Adsorptive/photo-catalytic process for naphthalene removal from aqueous media using in-situ nickel doped titanium nanocomposite

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/274261088
Adsorptive/photo-catalytic process for naphthalene removal from aqueous
media using in-situ nickel doped titanium nanocomposite
Article in Journal of Environmental Management · March 2015
DOI: 10.1016/j.jenvman.2015.03.008 · Source: PubMed
CITATIONS
34
READS
72
2 authors:
Some of the authors of this publication are also working on these related projects:
medical waste View project
Visible light driven photocatalyst development and application View project
Ajit Kumar Sharma
Lovely Professional University
77 PUBLICATIONS 2,254 CITATIONS
SEE PROFILE
Byeong-Kyu Lee
University of Ulsan
259 PUBLICATIONS 8,204 CITATIONS
SEE PROFILE
All content following this page was uploaded by Ajit Kumar Sharma on 29 March 2021.
The user has requested enhancement of the downloaded file.
Water Liberty Guide Freedom in New World Order

Adsorptive/photo-catalytic process for naphthalene removal from
aqueous media using in-situ nickel doped titanium nanocomposite
Ajit Sharma, Byeong-Kyu Lee*
Department of Civil and Environmental Engineering, University of Ulsan, Nam-gu, Daehak ro 93, Ulsan 680-749, Republic of Korea
a r t i c l e i n f o
Article history:
Received 27 December 2014
Received in revised form
3 March 2015
Accepted 5 March 2015
Available online 26 March 2015
Keywords:
TiO2/NiO nanocomposite
In-situ doping
Hydrophobic bonding
Sorption
Light phase
a b s t r a c t
The present study investigates the synthesis and characterization of in-situ nickel doped titanium
nanocomposite (TiO2/NiO) use as an adsorbent and a photo-catalyst for naphthalene removal from
aqueous phase. Nickel-titanium nanocomposites were synthesized by using an in-situ process for the
nickel doping and further calcined at 600
C for 6 h to produce the desired TiO2/NiO nanocomposite,
which was then characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared
(FTIR) spectroscopy, X-ray diffraction (XRD) and UVdVis analysis before and after naphthalene removal.
The removal of naphthalene was explored with effect of pH, time and initial concentration of naph-
thalene (2e25 mg/L) in the presence of dark and light phases. Naphthalene removal tests were con-
ducted under both batch and continuous flow conditions. A special column without any channeling
problem was successfully designed for the removal of naphthalene by continuous flow process in the
presence of visible light source. The removal was maximized at pH 6.5. The maximum amount of
naphthalene removed by TiO2/NiO(0.1) nanocomposite in the presence of visible light phase was
322.1 mg/g, which was 2.5 times greater than that of the parent TiO2. The removal of naphthalene ob-
tained during the breakthrough analysis was consistent with the batch equilibrium data.
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Naphthalene, a bicyclic aromatic hydrocarbon, is a priority
pollutant because of its high human toxicity at even low concen-
trations (Lair et al., 2008). Naphthalene is derived from coal tar
produced from heavy petroleum fractions during petroleum
refining. Naphthalene is extensively used in 2-naphthol synthesis,
pigments and precursors for various dyestuffs (Olmez-Hanci et al.,
2012). Naphthalene-derivative polycyclic aromatic hydrocarbons
(PAHs), such as acenaphthene, acenaphthylene and benzopyrene,
are recognized as toxic carcinogens. Petroleum refining, chemical
synthesis, coal gasification and petrochemical wastewaters are the
main sources for environmental naphthalene (Sener and Ozyılmaz,
2010; Liu et al., 2014). High naphthalene exposure may damage or
destroy red blood cells and the central nervous system and cause
hemolytic anemia and cancer in humans (Belin et al., 2014). Many
techniques investigated for naphthalene removal from water
included chemical oxidation, reverse osmosis, microbial
degradation, biofiltration, bioreactors, solvent extraction, adsorp-
tion and photo-catalytic processes (Ferella et al., 2013; Yang et al.,
2013; Shi et al., 2013; Andas et al., 2014; Rubio-Clemente et al.,
2014).
Removal methods of organic pollutants by a combined tech-
nique of adsorption and photo-catalytic processes are more useful
because they have low cost, large retention capability and more
efficiency for pollutant remediation using only a small amount
(Tang et al., 2011; Chen et al., 2013). TiO2 has been extensively used
as a photo-catalyst and as an adsorbent for naphthalene removal
from air and water due to its low cost, improved activity over a large
pH range, and long-term stability (Jing et al., 2013; Wang et al.,
2014; Rubio-Clemente et al., 2014). Titanium-based nano-
composites and metal oxide nanoparticles with large surface area
are advantageous to adsorb and degrade organics at even low
consumption (Ahmed et al., 2011; Tunçal and Uslu, 2015). The uses
of heterogeneous titanium catalyst are well reported for degrada-
tion of organic pollutant from aqueous media (Luis et al., 2011;
Chaoi et al., 2013; Ji et al., 2013). The carbon nanotube doped tita-
nate nanotube has been used as catalyst for degradation of benzene
with 90% mineralization (Tang et al., 2011). The reported removal
efficiency of phenolic organic compounds by adsorption and photo-
* Corresponding author.
E-mail address: bklee@ulsan.ac.kr (B.-K. Lee).
Contents lists available at ScienceDirect
Journal of Environmental Management
journal homepage: www.elsevier.com/locate/jenvman
http://dx.doi.org/10.1016/j.jenvman.2015.03.008
0301-4797/© 2015 Elsevier Ltd. All rights reserved.
Journal of Environmental Management 155 (2015) 114e122

