The document describes research on photoelectrocatalytic degradation of salicylic acid using sprayed gold doped iron oxide thin films. Gold doped iron oxide films were deposited via spray pyrolysis and characterized. XRD showed the films were polycrystalline hematite. SEM showed needle-shaped grains of 100-150nm. Electrical resistivity decreased with gold doping up to 2%. The 2% gold doped film had the highest photocurrent and degraded 75% of salicylic acid in 320 minutes under visible light irradiation, making it the best photoelectrode developed in the study.

1. Shri Ganeshay Namah
Photoelectrocatalytic Degradation of Salicylic
acid using Sprayed Gold Doped Iron Oxide Thin
Films
by
M.A. Mahadik
under the guidance of
Prof. (Dr.) C.H. Bhosale
Electrochemical Materials Laboratory,
Department of Physics,
Shivaji University,
Kolhapur - 416004

2. Outline of the presentation
Introduction
Experimental
Results and Discussion
PEC
 XRD
 Optical properties
 SEM
 Electrical resistivity measurements
 Photoelectrocatalytic degradation of salicylic acid
Conclusions
2

3. Introduction
Importance of problem
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
-2. µ m
)
Spectral distribution of sunlight. AM0 and AM1.5
with radiation distribution at 6000K.
2.5
6000 K black body
2.0
AM0 radiation
1.5
AM1.5 radiation
1.0
0.5
m
/
W
k
(
o
u
b
t
s
i
D
y
g
r
e
n
E
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Wavelength (µ m)
1.4
1.6
1.8
2.0
3

4. Methodology
Spray pyrolysis technique (SPT) is a simple and inexpensive
chemical deposition method for producing thin films
Schematic of spray pyrolysis showing its various parts
4

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
5

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
6

7. Results and Discussion
A
V
The variation of Isc and Voc at different
temperatures and Au doping
concentrations
hν > Eg
180
240
140
230
120
220
200
160
140
120
20
100
10
80
300
350
400
Subs trate Temperature (0C )
(a)
450
60
100
210
80
200
60
190
40
20
180
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Au doping percentage
(b)
7
V oc (mV)
30
Is c (µ A )
180
40
0
250
160
50
V oc (mV)
Isc (µ A )
PEC technique

8. X-ray diffraction pattern Au: Fe2O3 thin films on Glass substrates
PDF Card - 01-077-9924
Intensity (A.U.)
(116)
(104)
(110)
(006)
(024)
4 at % Au:Fe2O3
3 at % Au:Fe2O3
2 at % Au:Fe2O3
1 at % Au:Fe2O3
Undoped Fe2O3
20
30
40
50
2θ (Degree)
60
70
80
8

9. a
b
SEM of undoped and 2at % Au doped Fe2O3 thin film deposited
at 400 oC substrate temperature
9

10. 12
0.090
 ∆E 
ρ = ρ 0 exp

 kT 
10
ln ρ
9
8
7
undoped Fe2O3
6
1 at% Au:Fe2O3
5
2 at% Au:Fe2O3
4
A ctivation Energy (eV)
11
4 at% Au:Fe2O3
3 at% Au:Fe2O3
3
1.8
0.085
0.080
0.075
0.070
0.065
0.060
0.055
2.0
2.2
2.4
2.6
2.8
3.0
0.0
3.2
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Au Doping %
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 0.085
Fe2O3
5
4 at % Au 0.086
Fe O
10

11. 100
60
80
(eV.cm )
40
1 at % Au:Fe2O3
2 at % Au:Fe2O3
3 at % Au:Fe2O3
20
4 at % Au:Fe2O3
0
400
600
800
wavelength (nm)
1000
11
undoped Fe2O3
2
60
(ahv ) .10
Transmittance (%)
2
50
40
30
20
Undoped Fe2O3
1at% Au:Fe2O3
2at% Au:Fe2O3
3at% Au:Fe2O3
10
0
1.8
4at% Au:Fe2O3
2.0
2.2
2.4
2.6
Energy (eV)
Transmittance and band gap of Au doped Fe2O3 thin
films deposited at various Au doping concentrations
11

