Enhanced electrochemical degradation of 4-Nitrophenol molecules using novel Ti/TiO2-NiO electrodes

Article abstract of DOI:10.1016/j.molliq.2019.111108

Removal of 4-Nitrophenol (4-NP) compounds by the electrochemical degradation method using Ti/TiO₂-NiO electrodes was successfully conducted. This study aims to study the activity of Ti/TiO₂-NiO electrodes in the electrocatalytic degradation of 4-NP as organic compound pollutants. Ti/TiO₂-NiO preparation was carried out by the wet impregnation technique, then TiO₂-NiO composites were sprayed on the surface of Titanium electrodes. The electrode was characterized by X-Ray Diffraction (XRD), a Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Cyclic Voltammetry (CV). A Diffractogram XRD of TiO₂-NiO composites showed a characteristic peak of TiO₂-NiO at 2θ = 33°. Meanwhile, analysis of the SEM surface morphology showed that NiO with an average particle size of 22.07 μm can be attached to the surface of the Ti/TiO₂ plate. Electrocatalytic degradation of 4-NP compounds was found to be optimum at pH 11 and 80 min electrolysis time with a rate constant of 0.0373 min^?1. The electrochemical degradation exhibited the percentage of removing 4-NP rate of >95% with good electrode measurement stability.

Full text of DOI:10.1016/j.molliq.2019.111108

Accepted Manuscript
Enhanced electrochemical degradation of 4-Nitrophenol
molecules using novel Ti/TiO2-NiO electrodes
Ganjar Fadillah, Tawfik A. Saleh, Sayekti Wahyuningsih
PII:
S0167-7322(19)30589-6
https://doi.org/10.1016/j.molliq.2019.111108
111108
DOI:
Article Number:
Reference:
MOLLIQ 111108
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
30 January 2019
20 May 2019
30 May 2019
Please cite this article as: G. Fadillah, T.A. Saleh and S. Wahyuningsih, Enhanced
electrochemical degradation of 4-Nitrophenol molecules using novel Ti/TiO2-NiO
electrodes, Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2019.111108
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ACCEPTED MANUSCRIPT
Enhanced Electrochemical Degradation of 4-Nitrophenol
Molecules using novel Ti/TiO -NiO Electrodes
2
a*
b*
c
Ganjar Fadillah , Tawfik A. Saleh , Sayekti Wahyuningsih
aChemistry Department, Chemical Analysis Study Program, Faculty of Mathematics
and Natural Sciences, Universitas Islam Indonesia, Yogyakarta 55584
b
Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran
1261, Saudi Arabia
3
cChemistry Department, Faculty of Mathematics and Natural Sciences, Universitas
Sebelas Maret, Surakarta 57126
*
Corresponding author
E-mail address: tawfik@kfupm.edu.sa ; tawfikas@hotmail.com
Home Page: http://faculty.kfupm.edu.sa/CHEM/tawfik/publications.html
1

ACCEPTED MANUSCRIPT
ABSTRACT
Removal of 4-Nitrophenol (4-NP) compounds by the electrochemical degradation
method using Ti/TiO -NiO electrodes was successfully conducted. This study aims to
study the activity of Ti/TiO -NiO electrodes in the electrocatalytic degradation of 4-NP
as organic compound pollutants. Ti/TiO -NiO preparation was carried out by the wet
impregnation technique, then TiO -NiO composites were sprayed on the surface of
2
2
2
2
Titanium electrodes. The electrode was characterized by X-Ray Diffraction (XRD), a
Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and
Cyclic Voltammetry (CV). A Diffractogram XRD of TiO -NiO composites showed a
2
o
characteristic peak of TiO
2
-NiO at 2휃=33 . Meanwhile, analysis of the SEM surface
morphology showed that NiO with an average particle size of 22.07 μm can be attached
to the surface of the Ti/TiO plate. Electocatalytic degradation of 4-NP compounds was
found to be optimum at pH 11 and 80 minutes electrolysis time with a rate constant of
2
-1
0
.0373 min . The electrochemical degradation exhibited the percentage of removing 4-
NP rate of more than 95% with good electrode measurement stability.
Keywords: Nanotechnology; water purification; degradation; 4-Nitrophenol; Ti/TiO -
2
NiO
2

