Nanosized Titania-Nickel mixed oxide for visible light photocatalytic activity

Article abstract of DOI:10.1016/j.molliq.2020.113328

Colourful dyes are primarily used in the textiles, toys, food, inks, paper and plastics. These dyes are water soluble and contaminate the water. The dyes are not bio-degradable and sustain in the water for long time create diseases like bladder tumour and

Full text of DOI:10.1016/j.molliq.2020.113328

Journal Pre-proof
Nanosized Titania-Nickel mixed oxide for visible light
photocatalytic activity
Saravanan Rajendran, Devaraj Manoj, J. Nimita Jebaranjitham,
Baskaran Ganesh Kumar, G. Bharath, Fawzi Banat, Jiaqian Qin,
S. Vadivel, F. Gracia
PII:
S0167-7322(20)31363-5
DOI:
https://doi.org/10.1016/j.molliq.2020.113328
MOLLIQ 113328
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
4 March 2020
3 May 2020
7 May 2020
Please cite this article as: S. Rajendran, D. Manoj, J. Nimita Jebaranjitham, et al.,
Nanosized Titania-Nickel mixed oxide for visible light photocatalytic activity, Journal of
Molecular Liquids (2020), https://doi.org/10.1016/j.molliq.2020.113328
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Nanosized Titania-Nickel mixed oxide for visible light
photocatalytic activity
a*
b
c
d,e
Saravanan Rajendran, Devaraj Manoj, Nimita Jebaranjitham J, Baskaran Ganesh Kumar,
f
f
g
h
i
G. Bharath, Fawzi Banat, Jiaqian Qin, S. Vadivel, F. Gracia,
a
Faculty of Engineering, Department of Mechanical Engineering, University of Tarapacá, Avda,
General Velasquez, 1775, Arica, Chile
b
Key laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education,
School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology,
Wuhan 430074, China
c
PG Department of Chemistry, Women’s Christian College (An Autonomous Institution Affiliated to
University of Madras) College Road, Chennai- 600 006, Tamil Nadu, India.
d
Department of Chemistry, P.S.R. Arts and College, Sivakasi, TN, India
e
Department of Science and Humanities, P.S.R. Engineering college, Sivakasi, TN, India
f
Department of Chemical Engineering, Khalifa University, P.O. Box 127788, Abu Dhabi, United Arab
Emirates
g
Metallurgy and Materials Science Research Institute, Chulalongkorn University, Bangkok 10330,
Thailand
h
Department of Chemistry, PSG College of Technology, Coimbatore-641004, India
i
Department of Chemical Engineering, Biotechnology and Materials, University of Chile, Beauchef
8
51, 6th floor, Santiago, Chile
Corresponding Authors:
Dr. Saravanan Rajendran (saravanan3.raj@gmail.com)
1

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Abstract
Colourful dyes are primarily used in the textiles, toys, food, inks, paper and plastics. These
dyes are water soluble and contaminate the water. The dyes are not bio-degradable and sustain
in the water for long time create diseases like bladder tumour and chromosomal damage.
Hence dyes are the major cause of pollution and must be removed from domestic and drinking
water. The photocatalysts are energy-less technology for dye degradation and expected to solve
clean water problems. Most of the photocatalysts are metal oxides and absorbed in the ultra
violet region. But, sun light mostly consists of visible light, hence to use the sunlight
effectively the absorption spectrum of the photocatalysts must be tuned to the visible region.
Herein, we proposed visible light absorbed new TiO /NiO nanocomposite for methyl orange
2
dye degradation. The integration of NiO modified the TiO nanocomposite UV absorption
2
spectrum into visible light region. The photocatalyst was prepared using mechano-thermal
method and characterised using PXRD, TGA, FT-IR, HR-TEM, EDS, UV, PL and DRS
methods. The photocatalytic property was explored using the degradation of methyl orange and
compared the activity with different time intervals and wide range of pH. Within 60 minutes of
irradiation, 98% of degradation was observed. Similarly, at all pH range more than 50% of
degradation was observed, but the best performance (98%) was observed at pH=7 (neural).
