Jackson S.D., Hargreaves J.S.J. Metal Oxide Catalysis

760 19 Oxide Materials in Photocatalytic Processes

19.4

Improving Photocatalytic Activity

Because the band gap of TiO

2

is 3.2 eV it is deﬁ ned as a “ wide band gap semi-

conductor ” , with onset of the optical absorption band at about 350 nm [20] . Hence,

only 5% of the solar energy can be absorbed by TiO

2

. For this reason, considerable

research effort has been invested into increasing the photocatalytic activity of TiO

2

,

particularly by enhancing its ability to be activated by visible light. In general, two

approaches have been taken. One is to modify the band gap by addition of a sec-

ondary component, such as the adsorption of an organic dye or small amounts of

another, usually metallic element. Alternatively, the basic concepts of physics can

be used, and by changing the preparation methods producing photocatalytic par-

ticles of such dimensions that their band gaps are altered by quantum effects. Both

methods have been shown to have a considerable effect on the reactivity, as out-

lined in the following section.

19.4.1

Visible Light Sensitization by Adsorption of Organic and Inorganic Dyes

Considerable research effort has been invested in the combination of photocatalysts

with organic and inorganic dyes such as Erythrosin B [37] and cis - di(thiocyanato) -

N,N - bis(2,2 ′ - bipyridyl dicarboxylate)Ru(II) [38] . A huge number of potential dye -

sensitizers have been reported in the literature, but the ones with optimum

performance appear to be transition metal complexes derived from polypyridines

[Ru(II)], porphyrins, or phthalocyanines [Zn(II), Mg(II) or Al(III)] as ligands [39,

40] . The principle behind these systems is that the dyes absorb the visible radiation

and form excited states. From these states, electrons are injected into the conduction

band of the semiconductor oxide, thereby inducing a visible response in the oxide.

For effective function, the adsorbed dye needs to have an excited state located above

the bottom of the semiconductor band [41] and to have a strong interaction with the

oxide such that a fast and efﬁ cient electron junction is produced. Assuming these

considerations are met the results of such sensitization are (i) an increased efﬁ -

ciency of the excitation process, and (ii) an expansion of the absorption spectrum

of the semiconductor via excitation through the sensitizer. However, such dyes are

complex molecules and are not a low - cost option. This, together with the fact that

their thermal and/or photochemical stability is poor, can lead to poor lifetimes for

photocatalysts prepared in this manner [42] . However, if oxygen is excluded from

the system and the oxidation state of the dye is quenched with an appropriate elec-

trolyte, such a strategy has been demonstrated to be successful [43] .

19.4.2

Visible Light Sensitization by Anion Doping

More recently, visible light sensitization has been shown to be possible by doping

with small quantities of C [44 – 47] , N [48 – 50] , F [51, 52] , S [53, 54] , and to a lesser

extent with B [55, 56] , Cl and Br [57] , P [58], and I [59] . The work by Asahi and

coworkers [48] was the ﬁ rst to illustrate the effect that nitrogen doping has on the

photocatalytic properties of TiO

2

. Nitrogen - doped TiO

2

has since been shown to

catalyze the visible - light - initiated oxidation of organic substrates, and extensive

investigations have been conducted in order to characterize the photoelectro-

chemical properties of TiO

2 − x

N

x

with the goal of developing materials suitable for

the promotion of the water splitting reaction. Photoelectrochemical characteriza-

tion, together with theoretical calculations of the TiO

2 − x

N

x

materials indicate that

the addition of anions introduces states above the valence band of TiO

2

, owing to

the mixing of the O 2p and N 2p states [60] . However, how much of the effect of

anion doping is down to the narrowing of the band gap as predicted by Batzill and

coworkers [60] is a matter of some debate. Such doping of TiO

2

not only changes

the electronic properties of the oxide but also can induce the formation of oxygen

defect sites [61] . These sites can then act as charge trapping centers, reducing the

likelihood of electron – hole recombination. Irie and coworkers [62] suggested that

the N 2p levels are separated from the valence band (formed from O 2p states),

rather than mixed, thereby forming an isolated narrow band responsible for the

enhanced light sensitivity of the nitrided oxides. Also, some researchers have sug-

gested that the nitrogen exists as NO and that no direct Ti

–

N bonds are formed,

in contrast to the assumption that the nitrogen substitutes for the oxygen in the

lattice. Substantiation of this proposal has recently been published by Reyes - Garcia

