Science of Bamboo Charcoal: Study on Carbonizing Temperature of Bamboo Charcoal and Removal Capability of Harmful Gases

Abstract

We examined the relationship between the carbonizing temperature of bamboo carbide made from Moso bamboo (Phyllostachys pubescens) and the removal effect of harmful gases and odorants, and the use of a bamboo charcoal as a countermeasure for "Sick Building Syndrome" or "Chemical Sensitivity" and the use as a deodorant. With regard to the carbonizing temperature of the bamboo charcoal, a temperature sensor was installed inside each bamboo material and the carbonizing temperature was controlled at 500, 700 and 1000°C. The removal effect was tested for formaldehyde, toluene and benzene that are known to cause "Sick Building Syndrome" or "Chemical Sensitivity" and for ammonia, indole, skatole and nonenal as odorants. The formaldehyde removal effect was only slightly different in the charcoal at all the carbonizing temperatures. The benzene, toluene, indole, skatole and nonenal removal effect were the highest for the bamboo charcoal carbonized at 1000°C and tended to increase as the carbonizing temperature of the bamboo charcoal increased. The removal effect for ammonia was the highest on the bamboo charcoal carbonized at 500°C. It is concluded that the effective carbonizing temperature is different for each chemical, and a charcoal must be specifically selected for use as an adsorbent or deodorant.

Full text

473
Journal of Health Science, 48(6) 473–479 (2002)
Science of Bamboo Charcoal: Study on
Carbonizing Temperature of Bamboo
Charcoal and Removal Capability of
Harmful Gases
Takashi Asada,a, b Shigehisa Ishihara,c Takeshi Yamane,d Akemi Toba,e Akifumi Yamada,a
and Kikuo Oikawa*, b
aNagaoka University of Technology, Kamitomioka-cho 1603–1, Nagaoka, Niigata 940–2188, Japan, bDepartment of Environmental
and Safety Sciences, Niigata University of Pharmacy and Applied Life Sciences, Faculty of Applied Life Sciences, Higashijima 265–
1, Niitsu, Niigata 956–8603, Japan, cProfesser Emeritus of Kyoto University, Tenjin, 3–23–12 Nagaoka-kyo, Kyoto 617–0824, Japan,
dKankyo Techno Consul, Kojidai 3–18–7, Nishi-ku, Kobe 651–2273, Japan, and eObama Bamboo Charcoal Product Association,
Mizutori 4–10–32, Obama, Fukui 917–0093, Japan
(Received March 11, 2002; Accepted August 6, 2002)
We examined the relationship between the carbonizing temperature of bamboo carbide made from Moso bam-
boo (Phyllostachys pubescens) and the removal effect of harmful gases and odorants, and the use of a bamboo
charcoal as a countermeasure for “Sick Building Syndrome” or “Chemical Sensitivity” and the use as a deodorant.
With regard to the carbonizing temperature of the bamboo charcoal, a temperature sensor was installed inside each
bamboo material and the carbonizing temperature was controlled at 500, 700 and 1000ºC. The removal effect was
tested for formaldehyde, toluene and benzene that are known to cause “Sick Building Syndrome” or “Chemical
Sensitivity” and for ammonia, indole, skatole and nonenal as odorants. The formaldehyde removal effect was only
slightly different in the charcoal at all the carbonizing temperatures. The benzene, toluene, indole, skatole and
nonenal removal effect were the highest for the bamboo charcoal carbonized at 1000ºC and tended to increase as the
carbonizing temperature of the bamboo charcoal increased. The removal effect for ammonia was the highest on the
bamboo charcoal carbonized at 500ºC. It is concluded that the effective carbonizing temperature is different for each
chemical, and a charcoal must be specifically selected for use as an adsorbent or deodorant.
Key words —–— bamboo charcoal, carbonizing temperature, Sick Building Syndrome, Chemical Sensitivity
trations of formaldehyde, toluene, xylene, p-dichlo-
robenzene, ethyl benzene, styrene, chlorpyrifos, di-
n-butyl phthalate, tetradecane, diethylhexyl phtha-
late, diazinon, acetaldehyde and fenobucarb at the
examination conference about problems of “Sick
House Syndrome” (indoor air pollution) in Febru-
ary 2002, concrete countermeasures to decrease
harmful indoor chemicals have not been indicated
till now.
We have studied the countermeasures against
“Sick Building Syndrome” using the removal capa-
bility of charcoal such as wood charcoal or bamboo
charcoal to adsorb chemicals. The adsorption of
chemicals on the charcoal is classified by physical
adsorption due to “van der waals attraction” or
chemical adsorption by a chemical reaction, and
characteristics of the adsorption are influenced by
the chemical structure of the surface and pore struc-
ture. Recently, the relation between the carbonizing
*To whom correspondence should be addressed: Department of
Environmental and Safety Sciences, Niigata University of Phar-
macy and Applied Life Sciences, Faculty of Applied Life Sci-
ences, Higashijima 265–1, Niitsu, Niigata 956–8603, Japan. Tel.:
+81-250-25-5160; Fax: +81-250-25-5161; E-mail: oikawa@
niigatayakudai.jp
INTRODUCTION
The carbide of trees such as wood charcoal or
bamboo charcoal has been used as a fuel for a long
time. Recently, they have been studied as a humid-
ity control substance,1) adsorbent,2) substance of
wastewater purification,3,4) and catalyst.5)
Recently, health problems such as “Sick Build-
ing Syndrome (Sick House Syndrome)” and “Chemi-
cal Sensitivity” are occurring due to an increase in
indoor air pollution from chemicals. Although the
Ministry of Health, Labour and Welfare of Japan has
established a guideline value for the indoor concen-