ACCEPTED MANUSCRIPT
INTRODUCTION
Global warming and the fast pace of industrial development is a significant factor
in triggering environmental pollution, especially pollution in sources of clean water. 4-
nitrophenol (4-NP) is a phenolic compound that has a nitro group and is quite widely used
in various industries such as petrochemical manufacturing, leather tanning (dark leather),
rubber (chemical rubber), wood preservation, fungicides and pharmaceuticals [1-3].
However, the wide use of 4-NP compounds is concerning due to their good solubility
level in the water, high level of toxicity, and the fact that they are not easily degraded by
the environment [4]. Short term exposure to 4-NP may harm human’s health as it leads
to respiratory problems, headaches, and cyanosis, while long-term exposure to 4-NP can
cause gene mutations in organisms and injury to blood cells [5]. Therefore, degradation
of the contamination of 4-NP compounds in water is a topical and crucial issue to study.
Several previous studies have revealed ways to eliminate the content of 4-NP in water by
means of adsorption [6, 7], denitrification [8], ozonation [9, 10], photodegradation [1, 11]
and electrodegradation [12, 13].
However, currently, there are only a few types of research on the use of
electrodegradation to remove 4-NP from the water. This underlines that this topic is
underdeveloped despite the fact that the degradation of a compound electrochemically is
known to offer many benefits since it is easy to operate, affordable, environmentally
friendly and more effective [14]. Also, the addition of electrical potential to the
electrodegradation system can increase the electron transfer rate and electric current to
increase the activation of the material used as an electrode and the degradation process of
organic compounds [15]. In this study, TiO -NiO-based electrode composites will be
2
3

ACCEPTED MANUSCRIPT
developed to coat Ti electrodes since the electrode is an important component in the
process of electrochemical degradation.
At present, the most commonly used electrodes for degradation are Pt, carbon,
and graphite electrodes [16-18]. However, these electrodes are not highly recommended
since they are expensive, have unstable prices, and are easy-to-fall which may impede an
optimum degradation process. In fact, several studies have reported that the making of
electrodes by combining several semiconductor materials provides sufficient results such
as Ti/RuO
2
-Pt [19], Ti-IrO
2
-Pt [20], RuO
2
-PdO-TiO
2
/Ti [21], and Ti/SnO
2
-Sb
2
O
5
-IrO
2
[
22]. Previous research has reported that TiO
2
is able to degrade and eliminate organic
, SO 2-, NH -
, and NO [23, 24].
compounds and produce final products in the form of CO
2
4
4
3
However, the use of TiO
2
powder to degrade organic compounds is less efficient because
TiO powder is easily dispersed in water, making it difficult to regenerate. This is the
2
reason why its use for the photodegradation process is limited because the light radiation
used is not able to activate all of the photocatalyst particles due to its extremely turbid
mixtures. Therefore, the making of a semiconductor thin layer on an electrode substrate
is considered as an innovation to obtain anode electrodes that are easy to handle because
they can easily separate electrodes from degraded solutions and are easy to regenerate.
The TiO
2
-NiO composite is one way to reduce the weakness of TiO material
2
which has a high energy gap (3.23eV). NiO is one of the metal oxides which has a low
energy gap and good electrochemical and conductivity activity in the form of composites
such as Ti/Co-NiO [25], CNT@NiO [26, 27] and graphene/NiO [28]. In this study,
Ti/TiO -NiO electrodes have been developed for the degradation of organic compounds
2
as pollutants in water such as 4-NP. This TiO -NiO composite can show good
2
4

