9986
J. Phys. Chem. 1995, 99, 9986-9991
Effect of Inert Supports for Titanium Dioxide Loading on Enhancement of Photodecomposition Rate of Gaseous Propionaldehyde Norihiko Takeda, Tsukasa Torimoto, Srinivasan Sampath, Susumu Kuwabata, and Hiroshi Yoneyama* Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamada-oka 2-1, Suita, Osaka 565, Japan Received: January 27, 1995; In Final Form: April 17, 1995@
Effects of the use of inert supports for Ti02 loading on photocatalyzed decomposition of propionaldehyde in the gas phase was investigated for mordenite support with various amounts of Ti02 loading and for several kinds of supports such as other zeolites, alumina, silica, and activated carbon. The adsorption constant and the amount of adsorption of propionaldehyde were evaluated for Tiorloaded supports by obtaining Langmuir adsorption isotherms. By correlating these parameters to the photodecomposition rates of propionaldehyde, the involvement of the support in the photodecomposition reaction is clarified. The photocatalytic activity of Ti02 on mordenite having various amounts of Ti02 loading increases with increase in the amount of loaded Ti02 up to an optimum value (ca. 50 wt %), beyond which a decreasing tendency of the activity appeared. In the region of ascending activity, plenty of adsorbed substrate is available and the activity is controlled by the content of Ti02, while in the region of descending activity, the decrease in the amount of adsorbed substrate due to a decrease in the occupancy of the support by the Ti02 loading is responsible for the activity decrease. The photocatalytic activities are greatly influenced by the kind of inert supports used and show a volcano type dependence on the adsorption constant of the Ti02-loaded supports. In cases where the adsorption constant is low, the decomposition rate is determined by the amount of adsorbed substrate, while if the adsorption constant is very high, plenty of adsorbed substrate is available on the support, but it is not mobile to the loaded TiOz. We conclude that the use of an inert support having a medium adsorption constant is necessary to obtain the highest activity, where a high amount of adsorbed substrate that can be supplied to Ti02 particles is available.
Introduction The rate of photoinduced heterogeneous reactions on semiconductor particles is usually influenced by the concentration of the substrate of the interest, and the lower the concentration the lower the reaction rate. Such an effect of the concentration of substrates can be analyzed by employing appropriate techniques in kinetic studies of the heterogeneous reactions,'-5 for example, to determine the rate constant, but if one wants to use photoinduced reactions in application fields such as photosynthesis and photodetoxification, a high reaction rate is desired. This is especially true for light-induced decomposition of organic substrates on titanium dioxide catalysts, which have been gaining popularity for developing a new technology for water1-l7 and air remediation.'s-28 In those cases the concentration of target substance is usually at a ppm level or below, but the decomposition at high rates is more desirable. A recent publication by us has demonstrated that the use of activated carbon as a support for Ti02 loading remarkably enhanced the decomposition rate of 3,5-dichloro-N-( 1,l'-dimethy1-2-propynyl)ben~amide,~~ whose popular name is propizamide. Similar enhancement in the decomposition rate by the support is also noticed for photodecomposition of pyridine over TiO2-loaded zeolite in the gas phase,30 although the effect of the zeolite support in that case was relatively small. We speculate that the enhancement of the decomposition rate of these substrates was due to condensation of the organic substrates on the support, providing a high-concentration environment around the loaded TiO2. However, the use of inert supports is not always effective in remarkably enhancing the @
Abstract published in Advance ACS Absrracfs, June 1, 1995
0022-365419512099-9986$09.0010
rate of photoinduced reactions of substrates of interest.'9h,c.31-33 For example, the use of A1203 and Si02 supports enhanced little the rate of photodecomposition of pentafluorophenol and decafluorobiphenyl in aqueous solution with use of Ti02 photo catalyst^,^^ and the use of activated carbon support did not greatly enhance the rate of photooxidation of gaseous NO2 and NO on the loaded TiO2, although the activated carbon support concentrated these gaseous species on their surface by Considering these results, some factor of the supports seems to play an important role in determining the rate of photodecomposition of organic substances in dilute concentrations. In the present study, we have focused on the effect of the adsorption constant of the support on the photodecomposition of propionaldehyde over Ti02 and found that the decomposition rate is dramatically changed by the adsorption constant of the support. Experimental Scction Supports used for Ti02 loading were powder particles of silica (Japan Aerosil200CF), alumina (Japan Aerosil Aluminum oxide C), activated carbon (Wako Pure Chemicals), mordenite (Tosoh TSZ-640NAA), femerite (Tosoh, TSZ-7 10 KOA), X-type zeolite (Tosoh Zeolum F-9), and three kinds of A-type zeolites (Tosoh, Zeolum A-3, A-4, and A-5). In this paper these are termed adsorbents. Other chemicals used in this study were of reagent grade and purchased from Wako Pure Chemicals. Aqueous solutions were prepared using doubly distilled water. A typical procedure of the preparation of Tiorloaded mordenite was as follows: 3.7 cm3 of titanium tetraisopropoxide was added drop by drop to 15 cm3 of 1 M HN03 aqueous
