Visible light induced enhanced photocatalytic degradation of organic pollutants in aqueous media using Ag doped hollow TiO2 nanospheres

Article abstract of DOI:10.1039/c5ra03421c

The silver doped hollow TiO₂ (Ag-h-TiO₂) nanoparticles were synthesized by a sacrificial core (AgBr) method. The Ag doping and the core removal was done simultaneously during the dissolution of the core in (NH₄)OH solution. The mean particle size of synthesized Ag-h-TiO₂ nanoparticles is 17.76 ± 2.85 nm with a wall thickness of ～2.5 nm. The hollow structured nanoparticles have 103.2 m² g^-1 more specific surface area compared to solid TiO₂ nanoparticles. The suitability of these synthesized hollow nanoparticles as photocatalyst were tested for the photocatalytic degradation of three important different classes of organic compounds such as nitrobenzene (NB), metronidazole (MTZ) antibiotic, and methylene blue dye (MBD) in aqueous solution under irradiation of visible light. Photodegradation studies show there is a significant enhancement of the degradation efficiency of the TiO₂ after the hollow structure formation and silver doping. The recycling tests of the catalysts show only ～10% decrease in efficiency for NB and MTZ degradation after sixth cycle of reuse. The light emission capacity in terms of quantum yield (QY) is enhanced by 18.7% for Ag-h-TiO₂ than that of pure TiO₂ nanoparticles.

Full text of DOI:10.1039/c5ra03421c

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: S. S. Boxi and S.
Paria, RSC Adv., 2015, DOI: 10.1039/C5RA03421C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
Visible Light Induced Enhanced Photocatalytic Degradation of Organic
2
Pollutants in Aqueous Media Using Ag Doped Hollow TiO Nanospheres
*
Siddhartha Sankar Boxi, Santanu Paria
Interfaces and Nanomaterials Laboratory, Department of Chemical Engineering, National
Institute of Technology, Rourkela 769 008, Orissa, India.
Abstract:
The silver doped hollow TiO
core (AgBr) method. The Ag doping and the core removal was done simultaneously during
the dissolution of the core in (NH )OH solution. The mean particle size of synthesized Ag-h-
TiO nanoparticles is 17.76 ± 2.85 nm with the wall thickness ~2.5 nm. The hollow
structured nanoparticles have 103.2 m /g more specific surface area compared to that of solid
TiO nanoparticles. The suitability of this synthesized hollow nanoparticles as photocatalyst
2 2
(Ag-h-TiO ) nanoparticles were synthesized by a sacrificial
4
2
2
2
were tested for the photocatalytic degradation of three important different classes of organic
compounds such as nitrobenzene (NB), metronidazole (MTZ) antibiotic, and methylene blue
dye (MBD) in aqueous solution under irradiation of visible light. Photodegradation studies
show there is a significant enhancement of the degradation efficiency of the TiO
hollow structure formation and silver doping. The recycling tests of the catalysts show only ~
0% decrease in efficiency for NB and MTZ degradation after sixth cycle of reuse. The light
2
after the
1
2
emission capacity in terms of quantum yield (QY) is enhanced by 18.7% for Ag-h-TiO than
that of pure TiO nanoparticles.
2
2
Key words: Hollow nanoparticles, Ag doped TiO , photodegradation, visible light, quantum
yield.
*
To whom correspondence should be addressed. E–mail: santanuparia@yahoo.com, or
sparia@nitrkl.ac.in; Fax: +91 661 246 2999

RSC Advances
Page 2 of 25
View Article Online
DOI: 10.1039/C5RA03421C
1. Introduction
Metal oxide semiconductor nanoparticles play an important role in different areas of science
1–3
4–6
7,8
and engineering such as photo catalysis,
solar cells,
Li-ion batteries,
piezoelectric
9
,10
11
12,13
devices,
fuel cells, sensors,
and so on. The photo catalytic degradation of organic
pollutants is considered as one of the advanced environmental remediation process in recent
years over the conventional processes such as membrane filtration, adsorption. Among
several metal oxide semiconductor nanoparticles TiO
2
is one of the promising photocatalysts
because of its relatively higher efficiency, low toxicity, long term stability, low cost,
14–16
photoinduced strong oxidation activity properties.
However, the application of pure TiO
2
as a photocatalyst is limited in visible light because of its high band gap (3.03 eV for rutile
and 3.18 eV for anatase). Because of this reason, the development of visible light induced
2
TiO photocatalyst with higher efficiency is highly essential to make the industrial process
more feasible and economic. Since the reduction of band gap enhance the photocatalytic
activity of a photocatalyst under visible light, significant efforts have been made till now to
17,18
19
20
21
22
dope different elements into the TiO
2
host lattices such as, Fe,
Sn, Sm, Nd, and so on. In addition to the band gap of a photocatalyst, the surface area
is also extremely important to enhance the activity of a catalyst. In this regard, TiO with
Mn, Mg, Cr, Co,
2
3
24
25
2
26
27
28
different morphologies such as nanowires, nanotubes, nanorods have been studied.
More advanced material like hollow nanoparticles along with doping have attracted
considerable interests because of its larger surface area along with some important properties,
29–32
such as low density, good surface permeability and high light-harvesting efficiencies,
The TiO photocatalysts are not only used for the remediation of contaminated water but also
2
33
34
useful in air purification, cathodic catalyst for low-cost fuel cell. Some studies are also
35
available on hollow TiO
2
nanoparticles doped with different elements such as Nd, N and
36
37
38
Ce, Sn, Bi, in all these studies the C was used as the core and it was removed by
3
+
calcination. The other template such as polystyrene was used for Sm doped hollow TiO
2
39
structure. Sulfur doped hollow sphere TiO
2
was also synthesized by our group, where S
40
was doped during the removal of the sacrificial S core. Considering catalytic properties of
TiO , incorporation of noble metal like Ag to hollow TiO structure is important because of
its unique characteristics in resonant collective oscillations of the conduction electrons by
2
2
41,42
electromagnetic radiation and the localized surface plasmon resonance (SPR).
Since
4
3,44
nanoscale silver has good antibacterial property,
Ag doped TiO nanoparticles also show
2
45–47
similar property.
Silver-TiO composite hollow nanoparticles was reported by template
2
48
49
free method and PSA latex templated method as a visible light active photocatalyst.

Page 3 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
2
Recently, Ag and AgCl doped TiO hollow nanoparticles were synthesized using polystyrene
50
particles as template for getting a visible light active photocatalyst.
It has been noted from most of the literature that the doped hollow structure was
formed after removing the core, and the doping was achieved in the presence of some extra
precursor. However, a single step method for the core removal and doping could make the
process simple.
As mentioned before, a significant fraction of research activities is going on
2
environmental remediation of organic pollutants using TiO nanoparticles. The main
advantage of this process over the other conventional separation processes is toxic pollutants
can be converted to useful or nontoxic compounds. Different classes of organic compounds
such as aromatics (benzo compounds, phenolic compounds, naphthalene, trinitrotoluene, etc),
phermaceutical products (antibiotics, antipyretic etc.), dyes (synthetic dyes, reactive dyes, azo
dyes, basic cationic dyes etc.), some volatile organic compounds (formaldehyde, methylene
chloride, ethylene glycol, etc) can be degraded using this catalysts. The benzo compounds
such as nitrobenzene are highly toxic organic compound mainly used for the production of
aniline, paper and pulp, pesticides, dyes, explosives, cosmetics, pharmaceuticals, and so on.
5
1–53
The long term exposure of nitrobenzene to the environment, even at low concentration,
causes risks to human, such as liver or kidney damage, lung irritation, increase heart rate,
skin problem, vomiting, etc. Therefore, removal of nitrobenzene from the environment is a
major concern. Degradation of nitrobenzene in effluent water is difficult by conventional
chemical method because of the nitro group which has strong electron withdrawing property
and inhibits its oxidation, or by biological method because of its toxic and mutagenic effect
5
4,55
on the biological systems.
Apart from aromatic compounds, the presence of
pharmaceutical products for instance antibiotics in the environment, even at low
5
6,57
concentrations, causes the growth of antibiotic-resistant bacteria
and creates microbial
58,59
population,
which may cause of ineffectiveness of the present forms of treatment and
major epidemics. Metronidazole (MTZ) is one such type of antibiotic which is primarily used
for the infectious diseases caused by anaerobic bacteria and protozoa. Complete removal of
metronidazole from the environment by conventional method is difficult because of its low
degradability and high solubility in water. Dye contamination is another critical
environmental problem and addressed by several researchers till now. The sources of
synthetic dyes in wastewater are from different industries such as, textile, dye and dye
intermediates, paper and pulp, printing, colour photography, petroleum industries, and so on.
6
0,61
Continuous discharge of dye-bearing effluents from these industries into natural stream

