FTIR study of adsorption and photochemistry of amide on powdered
TiO
2: Comparison of benzamide with acetamide
L.-F. Liao, C.-F. Lien, D.-L. Shieh, F.-C. Chen and J.-L. Lin*
Department of Chemistry, National Cheng Kung University, 1 Ta Hsueh Road, Tainan, Taiwan, Republic of China. E-mail: jonglin@mail.ncku.edu.tw
Received 8th May 2002, Accepted 19th July 2002
First published as an Advance Article on the web 20th August 2002
FTIR has been used in situ to investigate the adsorption, thermal transformation, and photoreactions of benzamide on TiO2. The reaction pathways are compared to the case of acetamide. Our reaction system is
focused on the vapor–solid surface reactions, which are complementary to the reactions catalyzed in the solution phase. Benzamide is adsorbed molecularly or dissociatively to generate C6H5CONH by losing one
amino hydrogen at 35C. Upon raising the TiO
2surface temperature, C6H5CN and C6H5COO are produced.
Under photoirradiation in O2, adsorbed benzamide and C6H5CONH are transformed into surface species of
NCO, C6H5COO, and C6H5CN and gaseous CO2, revealing versatile photoreaction pathways. These surface
intermediates were not found in a previous study of benzamide photodecomposition catalyzed by TiO2in the
solution phase. Similar reaction pathways were found for acetamide on TiO2. It is worthy of note that –CONH2
on TiO2is transformed into –CN thermally and photochemically. –CN reacts reversibly with surface OH
groups to form –CONH2.
Introduction
Semiconductor oxides are of much interest in electrochemistry, photocatalysis, energy conversion, and sensor technology. Heterogeneous photocatalysis by TiO2appears promising for
transforming organic pollutants in aqueous solution into environmentally innocuous species and has attracted much attention recently.1Photoreactions of organic compounds with special functionality, such as carboxylate2–10 and amide groups,11–13have been studied in solution in the presence of
TiO2. In a previous study of the photodegradation of
benza-mide to CO2and nitrate ions in aerated TiO2aqueous
suspen-sions, trihydroxybenzamide and trace amounts of parabenzo-quinone and hydroxyparabenzo-quinone were detected, by a combination of HPLC, GC/MS, and UV spectroscopy, as reaction inter-mediates present in the aqueous solutions.11However in these
previous studies of benzamide catalyzed by TiO2in suspension
systems, the subjects of adsorption and surface intermediate are not described, presumably due to the limitation of surface analytical techniques. In the present research, we apply in situ Fourier-transform infrared spectroscopy to study the adsorp-tion and reacadsorp-tions of benzamide on TiO2with the focus being
on the surface chemistry. The results obtained are also com-pared with our previous study of acetamide using the same technique.14We investigate these two compounds as a model for amide (the –CONH2 amide group is attached to methyl
for acetamide and to phenyl for benzamide) and find similar reaction pathways for the amide group on TiO2.
Experimental
The preparation of TiO2powder supported on a tungsten fine
mesh (6 cm2) has been described previously.15In brief, TiO 2
powder (Degussa P25,50 m2g 1, anatase 70%, rutile 30%) was dispersed in water/acetone solution to form a uniform mixture which was then sprayed onto a tungsten mesh. The TiO2 sample was then mounted inside the IR cell for
simultaneous photochemistry and FTIR spectroscopy. The IR cell with two CaF2windows for IR transmission down to
1000 cm 1 was connected to a gas manifold which was pumped by a 60 l s 1turbomolecular pump with a base pres-sure of1 10 7Torr. The TiO
2sample in the cell was heated
to 450C under vacuum for 24 h by resistive heating. The
tem-perature of the TiO2sample was measured by a K-type
ther-mocouple spot-welded on the tungsten mesh. Before each run of the experiment, the TiO2sample was heated to 500C
in vacuum for 2 h. After the heating, 10 Torr O2was
intro-duced into the cell as the sample was cooled to 70C. When
the TiO2 temperature reached 35C, the cell was evacuated
for gas dosing. The TiO2surface after the above treatment still
possessed residual hydroxy groups. O2 (99.998%) was
pur-chased from Matheson. Benzamide (95%,Wako) and aceta-mide (98%, Merck) are solid at room temperature and were well-outgassed in vacuum before introduction to the cell. Ben-zonitrile (>99%, Merck) and acetonitrile (99.97%, Tedia) were purified by several freeze–pump–thaw cycles. The pressure was monitored with a Baratron capacitance manometer and an ion gauge. In the photochemistry study, both the UV and IR beams were set at 45to the normal of the TiO
2sample. The
UV light source used was a combination of a Hg arc lamp (Oriel Corp.) operated at 350 W, a water filter, and a band pass filter with a band width of100 nm centered at 320 nm (Oriel 51650) or 400 nm (Oriel 51670). Infrared spectra were obtained with a 4 cm 1resolution by a Bruker FTIR spectrometer with a MCT detector. The entire optical path was purged with CO2
-free dry air. The spectra presented here were ratioed against a clean TiO2spectrum providing the metal oxide background.
