Potential continuous removal of toluene by ZnO nanorods grown on permeable alumina tube filters

Article abstract of DOI:10.1039/c6ra07801j

Vertical ZnO nanorods were successfully grown on the crystalline surface of an Al₂O₃ microfilter by the simple technique of evaporation of prepared solution at atmospheric pressure (ESAP) for photocatalytic degradation of toluene. The nanorods were grown from evaporated solution at low temperatures of 300, 400, and 500 °C. The crystalline structure and morphology of the deposited films were evaluated by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM), respectively. The aqueous photocatalytic activity of the samples was measured by degradation of Methylene Blue (MB) dye. Toluene photodegradation was studied using a tubular photoreactor under various gas concentrations, flow rates (FR), relative humidities (RH), reaction temperatures (RT), and using various light sources. The grown ZnO nanorods were highly uniform and hexagonal wurtzite crystals with mono-sized nanorods. For the nanorods grown at 300 °C, the photocatalytic investigation showed approximately 98% degradation of MB for the first 20 minutes of UV light irradiation. The toluene degradation results indicated that alterations in gas concentration and flow rate affect the toluene degradation ability by direct and indirect oxidation and reduction mechanisms and the absorption capability of the ZnO nanorods' surface. In this system, 20% relative humidity and 30 °C reaction temperature were found to be the optimum conditions for maximum toluene conversion.

Full text of DOI:10.1039/c6ra07801j

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: F. Ghanbari, M.
Eskandari, P. Nazari, S. Gharibzade, S. Kohnehpoushi and B. Abdollahi Nejand, RSC Adv., 2016, DOI:
10.1039/C6RA07801J.
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

Please do not adjust margins
Page 1 of 13
RSC Advances
View Article Online
DOI: 10.1039/C6RA07801J
Journal Name
ARTICLE
Potential continuous removal of toluene by ZnO nanorods
grown on permeable alumina tube filters
Faegheh Ghanbaria, Mehdi Eskandari a,b, Pariya Nazaric, Saba Gharibzadehc, Saman
Received 00th January 20xx,
Accepted 00th January 20xx
Kohnehpoushia,b,Bahram Abdollahi Nejanda,b*
Vertical ZnO nanorods were successfully grown on crystalline surface of Al2O3 microfilter by the simple technique of
Evaporation of Prepared Solution at atmospheric Pressure (ESAP) for photocatalytic degradation of Toluene. The nanorods
were grown from evaporated solution at low temperatures of 300, 400, and 500℃. The crystalline structure and morphology
of the deposited films were evaluated by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-
SEM), respectively. Aqueous photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye.
Toluene photo degradation was studied using the tubular photoreactor under various gas concentrations, flow rate (FR),
relative humidity (RH), reaction temperature (RT), and various light sources. The grown ZnO nanorods were highly uniform
and hexagonal wurtzite crystals with mono-sized nanorods. For the nanorods grown at 300 ℃, the photocatalytic investigation
showed approximately 98% degradation of MB for the first 20 minutes of UV light irradiation. The toluene degradation results
indicated that alteration in gas concentration and flow rate affects the toluene degradation ability by direct and indirect
oxidation and reduction mechanisms and absorption capability of ZnO nanorods surface. In this system, 20% relative humidity
and 30℃ reaction temperature were found as optimum condition in maximum toluene conversion.
DOI: 10.1039/x0xx00000x
www.rsc.org/
nanorods, such as high surface area, less grain boundaries, direct
path of electron transportation, engineering direction of
structure, chemical and thermal stability, and excellent
1. Introducꢀon
Volatile organic compounds (VOCs) are common air pollutants
and can be found in both outdoor and indoor environments.
Many VOCs are known to be toxic and considered to be
carcinogenic. Recently, photocatalytic oxidation (PCO) has
received growing interests as a promising technology for the
photocatalytic properties, there are numerous studies on
synthesis and characterization of aligned and non-aligned
structures 13-16
.
The process of vertical growth is highly attractive because of its
antenna structure and ability to absorb the wide range of
irradiated light beams. ZnO films have been grown using various
techniques including chemical vapor deposition (CVD)17, vapor
phase epitaxy 18, molecular beam epitaxy 19, DC reactive
magnetron sputtering 20, 21, sol-gel 22, and hydrothermal methods
23. Here, the electrodeposition 24, hydrothermal23 and CVD
17growth techniques are among the more common techniques for
preparing the vertically grown nanorods.