and coworkers, who have shown a range of nitrogen - containing species within

TiO

2

by a combination of solid - state NMR and ESR spectroscopies, but observed

no evidence for direct substitution of lattice oxygen [62] . However, the substitution

of C for lattice O within TiO [2] has been suggested by density functional theory

methods [63] . The resulting structure, being structurally the same as the parent

oxides, has enhanced photoactivity in the visible spectrum owing to the resulting

unoccupied impurity state occurring in the band gap. The degree of band gap

narrowing is variable and depends upon the synthesis technique but values of

2.32 eV [44] and 2.0 eV [64] have been reported in materials prepared by simple

thermal treatment of the carbon - modiﬁ ed sample in air. Some reports have sug-

gested that optimum performance of modiﬁ ed TiO

2

materials can be obtained by

treatment with a combination of dopants. Signiﬁ cant visible response has been

reported using a combination of N, together with F [51] and C [65] .

19.4.3

Visible Light Sensitization by Metal Ion Implantation Techniques

Another method for improving the efﬁ ciency of semiconductor oxides is the addi-

tion of transition metal cations within the photocatalyst structure [6] . Such modi-

ﬁ cation of the structure has several effects, although the primary aim of such

preparations is the expansion of the absorption into the visible spectrum. In

certain cases, the metal dopants can act as electron/hole trappers, leading to an

increase in the charge carrier lifetimes and by doing so reducing the likelihood of

recombination processes [7, 66] . This occurs through the following processes:

19.4 Improving Photocatalytic Activity 761

762 19 Oxide Materials in Photocatalytic Processes

M e M electron trapping

cb

nn+− −

(

)

+

+→

()

1

(19.8)

M h M hole trapping

vb

nn++ +

(

)

+

+→

()

1

(19.9)

If the M

n +

/M

( n − 1)+

pair is located below the conduction band edge and the energy

level for M

n +

/M

( n +1)+

above the valence edge then the trapping of electrons and holes

would take place, affecting the lifetime of the charge carriers. The effect of the

addition of metallic dopants is therefore a complex one and differentiating the

individual effects is not simple. The efﬁ ciency of a metal ion dopant depends on

whether it serves as a mediator of interfacial charge transfer or as a recombination

center. Its efﬁ ciency as an electron/hole trap is related to several factors including

the dopant concentration, its energy level within the semiconductor lattice, its

electronic conﬁ guration, its distribution within the semiconductor, and the elec-

tron donor concentration. When metal ions are incorporated into the TiO

2

by

conventional methods such as impregnation, a small absorption band is visible

between 400 and 550 nm as a shoulder due to the formation of impurity levels in

the band gap of the parent oxide [21] (Figure 19.3 ). However, in order to directly

modify the band gap of the semiconductor, rather than simply insert an additional

impurity energy level, a modiﬁ ed preparation technique can be used that applies

transition metal ions at high acceleration energy (50 – 200 keV) [6, 42, 67, 68] . When

the semiconductor is bombarded by such high - energy transition metal ions, the

ions have been shown by a variety of spectroscopic techniques, including SIMS,

EXAFS, and ESR, to be implanted into the lattice without destroying the underly-

ing surface structure of the oxide. Rather than producing a small shoulder in the

absorption band a much more signiﬁ cant and smooth shift is observed to higher

wavelength, indicating that the resulting band gaps of the materials prepared in

Figure 19.3 Schematic band structures of TiO

2

, impregnated TiO

2

, and ion implanted TiO

2

.

this manner are signiﬁ cantly smaller than those of either the parent semiconduc-

tor or the parent oxide modiﬁ ed by conventional impregnation techniques.

Materials prepared by simple impregnation methods have been shown to exhibit

a signiﬁ cantly lower photocatalytic activity than their parent oxides when illumi-

nated solely with UV light. This has been accounted for by the dopants outside

the structural framework acting as recombination centers for electron – hole pairs.

Materials prepared by the ion implantation method showed no such decrease

[21] .