catalytic degradation methods using TiO2/activated carbon com-
posite was 54.14 and 13.88%, respectively (Ngamsopasiriskun et al.,
2010). TiO2-supported glass raschig rings have been used as a
catalyst for naphthalene removal (Garcia-Martinez et al., 2005).
Nickel-supported catalysts have been widely used for hydrogena-
tion, methanation and hydrocracking of naphthalene in industrial
chemical processes (Monteiro-Gezork et al., 2007, 2008;
Sreethawong et al., 2011). Zeolite modified with Ni was also used
as an adsorbent for naphthalene adsorption (Thomas et al., 2010).
In this study, nickel was selected as the alternative dopant into ti-
tanium because of its wide application as a catalyst with extraor-
dinary electrical, catalytic, redox and thermal properties (Yi et al.,
2007; Nakhate et al., 2010) for PAH removal. Nickel has been
considered the most suitable metal in hydro-treating, steam-
reforming reactions and photo-catalysis (Yi et al., 2008; Olya et al.,
2013). Thus, the incorporation of nickel oxide into titanium might
improve its effectiveness for naphthalene removal from water.
Nickel oxide-incorporated titanium (IV) agglomerate might
enhance their material properties such as surface sorption and
photo-induced catalysis. However, only insufficient research has
been conducted to investigate the technology of an in-situ doping
for nickel oxide nanoparticles incorporation into titanium dioxide.
The removal efficiency through batch process is not very
commercially applicable due to insufficient contact between
adsorbent and adsorbate in purification system for equilibrium. For
commercialization of organic compound removal/degradation, a
packed bed column is the most appropriate system to utilize the
adsorbent/catalyst and improve wastewater purification. However,
the applicability of the adsorbent/photo-catalyst towards naph-
thalene from aqueous solution by a column method in the presence
of light has not been researched.
Therefore, this study investigated the synthesis of nickel-doped
titanium nanocomposite and its ability to remove aqueous naph-
thalene from wastewater in a packed down-flow column method.
The naphthalene removal was studied by batch sorption and
continuous flow process with a fixed bed column in visible light
irradiation and dark phase. The designed column for naphthalene
removal was optimized with a bed height and a flow rate effects in
visible light irradiation.
2. Materials and methods
2.1. Chemicals used
Nickel nitrate 6-hydrate (purity 99.9%) and titanium (IV) iso-
propoxide (TIP) were used for synthesis of nanocomposite (Dae-
jung Chemical and Metals Co. Ltd., Korea). The naphthalene (N) was
obtained from Aldrich Chemical Company. Analytical grade chem-
icals were used for reagent preparation in double-distilled water.
2.2. Synthesis of TiO2/NiO nanocomposite
A novel nickel-doped titanium nanocomposite was synthesized
by in-situ metal doping with a modified solegel process. Nickel
nitrate 6-hydrate (Ni(NO3)2$6H2O) was doped in titanium solution
during the solegel synthesis of titanium NPs. In detail, TIP (7.44 mL)
was mixed with glacial acetic acid (14.32 mL) at 30 C for hydro-
lyzation, by adding 80 mL ethanol solution and stirring for 20 min
to form a homogeneous solution. Then 80 mL of nickel nitrate 6-
hydrate (0.01e1 M) in H2O was added into the above-mentioned
titanium solution. Nickel-doped titanium nanocomposites with
different nickel concentrations (0.01e1 M; hereafter represented by
TiO2/NiO(0.01), TiO2/NiO(0.1), TiO2/NiO(0.5) and TiO2/NiO(1) were
obtained by drop wise addition of 2 mL of 0.5 M NaBH4 into the
nickeletitanium solution under stirring at 30 C. The formation of
the in-situ nickel oxide-doped titanium dioxide (TiO2/NiO) nano-
composite was visually confirmed when the solution turned
slightly speckled white in color. The continuous stirring of mixture
solution was carried out for 12 h at 40 C to obtain a gel like mixture
formed by complete hydrolysis of the titanium dioxide and nickel
oxide. Thereafter, the gel mixture was placed into an oven for
16 h at 100 C for gelation process. Afterwards, the temperature
controlled furnace was used for calcination of gel material at 600 C
for 6 h to produce the desired mixed oxide nanocomposite.
The titanium dioxide was synthesized using the above proce-
dure at the identical conditions except for no addition of nickel
nitrate 6-hydrate (Sharma and Lee, 2013).
2.3. Characterization
The particle size analyzer (model Mastersizer using
hydro2000MU, Malvern Instrument) was used to analyze particle
size of TiO2 and the TiO2/NiO nanocomposite. Infrared spectra were
obtained by Nicolet Nexus 470 Fourier transform infrared (FTIR)
spectroscopy in the region 4000500 cm1
before and after
naphthalene removal. The surface textures of the TiO2/NiO nano-
composite were characterized by X-ray photoelectron spectroscopy
(XPS) using a Thermo Scientific K-Alpha XPS spectrometer. The
TiO2/NiO nanocomposites were further examined by X-ray
diffraction (XRD, Bruker AXN) in the 2q range of 10e80 crystal-
linity behavior. The changes of spectral region were identified by
comparing UVeVis absorption spectra at 300e700 nm wavelengths
using a UVeVis spectrophotometer (UV-1700 Shimadzu).
2.4. Batch sorption experiments as an adsorbent and as a photo-
catalyst
The naphthalene removal was optimized with change of pH and
dosage parameters using the TiO2/NiO nanocomposites, which
have different doped nickel concentrations as a sorbent/photo-
catalyst, in water bath shaker at 120 rpm and 30 C for 1.6 h. The
nanocomposite was used as an adsorbent in dark condition (no
light source) and used as a photo-catalyst in the presence of visible
light sources. The pH range from 4.0 to 8.0 was used to study the pH
parameter at100 mL of 5 mg/L naphthalene solution. The pH of the
solution was maintained by 0.5 M HCl or NaOH and equilibrium of
naphthalene removal was decided using 10 mg of TiO2/NiO nano-
composite. Subsequently, the reaction mixture was shaking with
preferred time and whatman 0.45 mm filter membrane was used for
filtration of mixture solution. Thereafter, the filtrate after suitable
dilution was analyzed by UVeVis spectrophotometer at 275.5 nm
(Anbia and Moradi, 2009). For the evaluation of the time to reach
equilibrium, the reaction time with shaking was varied from 5 to
100 min. The time equilibration was performed at 100 mL of 10 mg/
L naphthalene concentrations using 10 mg of nanocomposite in the
presence of visible light sources and dark condition. The reaction
solutions were filtered after being shaken for 100 min. In order to
evaluate the performance as an adsorption/photo-catalysis in the
presence of dark condition and visible light sources, one factor was
changed at a time keeping others fixed. The TiO2/NiO nano-
composite samples with different nickel molar ratios were used to
investigate the effect of nickel content for removal of naphthalene
under visible light irradiation and dark conditions. The initial
concentrations of naphthalene ranging from 2 to 25 mg/L were
studied for equilibrium of naphthalene removal. The amount of
naphthalene removed per one gram of the TiO2/NiO nano-
composite was estimated by the remainder of initial and final
naphthalene concentrations using equation (1) (Sharma and Lee,
2013).
A. Sharma, B.-K. Lee / Journal of Environmental Management 155 (2015) 114e122 115