Results and discussion
Adsorption of benzamide
Fig. 1 shows the IR spectra of benzamide after adsorption on TiO2at 35C and brief annealing at the indicated temperatures
4584 Phys. Chem. Chem. Phys., 2002, 4, 4584–4589 DOI: 10.1039/b204455m
in vacuum. In the 35C spectrum, absorption bands appear at
1190, 1428, 1451, 1532, 1606, 1654, and 3065 cm 1. The 1654 cm 1 bands, characteristic of the carbonyl stretching fre-quency, indicating the presence of benzamide molecules on TiO2at this temperature. However this frequency is lower than
the carbonyl absorption frequency at 1677 cm 1for benzamide in CHCl3 and CS2solutions or at 1715 cm 1 from
calcula-tion,16 revealing the interaction of the carbonyl oxygen with surface Lewis acid sites.14The adsorbed benzamide also con-tributes to the IR absorptions at 1190 and 1451 cm 1due to C–C stretching and C–H rocking, 1606 cm 1due to C–C and
N–H stretching, and 3065 cm 1due to C–H stretching. These band assignments are given on the basis of previously mea-sured and calculated IR absorptions of benzamide.16However
adsorbed benzamide cannot account for the two other bands at 1428 and 1532 cm 1 in the 35C spectrum. The simulta-neous appearance of two strong bands at1430 and 1530 cm 1 suggests the formation of the functional group of –CON–. In the adsorption of acetamide on TiO2,
CH3CONH(a)is generated with frequencies of 1439 and 1541
cm 1 due to symmetric and antisymmetric –CON– stretch-ing.14In Fig. 1, the spectral feature after heating to 100C is
about the same as that of the 35C spectrum. However, the carbonyl peak at 1654 cm 1is decreased upon further heating
to 150C, indicating the desorption or decomposition of
adsorbed benzamide. Meanwhile the absorptions located at 1413, 1512, and 2265 cm 1are enhanced. This trend continues
to 250C at which the bands appear at 1225, 1413, 1450, 1494,
1512, 1598, 2265, and 3070 cm 1. As to the bands at 1413, 1512, and 2265 cm 1, the former two bands are likely due to
the symmetric and antisymmetric –COO– group;17 the 2265 cm 1band is likely due to CN stretching based on the characteristic frequencies of specific functional groups. Fig. 2 and 3 obtained after adsorption of benzoic acid and
benzoni-trile confirm the assignment by the appearance of similar bands. Table 1 summarizes the observed band frequencies for the 35C and 250C spectra in Fig. 1 and their
approxi-mate vibrational mode assignment.
