july 6, 2017 - 北海道大学pcat.cat.hokudai.ac.jp/class/pc2017/20170706_bo_sapporo.pdf ·...

2017/07/06─Advanced Course in Environmental Catalytic Chemistry 1

July 6, 2017

Advanced Course in Environmental Catalytic Reaction Chemistry I 2

Advanced Course in Environmental Catalytic Chemistry I

understanding chemistry by understanding photocatalysisunderstanding photocatalysis by understanding chemistry

Division of Environmental Material Science, Graduate School of Environmental ScienceThe first semester of Fiscal 201708:45─10:15, Thursday at Lecture Room D103

Bunsho Ohtani (Ewa Kowalska/Mai Takashima)

Institute for Catalysis, Hokkaido University, Sapporo 001-0021, Japan011-706-9132 (dial-in)/011-706-9133 (facsimile)

[email protected]://pcat.cat.hokudai.ac.jp/pcat


objectives/goal/keywords

objectivesUnderstanding the mechanism of decomposition of pollutants, methods of photocatalysts preparation, design of practical photocatalytic reaction systems, and strategy for enhancement of photocatalytic activity.

goalTo understand principle of photocatalytic reaction from the standpoint of chemistry and strategy for practical applications. To obtain scientific method for research on functional solid materials.

keywordsPhotocatalyst, Photoinduced oxidative decomposition, Superhydrophilicity, Excited electron-positive hole, Structure-activity correlation, Higher photocatalytic activity, Visible-light response


schedule

(1) Apr 13 introduction of photocatalysis(2) Apr 20 interaction between substances and light(3) Apr 27 electronic structure and photoabsorption(4) May 11 thermodynamics: electron and positive hole(5) May 18 adsorption(6) May 25 environmental application of photocatalysis (Professor

Ewa Kowalska)(7) Jun 1 kinetic analysis of photocatalysis(8) Jun 8 steady-state approximation(9) Jun 15 kinetics and photocatalytic activity(10) Jun 22 artificial photosynthesis (Professor Mai Takashima)

Jun 29 (no class)(11) Jul 6 action spectrum analysis (1)(12) Jul 13 action spectrum analysis (2)(13) Jul 20 crystal structure(14) Jul 27 design and development of photocatalysts(15) Aug 3 summary: photocatalysis A--Z


comments on this lecture

Please send email in Japanese or English within 48 hours

to: [email protected]: pc2017MMDD-XXXXXXXX

[email protected](full name)(nickname)(comments and/or questions on today's lecture)


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


kinetics of photoinduced reaction

There are two limits: linear part and saturated part.

concentration of subsrate(s)

rate

of r

eact

ion

proportional to concentration

approaching to the limit, I

keh[S] + krr =

I keh[S]

I


concentration of substrate

• overall rate of photocatalytic reaction based on steady-state approximation for electron-hole pairs

r = I keh[S] / (keh[S] + kr) or

r = I keh[S] / kr (when keh[S] << kr)

• meaning of keh[S]: rate of SURFACE REACTION with electron-hole pairs with surface-adsorbed substrate

• two possible cases:(1) adsorption equilibrium during the reaction(2) non-equilibrium due to faster consumption of substrate on the surface

= diffusion-limited process


adsorption and photocatalytic activity

• the larger the adsorbed substrate(s), the higher the activity

• the larger the surface area, the larger the adsorbed amount

an examplelinear relation between the rate and adsorbed silver ion (J. Phys. Chem., 87 (1997) 3550.

Sr

eh kkIr


first-order kinetics

• two possible cases:(1) adsorption equilibrium during the

reaction in Henry fashion (or low-concentration part of Langmuirian fashion) for the equation

r = I keh[S]/ kr = (aI keh/kr)C

(2) non-equilibrium due to faster consumption of substrate on the surface= diffusion-limited process: The reaction rate is determined by the rate of diffusion with a constant a.

[S] ~ 0r = aC = bSC

S: specific surface area

light-intensity dependence

first order

vs.

at higher intensity region

zeroth order


Fick's law of diffusion

• rate (flux; J) of diffusion

• diffusion constant D include area of "hypothetical wall".

• J = DC if surface concentration is zero.

• for particles,

hypothetical wall = thin diffusion layer surrounding the surface

hypotheticalwall

x axis

xCDJ

lowconcentration

side

hypothetical wall high concentration

side


photocatalytic activity

• Assuming the definition of "photocatalytic activity" to be INTRINSIC ability of a photocatalyst to drive photocatalytic reaction, what is(are) the term(s) showing photocatalytic activity?

• C, I: reaction condition adjusted freely• S, K, : properties of solid (extrinsic ability)• keh, kr (or their ratio, keh/kr): intrinsic ability

Can we measure keh and kr from experimental results?

KC

SKCkkI

r r

1

eh


data analysis for photocatalysis

0 2 4 6 8 100

5x106

1x107

1.5x107

2x107

1/r

1/C

kSCkKSr1111

0 0.2 0.4 0.6 0.8 10

2x106

4x106

6x106

8x106

C/r

C

kKSC

kSrC 11

r = I kehSKC/ kr(1 + KC) = I (keh/kr)SKC/ (1 + KC)1/r = (1/kKS)(1/C) + 1/kS, where k = I (keh/kr)

• Plots (left and right) may give K and kS, but not k or kr, ke-h.