qe ¼ ðCo CeÞ V=W (1)
where qe is denoted for capacity of the removed naphthalene (mg/
g) on the TiO2/NiO nanocomposite, Co and Ce are denoted for initial
and final concentrations of naphthalene (mg/L), respectively, V is
the volume of the used aqueous naphthalene (L), and W (g) is the
mass of the TiO2/NiO nanocomposite used.
2.5. Column study in visible light source
A special column was designed to remove naphthalene from
aqueous solution in a continuous flow process with TiO2/NiO
nanocomposite applied as a photo-catalyst under visible light
irradiation. In order to control the column channeling problem
arising from the different sizes of packing sorbent particles, the
TiO2/NiO nanocomposite was synthesized by in-situ doping pro-
cess. During in-situ doping process in a sol gel method, particle
sizes of sorbent were controlled by the reaction speed, mixing and
dry processes. The particle size of the sorbent for naphthalene
removal was controlled larger than 100 mm. Fig. 1 presents a
schematic of designed column which was made by acrylic polymer
(Perspex) plastic. The designed column (Inner diameter ¼ 0.7 cm
and length ¼ 17 cm) was specially invented for the column break-
through analysis of naphthalene removal in the presence of visible
light. The column was filled with 1 and 2 g of TiO2/NiO nano-
composite (layer of nanocomposite ¼ 2 and 4 cm3
, respectively)
and underlain with a steel net sheet (d ¼ 0.001 cm). To improve and
maintain the flow distribution, glass wool (0.5 cm3
) and filter paper
were used for the column packing with TiO2/NiO nanocomposite.
The initial concentrations of naphthalene in the column test run for
naphthalene removal by photo-catalytic reaction were 5, 10 and
20 mg/L. The pH of the naphthalene solution was 6.5 and the
desired flow rate was set to 0.004e0.008 L/min with down-flow
mode. The passed naphthalene solutions were collated at
different time intervals from the exit of a designed column to
evaluate the breakthrough kinetics. The maximum naphthalene
removal efficiency was calculated by dividing the mass of the
removed naphthalene by that of the used TiO2/NiO nanocomposite.
The breakthrough analysis of naphthalene removal was optimized
with variations of flow rate, amount of TiO2/NiO nanocomposite as
a bed height and naphthalene concentration.
3. Results and discussion
3.1. Characteristics properties
3.1.1. Particle size distribution (PSD)
The photon correlation spectroscopy technique was used to
analyze the PSD of TiO2 and the TiO2/NiO nanocomposite (Fig. 2a
and b). The average size of TiO2 and the TiO2/NiO nanocomposite
was around 0.2 mm and ~100 mm, respectively. TiO2/NiO nano-
composite macro-particles are formed by in-situ doping process
with a significant increase in their size of approximately 60e75% as
compared to the parent TiO2 sample. During the in-situ doping
synthesis, nickel oxide nanoparticles may have been deposited on
the microporous structure of the titanium dioxide channel and
increased the particle size of composite.
3.1.2. FTIR study
The absorption peaks range from 3350 to 3400 cm1
and the
bands near 1720 cm1
correspond to the vibrations of the OH group
and surface adsorbed molecular water, respectively (Ahmed, 2012)
(Fig. 2c). The FTIR spectra of TiO2 and different concentrations of
NiO-doped TiO2 provide more information about the nickel con-
centration onto TiO2. In addition, the strong band at 1050 cm1
,
corresponding to the hydroxyl group of metal oxides (MOH), that
was observed on the TiO2/NiO nanocomposite before the adsorp-
tion was attributed to the overlap of the stretching vibration of the
eOH group of TiO2 and the eOH group of nickel oxide (TieOHeNi)
(Tada et al., 2011). The TiO2/NiO nanocomposite containing
different proportions of nickel oxide exhibited some small bands at
1215 cm1
that were also attributed to nickel oxide. The existence
of oxide group of nickel is essential to the photo-catalytic reactions,
where oxides of nickel are generated by photo-excited holes which
are producing hydroxyl radicals for catalysis or mineralization. The
peaks at 1610, 3410, and 2980 cm1
correspond to the surface hy-
droxyl groups on the titanium oxide and same peaks overlapped on
nickel oxides, indicating that they can be utilized as the active sites
for naphthalene removal (B. Gao et al., 2011). At different nickel
contents, the overlapped peaks intensities were changed. However,
in the TiO2/NiO(0.1) composite material, the peak intensity was
higher than that of the other composites. The change in the spec-
trum was observed after naphthalene was removed by the
adsorption/photo-catalytic of the nanocomposite, as shown in
Fig. 2d. The peak at 3410 cm1
represents a loss of surface hydroxyl
groups or amalgamation with organic compound on the nickel
oxide, indicating that they were the active adsorption sites for
naphthalene removal. The peak at 2980 cm1
represents surface
hydroxyl groups of the nanocomposites. After naphthalene was
removed, the peaks were merged and shifted to 2927 cm1
. The
TiO2/NiO nanocomposite peak at 1717 cm1
was attributed to the
ring-breathing modes of aromatic molecules and was shifted to
1726 cm1
after the naphthalene removal. The CdO stretch peak
observed at 1240 cm1
was due to nickel oxide incorporation in the
Fig. 1. Schematic of the column experiment for naphthalene removal study.
A. Sharma, B.-K. Lee / Journal of Environmental Management 155 (2015) 114e122
116

