Petroleum waste as raw materials for production of electricity by Photogalvanic solar cell

Article abstract of DOI:10.1016/j.molstruc.2021.130764

Petroleum industry produces a bulky rate of harmful environmental wastes. Recycling of these wastes to produce added value products is of prim importance. In this work, Synthesis of sodium 4-dodecyl benzene sulfonate (SDBS) anionic surfactant from petroleum waste was done through two steps method. The composition of the produced anionic surfactant was investigated by using FTIR, ¹HNMR, and 13CNMR spectra techniques. Anionic surfactant was applied in photogalvanic cell (PGC) for production of electricity. PGC can be described as an electrochemical cell where the change in both voltage and current arises from the generated photochemical changes in the reactants during the oxidation–reduction reaction in the cell. the recorded electrical cell performance are; maximum power (P_PP) 39.8μW, short circuit current (i_SC)145.2 μA, open circuit potential (V_OC) 490 mV, fill factor (FF) 0.65, conversion efficiency (η) 0.77%, and storage capacity t_0.565 min for system containing Tris (2,2′-bipyrdyl) Ruthenium (II) chloride hexahydrate (TBRC) as photosensitize, Oxalic acid (OX) as reductant, and (SDBS) as anionic surfactant under artificial illumination. The cell performance is optimized and the preliminary mechanism for the solar energy conversion in PGC is also proposed.

Full text of DOI:10.1016/j.molstruc.2021.130764

Journal of Molecular Structure 1243 (2021) 130764
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Petroleum waste as raw materials for production of electricity by
Photogalvanic solar cell
∗
Sawsan A. Mahmoud, A.S. El-Tabei, Samar H. Bendary
Egyptian Petroleum Research Institute. P.O. Box: 11727, Nasr City, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Petroleum industry produces a bulky rate of harmful environmental wastes. Recycling of these wastes to
produce added value products is of prim importance. In this work, Synthesis of sodium 4-dodecyl ben-
zene sulfonate (SDBS) anionic surfactant from petroleum waste was done through two steps method. The
composition of the produced anionic surfactant was investigated by using FTIR, 1HNMR, and 13CNMR
spectra techniques. Anionic surfactant was applied in photogalvanic cell (PGC) for production of elec-
tricity. PGC can be described as an electrochemical cell where the change in both voltage and current
arises from the generated photochemical changes in the reactants during the oxidation–reduction reac-
tion in the cell. the recorded electrical cell performance are; maximum power (PPP) 39.8μW, short circuit
Received 28 December 2020
Revised 15 May 2021
Accepted 22 May 2021
Available online 31 May 2021
Keywords:
Solar energy
Photogalvanic cell
SDBS anionic Surfactant
Conversion efficiency
current (iSC)145.2 μA, open circuit potential (VOC) 490 mV, fill factor (FF) 0.65, conversion efficiency (η)
ꢀ
0
.77%, and storage capacity t0.565 min for system containing Tris (2,2 -bipyrdyl) Ruthenium (II) chloride
hexahydrate (TBRC) as photosensitize, Oxalic acid (OX) as reductant, and (SDBS) as anionic surfactant un-
der artificial illumination. The cell performance is optimized and the preliminary mechanism for the solar
energy conversion in PGC is also proposed.
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
step in which the LAB is produced by the reaction of mono-olefins,
whether both internal and alpha olefins with benzene in the pres-
ence of HF as a catalyst.
The linear efficiency of linear Alkyl benzene (LAB) has been
clearly identified, and it is one of the most widely applied prod-
ucts. LAB is an organic compound with the structural formula
C H CnH (n + 1); n is often 11–12. LAB is almost used entirely
The DETAL process, in which n-paraffins are converted to olefins
by dehydrogenation and subsequent reaction with benzene using a
fixed bed catalyst this is newer technology and has several of the
stages depicted in the HF / n-paraffins process but it is principally
different in the benzene alkylation step, during which a solid-state
catalyst is employed. There is a developing Tran’s alkylation (TA)
stage to the DETAL process in which any higher alkylated benzene
(HAB) is contacted with additional benzene over a Tran’s alkylation
catalyst.