In this study, a fast and convenient technique for growing ZnO
nanorod arrays, named as evaporation of solution at atmospheric
pressure (ESAP), was applied for preparing the photoactive
alumina membrane. This method is similar to metal organic
chemical vapor deposition (MOCVD) used for growing ZnO
structures at the ambient pressure. As reported in the present
study, ZnO grown by ESAP method shows uniform nanorod
structures. As compared to other methods, such as vapor
synthesis approach and solution phase technique, this technique
has some merits including synthesis of single crystalline
nanorods with a hexagonal wurtzite crystalline structure, high
purity, high deposition rate, good crystallinity, density and
aspect ratio controllability, and uniformity. Moreover, in this
method, ZnO nanorods can be vertically grown at low
temperature and atmospheric pressure with low cost and ease of
removal of indoor and outdoor air pollutants, in particular VOCs
present at low ppb concentrations
1,
2. There are some
conventional air cleaning technologies such as filtration and
sorption3, which only transfer indoor pollutants to another phase,
but PCO has the potential to destroy a broad range of VOCs such
as benzene, toluene, ethylbenzene, and p-xylene (BTEX) to
carbon dioxide (CO2) and water (H2O) 4, 5. There are a large
number of photocatalytic materials including TiO2 indicating
permissible activity to degrade the VOCs. Zinc oxide (ZnO),
similar to titanium dioxide, is one of strongest photocatalytic
materials, which is less expensive and has an easy synthesis
process. Potential photocatalyst materials such as ZnO, TiO2,
and Bi4B2O9 could degrade the organic aqueous pollutants such
as methylene blue same as air pollutants according to their band
gap justification and engineering6, 7. The various structures of
ZnO have been achieved through applying various techniques
and parameters8-12. Because of unique properties of ZnO
a. Nanomaterial Research Group, Academic Center for Education, Culture and
Research (ACECR) on TMU, Tehran, Iran
b. Nanomaterials Group, Dept. of Materials Engineering, Tarbiat Modares
University, Tehran, Iran
c. Department of Physics, Tarbiat Modares University, Tehran, Iran
See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 13
ARTICLE
Journal Name
handling which can be quite appropriate for ZnO nanostructured tube (Fig. 2.b) coated by ZnO nanorods (Fig. 2.c,Vdi)e.wTArhticeleUOnVlinCe
growth on the porous structure substrate without decreasing the and LED lamps were placed in axis of reacDtoOrI:w10h.i1c0h39c/aCn6RirAr0a7d8i0a1teJ
flow rate of gas stream. However, there are few studies that on all interior region of alumina membrane, uniformly.
investigated the zinc oxide photocatalytic activity on removal
efficiency of toluene molecules. This work was conducted to
investigate the photocatalytic activity of various grain size of
ZnO nanorods on degrading the toluene as an example of BTEX
pollutants. The effective parameters of the photoreaction were
determined by investigating the toluene concentration at ppbv-
level, flow rate, relative humidity, reaction temperature, and light
sources.
2. Experimental procedure
Growth of aligned ZnO nanorods
ZnO nanorods were grown under atmospheric pressure condition
from evaporation of prepared solution. The solution was
Fig. 1. Schematic representation of the experimental set-up used
for the PCO of toluene in gas phase
.
prepared by solving the Zn(CH3COO)2.2H2O (Merck) in 50 mL
deionized water (DI). Polyvinylpyrrolidone (PVP) was used as a
primitive surfactant with weight ratio of 1:10 of PVP to zinc
acetate dihydrate. After completely dissolving PVP and zinc
acetate dehydrate in DI water, temperature of the solution was
To inject the toluene gas, a gaseous stream of toluene was
generated by toluene generator with carrier gas mixture of pure
nitrogen and oxygen. The nitrogen and oxygen flow rate ratio
was adjusted to 4:1. The humidity ratio was adjusted using the
water bubbler system with same nitrogen and oxygen ratio. All
gas streams were controlled by mass flow controller (APEX,
USA). Besides the 316 stainless steel pipe was chosen to carry
the gas stream. To get rid of any adsorbed pollutants, prior to any
experimental process, the alumina microfilter modified by ZnO
nanorods were heated up to 70 °C for 2 h.
set to 70
℃ and the solution was allowed to evaporate under
vigorous stirring conditions. After reducing the quantity of the
solution to 20 mL, it was poured into the clean alumina crucible.
The cylindrical alumina micro-filter was placed vertically on the
alumina crucible and other side of cylindrical micro-filter was
covered by alumina tablet. This system was laid in a furnace and
the furnace was set to different temperature of 300, 400, and 500
℃
. The temperature of the furnace was increased at the rate of
10 per minute until it reaches to 300, 400, and 500 . Once
the temperatures reached to 300, 400, and 500 , the annealing
℃
℃
℃
process was performed for 2 hours. To study the surface contact
between ZnO nanorods and alumina microfilter, a half portion of
prepared solution (25 mL decreased to 10 mL through the
previously mentioned preparation method), and growth
temperature of 300
℃ was chosen to carry out evaporation
process. The growth parameters were summarized in Table 1.