12. 10 cm
Photograph of Fluorine doped Tin oxide (FTO) thin films
by spray pyrolysis
F:SnO2 / glass
Rs = 5-10 Ω cm-2
t = 1 µm
10 cm

13. Photograph of undoped and 2at % Au doped Fe2O3 thin
films by spray pyrolysis
10 cm
13

14. Front side view of reactor
Closed view of reactor
Back side view of reactor
Back side of reactor
Photographs of single cell reactor with gasket for circulation of water
14

15. Extinction spectra of salicylic acid as a
function of time using 2 at % Au:Fe2O3 thin
film under visible light irradiation
3.5
2.5
2.0
min
1.5
1.0
0
20
40
80
160
240
320
(4)
(5)
(6)
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,
0.5
0.0
0.0
200
250
300
350
by pure Fe 2O 3 photoelectrode
400
by 2at% Au:Fe 2O 3 photoelectrode
-0.2
Wavelength ( nm )
-0.4
Plot of –ln (c/c0) verses
illumination time
ln ( Ext/Ext )
0
Extinction (A.U.)
3.0
k ' = kV (cm 3 s −1 )
k'
k " = (cm s −1 )
A
kVF
p = k" ' =
( M −1 )
i ph
-0.6
kPure =5.00x10-5
-0.8
k2 at%Au =7.63x10-5
-1.0
-1.2
-1.4
0
5000
10000
Time (sec)
15000
20000
15

16. 6
Ph o to c u rre n t (m A )
5
4
3
Electrolyte: 1 mM s alicylic acid
in 10 mM HclO
2
4
Flow rate : 12 L/h
Applied revers e bias : 1.5 V vs . s teel
1
Illumination : Vis ible Light (Tuns ten lamp)
Location: Phys ics , SUK
0
0
3000
6000
9000
12000
Time (Sec)
Plot of photocurrent as a function of degradation time for single Au doped
Fe2O3 electrode under sunlight
16

17. Photoelectrochemical degradation of salicylic acid (C6H4(OH)COOH) in
single reactor
At working electrode
(Fe 2 O 3 )O + hν ⇒ e- + h+ + Fe O
1) Fe
2
3
2
3
2)
3)
e- + h+ ⇒ heat (recombination)
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+
At counter electrode
1)
e - + O 2 ⇒ O 2-
2)
2 H + + O 2- ⇒ H2O
17

18. 20
40
COD
TOC
18
16
35
30
CO D (mg/L)
25
12
20
10
TO C (mg/L)
14
15
8
10
6
0
5000
10000
15000
20000
Reaction time (Sec)
Plot of COD and TOC as a function of reaction
time for single Au doped Fe2O3 electrode under
visible light source
COD = no. of O2*Concentration *32*1000
TOC= no. of C*12*Concentration*1000
18

19. Parameters and conditions for Salicylic acid degradation by
Fe2O3 based electrode under visible light (tungsten lamp)
Electrode
Electrolyte
Undoped Fe2O3 1mM Salicylic
acid
10mM HClO4
2at % Au
Fe2O3
1mM Salicylic
acid
10mM HClO4
Electrolyte
volume
(l)
Bias,
(V)
Mean photocurrent, iph,
(A)
Active
area
(cm2)
Rate
constant
(s-1)
Kinetic
Remaining
parameter
(M)
Time
require
d
(min)
0.150
1.5 (cell)
0.04
64
5.0 ×10-5
0.0072
37 %
320
0.150
1.5 (cell)
0.052
64
7.6×10-5
0.0084
25 %
320
19

20. Summary and conclusions
Phase and structure
Hematite, polycrystalline,
Rhombohedral
Morphology
needle shaped , with grains of size 100150 nm
Optimized deposition conditions
Ts= 400 oC
Conc = 0.1M
Qty = 50 ml
Au doping = 2at %
Film thickness
∼ Varies from 189 to 253 nm
1 mM Salicylic acid degradation in visible light 75 % in 320 min
using Au doped Fe2O3 single cell
2 at % Au doped Fe2O3 thin film is the best photoelectrode for removal of
salicylic acid
20

21. 21