0 1995 American Chemical Society
Photodecomposition Rate of Gaseous Propionaldehyde solution, followed by agitation for 2 h to give a transparent Ti02 sol in which 1.0 g of Ti02 was contained. The pH of the colloidal solution was adjusted to pH 3 with addition of 1 M NaOH solution after dilution of the colloid with 50 cm3 of water, resulting in a turbid Ti02 colloid. The pH adjustment was made to prevent destruction of the zeolite supports by reaction with acid, but since it caused an increase in viscosity of the solution due to gelation, the dilution with water was required. After adding an adequate amount of adsorbent to the Ti02 colloids, the resulting mixed suspension was agitated for 1 h at room temperature, followed by centrifugation and then washing with distilled water. The centrifugation-washing procedures were repeated several times until pH of the supematant became neutral. Then the isolated TiO2-loaded adsorbents were dried under vacuum and subjected to heat treatments at 300 "C for 1 h. The amount of loaded Ti02 on the adsorbents was determined by colorimetric analysis using sodium 1,2-dihydroxybenzene-3,5-disulfate(Tiron) as a complex agent.34 Naked Ti02 powder was prepared using the same procedures as described above except for addition of the adsorbent. The BET specific surface area of the prepared Ti02loaded adsorbents was determined by argon adsorption at liquid nitrogen temperature using a Model 2205 Shimadzu-Micromeritics surface area analyzer. X-ray diffraction analysis was applied to the prepared Ti02 using a Shimadzu XD-3A diffractometer. We use the term "photocatalysts" below in cases where there is no need to discriminate between the TiOz-loaded adsorbents and the naked TiO2. The photocatalysts were fixed on glass plates for photodecomposition experiments. For this purpose, 10 mg of each photocatalyst was dispersed in 2 mL of acetone, and the adequate amount of resulting suspension was spread over a glass plate (1 cm x 4 cm). After being dried, the glass plate was heated at 300 and 400 "C for 1 h each, followed by cooling to room temperature. Photodecomposition experiments were carried out using a Pyrex reaction cell (1.4 cm diameter, 9.5 cm height, 15 cm3 capacity) equipped with an air-tight stopcock. The outer mouth of the stopcock was sealed with a rubber septum through which sampling of gases was made intermittently during the course of the photodecomposition experiments. A photocatalyst-fixed glass plate was placed horizontally inside the reaction cell. Prior to the photodecomposition experiments, wet air prepared by passing air through water kept at 0 "C, in which water vapor of 4.6 Torr was contained,35 was passed through the cell for 10 min, and then the photocatalyst film was illuminated with a 10 W fluorescent black lamp for more than 2 h to photodecompose organic impurities adsorbed on the photocatalyst surface. The procedure of flowing the wet air followed by the illumination was repeated several times until no appreciable amount of C02 was evolved from the photocatalyst. At that stage, the wet air was introduced into the cell, and 0.10 cm3 of propionaldehyde vapor prepared by holding a propionaldehyde container at 15 "C was injected into the cell. The amount of propionaldehyde injected was 1.22 x low6mol, as calculated from the injected volume and its vapor pressure.36 After holding for more than 1 h to achieve the adsorption equilibrium of propionaldehyde between the photocatalyst film and the gas phase, the photocatalyst film was illuminated with use of the 10 W fluorescent black lamp at room temperature. The fluorescent black lamp had a nearly symmetrical distribution of the spectrum ranging from 300 to 430 nm with 352 nm at its peak. The light intensity was 1.8 mW cm-2 at the surface of the photocatalyst film, as determined by a Eppley Lab Model E-6 thermopile. The amount of C02 produced by the photodecomposition of propi-
J. Phys. Chem., Vol. 99, No. 24, 1995 9987 TABLE 1: BET Surface Areas of Various Adsorbents, 53 wt % Ti02-Loaded Adsorbents, and the Naked Ti02
adsorbent naked Ti02 Zeolum A-5 Zeolum A-3 Zeolum F-9 Zeolum A-4 alumina silica mordenite ferrierite activated carbon
specific surface specific surface area of calculated area of TiO2-loaded surface area of adsorbent/m2 g-' adsorbent/m2 g-' mixtureo/m2g-' 178 381 250 367 284 154 228 293 210 623
465 8.8 548 5.6 88 200 375 290 1130
322 93 381 92 133 189 211 234 654
a The expected specific surface area of the mixture of naked Ti02 and adsorbents (1: 1).