Thus, the TiO /NiO nanocomposite catalyst was effective in neutral, acidic and basic polluted
2
water treatment. The synthesised TiO /NiO nanocomposite is tuneable to visible light and
2
degrade the methyl orange dye in all pH range.
Keywords: Visible light; Photocatalyst; Methyl Orange; Nanomaterial; Degradation.
2

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1
. Introduction:
In recent years, the wide scale of manufacturing divisions are accumulating and causes a lot of
harmful effects in the environment. Predominantly, fabric industrial units regularly utilizes
toxic or destructive organic colourants for customised dying process [1]. The outlet of dying
sewages were generally untreated and immediately passed through our drinking aquatic bodies
that lead to engender numerous diseases for human and all other living species [1-2]. The
investigators are most passionate to discover and elucidate the above stated water problem [1-
3
]. In this connection, there are numerous physical and chemical methods emerging to resolve
the waste water problem.
Associated with other water-purification management methods, photocatalysis is an exclusive
technology since it is simple to operate and valuable proficiency via low-cost process.
Furthermore, in the recent times, nanocatalysts expressed an energetic characteristics to reduce
the organic contaminations [4]. Particularly, wide band gap nano semiconductors (TiO , ZnO,
2
SnO , CeO and NiO) show an outstanding photocatalytic degradation capability over toxic
2
2
organic pollutants [5]. When compared with other photocatalytic materials, nanosized titania
TiO ) has exhibited greater degradation ability of textile dyes due to its intrinsic positive band
(
2
position which effectively generated more electrons and holes, leads to abolish the organic
colourant through the exposure of UV light. The reality of TiO has a large bandgap material
2
(3.2 eV) which shows an inauspicious nature to accomplish the textile dyes under the
exploitation of visible source [5, 6].
Based on the prior literatures, it has been realised that the postponement of electron-hole
recombination process improves the photocatalytic competency of the catalyst. In this relation,
hybrid metal oxides were attracted a lot of researchers due to its enhanced photocatalytic
performance. On the other hand, the hybrid or coupled materials possess new potential
applications like optoelectronic, electrochemical devices, sensors, solar cells, photocatalysis
and biological imaging, etc. [4-12]. When matched with pure TiO performance, the coupled
2
or doped systems were exposed higher methyl orange and methylene blue degradation rate,
because of the presence of synergistic effect and higher surface area [6, 13]. Recent times,
TiO incorporated with other different bandgap systems (TiO -CeO , TiO - SnO , TiO -CuO,
2
2
2
2
2
2
3

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TiO -CdO etc.,) were exhibited active photocatalytic capacity under visible light or enriched
2
UV light degradation responses due to the addition of other system. The coupled materials
have the capability to engross visible light source and directed to create more photogenerate
electrons and holes. Further, the photogenerated electrons and holes transfer through hopping
mechanism due to newly generated larger band. [14, 15]. However, some of the previous
reports described when TiO coupled with NiO converts TiO to visibly active material [16,
2
2
1
7]. The results are contrary, due to the existing dual material that possess large bandgaps
(
TiO = 3.2 eV and NiO = 3.6 eV). The TiO and NiO materials are unable to absorb the visible
2
2
light, but absorb in ultraviolet region due to wide band gap of the materials. Therefore, we need
deep understanding of TiO -NiO system and its visible light induced photocatalytic mechanism
2
is still confused to explain.
In the present manuscript, TiO -NiO nanocomposite system was synthesized by novel method
2
via sol-gel combined with mechano-thermal synthesis process. The obtained TiO -NiO
2
properties were characterized by different examination tools such as PXRD, TEM and XPS
and their observed results were discussed herein. In addition, the core theme of existing study
is to recognize the visible light tempted photocatalytic degradation mechanism of nano TiO2-
NiO co-catalyst. We analysed the photocatalytic viability of TiO /NiO composite using
2
degradation of methyl orange. It was found that NiO/TiO acted as a co-catalyst for methyl
2
orange degradation. Within 60 minutes of irradiation, 98% of degradation was observed.