474 Vol. 48 (2002)
conditions and adsorption effect of chemicals has
been reported on the carbides of Cryptomeria and
Chamaecyparis.6–8) However, there has been a mis-
apprehension that all charcoals have the same ad-
sorption effect when used as a adsorbent or deodor-
ant. We examined the relation between the carbon-
izing temperature of bamboo carbide and its removal
effect for chemicals such as harmful gases and odor-
ants, and the use of bamboo charcoal as a counter-
measure against “Sick Building Syndrome” and
“Chemical Sensitivity” and the use as a deodorant.
MATERIAL AND METHODS
Production Method of Bamboo Charcoal —–—
Bamboo charcoal was made from Moso bamboo
(Phyllostachys pubescens). A charcoal kiln, which
was used to make the bamboo charcoal, can make
about 50 kg of bamboo charcoal at a time and can
mechanically control the temperature by setting the
carbonizing temperature. A temperature sensor was
installed inside of each bamboo material and the
ceiling of the charcoal kiln and temperature of each
sensor was monitored. The carbonizing temperature
was that of the inside temperature of each bamboo
material. Air was hold up and the temperature pro-
gram rate was 1ºC/min. After reaching the set car-
bonizing temperature, each bamboo material was
carbonized for about 1 hr at that temperature and
was then left to cool at the temperature of the char-
coal kiln. A yield of the bamboo charcoal was about
45% under the condition.
The bamboo charcoal was then crushed and
sieved, and a bamboo charcoal powder with a par-
ticle diameter of 25–125
µ
m was obtained. With re-
gard to the samples for the experiments, the bam-
boo charcoal powder was heated for 3 hr at 115 ±5ºC
to dry, and then left in a desiccator.
Measurement of Surface Area and Pore Size Dis-
tribution —–— ASAP 2010 micro pore system
(Shimadzu, Kyoto, Japan) was used for measuring
specific surface area and pore size distribution of 5–
20 Å. The adsorption of carbon dioxide was mea-
sured at an adsorption temperature of 194.65 K. Spe-
cific surface areas were determined from carbon di-
oxide isotherms from 0.03 to 0.15 of the relative
pressure range using the BET equation. The pore
size distributions were determined by HK (Harvath-
Kawazoe) method. The pore size distributions of
3.7–140000 nm was measured by the mercury in-
trusion porosimetry using Auto Pore III (Shimadzu).
Measurement of Electric Resistance —–— A digi-
tal multimeter 7537 01 (Yokogawa M&C Corpora-
tion, Tokyo, Japan), which can measure to 40 MΩ,
was used for measuring the electric resistance of the
bamboo charcoal.
Removal Test of Harmful Gas —–— The removal
effect of harmful gases was tested in a 5-liter sam-
pling bag (tedlar bag) (GL Sciences Inc., Tokyo, Ja-
pan). A 0.5 g bamboo charcoal piece for formalde-
hyde, ammonia, indole, and skatole or a 0.05 g piece
for formaldehyde, benzene, toluene, and nonenal was
placed in the sampling bag and a sealing clip iso-
lated the bamboo charcoal. Nitrogen was pumped
into the sampling bag and then each gas (formalde-
hyde, benzene, toluene, ammonia, indole, skatole,
and nonenal) was added at the specific concentra-
tion to the sampling bag using a gastight syringe.
The prepared sampling bag was incubated at 20ºC.
After the gas concentration in the sampling bag sta-
bilized, the bamboo charcoal and gas was mixed by
opening the sealing clip. The time mixing for the
bamboo charcoal and gas was initially 0. The con-
centration of the gas in the sampling bag was deter-
mined after 0, 1, 3, 5, 8, and 24 hr.
Method for Determination of Gas Concentration
—–— The concentration of formaldehyde was deter-
mined using a Formaldemeter 400 (JMS, Tokyo,
Japan). The concentration of ammonia was deter-
mined using Kitagawa’s detector AP-1 (Komyo
Rikagaku Kogyo, Tokyo, Japan) and Kitagawa’s
detector tube No.105SC (Komyo Rikagaku Kogyo).
The concentrations of indole and skatole were de-
termined using a portable type odor sensor XP-329
(COSMOS, Osaka, Japan). The concentrations of
benzene, toluene and nonenal were determined us-
ing a gas chromatograph GC-8A (Shimadzu), which
was equipped with a flame ionization detector (FID).
The packed column filled with polyethyleneglycol
20 M as the liquid phase on Chromosorb W (60–
80 mesh, AW-DMCS) for benzene and toluene, and
Thermon-3000 (5%) as the liquid phase on
Chromosorb W (80–100 mesh, AW-DMCS) for
nonenal was used. The temperatures of the column
and the injector were 100ºC and 150ºC for benzene
and toluene, and 150ºC and 200ºC for nonenal, re-
spectively. The concentration was determined by the
calibration curve method.
Measurement of Electron Spin Resonance —–—
Each bamboo charcoal was put in an measurement
of electron spin resonance (ESR) sample tube
(5 mm
φ
) and the ESR spectra (X-band) were mea-
sured using an ESR JES-TE200 (JEOL, Tokyo, Ja-