onaldehyde was determined by means of gas chromatography using a Yanaco G2800 gas chromatograph equipped with a TCD detector and a Porapak T column (Waters) at 100 "C. Helium was used as a carrier gas. Adsorbability of the photocatalyst films was evaluated as follows. The photocatalyst films, which had 1.0 mg cm-2 for 4 cm2 of glass plate, were prepared and placed in the reaction cell, and the wet air was introduced into the reaction cell kept at 25 "C. After 10 min, the propionaldehyde vapor was injected. Changes in the concentration of propionaldehyde were then monitored as a function of time by means of gas chromatography using an Ohkura Model 802 gas chromatograph equipped with a FID detector and a BX-10 column (GL Science) at 80 "C until no appreciable changes in the concentration were observed. From the concentration decrease obtained in this way, the amount of propionaldehyde adsorbed on TiO2-loaded adsorbents was determined. Results and Discussion Characterization of Catalysts. Observations by a scanning electron microscope revealed that the Ti02 particles of TiO2loaded adsorbents were dispersed fairly uniformly over the adsorbents used. The prepared Ti02 was mostly anatase, as determined by X-ray diffraction analysis. The specific surface area of the naked TiO2, the adsorbents used, and 53 wt % TiO2loaded adsorbents are listed in Table 1. The specific surface area of the 53 wt % TiO2-loaded adsorbents was roughly equal to those expected for 1:l mixtures of the adsorbents used and the naked Ti02 except for the cases of Zeolum A-3 and A-4 supports. These results indicate that the surface area of Ti02 particles is not seriously changed by the Ti02 loading onto the adsorbents. The discrepancies observed for the use of Zeolum A-3 and A-4 supports might result from partial destruction of the zeolite cage, because these are weak against acidic environments used for the Ti02 loading. The inner surface areas of Zeolum A-3 and A-4 were not included in the measured specific surface areas due to their very small micropore sizes ( < 4 A). Influence of the Amount of Loaded Ti02 on Photodecomposition of Propionaldehyde. Figure 1 shows the time course of COz evolution from illuminated TiOz-loaded mordenite of 5, 11, and 53 wt % TiO2. The photodecomposition of propionaldehyde to give C02 is given by eq 1 for its complete decomposition.
+
CH3CH2CH0 40,
-
3C02
+ 3H20
The weight of the catalyst films used was 1.0 mg cm-2 for all cases. The highest photodecomposition rate was obtained with
Takeda et al.
9988 J. Phys. Chem., Vol. 99, No. 24, 1995 0.1
I
0" 50
0
100
150
200
"
20
0
"
40
lllumlnationtime I min
"
60
"
80
'
J
100
Ti02content I w t %
Figure 1. Time course of the amount of C02 produced by the photodecomposition of propionaldehyde over the Ti02-loaded mordenite. 1.22 x mol of propionaldehyde was contained in the cell of capacity 15 cm3 containing 4.6 Torr of water vapor. The amount of catalyst film was 1.0 mg cm-2 including the supports. The Ti02 content in the catalyst used was 5 (O), 11 (A), and 53 (0)wt %. Illumination was performed with a 10 W fluorescent black lamp.
