Adsorption Properties and Potential Applications of Bamboo Charcoal: A Review

Abstract

Bamboo charcoal was produced by pyrolysis or carbonization process with extraordinary properties such as high conductivity, large surface area and adsorption property. These properties can be improved by activation process that can be done thermally or chemically. In this paper, carbonization and activation process of bamboo, its structural and adsorption properties will be presented. Herein, the adsorption properties of bamboo charcoal that has fully utilized in solar cell as the electrode, adsorbent for water purification and electromagnetic wave absorber are reviewed.

Full text

Adsorption Properties and Potential
Applications of Bamboo Charcoal: A Review
S.S.M. Isa1,*, M.M. Ramli1, N.A.M.A. Hambali1 , S.R. Kasjoo1 , M.M. Isa1 , N.I.M. Nor1 , N.
Khalid1 , and N. Ahmad1
1School of Microelectronic Engineering, Universiti Malaysia Perlis, Pauh Putra Campus, 02600 Arau,
Perlis, Malaysia
Abstract. Bamboo charcoal was produced by pyrolysis or carbonization
process with extraordinary properties such as high conductivity, large
surface area and adsorption property. These properties can be improved by
activation process that can be done thermally or chemically. In this paper,
carbonization and activation process of bamboo, its structural and
adsorption properties will be presented. Herein, the adsorption properties
of bamboo charcoal that has fully utilized in solar cell as the electrode,
adsorbent for water purification and electromagnetic wave absorber are
reviewed.
1 Introduction
Bamboo charcoal is made up from pieces of bamboo (5 years >) which undergoes a heat
treatment normally at 800-1200 °C (pyrolysis process). As early as 1486 AD, bamboo
charcoal has been used in various ways due to its tremendous extraordinary properties.
What makes this charcoal is so amazing is the carbonization process which creates a
product with an enormous surface area to mass ratio which has high ability to attract and
hold (adsorption) a wide range of materials, chemicals, minerals, radiowaves, humidity,
odours and harmful substances.
Among all, absorption property of this material is well discussed and has been utilized
in various applications such as household products (water filtration, humidity and odour
adsorbent, air freshener, fruits and vegetables saver etc.) and health and beauty products
(soap, powder, foot patch etc.). After carbonized, this material can be used as an efficient
absorbent. Depends on what it adsorbs, the carbonized bamboo also can become saturated
and act as the fertilizer. In another hand, the adsorbed impurities can be burned off without
destroying the adsorbent property, which means it can be reused. The adsorption properties
of bamboo charcoal can be improved and become a perfect absorbent when this material is
further activated either thermally or chemically. No longer limited to the previous
applications, recently, the bamboo charcoal has been applied as the working electrode
composite in dye sensitized solar cell to increase device efficiency [1], as the absorbent for
water purification [2] and microwave absorber in antenna [3].
* Corresponding author: sitisalwa@unimap.edu.my
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© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of
the Creative
Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).