RSC Advances
Page 4 of 25
View Article Online
DOI: 10.1039/C5RA03421C
and rivers poses severe environmental problems as toxic to useful microorganisms, aquatic
life, and human beings. So, suitable and efficient techniques are highly essential for the
treatment of these industrial effluents.
2
In this study Ag-h-TiO nanoparticles were synthesized through a sacrificial core
technique using AgBr as the core. The core was removed under a mild condition by
dissolving in ammonium hydroxide solution, and the silver doping was also achieved during
the dissolution of the core without any addition extra dopant precursor. After Ag doping, pure
anatase phase TiO
2
particles were obtained even after heating at 450 °C. The hollow structure
2
nanoparticles have higher surface area (198.3 m /g) compared to solid TiO
2
nanoparticles
To test the
2
62–66
(
95.1 m /g) and hollow structures reported by other researchers.
photocatalytic activity of the developed nanoparticles towards three important organic
compounds such as nitrobenzene (NB), metronidazole (MTZ), and methylene blue dye
(MBD) degradation studies were conducted with low catalyst dose and high initial MTZ
concentration compared to the studies reported till now. The obtained TiO particles are
2
having low band gap, anatase phase, high surface area, good crystallinity, and efficient
visible light induced photocatalytic property to degrade important organic compounds such as
nitrobenzene, antibiotic, and dye.
2
. Materials and Methods
.1 Materials
2
Reagent-grade silver nitrate (99.9%) and potassium bromide (99.3%) were purchased from
Rankem. Anionic surfactant sodium dodecyl benzene sulphonate (SDBS) (technical grade,
2 3 3 4
Cat No. 28995-7) and titanium (IV) butoxide (Ti[O(CH ) CH ] or TOBT, 97%) were
obtained from Sigma Aldrich. Ammonium hydroxide (25%), nitric acid (69% GR),
cyclohexane, and methylene blue dye were bought from Merck. Nitrobenzene was provided
by Nice Chemicals Pvt. Ltd. Metronidazole was supplied by J B Chemicals &
Pharmaceuticals Ltd. All the chemicals were used as it was received without any further
purification. Ultrapure water of 18.2 Mꢀ.cm resistivity and pH 6.4–6.5 was used for all the
experiments.
2.2 Methods
A sol-gel method was followed for the synthesis of silver doped hollow TiO nanoparticles
2
using AgBr as the sacrificial core. The AgBr nanoparticles were synthesized in aqueous

Page 5 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
67
SDBS media according to our previous reported study. The concentrations of both AgNO3
and KBr were maintained at 0.1 mM. After the formation of AgBr NPs the suspension was
sonicated using a bath sonicator for 20 min, TBOT was then added slowly under constant
stirring condition for uniform coating on the core surface. After 5 minutes of addition of
TBOT, HNO
condition. The AgBr/TiO
5,000 rpm for 20 min and washed thrice with ethanol and water mixture (2:1, v/v). Then the
3
was added to maintain the pH of ~2 and kept for 35 min under stirring
2
core/shell nanoparticles were then separated by centrifugation at
2
particles were dipped in ammonium hydroxide solution (2.5 mM) for 48 hrs for the
dissolution of AgBr core. The particles were separated and calcined at 450°C for 2 hrs to
improve the crystallinity. For quantum yield (QY) calculation of Ag-h-TiO
used as a reference (QY=0.14).
2
NPs, phenol was
2
Scheme 1. Schematic presentation for the formation of Ag-h-TiO nanoparticles.
2.3 Particles characterization
The particle size was measured initially by dynamic light scattering (DLS) using a Malvern
Zeta Size analyzer, (Nano ZS). The crystallinity of synthesized particles was characterized
using powder X-ray diffraction (XRD) (Philips, PW 1830 HT) with scanning rate of 0.01°/s
in the 2θ range from 20° to 70°. The size and shape of the particles were observed under a
field emission scanning electron microscope (FE-SEM) (FEI, Nova NanoSEM NPE212) and
transmission electron microscope (TEM) (FEI, Tecnai S-twin). The elemental composition of
the sample was analyzed by energy-dispersive X-ray spectroscopy (EDX) (Oxford
Instruments, model X-sight) attached to the HR-TEM (JEOL, JEM 2100). The light
absorbance and luminescence properties were also characterized by UV–vis–NIR
Spectroscopy (Shimadzu, UV-3600) and fluorescence spectroscopy (Hitachi, F-7000)
respectively. Fourier transform infrared spectroscopy (FT-IR) was carried out using an FT-IR
(Thermo Fisher Scientific, Nicolet iS10). The chemical composition of the samples and the
valence states of various elements were analyzed by X-ray photoelectron spectroscopy (XPS,
ULVAC-PHI, Inc., PHI 5000 Versa Probe II.). The surface area of the nanoparticles was
measured by Brunauer–Emmett–Teller (BET) technique (Quantachrome, USA).

RSC Advances
Page 6 of 25
View Article Online
DOI: 10.1039/C5RA03421C
2.4 Photocatalytic degradation
The photocatalytic activity of the synthesized catalyst was tested by the degradation of NB,
MTZ antibiotic, and MBD in aqueous solutions. For nitrobenzene degradation the initial
concentration of nitrobenzene and catalyst dose were maintained 61.5 mg/L and 0.05 g/L. For
MTZ degradation the initial concentration of the MTZ solution was maintained to 15 mg/L
for all experiments and the catalyst concentration was 0.5 g/L. The degradation studies were
conducted in a photoreactor equipped with a 125 W high pressure mercury vapour lamp
2
(λ
=435.8 nm, light intensity 27000 LUX, light energy 56
±
2 w/m ) placed about 12 cm away
from the solution. The solutions were stirred continuously using a magnetic stirrer. Prior to
each test, the lamp was turned on 10 min before in order to get a maximum light intensity.
The samples were magnetically stirred for 20 min in the dark to allow physical adsorption
equilibrium of NB, MTZ, and MBD on the catalyst surface. Then the suspension was
exposed to visible light irradiation under constant stirring condition. The sample was then
taken out and centrifuged to remove the nanoparticles after each 20 min interval for MTZ and
3
0 min interval for NB and MBD degradation. Then the concentration of the NB, MTZ, and
MBD solution were analyzed using a UV-Vis-NIR Spectrophotometer at its maximum
absorbance wavelength of = 267, 320, and 661 nm for NB, MTZ, and MBD, respectively.
λ
The cyclic degradation test was conducted to check the reusability of the photocatalyst. After
each cycle of degradation the catalyst was separated by centrifugation and was used for the
next cycle of degradation without any pre-treatment. The intermediate and final degraded
products during nitrobenzene degradation were analyzed by liquid chromatography-mass
(LC-MS) (Flexar SQ 300 MS, Perkin Elmer). The sample was extracted with cyclohexane
and 70% water/30% acetonitrile (v/v) mobile phase was used for the analysis.
3. Results and discussion
2
3.1 Synthesis of hollow TiO particles
The hollow particles were synthesized by the templated sacrificial core method using AgBr
as a core. In aqueous media the surface charge of AgBr nanoparticles is -15 to -25 mV.
Addition of anionic surfactant (SDBS) makes the surface charge of AgBr more negative (-
4
7.8 mV). The surface charge of TiO nanoparticles is positive, so, it is expected that the
2
2
TiO will favourably coat on the AgBr core surface because of the electrostatic attraction.
When ammonium hydroxide solution was added to the particle suspension, AgBr would try