Similarly, at all pH range more than 50% of degradation was observed, but the best
performance (98%) was observed at pH=7 (neural). At the end, it has been proposed that the
3
+
formation of p-n junction along with Ni states promotes more generation of electrons which
prevent electrons-holes recombination. The suppressed recombination endorses the prepared
system has an effectual influence to participate under visible light MO degradation processes.
2
. Experimental Section
2
.1. Materials
The following chemicals, nickel acetate, titanium tetra isopropoxide and citric acid were
purchased (Sigma-Aldrich) and used without further purification. Similarly, analytical grade
4

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methyl orange (for photocatalytic analysis) and isopropyl alcohol were purchased. Moreover,
Milli-Q water used during the preparation of TiO -NiO and photocatalytic experiments.
2
2
.2. Synthesis of nanosized TiO -NiO co-catalyst
2
The utilization of modern synthetic technique was performed to prepare nanosized TiO -NiO co-
2
catalyst which was reported in our previous literature [18]. At first, the sol-gel method was
considered to synthesize and purify the pre-calcinated TiO powder. Thereafter, mechanothermal
2
synthesis was instigated to attain the nanosized TiO -NiO co-catalyst. The preparation stages of
2
co-catalyst were divided into two parts and which was defined in short as follows: 30 ml of
prepared titanium tetra isopropoxide was liquified with 150 ml of prepared isopropyl alcohol in a
fume-cupboard which was placed under constant stirring condition. Additionally, 0.5 M of
aqueous citrate solution was prepared and gradually added in the prepared solution, then the
reaction solution was turned into gel and collected. Then the solution was subjected in a muffle
furnace at 150 ºC for 30 min. During the reaction time, the gel was transformed to a pre-
synthesized TiO powder material. After this, the mechanothermal process was prompted to
2
prepare TiO -NiO co-catalyst. In this method, the raw materials (nickel acetate of 100 mg of and
2
9
00 mg of pre-synthesized TiO powder material attained from the above sol-gel process) were
2
mixed and ground with agate pestle and mortar for ~3 h. The dehydration and decomposition
temperature of organic substances from the obtained mixed powder were analyzed through TGA
measurement. The samples were grounded and calcined in a muffle furnace at 450 C and
digested for 1 h. Then the calcined material was slowly cooled down to room temperature (4

C/min), which in turn the process assisted to produce nanosized mesoporous TiO -NiO co-
2
catalyst.
2
.3. Photocatalytic Experiment:
The theme of the present work is focused visible light degradation of organic dyes. In this
scenario, aquatic methyl orange solution was utilised as a standard organic dye (different pH
level). The photocatalytic testing procedure and their steps were defined in our previous reports
[
19, 20]. In the present analysis, the visible light was generated from SCIENCETECH (SF300
B)-AM 1.5G. During the photocatalytic activity, different dosage of catalysts (25 to 200 mg)
were monitored. Dark and visible light exposed methyl orange solutions were scrutinized by
UV–vis absorption spectrophotometer and GCMS (Perkin Elmer Autosystem).
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2
.4. Instrumentation
The thermal decomposition of the as-synthesized materials was analysed by Thermogravimetry
TGA-TA Instruments TGA Q50) with continuous flow of N with a heating rate of 10 °C/min.