Become the alternative to activated carbon, carbon nanotubes, graphene and other
carbon based materials, this element is the most notable among readily and renewable
biomass resources because bamboo is the fastest growing plants in Earth [4]. In this study,
bamboo charcoal production, structural and adsorption properties specifically in dye
sensitized solar cell, water purification and microwave absorber are reviewed.
2 Carbonization of camboo charcoal
Generally, Moso bamboo (Phyllostachys pubenscens) is used as the starting material in
the production. This bamboo is cut into small pieces and washed by boiling distilled water
for some hours and dried at temperature nearly 110 °C to remove moisture [5]. Then, the
carbonization process is held in the oven normally at N2 flow [2] at temperature over 800-
1200 °C at longer period hours. However, bamboo charcoal also can be produced at lower
temperature (500-900 °C) with different quality which has been presented in [2]. The fresh
bamboo charcoal produced from this process is the raw bamboo charcoal. This material
already has an extraordinary micro structure with high absorptive capacity.
Fig. 1. Bamboo (a) Moso, (b) charcoal and (c) powder.
3 Activation of bamboo charcoal
Activation of carbonized bamboo charcoal is important to improve the original structure
and increase the adsorption properties. It can be mixed with CO2 [2,6], HNO3 [2,7], NH3
[2,8] and many more before it is heated again at certain temperature (500-1200 °C) for
some periods. The annealed bamboo charcoal need to be cooled to a temperature between
170 to 240 °C before it serves as activated bamboo charcoal. The activation step is
important to increase the volume of the material, breaks some bonds of the turbostratic
carbon structures that form surface functional groups and removes non-crystallized carbons
from the bamboo charcoals.
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4 Structure and adsorption properties
Figure 2 shows the structure of bamboo charcoal before and after activation. As shown
in the figures, vascular bundles of the bamboo charcoal are arranged in various sizes. The
pore characteristics of this material can be macropore (> 50 nm), mesopore (2-50 nm) or
micropore (< 2nm). This pore characteristic and the resistant coefficient of this material are
affected by the temperature of carbonization and activation processes. As the temperature
increases, the material will change from insulator to semiconductor or even to conductor,
while the pore size is getting bigger. Normal and activated bamboo charcoal have the same
ability to absorb chemicals and substances from air and water, however the normal bamboo
charcoal has poor holding capacity compared to the activated forms. Other than surface
area to mass ratio, the excellent adsorption property is contributed by the van der Waals
force [11].
Fig. 2. Bamboo charcoal structure (a) after carbonization, (b) after activation [9] and (c) at higher
magnification [10].
5 As electrodes in dye sensitized solar cell
Conventionally in Dye Sensitized Solar Cell (DSSC), carbon based material and
titanium dioxide (TiO2) were employed as counter and working electrodes. However, TiO2
working electrodecan only absorb ultraviolet and several approaches including the use of
dopants such as nitrogen [12], hydrogen [13], metal [14] and others to introduce disorder in
the surface layer and narrow the band gap of TiO2 which can improve the photocatalytic
activities were done. The introduction of disorder and dopant at the surface would enhance
visible and infrared absorption [13]. Several initiatives using carbonaceous materials such
as graphene [15], carbon nanotubes [16] and hybrid graphene-carbon nanotubes [17] have
been performed in order to increase device efficiency due to their good conductivity and
high effective surface area. These materials can help the electron excitation and enhance
the light harvest efficiency of the photoanode and working electrode when hybridizing this
material with TiO2.
Aside from the stated carbon based materials, mesoporous carbon such as bamboo
charcoal also potentials to be used as the electrodes in DSSC. Carbonized bamboo
charcoal which undergoes heat treatment between 700 to 900 °C has the resistance
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coefficient between 0.12 to 11.9 Ωm which perfect as the electrode [10]. In other work,
Chen et al. [13] has proved that modified TiO2potentials to increase solar absorption by
altering the surface structure and its energy band. The black TiO2 (refer Fig. 3(a)) can be
resolved into two peaks compared to typical white TiO2. The changes in reflectance and
absorbance spectra at 806.8 nm suggest that the optical gap of the black TiO2 was narrowed
by intraband transition. Further analysis with XPS (Fig. 3(b)) also has been performed to
show the changes of density of states between typical TiO2 and modified TiO2 and the
results were illustrated in Fig. 3(c).
Recently, the best performance of bamboo charcoal in DSSC is 5.4% [1] attributed to
the porous of bamboo charcoal embedded in the nano-crystalline TiO2 which facilitates the
capability of dye absorption and the generation of electrons during exposure to the light.
However, the development of DSSC utilizing bamboo charcoal still in preliminary stage
and more improvements need to be done.
Fig. 3. Comparison between typical TiO2
and modified (a) powder forms, (b) Spectral absorbance, (c)
XPS spectra and (d) Illustration of density of states [13].