Table 1 Growth parameters of ZnO nanorods on the substrates
Growth
pressure
(Bar)
Growth rate Growth
Sample
( C/min)
temperature ( C)
S3
S4
S5
10
10
10
300
400
500
1
1
1
Photocatalytic oxidation reactor
Fig. 1 shows a schematic representation of the experimental set-
up used for the PCO of toluene in gas phase. As shown in Fig.
2.a, the experiments were conducted in continuous flow mode
using an annular flow-through reactor of about 314 mL, made of
316 stainless steel equipped with a high pressure mercury UV
lamp (400 W, Philips) and a blue–green LED (wavelength of
visible light ranged from 400 to 550nm). As previously
described, the photocatalytic medium was permeable alumina
Fig. 2. Designed photoreactor for degrading the toluene
molecules, Stainless steel photoreactor (a), permeable alumina
microfilter, schematic of ZnO nanords growth on the interior
surface of alumina microfilter (c), and gas permeation flow (d).
By assembling the reactor, the chamber of photoreactor was
washed by gas stream of nitrogen and oxygen gas mixture (N2/O2
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
ratio of 4:1). The standard operating conditions used for DSQ, USA) for the quantitative analyses of toluene vapor. The
View Article Online
DOI: 10.1039/C6RA07801J
irradiation experiments are summarized in Table 2.
chromatographic column of the GC-MS was an Rtx-1 capillary
GC column (26m long, 0.53mm i.d., 3 mm film thickness). The
operating conditions of the GC-MS were set as follows: injector
Table 2 Designed experimental condition of photoreactor
temperature: 200
column temperature (followed the sample injection) 60°C; which
was then increased from 60 to 100 by the set program. Besides,
℃, detector temperature: 200 ℃, and the
Parameters
Inlet
Temp. (K)
Reaction
Temp. (°C)
Value
Parameters
Relative
Humidity (%)
Irradiation area
(cm2)
value
Gas
25±2
10-60
℃
the helium carrier gas flow rate was 1mL min-1, helium make-up
gas was 50 mL min-1, and the sample volume was 200 mL. A
quantitative analysis of the gaseous products of reaction was
conducted using the standard equations for a linear calibration
response. The equation was generated for each standard
compound using a minimum of five different concentrations with
three replicates at each concentration. All correlation coefficients
(R2) of the linear calibration response curves exceeded 99.5%.
10-60 ±2
100-400
288.88
1.8
UV Irradiation
Intensity
Inlet Toluene
Conc.(ppbv)
(mW/cm2)
Visible
Irradiation
wavelength
(nm)
Inlet Toluene
Gas Flow (mL 100-400
min-1)
400-550
3. Results and discussion
3.1 ZnO nanorod characterization
3.1.1 Surface morphology of grown nanorods
To investigate the photocatalytic degradation of toluene by ZnO
nanorods, an experiments set was prepared. First, the
degradation ability of toluene contaminant with various grain
size of ZnO nanorods was investigated at constant toluene
concentration, flow rate, relative humidity, reaction temperature,
and UVC light irradiation. To investigate the effective
parameters in photodegradation of toluene by various sizes of
ZnO nanorods, toluene concentration, toluene gas flow rate,
relative humidity, reaction temperature, and light source
wavelength effects were studied.
Fig. 3 illustrates the FE-SEM images of vertical growth of ZnO
nanorods on crystalline alumina microfilter and pure glass
substrate. As the figure shows, ZnO grown on various growth
temperature possesses a hexagonal wurtzite crystalline structure,
implying that the growth temperature range of 300 to 500
℃ does
not affect the crystal structure of ZnO nanorods. Fig. 3 a, b and
c show vertical growth of ZnO nanorods on the crystalline
alumina microfilter. Fig. 3.d shows pure porous alumina
microfilter as a substrate. Using the crystalline substrate (such as
crystalline alumina substrate), the developed ZnO nanorods
indicated vertical structures (Fig 3.a, b, c, e, and f). This can be
explained by formation of widespread ZnO nucleation on the
crystallites of Al2O3 particles; and, subsequently, growing of
hexagonal structure of ZnO nanorods. Because of the crystalline
structure of Al2O3, the nucleated and grown ZnO nanorods
indicate high density and uniformity in size and length. In this
study, the crystalline Al2O3 microfilter was chosen to prepare the
crystalline sites for the growth of ZnO nanorods (Fig 3.a, b, c and
Fig 3.e). As shown in Fig 3.e, by decreasing the evaporated
solution up to half portion of previous solution, ZnO nanorods
grown on the surface of porous alumina substrate are more sparse
and shorter in length, in comparison with ZnO nanorods grown
from whole portion of prepared solution. This can be explained
by low accumulation of grown atoms and consequently low
seeding sites on the surface of the substrate. It is noteworthy that
the growing of ZnO nanorods in an approximately perpendicular
state on the alumina substrate was achieved without any other
primitive seeding process (Fig 3.e). Fig 3.f shows cross-section
image of developed ZnO nanorods on the porous alumina
microfilter. As the figure shows, because of porous structure of
alumina microfilter, ZnO nanorods are grown in some interior
parts of microfilter since the gaseous precursor permeate into
porous structure of alumina microfilter during the evaporation of
prepared solution.