(
2
The functional groups present in the nanocomposite were examined by Fourier transform
infrared (FT-IR) spectroscopy (Thermo scientific, Nicolet IS 50). The powder samples made as
-1
pellet using KBr high pressure technique and measured with the range in-between 4000 cm to
-1
4
00 cm . The nanocomposite crystallinity, phase and crystal structure of the materials were
identified by X-ray diffraction using D5000 diffractometer, Siemens, USA and measured with
CuKα1 (λ=1.5406 Å ) irradiation. The synthesized particle size and overall morphology were
2
calculated by a high-resolution transmission electron microscope (HR-TEM), FEI TITAN G 80-
3
00 (operated at 300 keV) and EDS analysis also carried out with same. The composite chemical
composition of the synthesized nanoparticles was predicted using X-ray fluorescence (XRF,
EDX-720, Shimadzu). The X-ray photoelectron spectroscopic measured using Thermo Scientific
Escalab 250Xi. The emission measurements were carried out using a Perkin Elmer
spectrofluorometer LS-55. The absorbance spectra of the prepared materials and degraded dye
samples were obtained using a Perkin Elmer Lambda 35 spectrometer.
3
. Result and discussion:
In the thermogravimetric consequence of pre-synthesized TiO and mixed raw materials, the co-
2
catalyst has subjected to find the decomposition physisorbed water, organic spices and suitable
calcination temperature for the formation of pure and hybrid oxide system and the corresponding
result was described in Fig 1.
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Fig 1. TGA result of the prepared materials
In Fig. 1, the result was perceptibly quantified that there are two most important weight losses
occured from the TGA curve of both pre-synthesized samples. Preliminary, weight loss (~ 4% to
6
%) of both samples was happened at 70 °C to 100 °C, which directs the surface of the pre-
synthesized samples that have water molecules evaporated in this temperature range. Further,
the secondary predominant weight loss (~15% to 22%) shows in 100 °C to 410 °C, point out the
decomposition of organic ingredient from the pre-synthesized samples. However, the TGA curve
of as-prepared co-catalyst sample was experienced with more weight losses (~22%) at slightly
higher temperature when compared with pre-synthesized of pure TiO (~15%) system due to the
2
existence of two different materials TiO and NiO. After that, there is no weight loss observed
2
between 410 °C and 800 °C which reflected the formation of crystallization achieved after 410
°
C. Hence, in this current study, the optimum calcination temperature was fixed at 450 °C based
on the TGA curve. After calcination process, the obtained yields of co-catalyst and its chemical
composition and structure purity were described via XRF and XRD measurements.
The XRF upshot was indisputably agreed that the prevailing elements viz., NiO and TiO were
2
originated from the synthesized co-catalyst scheme and their consistent quantities were shown in
the Table 1.
Table 1: XRF and XRD outcome of the prepared materials
Prepared
Sample
XRF
XRD
Structure (JCPDS No.) and Crystallite
Quantitative
Analysis –
Rietveld
lattice parameter
size (nm)
TiO2 NiO
TiO2
NiO
TiO2 NiO
TiO2
(%)
NiO+
(%)
(%)
(%)
Anatase-
Tetragonal
(21-1272)
Pure
TiO2
100 ------
-----
18.1
----
7.3
100
-----
4.90
a = b = 3.791 Å
and c = 9.508 Å
Anatase-
Cubic
(47-1049) 18.2
TiO -NiO
95.5
4.5
Tetragonal
95.10
2
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co-catalyst
(21-1272)
a=4.190 Å
a = b = 3.797 Å
and c=9.522 Å
Additionally, the XRD (the figure in the supporting information – SI 1) of the prepared co-
2
+
3+
catalyst has exhibited the anatase-tetragonal structure of TiO in joint with a cubic Ni /Ni peak
2
seemed at 43.18º and their resultant crystallite size, structural parameter was depicted in Table 1.
Therefore, the XRD result proved that the co-catalyst was in existence with mixed hybrid
structure which directed to generate several interfaces [21].