Figure 3. Rate constant of C02 evolution in the photodecomposition of propionaldehyde as a function of Ti02 loadings on mordenite. The amount of catalyst film used was 1.0 mg
:m 5 4
3
2 1
-
0
0
3
6
9
1 2 1 5
6
9
1 2 1 5
c, /
10.~r.4
60 ,
0
10
20 30 40 lllumlnationtime I min
50
Figure 2. Plots of the left-hand side of eq 3 as a function of the illumination time. The data used for the plots were obtained from Figure 1. The Ti02 content in the catalyst used was 5 (O), 11 (A), and 53 (0) Wt
%.
0
3
Figure 4. Relationship between the amount of the adsorption of
use of 53 wt % TiO2-loaded mordenite. Since 1.22 x mol of propionaldehyde was contained in the cell, the production of 3.66 x mol of C02 was expected when the complete decomposition was achieved. If it is assumed that the photodecomposition of propionaldehyde to C02 proceeded with the pseudo-first-order kinetics with respect to its concentration, the rate of C02 production at a given illumination time is given by eq 2. d(CO2Ydt = kc02{(CO*)max- (C02)l
propionaldehyde (Sad) and its gaseous concentration (C,) (a) and plots of the left-hand-side of eq 4 as a function of C, (b). Catalyst films of 1.0 mg cm-* on glass plate (4 cm2) were used. The loaded-Ti02 content was 27 (A), 53 (o), 72 (O), and 100 (0)wt %.
observed here seems to have resulted from differences in the amount of adsorbed propionaldehyde, as discussed below. The adsorption constant of TiO2-loaded mordenite, as well as that of the naked Ti02, was evaluated using the Langmuir adsorption isotherm, which is given by eq 4.37
(2)
where kco, is the apparent rate constant for C02 evolution, ( C O Z ) is ~ ~the ~ amount of C02 expected from complete decomposition of propionaldehyde (3.66 x mol), and (C02) is that obtained at a given illumination time. Integration of eq 2 gives eq 3.
(3) Plots of the left-hand side of eq 3 using the amount of CO:! given in Figure 1 as a function of the illumination time give fairly good linear relations, as shown in Figure 2. It was found that similar good linear relations were established also for different amounts of Ti02 loading. Then the pseudo-first-order rate constant of C02 evolution, kco2, was determined from the slope of the time course. Figure 3 shows kco2 as a function of the Ti02 content of the TiO2-loaded mordenite. With an increase in the amount of loaded TiO2, the rate constant increases up to an optimum value, beyond which a decreasing tendency appears. The dependence of kco2on the Ti02 content
(4) where Kad is the adsorption constant, Cs is the concentration of propionaldehydein the gas phase, s a d is the amount of adsorbed propionaldehyde on the TiO2-loaded mordenite, and SadmaX is its maximum value. Figure 4a shows the relation between the amount of adsorbed propionaldehyde on TiOz-loaded mordenite and the gaseous concentration of propionaldehyde used for the adsorption experiments. If Cs/&d is obtained from the results given in Figure 4a and is plotted against C,, good linear relationships are obtained between them for four different Ti02 loadings, as given in Figure 4b. By applying eq 4 to this linear relations, Kad and SadmaX are determined. The Kad values obtained are shown in Figure 5a, and those of SadmaX are 6.9 x mol for 27 wt % Ti02 loading, 6.4 x mol for 53 wt % loading, 6.1 x low6mol for 72 wt % loading, and 5.9 x mol for the naked Ti02. The value of Sad varies with the gaseous concentration of propionaldehyde in the reaction cell, as shown in Figure 4a. It is important to obtain Sad under the condition of photodecomposition experiments, which is repre-
J. Phys. Chem., Vol. 99, No. 24, 1995 9989
Photodecomposition Rate of Gaseous Propionaldehyde 4 ,
%I
c - 0 20
40
60
80
100
0
Ti02 content / wt %
'
0
8
0.5
s
8
1
'
'
1.5
"
'
a
2
'
2.5
3
Weight of the catalyst / mg cm.'
Figure 6. Dependence of the rate constant of COz evolution on the amount of 53 wt % Ti02-loaded mordenite on glass plate (4 cm2).
2!
