20170727 BO Sapporo -...

2017/07/27─Advanced Course in Environmental Catalytic Chemistry I 1

July 27, 2017

Advanced Course in Environmental Catalytic Reaction Chemistry I 2

special report

special report for extra (bonus) score (20 point)report on critical review on "photocatalysis" in Wikipedia, pointing out errors, misunderstanding and speculationsbased on the contents of this lecture.http://en.wikipedia.org/wiki/Photocatalysishttp://ja.wikipedia.org/wiki/光触媒

• Japanese or English• A4 size 2 pages• submission by email attachment• a PDF file is more preferable than a Word file• email title: pc20170727-XXXXXXXX• file name: pc20170727-XXXXXXXX.pdf (or .docx or .doc)• deadline of submission: July 27, 2017 23:59


coordination number rc/ra

8 cubic

2

linear3

triangle4tetrahedral

6

octahedral

0.154

0.225

0.414

0.732


displaying by VESTA

(left) displaying by VESTA(lower) a model made of paper


design and development of active photocatalysts

statistical analysiscrystal-shape dependenceEvonik P25


principle of photocatalytic reaction

electronic structure of semiconductors and insulatorsconduction and valence bands separated by bandgapphotoexcitation beyond the bandgap

e-

e-

h+

h+

photo-absorption

recombination

excitation

conduction band

valence band

relaxationreduction

oxidation

relaxation

1) photoexcitation= electron and hole

2) relaxation3a) reduction & oxidation

3b) recombination


We believe that ...

photocatalytic activity MUST be different whendifferent materials are used,

because activity MUST depend on physical and structural properties,

which CAN be controlled bypreparation and treatment processes,

and, therefore, we HAVE TO FINDproperties to be controlled

by clarifyingcorrelation between properties and activity.


liquid-phase syntheses of titania photocatalyst

in general, titanium compounds are hydrolyzed to titanic acid and then calcined to dehydrate and crystallize into titania

at higher calcination temperaturesmaller specific surface areahigher crystallinity = lower density of defects

Ti(OR)4alkoxide

TiX4halide

Ti(SO4)2sulfate

Ti(OH)4・TiO(OH)2hydrated titania/titanium hydroxide

amorphous titania

TiO2titania

hydrolysis calcination

dehydration/crystallization

statistical analysis of photocatalytic activity 9

anatase and rutile

• Activity decreases when anatase is transformed into rutile by high temperature calcination.

• possible reasons:(1) higher activity of anatase compared with that of rutile(2) decrease in specific surface area

dehydrogenation of 2-propanol（←）S.-i. Nishimoto, B. Ohtani, A. Sakamoto, T. Kagiya, Nippon Kagaku Kaishi 1984, 246.（↑）S.-i. Nishimoto, B. Ohtani, H. Kajiwara, T. Kagiya, J. Chem. Soc., Faraday Trans. 1 1985, 81, 61.

from titanium(IV) sulfate

from titanium(IV) tetra-2-propoxide

What is the reason for the decrease in activity when heated at high temperature?

How can we determine the reason(s)?


correlation between properties and activities

we have assumed (believed)...

(1) Anatase is better than rutile in photocatalytic activity.(2) The smaller the size of titania particles is, the better is their

photocatalytic activity.(3) The lower the density of crystal defects is, the better is photocatalytic

activity.(4) Nanostructured titanias show better photocatalytic activity.

titanias of mainly anatase crystallites show relatively

higher activity: correct

relatively higher activity of a titania photocatalyst is due

to anatase crystallites: incorrect


problem in getting proof

It seems rather difficult to obtain a set of particulate samples the difference of which is only crystal form, anatase and rutile.

same particle size and distributionsame specific surface areasame secondary particle sizesame number/density of crystalline defectssame ...but, anatase and rutile

Alternative way: Extraction of intrinsic dependence from the actual data of activity


Chem. Lett., 38(3), 238-239 (2009)

Correlation between structural and physical properties and photocatalytic activities for five kinds of reactions of 35 titania samples was obtained through multivariable analyses: photocatalytic activities were empirically reproduced by a linear combination of six properties with fair reliability. While a portion of results could be interpreted using a conventional mechanism, significant activity dependences on properties, not disclosed yet, were suggested.

Ohtani, B.; Prieto-Mahaney, O. O.; Amano, F.; Murakami, N.; Abe, R., J. Adv. Oxidat. Tech., 13, 247-261 (2010).


statistical multivariable analyses

to find out WHAT is/are the DECISIVE factor(s) for each reaction

by solving the matrix equation below to determine coefficients of each physical and structural properties

[rate]35×1 = [property]35×6 × [coefficient]6×1

rates and properties, were standardized using mean of data and standard deviation in order to make the calculated coefficients have the same weight being independent of properties, i.e., enabling direct comparison of partial regression coefficients (k).