naphthalene-loaded nanocomposite, showing that naphthalene
was chemically bound with the nanocomposite (Yan et al., 2014).
3.1.3. XPS study
The chemical oxidation states of the nanocomposites were ob-
tained from XPS analysis, as shown in Fig. 3. The XPS core levels of Ti
2p, the binding energies (BE) at 458.6 eV and 464.5 eV, are attributed
to the 2p3/2 and 2p1/2 peaks of TiO2 respectively, indicating pres-
ence of Tiþ4
. The binding energy of the Ti 2p1/2 peaks in the TiO2/
NiO(0.1) nanocomposite slightly decreased from 464.5 eV (in TiO2)
to 464.4 eV. After combining with naphthalene, the binding energy
of the Ti 2p peak was also slightly decreased to 464.2 eV in the TiO2/
NiO(0.1)-N sample, possibly due to the change of electronegativity
of the TiO2/NiO nanocomposite. When TiO2 was co-precipitated
with nickel oxide, nickel and the hydroxyl group in the TiO2/NiO
nanocomposite reacted with naphthalene in the adsorption removal
process. The O1s XPS peak spectrum can be ﬁtted with three char-
acteristic peaks (Z. Gao et al., 2011). Table 1 shows that the charac-
teristic peaks of O1s in the TiO2/NiO nanocomposite were shifted
after (TiO2/NiOeN) naphthalene sorption as compared with before
the sorption by TiO2/NiO(0.1). These peaks changes in the O1s re-
gions were due to surface oxygen species of TiO2/NiO nano-
composite. The surface oxygen species may be in the form of OeC
and O]C oxygen, which were more active for naphthalene removal.
This was attributed to the attraction of hydroxyl radicals followed by
the addition of oxygen and the elimination of hydroperoxyl radicals.
Thus, the TiO2/NiO nanocomposite provides greater removal due to
its adsorbing and photo-catalytic properties when excited by visible
light irradiation. In Ni 2p region, the binding energy at 853.4 and
869.8 eV were allocated to Ni 2p3/2 and Ni 2p1/2 of multiple split-
ting of Ni, respectively. Thus, the nickel element in the nano-
composite existed mostly in the oxidation state and the
combination of nickel with the TiO2 matrix after calcination was
attributed to the formation of NieOeTi bonds. After naphthalene
removal, the nickel peaks at 854.4 eV and 869.8 eV in the Ni 2p
spectra were shifted to 852.9 eV and 867.5 eV, respectively, with
change in intensity. These transitions of peaks may have been due to
the formation of a chargeetransfer complex of some of the sorbed or
degradation intermediates on the surface of the TiO2/NiO nano-
composite. The peaks shifted in the TiO2/NiO nanocomposite are
considered as the evidence of active sites which were used in photo-
catalysis during irradiation of visible light. The similar kinds of peaks
with different binding energy levels were also reported in tin doped
titanium dioxide study (Wang et al., 2010).
3.1.4. XRD study
Fig. 4 shows the X-ray diffraction patterns (XRD) of the TiO2 and
TiO2/NiO nanocomposites before and after naphthalene removal.
The XRD patterns of TiO2, anatase and rutile phases were observed
(Parayil et al., 2013). The peaks at 2q values of 25.1, 37.7, 48.0,
55.0 and 62.6 were ascribed to anatase phase and the peaks at 2q
values of 36.8, 38.6, 53.9, 68.8 were correspond to the rutile
Fig. 2. PSD of (a) TiO2 (average size ¼ 0.2 mm) and (b) TiO2/NiO(0.1) (average size ¼ 100 mm) and FT-IR spectrum of TiO2/NiO nanocomposite before (c) and after (d) naphthalene
removal.

phase. The XRD patterns of the TiO2/NiO nanocomposite revealed
that, with increasing nickel concentration the crystallite size of TiO2
decreases. The decrease in crystallite size can be associated to in-
crease in structural foible that prevents particle growth (Ren et al.,
2010). The Ni-based nanocomposite (TiO2/NiO(0.1)) had the opti-
mum nickel oxide nanoparticles content for the naphthalene
removal, this is because of the existence of Ni2þ
generates vacant
oxygen in the matrix of TiO2 to maintain charge neutrality (Yan
et al., 2014). A new peak of the naphthalene-loaded TiO2/NiO(0.1)
nanocomposite was observed in the XRD pattern at 2q ¼ 29.8
compared to the parent shown in the TiO2 sample.
3.1.5. UVeVis spectra study
The increase in the absorption of the TiO2/NiO nanocomposite at
450e500 nm indicates the enhanced photo-catalytic property in
the visible light region (Fig. S1). The association of nickel (Ni2þ
)
with titanium decreased the band energy, which increased the
absorption at 450e500 nm. The conduction band of the 3d level in
Ti4þ
overlapped with the d-level of nickel ion, which enhanced the
more absorption of visible light by bathochromic shift (Dolat et al.,
2014) for band gap transition. After naphthalene sorption by the
TiO2/NiO nanocomposite, the UVeVis spectra show the increased
absorption at 650e800 nm. This broad peak absorption may have
been due to the amalgamation from naphthalene and some other
organic intermediates.
3.2. Naphthalene removal in visible light and dark condition
3.2.1. Equilibrium of naphthalene with time
The removal of naphthalene onto the TiO2/NiO(0.1)
nanocomposite increases with time in both dark condition and
visible light irradiation (Fig. 5a). The naphthalene removal process
fast in the ﬁrst 30 min and removal was achieved 58.1 and 92.1 mg/
g in dark and visible light phases, respectively, onto the TiO2/
NiO(0.1) nanocomposite. The naphthalene removal was slowly
Fig. 3. XPS spectra and detailed peak distribution of Ti2p, O1s, and Ni2p for TiO2/NiO(0.1) nanocomposite and naphthalene-loaded TiO2/NiO nanocomposite (TiO2/NiO(0.1)-N).
Table 1
Characteristic groups and peak distributions of O1s by XPS analysis of TiO2/NiO
nanocomposite before and after naphthalene removal.
Characteristic groups (O1s) Peaks (eV)
TiO2 TiO2/NiO(0.1) TiO2/NiO(0.1)-N
C]O (C]O, COOR) 529.8 529.9 529.8
CeO (CeOH, COOR) 531.7 532.1 531.8
Water molecules 533.1 533.4 533.4
O1s peaks in XPS spectrum.
Fig. 4. XRD spectra of TiO2 and NiO-doped titanium nanocomposites with different
nickel concentration before and after naphthalene removal.
118