The techniques discussed above have all involved the preparation of powdered

photocatalysts with enhanced visible light activity. A method recently developed

for the preparation of thin - ﬁ lm photocatalysts with similar enhanced visible light

activity is the deposition by radio - frequency magnetron sputtering, in which a TiO

2

plate is used as the source material and pure Ar as the sputtering gas [68 – 71] . It

has been shown that the degree of absorption in the visible region is dependent

upon both the temperature of preparation and the Ar pressure [72] . Similarly,

nitrogen - doped materials have been prepared by the use of a mixed N

2

/Ar sput-

tering gas mixture [73, 74] . With low concentrations of substituted nitrogen ( < 2%),

a shoulder was observed in the UV - Vis absorption spectrum, but once concentra-

tions above 2% were substituted a smooth shift in the absorption spectrum towards

the visible region was observed. The band gaps of such materials were estimated

to be between 2.25 and 2.58 eV. Such nitrided TiO

2

thin ﬁ lms showed good activity

for the degradation of propan - 2 - ol diluted in water under visible irradiation [73] .

19.4.4

Physical Methods to Enhance Photocatalytic Activity

Quantum physics dictates that by reducing particle size to the nanometer scale, a

point is reached beyond which further decrease in the particle size will lead to

variation in the position of the valence and conduction bands, and in the gap

between the two [75, 76] . A variety of strategies have been suggested for controlling

particle size and structure in order to produce particles in such a size regime and

Table 19.2 includes some of them, together with the size range of the particles

formed if such strategies are followed.

Table 19.2 Examples of preparation strategy together with the resulting particle scales.

Length scale Examples

< 1 nm

TiO

2

clusters encapsulated in zeolites

1 – 10 nm TiO

2

nanoparticles forming periodic mesoporous powders

10 nm – 10 µ m

TiO

2

nanotubes

> 200 µ m

TiO

2

membranes/photonic crystals/photonic sponges

19.4 Improving Photocatalytic Activity 763

764 19 Oxide Materials in Photocatalytic Processes

TiO

2

can be prepared on the nanometer scale [20] , but the particles thus formed

tend to agglomerate. One strategy to avoid aggregation of the particles has been to

incorporate the TiO

2

clusters into the pores of a zeolite. Faujasite and zeolite β have

been used extensively for this purpose [77] . Zeolites do not absorb in the UV - Vis

region of the spectrum and hence it is possible to irradiate guest species anchored

within the micropores of the host material. Two strategies have been explored for

the incorporation of the TiO

2

into the zeolite, although both use molecular titanium

sources with a single titanium atom that subsequently oligomerizes to form Ti

–

O

–

Ti structures. In the ﬁ rst approach, TiCl

3

or TiCl

4

vapors are absorbed into a

partially or totally dehydrated zeolite structure, after which oligomerization is pro-

moted by thermal treatment in the presence of moisture [78, 79] . The level of

dehydration of the zeolite prior to the addition of the titanium source can give a

degree of control as to where the TiO

2

structures locate. The greater the degree of

dehydration the deeper into the microporous structure the TiCl

3

or TiCl

4

vapors

can enter. The main problem with this technique is the explosive and pyrophoric

nature of TiCl

3

and the highly corrosive HCl vapors formed upon hydrolysis which

can cause subsequent damage to the zeolite framework [80] . The second approach

is based upon the ion - exchange of the Na

+

counter - ions present in synthetic zeolites

by (Ti

=

O)

2+

titanyl salts. This approach has the signiﬁ cant advantage that the tita-

nium salts are non - corrosive and the ion - exchange process can be carried out in

aqueous solution [81] . Hydrolysis and oligomerization can then be carried out by

treatment of the titanyl salts at approximately 150 ° C.

TiCl H O TiO HCl

42 2

24+→+

(19.10)

TiO H O TiO H

2

22

2

++

+→ +

(19.11)

When low loadings of TiCl

4

were used, it was shown by UV - Vis spectroscopy

that isolated titanium atoms are formed, bonded to the zeolite surface either mono,

bi - or tripodally [82] . Increasing the loading led to the formation of aggregated

moieties with Ti

–

O

–

Ti linkages present. The photoreactivity of materials pro-

duced was shown to be signiﬁ cantly higher than Degussa P25 TiO

2

for the partial

oxidation of thianthrene [83] .

Incorporation of titanium oxide species within the framework of mesoporous

silicas has been shown to produce highly efﬁ cient photocatalytic materials.

Extremely careful preparation conditions [84] leads to highly structured materials

comprising anatase nanoparticles of dimension between 5 and 10 nm. The chan-

neled structure, together with the hydrophobic/hydrophilic character, are also key

features controlling their enhanced photoreactivity. The photocatalytic activity of

such mesoporous catalysts has been studied for the degradation of phenol in

aqueous solutions [85] . It was observed that for structured mesoporous materials

with low Ti content, the turnover frequency was four times greater than that for

standard P25.

