Journal of Materials Science and Engineering 5 (2011) 20-25
Elemental and Physical Effect of Carbon from Date’s
Frond after Activation by Phosphoric Acid
Norasyikin Mohd Mustapha1, Abdul Rahim Yacob1 and Hassan M. Al Swaidan2
1. Chemistry Department, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Joho, Malaysia
2. Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
Received: May 15, 2010 / Accepted: June 24, 2010 / Published: January 10, 2011.
Abstract: Date frond, a low-cost agricultural by-product abundant in Saudi Arabia was used as a precursor for the production of porous
carbons by chemical activation using phosphoric acid. The developed surface morphology was studied using thermogravimetry
analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and single point BET surface area. The result obtained from TGA
indicates major weight loss is during heating before 400 °C. In this study, thus this temperature was chosen to carbonize the date frond
after the chemical activation using phosphoric acid (H3PO4) at various concentrations. FTIR results show that the sample is
successfully converted from raw material to pure high surface area carbon. This study also shows that chemical activation at 60%
H3PO4 gives the highest surface area of 1138.0 m2·g-1. Field emission scanning microscope/energy dispersive X-ray Spectroscopy
(FESEM/EDAX) on the other hand shows that chemical activation will wash away some minerals during activation to create the high
surface area activated carbon.
Key words: Date fronds, chemical activation, phosphoric acid, activated carbon, FESEM-EDAX.
1. Introduction
Saudi Arabia is one of the world largest exporters of
dates. It is estimated that twelve million date-palm trees
exist in Saudi Arabia. Every year, about three million
trees were cut and pruned. Pruning process of dates tree
is estimated to yield a flow of about 75,000 tons of
fronds including thorn and foliar every year [1]. This
has little economical value and are sometimes disposed
off as waste or burnt and this might be harmful to the
environment. The abundance and availability of
agricultural by-product make them good source as the
raw materials for activated carbon production.
Activated carbon (AC) is well known for high
porosity and widely used as adsorbent, catalyst and
support. They can be prepared from variety of
precursor by chemical or physical activation. Previous
study by Yacob et al., physical activation of frond,
Corresponding author: Abdul Rahim Yacob (1960- ), male,
Ph.D., professor, research field: nanotechnology. E-mail:
manrahim@kimia.fs.utm.my.
thorn and foliar, showed the presence of foreign
materials during analysis [2]. Chemical activation on
the other hand, consists of impregnation of the raw
material with a strong dehydrating agent and then
heating the mixture to form activated carbon. In this
study, chemical activation is carried out using Saudi
Arabia date frond waste using phosphoric acid.
Advantage using phosphoric acid is that the activation
temperature is relatively low 400 °C, while the product
yield is comparatively higher [3].
The main objective of this study is to utilize date
frond for the production of high surface area activated
carbon by chemical activation with different
concentration of H3PO4 acid and to investigate the
morphology and minerals after washing.
2. Experiment
The preparation of activated carbon involves
selection of raw material, raw material analysis and
preparation of activated carbon.
Elemental and Physical Effect of Carbon from Date’s Frond after Activation by Phosphoric Acid
2.1 Selections of Raw Materials
The raw material obtained was date-palm tree part
after pruning, which consists of date’s fronds from
Riyadh, Kingdom of Saudi Arabia. The sample obtained
was cut to small pieces of about 1 to 2 cm in size.
2.2 Raw Materials Analysis
Thermogravimetric analysis (TGA) of date’s fronds
was carried using Mettler-TA 4000 Analysis.
Approximately, 5 to 10 mg of the samples was heated
from 40 to 900 °C with the heating rate 20 °C per
minute under controlled atmosphere of nitrogen flow.
2.3 Preparation of Activated Carbon
5 g of samples date’s frond was weight and mixed
with 15 mL of 10, 20, 30, 40, 50, 60, 70 and 80%
H3PO4 acid respectively. After that, the samples were
impregnated in muffle furnace at 110 °C for 1 h. The
process was then followed by activation for 3 h at
400 °C still in the furnace. Washing of prepared sample
was carried to clean the acid content of the prepared
activated carbon. The washing process was continued
until pH 7 was attained. The samples were then dried in
oven at 110 °C to remove any moisture content.
2.4 Characterization
Several techniques were used to characterize the
prepared activated carbon.