Fig. 2 shows the IR spectra of benzoic acid after adsorption on TiO2at 35C and brief annealing at the indicated
tempera-tures in vacuum. Absorption bands appear at 1025, 1070, 1094, 1155, 1181, 1307, 1425, 1452, 1500, 1520, 1592, 1604, 1663, and 3062 cm 1in the 35C spectrum. The characteristic
carbonyl stretching band of 1663 cm 1indicates the presence of benzoic acid molecules on TiO2. Similar to the case of
ben-zamide on TiO2, the interaction of the carbonyl group of
ben-zoic acid with surface Lewis acid sites leads to its lower frequency compared to the pure benzoic acid at 1695 cm 1.18 In this 35C spectrum, except for the two bands at 1425 and
1520 cm 1, adsorbed benzoic acid also contributes to all the other bands attributable to its C–C bending and stretching and C–H rocking and stretching. The amount of the surface benzoic acid decreases with increasing temperature, as indi-cated by the loss of intensity at 1663 cm 1, almost disappear-ing at 150C. In contrast, the 1425 and 1520 cm 1bands grow simultaneously with increasing temperature. In comparison to the –COO– symmetric and antisymmetric stretching frequen-cies for sodium benzoate (1421 and 1548 cm 1)19and for acet-ate on TiO2(1423 and 1532 cm 1),17the 1425 and 1520 cm 1
bands are assigned to –COO– stretching of benzoate on TiO2.
Table 2 summarizes the observed band frequencies for the 35C and 300C spectra in Fig. 2 and their approximate
vibra-tional mode assignment based on the IR frequencies of pure benzoic acid.18The results of Fig. 2 show that adsorbed ben-zoic acid is decomposed into benzoate with increasing tem-perature.
Fig. 3 shows the IR spectra of benzonitrile after adsorption on TiO2at 35C and brief annealing at the indicated
tempera-tures in vacuum. In the 35C spectrum, absorption bands are
Fig. 2 IR spectra of TiO2surface exposed to benzoic acid vapor for
21 h at 35C and then evacuated at the indicated temperatures for 1
min. All of the spectra were taken at35C with 50 scans. The
fre-quencies at the marked positions and their vibrational assignments are listed in Table 2. The TiO2sample used was 76 mg.
Fig. 1 IR spectra of TiO2 surface exposed to benzamide vapor for
42 h at 35C and then evacuated at the indicated temperatures for
1 min. During the benzamide dosing, the cell was evacuated from time to time to minimize possible surface contamination. All of the spectra were taken at35C with 50 scans. The frequencies at the marked
positions and their vibrational assignments are listed in Table 1. The TiO2sample used was 76 mg.
located at 1026, 1069, 1096, 1125, 1159, 1179, 1209, 1290, 1336, 1448, 1491, 1532, 1599, 1653, 2227, 2272, and 3066 cm 1. The characteristic CN stretching bands of 2227 and 2272 cm 1 indicate the presence of benzonitrile on TiO2. The small CN
band at 2227 cm 1is close to the 2230 cm 1band of pure
ben-zonitrile in the liquid state,20therefore it is attributed to physi-sorbed surface benzonitrile. The other CN band at 2272 cm 1 is 45 cm 1higher than that of the physisorbed benzonitrile and
is attributed to benzonitrile bonded to surface OH or Ti ion via its nitrogen lone-pair. This phenomenon is also observed in the case of CH3CN on TiO2.21In the 35C spectrum, except for
the 1532 and 1653 cm 1bands, adsorbed benzonitrile contri-butes to all the other bands on the basis of the IR frequencies of pure benzonitrile.20The appearance of the 1653 cm 1band
indicates that a compound with a carbonyl group is formed.
The broad band at 1532 cm 1is also observed in the benza-mide adsorption in Fig. 1 and is assigned to the antisymmetric stretching of –CON– of C6H5CONH(a). The –CON–
sym-metric stretching band (expected to be at1428 cm 1) seems to overlap with the 1448 cm 1band and appears as a shoulder on the right-hand side of this band in the 35C spectrum in Fig. 3. After heating the surface to 100C, the amount of
ben-zonitrile decreases, as evidenced by the reduction of the CN integrated intensity. Furthermore the ratio of the peak areas, 2227 cm 1/2272 cm 1, is less than that at 35C, indicating
that the 2227 cm 1 band is thermally less stable. Increasing the temperature to 100C also enhances the bands due to C=O at 1653 cm 1and CNO at 1532 cm 1. After further
heat-ing the surface to 300C, some benzonitrile molecules are still
present on the surface, as shown by the residual CN band at 2272 cm 1. Most importantly, the compounds with C=O or CNO groups vanish and the absorption feature of benzoate with the bands at 1413 cm 1and 1512 cm 1appears. Clearly, Fig. 3 shows that adsorbed benzonitrile is thermally trans-formed into benzoate. It is proposed that this process is through benzamide and C6H5CONH(a) as suggested by the
observation of the C=O (1653 cm 1) and –CNO– (1532 cm 1) bands. Thermal transformation of acetonitrile, through aceta-mide and CH3CONH(a), to acetate has been observed on
TiO2, ZnO, a-Fe2O3, and d-Al2O3.22–24The reaction of
acet-onitrile on the metal oxides to form acetamide and CH3CONH(a)is attributed to the involvement of surface OH
groups.22–24 Table 3 lists the frequencies observed in Fig. 3 and their corresponding vibrational modes. In Fig. 1, as adsorbed benzamide is heated to 250C, a CN band at 2265
cm 1appears due to the formation of benzonitrile. This is a dehydration reaction of benzamide which can be viewed as the reverse route of benzonitrile attacked by surface OH to form benzamide at 35C as shown in Fig. 3.