Page 7 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
to dissolve in ammonium hydroxide through the formation of soluble complex according to
equation 1. During the dissolution of AgBr, there is a chance of doping of Ag on TiO shell.
2
+
-
AgBr (s) + 2 NH
3
(aq)
→
Ag(NH
3
)
2
(aq) + Br
(1)
3.2 Characterization of particles by UV-Vis spectroscopy
UV-Vis spectroscopic study was done to investigate the light absorption property of the
nanoparticles, and the results are presented in Figure 1. The Figure shows that the sharp peak
of pure AgBr is present in the UV region (237 nm), and it disappears after the coating of
2 2
external shell layer of TiO on AgBr. Pure TiO is having major absorption below 350 nm
wavelength, and there is no absorption in the visible region, this is because of its high energy
band gap (3.2 eV). However, the UV-Vis spectra of Ag-h-TiO nanoparticles show a
2
significant absorption in 300-650 nm wavelength range. The shifting of absorbance in the
visible range is attributed to the fact of lowering of the band gap of the obtained nanoparticles
because of doping of Ag. In addition, noteworthy to mention that, the absorption intensity of
2 2
Ag-h-TiO is higher compared to that of pure solid TiO in both UV as well as in visible
regions. The increase in absorbance is also attributed to the fact of porous hollow structure
and formation of shell layer by the deposition of small particles. The band gap energy was
6
8
calculated using the equation E
gap (eV) and is the wave length (nm) of the absorption edges in the UV –Vis spectrum. It
has been found that the calculated band gaps are 2.69 and 3.29 eV for AgBr and TiO , which
g
= 1239.8/
λ
g
to support the above fact, where E is the band
λ
2
69
70
are in good agreement with the reported values of 2.7 eV and 3.28 eV respectively,
whereas, 2.48 and 2.25 eV for AgBr/TiO and Ag-h-TiO nanoparticles respectively. Since
the band gap of the TiO is reduced after the formation of doped hollow structure, it is
2
2
2
expected to be useful as good photocatalyst under the visible light irradiation, dye sensitized
solar cells, or other electrochemical applications.

RSC Advances
Page 8 of 25
View Article Online
DOI: 10.1039/C5RA03421C
2.0
1.5
1.0
0.5
0.0
AgBr
TiO
2
AgBr/TiO
2
Ag-hollow TiO
2
300
400
500
600
700
800
Wavelength (nm)
Figure 1. UV –Vis spectra of as synthesized AgBr, TiO
2
, AgBr/TiO
2
, and Ag-h-TiO
2
nanoparticles.
3.3 Characterization of particles by XRD
The crystallographic phases of the nanoparticles were identified by XRD technique. The
diffraction patterns of all particles are presented in Figure 2. For pure AgBr, the XRD pattern
displays peaks at 2
planes (111), (200), (220), (222), (400), and (420) of cubic structure (JCPDS card no.79-
149). For pure TiO , the anatase peaks were obtained at 2 value of 25.1, 36.5 and 62.3°
corresponding to the planes (101), (103), and (204) (JCPDS card no.71-1169). The peaks
rutile phase were obtained at 2 values of 27.3, 54.1, and 68.6° corresponding to the planes
θ value of 26.6, 30.9, 44.3, 55.2, 64.5, and 73.3° corresponding to the
0
θ
2
θ
(
110), (211), and (301) (JCPDS card no.76-0319). For AgBr/TiO core/shell nanoparticles the
2
XRD pattern shows the peaks of both AgBr and TiO
reduced and that of TiO
TiO NPs the TiO anatase peaks (2
2
, but the peak intensity of AgBr is
2
becomes more dominant mainly because of TiO
) were obtained at 25.6, 37.4, 48.6, and 63.2°
corresponding to the planes of (101), (103), (200), and (204) (JCPDS card no. 75-1537) with
the peaks of elemental silver at 2 values of 44.3 and 64.7, corresponding to the planes (200)
and (220) (JCPDS card no.03-0931) respectively. Additionally, another important
observation is the rutile peak at 2 = 27.3° is absent in the hollow structure, while compare
with pure TiO NPs. The XRD analysis also shows that the anatase TiO peak (2 ) of (101)
plane shifts from 25.1° to 25.6° after the formation of hollow structure, which attributed to
the silver doping to TiO lattices.
2
coating. For Ag-h-
θ
2
2
θ
θ
2
2
θ
2

Page 9 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
(
101)
*
(101)
*
TiO
2
Ag-h-TiO
2
(
110)
#
*
#
Anatase TiO
2
Rutile TiO
2
*
Anatase TiO
2
(103)
*
(103)
(211)
#
*
(204)
*
(200) (213)
*
(301)
#
*
(
200)
^
(101)
AgBr
AgBr/TiO
*
2
(
110)
#
+
(200)
+
*
AgBr
Anatase TiO
2
#
Rutile TiO
2
(220)
^
Ag Ti O
2
4 9
(
220)
+
(222)
(105) (222) (213)
(400)
+
*
*
25
35
45
theta (degree)
55
65
25
35
45
55
65
2
2 theta (degree)
Figure 2. The X-ray diffraction patterns of AgBr, TiO
nanoparticles.
2 2 2
, AgBr/TiO core/shell, and Ag-h-TiO
3.4 Characterization of particles by TEM and FE-SEM
2
The Figure 3a shows the TEM image of AgBr/TiO core/shell nanoparticles before expose to
ammonium hydroxide solution. The contrast difference between the core and shell in the
image indicates the formation of core/shell structure. The particles are spherical in shape, and
the size distribution is plotted in Figure 3c which indicates the mean particle size of 17.86 ±
2
2.46 nm and the shell thickness is ~ 2.5 nm. The TEM image of AgBr/TiO core/shell
particles after dissolution in ammonium hydroxide solution is presented in Figure 3b. The
particle size distribution is plotted in Figure 3d which shows mean particle size of 17.76 ±
2
.85 nm, which is almost same as it was before the dissolution. However, the average particle
size obtained by DLS measurement (S1, Supporting Information) was comparatively larger
20.79 nm) than that obtained by TEM measurement, this might be because of the adsorbed
(
6
7
surfactant layer and hydrated water molecules . The FE-SEM image (inset Figure 3b and

RSC Advances
Page 10 of 25
View Article Online
DOI: 10.1039/C5RA03421C
S2, Supporting Information) clearly shows some of the broken hollow spheres. The TEM
image of single contrast indicates the removal of core. So, the TEM and FE-SEM images
confirm the formation of hollow TiO
high resolution TEM image of Ag-h-TiO
spacing of 0.353 nm corresponding to the (101) plane for anatase phase TiO
no. 75-1537) previously confirmed by XRD. But there is no lattice fringe of rutile TiO
Ag, which confirms 100% anatase phase of TiO and no surface deposition of Ag. The Figure
b shows the selected area electron diffraction (SAED) pattern of the hollow particle by
focusing the electron beam on a single particle. The ring like diffraction pattern is indexed to
101) and (200) planes of TiO together with (200) diffraction of silver, which confirms the
presence of silver inside the crystal structure of TiO nanoparticles. The EDX in Figure 4c
2
particles after treatment with ammonia solution. The
nanoparticles (Figure 4a) shows lattice fringes
(JCPDS card
or
2
2
2
2
4
(
2
2
further confirms the presence of silver, titanium, and oxygen atoms. Some extra peaks of Cu
and C are mainly from TEM grids.
(a)
(b)
5
0 nm
50 nm
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Mean particle size - 17.86 nm
Std. Dev. - 2.46 nm
Mean particle size - 17.76 nm
Std. Dev. - 2.85 nm
(c)
(d)
10
12 14 16 18 20 22 24
Particle size (nm)
10 12 14 16 18 20 22 24
Particle Size (nm)
2 2
Figure 3. TEM images of (a) AgBr/TiO core/shell, and (b) Ag-h-TiO hollow nanoparticles,
inset shows FE-SEM image of a hollow broken particle (more hollow particles are shown in