2.4.1 Fourier Transform Infrared Spectroscopy
(FTIR) Analysis
About 1 mg of the solid samples before and after
activation was carried. The samples were grinded and
milled with 100 mg potassium bromide (KBr) to form a
fine powder. This powder was then compressed into a
thin pellet less than 7 tons for 5 minutes. The sample
was then analyzed using Shimadzu 8300 spectrometer
and the spectrum was recorded in a spectral range of
400-4000 cm-1.
2.4.2 FESEM and EDAX Analysis
The FESEM analysis was employed to study the
surface morphology and the porosity of the activated
21
carbon. The surface morphology and element
composition of the sample was analyzed using FESEM
6701F microscope with energy of 15.0 V couple with
EDX analyzer. The grounded sample was sputtered on
aluminium stub that covered with carbon cement tape.
The stub was place into the vacuum chamber of
FESEM instrument. The morphology scanning was
done in different magnification to obtain clear images.
3. Results and Discussion
3.1 Thermogravimetric Analysis of Raw Materials
Thermogravimetry analysis have been widely used to
study the thermal behavior of agricultural by-products.
This is therefore posible that thermal analysis would
also make an important contribution to knowlegde of
thermal behavior of biomass such as this date tree’s
fronds. Fig. 1 is the percentage weight loss during
thermalgravimetry analysis for palm dates frond. This
bar graph illustrate the weight lost that took place. The
first range of decomposition happened at 100-200 °C,
which represent 2.68% weight lost and is most probably
due to the surface moisture released by the sample
during heating. Second is from 200-300 °C, which
indicates further moisture, some bonded water and any
light hydrocarbon. The major weight lost of about
38.26% then occurred at temperature range of
300-400 °C. This is most probably represented by
chemical bonded water and the break down or the
decomposition of cellulose, hemicellulose and lignin to
carbon. Futher heating above 400 °C with weight loss
about 11.07% indicates the formation of volatile
materials from the activated carbon produced, like CO
and CO2 [2-6]. Thus, further heating will just reduce the
quantity of products of the high surface area carbon
produced.
3.2 Fourier Transform Infrared Spectroscopy (FTIR)
Analysis
Results from thermogravimetry analysis shows that
any excess of activation temperature above 400 °C will
transform the cellulose, hemicellulose and lignin to
22
Elemental and Physical Effect of Carbon from Date’s Frond after Activation by Phosphoric Acid
45
38.26
40
Weight Lost(%)
35
30
25
20
14.43
15
10
5
0
6.04
2.68
100 -200
200 -300
300 -400
400 -500
3.02
500 -600
2.01
600 -700
Temperature Range
Fig. 1
Fig. 2
Thermogravimetric analysis of date fronds.
FTIR Spectra for (a) Raw-DF, (b) AC-60%, (c) AC-C.
volatile materials [2]. Thus, for chemical activation the
temperature use was kept contact at 400 °C. Fig. 2
shows the comparison FTIR spectra of raw date frond
(Raw-DF), chemical activated carbon of date frond at
60% concentration of H3PO4 acid (AC-60%) and
commercial activated carbon (AC-C) for comparison.
Raw date frond (DF) in Fig. 2 shows the most
complicated and apparent spectrum. A strong and
broad adsorption peak appeared at 3,434.06 cm-1,
which corresponds to the stretching of O-H functional
group and this indicates the presence of bonded
hydroxide in the raw sample. There was another peak
observed at 2,930.44 cm-1 corresponding to the C-H sp3
stretching. A strong conjugated C=C peak also
observed around 1,633.83-1,638.32 cm-1. This sample
also shows four important absorption peaks at 1,251.06,
1,160.53, 1,113.89 and 1,053.53 cm-1 respectively
which represent the stretching of C-O f unctional group.
Elemental and Physical Effect of Carbon from Date’s Frond after Activation by Phosphoric Acid
From the spectrum, it can be suggested that the main
oxygen groups present in the raw-DF are carbonyl,
ethers and alcohols group which are normally present
in plant cellulose.
In contrast to the FTIR spectrum shown by raw-DF,
the spectrum AC-60% and AC-C illustrate less
absorption peaks, clearly, most of the absorption peaks
of functional groups were diminished. Although the
samples were prepared both by different activation
methods, there seem similarities in the vibration
patterns. Basically all the samples show a weak broad
peak around 3425.12-3440.32 cm-1, which indicates the
presence of hydroxide group in the samples. It is most
probably of the R-OH bonded like molecule in carbon.