ACCEPTED MANUSCRIPT
performance in the 4-NP degradation process because it can facilitate electron transfer
rates from water splitting to produce electrons for the 4-NP reduction process.
METHODOLOGY
Materials and apparatus
4
-Nitrophenol was purchased from Sigma Aldrich Singapore (molecular formula
N molecular weight 139.11), TiO with a particle size <100 nm (Sigma Aldrich),
.6H O (Sigma Aldrich), Titanium metal from Baoji Qixin Titanium Co.Ltd,
poly(vinyl alcohol) (PVA) (Merck), ethanol p.a. (Merck), NaCl (Sigma Aldrich), H
Merck). All of the chemical reagents used were of analytical grade.
The prepared materials were characterized by X-ray diffraction (XRD) (X’ Pert Pro
C
6
H
5
O
3
2
NiNO
3
2
2
O
2
(
Philips, Cu Kα radiation, λ = 0.154,056 nm, 2θ = 5 o - 80 o ), a scanning electron
microscope (SEM) MERLIN with a powerful 5000x zoom, a transmission electron
microscope (TEM, JEOL JEM-2100) and a potentiostats eDAQ ER466.
Synthesis of TiO -NiO composite
2
1
.145 grams of technical TiO
2
were added to 0.81 grams of NiNO
3
.6H O which had
2
been dissolved in 25 mL of distilled water. The solution was stirred for 60 minutes until
reach homogeneous solution. The green mixed solution was then oven heated at 110 °C
for 3 hours to increase the NiO crystals. Once the distilled water evaporated and a green
suspension was formed, it was calcinated at a temperature of 700 °C with a furnace speed
of 10 °C/minute.
Preparation of Ti/TiO
2
and Ti/TiO
2
-NiO electrodes
Preparation of Ti/TiO
2
electrodes was carried out by mixing 12.5 grams of
synthesized TiO
2
and 1 gram of PVA into 50 mL ethanol, then sterilized and sonicated
5

ACCEPTED MANUSCRIPT
for 15 minutes until they were dispersed. The TiO
2
dispersion was then sprayed on a
titanium plate and heated at 200 C for 15 minutes. Meanwhile, preparation of the Ti/
TiO -NiO electrodes was carried out by mixing 12.5 grams of synthesized TiO -NiO and
gram of PVA into 50 mL ethanol. Then they were sterilized and sonicated for 15
o
2
2
1
minutes until dispersed. The dispersion of TiO -NiO was then sprayed on a titanium plate
2
o
and heated at 200 C for 15 minutes.
Degradation of 4-NP electrocatalytic study
Electrochemical degradation of the 4-NP solution resulted from a batch system at
00 mL container capacity using 2 electrodes of Ti/TiO -NiO as an anode and Ti
1
2
electrode as a cathode (width of each electrode is + 1.5 cm, length is of 7 cm, and the
2
surface area of the electrode is of 7.5 cm ). 4-NP degradation was carried out in 50 mL
with an initial concentration of 10 mg/L in a supporting electrolyte solution of 500 mg/L
NaCl and 10 mM H
2
2
O . Various pH and electrolysis time were observed to produce
optimal degradation of the 4-NP molecules. The measurement of 4-NP solution
degradation was carried out using the cyclic voltammetry method in the potential range
of 0 to -1000 mV with a scan rate of 50 mV/s. % 4-NP degradation was calculated using
equation 1.
푖ꢀ−푖
푓
%
degradation =
x 100 %
(1)
푖ꢀ
Where i
i
is the current before degradation, and i
f
is the current after degradation. Then,
the kinetic constant can be calculated as following equation 2.
푑퐶
푑푡
푑퐴
ꢁ
ꢂ
= 푑푡 = -k. t or 푙푛 = 푙푛 = -k. t
(2)
ꢁ표
ꢂ표
Where C is the concentration of 4-NP after the degradation process and C
o
is the initial
concentration, then k can be determined from the plot of ln (C/C ) vs. t (the time reaction).
o
6