Page 11 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
Figure S2). Particle size distributions of (c) AgBr/TiO core/shell, and (d) Ag-h-TiO2
2
nanoparticles.
(
a)
(b)
TiO (101)
2
Ag (200)
TiO (200)
2
(
c)
Figure 4. (a) HR-TEM image (b) SAED pattern, and (c) EDX pattern of Ag-h-TiO2
nanoparticles.
3.5 Characterization of particles by XPS

RSC Advances
Page 12 of 25
View Article Online
DOI: 10.1039/C5RA03421C
For the further confirmation of the surface composition and the chemical states of Ag-h-TiO
nanoparticles, XPS analysis was carried out. The high resolution XPS spectra of Ag (3d), Ti
2p) and O (1s) are presented in Figure 5. The XPS peak at 462.9 eV corresponds to Ti 2p1/2
and 457.2 eV corresponds to Ti 2p3/2 in the Ti 2p region (Figure 5a). The slitting between
2
(
,
4+
Ti2p1/2 and Ti 2p3/2 is 5.9 eV which indicates the normal state of Ti in the mesoporous
7
1
anatase TiO
TiO crystal and peaks at 532.1 and 531.7 eV correspond to the adsorbed oxygen on TiO
surface. Figure 5c shows the Ag 3d3/2 and Ag 3d5/2 peaks at the binding energy of 366.5 and
72.6 eV, respectively with a slitting of the 3d doublet of 6.1 eV, which suggest the zero
2
.
The XPS peak (Figure 5b) at ~530 eV corresponds to the lattice oxygen of
2
2
3
+
72
valence silver instead of Ag ions within the material. So, the possible location of dopant is
attributed as the surface or in the interstitial sites of the host material. The TEM or FE-SEM
images confirm that there is no surface deposition of the silver on the particles. So, there is a
fair possibility of the silver doping in the interstitial sites of the host material.
Ti 2p
O 1S
Ag 3d
3/2
3/2
(
a)
(b)
(c)
Ag 3d
5/2
Ti 2P
1/2
4
eV
5
.7 eV
66 464 462 460 458 456 454 535 534 533 532 531 530 529 528 527
Binding energy (eV)
Binding energy (eV)
4
374 372 370 368 366 364
Binding energy (eV)
Figure 5. High resolution XPS narrow scan spectra of (a) Ti(2p), (b) O(1s), and (c) Ag(3d)
for Ag-h-TiO nanoparticles.
2
3
.6 Characterization of particles by BET analysis
The specific surface area of the pure and hollow doped TiO
BET technique. Before the adsorption-desorption study the sample was degasified for 1 hr at
2
nanoparticles was measured by
150°C temperature. The BET surface area of solid TiO and Ag-h-TiO nanoparticles are
2 2
2
2
9
5.1 and 198.3 m /g respectively. The Ag-h-TiO
2
nanoparticles are having 103.2 m /g more
surface area compare to that of solid TiO
2
. The obtained surface area of hollow structure TiO
2
2
62–66
is higher compared to the literature values of 38.9 - 123 m /g
This might be because of
the core removal technique and the final particle size. In most of the literature the core was
removed by calcinations but in our case the core is removed by dissolution at room
temperature. The high surface area hollow structure TiO is expected to be useful for the
2
catalysis or other applications.

Page 13 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
3.7 Photoluminescence activity of the synthesized nanoparticles
The photoluminescence (PL) properties of the synthesized nanoparticles were also checked
by the fluorescence spectroscopy in terms of light emission. The light emission data was
recorded between 500-600 nm wavelengths while excitation at 270 nm. The emission spectra
of AgBr, TiO
show emission in the visible region of wavelength ~ 543.8 nm. The intensities of emission
are in the following order: AgBr Ag-h-TiO AgBr/TiO TiO . The pure TiO have very
low intensity compared to pure AgBr and the intensity increases after the formation of
Ag-h-TiO NPs. The quantum yield (QY) was calculated for these materials from UV and PL
data (Equation SI1, Supporting Information) using phenol as the standard material (QY =
2 2 2
, AgBr/TiO , and Ag-h-TiO NPs are presented in Figure 6. All the particles
>
2
>
2
>
2
2
2
2
0.14). The QYs of TiO , AgBr, AgBr/TiO
2
, and Ag-h-TiO
2
NPs are 0.29, 0.498, 0.36, and
0
.477 respectively. So, the quantum yield of TiO
2
is enhanced by 18.7% after the formation
of hollow structure and Ag doping. From these results it can be pointed out that the Ag–
h-TiO nanoparticles has enhanced light emission property and QY compared to that of pure
TiO nanoparticles. So, the light emission properties along with the catalytic properties could
2
2
be utilized for better photocatalyst or dye sensitized solar cells applications.
AgBr
TiO
2
AgBr@TiO
2
Ag-h-TiO
2
500 510 520 530 540 550 560 570 580 590 600
Wave length (nm)
2 2 2
Figure 6. Light emission spectra of AgBr, TiO , AgBr/TiO , and Ag-h-TiO NPs after
excitation at 270 nm wavelength.
3.8 Photo catalytic applications of synthesized nanoparticles

RSC Advances
Page 14 of 25
View Article Online
DOI: 10.1039/C5RA03421C
2
The photocatalytic activities of the synthesized Ag-h-TiO nanoparticles were first tested for
the degradation of NB under the visible light irradiation. The degradation studies using pure
and Ag doped solid TiO (Ag-TiO ) were also employed as the photocatalyst for the
2
2
comparison purpose. The results of NB degradation in visible light are shown in Figure 7. It
has been found that the degradation process reaches a plateau level after 3.5 hrs of light
exposure time. The results show that at the plateau level, the degradation efficiencies of NB
are 58.46, 89.61, and 95.5% in the presence of TiO
respectively. The results clearly indicate that the maximum degradation of the NB was
obtained in the presence of the Ag-h-TiO NPs. The degradation results were also fitted with
2 2 2
, Ag-TiO , and Ag-h-TiO NPs
2
different kinetic models, and it was found that the first order kinetics fits well for all the
materials. The Figure 7b presents the reaction kinetics of NB degradation. The rate constants
(k) of the photocatalytic degradation reactions obtained from the experimental results are
-1
0
.0045, 0.0109, and 0.016 min for TiO , Ag-TiO , and Ag-h-TiO NPs respectively. The
2 2 2
2
rate constant of Ag-h-TiO photocatalytic process is about 3.6 and 1.5 times than that of pure
2 2
TiO and Ag-TiO photocatalytic processes respectively. A comparison at 50% degradation
times for NB shows 136.5, 41.5, and 27 min for TiO , Ag-TiO , and Ag-h-TiO
2
2
2
nanoparticles, respectively. These results reveal that Ag-h-TiO
2
nanoparticles have higher
photocatalytic activity compared to that of pure TiO and Ag-TiO NPs. This is attributed to
2 2
•
the fact that pure TiO
2
is having low yield of OH radicals because of recombination of the
charge carriers during photodegradation, which helps to oxidize the organic compound as
73
stated in our previous study.
2
In Ag doped TiO NPs the Ag dopant accepts the
photoinduced electrons and holes, which in turn act as electron/hole traps and prevents the
2
recombination of the charge carriers. In Ag-h-TiO NPs, addition to Ag doping it is having
2
more surface area (198.3 m /g as mentioned in the BET analysis) compared to solid TiO
2
2
(
95.1 m /g), which is useful for better catalytic processes. Additionally, as mention in the
+
XPS section, the presence of adsorbed oxygen on the TiO
2
surface allows the H
hydroxylation to form –Ti(OH)-O-Ti-(OH)- in the presence of water. During the
ꢂ
photodegradation, this compound may help to generate the photogenerated hole (h ) and
ꢀꢁ
•
74
finally turn to OH free radicals, which is beneficial for the photocatalysis.
comparing the degradation efficiency and PL intensity, it can be seen that Ag-h-TiO
having high degradation efficiency as well as PL intensity compared to that of pure TiO
While
is
. In
2
2
general, high PL intensity is due to the high recombination of electrons and holes. Our results
can be attributed in the following way. In the presence of doping, the reduction in