475
No. 6
pan) with conditions as follows: temperature, 23ºC;
microwave frequency, 9.18 GHz; microwave power,
8 mW; field, 327.5 mT ±5 mT; sweep time, 0.5 min;
modulation, 2
µ
T; amplitude, 100; time constant,
0.3 sec.
RESULTS
Measurement of Surface Area and Pore Size Dis-
tribution
Each specific surface area of the bamboo char-
coal carbonized at 500, 700 and 1000ºC was 360.2,
361.2 and 490.8 m3/g, respectively. Although the spe-
cific surface area of the bamboo charcoal carbon-
ized at 500ºC and that at 700ºC was slightly differ-
ent, that of 1000ºC was about 1.35 times as large as
that of 500ºC or 700ºC. The pore size distribution of
5–20 Å and 3.7–140000 nm was shown in Figs. 1
and 2. On the micro-pore range, a pore size peak of
the bamboo charcoal was about 6.5 Å and pore vol-
umes tended to increase as the carbonizing tempera-
ture of the bamboo charcoal increase. On the meso-
pore and macro-pore range, pore size peaks of the
bamboo charcoal carbonized at 500 and 700ºC were
about 60, 450 and 2250 nm, and that of 1000ºC was
about 15 nm, which was smaller than that of 500
and 700ºC. As the pore volume, that of 1000ºC was
the largest, and that of 500ºC was larger than that of
700ºC on the meso-pore range. On the macro-pore
range, the pore volume of 700ºC was the largest,
and that of 500ºC larger than that of 1000ºC.
Measurement of Electric Resistance
The electric resistance of the bamboo charcoal
carbonized at 500, 700, and 1000ºC were above
40 M, 104–105, and 10–100 Ω, respectively. The elec-
tric resistance decreased as the carbonizing tempera-
ture of the bamboo charcoal increased, that is, the
correlation between the carbonizing temperature and
the electric resistance of the bamboo charcoal was
negative. Because it is known that the correlation
between the carbonizing temperature and the elec-
tric resistance exists,6,9) the smelting degree of char-
coal can be estimated by measuring the electric re-
sistance. In this study, the smelting progress can be
confirmed as the carbonizing temperature of the
bamboo charcoal increases.
Removal Test of Harmful Gas
The results of the removal tests for benzene, tolu-
ene and formaldehyde are shown in Figs. 3, 4 and 5,
respectively. Bamboo charcoal carbonized at 1000ºC
had the best removal effect for benzene and toluene.
For the other carbonizing temperatures of 500 and
700ºC, the removal effect was poor compared to that
at 1000ºC. The removal effect for benzene and tolu-
ene tend to increase as the carbonizing temperature
Fig. 1. Pore Size Distribution of 5–20 Å (Horvath-Kawazoe
Differential Pore Volume Plot)
Fig. 2. Pore Size Distribution of 3.7–140000 nm (Log
Differential Intrusion)
Fig. 3. Time Course of Benzene Concentration in Sampling Bag

