環境触媒化学特論i 2pcat.cat.hokudai.ac.jp/class/pc2020/20200514_bo_sapporo.pdf2020/05/14...

Advanced Course in Environmental Catalytic Chemistry (02) 1

2020/05/14

環境触媒化学特論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 202008:45─10:15, Thursday on Zoom

Bunsho Ohtani (Ewa Kowalska)

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

https://pcat.cat.hokudai.ac.jp/cgi-bin/class/db_class_e.cgi?mode=display_pc2020


"lecture" web page


"pc2020" web page


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) May 7 introduction of photocatalysis(2) May 14 interaction between substances and light(3) May 21 electronic structure and photoabsorption(4) May 28 thermodynamics: electron and positive hole(5) June 4 environmental application of photocatalysis(6) June 11 adsorption(7) June 18 kinetic analysis of photocatalysis(8) June 25 steady-state approximation(9) July 2 kinetics and photocatalytic activity(10) July 9 action spectrum analysis (1)(11) July 16 action spectrum analysis (2)(12) July 23 crystal structure (1)(13) July 30 crystal structure (2)(14) August 6 design and development of photocatalysts (1)(15) August 13 design and development of photocatalysts (2)

(questionnaire)


format

Please send email in Japanese or English within 72 hoursto: [email protected]: pc2020MMDD-XXXXXXXX

[email protected](full name)(nickname)(what is learnt from today's lecture) + (questions if any)[blank line](answer for question 1)(answer for question 2)(answer for question 3)・・


email example

to

subject

(same as subject)email addressfull namenicknamecomment(s)question(blank line)answer 1answer 2answer 3・・

pc20200514-57388301

pc20200514-57388301

Advanced Course in Environmental Catalytic Chemistry (02) 9photocatalysis industries in Japan = ca. 550 million USD (2018)

exterior

interior

road related

purifier living ware

others

88%4%

1%5%2%

0.1%


photocatalysis: two major phenomena

superhydrophilicity: the surface of photocatalytic (titania) coatings becomes super hydrophilic, i.e., contact angle to be almost zero.

photocatalytic oxidation: organic and inorganic compounds are oxidized under air to be inorganic materials, i.e, mineralization.

left: photocatalytic/right: ordinary

mechanism


titanium(IV) oxide (titania) as a photocatalyst

no change after reaction = "catalyst"

no reaction in the dark = "safe" and environ-mentally benign

very popular and cheap material

especially strong oxidizing power when irradiated

white or colorless = no effect on appearancebut, requires ultraviolet irradiation

highphoto-stability

superiorredox ability availability

notpoisonous& natural

titanium(IV) oxideTiO2

titania


practical applications

Q Which application impressed you the most? What is the reason for that?

Q What is the general chemical reaction(s) included in the practical applications of photocatalysis? Show a reaction formula(s).


chemical reactions in practical photocatalysis

(1) Photocatalysts such as titanium(IV) oxide coated or fixed onthe solid materials adsorb organic compounds from water or air.

(2) The adsorbed organic compounds are completely decomposedinto carbon dioxide (mineralization).

(3) The surface of photocatalytic coatings becomes super-hydrophilic.

point 1: Molecular oxygen (O2) in air leads to mineralizationpoint 2: Reduction as a counterpart of oxidation is for O2.point 3: Intermediate species from O2 are known to act as oxidants.point 4: In the absence of O2, other reduction reactions may proceed.

mechanism


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 & oxidation3b) recombination

伝導帯

価電子帯

緩和

再結合


catalysis and photocatalysis

• Catalysis and photocatalysis should be thought different.• There are many common methods for characterization

catalysis

photo-catalysis

catalysis

photo-catalysis

catalysisphoto-

catalysis


photoexcitation

Photoreaction proceeds through

excited state.

various excited states• electronic (ultraviolet-visible): photosynthesis,

photocatalysis• vibrational (infrared): water warmed by sunlight• rotational (microwave): microwave oven

the easiest way for making excited states:

photoabsorption


what is electromagnetic wave?

Light is electromagnetic wave. Which are electromagnetic waves?alpha beam, beta beam, gamma beam, X ray, ultraviolet light, visible light, infrared light, microwave, radio wave, electron beam

振動方向は互いに直交

波長

電場の振動磁場の振動

光の進行方向


Q: speed of light?

• The shorter the wavelength, the higher the energy.

• The speed of light is constant in vacuum, not depending on its wavelength:

• number of vibration per unit time = frequency (Hz)

• wavelength x frequency = (speed of light)

• (speed of light)/wavelength = frequency


Q: speed of light

• The shorter the wavelength, the higher the energy.

• The speed of light is constant in vacuum, not depending on its wavelength:ca. 3 x 108 m s-1

• number of vibration per unit time = frequency (Hz)

• wavelength x frequency = (speed of light)

• (speed of light)/wavelength = frequency


light: wave and particle (at the same time)

• no weight• electron: particle and wave at the same time with weight


energy of light

• Even if the total energy is the same, the effect of light may different depending on the energy of each photon.


Q: boundary of ultraviolet and visible light

various electromagnetic wave

Q: Answer the boundary wavelength of ultraviolet and visible light.