Characterization of deposited layers
To study the microstructure and morphology of the deposited
films, FE-SEM (S4160 Hitachi Japan) was used. The phase
structures were also investigated using the XRD apparatus
(Philips Expert- MPD). XRD tests were carried out at θ-2θ mode
using Cu-Kα with wavelength of 1.5439Å radiation. The optical
characteristics of deposited films were analyzed using the UV-
vis spectroscopy within the wavelength range of 190-1000 nm
(Avantes, AvaLight-D (H)-S, Netherlands). The aqueous
photocatalytic activity of prepared films was investigated by
degradation of 10 ppm aqueous MB solution (20 ml). Besides, to
investigate the photocatalytic activity of grown nanorods, 0.01
grams of ZnO nanorod/Al2O3 seed layer was mixed with
prepared methylene blue solution. The wavelength and power of
the UV-lamps used in these experiments were 365 nm and 400W,
respectively. The wavelength of visible-light ranged from 400 to
550nm by using a blue–green LED. The LECO analysis (USA)
has been used for determining the contents of nitrogen and
carbon atoms. The degradation of MB by ZnO nanorods was
determined by measuring the absorption intensity at its
maximum absorbance wavelength of λMB = 661 nm, by using a
UV–Vis spectrophotometer (Avantes, AvaLight-D (H)-S,
Netherlands).
Sampling and analysis of toluene photodegradation process
To determine toluene and gas phase reaction, during the UV
irradiation, toluene and gas phase reaction intermediates were
As shown in Fig 3. a, b, and c, various ZnO nanorod growth and
annealing temperatures indicate various structures and
dimensions. The ZnO nanorods were approximately uniform and
70 nm in diameter (Fig 3.a). By increasing the temperature up to
collected for 10–30 min at regular time intervals and at flow rate
of 30 mL min-1 using multibed solid sorbent tubes. The gas
analysis system was composed of a GC-MS (Focus GC and
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 13
ARTICLE
Journal Name
400 , ZnO nanorods diameter is reached to 100 nm. This can precursor delivery to all nucleated sites which cause limited
℃
View Article Online
be explained by diffusion of ZnO atoms which results in radial growth of ZnO nanorods and decreasDinOgI: 1t0h.1e03g9/rCo6wRnA07Z8n01OJ
growth of ZnO nanorods. By increasing the temperature up to nanordos numbers. On the other side, as previously noted, higher
500
℃, the ZnO nanorods dimension is increased up to 180 nm. temperature of 400 and 500℃ can provide higher zinc and
As shown in Fig 3.a, b, and c, an increase in growth temperature, oxygen diffusion condition to grow bigger ZnO nanorods in
unlike the ZnO nanorods dimension, leads to the decrease in diameter.
number of grown ZnO nanorods.
a
b
Fig. 3. The FE-SEM images of ZnO nanorods grown at various
growth temperatures of 300, 400 and 500
℃ on Al2O3 micorfilter
(a, b, and c), pure microfilter (d), perpendicular ZnO nanorods
on interior surface of alumina microfilter (e) and cross section
image of ZnO grown nanorods on the interior surface of alumina
microfilter (f)
Growth of ZnO nanorods starts by nucleation followed by
growth of ZnO nanorods from nucleated sites. Hence, the
nucleation sites numbers, growth temperature, and concentration
of evaporated solution could affect the microstructure of grown
ZnO structure. According to the fact that in the present work the
deposition condition including concentration of solution,
substrate, distance between substrate and evaporation source
were kept constant and only the evaporation and growth
temperature were changed, the microstructure changes would
come from the temperature differences. As shown in Fig. 3a, the
Fig. 4. The XRD spectrum of ZnO nanorods on Al2O3 microfilter
in various growth temperature of 300, 400 and 500
the magnified XRD spectrum of ZnO nanorods (b)
℃ (a), and
3.1.2
Structural characterization of thin films
The structure of ZnO nanorods can be affected by important
factors such as growth rate, annealing temperatures, impurities,
dopants, and size of seed crystallites. Fig. 4 depicts the XRD
patterns of ZnO nanorods grown on the crystalline dense alumina
substrates. The results show the high purity of hexagonal
wurtzite structure of ZnO without appearance of any other kinds
of ZnO crystals. Crystallization of ZnO nanorods in a hexagonal
wurtzite structure is confirmed with microstructure investigation
(Fig. 3). As shown in Fig. 4, the high crystallinity of ZnO
nanorods is achieved by using the Al2O3 crystalline substrate.