476 Vol. 48 (2002)
Fig. 4. Time Course of Toluene Concentration in Sampling Bag
Fig. 5-1. Time Course of Formaldehyde Concentration in
Sampling Bag on 0.5 g Bamboo Charcoal
Fig. 5-2. Time Course of Formaldehyde Concentration in
Sampling Bag on 0.05 g Bamboo Charcoal
of the bamboo charcoal increases. The bamboo char-
coal at all carbonizing temperatures removed form-
aldehyde well, and the removal effect for formalde-
hyde was only slightly different for the bamboo char-
coal at all carbonizing temperatures. When the
weight of the bamboo charcoal was reduced and the
primary formaldehyde concentration was increased,
the removal effect of formaldehyde tended to in-
crease as the carbonizing temperature of the bam-
boo charcoal increased similar to benzene and tolu-
ene. However, for an indoor condition, the differ-
ence in the removal effect for formaldehyde was not
clear, and all the bamboo charcoals carbonized at
500–1000ºC had equal removal effects.
Removal Test of Odorant
The results of removal test for ammonia, indole,
skatole and nonenal are shown in Figs. 6, 7, 8 and 9,
respectively. Bamboo charcoal carbonized at 500ºC
had the highest removal effect for ammonia. The
bamboo charcoal carbonized at the other tempera-
tures of 700 and 1000ºC had a poor removal effect
for ammonia compared to that at 500ºC. For indole,
skatole and nonenal, the bamboo charcoal carbon-
ized at 1000ºC had the highest removal effect. The
bamboo charcoal carbonized at the other tempera-
Fig. 6. Time Course of Ammonia Concentration in Sampling
Bag
Fig. 7. Time Course of Indole Concentration in Sampling Bag

477
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tures of 500 and 700ºC had a poor removal effect
for indole, skatole and nonenal compared to that of
1000ºC. The removal effect for these odorants tended
to increase as the carbonizing temperature increased.
Measurement of Electron Spin Resonance
The ESR spectra of a bamboo charcoal carbon-
ized at 200, 300, 400, 500, 700 and 1000ºC are shown
in Fig. 10. Radical species with ESR activity were
detected in the bamboo charcoal carbonized at 300–
500ºC. Many radical species were detected in the
bamboo charcoals carbonized at 500ºC. The detec-
tion of the radical species decreased as the devia-
tion increased from the carbonizing temperature of
500ºC, and the radical species were hardly detected
in the bamboo charcoals carbonized at 200, 700 and
1000ºC.
DISCUSSION
The indoor guideline concentration for volatile
organic carbon (VOC) has been prescribed for
13 chemical species by the Ministry of Health, Labor
and Welfare of Japan. They include formaldehyde,
toluene, xylene, p-dichlorobenzene, ethylbenzene,
styrene, chlorpyrifos di-n-butyl phtalate, tetradecane,
di(2-ethylhexyl)phthalate, diazinon, acetoaldehyde
and fenoucarb. Of these chemicals, formaldehyde,
which is released from the adhesives in plywood,
etc., is the main chemical causing “Sick Building
Syndrome,” and the indoor guideline concentration
for formaldehyde is 100
µ
g/m3. In this study, al-
though the primary concentration of formaldehyde
in a 5 l sampling bag was about 35 times the guide-
line concentration, a 0.5 g piece of bamboo char-
coal carbonized at 1000ºC reduced the concentra-
tion of formaldehyde to less than the guideline con-
centration after 24 hr. For toluene used as a solvent
in paint, although the primary concentration of tolu-
ene in the 5 l sampling bag was about 1000 times
the guideline concentration, a 0.05 g piece of bam-
boo charcoal carbonized at 1000ºC reduced the con-
centration of toluene to less than 1/100 the initial
concentration after 24 hr. Although the guideline
concentration was not established for benzene, it is
considered that benzene can become a reference for
toluene, xylene, p-dichlorobenzene, ethylbenzene
and styrene, etc., as it has a similar benzene ring
structure. Practically, the removal effects for ben-
zene and toluene were almost equal. It is presumed
that bamboo charcoal carbonized at a temperature
Fig. 8. Time Course of Skatole Concentration in Sampling Bag
Fig. 9. Time Course of Nonenal Concentration in Sampling Bag
Fig. 10. ESR Spectra of Bamboo Charcoal Carbonized at a
Temperatures of 200, 300, 400, 500, 700 and 1000ºC
℃
℃
℃
℃
℃
℃
℃
℃