Page 15 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
recombination continues up to the certain limit of doping percentage (optimum doping) and
7
5,76
then again recombination starts increasing with the increasing doping %.
From the EDX
study it is seen that 9.02% doping is achieved, which is higher compared to optimum doping
7
3
percentage (1%) for TiO
time, as the surface area of hollow particles is higher than solid TiO
efficiency is more because of more adsorption of dye molecules. The reusability of Ag-h-
TiO NPs was tested by recycling the catalyst under the same condition, and the results are
2
,
we beleive because of that the PL intensity is high. At the same
2
, the degradation
2
plotted in Figure 7c. The results show there is a ~10.83% decrease (95.5 to 84.67%) in
degradation efficiency after sixth cycles. The turn over number (TON) of the photocatalyst is
calculated as 0.467, 0.716, and 0.763 mol/mol for the first cycle of the TiO
2 2
, Ag-TiO , Ag-h-
TiO , respectively. From the reported literatures (Table S1, Supporting Information) it is has
2
been found that more than 90% degradation efficiency of nitrobenzene was achieved either in
the presence high catalyst dose, low organic concentration, in the presence of UV light
irradiation, or in presence of some additives and at specific pH. In this regard, our catalytic
process is more effective in normal visible light and in the absence of any additives than the
already reported literatures.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3.5
.0
2.5
TiO
TiO
(a)
2
2
(b)
100 95.5 94.94
80
9
(c)
2.96 90.74 87.31
84.67
3
Ag-TiO
Ag-TiO
2
2
2
R =0.9922
Ag-h-TiO
Ag-h-TiO
2
2
2
.0
.5
6
0
0
2
R =0.983
1
4
1.0
.5
0.0
2
20
0
R =0.9836
0
0
25 50 75 100 125 150 175 200 225
Time (min)
0
25 50 75 100 125 150 175 200 225
Time (min)
1
2
3
Recycling number
4
5
6
Figure 7. (a) Photodegradation kinetics of nitrobenzene under visible light of high pressure
mercury vapour lamp using TiO , Ag-TiO and Ag-h-TiO NPs. (b) Fitting of first order
for the degradation of
2
2
2
kinetics with the experimental data. (c) Recycling test of Ag-h-TiO
nitrobenzene solution.
2
Further, to explore the degradation pathway of NB in the presence of TiO
2 2
, Ag-TiO , and
Ag-h-TiO photocatalysts, LC-MS study was conducted to identify different photo degraded
2
products. Based on the LC-MS results probable degradation path is proposed in Figure 8.
•
During the photodegradation, the OH radicals attack the nitrobenzene and subsequently
produce some aromatic compounds, such as benzene, phenol, catechol, resorcinol, and
hydroquinone. The hydroquinone again forms benzoquinone through the dehydrogenation.

RSC Advances
Page 16 of 25
View Article Online
DOI: 10.1039/C5RA03421C
Further degradation of the aromatic compounds happens through the ring cleavage and some
degraded product, such as propionic acid, n-butanol, di-ethyl ether, furan, orthoformic acid,
propanol, and acetic acid are formed.
Figure 8. Probable pathway for the degradation of nitrobenzene under visible light in the
2 2 2
presence of TiO , Ag-TiO , and Ag-h-TiO .
2
Since the Ag-h-TiO nanoparticles show good photocatalytic degradation against the NB, the
same catalyst was also used to study the photodegradation efficiency on other two classes of
organic compounds such as metronidazole antibiotic and methylene blue dye under the
visible light irradiation. The degradation results (Figure 9a) show that at the plateau level the
degradation of MTZ is 96.55% in the presence of Ag-h-TiO
2
2
NPs, while pure TiO and Ag-
7
3
TiO degraded 80.78 and 94.39% of MTZ.
The rate constant of the photocatalytic
2
-1
degradation reactions obtained from the experimental results is 0.0269 min for Ag-h-TiO
NPs. The results of reusability test of Ag-h-TiO NPs (Figure 9b) show there is a ~10.76%
decrease (96.55 to 85.79%) in degradation efficiency after sixth cycles. It can be noted that
the difference between hollow and solid TiO is not significant (~2%), in spite of
significantly high surface area for hollow particles, which can be attributed to the low initial
2
2
2

Page 17 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
MTZ concentration. So, the initial concentration of MTZ was increased to 30 mg/L and it has
been found that after 2 hrs the Ag-TiO and Ag-h-TiO NPs degraded 88.5 and 94.77% MTZ
2
2
-1
(
2 2
Figure 9c) with rate constants 0.019 and 0.024 min (Figure 9d) for Ag-TiO and Ag-h-TiO
NPs respectively. These results indicate that, when the concentration of organic molecules is
high hollow particles show better efficiency. Our approach of MTZ degradation is noble
compared to the reported conventional method as well as photocatalytic degradation
approach as discussed in the Supporting Information (Table S2). The surface chemistry of
Ag-h-TiO
spectroscopy. The FT-IR results (Figure S3, Supporting Information) show there is no
significant peak change between the virgin Ag-h-TiO and recycled Ag-h-TiO after
2
photocatalyst was studied before and after degradation of MTZ solution by FT-IR
2
2
-1
degradation. The broad absorption peak at 3373 and 2359 cm are associated with the
asymmetric and symmetric stretching vibrations of the Ti–OH group. The peaks in the range
-1
4
00-1000 cm are the contribution of anatase phase Ti-O. So, these results strongly suggest
that the degradation of MTZ solution is due to the photocatalytic degradation instead of any
chemisorption or physisorption of MTZ on the catalyst surface.
1.0
0.8
0.6
0.4
0.2
0.0
Relative concentration (C/C )
0
3.5
3.0
96.55
(b)
100
94.91 92.71
(
a)
8
8.76
8
7.14 85.79
ln(C /C)
0
80
60
40
20
0
2
.5
.0
2
R =0.9797
2
1.5
1
.0
.5
0
0.0
0
20
40
60
80
100
120
1
2
3
Recycling number
4
5
6
Time (min)
1.0
0.8
0.6
0.4
0.2
0.0
Ag-TiO
3.0
Ag-TiO
2
(
c)
2
(d)
Ag-h-TiO
Ag-h-TiO
2
2
2
2.5
2.0
1.5
1.0
0.5
R =0.992
2
R =0.9932
0.0
0
20
40
60
80
100
120
0
20
40
60
80
100
120
Time (min)
Time (min)
Figure 9. (a) Photodegradation kinetics and fitting of first order kinetics with the
experimental data of MTZ degradation under visible light of high pressure mercury vapour
lamp using Ag-h-TiO
2
NPs with 15 mg/L of initial MTZ concentration. (b) Recycling test of
Ag-h-TiO for the degradation of MTZ solution. (c) Photodegradation kinetics and (d) Fitting
2