ACCEPTED MANUSCRIPT
RESULTS AND DISCUSSION
Preparation of Ti/TiO -NiO electrodes and their characteristics
This research used commercial Titanium metal from Baoji Qixin Titanium Co.Ltd
as the electrode. The Ti metal was then thinly coated with TiO powder and the TiO -NiO
composite was synthesized by a spray technique. The diffractogram of XRD from Ti,
Ti/TiO , TiO -NiO and Ti/TiO -NiO is shown in Figure 1. These results show that in
2
2
2
2
2
2
diffractogram Ti there are characteristic peaks that appear at certain diffraction angles
which are the result of the diffractogram of Ti compounds. The peaks include 2θ = 35o
o
o
o
(
d100 = 2.5550 Å), 2θ = 38 (d002 = 1.0130 Å), 2θ = 40 (d101 = 2.2430 Å), 2θ = 53
o
o
(
d102 = 1.7262 Å), 2θ = 62 (d110 = 1.4753 Å), and 2θ = 70 (d103 = 1.3320 Å) which
is the area of Ti metal characterization in accordance with JCPDS standard No. 44-1294.
The diffractogram of Ti/TiO2 is shown that the result shows that in difractogram Ti/TiO
2
o
there are characteristic peaks as TiO
2
anatase phase. The peaks include 2θ = 25 (d101 =
o
o
o
3
1
2
.4967 Å), 2θ = 37 (d004 = 2.3679 Å), 2θ = 48 (d200 = 1.8874 Å), 2θ = 54 (d105 =
o
.6931 Å), and 2θ = 62 (d211 = 1.6674 Å) in accordance with JCPDS standard No. 78-
486. The shape of the diffractogram that resembles amorphous characterizes amorphous
silica. Referring to the previous research [29, 30], coating TiO -NiO composite material
2
on Ti metal will produce Ti/ TiO
2
-NiO electrode material. From the results of the practice,
o
the peaks show the presence of TiO
2
-NiO composites in area 2θ = 35 (d100 = 2.5550 Å),
o
o
o
2
θ = 38 (d002 = 1.0130 Å), 2θ = 40 (d101 = 2.2430 Å), 2θ = 53 (d102 = 1.7262 Å), 2θ =
2o (d110 = 1.4753 Å), and 2θ = 70 (d103 = 1.3320 Å) in accordance with JCPDS standard
o
6
No. 33-0960. Compared to the result of the previous research, as mentioned earlier, the
results in this study are in accordance with the literature. Some of the literature states that
the phase of TiO
2
will be observed as anatase, rutile phase TiO
2
and NiTiO . Addition of
3
7

ACCEPTED MANUSCRIPT
Ni metal oxide can increase the thermal resistance of TiO
it can hold the anatase structure into rutile.
2
to phase transformation so that
Ti
Ti/TiO2
TiO -NiO
2
Ti/TiO -NiO
2
0
10 20 30 40 50 60 70 80 90
 (degree)
2
Figure 1. XRD patterns of Ti, Ti/TiO
2
, TiO
2
-NiO, and Ti/TiO -NiO electrodes.
2
a.u. refers to arbitrary unit
Figure 2 shows the results of the SEM morphological characterization of the Ti,
and Ti/ TiO -NiO electrodes. The surface of the Ti electrode has a homogeneous
and smooth surface as shown in Figure 2a. This is also the same for the morphological
appearance of the Ti/ TiO electrodes since there is no significant difference between the
surface of the Ti electrode and Ti/TiO . However, on the Ti/TiO -NiO electrodes, the
Ti/TiO
2
2
2
2
2
electrode surface was not homogeneous and smooth, and it was not evenly distributed
with the addition of NiO metal oxide on the electrode surface with an average particle
size of 22.07 μm. This shows that TiO
well on the surface of the electrode as shown in Figure 2c. While TEM images are shown
in Figure 3. The image characterization shows agglomerization of TiO -NiO particles.
2
-NiO oxide was successfully formed and bonded
2
However, from the XRD pattern and TEM images reveal that the material oxide has
8

