20130620 BO Sapporo.pptx 復元済み -...

2013/06/20─Advanced Course in Photocatalytic Reaction Chemistry 1

June 20, 2013


schedule

(1) April 11 introduction of photocatalysis(2) April 18 interaction between substances and light(3) April 25 electronic structure and photoabsorption(4) May 2 thermodynamics: electron and positive hole(5) May 9 adsorption(6) May 16 (Professor Ewa Kowalska)(7) May 23 kinetic analysis of photocatalysis (8) May 30 steady-state approximation(9) June 6 kinetics and photocatalytic activity(10) June 13 kinetics and action spectrum analysis (1)(11) June 20 action spectrum analysis (2) and crystal

structure of photocatalysts(12) June 27 (Professor Mai Takase)(13) July 4 design and development of photocatalysts (1)(14) July 11 design and development of photocatalysts (2)(15) July 18 design and development of photocatalysts (3)

July 25August 1


Advanced Course in Photocatalytic Reaction Chemistry

understanding chemistry by understanding photocatalysisunderstanding photocatalysis by understanding chemistry

Division of Environmental Material Science, Graduate School of Environmental ScienceThe first semester of Fiscal 201308:45─10:15, Thursday at Lecture Room D103

Bunsho Ohtani, Ewa Kowalska and Mai Takase

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

[email protected]://www.hucc.hokudai.ac.jp/~k15391/


objectives/goal/keywords

<< objectives >>Understanding the mechanism of decomposition of pollutants, methodsof photocatalysts preparation, design of practical photocatalytic reactionsystems, and strategy for enhancement of photocatalytic activity.

<< goal >>To understand principle of photocatalytic reaction from the standpointof chemistry and strategy for practical applications. To obtain scientificmethod for research on functional solid materials.

<< keywords >>Photocatalyst, Photoinduced oxidative decomposition, Superhydro-philicity, Excited electron-positive hole, Structure-activity correlation,Higher photocatalytic activity, Visible-light response


schedule

(1) April 11 introduction of photocatalysis(2) April 18 interaction between substances and light(3) April 25 electronic structure and photoabsorption(4) May 2 thermodynamics: electron and positive hole(5) May 9 adsorption(6) May 16 (Professor Ewa Kowalska)(7) May 23 kinetic analysis of photocatalysis (8) May 30 steady-state approximation(9) June 6 kinetics and photocatalytic activity(10) June 13 kinetics and action spectrum analysis (1)(11) June 20 action spectrum analysis (2) and crystal

structure of photocatalysts(12) June 27 (Professor Mai Takase)(13) July 4 design and development of photocatalysts (1)(14) July 11 design and development of photocatalysts (2)(15) July 18 design and development of photocatalysts (3)

July 25August 1


comments on this lecture

Please send email in Japanese or English within 48 hours

to: [email protected]: pc2013MMDD-XXXXXXXXbody:(full name)(nickname)(comments and/or questions on today's lecture)


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 S

r

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

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

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

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

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

AA

BAA

1 CKCCkSKr


action spectrum analysis

action spectrum analysisstatistical analysis


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

11

22

33


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


visible-light responsive photocatalyst

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

titaniawithcolor

titaniawithcolor

titaniatitaniavisible lightresponsive

titania

visible lightresponsive

titania=/


photoreaction/photocatalytic

reaction

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)].

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

2013/06/20─Advanced Course in Photocatalytic Reaction Chemistry 22quantum efficiency 22

quantum efficiency (yield)

• the first principle of photochemistry: only molecules absorbing a photon can react• number ratio of reacted molecules to absorbed photons, assuming single photon

process:

n(reacted molecules) / n(absorbed photons)

• Processes of heterogeneous photocatalysis may contain reactions with multiple electrons or holes, e.g., water photolysis to give oxygen.