6
5
2
as a feedstock in the production of Linear Alkyl benzene Sulfonate
(
LABS), LAB is primarily produced as an intermediate component in
the production of surfactants for detergent use. LABS have emerged
as the main predominant precursor of biodegradable detergents
since the 1960s. LAB preparation is complex and has a high-cost
production. There are various methods for producing linear alkyl-
benzene as shown in Fig. 1 [1]. n-paraffins are dehydrogenated into
olefins within the HF / n-paraffins process, and hydrogen fluoride
is used as a catalyst during the subsequent reaction with benzene.
This method accounts for the majority of the world’s installed LAB
production. PACOL stage involves the conversion of n-paraffins to
mono-olefins (typically internal mono-olefins) using DEFINE Unit.
The primary purpose of the DEFINE Unit is to transform resid-
ual diolefins into mono-olefins. The productivity and quality of the
LAB is improved by a PEP unit, which is basically an aromatic
removal unit introduced before the alkylation step. An alkylation
Chlorination of n-paraffins into mono–chloro-paraffins followed
by alkylation of benzene using aluminum chloride (AlCl ) catalyst
3
is part of the Friedel-Crafts alkylation process, which one of the
oldest commercial routes to LAB [2].
This paper discusses the linear alkyl benzene extracted from
petroleum waste to obtain surfactants with high surface activity
and applied in solar energy conversion.
Surfactants have great importance in many environmental fields
such as detergents (54%); as associates for textiles, leather and pa-
per (13%); in chemical processes (10%) such as water treatment and
electrical energy production; in cosmetics and medicines (10%); in
the food industry (3%); and agriculture (2%) and as antibacterial
∗
Corresponding author.
[
3].
E-mail address: samar.epri90@gmail.com (S.H. Bendary).
https://doi.org/10.1016/j.molstruc.2021.130764
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 1. DETAL Process for LAB Production.
Fig. 2. SDBS structure.
Critical micelle concentration (CMC) is an important factor af-
fecting the performance of the PGC, which maximizes the out-
put value [4]. PGC considered one of the types of the solar cells
responsible for the conversion of the solar energy as they are a
prominent example of photochemical systems, which consists of
electrodes that are dipped in a mixture of different l solutions
of photosensitive dye, Surfactants, and reductant. The purpose of
adding Surfactant is to increase the solubility and stability of the
dye and consequently improving and stabilizing PGC performance.
PGC through light on the Photoelectric effect, where light has a
strong impact on the electrode potential, due to the occurrence of
a photomechanical process in the greater part of the electrolyte
which occur on the surface of the electrode. Mixing occurs clearly
between the types of solar cells where many believe that the dif-
ference between the photovoltaic cell and the PGC is unnoticeable
but there is a clear difference where the mechanism process in
producing electricity is completely different. The photovoltaic cells
depend on the direct excitation of the electron by the photon to
produce electricity while the PGC rely on photonic molecule exci-
tation that stimulates chemical reactions to deliver products. The
PGC can also split into two groups by using semiconductors as an
electrode.
Adwic, Egypt. TBRC, OX and Sodium hydroxide were provided from
Sigma-Aldrich. Isopropanol was purchase from Bio. Chem. Egypt.
There are also glassware and simple equipment used in the
measurements of the PGC as; platinum electrode (Pt), saturated
calomel electrode (SCE), a digital pH meter (HANNA Model-212),
a microammeter (Extech EX420 Autoranging), a carbon pot as the
resistance variation device were used, H-glass tube and tungsten
lamp200W (Philips) as artificial light source.