A development in the use of structured TiO

2

has been the production of new

one - dimensional materials such as nanotubes, nanoﬁ bers, and nanowires [86 –

88] . TiO

2

nanotubes have a relatively high surface area compared with bulk

titania powder but, most interestingly, time - resolved diffuse reﬂ ectance spectros-

copy has shown that charge recombination is disfavored by the tubular morphol-

ogy. Such nanotubes can be relatively easily prepared starting from conventional

nanoparticles such as P25. Such particles are digested in strong base in an

autoclave at 150 ° C for several hours [89] . Annealing of the resulting material at

400 ° C for 3 h results in nanotubes composed exclusively of anatase. Laser ﬂ ash

photolysis has shown that photogenerated holes on nanotubes have an average

half - life approximately six times that of conventional TiO

2

of an equivalent BET

area [89] .

Only a small percentage of the solar ﬂ ux can be absorbed by powdered metal

oxide semiconductors. Hence considerable research effort has been invested in

trying to modify the composition of such materials by chemical means, in order

to enhance absorption in the visible region, and several examples of methods

developed with this aim have been discussed earlier. In addition to such strate-

gies, one physical approach is to increase the optimum light path, leading to

entrapment of the light in the material. This methodology enhances light absorp-

tion by increasing the light path through the material in what are known as

photonic crystals [90, 91] . Since the light is trapped within the crystal there is a

signiﬁ cant enhancement in the likelihood of electron – hole pair formation, par-

ticularly at the onset of the absorption band where the speciﬁ c absorption of the

material is very low. The fundamental concept of a photonic crystal is the struc-

turing of the space creating a periodic dielectric constant ﬁ eld in the scale of the

visible light wavelength [92] . This spatial structuring produces coherent Bragg

diffraction patterns that forbid light of the corresponding wavelength propagating

through the material. At the Bragg diffraction frequencies, photons propagate

with greatly reduced velocity and are known as “ slow ” photons. Crucially, if the

slow photons exhibit energy which overlaps the absorption band of the material

then the enhancement of the light absorption occurs as a consequence of the

increase of the effective optical path length through the material. Ozin and

coworkers prepared an inverse opal constituted of anatase nanocrystals ordered

around monodisperse empty spheres of dimension between 280 and 500 nm. The

system was investigated for the degradation of methylene blue. Using white light

illumination, it was observed that the optimum void dimension was 300 nm, for

which a photocatalytic activity enhancement of 2.3 was observed with respect to

TiO

2

nanoparticles [93] .

A further development of the opal structure was developed by Meseguer and

coworkers, who expanded the concept to form a photonic sponge [94] . In this

conﬁ guration, rather than having a monodispersion of spherical voids of a single

dimension, the sponge has an appropriate distribution of differing size spheres,

resulting in the trapping of an entire region of energy within a particular spectral

region. Hence, with appropriate preparation, a sponge can be prepared that traps

most of the visible spectrum. Such materials, when tested for the degradation of

succinonitrile, have been reported to have their photocatalytic activity enhanced

by an order of magnitude in comparison to TiO

2

nanoparticles [20] .

19.4 Improving Photocatalytic Activity 765

766 19 Oxide Materials in Photocatalytic Processes

19.4.5

Potential - Assisted Photocatalysis

Potential - assisted photocatalysis combines the advantages of photocatalysis with

those of electrocatalysis. It is a combined technology that improves the efﬁ ciency

of photocatalysis by the application of an external potential. This potential differ-

ence can either be simply a result of the resting potentials of the differing elec-

trodes, or the application of an external electrically applied bias. This concept was

ﬁ rst introduced by Honda and Fujishima, as they demonstrated the photoelectro-

catalysis of water under the inﬂ uence of an anodic bias [1] .

Figure 19.4 shows a schematic representation of a photoelectrochemical cell.

Photo - generated electrons are driven through the external circuit as a result of the

potential difference across the cell. Hence, oxidation and reduction reactions occur

at different electrodes of the device. Photoelectrochemically active semiconductor

devices have been prepared from colloidal ZnO, TiO

2

, SnO

2

, and WO

3

[95] . In a

photoelectrochemical cell the photocurrent observed provides a direct measure-

ment of the reaction rate.