• quantum efficiency for heterogeneous photocatalysis:

n(electrons or holes used in reaction) / n(adsorbed photons)

r (electrons or holes used in reaction) / r (adsorbed photons)

• apparent quantum efficiency

r (electrons or holes used in reaction) / r(incident photons)

where r(incident photons) is a light flux (I).

I

I

2013/06/20─Advanced Course in Photocatalytic Reaction Chemistry 23quantum efficiency 23

number of electrons or holes for reaction

example 1: acetic acid decomposition

CH3COOH + 2O2 2CO2 + 2H2OAssuming the reduction of 1 mol of oxygen (O2) into 2 mol of water requires 4 positive holes, 8 mol of electron-hole pairs are used in this stoichiometry. Therefore, 1 mol of carbon dioxide production corresponds to 4 mol of photons, at minimum.

example 2: acetaldehyde decomposition

CH3CHO + 5/2 O2 2CO2 + 2H2OAssuming the reduction of 1 mol of oxygen (O2) into 2 mol of water requires 4 positive holes, 10 mol of electron-hole pairs are used in this stoichiometry. Therefore, 1 mol of carbon dioxide production corresponds to 5 mol of photons, at minimum.

example 3: water splitting

2H2O O2 + 2H2Assuming the production of 1 mol of oxygen (O2) from water requires 4 positive holes, 4 mol of electron-hole pairs are used in this stoichiometry. Therefore, 1 mol or 2 mol of oxygen or hydrogen production corresponds to 4 mol of photons, at minimum.


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


power meter

irradiation port

thermopile

wavelength adjustment

xenon arc

cell holders

0.1-18 mW cm-2

FWHM ca. 20 nm0.1-18 mW cm-2

FWHM ca. 20 nm


non and S-doped titania for MB decomposition

S-doped TiO2S-doped TiO2

P-25P-25


MBMB

Yan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B., Chem. Phys. Lett., 429, 606-610 (2006).


photochemical MB decomposition


P-25P-25

MB insuspension

MB insuspension


titania photocatalysts for AcOH decomposition

S-dopedS-doped

P-25P-25

S-doped titania clearly showed the activity under visible-light irradiation.

P-25P-25




lens optical filter

reaction cell

stirrer

water bath

liquid-phase photocatalytic reaction

"sharp-cut"optical filter

(example)L-42

actual limiting wavelength

wavelength

center of 5 and 72% trans-mission

skipskip


pseudo action spectrum

• action spectrum measured by "sharp-cut filters": pseudo action spectrum• corresponding to integral of "true" action spectrum• plateau part of "pseudo action spectrum" suggests no photoreaction occurring

at that wavelength region

action spectrum

pseudoaction spectrum

wavelength

appa

rent

qua

ntum

yie

ld


P-25/MB photocatalytic reactionpseudo action spectrum corresponds to integral of "true" action spectrum

pseudo action spectrum

300 400 500 600 7000.000

0.001

0.002

0.003

0.004

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

r /µm

ol m

in-1

app

/nm

action spectrum

integral of action spectrum


collection of papers of less expected citations

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

cited 60 times by June 2011


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

skipskip


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 / n

m

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/ n

m

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 / n

m

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 >> AR >> A

R AR A

A >> RA >> R

oxygen evolution & silver metal deposition

decomposition of acetic acid

inner-filter effectby rutile

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)

CH3COOH(CO2)

CH3CHO(CO2)

CH3CHO(CO2)

CH3OH(H2) <Pt>

CH3OH(H2) <Pt>

Ag+

(Ag/O2)Ag+

(Ag/O2)

amorphous

91

100

120 56

anatase

rutile

P25

skipskip

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

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

skipskip


comments on this lecture

Please send email in Japanese or English within 48 hours

to: [email protected]: pc20130620-XXXXXXXXbody:

full namenicknamecomments on this lecturequestion(s) JPY1,200 (77%) JPY3,500 (79%)

pc20130620-12345678

20130620 BO Sapporo.pptx 復元済み -...

Documents

Transcript of 20130620 BO Sapporo.pptx 復元済み -...