The presence of functional group of prepared catalyst was analysed by FT-IR spectra and their
corresponding consequence was displayed in Fig 2. The hydroxyl (OH), carbonyl (C=O), and
metal oxide (M-O) functional bonds are diagnosed from pure TiO system which are appeared at
2
-1
-1
-1
-1
3
445 cm (OH), 1558 cm (C=O), 1420 cm (C=O) and 660 cm (O-Ti-O). Similarly, the co-
catalyst system was shown all the above stretching vibration modes along with O-Ni-O seemed
-1
at 570 cm [22] Hence, the FT-IR spectra were proved the existing functional group of the
.
prepared system which demonstrated the formation of co-catalyst.
Fig 2 FT-IR spectrum of the prepared materials
The prepared co-catalyst size and shape evidence were predicted with the reflection of TEM
micrographs. The TEM image (Supporting Information – SI 2, Fig. 2a) has showed that the
spherical shaped tiny NiO nanoparticles were reliably dispersed over the surface of TiO From
2
.
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the HR-TEM image, shown in Supporting Information – SI 2, Fig. 2b, the d-spacing value of
attained grains or crystallites were completely analysed. The pattern has clearly indicated that
0
.352 nm (101), 0.243 nm (103) and 0.237 nm (004) planes of TiO (Anatase-Tetragonal, JCPDS
2
NO: 21-1272) including 0.241 nm (111), 0.208 nm (200) and 0.147 nm (220) plane of NiO
Cubic, JCPDS NO: 21-1272). The HR-TEM results were unambiguously complemented by
(
XRD analysis. In HRTEM analysis, the decorated circular portion has been specified after the
accumulation of NiO nanoparticles into TiO surface. The nanocomposite formation has created
2
dislocation and more interfaces are commanded to generate line defect which offers oxygen
vacancies [23]. The EDS pattern (Supporting Information – SI 2, Fig. 2c) has apparently
conveyed that the synthesized co-catalyst consisted of Ni, Ti, O and Cu elements.
Table 2: XPS and UV-vis outcome of the prepared materials
UV-Vis absorption
XPS
Bandgap energy
calculated from Tauc
Plot
Start
Binding Binding
Existing energy energy Area
eV CPS. eV
End
Atomic
%
Sample
elements
eV
Ti2p
466
452
36418.3
29.29
3.18 eV (390 λ)
Pure
TiO2
O1s
534
464
525
450
32226.78 70.71
48845.82 27.35
44723.81 68.29
Ti2p
2
.89 eV (429 λ)
O1s
Ni2p
533
886
527
850
TiO -NiO
2
co-catalyst
19968.11
4.36
The composition and their oxidation state of surviving elements in the prepared co-catalyst were
examined by XPS measurement. The XPS pattern has recognized the presence of Ti, Ni, and O
elements and their binding energies were totally resolved through C 1s (284.6 eV) as a reference.
The XPS images (supporting information – SI 3) and their conforming data were organized in
Table 2. The HR-XPS co-catalyst scheme comprised with two symmetric peaks of titania (Ti 2p)
were perfectly tailored with the use of Gaussian functions and their variation is 5.7 eV that was
4
+
3+
2+
referenced to Ti state. On the other hand, Ni 2p has exhibited Ni and Ni states and the O 1s
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peaks were associated with NiO, Ni O , TiO and hydroxyl in the co-catalyst. Interrelated with
2
3
2
pure TiO analysis, the co-catalyst possess lower binding energies that recommend surface
2
modifications which provided more interfaces [24]. Hence, the XPS results suggested that clearly
3
+
the Ni was associated in TiO - NiO co-catalysts system.
2
The core strategy of this present study, effectively prompting the photocatalytic activity of TiO2
nanostructure by the way of combination of NiO material. In this connection, finding the changes
in the optical bandgap of the synthesized co-catalyst is essential due to utilization of specific
wavelength of light in the catalytic reaction [25]. The UV-vis absorption spectrum of the
prepared materials was shown in Fig. 3. The result of pure material is demonstrated that well
crystallinity was identified via the absorption spectrum of pure material, which reflect very sharp
edge is at 390 nm. Concurrently, the co-catalyst spectrum was displayed broad edge (410 - 430
nm) which stated that the prepared co-catalyst contains amorphous materials [26]. The embodied
inset figure labelled the optical bandgap of the prepared materials were estimated from Tauc plot
[
27] and the values are shown in Table 2.