The crystallites of Al2O3 particles provided the suitable sites for
nucleation and growth of ZnO nanorod crystals. This can be
explained by crystalline structure matching of α-Alumina and
hexagonal wurtzite crystals. The observed diffraction peaks can
be indexed to those of hexagonal wurtzite ZnO (JCPDS 89-
300
nucleation and growth of ZnO nanorods. This means, at higher
temperature of 400 and 500 , the same nucleation and growth
℃ evaporation and growth temperature is enough high in
℃
could happen as confirmed by Fig. 3b, and c. Besides, increasing
the growth temperature would incline the evaporation rate and
accordingly the growth rate. Hence, evaporation of solution at
lower temperature of 300
℃ provides enough time to deliver the
zinc precursors to more nucleated area which result in higher
number of ZnO nanorods growth possibility, while at higher
temperatures, the high evaporation rate would confine the
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
0510). The lattice parameters obtained for reference ZnO of ZnO crystals. The presence of the carbon and niVtierwogAertincleinOntlhinee
nanoparticles are a=3.244 Å and c=5.198 Å in close agreement structure grown in 300 °C is affirmed by DLOEIC: 1O0.1a0n39a/lCys6iRsA0w7h8i0c1hJ
with other reported values 25. As shown in Fig 4.a, by increasing was 7 and 1% for carbon and nitrogen, respectively.
temperature, the crystallinity of the structure is improved and the In the hexagonal structure of ZnO, the plane spacing is related to
crystallite size is increased. As frequently reported, the crystal the lattice constants a, c, and Miller indices h, k, and l, by the
size can be calculated by Debby Scherrer equation. The following relation 26
calculated crystal size of grown ZnO nanorods are 12.65, 29.7 1/d2=4/3((h2+hk+k2)/a2) + (l2/c2)
and 31.15 nm for growth temperatures of 300, 400, and 500 For the (100) orientation, the lattice constant a is calculated as a=
respectively. As shown in Fig 4.a, the crystallographic pattern of λ/√3sinθ, and for the (002) orientation, the lattice constant c is
ZnO nanorods grown at 300 indicates some leftward shifts in calculated as c= λ/sinθ.
.
℃
,
℃
angles, as compared to the reference ZnO nanocrystals. In this The calculated d spacing of (100) face is expanded from 2.8093
work, PVP, which has enough sources of carbon and nitrogen for Å of reference ZnO to 2.8173 Å of the C/N-loaded ZnO in the
loading in the structure of wurtzite, was used as a surfactant. growth temperature of 300℃. As shown in Table 3, lattice
Considering the fact that the radius of carbon, nitrogen, and parameters of a and c are increased simultaneously, which can
oxygen are 70, 65 and 60 picometers, respectively, by be attributed to carbon and nitrogen effects on the ZnO lattice.
substitution of carbon and nitrogen instead of oxygen atoms in According to the structure reported by U. Seetawan et al 27, a and
the wurtzite structure, there will be an expansion in the wurtzite b parameters are correlated with bond length of Zn-Zn, and c is
structure, during the ZnO nanorods growth. This will lead to a corresponded to bond length Zn-O. In this study, the increases in
strain in the crystallographic structure of wurtzite. This means a and c can be explained by substitutional and interstitial
that through the evaporation of the prepared solution, the carbon placement of carbon and nitrogen.
or nitrogen content molecules are evaporated simultaneously
with zinc atoms and probably are loaded in the growing structure
Table 3 The crystallographic characteristics of ZnO nanorods in the various growth temperatures of 300, 400, and 500 C.
