Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
204
Prediction of H
2
O
2
Electrogeneration on a RVC Cathode in
a Parallel-Plate Cell for Treatment of Industrial Effluents
Yaneth Bustos-Terrones
1
, Jesús Gabriel Rangel-Peraza
2
, Antonio Sanhouse
1
, Ma. Neftalí Rojas-Valencia
3
, Alberto
Álvarez-Gallegos
4
1- División de Estudios de Posgrado e Investigación Ingeniería Ambiental. Instituto Tecnológico de Culiacán. Av. Juan de Dios
Batís 310. Col. Guadalupe, 80220. Culiacán, Sinaloa, México.
2- División de Estudios de Posgrado e Investigación Ingeniería Ambiental. Instituto Tecnológico de Culiacán. Av. Juan de Dios
Batís 310. Col. Guadalupe, 80220. Culiacán, Sinaloa, México.
3- Universidad Nacional Autónoma de México, Instituto de Ingeniería, Coordinación de Ingeniería Ambiental, México D.F.
4-
Centro de Investigación en Ingeniería y Ciencias Aplicadas (CIICAp).Universidad Autónoma del Estado de Morelos (UAEM).
Av. Universidad 1001. Col. Chamilpa, 62209. Cuernavaca, Morelos, México.
Received: 11/10/2015 Accepted: 09/11/2015 Published: 30/12/2015
Abstract
A parallel-plate cell was built to electrochemically generate H
2
O
2
using two sizes of reticulated vitreous carbon (RVC) as
cathode and stainless steel mesh as anode. It was possible to predict H
2
O
2
electroproduction on a RVC cathode in a parallel-plate
cell according to Faraday’s law. Two RVC cathode lengths were evaluated. For the small RVC cathode (1.25 x 5 x 1cm)
different current values were evaluated. From this experimental setup, the optimal current obtained was 80 mA achieving H
2
O
2
production efficiency of 81%. Experimental results were compared with theoretical results and it was found that the model fitted
the experimental results fairly well (variation 0.5%). For the large RVC cathode (2.5 x 5 x 1cm), another set of different current
values was evaluated. From this experiment, the optimal current was determined to be 170 mA with an H
2
O
2
production
efficiency of 54%. These experimental results were also compared with theoretical results generating also a fairly good fit
between them (variation 1.5%). Finally, using the large RVC cathode the removal of the dye BB9 (0.08 mM) was evaluated, 94%
discoloration was achieved after 15 min of electrolysis and 90% of COD was achieved after 60 min.
Key words: Prediction, H
2
O
2
production, parallel-plate cell, RVC design, BB9.
1 Introduction
1
The wastewater from the textile industry is
characterized by the high amount and persistence of its
contaminants. Textile industries generate effluents which
are characterized by strong color, high COD and wide pH
variation. When color is due to the presence of reactive
dyes, it is an environmental problem because reactive dyes
are usually difficult to biodegrade and they can remain in
the environment for an extended period of time [1-3].
Electrochemical treatments are among of the most
important oxidation processes because of their versatility,
environmental compatibility and effectiveness in degrading
different organic pollutants [4]. One of the methods used
for treating industrial effluents containing organic
pollutants, especially dyes used in the textile sector, is by
using H
2
O
2
as oxidizing agent [5-8].
Corresponding author: Yaneth Bustos-Terrones. División
de Estudios de Posgrado e Investigación. Instituto
Tecnológico de Culiacán. Culiacán, Sinaloa, México. E-
Mail: yabustoste@conacyt.mx, Tel.: +556677133804
Ext.1303.
