Materials Science Forum Vols. 561-565 (2007) pp. 1417-1420
online at http://www.scientific.net
© (2007) Trans Tech Publications, Switzerland
Online available since 2007/10/02
A Study of Testing the Nanocatalyst Decomposition Efficiency of
Methanol (CH3OH) and Ethanol (C2H6O)
Ching-Song Jwo1,a, Chien-Chih Chen2,b, Ho-Chang3,c, Sih-Li Chen 4,d and
Chi-Hsiang Lin 1,e
1.
Department of Energy and Refrigeration Air-Conditioning Engineering, National Taipei University
of Technology, Taipei, Taiwan, R.O.C.
2.
Graduate Institute of Mechanical and Electrical Engineering, National Taipei University of
technology, Taipei, Taiwan, R.O.C.
3.
Graduate Institute of Mechanical Engineering, National Taipei University of technology, Taipei,
Taiwan, R.O.C.
4.
Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.
a
email:[email protected], bemail:[email protected], cemail: [email protected],
d
email: [email protected], eemail: [email protected]
Keywords: photocatalyst, UV, Methanol and ethanol, TiO2
Abstract. This research carries out an inexpensive, rapid and novel exercise, which is applied to
perform the photocatalyst decomposition effectiveness of Methanol and Ethanol in gaseous form.
The major devices of this applicable measurement developed by this practice are only utilizing
ultraviolet-visible spectrophotometer and quartz cuvette, and the experimental procedures are
straightforward and speedy. In the conduct experiments, Methanol and Ethanol with a specific
concentration is initially injected into an enclosed quartz cuvette. Then the cuvette is put in
ultraviolet- visible spectrophotometer to measure the Methanol and Ethanol concentration, so as to
obtain an unique UV absorbance spectrum at its particular concentration. In the conduct
experiments of measuring photocatalyst decomposition efficiency, the self-made (SANSS)
nanocatalyst TiO2 is initially coated in the quartz plate, and put into the quartz. Then a specific
concentration of methanol alcohol and ethanol is injected into the quartz cuvette under the UV
irradiation exposure, so as to carry out photodecomposition of Methanol and Ethanol experiment.
After that, the cuvettes are then put into the ultraviolet-visible spectrophotometer for measuring the
absorbance intensity of UV spectrums in order to produce degradation chart. The preliminary
results point out that the self-made nanocatalyst TiO2 has exceptionally outstanding decomposition
efficiency which further points out the fact that, when UV irradiation for 60minutes, the gaseous
Methanol can be reduced to 3.8% of the original sample, and the gaseous Ethanol can be reduced to
6% of the original sample. But when exercising with commercial nanocatalyst TiO2 to undergo the
same process exactly under the same circumstances, the residue gaseous concentration can only be
reduced to 17% and 16% of the gaseous Methanol and Ethanol original sample.
1. INTRODUCTION
At present, air and water pollution is the major problem that many countries need to solve as it
directly affects the quality of life. There are two types of air pollution, namely indoor and outdoor.
Indoor air pollution mainly comes from the vapors or fumes emitted from materials used in
construction, furniture, bathrooms and kitchens [1]. VOCs, Formaldehyde and Ammonia are the
commonest vapors emitted that are noxious and harmful [2]. Even at very low concentrations, they
are easily noticeable. Although it may not be harmful at that concentration, it will cause odor
problems in closed public spaces [3]. Traditionally, the common materials that are used to treat
noxious odor molecules in the air are activated carbon and Zeolite[4]. However, these absorbents
cannot be regenerated and need to be changed constantly. Therefore, mild and long-lasting
photocatalysts are very suitable for the removal of low concentrations of noxious molecules and at
the same time refresh air. The theory of photocatalyst decomposition VOC is [5]: By the activation
of light, moisture and oxygen, molecules which are in contact with the photocatalyst are converted
into hydroxide radicals, extra-oxygen ions and hydrogen peroxide. When organic pollutants in the
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PRICM 6
vapor phase come in contact with the active substances, they are oxidized to H2O and CO2, or into
smaller organic molecules, which can readily be further decomposed by microorganisms.
The kinetics of the Langmuir Hinshelwood model [6] is as below:
c
ln o + K (co − c ) = k r Kt
(1)
c
Where, kr is the reaction constant, K is the absorption constant, co is the initial reaction
concentration, and c is the testing concentration. Substituting the experimental results into the
above equation and plotting the reaction rate vs. Concentration, we can obtain the reaction rate
constant. The equation can be simplified as:
c
ln o = kat
(2)
c
Where " ka " is the reaction rate constant.
