1PACCON 2013

Zinc Oxide Nanorods-Based Catalysts for Visible Light Photocatalysis

Supamas Danwittayakul

Mayuree Jaisai,Panida Muangkasem,

Thammarat Koottatep

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Outline

1. Introduction

2. Experimental

3. Results and Discussion

4. Conclusions

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Introduction

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Photocatalysis of Metal Oxide4

Metal Oxides Bandgap (eV)

TiO2 3.2

ZnO 3.4

MOh h h h h h

e- e- e- e- e- e-

Organic molecule

OHOH-

O2-

CO2 + H2O

O2

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Very low quantity of UV light in the solar spectrum

Wavelength (nm)

Photon Energy (eV)

Rad

iati

on E

ner

gy (

kW

/m2 .n

m)

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Increase an effective surface area

Manipulate defective sites in the structure

Hypothesis

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7ZnO Nanorods

Wurtzite structure

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Hypothesis I

Phototcatalysis of Doped-Metal Oxide

OH-OH•

O2-

Organic molecule CO2 + H2O

h+

e-

O2

e- e-

e-

e-

h+h+

h+

h+

MO

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Hypothesis II

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Experimental

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Hydrothermal Growth of ZnO

Repeat several cycles350o

C Furnace

2 mM Zn(CH3COO)2

Temp. >350CAnnealed at 350CFor 5 hr

350oC Furnace

95oC

95oC Oven

[Zn(NO3)2+HMT]: 5 mMTemp. 95C for 15 hr

Annealed at 350CFor 1 hr

Seeding of ZnO Nanoparticles

Growth of ZnO Nanorods

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350oC Furnace

95oC

95oC Oven

[Zn(NO3)2+HMT]: 20 mM + MnC4H

6O

4.4H

2O

Temp. 95C for 15 hrAnnealed at 350CFor 1 hr

Mn doped ZnO nanorods

Mn2+: 0.05%, 0.1%, 0.5%, 1%, 3%

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Photocatalytic activity test

C0 – C

C0

x 100DE =

ln(C/C0) = - kt

Degradation Efficiency

Kinetic Calculation

- Methylene blue aqueous solution : 1 x 10-5 Molar- Nanocatalyst coated specimen size : 4 x 0.5 x 1 cm- Quartz cuvette volume : 7.5 ml- Tungsten-halogen light source (275 W) with 10-11 klux intensity

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Results & Discussion

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Morphology of Pure ZnO Nanorods

ZnO 1 mMZnO 1mM130nm, 1.4μm

ZnO 5mM130nm, 1.6μm

ZnO 10mM130nm, 1.7μm

ZnO 20mM154nm, 2μm

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Dimension of ZnO Nanorods

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Photocatalytic Activity of Pure ZnO Nanorods

C0 – C

C0

x 100DE =

ln(C/C0) = - kt

0 20 40 60 80 100 120 140 160 180 2000

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20

30

40

50

60

70

80

90

Z nO1mMZnO5mMZnO10mMZnO20mM

Deg

rad

ati

on

%

Time (min)

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t1/2 = haft life of first order reaction = ln(2)/k

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CatalystS.S.A(m2/g)

Degradation(%)

R2 k(min-1)

t1/2

(min)

ZnO 1mM 35.4 67 0.9934 0.0073 94.95

ZnO 5mM 35.4 74 0.9907 0.0078 88.87

ZnO 10mM 38.8 76 0.9916 0.0089 77.88

ZnO 20mM 45.3 80 0.9792 0.0093 74.53

~ 16 % photocatalytic activity can be enhanced by an increase of effective surface area

Photocatalytic Activity of Pure ZnO Nanorods

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Mn doped ZnO catalysts

Mn 0.1%

Mn 0.5%

Mn 1% Mn 3%

Mn 0.05%

ZnO 20mM

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0 20 40 60 80 100 120 140 160 180 2000

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20

30

40

50

60

70

80

90

Z nO20mM005Mn/Z nO01Mn/Z nO05Mn/Z nO1Mn/Z nO3Mn/Z nO

Time (min)

Deg

rad

ati

on

%

C0 – C

C0

x 100DE =

ln(C/C0) = - kt

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Photocatalytic Activity of Mn doped ZnO Nanorods

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Photocatalytic Activity of Mn Doped ZnO catalysts

~ 4.76% photocatalytic activity can be enhanced upon using0.05Mn/ZnO nanocomposites

Catalyst Degradation(%) R2 k

(min-1)t

1/2(min)

ZnO20mM 80 0.9792 0.0093 74.53

0.05Mn/ZnO 84 0.9725 0.0102 67.95

0.1Mn/ZnO 83 0.9903 0.0096 72.20

0.5Mn/ZnO 62 0.9889 0.0079 87.741Mn/ZnO 48 0.8893 0.0060 115.52

3Mn/ZnO 47 0.7884 0.0040 173.28

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Conclusions

ZnO nanorods on porous ceramic substrates were successfully synthesized through hydrothermal technique.

ZnO catalyst with larger surface area (45m2.g-1) is 16% more active than that lower surface area ZnO catalyst (35-39 m2.g-1)

An enhancement of 4.76% in the photocatalytic activity could be improved by doping pure ZnO nanorods with 0.05% Mn(II).

Mn doped ZnO nanorods can be good candidates for visible photocatalysis.

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Acknowledgements

National Research Council of Thailand (NRCT)

National Metal and Materials Technology Center (MTEC)

Asian Institute of Technology (AIT)

National Nanotechnology Center (NANOTEC)

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Thank You For Your Attention

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35.4 35.438.8

45.3S.S.A.

ZnO1mM ZnO5mM ZnO10mM ZnO20mM130

135

140

145

150

155

160

0.0

0.5

1.0

1.5

2.0

2.5Width Length

Wid

th (

nm

)L

ength

(µm

)

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Width and length of ZnO nanorods grown on porous ceramic substrate through hydrothermal process with different growth solution concentrations

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