O 0.8 20
S 40
9 60
i 80
100
Ti02 content / W %
Figure 5. Influence of the loaded-Ti02 content on the adsorption constant of propionaldehyde (&) (a) and the the amount of adsorbed propionaldehyde (Sadphoto) under the conditions of photodecomposition experiments (b). Catalyst films of 1.0 mg cm-* on 4 cm2of glass plate
were used. sented as and 5.
SadPhoto.
The
SadPhoto
was evaluated by using eqs 4
cov= C,V + Sad
(5)
where COis the total concentration of propionaldehyde, V is the reaction cell volume, and thus CoV is 1.22 x mol. The values of K a d and SadmaX given above were used in the calculation. Figure 5 shows dependence of K a d and SadPhoto determined in this way on the Ti02 content of TiOyloaded mordenite. For Ti02 contents lower than about 50 wt %, K a d and SadPhoto are almost constant and independent of the Ti02 contents. By comparing the dependence of the photodecomposition rate on the Ti02 content (Figure 3) with that of SadPhoto or K a d given in this figure, we noticed that for the Ti02 loadings less than about 50 wt % the decomposition rate is simply proportional to the Ti02 content, and the amount of adsorbed propionaldehyde does not have any significant effect. Beyond about 50 wt % loading of TiO2, however, the rate constant decreases with increasing the Ti02 loading, as shown in Figure 3. The same tendencies appear for K a d and SadPhoto. We concluded from these findings that, up to about 50 wt % Ti02 loading, the decomposition rate is controlled by the amount of TiO2, and beyond this critical value the amount of adsorbed propionaldehyde determines the decomposition rate. The decrease in the amount of adsorbed propionaldehyde seems to result from decrease of occupancy of the mordenite support with increase of the Ti02 loading (Figure 5b). This is because K a d of the photocatalyst decreases with increase in the Ti02 loading, as shown in Figure 5a, due to the smaller value of K a d of Ti02 than that of mordenite. These results strongly suggest that propionaldehyde adsorbed on mordenite is involved in the photodecomposition reaction. The most likely process of the involvement of propionaldehyde adsorbed on the support will be surface diffusion to Ti02 particles. Effect of the Amount of Photocatalyst on the Decomposition Behavior. The photodecomposition rate of propionaldehyde was influenced by the amount of the catalyst on the glass plate. Figure 6 shows the effect of the amount of 53 wt %
Ti02-loaded mordenite films on k o 2 . It is obvious that kcoz increases with increase of the amount of the catalyst up to 1.0 mg cm-2, beyond which a decreasing tendency appears. With increase in the amount of the catalyst, the thickness of the catalyst films increases. It was determined that a 1.0 mg cm-2 catalyst film had the transmittance of 1% at 352 nm. This means that the illuminated photons were effectively utilized in photoexcitation of the loaded Ti02 in that case. The observed dependence is then explained reasonably in terms of utility of Ti02 particles in photoexcitation. Up to 1.0 mg cm-2, almost all of the loaded Ti02 particles contained in the catalyst film are effectively photoexcited, resulting in the increase of the decomposition rate with increasing the amount of photocatalyst, as observed, but with further increase of the amount of the catalyst film, the degree of photoexcitation of the loaded Ti02 particles decreases. Considering that the total amount of propionaldehyde used was 1.22 x IOp6 mol, the photocatalyst films adsorb almost all propionaldehyde molecules in the reaction cell if the photocatalyst film exceeds 1.0 g cm-', as judged from the results given in Figure 5b. Since a fraction of loaded Ti02 is not utilized in photoexcitation under such conditions, propionaldehyde adsorbed in the dark part of the catalyst has to diffuse to illuminated Ti02 particles near the film surface before being photodecomposed. Due to a slow diffusion rate, the decomposition rate must decrease in such cases, as shown in Figure 6. Effects of Adsorbability of Supports on the Photodecomposition Rate. As described above, adsorbability of TiO2loaded mordenite influenced the photodecomposition rate of propionaldehyde. To investigate the effect of adsorbability on the decomposition rate in more detail, relations between the adsorbability of adsorbents for propionaldehyde and the photodecomposition rate were investigated using a variety of adsorbents as the supports for Ti02. Figure 7 shows the time course of the C02 evolution with illumination of 53 wt % Ti02loaded mordenite, activated carbon, and Zeolum F-9 and A-3. The amount of the catalyst films was fixed to 1.0 mg cm-*, which gave transmittance of about 1% at 352 nm in all cases. The same adsorption experiments as shown in Figure 4 for TiO2loaded mordenite were applied to these catalyst films to determine the adsorption constant Kad and the maximum adsorption Sadmax. Obtained results are given in Table 2. By applying these values to eqs 4 and 5, the amount of the adsorbed substrate under the condition of photodegradation experiments, S,dPhoto, was determined using the same method as described above. Figure 8a shows SadPhoto values as a function Of K a d values determined. As shown in Figure 8a, SadPhoto increases with K a d up to 4 x lo4 M-' and becomes constant with further increase of Kad. By comparing SadPhoto given in Figure 8a with the specific surface area given in Table 1, we noticed that SadPhoto is not determined by the specific surface area. It must be
Takeda et al.