Fig 3 UV-vis absorption spectrum of the prepared materials (inserted image represented
bandgap determination using Tauc plot)
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The prepared co-catalyst shows lower bandgap due to established strong interfaces in-between
TiO and NiO materials which promotes easier to transfer electrons in the conduction band NiO
2
to TiO [17, 28]. For additional intention behind the reason of decreasing the band gap is the
2
3
+
survival of line defect and Ni ions which are persuading intermediate state between the
bandgap of NiO/TiO system [28]. When compared with pure system, the co-catalyst having
2
intermediate state that makes delay for electrons-holes recombination process that reduces the PL
intensity (Fig. 4). Concluded from the observation of UV-vis absorption and PL outcomes,
during the photocatalytic reaction, the newly created intermediate states are effective and prevent
the recombination process [19]. The suppression of recombination process encourage more
number of electrons and holes to participate in the TiO -NiO catalytic process.
2
Fig 4 PL spectrum of the prepared materials
In this study, the competence of visible light photocatalytic reaction of TiO -NiO catalyst has
2
been monitored through the examination of methyl orange (MO) degradation. Primarily, the
photolysis performance of MO has examined by visible light irradiation (~1 h), and their
consistent absorption results recommended that the MO dye has shown no changes in the
absorption which postulates that the MO dye has shown a constant photostability. We know that,
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the pure TiO system has incapable to generate electrons and holes under visible light
2
illumination due to its wide band gap (~3.2 eV). Further, to find the optimal amount of TiO -NiO
2
-3
catalyst, a series of MO degradation experiments (concentration of MO is 3 X 10 M) were
carried out. In these reaction, different quantities of TiO -NiO material (from 25 mg to 200 mg
2
of catalyst/L of MO dye) were used for MO degradation. During regular interval of irradiation,
the elimination of MO efficiency was calculated, and their corresponding results were shown in
Fig 5 a. The removal of MO results conclusively described that the degradation percentage is
increased while loading 25 mg to 100 mg of catalysts. After that, the higher dosage (150 mg and
2
00 mg) shows comparable and slightly decreasing degradation rate. Because, high amount of
catalysts reduce the light transmission during the photoreaction [29, 30]. Therefore, in the above
observation, we optimized 100 mg of TiO -NiO catalyst that shows better degradation result
2
while compared with other quantities.
The manufacturing sewage generally have a wide range of pH values and it play a significant
role during the degradation reaction. Henceforward, attempting with different pH of MO has
been carried by evaluating the performance of optimal quantity of prepared TiO -NiO catalyst
2
(100 mg) verses different pH value. In Fig 5b, it clearly exhibits the different pH value
effectually influence on the degradation. Based on degradation (acid and alkaline medium)
results, pH=7 displayed higher degradation (98 % for 60 minutes). Because of accumulation of
charge on the surface of the catalysts (TiO -NiO), it may influence the dispersibility of the
2
reaction suspension. The comparable remark was described in the preceding literatures [29, 30].
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Fig 5. Photocatalytic degradation of (a) Different quantities of TiO -NiO materials and (b)
2
Different pH of MO solution
The pathway diagram and GC-MS results help to clearly identify the intermediates and final
4
+
2+
outcomes of the photocatalytic reaction (Fig 6a). The catalyst (TiO -NiO) consists of Ti , Ni ,
2
3
+
Ni states (which were identified by XPS results). The occurrence of NiO and TiO creates the
2
3
+
formation of p-n junction and the presence of Ni having additional capability to absorb the
visible light and initiating the photocatalytic process [31, 32]. The schematic representation of
photocatalytic degradation of TiO -NiO system is shown in Fig 6b. Furthermore, the persisting
2
3
+
Ni generates dislocation on the surface of the TiO -NiO system which prompts more electrons
2
facilitate during the photocatalytic reaction [31, 32]. The dislocation has clearly acknowledged in
HR-TEM image (Supporting Information – SI 2, Fig. 2b). Hence, the formation p-n junction
3
+
along with Ni states promotes more generation of electrons and prevention of electrons-holes
recombination which endorses the prepared system has an effectual influence to participate in
visible light MO removal processes.