The main instrument used in this study is a VU/VIS spectrophotometer equipped with a quartz
cuvette. The experimental procedures are simple and fast. Our results prove that our simple and
convenient methods are new techniques for sample pre-treatment and the measurement of TiO2
photocatalyst photo-degradation efficiency.
2. EXPERIMENTAL DETAILS
The schematic diagram of the experimental setup is shown in Fig.1. A fixed-gas analysis device
equipped UV/VIS spectrophotometer (Thermo) with a wavelength range of 190~1100 nm was used.
Quartz cuvettes (Hellma), volume 3 mL; UV lux gauge: (UVP MS-100), measuring range: 0.00 to
19.99 mW/cm2; UV light tube for irradiation of quartz cuvette was a Japanese-made 254 +185nm
tube, luminance 0.30mW/cm2; Sample treatment technique: 0.001 mL samples of various
concentrations of liquid, Methanol and Ethanol were injected into separate quartz colorimetric
troughs. Then each quartz trough was transferred to the spectrophotometer for UV exposure. The
first photocatalyst used in this experiment was a nanofluid TiO2, which was prepared by us with the
Submerged Arc Nano particle Synthesis System, SANSS. The nanoparticles produced from the
process are Anatase TiO2, indicating a good nanoparticle dispersion with a mean particle size below
10 nm. The second nanofluid TiO2 was prepared by diluting a commercial Degussa P25
photocatalyst powder. Quartz glass substrates were coated with two types of nanofluid TiO2, and
then to calcine at 60°C. This process was repeated three times in order to fix the TiO2 onto the
quartz glass substrates. Then the different photocatalyst-coated quartz glass substrates were inserted
into separate quartz cuvettes. Each quartz cuvette was then transferred to the UV/VIS
spectrophotometer to investigate the influence of various operational parameters on the efficacy of
Methanol and Ethanol decomposition by photocatalyst under UV.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
µL0
UV spectrophotometer
RSS- 232
Comput er
Injection
Quartz
Glass
UVC light
Quartz
cuvette
Quartz
Glass
UV light
Sensor
Fig.1. Schematic diagram of the experiment device
Materials Science Forum Vols. 561-565
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3. RESULTS AND DISCUSSION
The major purpose of this work is to test the photocatalyst efficiency of the self-made nano
materials towards the alcoholic organic pollutants and obtain a correlation between chemical
dispersion and reaction characteristics [7]. Experiment would firstly observe whether quartz cuvette
can directly adsorb Methanol and Ethanol. Upon complete evaporation and stablization of gaseous
concentration, the adsorption spectrum diagram of gas remains almost the same within 30 minutes,
so its adsorption volume can be neglected. The experiment result of Methanol under the exposure of
direct light is shown in Figure 2 and 3. Methanol is made up of C-H, C-O and O-H bonds, and
according to Legan [8], C-H destruction bond energy is 289.7nm, C-O is 334.4nm, so when a
fluorescent tube emits a light source of 254 + 185 nm, it can easily destroy the structure of
Methanol. It is known form the figure that, ultra violet ray of 254 + 185 nm can lower the Methanol
gas having 190 nm adsorption spectrum value from 0.55 to 0.226 within 30 minutes. In the
photodegradation process, the photodecomposition efficiency of Methanol can be calculated by the
change in adsorption value. It finds out that under wavelength of 190nm, the first time of the change
of the light decomposition of Methanol can be observed as well as further works to undergo
decomposition reaction. Figure 3 indicates that Degussa P25 can decompose the light spectrum
value of Methanol gas adsorption from 0.55 to 0.085 after 30 minutes. Experiment result of SANSS
TiO2 decomposing Methanol gas shows that it drops from 0.55 to 0.017.
Experiment result of direct light exposure towards Ethanol is shown in Figure 4. Ethanol is made
up of C-H, C-C, C-H and O-H bond. C-H destruction bond energy is 289.7nm, C-C is 346.1nm and
C-O is 334.4nm, so the light source of 254+185nm wavelength emitted by the fluorescent light can
easily destroy the structure of Ethanol. Upon 10 minutes of directly light decomposing the Ethanol
gas and the same observation under the wavelength of 190nm, result shows that adsorption
spectrum value drops from 0.53 to 0.344 after 40 minutes. The photocatalytic efficiency of Degussa
P25 decomposition Ethanol is to reduce the Ethanol gas adsorption spectrum value (190nm) from
0.53 to 0.098 within 40 minutes. Experiment result of SANSS TiO2 decomposing Ethanol gas
shows that the adsorption spectrum value of 190nm ethanol gas drops from 0.53 to 0.285, and 0.184
within 20 minutes, 0.097 within 30 minutes and 0.028 within 40 minutes.