Photooxidation of adsorbed benzamide
Fig. 4 shows the IR spectra before and after the indicated light exposure times for adsorbed benzamide initially in 10 Torr of O2. In the region of 2100–2450 cm 1, it is found that two
absorption bands at 2202 and 2265 cm 1quickly appear and continue to be present on the surface during the 180 min light irradiation. A few tens of minutes after the UV lamp is turned on, a band at 2349 cm 1is generated and assigned to gaseous CO2. The bands at 2202 and 2265 cm 1belong to CN
stretch-ing. The 2202 cm 1 is attributed to NCO
(a) which is also
observed in the photodissociation of CH3CN on TiO2 21
due Fig. 3 IR spectra of TiO2surface exposed to0.7 Torr benzonitrile
vapor at 35C and then evacuated at the indicated temperatures for
1 min. All of the spectra were taken at35C with 50 scans. The
fre-quencies at the marked positions and their vibrational assignments are listed in Table 3. The TiO2sample used was 96 mg.
Table 1 Infrared frequencies and approximate assignments for adsorbed benzamide on TiO2at 35C and 250C
Temperature
Assignment 35C 250C
3065 3070 C–H stretch
— 2265 C==N stretch from C6H5CN(a)
1654 — C=O stretch 1606 1598 C–C, N–H stretch
1532 — CON stretch from C6H5CONH(a)
— 1512 COO stretch from C6H5COO(a)
— 1494 C–C stretch, C–H rock 1451 1450
1428 — CON stretch from C6H5CONH(a)
— 1413 COO stretch from C6H5COO(a)
— 1225 C–C stretch, C–H rock, C–O, N–H bend 1190 — C–C stretch, C–H rock
Table 2 Infrared frequencies and approximate assignments for adsorbed benzoic acid on TiO2at 35C and 300C
Temperature
Assignment 35C 300C
3062 3071 C–H stretch
1663 — C=O stretch from C6H5COOH(a)
1604 1602 C–C stretch 1592 1592
1520 1520 COO stretch from C6H5COO(a)
1500 1495 C–C stretch, C–H rock 1452 1451
1425 1412 COO stretch from C6H5COO(a)
1307 1310 C–C stretch, C–H rock 1181 1180 1155 1152 1094 1094 C–C stretch, C–C bend 1070 1170 1025 1026
to the C–C bond scission and is identified on various sur-faces.21The other band at 2265 cm 1is also observed in the
surface heating of adsorbed benzamide in Fig. 1 and assigned to the CN stretching frequency of benzonitrile. In the region of 1250–1800 cm 1, the spectrum features also change with
light irradiation. After 180 min, absorption IR bands appear
at 1351, 1415, 1452, 1559, and 1609 cm 1. The two strong, broad bands at 1351 and 1559 cm 1 are assigned to –COO– stretching of HCOO(a) which has been thoroughly studied
on TiO2.25 The 1415 cm 1 may be due to the symmetric
stretching of benzoate molecules. The other two bands at 1452 and 1609 cm 1are likely due to C–C stretching of the benzene ring of unreacted benzamide, benzoate, or benzoni-trile. Since the surface temperature is increased to70C
dur-ing the light exposure, a separate experiment was carried out using the same experimental conditions as that of Fig. 4 and holding the surface temperature at 70C for 180 min without
light exposure. The bands observed after the UV illumination in Fig. 4 are not found in this thermal control experiment, indi-cating that the reaction products observed in Fig. 4 are due to a photoeffect. In the present photoreaction study of adsorbed benzamide, it is possible to identify surface intermediates in situ during the photoirradiation. This investigation of the vapor–solid reaction is complementary to those performed in the liquid phase in which surface processes are difficult to explore and the complexity due to the presence of solvent has also to be taken into account. The reaction products of CO2, NCO, C6H5COO, and C6H5CN observed in Fig. 4 in