2
.2. Synthesis of SDBS
SDBS was synthesized through two steps:
1
Sulfonation of LAB was carried out as follow:
.5 mole of fuming sulfuric acid containing (7–8% sulfur triox-
1
ide) was added drop wise to 1 mole of LAB with vigorous stirring
to avoid foaming. After complete addition, the reaction tempera-
ture is kept at 35–50 °C for 3 hrs. Then the reaction mixture was
cooled to ambient temperature and poured slowly into a separat-
ing funnel containing concentrated HCl mixed with crushed ice.
Then the mixture was shaken for 15 min and linear alkyl benzene
sulphonic acid (LABSA) was extracted from aqueous layer dissolved
with diethyl ether. Ether extracts was then evaporated in a rotary
evaporator. (LABSA) was obtained as a dark brown liquid.
We hereby focus on the synthesis of SDBS from petroleum
waste and characterize through different spectral techniques. The
product is mixed with OX as a reducing agent and TBRC as photo-
sensitizer to improve the conversion efficiency of the PGC.
1 2 Sodium salt formation
Sodium salt of sulfonic acid was prepared by neutralization of
the obtained sulfonic acid of LAB using10% aqueous sodium hy-
droxide with constant stirring. The obtained sodium salt was then
dissolved in isopropyl alcohol, shake, left for 10 min to settle and
get two separate layers. The upper organic layer consists mainly of
surfactant-isopropanol solution while the aqueous inorganic layer
consists of inorganic sulfate and the excess sodium hydroxide. The
2
. Experimental
2
.1. Materials
LAB is a local raw material provided from Al- Amria Petroleum
Refining Company. Sulfuric acid, Hydrochloric acid, Di ethyl ether
2

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 3. (A) PGC parts. (B) Technique of PGC operating mechanism.
−
1
upper layer was taken and the solvent was removed using a rotary
evaporator to obtain the anionic surfactant SDBS Fig. 2.
The appearance of two vibrational bands at 1171.91–1120 cm
confirmed the R-SO2-R/ (Sulfones). A shoulder at 1080–1010 indi-
cate the presence of R-SO H, where R = the aromatic ring. The vi-
3
−1
2
.3. Chemical structure
brational band at 678.94cm is due to C–H out of plane bending
while the band at 1035 is due to C–H in plane bending of ben-
zene ring. The C–H wag of the para-substituted benzene ring falls
The chemical structure of the SDBS was confirmed by FTIR, 1
at 843 and 884 cm 1. The bands at 580 and 678 cm confirm the
−
−1
HNMR, and 13C NMR. FTIR was carried out using ATI Mattson In-
finity series TM (Pine Instrument Company, Grove City, PA), Bench
top 961 controlled by Win First TM V2.01 software. The measure-
ment of 1 HNMR was done in DMSO using BRUKER. 13 CNMR anal-
ysis was carried out using Brucker instrument in DMSO.
stretches of S-O bond.
Fig. 4B shows the 1H NMR (DMSO–d ) spectrum of SDBS. Dif-
6
ferent peaks observed at δ=0.72 ppm (t, 3H, C H CH (CH ) CH C
6
4
2
2
9
2
H ); δ=0.739 ppm (m, 2H, C H CH (CH ) C H CH ); δ=1.116 ppm
3
6
4
2
2
9
2
3
(
m, 18H, C H CH (C H ) CH CH ); δ=1.5 ppm (t, 2H, C H CH C
6
4
2
2
9
2
3
6
4
2
2
.4. Method for preparation PGC
H2 (CH2)9CH3); δ=2.59 ppm (t, 2H, C6H4C H2CH2 (CH2)9CH3);
δ=6.36 ppm (s, 1H, SO H); δ=7.07 (d, 2 H, Ar-H); 7.5 (d, Ar-H).