increased and equilibrium was achieved within 40 min, afterwards,
no further increase in the removal efficiency was observed up to
1.6 h. The maximum removal capacity was 62.1 and 98.4 mg/g by
TiO2/NiO(0.1) application after 1.6 h in dark and visible phases,
respectively, with 100 mL of 10 mg/L concentration of naphthalene.
However, in the case of TiO2 in dark and visible phase, the
maximum removal capacity was only 18.9 and 30.1 mg/g,
respectively.
3.2.2. pH effect
The pH effect for naphthalene removal by the TiO2/NiO in dark
and visible light phases was assessed at pH ranging from 4 to 8
(Fig. 5b). The test run was conducted with 100 mL of 5 mg/L con-
centration of naphthalene using 10 mg nanocomposite dose. The
maximum naphthalene removal was observed at pH 6.5, which is
an almost neutral pH value in both dark and visible light phases. It
was concluded that hydrophobic bonding is more effective driving
force as compared to electrostatic force for naphthalene removal
onto the TiO2/NiO nanocomposite at near neutral or slight acidic
pH. This is attributed to the hydrophobic basal planes of the TiO2/
NiO nanocomposite which was interacted to nonpolar poly-
aromatic structure of the naphthalene molecule by hydrophobic
bonding. The removal efficiency of naphthalene is relatively lower
in acidic (pH 6.0) and alkaline (pH 7.0) media than at pH 6.5
because more Hþ
or OH
ions compete with the hydration of the
TiO2/NiO nanocomposite surface, respectively (Abu-Elella et al.,
2013). At optimum pH 6.5, the surface of TiO2/NiO
nanocomposite hydrated with eTieOHeNi due to the reaction
withdOH ions or with H2O by transfer of electron through local-
ized holes to form hydroxyl radicals which improved the naph-
thalene removal during visible light irradiation. Thus, the
maximum naphthalene removal by TiO2 at pH 6.5 in dark and
visible light phases was 14.5 and 19.9 mg/g, respectively. In case of
TiO2/NiO nanocomposite, removal efficiency in dark condition and
in the presence of visible light irradiation was 28.9 and 48.8 mg/g,
respectively, which was 2.5 times more efficient than the parent
TiO2 material.
3.2.3. Equilibrium isotherm
The isotherm data were explored with the Langmuir (Fig. 5c)
and the Freundlich (Fig. 5d) isotherms (Sharma and Lee, 2013) in
the presence of dark and visible light phases. The Langmuir
isotherm describes the monolayer adsorption arise by finite num-
ber of similar surface sites and is represented in the linear form
shown in Equation (2):
Fig. 5. Removal of naphthalene according to (a) contact time, (b) Effect of pH and Equilibrium data shows (c) Langmuir and (d) Freundlich isotherm by TiO2 and TiO2/NiO in the dark
and visible phases.

qe ¼ qmaxbCe=ð1 þ bCeÞ (2)
where qe is the equilibrium quantity of naphthalene removed by
nanocomposite (mg/g), Ce is the equilibrium of naphthalene con-
centration (mg/L), qmax is the maximum uptake (mg/g) indicating
uptake through monolayer sorption, and b is the binding constant
(L/mg) of sorption. The parametric values obtained for the various
constants are given in Table 2. It is evident from the data that the
maximum naphthalene removal capacity from aqueous solution by
the TiO2/NiO(0.1) nanocomposite was 2.5 times greater in visible
light phase and 1.5 times higher in dark condition as compared
with the parent TiO2 material. The high sorption capacity of the
TiO2/NiO nanocomposite for naphthalene was attributed to the
formation of strong naphthaleneeOHeTi/Ni bonds. In addition, the
increased adsorption capacity of the TiO2/NiO nanocomposite was
attributed to the strong soft acid-soft base interactions between
naphthalene and the hydroxyl groups on the TiO2/NiO nano-
composite surface.
The Freundlich isotherm valid for multilayer sorption with
heterogeneous surface energy and is indicated in linear form
shown in Equation (3):
In qe ¼ In Kf þ 1=nIn Ce (3)
where Kf is the sorption efficiency (mg/g) and n is sorption intensity
related with an empirical parameter, which is change with the
heterogeneity of the nanocomposite. Higher values of 1/n represent
better favorability of adsorption. It is evident from Table 2 that the n
values ranged between 0.40 and 0.88 with a regression coefficient
of 0.90e0.92, indicating the strong sorbentesorbate interaction.
3.2.4. Effect of nickel doping
To evaluate the effect of nickel filling onto the titanium for
naphthalene removal, test runs were conducted with four different
nickel concentrations (0.01, 0.1, 0.5 and 1 M) (Fig. S2). The naph-
thalene removal efficiency was 32.4, 62.1, 64.5 and 68.1% with TiO2/
NiO(0.01), TiO2/NiO(0.1), TiO2/NiO(0.5), and TiO2/NiO(1) nano-
composites in dark condition, respectively, indicating that
increased nickel content increases number of binding sites avail-
able for naphthalene removal. However, in visible light phase,
naphthalene removal efficiencies of 64.5, 98.4, 68.9, and 51.2% were
observed with a similar combination, respectively. For the period of
irradiation through visible light, the significant effect of the nickel
loading on the removal efficiency was associated with the recom-
bination of electronehole pairs. The increase in the naphthalene
removal efficiency caused by the photo-catalytic activity in visible
light phase was much higher for the TiO2/NiO(0.1) nanocomposite
than for the other nickel loadings. In the TiO2/NiO(1) nano-
composite, the naphthalene removal efficiency was lower in visible
light phase than in dark condition. At higher nickel loading, the
nanocomposite can block some active sites and reduce the effec-
tiveness of the active phases. Adequate nickel loading (0.1 M) can
enhance the generation rate of electron/hole pairs and thereby
enhance the naphthalene removal. In the TiO2/NiO(0.1) nano-
composite, during irradiation through visible light, the conduction
band of TiO2 formed electron and which were transferred to Ni or
Ni(OH)2 loaded on the TiO2. This depress the electronehole
recombination efficiently, and therefore enhanced the decompo-
sition of naphthalene (Dolat et al., 2014). Thus, the use of an optimal
combination of nickel TiO2/NiO(0.1) is the most effective for opti-
mizing the naphthalene removal results.
3.2.5. Column study for breakthrough analysis in light phase
Fig. 6 describes the breakthrough curves obtained for three
naphthalene concentrations (5, 10 and 20 mg/L) through contin-
uous flow process by column method. The column packed with the
TiO2/NiO nanocomposite, having a particle size around 100 mm, in
the presence of visible light at natural pH. The breakthrough time
can be explained as the time at which the effluent of naphthalene
concentration is similar to the inlet concentration of naphthalene.
The parametric values obtained from the column experiment are
given in Table 3. Among three tested column flow rates (0.004,
0.006 and 0.008 L/min), the naphthalene removal efficiency was
decreased with lowering breakpoint times as the flow rate was
increased. This performance was concluded by the fact that naph-
thalene removal is decreased due to lacking of contact time be-
tween naphthalene solution and bed of the column. The inadequate
time diminish the bonding capacity and contact period for photo-
catalytic removal of naphthalene in the light phase (Garcia-
Martinez et al., 2005). Even though the mass transfer zone was
more shortened at the higher flow rate, the naphthalene removal
was maximized at 0.004 L/min flow rate. In the evaluation of the
naphthalene removal efficiency data, the total removal capacities
were consistent with equilibrium of batch process. The naphtha-
lene breakthrough takes shorter time with increasing inlet naph-
thalene concentrations due to the saturation of the TiO2/NiO
nanocomposite.
3.2.6. Removal mechanism
The validity of the Langmuir and Freundlich models for the
naphthalene removal process was confirmed by the presence of the
structural heterogeneity (hydrophilic edges with hydrophobic
surfaces) property of TiO2/NiO nanocomposite, as shown in Scheme
1. The naphthalene removal in dark phase was concluded that
Table 2
The correlation values and isotherm constants for the removal of naphthalene by
TiO2 and TiO2/NiO nanocomposite in dark and visible phases.
Isotherm model Parameter Dark phase Visible phase
TiO2 TiO2/NiO TiO2 TiO2/NiO
Langmuir isotherm qmax (mg/g) 26.2 172.4 136.9 322.1
b (mL/g) 29.3 24.1 17.7 32.6
R2
0.989 0.974 0.961 0.992
Freundlich isotherm Kf 7.62 132.9 11.09 13.7
1/n 0.373 0.478 0.493 0.883
R2
0.891 0.928 0.871 0.919
Fig. 6. Column breakthrough curves for naphthalene on TiO2/NiO(0.1) nanocomposite
in visible phase.
120