Hydrogen peroxide is considered to be an
environmentally friendly chemical; since it leaves no
hazardous residues as other oxidants do [9-14]. It is a
powerful and versatile chemical, since it reacts both as
reducer and as oxidant. It is effective throughout the pH
range, has high oxidation potential and, being a liquid, is
easier to use [3,15-17]. For all these properties, H
2
O
2
is
used in a large number of applications, such as in pulp,
paper and textile bleaching, chemical synthesis, metallurgy,
electronic industry, water disinfection and detoxification of
industrial effluents [18-22]. It has been reported that H
2
O
2
can be electrochemically generated by reducing dissolved
oxygen in acidic solutions [9,14]. The generated H
2
O
2
can
be coupled with Fe
2+
to produce Fenton’s reagent for either
degradation or synthesis of organic compounds [23-25].
Electroproduction of Fenton reagent involves two
electrode processes, resulting in hydrogen peroxide
production at the cathode and evolution of oxygen at the
anode [21]. Reticulated vitreous carbon (RVC), carbon,
graphite felt or gas diffusion electrodes are used in H
2
O
2
electrogeneration process [26]. These electrodes have been
used in a variety of applications ranging from fuel cells to
Journal web link: http://www.jett.dormaj.com
J. Environ. Treat. Tech.
ISSN: 2309-1185
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
205
water and wastewater treatment and several studies focused
on the carbon layer structure and the addition of catalyst to
favor a particular reaction have been conducted [12]. RVC
is a useful electrode material, particularly where high
current densities, low electrical/fluid flow resistance,
minimal cell volume loss to electrodes and large capacity to
hold infused materials within controlled pore sizes are
required. RVC has low density, low thermal expansion,
high corrosion resistance and high thermal and electrical
conductivities. It is an open-pore foamy material of
honeycomb structure composed solely of vitreous carbon
with exceptionally high void volume, high surface area,
rigid structure and very high resistance to temperatures in
non-oxidizing environments [13]. The skeletal structure of
the material is brittle and needs support and its low
volumetric carbon content means that care has to be taken
to ensure uniform potential and current distribution through
the material. For all these characteristics, RVC has been
considered a good cathode material in H
2
O
2
electrochemical generation [14]. This electrochemical
technique leads to the chemical degradation of organic
pollutants. The huge production rate of synthetic dyes and
their intensive usage in the textile and other industries
generates large quantities of colored wastewaters [27-28].
In this study, simulated and experimental H
2
O
2
generation was conducted using a RVC cathode in a
parallel-plate cell to estimate the H
2
O
2
concentration
achieved. Influential parameters such as cathodic potential,
oxygen purity and mass flow rates, cathode surface area,
pH of the solution and inert supporting electrolyte
concentration were systematically examined during the
experimental procedures and contrasted against the
simulation results. Moreover, the performance of a parallel
plate electrochemical cell that can activate H
2
O
2
to oxidize
organic molecules in toxic industrial effluents was also
determined in this study. A series of tests were conducted
in order to evaluate the oxidation of organic dye BB9.
2 Materials and Methods
2.1 Electrochemical modeling
The electrochemical model used is mainly based on the
hypothesis that the electrochemical cell always works in
steady state and that the main electrochemical oxidation
and reduction reactions are those depicted in Eq. (1) and
(2). Electrochemical reactions (shown in Figure 1) were
used to develop the model considering the following
conditions: 1) the potential difference applied corresponds
to the limiting current observed; and 2) the electrochemical
reactions selected are the only ones that occur, therefore,
the most important electrochemical transformation can be
evaluated by Faraday’s law [7-9].
222
22 OHeHO
(1)
OH2e4H4O
22
(2)
2.2 Electrochemical experimental setup
Electrolysis were carried out using a potentiostat
(AMEL 2051) coupled to a programmable function
generator connected to the electrochemical cell. The
electrochemical cell, also known as electrochemical cell,
reproduces a parallel-plate cell model. This type of reactor
is the most common in the industry because of its numerous
advantages such as: easy construction and assembly,
variety of fabrication materials, uniform potential
distribution, ease of operation, scaling up potential,
different electrode configurations, simple electrical
connections, and mass transport control [19]. The hydraulic
circuit and the flow-cell of the reactor used are very similar
to that showed elsewhere [21], see Figure 2.