9990 J. Phys. Chem., Vol. 99, No. 24, I995
_0
0 20
EO
60
40
100
1
2
3
Kad
120
illumination time / mln
0.1
4
5
6
7
8
I lo4 M”
,
I
Figure 7. Time course of COz evolution in the photodecomposition of propionaldehyde over 53 wt % TiOz-loaded adsorbents of varous mol of propionaldehyde and 4.6 Torr of water vapor kinds. 1.22 x were contained in a cell of 15 cm3 capacity. The amount of catalyst film was 1.O mg cm-2 on glass plate (4 cm2). The supports used were mordenite (0). activated carbon (A), Zeolum F-9 (a),and Zeolum A-3 (0). The illumination was performed with a 10 W fluorescent black lamp.
TABLE 2: Adsorption Constant (find) and the Maximum Amount of Adsorbed Propionaldehyde (Sadmax) on the Various 53 wt % TiOz-Loaded Adsorbents and the Naked TiOz, Determined by Using the Langmuir Adsorption Isotherm adsorbent Zeolum A-5 Zeolum A-3 Zeolum F-9 Zeolum A-4 alumina silica mordenite ferrierite activated carbon naked Ti02
Kadl1o4 M-
‘
S,dmax”/o-6mol
0.78 0.87
4.5
1.2 1.5 1.5 2.5
7.0 6.0
3.1 7.0
6.4 8.7 5.6
0.64
5.9
4.5
3.9 5.9 3.8
remarked here that the loaded Ti02 content was 53 wt % for all the adsorbent supports used. If kcol is determined by applying the results shown, for example, in Figure 7 to eq 3 and if the obtained values are plotted as a function of Kad, the results shown in Figure 8b are obtained. Apparently a volcano type dependence of kco2on Kad is seen. Too much or too little Kad causes a noticeable decrease in the decomposition rate. The following discussion derives from the results given in Figure 8. In cases where an adsorbent has a small adsorption constant as in the case of Zeolum A-3, A-5, and F-9, the amount of adsorbed propionaldehyde is small due to their low adsorption strength, and then the decomposition rate is determined by the amount of adsorbed propionaldehyde. With increase in the adsorption constant, the amount of adsorbed propionaldehyde becomes greater, providing a high-concentration environment of propionaldehyde around Ti02. However, if the adsorption constant of the supports is very great, as in the case of femerite and activated carbon, the adsorbed propionaldehyde on the support cannot move easily to the Ti02 particles due to their high adsorption strength, even if a large concentration gradient exists between the Ti02 particles and their vicinities. The rate of decomposition in those cases must be determined by a rate of supply of adsorbed propionaldehyde to Ti02 particles from the support adjacent to particles or by a rate of collision of gaseous propionaldehyde onto Ti02 particles. In either case, a high decomposition rate does not seem to be achieved. The highest decomposition rate is then obtained at the adsorbent supports of a medium adsorption strength where a fairly high amount of adsorbed propionaldehyde is available and is mobile under the presence of its concentration gradient around the Ti02 particles.
