The photogalvanic effect involve the excitation of a molecule by

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‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
Generation of Photocurrent using Rhodamine B
Dye and visible Light
Hassan A. Habeb
Saja S. Jabbar Al-Taweel
Nabeel A. Abed –Al-rudha
College of Education?
College of Scienc
College of Education
University o f Al- Qadisiya
(NJC)
(Receivedon
29/5/2007)
(Accepted for publication on 22/8 /2007)
Abstract
The photo galvanic effect was studied in a system of photogalvanic cell, containing
rhodamine B as photosensitizer, EDTA as reductant, and sodium lauryl sulphate as surfactant.
The electrical outputs of this cell were 210 mV and 70μA respectively. The storage capacity
of the cell was 20 min in dark after 55 min of illumination. The effect of different parameters
on electrical output of this system were studied such as; pH, temperature, light intensity,
concentration of dye, concentration of EDTA, and concentration of NaLS. Also, a mechanism
of generation of photocurrent in this cell has been proposed.
‫الخالصة‬
‫ليم م م م م ممة ليا يم م م م م ممة و م م م م م ممب ة‬
EDTA ‫ال ليم م‬
‫ممام‬
‫م م م م م مماث ي تم م م م م ممو‬
‫اام ممةن رك مما‬
‫ مماي رو ممبةمر لم‬70‫ولت و‬
‫مممممم‬
‫ال م م م م م ممو‬
‫وا يةل ممةن ي مما‬
‫ممو‬
‫تم م م م م ممث د ارسم م م م م ممة التم م م م م ممليةر الكليم م م م م مما‬
‫مت س ممو‬
Rhodamine.B(RB)‫الم مرودامةن‬
.‫ مر ب عال سط يا‬NaLS ‫عامل م تزل و بريتات لوريل ال ودةوث‬
‫ مل‬210 ‫لهذه ال لية ا ا‬
‫تمت د ارسمة بعم‬.‫ دقيقمة‬55 ‫ال ممث بعمد شم ن ال ليمة لممد‬
‫باسممت داث هممذه ال ليممة وشممملت تممليةر الدالممة ال ام ممية ودرجممة‬
‫والتيار ال و‬
‫وجد إن الجهد ال و‬
‫ دقيقة‬20 ‫إن سعة ال زن لهذه ال لية ه‬. ‫التوال‬
‫يمماء تولةممد التيممار ال ممو‬
‫العوامممل الم م ير ل م‬
‫تث و ممع يليممة ا ت ار ممية‬. ‫ لم الت موال‬NaLS‫ و‬EDTA ‫ال مرار وشممد ال مموء السمماقك تر ةممز ممل مممن ال ممب ة و‬
.‫هذه ال لية‬
474
‫لعملية تولةد التيار ال و‬
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
The photogalvanic effect of photoredox
Introduction
The generation of electrical energy by
couples have also investigated by many
conversion and storage of solar radiation
workers all over the world, for instance
has a good attention from chemist and
Potter and Thaller
, Kaneko and Yamada
11)
, Aliwi et al
energy is one from many renewable
of
energy
especially
, Ikawa and Yamase
(6)
physician scientists. The utility of solar
sources
(4)
(12)
(7)
, Ameta et al (8-
Gangotri et al
(13-14)
Meena et al.(15) ,and Genwa and Chouhan
in
(16)
photogalvanic cells, so the photogalvanic
. In all works, the conversion efficiency
cells are worthwhile source of energy and
of these cells are quite low (0.03-0.1%) (11)
have future applications and uses. The
which due to the fast back electron transfer
photogalvanic
the
and other deactivated physical processes
excitation of a molecule by photon and a
beside the special phenomenon of dyes
chemical reaction occurs to yielding new
such as lower stability of absorbers and
chemicals (high-energy products) which
aggregates of dye molecule around the
save the chemical energy.
electrodes. Recently, an attention has been
effect
involves
paid
The photogalvanic effect was first
reported by Rideal and Williams
(1)
to
use
photosensitizers
but
of
systems
(dyes
&
containing
complexes),
first
reductants (EDTA, ascorbic acid, etc) and
photogalvanic cell in 1940 at USA by
micelles (surfactants) for improved the
using thionine –Fe+2 system which serve as
solar energy conversion and storage (17-19).