Figure 1: Main electrochemical reactions carried out in the electrochemical
cell. Anolyte: 1L 0.8 M H
2
SO
4
and Catholyte: 1L 0.05 M Na
2
SO
4
at pH≈2
with O
2
feed.
The electrochemical cell is coupled to a hydraulic
circuit which includes a pair of glass containers [13,14];
one for the anolyte and one for the catholyte, both having a
volume of 1000 mL. The connections of the components of
the circuit are made with hose and valves. During the
electrolysis, oxygen was dosed in the catholyte to keep it
saturated of oxygen. Hydrogen peroxide released in the
reaction was measured by titration with permanganometric
method (KMnO
4
). Flow rate through the reactor was 10
Lmin
-1
for both catholyte and anolyte. Finally, a potential
difference was applied to the cell in order to start the
electrolysis (by a potentiostat BK Precision
®
).
The electrochemical cell prototype is constituted by
four blocks of acrylic. Between them, a rubber gasket
(hydraulic seal) was placed to prevent leakages. The blocks
of acrylic (12 x 26 x 1 cm) were assembled with screws.
Likewise, the electrochemical cell is divided into two
compartments (cathodic and anodic compartments) in
which the cathode and anode are placed, respectively. Both
compartments are separated by a membrane (Nafion
®
117)
in order to avoid the mixture of the anolyte and catholyte
fluids in the cell. However, due to its permeable capacity,
the membrane allowed cations flux. What was intended is
that protons of the anolyte, due to their high concentration,
migrate to the catholyte compartment through the
membrane surface. Anolyte and catholyte were kept in
circulation by pumps (Iwaki Magnet Pump). Each
compartment has inlets and outlets to allow fluids to flow
from and to it. Moreover, each electrode has a feeder for
power supply connection. The flow-cell setup used is very
similar to that proposed by Alvarez-Gallegos and Pletcher
[14], see Figure 3.
O
2
+
2H
3
O
+
H
2
O
H
2
O
2
Anode Fe
(Stainless steel mesh)
Fe
2+
Fe
3+
Fe
2+
2H
3
O
+
Membrane (Nafion
®
117)
Catholyte section
Anolyte section
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
206
Figure 2: Hydraulic structure of the electrochemical cell
2.3 Electrode design
Reticulated vitreous carbon (RVC), 60 pores per linear
inch (ppi) (Electrolytica Inc., NY), having a specific
surface area of 40 cm
2
cm
-3
was selected as the cathode
material. The design was based on a cube-like shape having
various dimensions (thickness, width and length). The
width of the electrode is not a particularly troublesome
parameter. However, the width of the electrode is linked to
the cross sectional area A
x
of the reactor canal and this
parameter is related to the linear velocity of the electrolyte.
According to Figueroa et al [21], a cross sectional area of
0.0005 m
2
was considered. From the width x thickness =
cross sectional area relationship, an electrode width of 0.05
m and an electrode thickness of 0.01 m were considered.
Once the dimensions (thickness and width) of the
tridimensional electrode were selected, the production of
hydrogen peroxide was conducted by the passage of the
(oxygen saturated) electrolyte through the tridimensional
electrode. The dissolved oxygen takes the electrons
available on the electrode surface to convert into hydrogen
peroxide [14]. Thus, the production of hydrogen peroxide is
a function of the length of the electrode. For this reason,
various RVC cathode lengths were evaluated.
A small RVC cathode (1.25 x 5 x 1 cm) and a large
RVC cathode (2.5 x 5 x 1 cm) were evaluated. Superficial
cathode area in the direction of current flow was 6.25 and
12.5 cm
2
, respectively. For the small RVC cathode, the
following current values were evaluated: 60, 80, 100, 120
and 140 mA, with variable voltage. In the case of the large
RVC cathode, another set of different current values were
tested (170, 180, 190, 200 and 250 mA) with variable
voltage. The potential applied to initiate the electrolysis
was 2.0 V, and since the current remained constant, the
applied potential was increased to 3.0V after 180 min for
both RVC. Different currents were evaluated for different
concentrations of H
2
O
2
and the optimal current values were
determined based on the efficiency gains. The RVC
electrode was attached to stainless steel, the rest of the
collector’s surface was isolated by insulating paint in order
to ensure that all the current went to the RVC electrode.