Finally, the spectra for the prepared activated carbon
from date’s frond chemical activated at 60%
phosphoric acid when comparable to the commercial
activated carbon, there seem a great similarity. This
might indicate that the prepared activated carbon is of
similar in grade and standard of that the commercial
prepared carbon. The functional groups present in the
samples were tabulated in Table 1.
3.3 Influence of the H3PO4 Concentration on Surface
In this study, the surface area for the raw date fronds
was only 4.6 m2·g-1. Fig. 3 illustrates the surface area
of activated carbon produced at different
concentration of H3PO4 acid. It was shown that the
surface area of activated carbon produced increase
with the increases of phosphoric acid concentration. It
may be spaculated that higher acid concentration,
would enhance porosity development. From the graph,
it shows that the highest surface area, 1,139 m2·g-1 of
activated carbon produced is belong to 60% of H3PO4
(AC-60%) acid used during the activation process. A
decrease in surface area is noticed at 70% and 80%
H3PO4 acid, which may attributed to the rupture of
activated carbon morphology and also the formation
of a layer of polyphosphate (a skin) over the
developing pore structure protecting it from excessive
gasification. This result is supported by Girgis [8],
23
Table 1 Wave number of some functional groups present
in the samples.
Sample
Wave number (cm-1)
Raw date
3,434.06
fronds
2,930.44
1,635.58
1,251.06, 1,160.53,
1,113.89, 1053.53
AC-60% 3,425.12
AC-C
3,430.56
Functional group
O–H stretching
C–H (sp3) stretching
C=C (conjugated) stretching
C–O stretching
O–H stretching
O–H stretching
Fig. 3 Single point BET surface area of activated carbon at
different concentration of H3PO4.
which indicate that higher acid concentration were not
accompanied by a respective improvement in porosity,
however collaption of the structured pore of the
activated carbon.
The washing process on the activated carbons
produced play important role of porosity evolution.
After activation, most of the activant is still in the
particle and intense washing to eliminate it produces
the porosity. It was found by Girgis [8] that there is a
good agreement between the volume of micropores and
the volume occupied by the acid phase existing at the
activation temperature. The entrapped polyphosphates
in the final product will appear in the form of high ash
content as well as impart an acidic character on the
carbon product. The high content of ash will be
responsible lower the surface area of activated carbons
produced. Finally, to overcome this, washing process
was done until pH 7 is achieved which indicate all the
acid content were successfully removed from the
activated carbon [7-9].
24
Elemental and Physical Effect of Carbon from Date’s Frond after Activation by Phosphoric Acid
3.4 FESEM Analysis
3.5 EDAX Analysis
Energy Dispersive X-ray (EDX) analysis was
carried out on the surface of activated carbons. The
value or the data obtained with EDX analysis is only a
rough estimation of the surface elemental composition.
It should not be regarded as an absolute composition of
the activated carbon.
016
Counts
The FESEM micrographs provide information on
the structural changes in the palm date frond for
anatomy during the activation process. Fig. 4 shows
raw palm date frond (R-PDF) before and after
activation. Fig. 4a shows the micrograph of R-PDF at
500x magnification. The surface of R-PDF is curly
form resulted from the presence of cellulose,
hemicelluloses and lignin in the raw material without
any cracks and crevices. This would account for its
poor or negligible BET surface area.
The framework development was so rapid in Fig. 4b,
resulting in too much cavities and leads to crack
formation. Due to this well developed pores, the
AC-60% possessed high BET surface area. Fig. 4b
shows the micrograph of AC-60% at 5000x magnification. The micrograph magnifies the internal cavities,
which are now clearly visible. Direct measurement
from the micrograph shows that the average pore
diameter is 5.23 μm. The surface of the AC-60% seems
to be clearer and smoother than R-PDF surface due to
the removal of volatile compounds and impurities
during the activation process and followed by
phosphoric acid-wash. It can bee seen that there are
solid appeared in the pores of AC-60% where some
small white particles are scattered on the surface of the
carbon, probably due to the residue of the activating
agent, phosphoric acid which was not washed all out
during the activation process.
8000
7200 C
6400
5600
4800
4000
3200
2400
O
P
1600
Si
800
0
0.00 0.80 1.60 2.40 3.20 4.00 4.80 5.60 6.40 7.20
keV
(b)
Fig. 5 EDAX (a) before and (b) after activation using
H3PO4 acid.