ACCEPTED MANUSCRIPT
highly crystallinity and each grain corresponds to single crystalline. The bright and dark
contrast on the surface of materials as shown in Figure 3 reveal that the materials have a
large surface so that the target analyte can optimally adsorb on the surface of electrode
during electrodegradation process. Moreover, some references reported that the dark and
bright contrast due to difference in average atomic number and particle size of TiO
2
and
NiO, respectively [31, 32]. The results of elemental analysis showed that the composition
of Ti/TiO -NiO material contained 10.20% Ti, 9.90% Ni, and 80% O.
2
A
B
C
Ni
O
100 μm
100 μm
100 μm
Figure 2. SEM morphological characterization of (a) Ti, (b) Ti/TiO
2
, and (c) Ti/TiO -
2
NiO electrodes
Figure 3. TEM and surface morphological characterization of Ti/TiO -NiO
2
9

ACCEPTED MANUSCRIPT
In addition, electrode characterization was done by measuring the electrode
current response using cyclic voltammetry. Measurements were made on Ti, Ti/TiO
Ti/TiO -NiO electrodes with a voltammogram in Figure 4. Based on the cyclic
voltammogram, it is apparent that the peak current produced by Ti/TiO -NiO electrodes
is greater than that of the Ti and Ti/TiO electrodes. This proves that the modification of
other oxides on Ti/TiO electrodes as a composite can increase the electron transfer rate
2
and
2
2
2
2
so that the electrons produced will be relatively more numerous and produce a greater
current response. This also corresponds with previous studies revealing that the presence
of Ni (II) in composite systems can increase the conductivity of electrodes. In addition,
besides the doping of other oxides, the increase in current and conductivity of the
electrode is also influenced by several other factors such as the active surface of TiO , so
2
that the electron transfer rate will occur faster which causes greater current and
conductivity. These results also correspond to the results of the measurement of the
crystal size of TiO
using the Scherrer equation reveals that the crystal size of TiO
3.2 + 0.3 nm, while in the Ti/ TiO -NiO electrodes it is 16.8 + 0.2 nm. This proves that
2
material from XRD diffractogram data. The calculation of crystal size
2
on Ti/TiO electrodes is
2
2
2
the presence of NiO can change the crystal size structure of TiO2, and thus prevent TiO
2
crystals from growing normally during the crystallization process.
1
0

ACCEPTED MANUSCRIPT
Figure 4. Cyclic voltammogram of Ti, Ti/TiO
2
, and Ti/TiO -NiO in 5 mmol L-1
2
-1
K
3
[Fe(CN) ]/K [Fe(CN) ] solution containing 0.1 mol L KCl
6
4
6
Additionally, the surface coverage of electrode can be determined by cyclic
voltammetry [33, 34] in various scan rate and calculated as following equation 3.
ꢃ(1−훼)ꢃ훼퐴퐹2푣훤
i
p
=
(3)
2.718RT
where n is the total of number electron involved in the electroreduction of 4-NP, T is the
standard temperature (T=298 K), v is the scan rate, F is the Faraday constant (96,485 C
−
1
−1
−1
mol ), R the gas constant (8.314 J mol K ), A is the geometrical area of electrode
2
(
A=0.07 cm ), α is the electron transfer coefficient, n
α
is the number of electrons involved
and α can be
in the rate determining step, and Γ is surface coverage of electrode. The n
α
determined by the linear curve between potensial reduction of 4-NP vs ln scan rate as
following equation 4. Figure 5 shows the curve of scan rate of electroreduction of 4-NP
vs current response to determine the surface coverage of the Ti/TiO
pa = const. + [0.02569 (1−α)n ] ln v ( T = 298 K)
2
-NiO electrodes.
(4)
E
α
1
1