The cathode was placed in one of the acrylic blocks, as
shown in Figure.4.
Figure 3: Electrochemical cell comprising a membrane, a cathode RVC and
a stainless steel anode
Figure 4: RVC cathode attached to a stainless steel collector using carbon
glue, the rest of the collector was painted in order to isolate it and placed in
an electrochemical cell top
Stainless steel mesh (304 SS, 10.5 x 6.5 cm) with a
slash to connect it to the power supply was selected as the
anode material with the position near the membrane,
between two gaskets, so the anode is placed a few
millimeters away from the RVC cathode. Said material is
characterized by its high resistance to corrosion and its low
cost.
2.4 Oxidation of industrial effluents
Electrolytes were prepared for electrolysis purposes in
order to evaluate the electrogeneration of H
2
O
2
. The
catholyte was constituted by: 1L of 0.05 M Na
2
SO
4
at
pH≈2, adjusted with H
2
SO
4
. The anolyte contained 1L of
0.8 M H
2
SO
4
. Since high electrolyte concentrations are not
usually feasible for effluent treatment by H
2
O
2
electrogeneration, the inert supporting electrolyte (i.e.,
Na
2
SO
4
) was used only at the low concentration described
earlier [3]. For dye degradation, 0.001 M FeSO
4
.7H
2
O was
added to the catholyte to activate H
2
O
2
. Synthetic
wastewater was prepared using organic azo dyes
(distributed by Ciba Specialty Chemicals). A concentration
O
2
Catholyte
Anolyte
Pump
Potentiostat
Electrochemical
cell
88888888
▲ ◄ ►
▼ ◄ ►
Anode
Membrane
Cathod
e
Catholyte
Inlet
Catholyte
Outlet
Anolyte
Inlet
Anolyte
Outlet
Stainless Steel
collector
Thickness
Length
Width
Cathode
Electrochemical cell tops
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
207
of 0.08 mM BB9 was evaluated for discoloration using the
electro-assisted Fenton reaction. The discoloration was
observed by absorbance in a spectrophotometer (Thermo
Scientific Genesys 10UV). Finally energy consumption
(E
W
, in WhL
-1
) was calculated from Eq. (3), taking into
account the electrolysis time (t
electrolysis
, in h), assuming an
average cell current (I
Cell
, in Amperes), cell voltage (E
Cell
,
in Volts) and the volume of catholyte (V
Catholyte
, in L).
Catholite
iselectrolysCellCell
W
V
tIE
E
(3)
This approach could be attractive for effluent treatment
because of its low energy consumption for color removal in
industrial effluents [21].
3 Results and Discussion
3.1 Electrochemical predictive model
The hypothesis was that the electrochemical cell works
in a steady state, where the parameters do not vary with
time and thus the volumetric flow (m
3
s
-1
) is constant. The
initial concentration of the electroactive species decreases
as a function of the electrode length and the current
observed anywhere in the electrode corresponds to the limit
current. Under mass transport limitations, the overall
performance of a cell can be written in terms of the average
mass transport coefficient,

, as described in Eq. (4):
22
,22
2)(
OOmeeL
ckVAFOHI
(4)
Where I(H
2
O
2
)
L
is the limiting current (amperes) for
H
2
O
2
production; is the Faraday constant (96,485 C mol
-
1
), A
e
is the specific area (4000 m
2
m
-3
) and V
e
the specific
volume (thickness x width x length) of the RVC cathode,
c
O2
is the O
2
concentration, k
mO2
is the mass transport
coefficient for O
2
, and ɸ is the current efficiency for H
2
O
2
production [14,19].