Growth
Temperature
(°C)
a
C
d spacing (°A)
(100)
Sample
2θ ( )
Crystal size (nm)
ε= d/d
(°A)
(°A)
S3
S4
S5
300
400
500
31,76
31,98
31,85
2,817
2,798
2,813
12.6
29.7
31.1
3.26
3.24
3.25
5.219
5.215
5.204
28×10-4
13×10-4
12×10-4
JCPDS 89-0510)
-
31.89
2.809
-
3.244
5.198
-
As shown in Fig 4.b, there exists an approximate shift of 2θ = adequate to remove the oxygen vacancy. This result is confirmed
0.22 ° to larger angles from growth temperature of 300 to 400 by previous studies which reported the stability of oxygen
. This can be explained by the drop in the level of loaded vacancy up to 400
31, 32. The calculated d spacing of (100)
carbon or nitrogen in the structure of ZnO nanorods once the facet increased again to 2.8129 Å in the growth temperature of
temperature rises up to 400 because of the improvement in structure with ambient
21. By ejecting the carbon or 500
℃
℃
℃
℃
℃
nitrogen atoms out of the structure some obvious contraction is oxygen. The strain of structure is slightly decreased by
observed. This means that, time, temperature, and oxygen increasing temperature from 28 × 10-4 to 12 × 10-4 (Table 3).
contents in the autoclave atmosphere could not provide the 3.1.3 Film optical properties
oxygen substitutional state to form the ZnO structures. This Fig. 5 shows the optical absorbance spectra of ZnO nanorods
process leads to a kind of defect reported as an oxygen vacancy grown on crystalline Al2O3 particles and pure crystalline Al2O3
28, 29
which has been reported as a major defect in the ZnO particles which were peeled off from substrate and ultrasonically
structure 30. The calculated d spacing of (100) facet is decreased dispersed in the deionized water. The band gap of ZnO nanorods
to 2.7983 Å in the growth temperature of 400
℃ due to the large was determined from the cut-off wavelength as 1240/λm, where
contraction effects in the ZnO structure. The falling a and c λm is the wavelength value corresponding to the typical
parameters are in close agreement with ejecting carbon and absorption peak. As shown in Fig. 4, the cut-off wavelength of
nitrogen atoms out of substitutional and interstitial locations. By ZnO nanorods appeared in 363 nm. The cut-off wavelength
increasing the growth temperature up to 500
0.13 shift to a smaller angle is observed. This means that by eV. The optical absorption edge of ZnO nanorods for ZnO
rising the temperature up to 500 the time and temperature are
℃, another 2θ = corresponded to the calculated ZnO nanorods band gaps at 3.41
℃
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 13
ARTICLE
Journal Name
structures grown at 300
identical.
℃
and 500
℃
was approximately valence and conduction bands to absorb the largerViwewaAvreticlelenOgntlihnse
DOI: 10.1039/C6RA07801J
and produce electron-hole pairs (Fig 6.b). Simultaneous with
ZnO/Al2O3 mixture, the photocatalytic properties of the pure
powder of Al2O3 have also been investigated in this work. For
pure crystalline Al2O3 particles, the result revealed no obvious
changes in methylene blue degradation in 40 minutes of UV and
visible irradiation.
a
Fig. 5. Normalized UV-vis absorbance spectroscopy of ZnO
nanorods grown on Al2O3 microfilters and pure Al2O3 particles.
3.1.4 Chemical photoactivity
Due to the fact that in this work the effects of relative humidity
are investigated, the aqueous photocatalytic properties of ZnO
nanorods should to be studied since the water molecule interfere
in the oxidation and reduction reactions. Fig. 6 illustrates the
aqueous photocatalytic degradation ability of the ZnO nanorods
grown on the crystalline Al2O3 by ultraviolet and visible light.
As shown in Fig. 6. a, the ZnO nanorods indicate desirable
properties in terms of the fast degradation methylene blue. In the
first 10 minutes of irradiation, approximately 78 % of methylene
blue was degraded by ZnO nanorods prepared at 300
℃. By
continuing the irradiation up to 20 min, approximately 98 % of
MB was degraded. This means that vertically grown ZnO
nanorods display the desirable capability of rapidly degrading
dyes such as methylene blue, which can be attributed to the high
surface area and crystalline structure of ZnO nanorods. By
increasing the growth temperature up to 400
℃ and alternatively
up to 500 , MB degradation was decreased. The photocatalytic
℃
activity can be influenced by parameters such as the crystallinity,
grain size, crystal size, oxygen, and metal vacancy, as well as
loading the metallic and non-metallic atoms in the structure.
Although increasing the crystallinity of ZnO nanorods could
improve the photoactivity properties of ZnO nanorods, the grain
and crystal size, carbon or nitrogen loading effect, and oxygen
vacancy play more important roles in the photocatalytic activity.
Fig. 6 Photocatalytic degradation of MB by ZnO nanorods
grown on Al2O3 microfilters under UV (a) and visible light (b)
irradiation.
3.2. Photocatalytic degradation of Toluene
In other words, the ZnO nanorods grown at 300
℃ show the best
To investigate the photocatalytic degradation of Toluene by ZnO
nanorods, a set of experiments were conducted.