the photoirradiation of adsorbed benzamide show that versa-tile reaction pathways exist. The last three products involve chemical changes of the amide group of benzamide. NCO is formed by dehydrogenation of the –CONH2group and
scis-sion of the C–C bond between the benzene ring and the amide group. C6H5CN is formed by the loss of one oxygen and two
hydrogen atoms of benzamide. C6H5COO results from the
replacement of the NH2 group. Although multiple reaction
routes are identified, they do not necessarily account for all the reactions occurring. In our previous study of the photoox-idation of benzene on TiO2using the same technique, phenoxy
groups were identified as a reaction product.26It would not be
surprising if a similar type of oxygen addition to the benzene ring might occur in the benzamide case. However due to the presence of a strong, broad absorption feature in the region of 1250–1800 cm 1 in Fig. 4, products other than CO2,
HCOO, NCO, C6H5COO, and C6H5CN are not detected.
Scheme 1 summarizes our findings in this study for benzamide. It is found that acetamide on TiO2also shows similar reaction
pathways.
Adsorption and photooxidation of acetamide
Fig. 5 shows the comparison of the spectral features of adsorbed acetonitrile and acetamide subjected to surface heat-ing or photoillumination. Fig. 5(a) shows the spectra obtained after exposure of a clean TiO2surface to 2 Torr of acetonitrile
followed by evacuation at 35C and 200C. Adsorption of
acetonitrile at 35C produces IR bands located at 1367, 1415, 1433, 1469, 1537, 1578, 1650, 2279, and 2306 cm 1. Adsorbed acetonitrile is responsible for the characteristic, strong bands of 1367, 2279, and 2306 cm 1which are assigned to symmetric bending of CH3and stretching of CN.
Adsorp-tion of acetonitrile on TiO2at 35C, generates not only
mole-cularly adsorbed acetonitrile but also acetamide and CH3CONH(a)whose formation is verified by the similar
fre-quencies from acetamide adsorption shown in the 35C
spec-trum of Fig. 5(b) obtained by exposing a clean TiO2surface
Table 3 Infrared frequencies and approximate assignments for adsorbed benzonitrile on TiO2at 35C and 300C
Temperature
Assignment 35C 300C
3066 3074 C–H stretch
2272 2272 C==N stretch from C6H5CN(a)
2227 —
1653 — C=O stretch 1599 1600 C–C stretch
1532 — CON stretch from C6H5CONH(a)
— 1512 COO stretch from C6H5COO(a)
1491 1494 C–C stretch, C–H rock 1448 1441
— 1413 COO stretch from C6H5COO(a)
1336 — C–C stretch, C–H rock,
C–N stretch from C6H5CONH2(a)
1290 1309 C–C stretch, C–H rock 1209 — 1179 1181 1159 1161 1125 — C–C stretch, C–C bend 1096 1094 1069 1071 1026 1025
Fig. 4 IR spectra taken before and after the indicated times during photoirradiation of adsorbed benzamide in 10 Torr of O2. The
benza-mide-adsorbed TiO2 surface was prepared by exposing a clean TiO2
surface to benzamide vapor for 42 h followed by evacuation at 35C. All of the spectra were taken with 5 scans. The wavelength used
to the vapor of acetamide for 25 min. The band at1650 cm 1
is related to the C=O of aectamide and the bands at1430, 1470, and 1540 cm 1
to the CON of CH3CONH(a). The
reaction of acetonitrile on the surface to produce acetamide and CH3CONH(a) is due to surface hydroxy groups that
nucleophilically attack the carbon of the CN group.22–24 In Fig. 5(a), heating the surface to 200C leads to a decrease in adsorbed CH3CN and the shift of the CN frequencies to
2292 and 2319 cm 1, meanwhile new bands appear at 1441 and 1541 cm 1. These two bands are characteristic –COO– stretching frequencies of CH3COO(a).