Modeling the production of H
2
O
2
aims
to predict the amount of H
2
O
2
accumulated during a given
time. The amount of H
2
O
2
obtained is represented by
Faraday’s law [19], Eq. (5) as:
F
q
m
OH
2
22
(5)
Where m
H2O2
is the amount (moles) of H
2
O
2
when the
electrolyte saturated with O
2
passes through the length of
the three-dimensional electrode; q is the theoretical charge
(in coulombs) passed through the cell and Φ is the current
efficiency for hydrogen peroxide production. Combining
Eq. (4) and Eq. (5), H
2
O
2
production is obtained as a
function of the residence time in Eq. (6). The residence
time along the electrode is equal to the electrode length
divided by the linear velocity of the electrolyte. We thus
obtain Eq. (7):
2222
, OOmeeOH
ckVAtm
(6)
2222
, OOmeeOH
ckVA
v
L
m
(7)
Where: is the electrolysis time. The rest of the
parameters have already been defined. The
electrogeneration of H
2
O
2
is simulated through O
2
concentration. During the passage of an O
2
saturated
aqueous solution through a 60 ppi RVC cathode, O
2
is
reduced as a function of the length of the electrode, while
H
2
O
2
and H
2
O are concurrently generated [19]. For
instance, a RVC piece may be hypothetically divided into
five 0.5 cm long segments. The parameters of each segment
being the same, and the volume of each segment being 0.5
x 5 x 1 cm, O
2
concentration progressively diminishes from
the first to the last segment (see Figure 5).
Figure 5: Simulation of H
2
O
2
electrogeneration through O
2
reduction
3.2 Experimental electrochemical tests
After obtaining the theoretical results, experimental
tests were performed. H
2
O
2
electroproduction was carried
out in a parallel-plate electrochemical cell divided by a
cationic membrane (Nafion
®
117) by means of O
2
reduction
in the RVC (60 ppi) cathode. The catholyte was kept
saturated with industrial oxygen. The anolyte and catholyte
fluids remained constant (10 Lmin
-1
) and were kept at room
temperature and under atmospheric pressure. Samples (10
mL) were taken every 30 minutes, and H
2
O
2
concentration
was immediately determined by the permanganate method
(KMnO
4
) during an electrolysis total time of 180 min.
Experiments were performed with different currents and
two different-sized RVC cathodes, as stated in section
2.3.The water reaches the bottom of the cover and passes
through the cathode and continues its journey to the top of
the plate. The efficiency in the production of hydrogen
peroxide was evaluated by means of the relation between
the theoretical and experimental slopes as shown in Eq. (8).
100
.
.
x
slopelTheoretica
slopealExperiment
Efficiency
(8)
The experimental slope was obtained by plotting the
electrogenerated H
2
O
2
concentration as a function of the
charge (q). In every electrolysis experiment, the slope was
Width of the cathode
Length of the
cathode
Cathode segments
O
2
saturated
Dissolved
oxygen
concentration
y
x
z
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
208
assessed by the least-squares method [19]. The theoretical
slope is related to current efficiency by the production of
hydrogen peroxide according to Faraday’s law (Eq. 9):
nF
It
cVm
(9)
Where m is the number of moles of H
2
O
2
; n the number
of electrons transferred (2 electrons in this case); I is the
current (amperes); t is the time (sec); c is the molar
concentration of H
2
O
2
; V is the volume (liters) and q is the
electrical charge (C). Faraday’s law can be represented as a
straight line with a positive slope

, intercepting the
origin in the m versus q plane (Eq. 10). This equation is a
straight line: y
=
a
+ mx, where the intercept (a) is zero and
the slope (m) is

.
q
VnF
c
1
(10)
Figure 6 shows the main results of the production of
H
2
O
2
as a function of the current applied in the
electrochemical cell using the small RVC cathode (1.25 x 5
x 1 cm). The total amount of electrogenerated hydrogen
peroxide was at the catholyte after 180 min of electrolysis.