3
Firstly, H-shaped glass tube was manufactured and darkened
The spectral characteristic indicates that the compound could
be aromatic with aliphatic side chains with sulfonate group de-
picted in Fig. 4C. The presence of signals in the region between
7.65 ppm and 7.12 ppm in the 1H NMR and resonance at 126
and 127 ppm in the 13C NMR confirmed the presence of the
aromatic ring. Moreover, the peak pattern in the 1H NMR spec-
trum corresponds to the protons on the aromatic ring having para-
substitutions. Signals in the region between 2.0 and 0.75 ppm in
1H NMR spectrum and in the range 120–130 in the in the 13C
NMR spectrum. The magnetic resonance at 125.95, 126.61, 127.21,
and 127.32 ppm confirm the presence of 1, 4 di-substituted ben-
zene ring. The presence of 14.5–47.27 ppm confirmed the presence
of the long-chain aliphatic group.
while keeping one side illuminating. Secondly, the tube was filled
with a known concentration mixture of TBRC, OX, and SDBS with
maintaining the total volume of the cell at 25 ml. A fixed distance
between the two electrodes (2 cm) was used in this study. The
2
Pt (area 0.5cm ) and SCE electrodes are placed in the illuminated
side and dark one of H- tube, respectively. The tungsten lamp is
used as a light source with water filter to avoid IR radiation. Fi-
nally, each of the terminals of the electrodes is connected to a dig-
ital pH meter and micro-ammeter through a key and resistance to
measure both the voltage and the current produced by the pho-
toelectric cell. Fig. 3 shows the PGC structure and mechanism of
operation.
3. Results and discussion
3.2. Determination of the voltage-current curve in the PGC
3
.1. FTIR and 1HNMR spectra of SDBS
The results of the voltage and current are recorded by putting
the PGC in the dark while keeping the circuit open until stable po-
tential is achieved. The water filter is placed between the cell and
the lamp to cut off the infrared which could negatively affects the
cell and leads to decrease the performance. Upon illumination, the
photovoltaic voltage (V) and the photocurrent (i) are generated by
the system. After cell charging, the cell parameters such as max-
imum voltage (Vmax), open circuit potential (Voc), maximum cur-
Fig. 4A-C shows the FTIR, 1HNMR, and 13C NMR spectra of
−1
SDBS. Fig. 4A shows characteristic bands observed at 2859.56cm
−1
and 2925.63cm
two alkyl groups. 3382 and 3032 cm
stretches of aromatic ring. The vibrational bands at1409, 1459.78
assigned to the presence of -C-H stretching of
−1
assigned to the =C–H
and 1593 cm 1 confirmed the presence of C–C bonds of aromatic.
−
3

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 4. A-C: FTIR, 1H–NMR and 13CNMR spectra of SDBS.
rent (imax), and equilibrium balance (ieq) or short circuit current
isc) are measured. I-V curve was obtained by registering different
Vpp × Ipp
(
η% =
× 100%
(2)
data of the voltage by changing the resistance value so that the po-
tential current data are obtained until the value of the zero-current
reached. The curve study shows the highest amount by which the
cell can be used. The cell is operated at highest power (i.e., power
at power point Ppp) at corresponding external load to study its
performance by monitoring the change in current and potential
with time. After establishing the I-V curve and recording the result
product the fill factor and conversion efficiency were calculated.
Fill factor is defined as the ratio of the maximum (actual) en-
ergy that can be obtained from solar cells to the theoretical value
Eq (1).
10.4mW cm − 2 × A
where (VPP i.e., potential at power point), (IPP i.e., current at power
point) and (A) is the area of Pt electrode.
The PGC charges were studied in a PGC system and the effects
of different variables were discussed in order to achieve the high-
est conversion efficiency [5-20] as; the variation in the pH values
of the solution, and variation in the concentration of TBRC, SDBS
and OX.
3
.3. Influence of the variation of pH
While conversion efficiency known as the ability to convert the
amount of forthcoming solar radiation to electricity Eq (2). Both
can be expressed as follow:
The effect of the variation of the pH concentration of complex
solution, TBRC–OX and SDBS in PGC has been discussed by fab-
ricating the six PGC. So that the concentrations of TBRC, OX and
SDBS are the same for all cells but the NaOH (i.e. pH) concentra-
tion is different. The pH values were adjusted at 1.1, 1.2, 1.4, 7.0,
Vpp × Ipp
FF =
(1)
Voc × Jsc
4

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 5. a and b: I-V curve (a) and the variation of the potential and current with pH (b).