(2,3)
Rabinowitch
made
the
and
The present work aims to study the
conversion the energy to Fe+2 ions and the
rhodamine B-EDTA-NaLS system in a
results of this cell were 1.09 V and 1.73
photogalvanic cell for conversion and
μA
mW/cm2).
storage of solar energy. The effect of dye
first observed in 1839 the
concentration, pH, temperature, incident
generation and flow of current between
light intensity, EDTA concentration, and
unsymmetrical
NaLS concentration have been studied.
absorber
of
under
Becquerel
incident
sun
(4,5)
light
photons
(70
illuminated
metal
electrodes in sun light
kept in amber-coloured containers for
Methodology
Rhodamine B dye (RB) (Figure
protect it from sun light
(16)
. A mixture of
(1)), EDTA, sodium hydroxide supplied by
dye solution and other additives were taken
Aldrich. Sodium lauryl sulphate (NaLS)
in an H-shaped glass tube of capacity 50
and citrate buffer were supplied by Fluka
cm3 (11). Two platinum electrodes (1x1cm)
AG. All the chemicals were used without
were
further purification and all the solutions
electrodes. The wholly cell was placed in
were prepared in doubly distilled water and
a
475
used
as
thermostat
illuminated
water
path
and
dark
(HAAKE
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
(20)
circulator) .The whole system was first
described by Haatchard
. Cintra-5 GBC
placed in dark till a stable potential was
Scientific equipment spectrophotometer
obtained, then the one arm of the cell was
was used to recording the UV-visible
exposed to a 200W tungsten lamp and the
spectra of dye in wavelength range
The
between 300 –800 nm by using 1 cm path
photopotentials were measured by a digital
length quartz cell. In all experiments the
multimeter
were
cell was irradiated with tungsten lamp for
measured by digital pH meter (PW 9420
55 minutes by variation of pH, light
pH
intensity,
other one was kept in dark
meter).
and
(15)
.
photocurrents
The
two
half-cell
were
concentration
of
dye,
separated by a sintered glass disc. The
concentration of EDTA, concentration of
electrodes were pretreated by immersed
NaLS, and temperature.
them in dilute hydrochloric acid solution
for 1 h (12) .The incident light intensity was
measured actinometrically by the method
COOH
ClN
O
N
Figure (1): The chemical structure of Rhodamine B
The
electrical
output
of
Results and Discussion
The spectrum of rhodamine B dye
photogalvanic cells is affected by several
locates in the visible range with λmax
factors involves effect of pH, temperature,
545nm
and
and
high
coefficient ε (1.9x10
molar
4
absorption
-1
-1
l.mol cm ). The
light
intensity,
concentration
of
reductant, concentration of surfactant, and
rhodamine B dye shows a good stability on
concentration
irradiation with tungsten lamp as shown in
efficiency of present cell was examined by
Figure (2). From these data, the use of this
following the variation of photopotential
dye as photosensitizer in performance of
and photocurrent with time. Figure (3)
photogalvanic cell is worthwhile.
illustrate the variation of electrical output
of
photosensitizer.
with irradiation time.
476
The
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
It is seen that electrical output of
From the obtained results Figure (7), it
present photogalvanic cell is found to
seen
that
a
linear
relation
increase as the pH increases. It is observed
electrical output and temperature. But the
from Figure (4) that the photopotential and
photocurrent
photocurrent reach the maximum value at
photopotential decreases. This attributed to
pH=10, and then decreases on further
decreased in internal resistance of the cell
increase in pH. It is clear that this
at higher temperature (16).
increases
between
and
the
photogalvanic cell is sensitive to the pH
The dependence of electrical output
variation. Generally the pH of optimum
on variation of dye concentration has been
condition for reductant has a relation with
studied. It is seen from Figure (8) that
its pKa and the best pH is higher than pKa
lower concentrations of rhodamine B dye
(15, 16)
causes a decreases of photopotential and
.