The influence of current on time-dependent changes of
H
2
O
2
concentration can be observed. By increasing current
density, H
2
O
2
generation rate increased mainly due to a
greater charge passed into the cell. Indeed, H
2
O
2
concentration accumulated in the solution is roughly
proportional to applied current, and current at the beginning
of the process is the same for all the processes.
Figure 6: Electroproduction of hydrogen peroxide in an electrochemical cell,
using the small 60 ppi RVC cathode (1.25 x 5 x 1 cm) and stainless steel
anode, Catholyte: 1 L 0.05 M Na
2
SO
4
, pH≈2 and Anolyte: 1 L 0.8 M
H
2
SO
4
.
Figure 7 shows the different amounts of H
2
O
2
generated with different applied currents using the large
RVC cathode (2.5 x 5 x 1 cm). It is significant that the
greatest amount of H
2
O
2
was observed by applying a
current of 180 which is very similar to applying a current of
170 but with the latter the highest efficiency of the four
evaluated currents was obtained. For both RVC volumes,
when ∆E
cell
< 2Volts was applied, little current was
observed but H
2
O
2
was not detected, being probably under
the limit of detection of the permanganate method. Under
the condition: 2Volts<∆Ecell<3Volts, some current was
observed and H
2
O
2
concentration was detected. Besides,
electrode thickness is important because, as it increases,
potential drop (∆E, in volts) through the electrode also
increases.
Figure 7: Electroproduction of hydrogen peroxide in an electrochemical cell
using the large 60 ppi RVC cathode (2.5 x 5 x 1 cm) and stainless steel
anode. Catholyte: 1 L 0.05 M Na
2
SO
4
, pH≈2 and Anolyte: 1 L 0.8 M
H
2
SO
4
.
The efficiency of every current applied for the two
cathodes tested was obtained and the results are presented
in Table 1. According to Table 1, when using the small
RVC cathode (1.25 x 5 x 1 cm), the higher efficiency was
obtained at 80 mA generating a concentration of 3.75 mM
H
2
O
2
, this current value being considered optimum. Using
the large RVC cathode (2.5 x 5 x 1 cm), the highest
efficiency was achieved at current value of 170 mA. The
generated H
2
O
2
concentration was 5.3 mM. In this case the
optimal current was 170 mA (the same current was used for
prediction).
Figure 8 shows the comparison among experimental
and theoretical data for H
2
O
2
production under the
experimental conditions tested using the small RCV
cathode (1.25 x 5 x 1 cm). H
2
O
2
was accurately predicted
by the model with an error rate of 0.5%.
Figure 9 shows the comparison among experimental
and theoretical data for H
2
O
2
production using the large
RVC cathode (2.5 x 5 x 1 cm).Theoretical results generated
with the model fitted reflect experimental trends fairly
close (1.5% error rate).Both error values are considered
small so it can be said that it is feasible to predict H
2
O
2
electrogeneration by Faraday's law [15]. Moreover, it was
found that electrode thickness was important because as it
increases, the potential drops (∆E, in volts) through the
electrode. In order to oxidize the organic matter, activating
H
2
O
2
in presence of Fe
2+
ions is required to produce
Fenton’s reagent. Thus, H
2
O
2
will activate immediately
after being electrogenerated.
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
209
The amount of active H
2
O
2
was evaluated with the
concentration obtained experimentally. It was found that
about 90% of the generated H
2
O
2
is activated to act as a
powerful oxidant. According to previous reports [1],
hydrogen peroxide production and current efficiency were
higher in alkaline solution. However, as regards wastewater
application, it is worth noticing that the efficiency is quite
good even in acidic conditions because the electrolyte
increases the pH level in the reaction zone, enhancing thus
H
2
O
2
formation [10,15].