ACCEPTED MANUSCRIPT
Figure 5. Plot of current response of electroreduction of 1 mM 4-NP vs scan rate and
potential vs logarithm of scan rate
From these results, if a flat surface electrode is assumsed, the average surface of Ti/TiO -
2
-7
-2
NiO electrode is estimated approximately about 2.98 x 10 mol m . The result presents
that the Ti/TiO -NiO electrodes has a higher surface accumulation for adsorption of 4-NP
2
on the surface electrode.
Electrochemical Degradation Study of 4-NP
Optimization of pH and electrolysis time during the degradation process at a
potential of 5 V has been carried out. The results showed that the degradation of 4-NP
was optimum at pH 11. In acidic and slightly acidic solutions, the 4-NP molecule will
undergo hydrolysis and the Ni molecules will dissolve resulting in some changes in the
surface of the electro-structure which cause a low percentage of degradation. Meanwhile,
at an alkaline pH, the 4-NP molecule will ionize so that the molecules are completely
-
dissolved in the system. Hence, the high OH concentration allows it to increase the
1
2

ACCEPTED MANUSCRIPT
amount of hydroxyl radicals formed leading to a more optimum degradation process. The
results of the pH measurements are shown in Figure 6.
1
00
0.5
0.4
0.3
0.2
0.1
0.0
9
8
7
6
5
0
0
0
0
0
%
C/C
degradation
o
0
2
4
6
8
10
12
14
pH
-1
Figure 6. Effect of pH to degradation of 4-NP 10 mg L in a supporting electrolyte
solution of 500 mg/L NaCl and 10 mM H
2
2
O with 60 minutes electrolysis time
-1
Figure 7. Effect of electrolysis time in degradation of 4-NP 10 mg L with a supporting
electrolyte solution of 500 mg/L NaCl and 10 mM H at pH 11.0
2
O
2
The effect of electrolysis time on 4-NP degradation was obtained optimally in 80 minutes.
The effect of the electrolysis time on 4-NP degradation is shown in Figure 7. From the
plots, it can be seen that lengthening the electrolysis time given to the system can
significantly reduce the concentration of 4-NP. This proves that the electrolysis time is
1
3

ACCEPTED MANUSCRIPT
sufficient to signify the degradation of organic compounds, especially 4-NP. Ti/TiO -NiO
2
electrodes show a relatively shorter time for the degradation of 4-NP compared to Ti
electrodes and Ti/TiO electrodes. The calculation of the kinetic rate constant shows that
the Ti/TiO -NiO electrode has a value higher than the Ti and Ti/TiO electrodes. The
linear plotting between the ln(C/C ) versus the electrolysis time (t) indicates that the
2
2
2
o
degradation followed the first-order kinetics mechanism. The kinetics rate constant (k)
can be determined from the slopes of the linear regression. The calculation of the kinetics
rate constant shows that the Ti/TiO
2
-NiO electrode has a value higher than the Ti and
Ti/TiO electrodes. The calculation results of the degradation rate and a comparison with
2
several previous studies are shown in Table 1.
Table 1. The degradation rate of 4-NP using Ti, Ti/TiO
2
and Ti/TiO
2
-NiO electrodes
Reference
Materials*
Degradation Rate,
Method
-1
k (min )
0.0021 + 0.0002
0.0071 + 0.0008
0.0373 + 0.0046
0.0054
Ti ed.
electrochemical
electrochemical
electrochemical
photocatalysis
photocatalysis
this work
this work
this work
[35]
Ti/TiO
Ti/TiO
2
ed.
-NiO ed.
2
Ag@CeO
rGO-ZnS
Ag-MOF
0.0300
[36]
0.1980
catalytic reaction [37]
Bi
TiO
2
O
2
3
0.0290
0.0051
0,7044
0.0058
photocatalysis
photocatalysis
photocatalysis
photocatalysis
electrochemical
[11]
[11]
[38]
[39]
[40]
Au-NPs-NGQDs
ZnO
Ce-PbO
2
ed.
0.0377
*
ed. refers to electrodes
The lengthy electrolysis time allows for high production of hydroxy radicals leading
to a more optimal degradation process. When referring to measurements using a cyclic
voltammogram (CV), it is noticeable that the 4-NP structure experiences some changes
before and after the degradation process. The mechanism for the breakdown of the 4-NP
1
4