Table 1
Table 2
Influence of the variation of pH on the performance of PGC.
Influence of the variation of SDBS surfactant concentration on the electrical out-
put.
pH
SDBS × [10 − M]
3
Parameters
1.1
1.2
1.4
7
8
12
Parameters
1
1.5
2
2.5
3
5
Photo potential (mV)
470
490
430
347
250
45.5
5.1
180
33.1
2.4
Photocurrent (μA)
126.1
32.5
0.55
0.62
145.2
39.8
0.56
0.77
118.7
27.1
0.53
0.52
65.0
10.4
0.46
0.21
Photo potential (mV)
380
400
450
490
460
340
Ppp (μW)
Photocurrent (μA)
93.1
18.1
0.51
0.35
105.2
21.8
0.52
0.42
120.7
29.3
0.54
0.56
145.2
39.8
0.56
0.77
134.5
34.1
0.55
0.65
82.1
13.8
0.47
0.27
FF
0.44
0.10
0.40
0.05
Ppp (μW)
ŋ%
FF
ŋ%
–3
–3
−4
M; Pt
[
SDBS] = 2.5 × 10 M; [OX] = 1.9 × 10 M; [TBRC] = 4.1 × 10
2
–2
[TBRC] = 4.1 × 10 M; [OX] = 1.9 × 10 M; pH 1.2; Pt electrode area 0.5cm2,
−4
–3
electrode area 0.5cm , light intensity = 10ꢀ4 mW cm
.
–2
light intensity = 10ꢀ4 mW cm
.
8
.0, and 12.0. The results are depicted in Table 1 and Fig. 5a &b
which show the I-V curve and the variation of the potential and
current with pH. The PGC showed a maximum potential of 470,
dye-surfactant system indicating the tunneling of photoelectron
from micellar to aqueous phase. Whereas Bhowmik et al., [23] and
Mukhopadhyay and Bhowmik [24] observed a photoinduced trans-
fer of electron between micelles and dye during a charge trans-
fer interaction. The electron photo-ejection from dye-surfactant de-
pends on the micelle charge. The results of these methods for dye-
surfactant interaction supposed that the opposite charged dye and
surfactants are the strongest interaction while the same charged
have zero interaction. In this system, the opposite charged SDBS
and TBRC have stronger electrostatic force of attraction which
dominant over the electrostatic repulsive force of same charged of
individual TBRC / SDBS molecules. Table 2 and Fig. 6a &b show I-V
curve and Variation of the SDBS concentration. It shows that the
4
90, and 430 mV in the acidic pH values of 1.1, 1.2, and 1.4, re-
spectively. . In acidic medium at pH =1.2 the highest values of
Voc = 490 mV, isc=145.2 μA, (FF=0.56), and η =0.77%. On the
other hand, at pH1.4 the PGC produce the lowest Voc and isc as
it recorded 430 mV and 118.7 μA. This is due to the degradation
of the dye molecules in very strong acidic environment and inef-
ficient light harvesting [21]. On the other hand, in alkaline media
the lowest Voc of 180 mV was recorded due to the combination
−
of OH (from the NaOH used in this system) with the cationic
reductant (formed upon electron donation from the reductant to
the dye), and inhibits the regeneration of the reactive species in
its original form and leading to poor performance of the cell.
−
3
maximum cell output as VOC, iSC, FF and η using 2.5 × 10 M of
surfactant and any increase or decrease after that leads to signifi-
cant decrease in cell performance.