0
1
2
3
4
5
6
7
8
Kad I lo4 M-’ Figure 8. (a) Amount of adsorbed propionaldehyde on TiOJoaded
adsorbents (Sdphoto) under the conditions of photodecomposition experiments as a function of the adsorption constant (Ka& (b) Relationship between the rate constant of CO:! evolution and Kad. The rate constant was determined with use of 0.5 mg cm-* catalyst films for naked Ti02 and 1.0 mg cm-2 catalyst films for 53 wt 8 TiOz-loaded adsorbents. Naked Ti02 (a) and TiOz-loaded Zeolum A-5 (b), Zeolum A-3 (c), Zeolum F-9 (d), Zeolum A-4 (e), alumina (f),silica (g), mordenite (h), femerite (i), and activated carbon (i).
Conclusion Investigations in the present study on photodecomposition of propionaldehyde over Ti02 loaded on various inert supports have revealed that the inert support influences the apparent photocatalytic activities if it possesses a relatively high adsorbability. In cases of using such suitable supports, the amount of loaded Ti02 also affects the apparent activity. The use of a support having an appropriate adsorbability has great significance in practical applications for the photodestruction of pollutants of very dilute concentrations; the support can eliminate the pollutants from the atmosphere by adsorption, and the substrates concentrated in the support around the loaded Ti02 particles are involved in the photodestruction, resulting in enhancement of the photodestruction rate. However, the use of supports of too low and too high adsorption strength is inadequate to obtain such significant effects. Since the adsorption strength of one kind of support must be different for various kinds of target substrates, it seems necessary to select a support after screening its effect on the photodecomposition rates. Acknowledgment. This research was supported by Grantin-Aid for Developmental Scientific Research No. 06555260 from the Ministry of Education, Science, and Culture. References and Notes (1) Ollis, D. F.; Pelizzetti, E.: Serpone, N. Photocatalysis; Fundamentals and Applications; Serpone, N.; Pelizzetti, E., Eds.; Wiley: New York, 1989; Chapter 18. (2) Ollis, D. F.; Pelizzetti, E.: Serpone, N. Environ. Sci. Technol. 1991, 25, 1522. (3) Fox, M. A.; Dulay, M. T. Chem. Rev. 1993, 93, 341. (4) Mills, A.; Davies, R. H.; Worsley, D. Chem. Soc. Rev. 1993, 22, 417.
(5) Pelizzetti, E.; Minero, C. Electrochim. Acta 1993, 38, 47. (6) Yoneyama, H.; Takao, Y.; Tamura, H.: Bard, A. J. J. Phys. Chem. 1983, 87, 1417. (7) Miyake, M.; Yoneyama. H.; Tamura, H. J. Caral. 1979, 58, 22.
Photodecomposition Rate of Gaseous Propionaldehyde (8) (a) Pruden, A. L.; Ollis, D. F. J. Catal. 1983, 82, 404. (b) Hsiao, C.-Y.; Lee, C.-L.; Ollis, D. F. J. Catal. 1983, 82, 418. (9) Hashimoto, K.; Kawai, T.; Sakata, T. J. Phys. Chem. 1984, 88, 4083. (10) (a) Matthews, R. W. J. Catal. 1986, 97, 565. (b) Matthews, R. W. J. Phys. Chem. 1987, 91, 3328. (c) Matthews, R. W. J. Catal. 1988, 111, 264. (11) Turchi, C. S.; Ollis, D. F. J. Catal. 