nonpolar organic moieties are initially adsorbed onto the hydro-
phobic surface of TiO2/NiO nanocomposite and combined with
monolayer surface until saturation. Then sorption through het-
erogeneity was occurred by means of interaction of the previously
sorbed organic moieties with the organic compound to be sorbed.
This phenomenon is suggested that the naphthalene is adsorbed
onto the surface of TiO2/NiO nanocomposite through hydrophobic
bonding force (Sener and Ozyılmaz, 2010; Shi et al., 2013). However,
in light phase, the TiO2/NiO nanocomposite also plays an important
role as a photo-catalyst for the naphthalene removal. In the photo-
catalytic process, photo-excitation occurs by the incident photon
energy which requires higher than the band gap energy. The TiO2/
NiO nanocomposites are generated electronehole pairs during
irradiation of visible light. The electrons trapped by nickel are
scavenged not by superoxide radicals but by oxygen molecules. The
electron transfer to oxygen molecules produces radicals of super-
oxide. Moreover, surface of TiO2/NiO nanocomposite is hydrated
with eTieOHeNi due to the reaction with eOH ions or with H2O by
transfer of electron through localized holes to form more hydroxyl
radicals. These hydroxyl radicals and superoxide are strong oxi-
dants and can enhance the degradation/mineralization of naph-
thalene (Aucott et al., 2005; Zhou et al., 2011). Thus, a large amount
of hydroxyl radicals can lead to mineralization and transformation
of naphthalene into CO2 and H2O.
4. Conclusion
TiO2/NiO nanocomposites sized approximately 100 mm were
obtained by in-situ nickel doping onto titanium texture via the
solegel method. Naphthalene at a concentration range of 2e25 mg/
L was removed from aqueous solutions by using the TiO2/NiO
nanocomposite as both an adsorbent and a photo-catalyst. Naph-
thalene was initially sorbed onto the hydrophobic basal surface of
the TiO2/NiO nanocomposite as an adsorbent with hydrophobic
bonding forces. Naphthalene was degraded on the surface of the
TiO2/NiO nanocomposite used as a photo-catalyst due to a char-
geetransfer complex that was identified by peak transitions in the
XPS spectra. The maximum removal capacities of naphthalene
(322.1 mg/g) with TiO2/NiO(0.1) nanocomposite were around 2.5-
Table 3
Column breakthrough removal of naphthalene during removal on TiO2/NiO(0.1)
nanocomposite under flow conditions in visible phase.
S. no Cin (mg/L) Bed height
(cm)
Flow rate
(L/min)
VolR R3
(m/s)
Through-put
volume (L)
Capacity
(mg/g)
1 5 2 0.004 1.73 64.8 312.05
2 10 2 0.004 1.73 40.8 316.41
3 20 2 0.004 1.73 28.8 320.12
4 5 2 0.006 2.59 72.2 317.85
5 5 2 0.008 3.46 80.5 313.52
6 5 4 0.004 1.73 178.6 310.25
VolR R3
(m/s) is superficial liquid velocity.
Scheme 1. Proposed schematic mechanism for naphthalene removal by TiO2/NiO nanocomposite.