3
.4. Influence of the variation of SDBS concentration
By applying a low concentration there are a limited number
of surfactant molecules available to transfer the electron and de-
crease solubility of the TBRC. On the other hand, High concentra-
tion of the surfactant molecules impedes the movement of the dye
molecules to the electrode thus results in a decrease in the output
energy. Moreover, the formation of rod-like micelles, which leads
to an increase in viscosity and also decrease in the cell’s output
[25].
Previous studies were conducted on PGCs in presence/absence
of the surfactant in solution. The results show that the cell con-
taining SDBS recorded the highest results compared to others, due
to the improvement the solubility of the dye, increase the stability
in the solution, and increases life time of the excited state of dye
molecule. These could lead to increase in the output energy and
consequently increased the η., SDBS also enhances η by suppress-
ing the thermal back electron transfer and promoting the processes
of electron transfer to photosensitizer, and in turn to Pt electrode.
As mentioned previously, CMC point is a major factor in de-
termining the cell performance, as the maximum conversion effi-
ciency is recorded around CMC also the photo-ejection of electron
from surfactant depends on charge of micelle [4]. The negative po-
tential in an anionic micelle’s aggregation promotes the ejection
of electron and thus increases the performance of the PGC. Alka-
litis et al., [22] has observed the photo-ejection of electron from
3.5. Influence of the variation of TBRC concentration
In recent years, there has been a remarkable growth and eval-
uation in the field of harmonization and organometallic chemistry
of Ruthenium complex. Photocells based on [Ru(bipy) 2 , have sev-
+
3
eral advantages over some of the better known PGC systems such
as; (i) favorable photoelectrochemical properties, (ii) The oxidation
and reduction properties appropriate to the state of metal to ligand
5

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 6. a and b: I-V curve (a) and Variation of Potential and Current with SDBS concentration (b).
Table 3
Influence of the variation of TBRC photosensitizer concentration on the electrical output.
TBRC[M]
–3
–4
–4
–4
4.6 × 10 −4
Parameter
4.1 × 10
3 × 10
3.5 × 10
4.1 × 10
photo potential (mV)
380
410
475
490
460
Photocurrent (μA)
80.3
30.5
0.48
0.29
101.7
21.7
0.52
0.42
137.8
36.00
0.55
0.70
145.2
39.8
0.56
0.77
119.5
29.67
0.54
0.56
Ppp (μW)
FF
ŋ%
–
3
–3
2
[
SDBS] = 2.5 × 10 M; [OX] = 1.9 × 10 M; pH 1.2; Pt electrode area 0.5cm ; light inten-
sity = 10ꢀ4 mW cm–2.
charge transfer (MLCT), (iii) their relatively long-life time. Ru" tris-
shows the UV spectra for different concentrations of TBRC and it
ꢀ
2+
−4
2
,2 -bipyridyl complex, Ru(bipy)3 , absorbs light in the visible re-
confirmed that the concentration at 4.1 × 10
M recorded the
gion at about 350 nm to yield a set of metal-ligand charge-transfer
highest visible light absorption. At low concentration of the TBRC,
there is a restricted number of Photosensitizer atoms expected to
absorb photons and give provide an electron to the Pt electrode
in the cell so, there is a decrease in the cell’s output while high
concentration of TBRC (i) doesn’t allow the ideal light intensity to
arrive at the particles close to the electrodes and thus, there was
a fall in the power of the cell; (ii) due to the high concentration
there are short lived excited dye states therefore, an excited dye
molecule must reach Pt within its short life for electron donation.
Only those dye molecules that exist and absorb photons near Pt
have greater chance for electron donation to Pt electrode; (iii) on
the other hand, an increased concentration of the dye under op-
erating conditions may also lead to an acceleration of recombina-
tion between the injected electrons and dye molecules causes a fall
down in the output current and voltage and thus a decrease in the
η occurs.