Langmuir-Hinshelwood mechanism

• bimolecular reaction: reaction of two substrates, A and B adsorbed on surface with a reaction rate constant k.

• Common surface cites adsorb substrates A and B with equilibrium constants, KA and KB, respectively.

• Both A and B are adsorbed on the surface in Langmuirian fashion, with a total (saturated) concentration of the surface sites, S.

• Assuming the bulk concentration of A and B, CA and CB, respectively, rate r is proportional to surface concentrations of A and B, and then:

2BBAA

BBAA2

1 CKCKCKCKkSr


Eley-Rideal mechanism

• bimolecular reaction: reaction of two substrates, A and B, adsorbed on surface and coming from the bulk, respectively, with a reaction rate constant k.

• Surface cites adsorb substrates A with equilibrium constants, KA.• A is adsorbed on the surface in Langmuirian fashion, with a total

(saturated) concentration of the surface sites, S.• Assuming the bulk concentration of A and B, CA and CB, respectively,

rate r is proportional to surface concentration of A and B in the bulk, and then:

AA

BAA

1 CKCCkSKr


action spectrum analysis

action spectrum analysisstatistical analysis

action spectrum analysis 17

super hydrophilicity & oxidative decomposition

Photoirradiation onto titania surface induces super hydrophilicity to make water-contact angle to be almost zero.1

Photoirradiation onto titania film decomposes adsorbed methylene blue.

titania-coated : ordinary glass


photocatalytic reaction

Photocatalytic reaction is a kind of photoreaction and therefore cannot be a series reaction: a parallel reaction initiated by photoabsorption with short-live species, e.g., photoexcited electrons and positive holes

electron-holepair

recombi-nation

photo-absorption

redox(chemical)reaction

1

2

3


necessary conditions for photocatalytic reactions

reaction initiated by photoabsorption of photocatalyst• (generally accepted) blank test: Copresence of 3 requisites, photoirradiation,

photocatalyst (solid material) and reaction substrate(s) is indispensable.• Photoreaction initiated by photoabsorption of a compound adsorbed by a solid

surface and subsequent electron injection also requires 3 requisites.• action spectrum analyses: possible sole technique to prove what absorbs light to

initiate the photoreaction• checking product(s): adsorption can decrease the amount of substrate(s);

stoichiometry

photoabsorber (= photocatalyst) remaining unchanged• checking turnover frequency: molar ratio of product(s) to photocatalyst to be

more than unity

20

juice16 juice 16

beer 33beer33

逆converse

裏inverse

裏inverse

逆converse

対偶contra-positive

beer16killer

21


PClight &solid &S

逆converse

notPC

light ||solid ||S

notPC

light ||solid ||S

逆converse

裏inverse

裏inverse

photo-cataly-sis (PC)

light &solid &subst-rate (S)

&: AND||: OR__: NOT

notPC

light &solid & Skiller e.g. dye-sensitized

reaction

22


PClight ||solid ||Skiller

PClight &solid &S

逆converse

notPC

light ||solid ||S

notPC

light ||solid ||S

逆converse

裏inverse

裏inverse

photo-cataly-sis (PC)

light &solid &subst-rate (S)

&: AND||: OR__: NOT


visible-light responsive photocatalyst

white titania (TiO2) absorbing only ultraviolet light giving color by SOME treatment(s)activity under visible-light irradiation?

titaniawithcolor

titaniavisible lightresponsive

titania=/

24


VIS-in-ducedPC

VIS photoabsorptionkiller

VIS-in-ducedPC

VIS photo-absorption

逆converse

notVIS-PC


notVIS-PC


逆converse

裏inverse

裏inverse

VIS-in-ducedPC


&: AND||: OR__: NOT


photoreaction/photocatalytic

reaction

wavelength 1

wavelength 2

wavelength 3

wavelength 4

response (product, current...)

・・・

measurement of action spectrum

• plots of apparent quantum efficiency (response normalized by number of incident photons) versus wavelength

wavelength

appa

rent

qua

ntum

effic

ienc

y

1 23

4

5

6


action spectrum

wavelength/nm wavelength/nm

wavelength/nm

photoabsorptionefficiency

appa

rent

qua

ntum

effic

ienc

y

quantumefficiency

example: discrimination of active crystalline phase in anatase-rutile mixtures

T. Torimoto, et al., Phys. Chem. Chem. Phys., 4, 5910-5914 (2002).

action spectrum= apparent quantum

efficiency


action spectrum analysis

J. Chem. Soc., FaradayTrans.1, 81, 2467 (1985).

appa

rent


action spectrum measurement (1)

light source / monochromator / reaction cell

reaction cell

monochromator

xenon arc

cell holder

ca. 0.1 mW cm-2

FWHM: ca. 20 nm


simultaneous irradiation

action spectrum measurement (2)

power meter

irradiation port

thermopile

wavelength adjustment

xenon arc

cell holders

0.1-18 mW cm-2

FWHM ca. 20 nm


methylene blue as a substrate

Proving that MB is inappropriate as a test compound for the reaction under visible-light irradiation by action spectrum analyses.