RSC Advances
Page 18 of 25
View Article Online
DOI: 10.1039/C5RA03421C
2 2
of first order kinetics with the experimental data of MTZ using Ag-TiO and Ag-h-TiO NPs
with 30 mg/L initial concentration of MTZ.
The MBD degradation was carried out under the visible light with 25 mg/L initial
concentration of dye and the catalyst concentration of 0.25 g/L. The degradation results are
presented in Figure S4, Supporting Information. The dye degradation efficiency of Ag-h-
TiO
MBD under the visible lamp using Ag-h-TiO
Information). Similar to previous study Ag-h-TiO
degradation test under the same condition and found there is a decrease in efficiency of ~
0.47% (96.77 to 86.3%) after sixth cycle of photodegradation (Figure S4d, Supporting
Information).
For each type of organic compound degradation, two sets of reference studies, (i)
2
is 96.77 % after 3 hrs exposure time. The rate constant of photocatalytic degradation of
-1
2
NPs is 0.0216 min (Figure S4c, Supporting
2
sample was further selected for cyclic
1
organic solution + catalyst in dark and (ii) only organic solution under visible light irradiation
were carried out. The first was to test only adsorption capacity. Since the catalyst
concentration was low, there was no significant change found because of adsorption. So we
confirmed that the concentration change was only because of degradation.
4. Conclusions
The hollow TiO
2
nanoparticles were synthesized by a sacrificial core method using AgBr as
sacrificial core. During the removal of core, Ag was doped in the interstitial sites of the host
TiO . The obtained Ag-h-TiO nanoparticles are purely in anatase phase and good crystalline
2
2
in nature. The mean particle size is 17.76 ± 2.85 nm with wall thickness of ~ 2.5 nm. The
2
increase of surface area for hollow nanoparticles is 103.2 m /g more compared to that of solid
TiO
2
nanopaticles. Apart from the surface area, the quantum yield of Ag-h-TiO
2
nanoparticles also increases to 18.7% compared to that of pure solid TiO
2
nanoparticles. The
nanoparticles were used for the photo degradation of NB, MTZ antibiotic and MBD. The
maximum NB degradation was obtained 95.5% under visible light irradiation for 3.5 hr. The
metronidazole degradation efficiency was found to be 96.55 and 94.77% under the irradiation
of visible light for the initial MTZ concentration of 15 and 30 mg/L with catalyst dose of 0.5
g/L. The Ag-h-TiO
2
NPs show only 10.47% decrease in degradation efficiency even after
nanoparticles may also be useful for dye
sixth cycle of reuse. The synthesized Ag-h-TiO
2
sensitized solar cells and other electrochemical applications.
Acknowledgments

Page 19 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
The financial support from the Council of Scientific and Industrial Research (CSIR), Grant
No. 22(0527)/10/EMR-II, for this project is gratefully acknowledged. S.S.B. thanks CSIR,
India, for a Senior Research Fellowship to pursue this work. Authors are grateful to Indian
Institute of Technology, Kharagpur, India, for providing their XPS facility. Authors also
acknowledge the Saha Institute of Nuclear Physics, Indian Association for the Cultivation of
Science, Kolkata, India, for giving the opportunity to access their TEM facility.
References
1.
Liqiang, J.; Honggang, F.; Baiqi, W.; Dejun, W.; Baifu, X.; Shudan, L.; Jiazhong, S.
Effects of Sn Dopant on the Photoinduced Charge Property and Photocatalytic Activity
2
of TiO Nanoparticles. Appl. Catal., B: Environmental 2006, 62, 282-291.
2.
Zeng, H.; Cai, W.; Liu, P.; Xu, X.; Zhou, H.; Klingshirn, C.; Kalt, H. ZnO-Based
Hollow Nanoparticles by Selective Etching: Elimination and Reconstruction of
MetalSemiconductor Interface, Improvement of Blue Emission and Photocatalysis.
ACS Nano 2008, 2, 1661-1670.
3.
He, W.; Kim, H. k.; Wamer, W. G.; Melka, D.; Callahan, J. H. Photogenerated Charge
Carriers and Reactive Oxygen Species in ZnO/Au Hybrid Nanostructures with
Enhanced Photocatalytic and Antibacterial Activity. J. Am. Chem. Soc. 2014, 136, 750
-
757.
4
.
.
Jose, R.; Thavasi, V.; Ramakrishna, S. Metal Oxides for Dye-Sensitized Solar Cells. J.
Am. Ceram. Soc. 2009, 301, 289-301.
5
Guo, J.; She, C.; Lian, T. Ultrafast Electron Transfer between Conjugated Polymer and
Antimony-Doped Tin Oxide (ATO) Nanoparticles. J. Phys. Chem. C 2008, 112, 4761-
4
766.
Tubtimtae, A.; Arthayakul, K.; Teekwang, B.; Hongsith, K. MnTe Semiconductor-
Sensitized Boron-Doped TiO and ZnO Photoelectrodes for Solar Cell Applications. J.
6.
7.
8.
2
Colloid Interface Sci. 2013, 405, 78-84.
Reddy, A. L. M.; Shaijumon, M. M.; Gowda, S. R.; Ajayan, P. M. Coaxial
MnO
2
/Carbon Nanotube Array Electrodes for High-Performance Lithium Batteries.
, 1002-1006.
Nano Lett. 2009,
9
Chan, C. K.; Peng, H.; Twesten, R. D.; Jarausch, K. Zhang, X. F.; Cui, Y. Fast,
Completely Reversible Li Insertion in Vanadium Pentoxide Nanoribbons. Nano Lett
2
007, 7, 490-495.

RSC Advances
Page 20 of 25
View Article Online
DOI: 10.1039/C5RA03421C
9
1
1
1
1
.
Kimura, T., Dong, Q.; Yin, S.; Hashimoto, T.; Sasaki, A.; Sato, T. Synthesis and
Piezoelectric Properties of Li-doped BaTiO by a Solvothermal Approach. J. Eur.
3
Ceram. Soc. 2013, 33, 1009-1015.
0. Yang, Q.; Guo, X.; Wang, W.; Zhang, Y.; Xu, S.; Lien, D. H.; Wang, Z. L. Enhancing
Sensitivity of a Single ZnO Micro-/Nanowire Photodetector by Piezo-phototronic
Effect. ACS Nano 2010,
1. Kamat, P.V. Graphene-Based Nanoarchitectures. Anchoring Semiconductor and Metal
Nanoparticles on a Two-Dimensional Carbon Support. J. Phys. Chem. Lett. 2010,
20–527.
2. Sun, Y. F.; Liu, S. B.; Meng, F. L.; Liu, J. Y.; Jin, Z.; Kong, L. T.; Liu, J. H. Metal
Oxide Nanostructures and Their Gas Sensing Properties: A Review. Sensors 2012, 12
610-2631.
4, 6285-6291.
1,
5
,
2
3. Hassan, H. S.; Kashyout, A. B.; Soliman, H. M. A.; Uosif, M. A.; Afify, N. Effect of
reaction time and Sb doping ratios on the architecturing of ZnO nanomaterials for gas
sensor applications. Appl. Surf. Sci. 2013, 277, 73-82.
1
4. Zaleska, A. Doped-TiO : A Review. Rec. Patents Eng. 2008,
2, 157-164.
2
1
5. Liu, Y.; Li, J.; Zhou, B.; Chen, H.; Wang, Z.; Cai, W. A TiO
2
-Nanotube-Array-Based
Photocatalytic Fuel Cell using Refractory Organic Compounds as Substrates for
Electricity Generation. Chem. Commun. 2011, 47, 10314–10316.
1
1
1
1
2
6. Cao, S.; Yeung, K. L.; Yue, P. L. An Investigation of Trichloroethylene Photocatalytic
Oxidation on Mesoporous Titania-Silica Aerogel Catalysts. Appl. Catal., B:
Environmental 2007, 76, 64-72.
3
+
2
7. Zhu, J.; Chen, F.; Zhang, J.; Chen, H.; Anpo, M. Fe -TiO Photocatalysts Prepared by
Combining Sol–gel Method with Hydrothermal Treatment and their Characterization.
J. Photochem. Photobiol., A: Chemistry 2006, 180, 196-204.
8. Wang, W.; Zhang, J.; Chen, F.; He, D.; Anpo, M. Preparation and Photocatalytic
3
+
Properties of Fe -Doped Ag@TiO
008, 323, 182-186.
9. Deng, Q. R.; Xia, X. H.; Guo, M. L.; Gao, Y.; Shao, G. Mn-doped TiO
with Remarkable Visible Light Photocatalytic Activity. Mater. Lett. 2011, 65, 2051-
054.
2
Core–shell Nanoparticles. J. colloid interface sci.
2
2
Nanopowders
2
0. Behnajady, M. A.; Alizade, B.; Modirshahla, N. Synthesis of Mg-Doped TiO2
Nanoparticles under Different Conditions and its Photocatalytic Activity. Photochem.
photobiol., 2011, 87, 1308-1314.