test photocatalytic reactions for 35 titanias

(a) oxygen evolution along with silver metal deposition

4Ag+ + 2H2O = 4Ag + O2 + 4H+

(b) methanol dehydrogenation

CH3OH = HCHO + H2

(c) oxidative decomposition of acetic acid in water

CH3COOH + 2O2 = 2CO2 + 2H2O

(d) oxidative decomposition of acetaldehyde in air

CH3CHO + 5/2O2 = 2CO2 + 2H2O

(e) synthesis of pipecolinic acid from L-lysine

L-lysine = PCA + NH3


physical properties used for analysis

BET specific surface area by BET method

PPS primary particle size by Scherrer equation

SPS secondary particle size by particle analyzer

DEF density of defective sites by Ti(III) formation

ANA its presence/absence (OR anatase ratio)

RUT its presence/absence (OR rutile ratio)

Phys. Chem. Chem. Phys., 2003, 5, 778–783


statistical multivariable analyses

anatase/rutilesecondary particle sizedensity of defects

(a) 4Ag+ + 2H2O = 4Ag + O2 + 4H+

(b) CH3OH = HCHO + H2(c) CH3COOH + 2O2 = 2CO2 + 2H2O(d) CH3CHO + 5/2O2 = 2CO2 + 2H2O

(e) L-lysine = PCA + NH3


anatase and rutile

• Activity decreases when anatase is transformed into rutile by high temperature calcination.• possible reasons:

(1) higher activity of anatase compared with that of rutile(2) decrease in specific surface area

dehydrogenation of 2-propanol（←）S.-i. Nishimoto, B. Ohtani, A. Sakamoto, T. Kagiya,

Nippon Kagaku Kaishi 1984, 246.（↑）S.-i. Nishimoto, B. Ohtani, H. Kajiwara, T. Kagiya, J.

Chem. Soc., Faraday Trans. 1 1985, 81, 61.

from titanium(IV) sulfate

from titanium(IV) tetra-2-propoxide


correlation between band gap and CB position

Scaife's plot

D. E. Scaife, Solar Energy, 25, 41-54 (1980).

flat-band potential =

conduction band bottom

-1

band gap = distance

between CB and VB

VB

CB


valence band

conductionband

(-0.20 V) (+0.04 V)

anatase

electronic structure of anatase and rutile

rutile

-0.05 V (O2-./O2)

0 V (H2/H+)

1.23 V (H2O/O2)

G. Rothenberger, J. Moser, M. Grätzel, N. Serpone, D. K. Sharma, J. Am.

Chem. Soc. 1985, 107, 8054.

potential vs. NHE at pH = 0

0.79 V (Ag/Ag+)


valence band(mainly orbitals of

oxygen)

conduction band(mainly orbital of

titanium)

valence band(mainly orbitals of

sulfur)

conduction band(mainly orbital of

metal)

metal sulfide

band structure of metal oxides and sulfides

doped nitrogen/sulfur orbitals

TiO2

metal oxide

level of oxygen

reduction

level of hydrogen production

WO3

decahedral anatase titania 22

any others???

physical and structural properties

crystalline form: anatase, brookite or rutile for titaniaspecific surface areaprimary (secondary) particle sizedensity of crystalline defects: recombination center


a

TEM images of highly crystalline meso particles

anatase titania particles prepared by HyCOM methodKominami, H.; Matsuura, T.; Iwai, K.; Ohtani, B.; Nishimoto, S.-i.; Kera, Y. Chem. Lett.1995, 24, 693-694.

anatase titania particles prepared by THyCA methodKominami, H.; Kato, J.-i.; Murakami, S.-y.; Kera, Y.; Inoue, M.; Inui, T.; Ohtani, B. J. Mol.

Catal. A Chem. 1999, 144, 165-171.

5 nm

50 nm


Degussa (Evonik) P25


natural crystals of anatase

bipyramidal structure: octahedralexposing 8 equivalent (101) planes

(101)

O

Ti


octahedral anatase titania particles (OAP)prepared by hydrothermal reaction of bundled titanate nanofibers


decahedral (DAP) anatase particles

cutting off octahedral particlesexposing two {001} facets

001

101

101

011

011

100 nm

fujikura001 decahedral anatase titania 28

gas-phase reaction oftitanium(IV) chlorideat 1473 K

particle size: 40-150 nmBET surface area: 10-40 m2 g-1

highly crystalline anataselow density of crystalline defects

decahedral anatase titania particles (DAP)

(001)

(101)


photocatalytic activity compared with P25

dehydrogenation of methanol oxidative decompositionA： Pt source = H2PtCl6 A： 5vol% CH3COOHB： Pt source = [Pt(NH3)4]Cl2 B： 50vol% CH3OH

Amano, F.; Prieto-Mahaney, O. O.; Terada, Y.; Yasumoto, T.; Shibayama, T.; Ohtani, B., Chem. Mater. 2009, 21, 2601-2603.