1990, 122, 178. (12) Peterson, M. W.; Turner, J. A.; Nozik, A. J. J. Phys. Chem. 1991, 95, 221. (13) (a) Gerischer, H.; Heller, A. J. Phys. Chem. 1991, 95, 5261. (b) Jackson, N. B.; Wang, C. M.; Luo, Z.; Schwitzgebel, J.; Ekerdt, J. G.; Brock, J. R.; Heller, A. J. Electrochem. SOC. 1991, 138, 3660. (c) Rosenberg, I.; Brock, J. R.; Heller, A. J. Phys. Chem. 1992, 96, 3423. (14) (a) Vinodgopal, K.; Hotchandani, S.; Kamat, P. V. J. Phys. Chem. 1993, 97,9040. (b) Stafford, U.; Gray, K. A,; Kamat, P. V. J. Phys. Chem. 1994, 98, 6343. (c) Vinodgopal, K.; Stafford, U.; Gray, K. A,; Kamat, P. V. J. Phys. Chem. 1994, 98, 6797. (15) (a) Wold, A. Chem. Mater. 1993, 5, 280. (b) Papp, J.; Soled, S.; Dwight, K.; Wold, A. Chem. Mater. 1994, 6 , 496. (16) (a) Serpone, N.; Lawless, D.; Disdier, J.; Hemnann, J.-M. Langmuir 1994, 10, 643. (b) Minero, C.; Pelizzetti, E.; Terzian, R.; Serpone, N. Langmuir 1994, 10, 692. (17) (a) Carraway, E. R.; Hoffmann, A. J.; Hoffmann, M. R. Environ. Sei. Technol. 1994, 28, 786. (b) Choi, W.; Termin, A,; Hoffmann, M. R. Angew. Chem., Int. Ed. Engl. 1994, 33, 1091. (18) Courbon, H.; Formenti, M.; Juillet, F.; Lisachenko, A,; Martin, J.; Teichner, S. J. Kine?. Catal. 1973, 14, 84. (19) (a) Ibusuki, T.; Takeuchi, K. Atmos. Environ. 1986, 20, 1711. (b) Ibusuki, T.; Kutsuna, S.; Takeuchi, K.; Shinkai, K.; Sasamoto, T.; Miyamoto, M. Trace Metals Environment 3 (Photocatalytic Purl3cation and Treatment of Water and Air); Ollis, D. F., AI-Ekabi, H., Eds.; Elsevier: Amsterdam, 1993: p 375. (c) Ibusuki, T.; Takeuchi, K. J. Mol. Catal. 1994, 88, 93.
J. Phys. Chem., Vol. 99, No. 24, 1995 9991 (20) Ohtani, B.; Ueda, Y.; Nishimoto, S.; Kagiya, T.; Hachisuka, H. J. Chem. Soc., Perkin Trans. 2 1990, 1955. (21) (a) Dibble, L. A,; Raupp, G. B. Catal. Lett. 1990,4, 345. (b) Dibble, L. A,; Raupp, G. B. Environ. Sei. Technol. 1992, 26, 492. (22) Su%ki, K.; Satoh, S.; Yoshida, T. Denki Kagaku 1991, 59, 521. (23) Peral, J.; Ollis, D. F. J. Catal. 1992, 136, 554. (24) Nimios, M. R.; Jacoby, W. A.; Blake, D. M.; Milne, T. A. Environ. Sei. Technol. 1993, 27, 732. (25) Yamazaki-Nishida, S.; Nagano, K. J.; Phillips, L. A,; CerveraMarch, S.; Anderson, M. A. J. Photochem. Photobiol. A: Chem. 1993, 70, 95. (26) Lichtin. N. N.: Avudaithai. M.: Berman. E.: Dong. J. Res. Chem. Intermed. 1994, 20, 755. (27) Tunesi, S.; Anderson, M. J. Phvs. Chem. 1991, 95, 3399. (28) (a) Dagan, G.; Tomkiewicz, M:J. Phys. Chem. 1993, 97, 12651. (b) Tomkiewicz, M.; Dagan, G.; Zhu, Z. Res. Chem. Intermed. 1994, 20, 701. (29) Uchida, H.; Itoh, S.; Yoneyama, H. Chem. Lett. 1993, 1995. (30) Sampath, S.; Uchida, H.; Yoneyama, H. J. Catal. 1994, 149, 189. (31) Palmisano, L.; Schiavello, M.; Sclafani, A,; Coluccia, S.; Marchese, L. New J. Chem. 1988, 12, 847. (32) Minero, C.; Catozzo, F.; Pelizzetti, E. Langmuir 1992, 8, 481. (33) Fox, M. A,; Doan, K. E.; Dulay, M. T. Res. Chem. Intermed. 1994, 20, 711. (34) Yoe, J. H.; Armstrong, A. R. Anal. Chem. 1947, 19, 100. (35) Lide, D. R., Frederikse, H. P. R., Eds. CRC Press Handbook of Chemistry and Physics, 75th ed.; CRC Press: Boca Raton, 1994; pp 6-15. (36) Hata, K., Ed. Kagaku Binran; Maruzen: Tokyo, 1984; Vol. 11, pp 11-111. (37) Pichat, P.; Henmann, J.-M. Photocatalysis: Fundamentals and Applications; Serpone, N., Pelizzetti, E., Eds.; Wiley: New York, 1989; Chapter 8.
-
JP950281A