8

7

5

2

-1

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

-13

-14

6

4

3

1

0

-2

dm

mm

μm

nm

Å

pm

km

m

cm

波長/10 mn

可視光

紫外光

エックス線

赤外光

エネルギー /10 Jn

周波数/10 Hzn

0

1

3

6

9

11

12

13

14

15

16

17

18

19

20

21

22

2

4

5

7

8

10

kHz

MHz

GHz

THz

-33

-32

-30

-27

-24

-22

-21

-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-31

-29

-28

-26

-25

-23

aJ

fJ

pJ

-9

-8

-6

-3

0

2

3

4

5

6

7

8

9

10

11

12

13

-7

-5

-4

-2

-1

1

μJ

mJ

J

kJ

MJ

GJ

TJ

ガンマ線

マイクロ波

電波

-14

-13

-11

-8

-5

-3

-2

-1

0

1

2

3

4

5

6

7

8

-12

-10

-9

-7

-6

-4

/10 eVn

/10 J moln -1


Q: boundary of ultraviolet and visible light

8

7

5

2

-1

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

-13

-14

6

4

3

1

0

-2

dm

mm

μm

nm

Å

pm

km

m

cm

波長/10 mn

可視光

紫外光

エックス線

赤外光

エネルギー /10 Jn

周波数/10 Hzn

0

1

3

6

9

11

12

13

14

15

16

17

18

19

20

21

22

2

4

5

7

8

10

kHz

MHz

GHz

THz

-33

-32

-30

-27

-24

-22

-21

-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-31

-29

-28

-26

-25

-23

aJ

fJ

pJ

-9

-8

-6

-3

0

2

3

4

5

6

7

8

9

10

11

12

13

-7

-5

-4

-2

-1

1

μJ

mJ

J

kJ

MJ

GJ

TJ

ガンマ線

マイクロ波

電波

-14

-13

-11

-8

-5

-3

-2

-1

0

1

2

3

4

5

6

7

8

-12

-10

-9

-7

-6

-4

/10 eVn

/10 J moln -1

ca. 400 nm

various electromagnetic wave

Q: Answer the boundary wavelength of ultraviolet and visible light.


boundary of ultraviolet and visible light

• "Visible" means one can see the light.• The wavelength of light sensible is different individually.• Ordinary speaking, it is approximately 400 nm, certain

people can be sensible for the light of wavelength shorter than 380 nm


Q: Why leaves look green?

interaction of light and substancesthe three primary colors: red, green and blueThink complimentary color(s).


Q: Why leaves look green?

interaction of light and substancesthe three primary colors: red, green and blueThink complimentary color(s).

(1) Solar radiation contains all light of colors (white).

(2) Chlorophyll in leaves absorbs the light of red and blue (blue-violet).

(3) Remaining green light is reflected to make leaves look green.


Q: Draw photoabsorption spectrum of chlorophyll.

• electronic absorption spectrum = UV-Vis: extent of photoabsorption is plotted against wavelength

• hint: wavelengths of red and blue lights are 650 nm and 450 nm.


Q: Draw photoabsorption spectrum of chlorophyll.

• electronic absorption spectrum = UV-Vis: extent of photoabsorption is plotted against wavelength

• hint: wavelengths of red and blue lights are 650 nm and 450 nm. • chlorophyll c


light and shadow

three colors of shadow

V+Y=W

W-V=YW-Y

=V

W-V-Y=B

at Soun-kyo


Z-scheme in photosynthesis

• two-step photoexcitation with P680 and P700 (figures show wavelength of photoabsorption)

• photosystem I: accepting electron from photosystem II and reduce NADP+ into NADPH as an energy source

• photosystem II: oxidizing water into molecular oxygen and release electron to photosystem I

• photoabsorption of Q-band (longer wavelength), but not Solet band (shorter wavelength)


interaction between light and substance

• electronic/vibrational/rotational energies are "quantized", i.e. discrete level of energy

• energy gap: energy difference between the levels• Only light of energy which is the same as energy gap is absorbed.• photoabsorption = excited state• Excited state must release the energy to go back to ground state.


electronic energy

atom as a fundamental particle of substancepositively charged nucleinegatively charged electronselectrostatic interaction between themelectron: wave and particle at the same timequantum theory to interpret bothdiscrete energy level = quantization


vibrational energy

molecule: assembly of atomschemical bond: electron(s) existing between nucleus"Spring" is assumed for chemical bonds.quantized


format

Please send email in Japanese or English within 72 hoursto: [email protected]: pc2020MMDD-XXXXXXXX

[email protected](full name)(nickname)(what is learnt from today's lecture) + (questions if any)[blank line](answer for question 1)(answer for question 2)(answer for question 3)・・


email example

to

subject

(same as subject)email addressfull namenicknamecomment(s)question(blank line)answer 1answer 2answer 3・・

pc20200514-57388301

pc20200514-57388301

2020/05/14Advanced Course in Environmental Catalytic Chemistry I"lecture" web page"pc2020" web pageobjectives/goal/keywordsscheduleformatemail examplephotocatalysis industries in Japan = ca. 550 million USD (2018)photocatalysis: two major phenomenatitanium(IV) oxide (titania) as a photocatalystpractical applicationschemical reactions in practical photocatalysisprinciple of photocatalytic reactioncatalysis and photocatalysisphotoexcitationwhat is electromagnetic wave?what is electromagnetic wave?Q: speed of light?Q: speed of lightlight: wave and particle (at the same time)energy of lightQ: boundary of ultraviolet and visible lightQ: boundary of ultraviolet and visible lightboundary of ultraviolet and visible lightQ: Why leaves look green?Q: Why leaves look green?Q: Draw photoabsorption spectrum of chlorophyll.Q: Draw photoabsorption spectrum of chlorophyll.light and shadowZ-scheme in photosynthesisinteraction between light and substanceelectronic energyvibrational energyformatemail example

環境触媒化学特論i 2pcat.cat.hokudai.ac.jp/class/pc2020/20200514_bo_sapporo.pdf2020/05/14...

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