3.2.1 Effect of ZnO nanorods grain size
photoactivity properties probably because of the carbon or
nitrogen content in the ZnO structure that was affirmed by LECO
result and XRD pattern in Fig. 4. By increasing the temperature
Nanostructured zinc oxide ZnO has a wide band gap for
generating the electron–hole pairs. Photocatalytic reaction shows
strong potential of degrading the VOCs, including BTEX
pollutants. In the same environmental conditions of
photocatalytic effects, two major parameters affect the
photocatalytic properties: i) generation of strong electron-hole
pairs and prohibition of recombination; and ii) specific surface
area of ZnO nanostructure which can be exposed by light
irradiation. As previously described, nitrogen and carbon loaded
in the grown zinc oxide nanorods improved the photocatalytic
up to 400
ejection of carbon and nitrogen atoms and the onset of oxygen
vacancy. Once the temperature rises up to 500 , the
photocatalytic activity decreased because of the growing
crystalline and grain size of the ZnO nanorods, which leads to
the lower surface area. As shown in Fig 6.b, degradation ability
of Mb by ZnO nanorods in visible light irradiation shows
interesting capability in activation of grown ZnO nanorods in
low energy light irradiation. This can be described by carbon and
nitrogen loading with ZnO nanorods which can adjust the ZnO
℃, the photocatalytic activity decreased due to the
℃
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
properties of ZnO nanostructures. This improvement has been accessible surface area (with further mass ratio). Besides, in the
View Article Online
widely studied 21, 33, 34. Furthermore, despite the fact that specific heterogeneous reactions, the accessible surface area of deposited
DOI: 10.1039/C6RA07801J
surface area of grown ZnO nanorods is less than that of ZnO nanorod structure is apparently much more than that of spherical
nanoparticles, once loading these materials as a single layer on nanoparticles
the substrate surfaces, using ZnO nanorods indicates much more
Table 4 Calculated and measured specific surface area of ZnO nanorods
Value
Parameter
300
400
500
ZnO nanorods dimension
(nm)
2a1=70
2a2= 100
2a3= 180
Total Mass of Deposited
ZnO (gr)
Number of ZnO nanorods
Volume of Single ZnO
nanorods (cm3)
0.722
3×1015
0.722
0.722
1.5×1015
5.42×10-15
0.5×1015
2.68×10-15
16.84×10-15
Specific Surface of single
ZnO nanorods (m2)
Calculated Total Specific
Surface of ZnO nanorods
(m2)
168×10-6
240×10-6
432×10-7
5.290×1011
3.603×1011
1.99×1011
Measured Total Specific
Surface of ZnO nanorods
(per 0.722 gr)
465
382
269
As mentioned before, the various conditions of ZnO nanorods Fig. 7. Degradation of toluene molecules by various ZnO
growth are chosen to achieve different size of ZnO nanorods. nanorods grown at 300, 400 and 500 and various irradiation
℃
Due the fact that the whole mass quantity of evaporated solution light sources of UV (a) and visible light (b).
is the same, the total deposited mass quantity of ZnO nanorods
will be the same. Hence, the number of grown ZnO nanorods on Fig. 7 shows photodegradation of toluene by various grain size
the alumina microfilter substrates rises up by decreasing the ZnO of ZnO nanorods under ultraviolet and visible light irradiation.
nanorods diameter. Moreover, a decrease in the ZnO nanorods Here, 200 ppbv of toluene gas stream with 200 mL min-1 flow
dimension leads to the increase in the total surface area (Table rate and 10% relative humidity at 25
℃ was chosen to study the
4).
effects of various grain size zinc oxide nanorods. As shown in
Fig. 7.a, by irradiation of UV light, approximately 85, 65, and
25% of toluene is degraded by first 10 minutes UV irradiation on
grown ZnO nanorods at 300, 400, and 500 °C, respectively. By
continuing the irradiation, just 15, 8, and 6% of toluene was
degraded on grown ZnO nanorods at 300, 400, and 500
℃,
respectively. Therefore, by the first cycle of gas permeation
through the ZnO nanorods, the majority of toluene molecules
break down and turn into other lightweight by-products.
Decreasing the efficiency of degradation in the next cycles can
be explained by the less interaction of toluene molecules with
·
OH and superoxide species. It must be noted that the
photocatalytic reactions including oxidation and reduction of
pollutants takes place by direct and indirect oxidation-reduction
reactions. Some works have been conducted on improving the
surface adsorption of BTEX molecules to increase degradation
efficiency 35, 36. Unlike the present study, they followed two
mechanisms including: a) adsorption and b) degradation, to
interfere in breaking down the pollutants. As shown in Figs. 7
and Fig. 3, permeation through the ZnO nanorods in horizontal
and vertical moods prepares appropriate condition for enhancing
the direct oxidation of toluene molecules. Thus, this causes a
major degradation of toluene molecules at the first cycle of
reaction (Fig. 7). As shown in Fig.7.a, an increase in the
nanorods dimension and decrease in the specific surface area
b
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 8 of 13
ARTICLE
Journal Name
leads to a dynamic drop in toluene degradation potential. Fig. 7.b decreasing. Flow rate determines retention timVeiewofArtitcolelOunelninee
DOI: 10.1039/C6RA07801J
shows photodegradation of toluene molecules under visible light molecules interact with reduction and oxidation species of
irradiation.