∗
2+
excited states denoted Ru(bipy)3 , equation (3). These species
are strong reducing agents, deliver an electron to the oxidiz-
ing substrates and generating RuIII tris-2,2 -bipyridyl, Ru(bipy)3
ꢀ
3+
,
equation (4). The latter, being a relatively strong oxidizing agent
and may be reduced to ground state Ru- (bipy)32 , equation (5).
The three equations constitute a photodriven cycle, which may
be possible to exploit within schemes for the photochemical cleav-
age of water and conversion of solar energy into electrical energy
within a PGC [26,27].
+
The observed VOC depends upon the incident light intensity and
on the surfactant used in the cell and under typical conditions po-
tentials of 380 to 490 mV have been observed. The long-term sta-
bility of the system is relatively good since only approximately 20
percent of the ruthenium complex is degraded after 6 days on a
cycle of exposure of the cell to a 500 W tungsten lamp for 10 s/min
[
28].
Table 3 and Fig. 7a and b show I-V curve and Variation of pho-
3
.6. Influence of the variation of the OX reductant concentration
topotential and photocurrent with TBRC concentration. the maxi-
mum cell outputs from of photovoltaic power, photoelectric cur-
rent, power at the power point, FF and η were obtained at con-
centration of 4.1 × 10 M TBRC and the change in concentration
by increasing/decreasing. The decrease in the concentration after
that leads to a significant reduce in the cell performance. Fig. 8
The reducing agent plays an active role in the basic principle of
PGC. TBRC in the presence of the OX reductant shows high VOC and
iSC, indicating its electro-active nature and the electron exchange
between dye and OX molecules. This confirms the formation of
the reduced and oxidized states of OX. This fact is supported by
−4
6

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Fig. 7. a and b: I-V curve (a) and Variation of photopotential and photocurrent with TBRC concentration (b).
Different concentration of the OX was discussed in Table 4 and
Fig. 9a and b show J-V curve and Variation of the OX concentra-
tion, the result show that the electrical output of the PGC was
increase to the maximum and optimum value; thereafter, it was
found to decrease. The optimum cell performance was observed at
−3
1
.9 × 10 M concentration of the OX reductant. The electrical out-
put is low at a lower concentration range of the OX reductant be-
cause there are fewer molecules to donate electrons to the excited
molecules of the TBRC photo-sensitizer while a higher concentra-
tion of the OX reductant may hinder the movement of the TBRC
molecules towards the electrodes in the desired time limit and
may also promote back electron transfer from the TBRC molecules
to the OX reductant molecules [32]. The hydrolysis of OX occurs in
two steps as follows:
−
+
H2C2O4 → H C2O4 + H ; pKa = 1.27
Fig. 8. Fig. 8: UV–vis absorption spectra of different concentrations of TBRC.
−
−2
+
H C2O4 → O4
C2 + H ; pKa = 4.27
The two acid dissociation constants, pKa1
=
1.2 and
published literature. In an illuminated region of the cell a pho-
ton excites an electron from the ground state orbital (HOMO) to a
higher energy orbital (LUMO) (i.e., the excited singlet state, which
collapses to the excited triplet state through inter-system crossing
pKa2 = 4.2,38 suggest that all three forms of oxalate are present
−
−2
in solution. The formed fragments H C O4, HC O , and C O
4
2
2
2
4
2
−
are known to be e aq and OH, scavengers [33-36]
−
The formed HC O4 could be mineralized and form CO2 and
2
(
ISC)) of TBRC photosensitizer. The formation of the excited state
−
H O which cause
2
a
fall in electrical output. HC O
4
+
½
2
forms a vacancy in the ground state that can be filled by an elec-
tron donor such as OX reductant because the redox potential of the
excited TBRC state is higher than that of the OX reductant. The net
result is that an excess electron is produced in the higher energy
state of the TBRC molecule. The excited state of dye molecule can-
not hold this excess electron for long therefore; this electron can
be donated to an electron exchanger (Pt electrode). The electrons
from the Pt electrode (high potential) flow through the external
circuit to SCE (low potential) produce electric current [29]. At SCE,
the TBRC molecules in solution accept electrons because the redox
potential of the ground state of dye is higher than that of SCE. In
this way, the PGC enables solar energy conversion into solar power
+
O2 + H → 2CO2 + H O
2
Also, upon irradiation there are series of reaction which could
+
be occurred and affect the electrical output as follows H O → H
2
−
.