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Fig 6. Photocatalytic degradation of (a) Degradation pathway of dye Methyl orange
(b) Schematic diagram of photo electron-hole generation
Conclusion:
With the intention of tuning UV absorption of TiO to visible region, NiO is integrated and
2
prepared the TiO /NiO nanocomposite. The TiO /NiO composite was prepared using mechano-
2
2
thermal method. The NiO integration in TiO was successful and analysed using the UV-visible
2
absorption spectrum, PXRD and TEM analysis. The NiO integration migrated the band gap of
TiO nanoparticles from 3.18 eV to 2.89 eV and estimated using Kubelka-Munk conversion. The
2
TEM micrographs showed that TiO and NiO are composited together with signature planes of
2
TiO (1 0 1), (1 0 3), (0 0 4) and NiO (2 0 0), (1 1 1) and (2 2 0). Notably, through XRF analysis,
2
mere 4.5% of NiO integration shifts the TiO absorption to visible spectra. The PXRD analysis
2
exhibited that NiO integration did not alter the crystal structure of TiO (anatase, JCPDS# 21-
2
1
272) phase and NiO ( JCPDS = 47-1049) has been presented as a cubic phase. The XPS
analysis proved that the oxidation state of nickel as 2+, 3+ and titanium as 4+. In summary,
synthesised TiO /NiO composite, characterised completely and successfully tuned the absorption
2
spectrum to the visible region.
It has been analysed the photocatalytic viability of TiO /NiO composite using degradation of
2
methyl orange. It was found that NiO/TiO acted as a co-catalyst for methyl orange degradation.
2
We compared the photocatalytic activity with different time intervals and wide range of pH.
Within 60 min of irradiation, 98% of degradation was observed. Similarly, at all pH range more
than 50% of degradation was observed, but the best performance (98%) was observed at pH=7
(
neural). Thus, the TiO /NiO nanocomposite catalyst was effective in neural, acidic and basic
2
polluted water treatment. The synthesised TiO /NiO nanocomposite is tunable to visible light
2
and degrade the methyl orange dye in all pH range. The mechanism of methyl orange
degradation was analysed using GCMS analysis. The entire pathway of degradation was
3
+
followed and identified. We propose that the formation of p-n junction along with Ni states
promotes more generation of electrons which prevent electrons-holes recombination. The
suppressed recombination endorses the prepared system has an effectual influence to participate
visible light MO degradation processes.
Acknowledgements
1
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The authors (S.R., F.G.) acknowledge the support of CONICYT through the project
CONICYT/FONDAP/15110019. The author (S.R) acknowledge FONDECYT Government of
Chile (Project No.: 11170414), for the support to carry out this project.
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Credit author statement
Saravanan Rajendran, Baskaran Ganesh Kumar
Writing- Original draft preparation,
-
Saravanan Rajendran, Devaraj Manoj, and Nimita Jebaranjitham J
Conceptualization, Methodology, Reviewing and editing
Saravanan Rajendran, G. Bharath, Fawzi Banat, Jiaqian Qin, S. Vadivel, F. Gracia,
Visualization, Investigation, characterization and discussion, software validation.
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No conflict of interest
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0

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Highlights


TiO -NiO nanocomposite system prepared by new method (sol-gel along with mechano-
2
thermal process).
3
+
The formation p-n (TiO -NiO) junction along with Ni states prevent electrons-holes
2
recombination.


The incorporation of NiO generate line defect on the TiO surface.
2
3
+
The presence of Ni and line defect were promoted the visible light activity.
2
1