17
Table 4 summarizes the frequencies observed in Fig. 5(a) and the vibrational modes of the responsible surface species. In Fig. 5(b) after acetamide
adsorption at 35C followed by temperature increase to 200C, CN-containing species,evidenced by the 2292 and
2319 cm 1bands, are formed. Since the IR absorption feature of these two bands, including the position, shape, and relative intensity, is identical to those of adsorbed acetonitrile at the same temperature, it is concluded that acetamide or CH3CONH(a)is thermally converted to acetonitrile by losing
H2O or OH respectively. Furthermore, it is found that
photo-illumination of acetamide and CH3CONH(a)on TiO2at 320
nm in O2also generates acetonitrile, as shown in Fig. 5(c) by
the appearance of the bands at2292 cm 1and2319 cm 1
after 30 min UV exposure. Photoillumination of adsorbed acetamide at 400 nm is also studied in the present research and similar results are obtained. Since the wavelength of the light used is transparent to acetamide,27 it suggests that the photoreactions observed are mediated by TiO2.
Acetamide and benzamide have similar thermal and photo-chemical reactions for the amide group. Many organic mole-cules can be effectively photooxidized on TiO2 with UV
illumination. As TiO2accepts photons with energy higher than
its bandgap (3.2 eV), electron–hole pairs can be produced and these migrate to the surface where they initiate redox reactions of adsorbates.28 OH
radicals, possibly from the reaction of surface hydroxy groups or water with holes, have been pro-posed to be the oxidizing agent.29–32 In previous studies of the interaction of O2with the TiO2surface upon UV
irradia-tion, EPR spectroscopy has shown the existence of O2 ,
O3 , and O2 3
,33which can behave as oxidants. The initiating mechanism of photooxidation for amides on TiO2is still under
discussion.
Conclusion
In brief, on TiO2at 35C benzamide is molecularly adsorbed
or dissociates to form C6H5CONH(a). Surface heating to
higher temperature leads to the production of C6H5CN and
C6H5COO(a). In the photochemistry of benzamide on TiO2,
CO2is produced in the gas phase, while NCO(a)(isocyanate),
HCOO(a), C6H5COO(a), and C6H5CN(a) are produced on
the surface. The latter four species were not identified in a pre-vious study of benzamide photodecomposition in solution. The formation of benzoate may involve the substrate oxygen. Acetamide also shows similar reaction pathways for the amide group. This research presents complementary results to the solution studies and gives, in combination with the solution results, a more complete understanding of the benzamide photoreaction catalyzed by TiO2.
Acknowledgements
We acknowledge financial support from the National Science Council of the Republic of China (NSC 90–2113–M–006–024).
References
1 M. A. Fox and M. T. Dulay, Chem. Rev., 1993, 93, 341. 2 J. M. Kesselman, O. Weres, N. S. Lewis and M. R. Hoffmann,
J. Phys. Chem. B, 1997, 101, 2637.
3 Y. Nosaka, K. Koenuma, K. Ushida and A. Kira, Langmuir, 1996, 12, 736.
4 Y. Nosaka, M. Kishimoto and J. Nishino, J. Phys. Chem. B, 1998, 102, 10 279.
5 T. Sakata, T. Kawai and K. Hashimoto, J. Phys. Chem., 1984, 88, 2344.
6 H. Yoneyama, Y. Takao and H. Tamura, J. Phys. Chem., 1983, 87, 1417.
7 B. Kraeutler and A. J. Bard, J. Am. Chem. Soc., 1978, 100, 5985. 8 B. Kraeutler and A. J. Bard, J. Am. Chem. Soc., 1978, 100, 2239. 9 V. Brezova, M. Ceppan, E. Brandsteterova, M. Breza and
L. Lapcik, J. Photochem. Photobiol. A, 1991, 59, 385. Fig. 5 (a) IR spectra after the TiO2sample was exposed to0.7 Torr
acetonitrile at 35C and then evacuated at this temperature and 200C for 1 min. The two spectra were taken with 50 scans at35C. The
TiO2 sample used was 82 mg. (b) IR spectra after the TiO2 sample
was exposed to acetamide vapor for 25 min at 35C and then
evacu-ated at this temperature and 200C for 1 min. The two spectra were
taken with 50 scans at35C. The TiO
2sample used was 72 mg. (c)
IR spectra taken before and after 30 min photoirradiation of the adsorbed acetamide and CH3CONH at 320 nm in 10 Torr O2. Each
spectrum was recorded with 5 scans. The TiO2sample used was 72 mg.