DAP

P25

P25

P25

P25DAP

DAP

DAP

fujikura002 decahedral anatase titania 30

photocatalytic activity of decahedral particlesvery high activity in spite of relatively small specific surface area

4Ag+ + 2H2O4Ag + O2 + 4H+

2CH3CHO + 5O2

4CO2 + 4H2O

oxygen evolution

acetaldehyde decomposition

DAPs


effect of shape on photocatalytic activity

standardized observed ratesstan

dard

ized

exp

ecte

dra

tes

[rate]calc. = k(property)

(left) 4Ag+ + 2H2O = 4Ag + O2 + 4H+

(center) CH3OH = HCHO + H2(right) CH3COOH + 2O2 = 2CO2 + 2H2O

DAP

DAP DAP


precise control of heatingsmaller but highly crystallized particles: using

INFRARED furnace and PLATINUM plate to heat up a narrow range of space

stabilization of {001} facets to give decahedral particles: presence of chlorine (Cl2) during the reaction:

oil bath393 K

Ar

TiCl4

O2

to make efficient heating

baffle

vaporizerPt plate

4 cm width/1473 K

100 nm


photocatalytic activity

• left: decomposition of acetic acid in an aqueous solution (5%, 5 mL)/400-W high pressure mercury arc.

• right: decomposition of acetaldehyde (500 ppm) in air/xenon arc.

Sugishita, N.; Kuroda, Y.; Ohtani, B. Catal. Today 2011, 164, 391-394.


industrialization of DAP production

Showa Titanium (Toyama, Japan) has already built a pilot plant for DAP production in a few kilograms per hour scale

"head quarter"

Noriyuki Sugishita, Yasushi Kuroda, Bunsho Ohtani , "Preparation of Decahedral Anatase Titania Particles with High-Level Photocatalytic Activity", TOCAT6/APCAT5 (Sapporo), July 18-23, 2010.Catal. Today 164 (2011) 391-394.


gas-phase synthesis (third generation)

• localized heating using an infrared furnace and a platinum foil (1473 K)• reduced pressure at the reaction and collection parts• precise introduction of titanium(IV) chloride by a syringe feeder• coaxial flow of oxygen (outside) and titanium(IV) chloride (center) for effective

reaction and collection at a glass fiber filter• freeze drying after washings to avoid aggregation

O2 inlet

Ar/TiCl4 inletfilter

quartz tubeplatinum foil


dried at 393 K overnight

freeze-dried and heated samplesO2：1500 mL min-1・Ar：75 mL min-1・TiCl4（L）：3.0 mL h-1

200 nm1 µm

200 nm


粒子径（μｍ）

0.01 0.05 0.1 0.5 1 5 10 50 100 5000

10

20

30

40

50

60

70

80

90

100

0 0


0.01 0.05 0.1 0.5 1 5 10 50 100 5000

10

20

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50

60

70

80

90

100

3 q 3


0.01 0.05 0.1 0.5 1 5 10 50 100 5000

10

20

30

40

50

60

70

80

90

100

q 3


0.01 0.05 0.1 0.5 1 5 10 50 100 5000

10

20

30

40

50

60

70

80

90

00

freeze dried/as received

commercial

ＦＰ６

secondary particle size• smaller particle size/not so aggregated by heating

weig

ht

fraction

O2：1500 mL min-1・Ar：75 mL min-1・TiCl4（L）：3.0 mL h-1


0.01 0.05 0.1 0.5 1 5 10 50 100 500

10

20

30

40

50

60

70

80

90

100

3 3


0.01 0.05 0.1 0.5 1 5 10 50 100 5000

10

20

30

40

50

60

70

80

90

100

particle size/µm

washing and dried at 393 K

washing (NaOH) and dried at 393 K

particle size/µm


specific surface area as a function of concentrationopen circle: glass fiber filter/closed circle: quartz tubetop: oxygen//mL min-1, middle: argon/mL min-1, bottom: titanium(IV) chloride (liq)/mL h-1

2000750.6

2000752.5

20001002.5 1500

752.5

1500753.0

25001005

2500755 1500

1005

400 nm

400 nm

200 nm

200 nm


octahedral anatase titania particles (OAP)prepared by hydrothermal reaction of bundled titanate nanofibers

P25 41

Degussa (Evonik) P25 (Nippon Aerosil)

AEROXIDE TiO2 P 25Titanium Dioxide P25 (AEROSIL Technical Report 5)Titanium Dioxide P 25 (AEROSIL Technical Report 21) Japan Reference Catalyst TIO-4(2) (Catalysis Society of Japan)

One of the most popular photocatalystsOne of the most active commercial photocatalystsA de-facto standard for photocatalysts

What we know... as bulk propertiesspecific surface area of ca. 50 m2 g-1 = ca. 30 nm particlescontains both anatase and rutile (and amorphous) with the ratio of 70:30 or 80:20

P25 42

problems: crystal content analyses

(1) How can we measure the amorphous content?Conventional XRD technique cannot determine the amorphous content directly: rest of crystalline (anatase and rutile) phases

(2) How can we measure the crystal content?Textbooks say that the XRD peak intensities increase linearly with the increase of crystalline content: no guarantee of constant XRD peak intensity independent of the properties, e.g., crystalline size.Rietveld analysis may have the same problem.

(3) How can we obtain the standard crystal samples?

(4) Are there any effects on photocatalytic activity? Synergetic effect?


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大谷文章

某教授

光触媒の応用例について知り，その基本が化学であることを学びました．光と物質のかかわりについてさらに知りたいので本を調べてみます．

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