a)
b)
c)
d)
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6 As an absorbent in water purification
Many industries produce volatile compounds that can pollute the environment and harm
the human health. The common compounds include hydrocarbon compounds such as O2,
N2, sulphur, halogen and others. Generally, adsorbents were employed to remove the
pollutants from wastewater or waste gas. The adsorption capacity of the adsorbents comes
from the affinity of molecules, and is classified into physical adsorption, chemical
adsorption and catalytic action. Examples of adsorbent are activated clays, aluminium
oxide based materials, silica gel, ion exchangers, magnesia based materials, activated
carbon and others. Among all, the activated carbon is the most common used absorbent as
it is cheaper, easier to be used and recyclable. It has superior performance in dealing with
organic and toxic waste such as chrome, ozone, pesticide and others. In that matter,
bamboo charcoal is a potential cheaper alternative absorbent among carbon based material
such as carbon nanotubes [18, 19], graphene [19], graphene oxide [19] and others which
offers a larger specific area and greater pore volume which can perform a greater degree of
adsorption.
It has been shown that, the adsorption of bamboo charcoal is affected by the
carbonization temperature as shown in Fig. 4(a). As the temperature increased, the pore is
greater and the adsorption rate is increased. The adsorption of substances in water also
depends on the way the bamboo charcoal is activated. It has been investigated that bamboo
charcoal activated with HNO3(refer Fig. 4(b)) showed better surface area with the
introduction of acidic functional groups without destruction of pore structure compared to
the charcoal activated with CO2(refer Fig. 4(c)) which much depends on the activated
temperature [2]. Author also proved that charcoal activated by NH3 not present a promising
yield although the mesopore was increased with the applied temperature. However this
HNO3 activation process posses more functional groups and resulted higher water vapour
adsorption capacity at low humidity area.
Fig. 4. Water vapour adsorption-desorption of (a) bamboo charcoal, (b) activated CO2and (c)
activated HNO
3[2].
7 As an electromagnetic waves absorber
Due to the extensive effort towards gigahertz (Ghz) electronic system and
telecommunication devices, electromagnetic (EM) interference problems have raised
vastly. EM is defined as conducted or radiated electromagnetic signals which emitted by
(a)
(b)
(c)
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electrical circuits which under operation, perturb proper operation of surrounding
equipments which also may cause radioactive damage to living/biological species [3].
Thus, an effective shielding material in wide variety applications is needed. For this
purposes, Radar Adsorbing Material (RAM) has been applied from commercial and
electronic instrumentations to antenna system and military electronic devices which can be
produced under different forms such as conductive paints or rubber loaded with ferrite or
carbon which generally used for stealth military planes; or in foam or multilayered
topologies that commonly used as liners for all enclosures in which reflection waves has to
be minimized such as an anechoic chambers. But, the existing adsorption solution is still
facing very low power loss.
Recently, the focus on the research on designing shielding material which works by
adsorption was boosted all over the world. Most of the proposed material was based on
polymeric materials in order to take the advantages of their lightness, low cost, easy
shaping and others. There are three main strategies on producing the adsorbing material: 1)
dispersion of metallic fillers, fibers or nanoparticles within polymer matrix which can
increase the interaction with the electromagnetic radiation; 2) using conductive polymers
such polyaniline (PANI) and polydimethylsiloxane (PDMS) and 3) dispersion carbon based
electrically conductive polymer matrices. Based on that, carbon material like carbon black
[20], carbon nanotubes [21] and graphene [22 - 24] have been used as the polymeric filler
because of their extraordinary properties. However the production of these carbon materials
is expensive and some of the materials are facing impedance match mechanism that may
harmful to the EM adsorption properties [24]. Besides, the carbon based dielectric
absorbers have narrow absorbing frequency bandwidth [25]. Therefore, a development of
the EM absorbing material with low density, high thermal stability, high absorption
properties, broad microwave frequency bandwidth as well as cheaper solution is highly
demanded. Based on that demands, bamboo charcoal can be a magnificent alternative as
this material has similar high conductivity, large surface area and extremely higher
adsorption properties.
8 Conclusion
In this paper, the properties and potential applications are reviewed. The magnificent
adsorption property of this material becomes the main highlight which it can be fully
utilized in various potential applications such as electrode in solar cell, absorbent for water
treatment and wave absorber in antenna. This adsorption property can be influenced by the
carbonization temperature, the activation process and activation precursor as the pore is
getting larger and the surface area is improved.
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