Photoelectrocatalytic Degradation of Salicylic acid using Sprayed Gold Doped Iron Oxide Thin

Films

M.A. MahadikM.A. Mahadik

Shri Ganeshay Namah

Electrochemical Materials Laboratory,Department of Physics,

Shivaji University, Kolhapur - 416004

under the guidance of

Prof. (Dr.) C.H. Bhosale

by

2

Outline of the presentationOutline of the presentation

IntroductionExperimentalResults and DiscussionPEC XRD Optical properties SEM Electrical resistivity measurements Photoelectrocatalytic degradation of salicylic acid

Conclusions

IntroductionExperimentalResults and DiscussionPEC XRD Optical properties SEM Electrical resistivity measurements Photoelectrocatalytic degradation of salicylic acid

Conclusions

3

Introduction

Recently, TiO2 (Eg = 3.2 eV):promising material but absorbs ~ 3-4% of solar spectrum Alternative Fe2O3 with band gap (2.2 eV) absorbs ~ 40% visible light

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0En

erg

y D

istr

ibu

tio

n (

kW/m

-2.m

m)

Wavelength (mm)

Spectral distribution of sunlight. AM0 and AM1.5 with radiation distribution at 6000K.

6000 K black body

AM0 radiation

AM1.5 radiation

Importance of problem

4

MethodologyMethodologySpray pyrolysis technique (SPT) is a simple and inexpensive chemical deposition method for producing thin filmsSpray pyrolysis technique (SPT) is a simple and inexpensive chemical deposition method for producing thin films

Schematic of spray pyrolysis showing its various partsSchematic of spray pyrolysis showing its various parts

5

Experimental

Precursors Ferric trichloride (FeCl3. 6H2O, M.W= 270.29 g mol-1) (AR grade, 98.8% pure) by s.d. fine-chem limited, Mumbai.

Chloroauric acide (HAuCl4).3H2O, MW = 393.83 gm mol-1) (LR grade, 49.0 % pure) supplied by s.d. fine-chem limited, Mumbai.

Solvent Absolute Ethanol

Deposition temperature 400 0C

Concentration of FeCl3 0.1 M

Doping percentage of gold Varies from 1-4 at %

Spray rate 4 cc/min

6

Undoped 1 at % 2 at % 3 at % 4 at %

Photograph of undoped and Au doped Fe2O3 thin films deposited on glass and FTO substrates

7

A

V

h > Eg The variation of Isc and Voc at different temperatures and Au doping

concentrations

300 350 400 4500

10

20

30

40

50

Substrate Temperature(0C)

I sc(mA

)

60

80

100

120

140

160

180

200

Voc (m

V)

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.520

40

60

80

100

120

140

160

180

Au doping percentage

I sc

(mA

)

180

190

200

210

220

230

240

250

Voc

(mV)

(a) (b)

Results and Discussion

PEC technique

8

X-ray diffraction pattern Au: Fe2O3 thin films on Glass substrates

20 30 40 50 60 70 80

4 at % Au:Fe2O

3

3 at % Au:Fe2O

3

2 at % Au:Fe2O

3

1 at % Au:Fe2O

3Inte

nsi

ty (

A.U

.)

2(Degree)

Undoped Fe2O

3

(10

4)

(11

0)

(00

6)

(02

4)

(11

6)

PDF Card - 01-077-9924

9

SEM of undoped and 2at % Au doped FeSEM of undoped and 2at % Au doped Fe22OO33 thin film deposited thin film deposited

at 400 at 400 ooC substrate temperatureC substrate temperature

a b

10

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.055

0.060

0.065

0.070

0.075

0.080

0.085

0.090

Act

ivat

ion E

ner

gy

(eV)

Au Doping %1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

3

4

5

6

7

8

9

10

11

12

undoped Fe2O

3

1 at% Au:Fe2O

3

2 at% Au:Fe2O

3

3 at% Au:Fe2O

3

4 at% Au:Fe2O

3

ln

1000/T (K-1)

Sr No. Sample name

Activation energy

1 Undoped Fe2O3

0.085

2 1at % Au Fe2O3

0.076

3 2at % Au Fe2O3

0.058

4 3 at % Au Fe2O3

0.085

5 4 at % Au Fe2O3

0.086

kT

Eexp0

11

Transmittance and band gap of Au doped Fe2O3 thin films deposited at various Au doping concentrations

400 600 800 10000

20

40

60

80

100

undoped Fe2O

3

1 at % Au:Fe2O

3

2 at % Au:Fe2O

3

3 at % Au:Fe2O

3

4 at % Au:Fe2O

3

wavelength (nm)

Tra

nsm

ittan

ce (%

)