To determine the reaction rate constant, the time vs. concentration change curve of Methanol
under SANSS TiO2 light emission needs to fit into equation (1), because the photocatalytic
decomposition efficiency of organic gas factor is normally calculated under Langmuir-Hinselwood
reaction mechanism. Fig. 6 show the value of the Methanol rate constant ka with SANSS TiO2
calculated by fitting into equation (1) is 0.1min-1, and Fig. 7 show the value of the Ethanol rate
constant with SANSS TiO2 is 0.06min-1. Experimental results have shown that the degradation
reaction rate constant of the self-made TiO2 nanocatalyst have improved a lot than P25 and the
prepared TiO2 possesses good photocatalytic activity in decomposing the Methanol and Ethanol.
0.6
0.6
Methanol
Photocomposition with SANSS TiO2
Methanol
Photodecomposition with P25 TiO2
Direct photocomposition
Direct photodecomposition
0.5
Absorbance (a. u.)
Absorbance (a. u.)
0.5
0.4
0.3
0.2
0.1
0.4
0.3
0.2
0.1
0
0
190
192
194
196
198
200
202
Wavelength (nm)
204
206
208
210
190
192
194
196
198
200
202
204
206
208
210
Wavelength (nm)
Fig. 2. Degradation of Methanol with/without Fig. 3. Degradation of Methanol with/without
SANSS TiO2 under UV exposure for 30min
P25 TiO2 under UV exposure for 30min
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PRICM 6
0.6
0.6
Ethanol
Photodecomposition with SANSS TiO2
Ethanol
Photodecomposition with P25 TiO2
Direct photodecomposition
Direct photodecomposition
0.5
Absorbance (a. u.)
Absorbance (a. u.)
0.5
0.4
0.3
0.2
0.1
0.4
0.3
0.2
0.1
0
0
190
192
194
196
198
200
202
204
206
208
210
190
192
194
196
Wavelength (nm)
198
200
202
204
206
208
210
Wavelength (nm)
Fig. 4. Degradation of Ethanol with/without Fig. 5. Degradation of Ethanol with/without
SANSS TiO2 under UV exposure for 40min
P25 TiO2 under UV exposure for 40min
1.4
1.4
Methanol
Surface absorb
Direct photodecomposition
Photodecomposition with P25 TiO2
Ethanol
Surface absorb
Direct photodecomposition
photodecomposition with P25 TiO2
1.2
Photodecomposition with SANSS TiO2
Concentrationchange (C/Co)
Concentrationchange (C/Co)
1.2
1
0.8
0.6
0.4
photodecomposition with SANSS TiO2
1
0.8
0.6
0.4
0.2
0.2
0
0
0
5
10
15
Time (t/min)
20
25
30
0
10
20
30
40
Time (t/min)
Fig. 6 Decomposition of Methanol before and Fig. 7 Decomposition of Ethanol before and
after the photocatalysis of TiO2 particle
after the photocatalysis of TiO2 particle
4.CONCLUSIONS
This experiment successfully uses the quantitative and qualitative characters of UV/VIS
spectrophotometer to observe the adsorption volume of the gas by adsorption value, and determine
the degradation rate of the gas. Experiment discovers that without the emission of ultra violet ray,
SANSS TiO2 and Degussa P25 are not capable of decomposition but they will increase the total
surface area of the adsorption and change the surface characteristics, so that the speed of the organic
gas adsorption is faster than the surface of the quartz cuvette. It is found in the experiments of
decomposing Mathanol and Ethanol that, since they have weaker bond strength, direct
decomposition of ultra violet UVC can achieve a satisfying result. In the aspect of decomposition
efficiency, by observing the experiment of the catalysis Methanol and Ethanol of SANSS TiO2 with
UV/VIS shows that its reaction rate constant is up to 0.1 and 0.07 min-1 respectively, and the
reaction rate constant of Degussa P25 is 0.06 and 0.04 min-1 only. Comparing the efficiency of two
kinds of TiO2 photocatalysts in decomposing Methanol and Ethanol, it is found that ka value can
reflect the level of active energy required by these two photocatalysts. The higher the ka value that
the lower the required active energy and the faster the processing of reaction.
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