19.5

Conclusions

In a heterogeneous photocatalytic system, the efﬁ ciency for any chemical trans-

formation depends upon the photoactivity of the adsorbate molecule and the cata-

lyst substrate. In the case of a reactive semiconductor metal oxide, the catalyst can

either provide energy levels to mediate electron transfer between adsorbate mole-

cules (by temporarily accommodating an electron) or alternatively by acting as both

an electron donor (derived from the photogenerated electron in the conduction

band) and an electron acceptor (derived from the photogenerated hole in the

valence band). Hence the band structure of the substrate plays a crucial role in

Figure 19.4 Schematic representation of a

photoelectrocatalytic process.

References 767

the reactivity of the oxide. A small change in the electronic structure of the mate-

rial can lead to a signiﬁ cant change in the band structure. Such electronic modiﬁ -

cation can be achieved in a variety of ways, including the addition of dye sensitizers

or cationic and anionic dopants, or alternatively the physical manipulation of the

particles at a nanometer scale resulting in the alteration of the band structure as

a result of quantum effects. Such methods, or a combination of methods, can be

used to alter the absorption characteristics of the oxides resulting in their activity

in the visible region of the spectrum, a vital characteristic for commercial viability.

The ability to use fundamental design principles based upon modern experimental

and theoretical techniques coupled with the ever - increasing cost of, and demand

for energy, means semiconductor photocatalysis is a rich area for both scientiﬁ c

and technological development in the twenty - ﬁ rst century.

References

1 Fujishima , A. and Honda , K. ( 1972 )

Nature , 37 , 238 .

2 Linsebigler , A.L. , Lu , G. and Yates ,

J.T. ( 1995 ) Chemical Reviews , 95 ,

735 .

3 Hoffmann , M.R. , Martin , S.T. , Choi , W.

and Bahnemann , D.W. ( 1995 ) Chemical

Reviews , 95 , 69 .

4 Mills , A. , Davies , R.H. and Worsley ,

D. ( 1993 ) Chemical Society Reviews , 22 ,

417 .

5 Kamat , P.V. ( 1993 ) Chemical Reviews , 93 ,

267 .

6 Anpo , M. ( 1997 ) Catalysis Survey from

Japan , 1 , 169 .

7 Carlson , T. and Grifﬁ n , G.L. ( 1986 )

Journal of Physical Chemistry , 90 , 5896 .

8 Blake , D.M. (2001) Bibliography of work

on the heterogeneous photocatalytic

removal of hazardous compounds from

water and air (Update Number 4),

Technical Report, National Renewable

Energy Laboratory, Golden, CO.

9 Bhatkhande , D.S. , Pangarkar , V.G. and

Breenackers , A.A.C.M. ( 2001 ) Journal of

Chemical Technology and Biotechnology

(Oxford, Oxfordshire: 1986) , 77 , 102 .

10 Demeestere , K. , Dewulf , J. and Van

Langenhove , H. ( 2007 ) Critical Reviews in

Environmental Science and Technology ,

37 , 489 .

11 Fagnoni , M. , Dondi , D. , Ravelli , D. and

Albini , A. ( 2007 ) Chemical Reviews , 107 ,

2725 .

12 Palmisano , G. , Augugliari , V. , Pagliaro , M.

and Palmisano , L. ( 2007 ) Chemical

Communications , 425 .

13 Palmisano , L. and

Sclafani , A. ( 1997 )

Heterogeneous Photocatalysis , John Wiley &

Sons, Ltd , Chichester , p. 109 .

14 Col ó n - Ib á nez , G. , Belver - Coldeira , C. and

Fern á ndez - Garc í a , M. ( 2007 ) Synthesis,

Properties and Applications of Oxide

Nanomaterials , John Wiley & Sons, Inc. ,

Hoboken, NJ , p. 491 .

15 Fox , M.A. and Dulay , M.T. ( 1993 ) Chemical

Reviews , 93 , 341 .

16 Zhao , J. and Yang , X. ( 2003 ) Building and

Environment , 38 , 645 .

17 Peral , J. and Ollis , D.F. ( 1997 ) Journal of

Molecular Catalysis A – Chemical , 115 ,

347 .

18 Xu , Y. and Schoonen , M.A.A. ( 2000 )

American Mineralogist , 85 , 543 .

19 Cao , L. , Huang , A. , Spiess , F. and Suib ,

S.L. ( 1999 ) Journal of Catalysis , 188 , 48 .

20 Aprile , C. , Corma , A. and Garcia , H.

( 2008 ) Physical Chemistry Chemical Physics ,

10 , 769 .