Page 21 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
2
1. Jaimy, K. B.; Ghosh, S.; Sankar, S.; Warrier, K. G. K. An Aqueous Sol–gel Synthesis
of Chromium(III) Doped Mesoporous Titanium Dioxide for Visible Light
Photocatalysis. Mater. Res. Bull. 2011, 46, 914-921.
22. Iwasaki, M.; Hara, M.; Kawada, H.; Tada, H.; Ito, S. Cobalt Ion-Doped TiO
2
Photocatalyst Response to Visible Light. J. colloid interface sci. 2000, 224, 202-204.
23. Kiraz, N.; Burunkaya, E.; Kesmez, Ö.; Çamurlu, H. E.; Asiltürk, M.; Ye
ꢀil, Z.;Arpaç,
E. Preparation of Sn Doped Nanometric TiO Powders by Reflux and Hydrothermal
2
Syntheses and their Characterization. J. Sol-Gel Sci. Technol. 2011, 59, 381-386.
4. Xiao, Q.; Si, Z.; Yu, Z.; Qiu, G. Sol–gel Auto-combustion Synthesis of Samarium-
Doped TiO2 Nanoparticles and their Photocatalytic Activity under Visible Light
Irradiation. Mater. Sci. Eng.: B 2007, 137, 189-194.
2
25. Hewer, T. L. R.; Souza, E. C. C.; Martins, T. S.; Muccillo, E. N. S.; Freire, R. S.
Influence of Neodymium Ions on Photocatalytic Activity of TiO Synthesized by Sol–
2
gel and Precipitation Methods. J. Mol. Catal. A: Chemical 2011, 336, 58-63.
6. Ji, L.; Wang, Z.; Li, Z.; Liang, J. Preparation of Aligned Titania Nanowires with an
Aligned Carbon Nanotube Composite Template. Mater. Lett. 2008, 62, 1979-1982.
7. Grandcolas, M.; Ye, J.; Hanagata, N. Combination of Photocatalytic and Antibacterial
Effects of Silver Oxide Loaded on Titania Nanotubes. Mater. Lett. 2011, 65, 236-239.
8. Zhang, Y.; Gao, Y.; Xia, X. H.; Deng, Q. R.; Guo, M. L.; Wan, L.; Shao, G. Structural
2
2
2
2
Engineering of Thin Films of Vertically Aligned TiO Nanorods. Mater. Lett. 2010,
64
, 1614-1617.
29. Morey, M. S.; Bryan, J. D.; Schwarz, S.; Stucky, G. D. Pore Surface Functionalization
of MCM-48 Mesoporous Silica with Tungsten and Molybdenum Metal Centers:
Perspectives on Catalytic Peroxide Activation. Chem. Mater. 2000, 12, 3435-3444.
30. Okada, K.; Shimai, A.; Takei, T.; Hayashi, S.; Yasumori, A.; MacKenzie, K. J. D.
Preparation of Microporous Silica From Metakaolinite by Selective Leaching Method.
Microporous Mesoporous Mater. 1998, 21, 289-296.
31. Cochran, J. K. Ceramic Hollow Spheres and their Applications. Curr. Opin. Solid State
Mater. Sci. 1998, 3, 474 –479.
3
2. Syoufian, A.; Inoue, Y.; Yada, M.; Nakashima, K. Preparation of Submicrometer-
Sized Titania Hollow Spheres by Templating Sulfonated Polystyrene Latex Particles.
Mater. Lett. 2007, 61, 1572-1575.

RSC Advances
Page 22 of 25
View Article Online
DOI: 10.1039/C5RA03421C
3
3
3
3
3
3. Cui, L.; Wang, Y.; Niu, M.; Chen, G.; Cheng, Y. Synthesis and visible light
photocatalysis of Fe-doped TiO mesoporous layers deposited on hollow glass
2
microbeads. J. Solid State Chem. 2009, 182, 2785-2790.
4. Ma, G.; Jia, R.; Zhao, J.; Wang, Z.; Song, C.; Jia, S.; Zhu, Z. Nitrogen-Doped Hollow
Carbon Nanoparticles with Excellent Oxygen Reduction Performances and Their
Electrocatalytic Kinetics. J. Phys. Chem. C 2011, 115, 25148–25154.
5. Wang, C.; Ao, Y.; Wang, P.; Hou, J.; Qian, Preparation, Characterization and
2
Photocatalytic Activity of the Neodymium-Doped TiO Hollow Spheres J. Appl. Surf.
Sci. 2010, 257, 227-231.
6. Wang, C.; Ao, Y.; Wang, P.; Hou, J.; Qian, J. Preparation of Cerium and Nitrogen Co-
Doped Titania Hollow Spheres with Enhanced Visible Light Photocatalytic
Performance. Powder Technol. 2011, 210, 203-207.
7. Wang, P.; Wu, J.; Ao, Y.; Wang, C.; Hou, J.; Qian, J. Preparation and Enhanced
Photocatalytic Performance of Sn Ion Modifi ed Titania Hollow Spheres. Mater. Lett.
2
011, 65, 3278-3280.
38. Xu, J.; Chen, M.; Fu, D. Study on Highly Visible Light Active Bi-Doped TiO2
Composite Hollow Sphere. Appl. Surf. Sci. 2011, 257, 7381-7386.
2
39. An, G.; Yang, C.; Jin, S.; Chen, G.; Zhao, X. Hollow TiO :Sm3+ Spheres with
Enhanced Photoluminescence Fabricated by a Facile Method using Polystyrene as
Template. J. Mater. Sci. 2013, 48, 5483-5488.
40. Chaudhuri, R.G.; Paria, S. Visible Light Induced Photocatalytic Activity of Sulfur
Doped Hollow TiO Nanoparticles, Synthesized Via a Novel Route. Dalton Trans.
2
2
014, 43, 5526-5534.
4
1. Awazu, K.; Fujimaki, M.; Rockstuhl, C.; Tominaga, J.; Murakami, H.; Ohki, Y.;
Yoshida, N.; Watanabe, T. A Plasmonic Photocatalyst Consisting of Silver
Nanoparticles Embedded in Titanium Dioxide. J. Am. Chem. Soc. 2008, 130, 1676-
1
680.
2. Tian, Y.; Tatsuma, T. Mechanisms and Applications of Plasmon-Induced Charge
Separation at TiO Films Loaded with Gold Nanoparticles. J. Am. Chem. Soc. 2005,
27, 7632-7637.
4
2
1
43. Sondi, I.; Salopek-Sondi, B. Silver Nanoparticles as Antimicrobial Agent: a Case
Study on E. coli as a Model for Gram-negative Bacteria. J. colloid interface sci. 2004,
275, 177-182.