1.8 2.0 2.2 2.4 2.60

10

20

30

40

50

60

Energy (eV)(a

hv)2

.10

11 (

eV.c

m) 2

Undoped Fe2O

3

1at% Au:Fe2O

3

2at% Au:Fe2O

3

3at% Au:Fe2O

3

4at% Au:Fe2O

3

10 cm

10 c

m

F:SnO2 / glassRs = 5-10 cm-2

t = 1 mm

Photograph of Fluorine doped Tin oxide (FTO) thin films by spray pyrolysis

13

10 cm

Photograph of undoped and 2at % Au doped Fe2O3 thin films by spray pyrolysis

14Photographs of single cell reactor with gasket for circulation of water

Front side view of reactor Closed view of reactor

Back side view of reactor Back side of reactor

15

200 250 300 350 4000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Wavelength nm)

0 20 40 80 160 240 320

Ext

inct

ion (A

.U.)

min

0 5000 10000 15000 20000-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0 by pure Fe2O

3 photoelectrode

by 2at% Au:Fe2O

3 photoelectrode

ln(E

xt/E

xt0)

Time (sec)

k2 at%Au

=7.63x10-5

kPure

=5.00x10-5

Extinction spectra of salicylic acid as a function of time using 2 at % Au:Fe2O3 thin

film under visible light irradiation

Plot of –ln (c/c0) verses illumination time

)6()('"

)5()('

"

)4()('

1

1

13

Mi

kVFkp

scmA

kk

scmkVk

ph

Where, V the volume, A is the area of electrode, p or k″’ the rate constant or kinetic parameter, F is Faraday's constant (96,500 mol−1), and total photocurrent iph,

16

0 3000 6000 9000 12000

0

1

2

3

4

5

6

Electrolyte: 1 mM salicylic acid

in 10 mM HclO4

Flow rate : 12 L/h

Applied reverse bias : 1.5 V vs. steel

Illumination : Visible Light (Tunsten lamp)

Location: Physics, SUK

Photo

curr

ent (m

A)

Time (Sec)

Plot of photocurrent as a function of degradation time for single Au doped Plot of photocurrent as a function of degradation time for single Au doped FeFe22OO33 electrode under sunlight electrode under sunlight

17

Photoelectrochemical degradation of salicylic acid (C6H4(OH)COOH) in single reactor

1) Fe2O3+ h e- + h+ + Fe2O3

At working electrode (Fe2O3)

At counter electrode

1) e- + O2 O2-

2) 2 H+ + O2- H2O

2) e- + h+ heat (recombination)3) h+ + OH- •OH

4) C6H4(OH)COOH + •OH [C6H4(OH)COOH ]*

5) [C6H4(OH)COOH ]* + •OH H2O + CO2

6) HO• + HO• H2O2

7) H2O2+ 2h+ O2 + 2H+

18

Plot of COD and TOC as a function of reaction Plot of COD and TOC as a function of reaction time for single Au doped Fetime for single Au doped Fe22OO33 electrode under electrode under

visible light source visible light source

0 5000 10000 15000 20000

6

8

10

12

14

16

18

20

CODTOC

Reaction time (Sec)

CO

D (m

g/L)

10

15

20

25

30

35

40

TOC

(mg/L)

COD = no. of O2*Concentration *32*1000TOC= no. of C*12*Concentration*1000

19

Parameters and conditions for Salicylic acid degradation by Parameters and conditions for Salicylic acid degradation by FeFe22OO33 based electrode under visible light (tungsten lamp) based electrode under visible light (tungsten lamp)

Electrode Electrolyte Electrolyte volume

(l)

Bias, (V)

Mean photo-current, iph,

(A)

Active area (cm2)

Rate constant

(s-1)

Kineticparameter

(M)

Remaining Time require

d(min)

Undoped Fe2O3 1mM Salicylic acid

10mM HClO4

0.150 1.5 (cell) 0.04 64 5.0 10-5 0.0072 37 % 320

2at % Au Fe2O3

1mM Salicylic acid

10mM HClO4

0.150 1.5 (cell) 0.052 64 7.610-5 0.0084 25 % 320

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Summary and conclusionsonclusions

Phase and structure Hematite, polycrystalline, Rhombohedral

Morphology needle shaped , with grains of size 100-150 nm

Optimized deposition conditions Ts= 400 oCConc = 0.1MQty = 50 mlAu doping = 2at %

Film thickness Varies from 189 to 253 nm

1 mM Salicylic acid degradation in visible light using Au doped Fe2O3 single cell

75 % in 320 min

2 at % Au doped Fe2O3 thin film is the best photoelectrode for removal of salicylic acid

21