478 Vol. 48 (2002)
of 1000ºC is effective for removing these chemi-
cals. At temperatures of 900–1000ºC, the carbon-
ization significantly progressed and the specific sur-
face area becomes the highest.7,8) In this study, the
specific surface area was the highest and the elec-
tric resistance was the lowest at 900–1000ºC. Al-
though specific surface areas of the bamboo char-
coal carbonized at 500 and 700ºC were slightly dif-
ferent, the removal effect of the bamboo charcoal
carbonized at 700ºC was higher than that of 500ºC.
The results make us conjecture that pores of micro-
pore range are especially concerned with the adsorp-
tion of benzene and toluene, because the pore vol-
ume of micro-pore range on the bamboo charcoal
carbonized at 700ºC is larger than that of 500ºC.
Therefore, it is considered that the removal of chemi-
cals, which depend on physical adsorption, is effec-
tive in bamboo charcoal carbonized at a tempera-
ture of 1000ºC, which has the largest specific sur-
face area and pore volume of the micro-pore range.
The bamboo charcoal showed a sufficient re-
moval effect for odorants such as ammonia, indole,
and skatole contained in the excreta of man or ani-
mals, and nonenal that is a human body odor to in-
crease with aging. Different from the other chemi-
cals, the removal effect for ammonia was the best
on the bamboo charcoal carbonized at 500ºC. The
concentration of ammonia decreased to under a con-
centration of 5 ppm, at which the odor is hard to
detect, from the primary concentration of 100 ppm
after 3 hr using the 0.5 g bamboo charcoal carbon-
ized at 500ºC. At that carbonizing temperature of
400–500ºC, the thermolysis of cellulose or lignin,
which are the main components of bamboo, actively
occurred and it is reported that acidic functional
groups such as carboxyl were formed by the ther-
molysis.8–10) In the ESR spectra measurement, many
radical species with ESR activity were detected on
the bamboo charcoal carbonized at 500ºC, so that
the existence of many carboxyl groups was pre-
sumed. Therefore, it was concluded that the bam-
boo charcoal carbonized at 500ºC, which has acidic
functional groups to be effective for the chemical
adsorption of ammonia, is more effective for the re-
moval of basic substances such as ammonia rather
than bamboo charcoal carbonized at 1000ºC, which
has a higher physical adsorption capability. It is pre-
sumed that the removal of other basic chemicals
would show a similar tendency. The removal effects
of other odorants such as indole, skatole, and nonenal
were the most effective in the bamboo charcoal car-
bonized at 1000ºC, which has a higher physical ad-
sorption capability, just like benzene and toluene.
Furthermore, because the results for toluene, ben-
zene and ammonia in this study showed tendencies
similar to that reported on wood charcoal,6,8) it is
considered that there is a relation between the capa-
bility of charcoal as an adsorbent and the carboniz-
ing temperature of the charcoal, but not the tree spe-
cies.
As a result of our study, it is concluded that the
effective carbonizing temperature is different for
each chemical and a specific charcoal must be se-
lected for each specific use as an adsorbent or de-
odorant. It is expected that charcoal can be effec-
tively used as a countermeasure against “Sick Build-
ing Syndrome” or as a deodorant.
Acknowledgements The measurement of specific
surface area and pore size distribution was supported
by Mr. Takeuchi and Mr. Ohotana (Shimadzu). The
measurement of pore size distribution by mercury
intrusion porosimetry was supported by Dr. Mori,
Mr. Yamada and Mr. Uchiyama (Nikki Chemical Co.,
Ltd., Niigata, Japan).
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