cited 180 times by March 2016


diffuse reflectance spectra in the unit of absorption normalized at 350 nm

1/2: wavelength giving half value to that at 350 nm

anatase-rutile mixture

fanataseanatase content estimated from XRD patterns

0

0.2

0.4

0.6

0.8

1

350 360 370 380 390 400 410 420

abso

rptio

n (n

orm

aliz

ed)

Wavelength / nm

Merck P-25

Wako(A)+CR-EL

CR-ELTIO-5

CR-EL(1473 K)360

370

380

390

400

0 0.2 0.4 0.6 0.8 1

1/

2/ n

m

fanatase

Merck

HombikatTIO-2

P-25

Wako(A)Merck+CR-EL

Wako(A)+CR-EL

TIO-5Aldrich(A<R)

Wako(R)CR-EL

CR-EL(1473K)

P-25(1473K)

0.5

skip


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


CH3OH HCHO + H2

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

CH3COOH + 2O2 2CO2 + 2H2O

action spectra of photocatalytic reaction

app

(nor

mal

ized

)0.5

00.2

0.40.60.8

1 (a)

00.2

0.40.60.8

1 (b)

0

0.2

0.4

0.6

0.8

1

350 360 370 380 390 400 410

Wavelength / nm

(c)


360

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

1/2

/ nm

fanatase

Merck

CR-EL

Merck+CR-ELP25TIO-5

Aldrich(A<R)

Wako(A)+CR-EL

Wako(R)

Hombikat

CR-EL(1473 K)

P25 (1473 K)

TIO-2Wako(A)

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

1/2

/ nm

fanatase

MerckP25

Wako(A)

Merck+CR-EL

Aldrich(A<R)TIO-5

CR-EL

Wako(R)Wako(A)+CR-EL

CR-EL(1473 K)P25 (1473 K)

TIO-2

360

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

1/2

/ nm

fanatase

Wako(R)CR-EL

Hombikat

Merck

Wako(A)

Merck+CR-EL(1:1)Aldrich(A<R)

TIO-5

TIO-2

CR-EL(1473 K)P25 (1473 K)

P25

dehyderogenation of methanol1/2 versus fanatase

absorption edge wavelengthanatase: ca. 370 nmrutile: ca. 410 nm

R >> A

R A

A >> R

oxygen evolution & silver metal deposition

decomposition of acetic acid

inner-filter effectby rutile


action spectra of anatase/rutile/P25

oxidative decomposition of acetic acid in an aqueous solution: carbon dioxide liberation

0

0.005

0.01

0.015

0.02

0.025

360 390 420 450

appa

rent

qua

ntum

effi

cien

cy (%

)

wavelength/nm

0

50

100

150

P25pure anatase pure rutile

reconstructed mixture

CH3COOH(CO2)

CH3CHO(CO2)

CH3OH(H2) <Pt>

Ag+

(Ag/O2)

amorphous

91

100

120 56

anatase

rutile

P25

skip

Ohtani, B.; Prieto-Mahaney, O. O.; Li, D.; Abe, R. J. Photochem. Photobiol. A Chem.216 (2010) 179-182.


hydrogen evolution from methanol

isolated anatase: Aisolated rutile: Rplatinization:

photodeposition (0.2 or 2wt% loading)

• negligible activity of all bare samples

• 0.2wt%-Pt loaded P25 ~ A + Pt/R (85:15)

• 2wt%-Pt loaded P25 ~ Pt/A + Pt/R (85:15)

comparable activity of Rwith A when platinized

photodeposition occurs preferentially on rutile particles

0

0.2

0.4

0.6

0.8

1

360 390 420

appa

rent

qua

ntum

effi

cien

cy

wavelength/nm

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A

0

0.2

0.4

0.6

0.8

1

360 390 420

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A

0

0.2

0.4

0.6

0.8

1

360 390 420

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A


action spectrum: case 2

wavelength/nm wavelength/nm

wavelength/nm

photoabsorptionefficiency

action spectrum

appa

rent

qua

ntum

effic

ienc

y

quantumefficiency

Change of (intrinsic) quantum efficiency, i.e., efficiency of electron-hole utilization depending on the irradiation wavelength

may induce

shift of action spectrum

skip


wavelength dependence100% anatase titania powders

dehydrogenation of methanol<platinum-loaded/under argon>

mineralization of acetic acid<under air>

CH3COOH + 2O2

2CO2 + 2H2OCH3OH

HCHO + H2


comments on this lecture

Please send email in Japanese or English within 48 hoursto: [email protected]: pc20170706-XXXXXXXX

[email protected]<full name><nickname><comments on this lecture><question(s) if any>


to: [email protected]

subject: pc20170706-12345678

pc20170706-12345678

[email protected]

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．

絶版になっている「光触媒標準研究法」はどこかで入手可能ですか．

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july 6, 2017 - 北海道大学pcat.cat.hokudai.ac.jp/class/pc2017/20170706_bo_sapporo.pdf ·...

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