Kumamoto University

酸化グラフェンの電気化学および触媒的応用

木田 徹也

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熊本大学 大学院先端科学研究部 物質材料科学部門

（工学部物質生命化学科）

Kumamoto University

• 電子伝導体 • プロトン伝導体

• 絶縁体 • プロトン伝導体

• 光還元 • 熱還元 • ヒドラジン還元

epoxide carbonyl hydroxyl carboxyl

Oxygen function groups Carbon Bonds

(defect)

酸化グラフェンのプロトン導電性

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プロトン伝導

proton

electron

電子/プロトン混合伝導 SO4

2-ドープ

プロトン伝導

混合導電性酸化グラフェン

エポキシ基がプロトン輸送サイト

J. Am. Chem. Soc., 135, 8097 (2013)

Angew. Chem., Int. Ed. 134, 6997 (2014) Chem. Commun., 50, 14527 (2014) Chem. Mater., 26, 5598 (2014)

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O O2

e-

H+

O

e-

e-

O

H2O

anode

e- e-

e-

cathode

H2

H2

H2 H+

H+ H+

H+

H+

H+

H+

Fuel cell

GO-based proton exchange membrane

Typical proton exchange membrane material

Hydrophilic site

Hydrophobic site

H+

Graphene Oxide

H+

H+ The protons move through hydrophilic domains

H+

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GO

dispersion

Cross-section

GO

membrane

Vacuum filtration

AFM image

Graphene oxide (GO)-membrane

Graphite powder

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Hummers' Method

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Catalysis of Graphene Oxide

Features

Large surface area

Acid catalyst

Separation is easy (being heterogeneous)

Inexpensive and environmentally friendly

High microwave absorptivity and thermal conversion

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π-π相互作用

sp2ドメイン

Proton path

Solid acid sites?

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Carbon

neutral

plants (ex, Rapeseed,

soybean, sesame)

CO2

Vegetable

oil Biodiesel

Photosynthesis

Generation

Fuel Production

Burning

Background and Motivation of the Study

Biodiesel has attracted attention from the viewpoint of carbon neutral.

What is Bio Diesel Fuel : BDF ?

The biodiesel abbreviate Bio Diesel Fuel, is a generic name of a fuel for diesel engines

made from plant/vegetable oil, which is one of many sources of biomass energy.

It has similar properties of light oil and its material composed of fatty acid methyl esters.

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Conventional BDF Production Process

By-products

Waste Oil

FFA

triglyceride

Methanol

Methanol

Esterification

Acid catalyst conditions

(e.g. H2SO4)

Base catalyst conditions (e.g. NaOH, KOH)

BDF

Glycerin

Alkaline

Wastewater

Products

Transesterification

R-COOH+CH3OH ⇄ R-COO-CH3+H2O

CH2-COO-R1 CH2-OH

CH-COO-R2 + 3 CH3OH ⇄ 3R-COO-CH3 + CH-OH

CH2-COO-R3 CH2-OH CH2-OH

CH-OH CH2-OH

CH2-COO-R1

CH-COO-R2 CH2-COO-R3

R1-COO-CH3

R2-COO-CH3 R3-COO-CH3

R-COOH

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Although the reaction rate is very slow,

transesterification reaction proceed even under acid catalyst.

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Microwave Heating Method

Electric field

Molecules with electric dipoles

Molecules turn in alternating electric field.

Collide to each other thus generating heat.

◇Internal and localized heating

◇High-speed and selective heating

◇High heating efficiency and fast response,

and temperature limiting nature

◇Clean energy

◇Good operation and work environment Microwave irradiation

Reactants are heated directly

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Mechanism of MW irradiation

Advantage of MW irradiation

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Synergy of Microwave Heating Method and

Functionalized Carbon-Based Catalyst

・MW heating

High-speed and selective heating

・Graphene Oxide

High microwave absorptivity

and thermal conversion

Under heterogeneous catalysis, the reaction takes place on

the internal and external surfaces of solid catalyst.

Graphene oxide has strong microwave absorptivity, the

irradiation directly acts on the catalyst forming ‘hot spots’,

with temperature far higher than the bulk temperature of

the mixture.

microwave

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Main Objectives

Use of carbon-based heterogeneous catalyst (GO)

under microwave heating method

One-pot esterification and transesterifications ・ ・

Waste Oil

triglyceride

+ Methanol

Esterification

BDF

GO

MW irradiation

Transesterification

FFA

R1-COO-CH3

R2-COO-CH3 R3-COO-CH3

CH2-COO-R1

CH-COO-R2 CH2-COO-R3

R-COOH

CH3OH

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Microwave oven

Fiberoptic

thermometer

Condenser (for methanol reflux)

Experimental Apparatus

Experiments

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Results & Discussion

Effect of GO as catalyst: (Esterification)

Effect of GO as catalyst

(reaction time = 5min, methanol/oleic acid molar ratio = 8:1, and MW power = 200 W)

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0

10

20

30

40

50

60

70

80

90Y

ield

［%

］

0.62 %

↓

No catalyst GO

(1 wt%)

Esterification reaction efficiently proceed

within a short reaction time of 5 min with the

GO catalyst.