21 Kitano , M. , Masaya , M. , Ueshima , M. and

Anpo , M. ( 2007 ) Applied Catalysis A:

General , 325 , 1 .

22 Mills , G. and Hoffmann , M.R. ( 1993 )

Environmental Science and Technology , 27 ,

1681 .

23 D ’ Oliveira , J.C. and Al - Sayyed , G. and

Pcihat , P. ( 1990 ) Environmental Science and

Technology , 24 , 990 .

768 19 Oxide Materials in Photocatalytic Processes

24 Janus , M. and Morawski , A.W. ( 2007 )

Applied Catalysis B – Environmental , 75 ,

118 .

25 Sclaﬁ ni , A. and Herrmann , J.M. ( 1996 )

Journal of Physical Chemistry , 100 , 13655 .

26 Carp , O. , Huisman , C.L. and Rellr , A.

( 2004 ) Progress in Solid State Chemistry ,

32 , 33 .

27 Dietbold , U. , Ruzycki , N. , Herman , G.S.

and Selloni , A. ( 2003 ) Catalysis Today , 85 ,

93 .

28 Burdett , J.K. , Hughbands , T. , Gordon ,

J.M. , Richardson , J.W. and Smith , J.

( 1987 ) Journal of the American Chemical

Society , 109 , 3639 .

29 Asahi , R. , Taga , Y. , Mannstadt , W. and

Freeman , A.J. ( 2002 ) Physical Review B ,

65 , 224112 .

30 Bickley , R.I. , Gonz á lez - Corre nˇ o , T. , Lee ,

J.S. , Palmisano , L. and Tilley , R.J.D.

( 1991 ) Journal of Solid State Chemistry ,

92 , 178 .

31 Ozawa , T. , Iwasaki , M. , Tada , H. , Akita ,

T. , Tanaka , K. and Ito , S. ( 2005 ) Journal

of Colloid and Interface Science , 281 , 510 .

32 Dindar , B. and Icli , S. ( 2001 ) Journal of

Photochemistry and Photobiology A:

Chemistry , 140 , 263 .

33 Yamaguchi , Y. , Yamazaki , M. , Yoshihara ,

S. and Shirakashi , T. ( 1998 ) Journal of

Electroanalytical Chemistry , 442 , 1 .

34 Khalil , L.B. , Mourad , W.E. and Rophael ,

M.W. ( 1998 ) Applied Catalysis B –

Environmental , 17 , 267 .

35 Bensalem , A. , Shafeev , G. and Bozon -

Verduraz , F. ( 1993 ) Catalysis Letters , 18 ,

165 .

36 Bamwenda , G.R. , Uesigi , T. , Abe , Y. ,

Sayama , K. and Arakawa , H. ( 2001 )

Applied Catalysis A: General , 205 , 117 .

37 Kamat , P.V. and Fox , M.A. ( 1983 )

Chemical Physics Letters , 102 , 379 .

38 O ’ Regan , B. and Gr ä tzel , M. ( 1991 )

Nature , 353 , 737 .

39 Choi , Y.M. , Choi , W.U. , Lee , C.H. ,

Hyeon , T. and Lee , H.I. ( 2001 )

Environmental Science and Technology , 35 ,

966 .

40 Cheung , S. , Fung , A. and Lam , M. ( 1998 )

Chemosphere , 36 , 2461 .

41 Zhang , J.Z. ( 2000 ) Journal of Physical

Chemistry B , 104 , 7239 .

42 Anpo , M. ( 2004 ) Bulletin of the Chemical

Society of Japans , 77 , 1427 .

43 Jin , Z. , Zhang , X. , Lu , G. and Li , S. ( 2006 )

Journal of Molecular Catalysis A – Chemical ,

259 , 275 .

44 Khan , S.U.M. , Al - Shahry , M. and Ingler ,

W.B. ( 2002 ) Science , 297 , 2243 .

45 Sakthivel , S. and Kisch , H. ( 2003 )

Angewandte Chemie – International Edition ,

42 , 4908 .

46 Tachikawa , T. , Tojo , S. , Kawai , K. , Endo ,

M. , Fujitsuka , M. , Ohno , T. , Nishijima , K. ,

Miyamoto , Z. and Majima , T. ( 2004 )

Journal of Physical Chemistry B , 108 , 19299 .

47

Li , Y. , Hwang , D. , Lee , N.H. and Kim , S. - J.