+
OH
HC2O4 + .−OH → HC2O4.− + −OH
−
In the presence of oxygen, this radical intermediate undergoes
bond cleavage and electron migration leading to the formation of
−
CO2 and a more stable carboxyl radical, CO2
(
dc current) with inherent storage capacity. The current carrier in
HC2O4.- → CO2+CO2−
the electrolyte is the diffusion-controlled ions. Ideally, the PGC sys-
tem acts as a (cyclic) light-driven electricity generator [30, 31]. The
photoinduced electron transfer from SDBS to TBRC photosensitizer
through a charge transfer (CT) interaction enhances the processes
of electron transfer to photosensitize.
Another reaction could be occurred in the solution,
−
+
HC2O4 + ½ O2 + H → 2CO2 + H2O
7

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Table 4
Influence of the variation in OX concentration on the electrical output of the cell.
OX concentration[M]
–3
–3
–3
–3
–3
Parameter
1 × 10
1.3 × 10
1.9 × 10
2.4 × 10
4 × 10
photo potential (mV)
360
440
490
410
306
Photocurrent (μA)
78.9
13.5
0.47
0.26
133.7
31.8
0.54
0.61
145.2
39.8
0.56
0.77
119.2
25.4
0.52
0.49
53.2
7.16
0.44
0.17
Ppp (μW)
FF
ŋ%
–
3
–4
2
[
SDBS] = 2.5 × 10 M; [TBRC] = 4.1 × 10 M, pH 1.2; Pt electrode area 0.5cm ; light inten-
–2
sity = 10ꢀ4 mW cm
.
Fig. 9. a and b: I-V curve (a) and Variation of Potential and Current with OX Concentration (b).
Fig. 10. Variation of the potential and power with the I–V characteristics of the cell. (1) Potential vs. current (2) Power vs. current.
4
. (I–V) characteristics of the cell
in the circuit was applied. After studying a series of variables on
the PGC, the highest outputs were reached for PGC containing
−
4
−3
−3
The Voc and isc of all these systems were measured with the
(4.1 × 10 M of TBRC, 2.5 × 10 M of SDBS, 1.9 × 10 M of OX
2
help of a digital pH meter (keeping the other circuit open) and
a microammeter (keeping the other circuit closed), respectively.
The electrical parameters in between these two extreme values
at pH 1.2, Pt electrode area 0.5cm and light intensity=10.4 mW
cm–2. Fig. 10 shows I-V curve and the power point (a point on the
curve where the output voltage and current are at a maximum)
was determined and FF, η were calculated by Eq (1) & Eq (2) as
indicated earlier. These data are summarized in Table 5.
(Voc and isc) were determined with the help of a carbon pot (log
470 K) connected in the circuit, through which an external load
8

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
Table 5
Output parameters of PGC.
–
3
–3
PGC system
Paramete
TBRC Conc., 4.1 × 10 , SDBS Conc., 2.5 × 10 , OX conc., 1.9 × 10–3,
2
–2
pH 1.2, Pt electrode area 0.5cm & light intensity =10.4 m cm
photo potential (mV)
Photocurrent (μA)
Ppp (μW)
FF
ŋ%
4
90
145.2
39.8
0.56
0.77
Fig. 11. Storage capacity of the cell (retrieval of the stored power in dark from the cell).
Fig. 12. Stability test of PGC at different time.
9

S.A. Mahmoud, A.S. El-Tabei and S.H. Bendary
Journal of Molecular Structure 1243 (2021) 130764
5. Storage capacity of PGC
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Declaration of Competing Interest
Authors declare that they have no conflict of interest.
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