3.3 Oxidation of a synthetic effluent
After predicting and evaluating H
2
O
2
generation, the
second stage of this work was to assess the oxidation of
organic compounds through the electro-assisted Fenton
process. The Fenton reaction was carried out in the
cathodic compartment where electro-generated H
2
O
2
reacted with the organic compounds in the presence of
Fe
2+
/Fe
3+
added as catalyst (Friedrich et al. 2004). The
catholyte was constituted by 0.05 M Na
2
SO
4
, 0.001M
FeSO
4
.7H
2
O (to activate H
2
O
2
), and 0.01 M H
2
SO
4
(to
ensure solution pH≈2.0) with O
2
feed. The anolyte was
prepared using the above mentioned amount but with 0.8 M
H
2
SO
4
.In this study, it is recognized that the chemical
interaction between H
2
O
2
and Fe
2+
/Fe
3+
produces a strong
intermediate oxidant (FeO
2+
) that is responsible for the
organic oxidation.
Using the higher surface area cathode (2.5 x 5 x 1 cm),
BB9 dye removal was evaluated (simulating an industrial
effluent, this dye was used because it is the most common
in jeans dyed fabrics). According to Eq. (1), one mole of
H
2
O
2
may accept up to two moles of electrons from the
organic matter available to be oxidized. This means that the
process may range from a highly selective oxidation in
organic electro synthesis to the oxidation of the organic
matter.
Figure 8: Concentration of hydrogen peroxide vs. electrolysis time for
experimental and theoretical data using the small RVC cathode (1.25 x 5 x 1
cm) and stainless steel anode. Catholyte: 1 L 0.05 M Na
2
SO
4
, pH≈2 and
Anolyte: 1 L 0.8 M H
2
SO
4
.
Figure 9: Concentration of hydrogen peroxide vs. electrolysis time for
experimental and theoretical data using the large RVC cathode (2.5 x 5 x 1
cm) and stainless steel anode. Catholyte: 1 L 0.05 M Na
2
SO
4
, pH≈2 and
Anolyte: 1 L 0.8 M H
2
SO
4
.
According to Eq. (11), it may be hypothesized that BB9
will lose 78 electrons during its oxidation. Furthermore,
considering Eqs. (1) and (11), the theoretical amount of
H
2
O
2
required to mineralize BB9 can be calculated using
Eq. (12).
HClNHSOHHCOeOHSClNHC
3422231816
378167836
(11)
OHHClNHSOHCOOHSClNHC
234222231816
4231639
(12)
If the amount of H
2
O
2
required to discolor a certain
quantity of BB9 is known, a stoichiometric equation could
be established. Because the concentration of H
2
O
2
generated and active within the reactor is known (4.8 mM),
the amount of BB9 to be oxidized was determined.
According to Figure 7 for large cathode, the greatest
amount of H
2
O
2
and the highest efficiency was observed by
applying a current of 170 mA and the greater amount of
H
2
O
2
produced is 5.3. It was determined that about 90% of
the H
2
O
2
generated was activated H
2
O
2
(it is estimated that
4.8 mM H
2
O
2
were used to carrying out the discoloration
process). The remaining 10% was not detected; possibly,
the couple Fe
2+
/Fe
3+
regeneration during the Fenton
chemistry is not efficient due to chemical speciation. Other
researchers report similar results [21].
The complete oxidation of BB9 in aqueous acidic
solution involves 78 electrons and hence the stoichiometric
conversion of 1 mol of BB9 requires 39 mol of H
2
O
2
according Eqs. (9) and (10). The process generates and
activates up to 4.8 mM of H
2
O
2
, thus the maximum
concentration of BB9 that can be eliminated is 0.12 mM.
Therefore a lower concentration of 0.8 mM of BB9 was
evaluated. From these experimental data, the following
results were found: using a concentration of 0.08 mM BB9,
94% discoloration was achieved after 15 min of electrolysis
using only 0.5 mM H
2
O
2
, the theoretical charge was 145.8
C and 0.079 WhL
-1
were consumed.
Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 4, Pages: 204-211
210
Table 1: Electrogenerated H
2
O
2
efficiencies obtained for
the different current values tested for the two RVC
electrodes. Electrolysis was performed in a divided
electrochemical cell (60 ppi 3D-RVC), stainless steel mesh
anode and catholyte: 0.05 M Na
2
SO
4
at pH≈2.0. Flow rate
was 10 Lmin
-1
, 180 min of electrolysis.
I
cell
mA
∆E
Cell
Volts
q/C
H
2
O
2
mM
Efficiency
(%)
E
W
WhL
-1
RVC size: 1.25 x 5 x 1 cm
60
2.0
648
2.8
79
0.360
80
2.1
864
3.75
81
0.504
100
2.3
1080
3.25
56
0.690
120
2.5
1296
3.45
50
0.900
140
2.7
1512
3.15
37
1.134
RVC size: 2.5 x 5 x 1 cm
170
2.1
1836
5.3
54
1.071
180
2.2
1944
5.37
52
1.188
190
2.6
2052
3.25
30
1.516
200
2.7
2160
3.12
28
1.620
250
2.8
2700
2.42
15
2.100
Figure 10 shows spectra recorded for a solution. The
discoloration was spectrophotometrically followed and the
water was considered discolored when an absorbance <10%
of the original was achieved at the catholyte. During BB9
discoloration, the spectrum showed absorbance vs
wavelength. Maximum absorbance was located at λ
max
=
665 nm. These results open a new perspective for further
experiments with higher concentrations of BB9 and longer
electrolysis time. To evaluate the oxidation organic, was
determined by chemistry oxygen demand (COD), where it
was found that at 40 min was obtained about 75% of
reduction and 60 min was reduced to 90% using 2.0 mM
H
2
O
2
.
Figure 10: BB9 Degradation. Spectra recorded for solution (1L) containing
0.08 mM BB9 at t=0 min using the large 60 ppi RVC cathode (2.5 cm x 5
cm x 1 cm). Both, stainless steel anode, Catholyte: 1 L 0.05 M Na
2
SO
4
pH≈2 and Anolyte: 1 L 0.8 M H
2
SO
4
with O
2
feed.
4 Conclusions
The electrochemical generation of H
2
O
2
was verified
experimentally and a predictive model based on the
Faraday’s law was developed. The experimental setup used
included two different sizes of 60 ppi RCV cathodes and a
stainless steel mesh anode using commercial oxygen to
oxygenate the catholyte and several different voltage values
were applied.
From experimental runs, the optimal current for the
small RCV cathode was 80 mA, with a generation of 3.75
mM H
2
O
2
, i.e., an electrolysis efficiency of up to 81%. This
trend was accurately predicted by the model with an error
rate of 0.5%. With regard to the large RVC cathode, the
optimal current was found to be 170 mA, twice as reported
for the small RVC, with a H
2
O
2
generation of 5.3 mM, i.e.,
a 54% efficiency. Theoretical results obtained with the
model fitted this trend fairly well with a 1.5% error rate.
Hydrogen peroxide concentrations were experimentally
measured to determine the activated percentage. It was
found that around 90% of the H
2
O
2
generated may act as a
strong oxidant.
It has been demonstrated that Fenton’s reagent can be
indirectly electroproduced in a flow-cell by cathodic
reduction of dissolved oxygen on a RVC surface. Using a
synthetic industrial effluent and the large RVC cathode, dye
BB9 removal was evaluated and 94% discoloration was
achieved after 15 min of electrolysis with 0.08 mM BB9.
Regarding COD, was reduced to 90% at 60 min.
Acknowledgments
The authors wish to thank CIICAp-UAEM for
providing the entire infrastructure for this work and
CONACYT for granting the economic support.
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