Azargohar, R., Dalai, A.K., 2008. Steam and KOH activation of biochar: experimental
and modeling studies. Microporous and Mesoporous Materials 110, 413–421.
Berman, Y., 2003. Process for preparing activated carbon from urban waste. United
States Patent 6558644.
Cao, N., Darmstadt, H., Soutric, F., Roy, C., 2002. Thermogravimetric study on the
steam activation of charcoals obtained by vacuum and atmospheric pyrolysis of
softwood bark residues. Carbon 40, 471–479.
Chandra, T.C., Mirna, M.M., Sudaryanto, Y., Ismadji, S., 2007. Adsorption of basic dye
onto activated carbon prepared from durian shell: studies of adsorption
equilibrium and kinetics. Chemical Engineering Journal 127, 121–129.
Davini, P., 2001. SO2 adsorption by activated carbons with various burnoffs
obtained from a bituminous coal. Carbon 39, 1387–1393.
Hameed, B.H., Hakimi, H., 2008. Utilization of durian (Durio zibethinus Murray) peel
as low cost sorbent for the removal of acid dye from aqueous solutions.
Biochemical Engineering Journal 39, 338–343.
Ho, Y.S., McKay, G., 1999. Pseudo-second order model for sorption processes.
Process Biochemistry 34, 451–465.
Kopac, T., Toprak, A., 2007. Preparation of activated carbon from Zonguldak region
coals by physical and chemical activations for hydrogen sorption. International
Journal of Hydrogen Energy 32, 5005–5014.
Lagergren, S., 1898. Zur theorie der sogenannten adsorption gelöster stoffe.
Kungliga Svenska Vetenskapsakademiens. Handlingar 24 (4), 1–39.
Önal, Y., Akmil-Basßar, C., Sarıcı-Özdemir, Ç., 2007. Investigation kinetics
mechanisms of adsorption malachite green onto activated carbon. Journal of
Hazardous Materials 146 (1–2), 194–203.
Pastor-Villegas, J., Gómez-Serrano, V., Durán-Valle, C.J., Higes-Rolando, F.J., 1999.
Chemical study of extracted rockrose and of chars and activated carbons
prepared at different temperatures. Journal of Analytical and Applied Pyrolysis
50, 1–16.
Wang, S., Zhu, Z.H., 2007. Effects of acidic treatment of activated carbons on dye
adsorption. Dyes and Pigments 75, 306–314.
Wang, X.S., Zhou, Y., Jiang, Y., Sun, C., 2008. The removal of basic dyes from aqueous
solutions using agricultural by-products. Journal of Hazardous Materials 157,
374–385.