Counts
(a)
Fig.4
(b)
FESEM of (a) R-PDF and (b) AC-60% H3PO4 acid.
2400
C
2100
1800 O
1500
1200
Pt
900
Cu
Pt Cl
CuMg
Ca
Pt
600
Na Si Pt Cl KK
Ca
Cu CuPt
300
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
(a)
011
Elemental and Physical Effect of Carbon from Date’s Frond after Activation by Phosphoric Acid
Table 2 Elemental analysis before and after chemical
activation using H3PO4 acid.
Elements
C
O
Na
Mg
Si
Cl
K
Ca
Cu
Pt
P
Before washing %
59.17
34.66
0.32
0.4
0.29
1.34
0.91
0.64
0.96
1.32
-
After washing %
77.28
20.64
0.2
1.87
The results on surface composition of EDAX for raw
R-PDF and activated carbon AC-60% samples was
shown by Figs. 5a and 5b respectively, while the
elemental before and after washing is tabulated by Table
1. Fig. 5a shows, before activation, raw materials
contain the highest amount of elements other than
carbon, such as oxygen, sodium, magnesium, silica,
chlorine and etc. These elements however, are washed
and diminished during the chemical activation process.
EDAX analysis in Fig. 5b shows that after the activation
process, only four elements comprising of carbon
(77.3%), oxygen (20.6%), silica (0.2%) and phosphorus
(1.8%), present respectively. In Table 2, the appearance
of phosphorus elements after activation can be explained
by the use of phosphoric acid as the activating agent in
the activation process. Thus, the phosphate ions in the
carbon come from the phosphoric acid used.
4. Conclusions
The TGA results demonstrate that the best
temperature for activation is 400 °C and any
temperature above might affect the product activated
carbon. Single point BET surface area for the activated
carbons prepared via different concentration of
phosphoric acid indicate AC-60% shows the highest
surface area of 1139 m2·g-1 compared to the raw date
fronds of only 4.6 m2·g-1 which is slightly better to the
commercial activated carbon. Finally, high surface area
carbon can be obtained by washing with phosphoric
and also purify the activated carbon.
25
Acknowledgments
The authors acknowledge Chemistry Department,
University Teknologi Malaysia and King Saud
University, Saudi Arabia for this work and the Ministry
of Science, Technology and Innovation (MOSTI) for
the financial support through the Fundamental
Research Grant Scheme (FRGS).
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
S.A.J. Radwan, Biological degradation of date-palm
fronds used in construction, The 6th Saudi Engineering
Conference, 2002, pp. 217-219.
N.M. Mustapha, M.A.A. Mustajab, A.R. Yacob, H.M.
Swaidan, Physical activation of Saudi Arabia date palm
tree’s foliar, frond and thorn, Journal IEEE Explore,
MIMT (2010) 511-517.
Y. Guo, D.A. Rockstraw, Physicochemical properties of
carbons prepared from pecan shell by phosphoric acid
activation, Journal of Bioresource Technology 98 (2007)
1513-1521.
D. Kalderis, S. Bethanis, P. Paraskeva, E. Diamadopoulos,
Production of activated carbon from bagase and rice husk
by a single-stage chemical activation at low retention
times, Journal of Bioresource Technology 99 (2008)
6809-6816.
J. Hayashi, T. Horikawa, I. Takeda, K. Muroyama, N.A.
Farid, Preparing activated carbon from various nutshells
by chemical activation with K2CO3, Journal of Carbon 40
(2002) 2381-2386.
T. Watari, H. Tsubira, T. Torikai, M. Yada, S. Furuta,
Preparation of porous carbon/silica composite from rice
husk powder, Journal of Ceramics Processing Reseacrh 4
(2003) 177-180.
A.R. Yacob, S.Z. Hanapi, Vicinisvarri inderan “nano
tungsten carbide supported on carbon from palm kernel
shell in remediation of chlorofluorocarbon (CFC-12)”,
Journal IEEE Explore (2009) 556-563.
B.S. Girgis, A.N. Hendawy, Porosity development in
activated carbons obtained from date pits under chemical
activation with phosphoric acid, Journal of Microporous
and Mesoporous Materials 52 (2002) 105-117.
Y.A. Rahim, S.N. Aqmar, D.R.S. Dewi, ESR study of
electron trapped on activated carbon by KOH and ZnCl2
activation, Journal of Materials Science and Engineering 4
(2010) 21-25.