The electrical output of present
photocurrent due to lowering of dye
photogalvanic cell also affected by the
molecule in the excited stat and donate the
change of concentration of reductant
electrons to electrode, and the greater
EDTA. Figure (5) shows that at lower
concentration
concentration of EDTA causes decreasing
decreasing in electrical output because the
in photopotential and photocurrent as a
high number of dye molecule are form an
result of decreasing of available reducing
inner filter and does not permit the photons
agent molecule for donating the electrons
to reaching the other dye molecules near
for oxidized dye molecules. While, in
the electrode. (15,16,21)
higher concentration also a decreasing in
of
dye
also
causes
a
Different intensities of light were
electrical out pout occur which attribute to
used
to
deduce
hindering the dye molecules from reaching
photogalvanic cell. It is observed from
the electrode surface by high number of
Figure
EDTA molecules (15).
photocurrent on increase of light intensity,
(9)
the
this
linear
on
output
increasing
of
of
Figure (6) illustrates that electrical
while the increasing of photopotential is
output of this cell increases when the
not linearly one. Generally the increasing
concentration
is
of light intensity causes an increasing in
increasing until reaching the optimum
number of photons that collide with
concentration, but on further increasing the
photosensitizer
photopotential
electrode and hence causes an increasing in
of
surfactant
and
NaLS
photocurrent
are
decreasing.
The
temperature
electrical
effect
on
of
variation
of
photopotential,
photocurrent and power has been studied.
477
molecule
output
besides
values
(16,
the
21)
.
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
Figure (2): Electroinc spectra of rhodamine B (1 x 10-4 M)
250
photocurrent
photopotential
200
150
100
mV
50
µA
0
0
25
50
75
100
Time(min)
Figure (3): Effect of variation of irradiation time [RB] = 0.00005M, [NaLS] = 0.006 M,
[EDTA] = 0.0075M, pH=9, light intensity =10.5µW/cm2, Temp=298K.
478
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
photocurrent
photopotential
225
mV
150
75
µA
0
10-3M
0
5
10
15
pH
Figure (4): Effect of variation of pH. [RB]=.00005M, [EDTA] =0.0075M, [NaLS] =0.006M,
Light intensity=10.5µW/cm2, Temp=298K.
photocurrent
photopotential
250
200
150
100
mV
50
µA
0
0
1
2
3
4
[EDTA] x 0.001M
Figure (5): Effect of variation of EDTA. Concentration. [RB]=0.00005M, [NaLS] =0.006 M,
pH=9, Light intensity=10.5µW/cm2, Temp=298K.
479
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, Volume 27 ,474-482
photocurrent
photopotential
250
mV
200
150
µA
100
50
0
0
5
10
103M
[NaLS] x 0.001M
10-4M
Figure (6): Effect of variation of NaLS concentration. [RB]=0.00005M, [EDTA] =0.00275
M, Light intensity=10.5µW/cm2, pH=9, Temp=298k.
photocurrent
photopotential
250
200
mV
150
100
µA
50
0
290
300
310
320
Temperature (K)
Figure (7): Effect of variation of temperature. [RB]=0.00005M, [NaLS] =0.006M,
[EDTA] =0.0075M, pH=9, light intensity=10.5µW/cm2.
480
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
National Journal of Chemistry,2007, 27 ,474-482
Volume
photocurrent
photopotential
250
200
mV
150
100
µA
50
0
0
0.2
0.4
0.6
0.8
[RB] x 0.0001M
Figure (8): Effect of variation of dye concentration. [NaLS]= 0.006 M, [EDTA] =
0.00275M, pH= 9, light intensity= 10.5µW/cm2, Temp= 298K.
photocurrent
photopotential
400
mV
300
200
µA
100
0
0
10
20
30
light intensity(µW/cm )
Figure (9): Effect of variation of light intensity. [RB]= 0.00005M, [NaLS] = 0.006M,
[EDTA] = 0.00275M, pH =9, Temp=298k.
481
National Journal of Chemistry,2007, 27 ,474-482
‫المجلد السابع والعشرون‬-2007-‫المجلة القطرية للكيمياء‬
Volume
Energy
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482