Page 23 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
4
4. Smetana, A. B.; Klabunde, K. J.; Marchin, G. R.; Sorensen, C. M. Biocidal Activity of
Nanocrystalline Silver Powders and Particles. Langmuir 2008, 24, 7457-7464.
5. Li, Q.; Mahendra, S.; Lyon, D. Y.; Brunet, L.; Liga, M. V.; Li, D.; Alvarez, P. J. J.
Antimicrobial Nanomaterials for Water Disinfection and Microbial Control: Potential
Applications and Implications. Water research 2008, 42, 4591-602.
4
4
4
4
4
5
6. Zhang, L.; Yu, J. C.; Yip, H. Y.; Li, Q.; Kwong, K. W. Ambient Light Reduction
2
Strategy to Synthesize Silver Nanoparticles and Silver-Coated TiO with Enhanced
Photocatalytic and Bactericidal Activities. Langmuir 2003, 19, 10372-10380.
7. Guin, D.; Manorama, S. V.; Latha, J. N. L.; Singh, S. Photoreduction of Silver on Bare
2
and Colloidal TiO Nanoparticles/Nanotubes: Synthesis, Characterization, and Tested
for Antibacterial Outcome. J. Phys. Chem. C 2007, 111, 13393-13397.
8. Xiang, Q.; Yu, J.; Cheng, B.; Ong, H. C. Microwave-Hydrothermal Preparation and
Visible-Light Photoactivity of Plasmonic Photocatalyst Ag-TiO Nanocomposite
2
Hollow Spheres Chem. Asian J. 2010, 5, 1466 – 1474.
9. Song, C.; Wang, D.; Gu, G.; Lin, Y.; Yang, J.; Chen, L.; Fu, X.; Hu, Z. Preparation
and Characterization of Silver/TiO Composite Hollow Spheres. J. colloid interface
2
sci. 2004, 272, 340-344.
0. Ji, P. L.; Kong, X. Z.; Wang, J. G.; Zhu, X. L. Characterization and Photocatalytic
Properties of Silver and Silver Chloride Doped TiO Hollow Nanoparticles. Chin.
2
Chem. Lett. 2012, 23, 1399-1402.
5
1. Piccinini, P.; Minero, C.; Vincenti, M.; Pelizzetti, E. Photocatalytic Mineralization of
Nitrogen-Containing Benzene Derivatives. Catal. Today 1997, 39, 187-195.
2. Bhatkhande, D. S.; Pangarkar, V. G.; Beenackers, A. A. C. M. Photocatalytic
Degradation of Nitrobenzene using Titanium Dioxide and Concentrated Solar
Radiation: Chemical Effects and Scaleup. Water res. 2003, 37, 1223-1230.
3. ElShafei, G. M. S.; Yehia, F. Z.; Dimitry, O. I. H.; Badawi, A. M.; Eshaq, G.
5
5
2
+
Degradation of Nitrobenzene at Near Neutral pH using Fe –Glutamate Complex as a
Homogeneous Fenton Catalyst. Appl. Catal., B: Environmental 2010, 99, 242-247.
4. O'connor, O. A.; Young, L. Y. Toxicity and Anaerobic Biodegradability of Substituted
5
Phenols under Methanogenic Conditions. Environ. Toxicol. Chem. 1989, 8, 853-862.
5
5. Zhao, L.; Ma, J.; Sun, Z. -z.; Zhai, X. -d. Catalytic Ozonation for the Degradation of
Nitrobenzene in Aqueous Solution by Ceramic Honeycomb-Supported Manganese.
Appl. Catal., B: Environmental 2008, 83, 256-264.

RSC Advances
Page 24 of 25
View Article Online
DOI: 10.1039/C5RA03421C
56. Elmolla, E. S.; Chaudhuri, M. Degradation of the Antibiotics Amoxicillin, Ampicillin
and Cloxacillin in Aqueous Solution by the Photo-Fenton Process. J. Hazard. Mater.
2
009, 172, 1476–1481.
57. Rysz, M.; Alvarez, P. J. J. Amplification and Attenuation of Tetracycline Resistance in
Soil Bacteria: Aquifer Column Experiments. Water Res. 2004, 38, 3705–3712.
58. Gilliver, M. A.; Bennett, M.; Begon, M.; Hazel, S. M.; Hart, C. A. Enterobacteria:
Antibiotic Resistance Found in Wild Rodents. Nature 1999, 401, 233–234.
59. Goni-Urriza, M.; Capdepuy, M.; Arpin, C.; Raymond, N.; Caumette, P.; Quentin, C.
Impact of an Urban Effluent on Antibiotic Resistance of Riverine Enterobacteriaceae
and Aeromonas spp. Appl. Environ. Microbiol. 2000, 66, 125–132.
6
0. Muruganandham, M.; Shobana, N.; Swaminathan, M. Optimization of Solar
Photocatalytic Degradation Conditions of Reactive Yellow 14 Azo Dye in Aqueous
TiO2. J. Mol. Catal. A 2006, 246, 154–161.
6
1. Chun, H.; Yizhong, W. Decolorization and Biodegradability of Photocatalytic Treated
Azo Dyes and Wool Textile Wastewater. Chemosphere 1999, 39, 2107-2115.
6
2. Guo, H.; Tian, D.; Liu, L.; Wang, Y.; Guo, Y.; Yang, X. Core–shell TiO microsphere
2
with enhanced photocatalytic activity and improved lithium storage. J. Solid State
Chem. 2013, 201, 137-143.
6
6
6
6
6
3. Karan, N.S.; Agrawal, A.; Pandey, P. K.; Smitha, P.; Sharma, S. J.; Mishra, D. P.;
2
Gajbhiye, N. S. Diffusion flame synthesis of hollow , anatase TiO nanoparticles.
Mater. Sci. Eng., B 2009, 163, 128–133.
4. Li, X.; Lv, K.; Deng, K.; Tang, J.; Su, R.; Sun, J.; Chen, L. Synthesis and
characterization of ZnO and TiO hollow spheres with enhanced photoreactivity.
Mater. Sci. Eng., B 2009, 158, 40–47.
5. Song, C.; Yu, W.; Zhao, B.; Zhang, H.; Tang, C.; Sun, K.; Wu, X.; Dong, L.; Chen, Y.
2
2
Efficient fabrication and photocatalytic properties of TiO hollow spheres. Catal.
Commun. 2009, 10, 650-654.
6. Zhang, F.; Zhang, Y.; Song, S.; Zhang, H. Superior electrode performance of
mesoporous hollow TiO microspheres through efficient hierarchical nanostructures. J.
2
Power Sources 2011, 196, 8618-8624.
7. Ray, M. Paria, S. Growth Kinetics of Silver Bromide Nanoparticles in Aqueous
Nonionic Surfactant Solutions. Ind. Eng. Chem. Res. 2011, 50, 11601-11607.

Page 25 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA03421C
6
6
7
7
7
7
8. Hamal, D. B.; Klabunde, K. J. Synthesis, Characterization, and Visible Light Activity
of new Nanoparticle Photocatalysts based on Silver, Carbon, and Sulfur-doped TiO2. J.
colloid interface sci. 2007, 311, 514-522.
9. Kawamura, G.; Sato, S.; Muto, H.; Sakai, M.; Lim, P. B.; Watanabe, K.; Inoue, M.;
Matsuda, A. AgBr Nanocrystal-Dispersed Silsesquioxane– Titania hybrid Films for
Holographic Materials. Mater. Lett. 2010, 64, 2648-2651.
0. Behnajady, M. A.; Eskandarloo, H.; Modirshahla, N.; Shokri, Investigation of the
Effect of Sol – gel Synthesis Variables on Structural and Photocatalytic Properties of
TiO
1. Zhang, H.; Wang, G.; Chen, D.; Lv, X.; Li, J. Tuning Photoelectrochemical
Performances of Ag-TiO Nanocomposites via Reduction/Oxidation of Ag. Chem.
Mater. 2008, 20, 6543–6549.
2. Du, J.; Zhang, J.; Liu, Z.; Han, B.; Jiang, T.; Huang, Y. Controlled Synthesis of
Ag/TiO Core-Shell Nanowires with Smooth and Bristled Surfaces via a One-Step
2
Nanoparticles. Desalination 2011, 278, 10-17.
2
2
Solution Route. Langmuirꢀ 2006, 22, 1307-1312.
3. Boxi, S. S.; Paria, S. Effect of Silver Doping on TiO , CdS, and ZnS Nanoparticles for
2
the Photocatalytic Degradation of Metronidazole under Visible Light. RSC Adv. 2014,
4
, 37752-37760.
74. Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemannt, D. W. Environmental
Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69-96.
75. Choi, W.; Termin, A.; Hoffmann, M. R. The Role of Metal Ion Dopants in Quantum-
Sized TiO : Correlation between Photoreactivity and Charge Carrier Recombination
2
Dynamics. J. Phys. Chem. 1994, 98, 13669-13679.
76. Liqiang, J.; Honggang, F.; Baiqi, W.; Dejun, W.; Baifu, X.; Shudan, L.; Jiazhong, S.
Appl. Catal. B: Environmental 2006, 62, 282-291.