( 2005 ) Chemical Physics Letters , 404 , 25 .

48 Ashai , R. , Morikawa , T. , Ohwaki , T. , Aoki ,

K. and Taga , Y. ( 2001 ) Science , 293 , 269 .

49 Sakthivel , S. , Janczarek , M. and Kisch , H.

( 2004 ) Journal of Physical Chemistry B , 108 ,

19384 .

50 Di Valentin , C. , Pacchioni , G. , Selloni , A. ,

Livaghi , S. and Giamello , E. ( 2005 ) Journal

of Physical Chemistry B , 109 , 11414 .

51 Li , D. , Haneda , H. , Hishita , S. and

Ohashi , N. ( 2005 ) Chemistry of Materials ,

17 , 2596 .

52 Li , D. , Haneda , H. , Labhsetwar , N.K. ,

Hishita , S. and Ohashi , N. ( 2005 ) Chemical

Physics Letters , 401 , 579 .

53 Umebayashi , T. , Yamaki , T. , Itoh , H. and

Asai , K. ( 2002 ) Applied Physics Letters , 81 ,

454 .

54 Demeestere , K. , Dewulf , J. , Ohno , T. ,

Salgado , P.H. and Langenhove , H.V.

( 2005 ) Applied Catalysis B – Environmental ,

61 , 140 .

55 Chu , S.Z. , Inoue , S. , Wada , K. , Li , D. and

Suzuki , J. ( 2005 ) Langmuir , 21 , 8035 .

56 Zhao , W. , Ma , W. , Chen , C. , Zhao , J. and

Shuai , Z. ( 2004 ) Journal of the American

Chemical Society , 126 , 4782 .

57 Luo , H. , Takata , T. , Lee , Y. , Zhao , J. ,

Domen , K. and Yan , Y. ( 2004 ) Chemistry of

Materials , 16 , 846 .

58 Lin , L. , Lin , W. , Zhu , Y. , Zhao , B. and Xie ,

Y. ( 2005 ) Chemistry Letters , 34 , 284 .

59 Hong , X. , Wang , Z. , Cai , W. , Lu , F. ,

Zhang , J. , Yang , Y. , Ma , N. and Liu , Y.

( 2005 ) Chemistry of Materials , 17 , 1548 .

60 Batzill , M. , Morales , E.H. and Diebold , U.

( 2006 ) Physical Review Letters , 96 , 26103 .

61 Ihara , T. , Miyoshi , M. , Iriyama , Y. ,

Matsumoto , O. and Sugihara , S. ( 2003 )

Applied Catalysis B – Environmental , 42 ,

403 .

References 769

62 Reyes - Garcia , E.A. , Sun , Y. , Reyes - Gil , K.

and Raftery , D. ( 2007 ) Journal of Physical

Chemistry , 111 , 2738 .

63 Irie , H. , Watanabe , Y. and Hashimoto ,

K. ( 2003 ) Journal of Physical Chemistry B ,

107 , 5483 .

64 Barborini , E. , Conti , A.M. , Kholmanov ,

L. , Piseri , P. , Podest à , A. , Milani , P. ,

Cepek , C. , Sakho , O. , Macovez , R. and

Sancrotti , M. ( 2005 ) Advanced Materials ,

17 , 1842 .

65 Noguchi , D. , Kawamata , Y. and

Nagatomo , T. ( 2005 ) Journal of the

Electrochemical Society , 152 , D124 .

66 Sclafani , A. , Mozzanega , M.N. and

Pichat , P.J. ( 1991 ) Journal of

Photochemistry and Photobiology A:

Chemistry , 59 , 181 .

67 Anpo , M. , Dohshi , S. , Kitano , M. , Hu , Y. ,

Takeuchi , M. and Matsuoka , M. ( 2005 )

Annual Review of Materials Research , 35 ,

1 .

68 Anpo , M. and Takeuchi , M. ( 2003 )

Journal of Catalysis , 216 , 505 .

69 Kitano , M. , Takeuchi , M. , Matsuoka , M. ,

Thomas , J.M. and Anpo , M. ( 2005 )

Chemistry Letters , 34 , 616 .

70 Matsuoka , M. , Kitano , M. , Takeuchi , M.

and Thomas , J.M. ( 2005 ) Topics in

Catalysis , 35 , 305 .