ACCEPTED MANUSCRIPT
compound is shown in Figure 7. The degradation of 4-NP in this study may be done
through various methods, one of which is a reduction of the nitro group to primary amine
and degradation by hydroxy radicals resulting from the breakdown of H
2
2
O compounds
in cathode. The 4-NP breakdown that becomes a 4-nitrocatechol intermediate compound
is triggered by the radical OH attack on the ortho position of 4-NP. However, the ortho
position at 4-NP is stabilized by the hydroxyl group at 4-NP. Hence, the attack from the
OH radicals will incline to the less stable position of the metha until 4-nitrocatechol is
formed. This compound is an intermediate compound that is less stable, making it easily
degradable into lower molecules [39]. The degradation that occurred at 4-NP in this study
did not reach a breakdown to lower components such as CO
2
and H O. However, the
2
breakdown of the 4-NP component only breaks the benzene group. This might occur due
to the production of OH radicals which are still lacking and the short time of electrolysis.
1
5

ACCEPTED MANUSCRIPT
Figure 7. Proposed electrochemical degradation pathway of 4-NP on Ti/TiO -NiO
2
electrode
-1
Figure 8. (a) COD test from the degradation of 4-NP 10 mg L at pH 11.0, (b)
-1
repeatability test of Ti/TiO -NiO electrode for degradation 4-NP 10 mg L at pH 11.0
2
1
6

ACCEPTED MANUSCRIPT
The breakdown of the 4-NP compound was also confirmed by COD analysis. COD is
usually used as an indicator of organic degradation in the wastewater. It was observed
that the presence of electrolysis using Ti/TiO
value to 30.12%. This shows that the mineralization process from 4-NP becomes a lower
molecular weight compound. In addition, in this study, the stability of Ti/TiO -NiO
2
-NiO electrodes was able to reduce the COD
2
electrodes was examined in 4-NP degradation. The results of the electrode stability testing
are shown in Figure 8. The stability test was carried out in a 10 mg/L 4-NP solution of
2
0 measurements. The results indicate that the electrodes have good measurement
stability in the measurement range because the RSD value of the measurement is smaller
than 11.31% as the percentage of its RSD Horwitz.
CONCLUSION
Ti/TiO
decomposition methods and have been used as electrodes for the degradation of 4-NP in
an aqueous medium. Under these optimal conditions, 4-NP removal using Ti/TiO -NiO
electrode of approximately more than 95% was reached with a degradation rate of 0.039
2
-NiO electrodes were successfully made in this study through thermal
2
-1
min . The degradation of the 4-NP compound was confirmed by the decrease
concentration and COD value. This shows that Ti/ TiO -NiO electrodes can be effectively
used as electrodes in 4-NP degradation, although this notion still requires further study,
especially into the effect of the addition of electron receptor compounds such as H
2
2
2
O .
From this study, the mechanism of 4-NP degradation does not occur directly but the
degradation can occour through the formation of OH radicals produced from the
breakdown of H
2
2
O compounds.
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1
7

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ACCEPTED MANUSCRIPT
Highlights


Ti/TiO -NiO electrodes were designed for electrochemical 4-
2
nitrophenol degradation
It exhibited high catalytic degradation with the constant rate 0.0373
min-1


Mechanism for the rate of degradation of 4-NP is proposed
The method is promising for real water treatment
2
0