Esterification reaction

R-COOH+CH3OH ⇄ R-COO-CH3+H2O

Esterification of oleic acid

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Results & Discussion

Comparison of catalysts: (Esterification)

Comparison of catalysts

(reaction time = 5min, methanol/oleic acid molar ratio = 8:1, and MW power = 200 W)

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30

40

50

60

70

80

90Y

ield

［%

］

Amberlyst-

15

ZrO2-

SO3H Graphite

Oxide GO

Acid content

Catalyst GO GrO ZrO2-SO3H Amberlyst-15

H+[mmol/g] 3.95 2.34 1.26 4.80

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(reaction time = 5min, methanol: oleic acid molar ratio = 8:1)

Comparison of Heating Methods: (Esterification)

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Results & Discussion

0

10

20

30

40

50

60

70

80

90

Yie

ld

［%

］

Conventional

heating

Microwave

irradiation Ultrasonic

irradiation

Mechanism of US irradiation

MW heating method is

a better choice

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Effect of methanol/oleic acid molar ratio on FAME yield.

(MW irradiation power = 200W, and amount of catalyst = 1 wt%)

Effect of methanol/ oleic acid molar ratio on FAME yield

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Results & Discussion

0 1 2 3 4 560

70

80

90

100

MW irradiation time [min]

Yie

ld [%

]

methanol/oleic acid molar ratio● 4/1△ 8/1 ▼ 12/1

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FIRST GENERATION

ETHANOL

• Sourced from Corn and

sugarcane

• Mature fermentation

technology

• Issue on food security

SECOND GENERATION

ETHANOL

• Sourced from biomass residues

• Requires advance technology to

make cellulose accessible

• Widely available

Ethanol fuel for internal combustion

engine and gasoline blend

additive

PRESENT

SCENARIO

IDEAL

SCENARIO

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Department of Applied

Chemistry and Biochemistry

• Non-edible natural biopolymer

• Structurally consists of d-glucose linked with β-1,4 glycosidic bond

• Difficult to depolymerize due to: • Flip-flop conformation

• Crystalline structure due to inter- and intra-chain hydrogen bonds

Cellulose

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Fiber Optic

Temperatur

e sensor

Pressure

sensor

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Cellulose

Graphene oxide

Water

Hydrolysate:

TOC, HPLC

Solid residue: dried

→ XRD, TGA

Microwave Power: 200 – 800 W

Reaction temperature: 120OC –

200OC

Reaction time: 0 – 60 min

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Effect of MW and GO on tramp and Heating rate

tramp = time to reach desired

reaction temp

MW+GO resulted to shorter

tramp and higher heating

rates

Desired temp (200OC) was

achieved within 30sec

(800W) to 162 sec (200W)

Higher heating rates help

suppress degradation of

polymers and occurrence of

side reactions (Rogalinski et

al., 2008)

Reaction conditions: 0.1 g MCC, 0.1g GO, 10ml water, 200OC, zero thold

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Temperature and reaction time-dependency of MCC hydrolysis

Lowest temperature for glucose generation began at 160OC, thold = 5min (0.7%)

Shortest time is at thold = 0 min, 200OC (1%)

GY% increased as temperature increased and reaction time (thold) prolonged

Highest GYwt% of

46% at 200OC, 1 hr

Reaction conditions: 0.1 g MCC,

0.1 g GO, 10ml water, 200 W

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Comparison with Previous Findings (Hydrolysis of Microcrystalline Cellulose)

Catalyst Cellulose:

Catalyst

(wt/wt)

Reaction

conditions

Time (hr) Glucose

Yield (%)

Rinaldi et al.,

2008

Amberlyst

15DRY 5*

373 K

(100OC) 5 0.9

Zhang et al.,

2012 C-SO3H-IL 2*

363 K

(90OC) 2 33

Suganuma

et al. C-SO3H 0.083*

373 K

(100OC) 3 4

Zhao et al.,

2014

Dispersed

GO 0.9*

423 K

(150OC) 24 49.9

This study GO + MW 1 473 K

(200OC) 1 46

as cited by Yabushita et al., 2014

*Amorphous cellulose, typically ballmilled

The present study yielded competitive glucose yield with shorter reaction time vs. previous studies

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Parallel/ Side reaction: Formation of Degradation Products

High selectivity

to Glucose

High heating

rates suppressed

formation of

degradation

products (DP)

such as Levulinic

acid and 5-HMF

DP started to

form at 200OC, 1

hr reaction

Reaction conditions: 0.1 g MCC, 0.1 g GO, 10ml water, 200OC, 200W

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Contribution of Tramp on depolymerization with MW only

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MW MW + GO

CrI, (%) Crystallite size

(nm) CrI, %

Crystallite size

(nm)

Avicel 74 ± 1 5.3 74 ± 1 5.3

200W (a) (a) 70 4.9

400W 73 5.4 67 4.9

600W 72 5.3 71 4.6

800W 73 5.4 63 1.9

With MW alone, no significant change in CrI and

crystallite size and no glucose generation, which

means cellulose polymer cleavage did not occur

Reaction conditions: 0.1 g MCC, 10ml water, 200OC, zero thold

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Proposed Mechanism 2

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Elevated T & P

Carbonization Crystalline cellulose

Glucose

Graphene

oxide

Decrystallization via

surface erosion

Amorphous cellulose

formation

Dissolution

Hydrolysis