(in visible phase) and 1.5-times (in dark phase) greater than those
with TiO2 as the parent material. The packed column designed for
studying naphthalene removal from wastewater was successfully
operated without channeling in the visible phase. The break-
through data of naphthalene uptake in the packed column was
similar to the batch process equilibrium data. This indicates that the
designed specific column reactor can also be effectively used as a
photo-catalytic process to enhance naphthalene removal from
aqueous solution.
Acknowledgments
This work was supported by a grant from the National Research
Foundation of Korea (NRF), funded by the Ministry of Education
(2013R1A2A203013138), and also by a basic science research pro-
gram through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education (2013R1A1A2065796).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jenvman.2015.03.008.
References
Abu-Elella, R., Ossman, M.E., Abd-Elfatah, M., Elgendi, A., 2013. Kinetic modeling
and isotherm study for naphthalene adsorption on boehmite nanopowder.
Desalin. Water Treat. 51, 3472e3481.
Ahmed, M.A., 2012. Synthesis and structural features of mesoporous NiO/TiO2
nanocompositesprepared by sol-gel method for photodegradation of methylene
blue dye. J. Photochem. Photobiol. A Chem. 238, 63e70.
Ahmed, S., Rasul, M.G., Brown, R., Hashib, M.A., 2011. Influence of parameters on the
heterogeneous photocatalytic degradation of pesticides and phenolic contam-
inants in wastewater: a short review. J. Environ. Manag. 92, 311e330.
Anbia, M., Moradi, S.E., 2009. Adsorption of naphthalene-derived compounds from
water by chemically oxidized nanoporous carbon. Chem. Eng. J. 148, 452e458.
Andas, J., Adam, F., Rahman, I.A., Taufiq-Yap, Y.H., 2014. Optimization and mecha-
nistic study of the liquid-phase oxidation of naphthalene over biomass-derived
iron catalyst. Chem. Eng. J. 252, 382e392.
Aucott, S.M., Kilian, P., Milton, H.L., Robertson, S.D., Slawin, A.M.Z., Woollins, J.D.,
2005. Bis(cyclopentadienyl)titanium complexes of naphthalene-1,8-dithiolates,
biphenyl 2,2¢-dithiolates, and related ligands. Inorg. Chem. 44 (8), 2710e2718.
Belin, S., Sany, T., Hashim, R., Rezayi, M., Salleh, A., Rahman, M.A., Safari, O.,
Sasekumar, A., 2014. Human health risk of polycyclic aromatic hydrocarbons
from consumption of blood cockle and exposure to contaminated sediments
and water along the Klang Strait, Malaysia. Mar. Pollut. Bull. 84, 268e279.
Chao, H.P., Lee, C.K., Juang, L.C., Han, Y.L., 2013. Sorption of organic compounds,
oxyanions,and heavy metal ions on surfactant modified titanate nanotubes. Ind.
Eng. Chem. Res. 52, 9843e9850.
Chen, M., Ding, W., Wang, J., Diao, G., 2013. Removal of azo dyes from water by
combined techniques of adsorption, desorption, and electrolysis based on a
supramolecular sorbent. Ind. Eng. Chem. Res. 52, 2403e2411.
Dolat, D., Ohtani, B., Mozia, S., ski, D.M., Guskos, N., Lendzion-Bielun, Z.,
Morawski, A.W., 2014. Preparation,characterization and charge transfer studies
of nickel -modified and nickel, nitrogen co-modified rutile titanium dioxide for
photocatalytic application. Chem. Eng. J. 239, 149e157.
Ferella, F., Stoehr, J., Michelis, I.D., Hornung, A., 2013. Zirconia and alumina based
catalysts for steam reforming of naphthalene. Fuel 105, 614e629.
Garcia-Martinez, M.J., Canoira, L., Blazquez, G., Da Riva, I., Alcantara, R., Llamas, J.F.,
2005. Continuous photodegradation of naphthalene in water catalyzed by TiO2
supported on glass Raschig rings. Chem. Eng. J. 110, 123e128.
Gao, B., Yap, P.S., Lim, T.M., Lim, T.T., 2011. Adsorption-photocatalytic degradation of
Acid Red 88 by supported TiO2: effect of activated carbon support and aqueous
anions. Chem. Eng. J. 171, 1098e1107.
Gao, Z., Du, B., Zhang, G., Gao, Y., Li, Z., Zhang, H., Duan, X., 2011. Adsorption of
pentachlorophenol from aqueous solution on dodecylbenzenesulfonate modi-
fied nickel-titanium layered double hydroxide nanocomposites. Ind. Eng. Chem.
Res. 50, 5334e5345.
Ji, Y., Zhou, L., Ferronato, C., Yang, X., Salvador, A., Zeng, C., Chovelon, J.M., 2013.
Photocatalytic degradation of atenolol in aqueous titanium dioxide suspen-
sions: kinetics, intermediates and degradation pathways. J. Photochem. Pho-
tobiol. A Chem. 254, 35e44.
Jing, Q., Yi, Z., Lin, D., Zhu, L., Yang, K., 2013. Enhanced sorption of naphthalene and
p- nitrophenol by nano-SiO2 modified with a cationic surfactant. Water. Res. 47,
4006e4012.
Lair, A., Ferronato, C., Chovelon, J.M., Herrmann, J.M., 2008. Naphthalene degrada-
tion in water by heterogeneous photocatalysis: an investigation of the influence
of inorganic anions. J. Photochem. Photobiol. A Chem. 193, 193e203.
Liu, G., Cai, Z., Zheng, M., 2014. Sources of unintentionally produced polychlorinated
naphthalenes. Chemosphere 94, 1e12.
Luis, A.M., Neves, M.C., Mendonca, M.H., Monteiro, O.C., 2011. Influence of calci-
nation parameters on the TiO2 photocatalytic properties. Mater. Chem. Phys.
125, 20e25.
Monteiro-Gezork, A.C.A., Effendi, A., Winterbottom, J.M., 2007. Hydrogenation of
naphthalene on NiMo- and Ni/Al2O3 catalysts: pre-treatment and deactivation.
Catal. Today 128, 63e73.
Monteiro-Gezork, A.C.A., Natividad, R., Winterbottom, J.M., 2008. Hydrogenation of