Table 4 Infrared frequencies and approximate assignments for adsorbed acetonitrile on TiO2at 35C and 200C
Temperature
Assignment 35C 200C
2306 2319 C==N stretch from CH3CN(a)
2279 2292
1650 C=O stretch from CH3CONH2(a)
1578 N–H bend
1541 COO stretch from CH3COO(a)
1537 CON stretch from CH3CONH(a)
1469 1469
1441 COO stretch from CH3COO(a)
1433 CON stretch from CH3CONH(a)
1415 C–H bend
10 I. Izumi, F.–R. F. Fan and A. J. Bard, J. Phys. Chem., 1981, 85, 218.
11 C. Maillard, C. Guillard and P. Pichat, New J. Chem., 1992, 16, 821.
12 K. Hustert, D. Kotzias and F. Korte, Chemosphere, 1983, 12, 55. 13 H. Hidaka, S. Yamada, S. Surnaga, J. Zhao, N. Serpone and
E. Pelizzetti, J. Mol. Catal., 1990, 59, 279.
14 C.–C. Chuang, W.–C. Wu, M.–X. Lee and J.–L. Lin, Phys. Chem. Chem. Phys., 2000, 2, 3877.
15 J. C. S. Wong, A. Linsebigler, G. Lu, J. Fan and J. T. Yates, Jr., J. Phys. Chem., 1995, 99, 335.
16 J. Palomar, J. L. G. De Paz and J. Catalan, Chem. Phys., 1999, 246, 167.
17 L.–F. Liao, C.–F. Lien and J.–L. Lin, Phys. Chem. Chem. Phys., 2001, 3, 3831.
18 J. H. S. Green, Spectrochim. Acta Part A, 1977, 33, 575. 19 K. Machida, A. Kuwae, Y. Saito and T. Uno, Spectrochim. Acta.
Part A, 1978, 34, 793.
20 S. Zou, C. T. Williams, E. K.–Y. Chen and M. J. Weaver, J. Phys. Chem. B, 1998, 102, 9039.
21 J. Zhuang, C. N. Rusu and J. Y. Yates, Jr., J. Phys. Chem. B, 1999, 103, 6957.
22 V. Lorenzelli, G. Busca and N. Sheppard, J. Catal., 1980, 66, 28. 23 J. C. Lavalley and C. Gain, C. R. Acad. Sci. Paris Ser. C, 1979,
288, 177.
24 H. Krietenbrink and H. Knozinger, Z. Phys. Chem. (Munich), 1976, 102, 43.
25 C.–C. Chuang, W.–C. Wu, M.–C. Huang, I.–C. Huang and J.–L. Lin, J. Catal., 1999, 185, 423.
26 W.-C. Wu, L.-F. Liao, C.-F. Lien and J.-L. Lin, Phys. Chem. Chem. Phys., 2001, 3, 4456.
27 J. G. Calvert, J. N. Pitts, Jr., Photochemistry, Wiley, New York, 1966.
28 R. B. Draper and M. A. Fox, Langmuir, 1990, 6, 1396. 29 G. Milles and M. R. Hoffmann, Environ. Sci. Technol., 1993, 27,
1681.
30 T. Y. Wei and C. Wan, J. Photochem. Photobiol. A., 1992, 69, 241.
31 A. Mills, S. Morris and R. Davies, J. Photochem. Photobiol. A., 1993, 70, 183.
32 S. Goldstein, G. Czapski and J. Rabani, J. Phys. Chem., 1994, 98, 6586.
33 P. Meriaudeau and J. C. Vedrine, J. Chem. Soc., Faraday. Trans., 1976, 72, 472.