71 Kikuchi , H. , Kitano , M. , Takeuchi , M. ,

Matsuoaka , M. , Anpo , M. and Kamat ,

P.V. ( 2006 ) Journal of Physical Chemistry

B , 110 , 5537 .

72 Kitano , M. , Takeuchi , M. , Matsuoka , M. ,

Thomas , J.M. and Anpo , M. ( 2007 )

Catalysis Today , 122 , 51 .

73 Kitano , M. , Funatsu , K. , Matsuoka , M. ,

Ueshima , M. and Anpo , M. ( 2007 )

Journal of Physical Chemistry B , 110 ,

25266 .

74 Kitano , M. , Kudo , T. , Matsuoka , M. ,

Ueshima , M. and Anpo , M. ( 2007 )

Materials Science Forum , 544 – 5 , 107 .

75 Yamashita , H. , Takeuchi , M. and Anpo ,

M. ( 2004 ) Encyclopedia of Nanoscience and

Nanotechnology , Vol. 10 (ed. H.S. Nalwa ),

American Science Publishers , Los

Angeles, CA , p. 639 .

76 Anpo , M. , Yamashita , H. , Ichihashi , Y. ,

Fujii , Y. and Honda , M. ( 1997 ) Journal of

Physical Chemistry B , 101 , 2632 .

77 Ikeue , K. , Yamashita , H. , Anpo , M. and

Takewaki , T. ( 2001 ) Journal of Physical

Chemistry B , 105 , 8350 .

78 Grubert , G. , Stockenhuber , M. ,

Tkachenko , O.P. and Wark , M. ( 2002 )

Chemistry of Materials , 14 , 2458 .

79 Bossmann , S.H. , Turro , C. , Schnabel , C. ,

Pokhrel , M.R. , Payawan , L.M. , Baumeister ,

B. and Woerner , M. ( 2001 ) Journal of

Physical Chemistry B , 105 , 5374 .

80 Kaipas , T. and Grifﬁ ths , R.F. ( 2005 )

Journal of Hazardous Materials , 119 , 41 .

81 Liu , X. , Iu , K. and Thomas , J.K. ( 1993 )

Journal of the Chemical Society – Faraday

Transactions , 89 , 1861 .

82 Klaas , J. , Schultz - Ekloff , G. and Jaeger ,

N.I. ( 1997 ) Journal of Physical Chemistry B ,

101 , 1305 .

83 Cosa , G. , Galletero , M.S. , Fernandez , L. ,

Marquez , F. , Garcia , H. and Scaiano , J.C.

( 2002 ) New Journal of Chemistry

, 26 , 1448 .

84 Bartl , M.H. , Boettcher , S.W. , Frindell , K.L.

and Stucky , G.D. ( 2005 ) Accounts of

Chemical Research , 38 , 263 .

85 Alvaro , M. , Aprile , C. , Benitez , M. ,

Carbonell , E. and Garcia , H. ( 2006 ) Journal

of Physical Chemistry B , 110 , 6661 .

86 McCann , J.T. , Marquez , M. and Xia , Y.

( 2006 ) Nano Letters , 6 , 2868 .

87 Zhong , Z. , Ang , T.P. , Luo , J. , Gan , H.C.

and Gedanken , A. ( 2005 ) Chemistry of

Materials , 17 , 6814 .

88 Xiong , C. and Balkus , K.J. ( 2005 ) Chemistry

of Materials , 17 , 5136 .

89 Tachikawa , T. , Fujitsuka , M. and Majima ,

T. ( 2007 ) Journal of Physical Chemistry C ,

111 , 5259 .

90 Hall , N. ( 2003 ) Chemical Communications ,

2639 .

91 Baba , T. ( 2007 ) National Photonics , 1 , 11 .

92 Ozin , G. and Yang , S.M. ( 2001 ) Advanced

Functional Materials , 11 , 95 .

93 Chen , J.I.L. , von Freymann , G. , Kitaev , V.

and Ozin , G.A. ( 2006 ) Advanced Materials ,

18 , 1915 .

94 Ramiro - Manzano , F. , Atienzar , P. ,

Rodriguez , I. , Meseguer , F. , Garcia , H.

and Corma , A. ( 2007 ) Chemical

Communications , 242 .

95 Vinodgopal , K. and Kamat , P.K. ( 1995 )

Solar Energy Materials and Solar Cells , 38

,

401 .

Jackson S.D., Hargreaves J.S.J. Metal Oxide Catalysis

Подождите немного. Документ загружается.