naphthalene on NiMo- Ni- and Ru/Al2O3 catalysts: LangmuireHinshelwood
kinetic modelling. Catal. Today 130, 471e485.
Nakhate, G.G., Nikam, V.S., Kanade, K.G., Arbuj, S., Kale, B.B., Baeg, J.O., 2010. Hy-
drothermally derived nanosized Ni-doped TiO2: a visible light driven photo-
catalyst for methylene blue degradation. Mater. Chem. Phys. 124, 976e981.
Ngamsopasiriskun, C., Charnsethikul, S., Thachepan, S., Songsasen, A., 2010. Kaset-
sart J. Nat. Sci. 44, 1176e1182.
Olmez-Hanci, T., Kartal, Z., Arslan-Alaton, I., 2012. Electrocoagulation of commercial
naphthalene sulfonates: process optimization and assessment of implementa-
tion potential. J. Environ. Manag. 99, 44e51.
Olya, M.E., Pirkarami, A., Soleimani, M., Bahmaei, M., 2013. Photoelectrocatalytic
degradation of acid dye using NieTiO2 with the energy supplied by solar cell:
mechanism and economical studies. J. Environ. Manag. 121, 210e219.
Parayil, S.K., Kibombo, H.S., Koodali, R.T., 2013. Naphthalene derivatized TiO2-car-
bon hybrid materials for efficient photocatalytic splitting of water. Catal. Today
199, 8e14.
Ren, S.B., Zhang, P., Shui, H.F., Lei, Z.P., Wang, Z.C., Kang, S.G., 2010. Promotion of Ni/
SBA-15 catalyst for hydrogenation of naphthalene by pretreatment with
ammonia/water vapour. Catal. Commun. 12, 132e136.
Rubio-Clemente, A., Torres-Palma, R.A., Pe~
nuela, G.A., 2014. Removal of polycyclic
aromatic hydrocarbons in aqueous environment by chemical treatments: a
review. Sci. Total. Environ. 478, 201e225.
Sener, S., Ozyılmaz, A., 2010. Adsorption of naphthalene onto sonicated talc from
aqueous solutions. Ultrason. Sonochem. 17, 932e938.
Sharma, A.K., Lee, B.K., 2013. Lead sorption onto acrylamide modified titanium
nanocomposite from aqueous media. J. Environ. Manag. 128, 787e797.
Shi, Q., Li, A., Zhu, Z., Liu, B., 2013. Adsorption of naphthalene onto a high-surface-
area carbon from waste ion exchange resin. J. Environ. Sci. 25 (1), 188e194.
Sreet-hawong, T., Sitthiwechvijit, N., Rattanachatchai, A., Ouraipryvan, P.,
Schwank, J.W., Chavadej, S., 2011. Preparation of Au/Y2O3 and Au/NiO catalysts
by co-precipitation and their oxidation activities. Mater. Chem. Phys. 126,
212e219.
Tada, H., Jin, Q., Nishijima, H., Yamamoto, H., Fujishima, M., Okuoka, S., Hattori, T.,
Sumida, Y., Kobayashi, H., 2011. Titanium(IV) dioxide surface-modified with iron
oxide as a visible light photocatalyst. Angew. Chem. Int. Ed. 50, 3501e3505.
Tang, Z.R., Li, F., Zhang, Y., Fu, X., Xu, Y.J., 2011. Composites of titanate nanotube and
carbon nanotube as photocatalyst with high mineralization ratio for gas-phase
degradation of volatile aromatic pollutant. J. Phys. Chem. C 115, 7880e7886.
Thomas, J.K., Gunda, K., Rehbein, P., Flora, T.T Ng, 2010. Flow calorimetry and
adsorption study of dibenzothiophene, quinoline and naphthalene over modi-
fied Y zeolites. Appl. Catal. B Environ. 94, 225e233.
Tunçal, T., Uslu, O., 2015. Industrial sludge remediation with photonic treatment
using TieAg nano-composite thin films: persistent organic pollutant removal
from sludge matrix. J. Environ. Manag. 149, 37e45.
Wang, E., He, T., Zhao, L., Chen, Y., Gao, Y., 2010. Improved visible light photo-
catalytic activity of titania doped with tin and nitrogen. J. Mater. Chem. 21,
144e150.
Wang, Y., He, Y., Lai, Q., Fan, M., 2014. Review of the progress in preparing nano TiO2:
an important environmental engineering material. J. Environ. Sci. China 26,
2139e2177.
Yan, Z., Yu, X., Zhang, Y., Jia, H., Sun, Z., Du, P., 2014. Enhanced visible light-driven
hydrogen production from water by anoble-metal-free system containing
organic dye-sensitized titaniumdioxide loaded with nickel hydroxide as the
cocatalyst. Appl. Catal. B Environ. 160e161, 173e178.
Yang, X., Li, J., Wen, T., Ren, X., Huang, Y., Wang, X., 2013. Adsorption of naphthalene
and its derivatives on magnetic graphene composites and the mechanism
investigation. Colloids Surf. A: Physicochem. Eng. Asp. 422, 118e125.
Yi, Q., Huang, W., Zhang, J., Liu, X., Li, L., 2007. A novel titanium-supported nickel
electrocatalyst for cyclohexanol oxidation in alkaline solutions. J. Electroanal.
Chem. 610, 163e170.
Yi, Q., Huang, W., Zhang, J., Liu, X., Li, L., 2008. Methanol oxidation on titanium-
supported nano-scale Ni flakes. Catal. Commun. 9, 2053e2058.
Zhou, B., Zhao, X., Liu, H., Qu, J., Huang, C.P., 2011. Synthesis of visible-light sensitive
M-BiVO4 (M¼ Ag, Co and Ni) for the photocatalytic degradation of organic
pollutants. Sep. Purif. Technol. 77, 275e282.
122
View publication stats

Adsorptive/photo-catalytic process for naphthalene removal from aqueous media using in-situ nickel doped titanium nanocomposite

Recommended

Recommended

More Related Content

Similar to Adsorptive/photo-catalytic process for naphthalene removal from aqueous media using in-situ nickel doped titanium nanocomposite

Similar to Adsorptive/photo-catalytic process for naphthalene removal from aqueous media using in-situ nickel doped titanium nanocomposite (20)

More from NOMADPOWER

More from NOMADPOWER (13)

Recently uploaded

Recently uploaded (20)

Adsorptive/photo-catalytic process for naphthalene removal from aqueous media using in-situ nickel doped titanium nanocomposite