reaction environment. As the direct contact oxidation and
As described in the methylene blue photodegradation study, in reduction reactions are more considerable than indirect reactions
addition to higher specific surface area of small diameter ZnO in the permeation systems, the toluene molecules interact with
nanorods, the grown ZnO nanorods at low temperature of 300
℃
interfacial electron-hole pairs and oxidation and reduction
(S3) shows high content of carbon and nitrogen which may radicals on the ZnO nanorod surface while passing through the
loaded into ZnO vurtzite structure in the growing step. This ZnO nanorods surface. Accordingly, by passing the inlet toluene
carbon and nitrogen atoms loading provides low energy electron- molecules through the jungle-like structure of ZnO nanorods, the
holes generation activity which result in higher toluene probability of toluene molecule degradation enhances because of
molecules photodegradation. In general, according to the fact the increased contact probability between toluene molecules,
that the probable direct contacting and adsorption of toluene interface oxidation, and reduction species. Subsequently, as
molecules on the surface of ZnO nanorods is more in higher shown in Fig. 8, increasing gas flow rate up to 200 mL min-1does
concentration of toluene molecules, the direct oxidation of not limit the surface contact of toluene molecules and reactive
toluene molecules by generated electrons would conduct faster species. As a result, degradation ability of ZnO nanorods does
and efficiently. Hence, as shown in Fig. 7a, the photodegradation not decrease. On the other hand, an increase in the gas flow rate
process at first 10 minutes for S3 and S4 which contains higher up to 400 mL min-1, the contact probability between toluene and
toluene concentration is quit considerable. Weaker toluene reactive species deceases. Furthermore, presence of water
photodegradation by S5 in comparison to S3 and S4 in same molecules on the ZnO nanorods surface affects the degradation
concentrations can attribute to weaker photodegradation ability efficiency of toluene molecules by changing the absorption
of grown ZnO nanordos at 500
ejecting from ZnO structure and lower specific surface area of the probability of toluene molecule absorption by wet surface of
grown ZnO nanorods at 500 . Besides, after 10 minutes of ZnO nanorods decreases.
℃ due to carbon and nitrogen ability of the surface. So, by increasing the inlet gas flow rate,
℃
photodegradation of toluene in circulating reactor, the
concentration of toluene molecules drops and the
photodegradation rate will decrees due to lower possibility of
toluene adsorption and degradation at lower concentrations. As
shown in Fig. 7.b, degradation of toluene molecules under higher
wavelength light shows capability of ZnO nanorods for being
activated under low energy light irradiation. Degradation rate of
toluene under visible light irradiation is apparently lower than
that of VU light. Unlike the degradation of toluene molecules
under UV light irradiation, 50, 40, and 30% of toluene molecules
were degraded by 70, 100, and 180 nm ZnO nanorods under 120
minutes visible light irradiation, respectively. As shown in table
4, the calculated and measured specific surface areas of ZnO
nanorods are obviously different. This indicates that by
decreasing the ZnO nanorods dimension, a major sidewall
surface effect is diminished due to sidewall attaching of ZnO
nanorods. This fact is illustrated in Fig. 3.
Fig. 8. Degradation of toluene molecules by ZnO nanorods at
various gas flow rates of 100, 200, 300, and 400 mL min-1.
3.2.2. Effect of inlet flow rate
3.2.3. Effect of inlet gas concentration
To investigate the gas flow rate on the degradation ability of ZnO
nanorods, various toluene gas flow rates with constant
concentration and relative humidity of 200 ppbv and 10% were
chosen, respectively. Since gas flow rate in circulated systems is
quite different from one-step permeation of toluene gas stream,
the effects of one-step permeation was investigated to study the
effect of gas flow rate on degradation of toluene molecules. As
shown in Fig. 8, the increased gas flow rate up to 200 mL min-1
leads to the considerable change in degradation efficiency of
toluene. However, by increasing the flow rate up to 400 mL min-
1n, the degradation efficiency of toluene gradually decreased. So,
one can state that in the low gas flow rates of 100 and 200 mL
min-1, the flow rate of inlet toluene gas does not sharply affect
the degradation efficiency; however, by increasing the flow
rates, the degradation efficiency of toluene molecules starts
Decreasing the VOCs pollutant such as BTEX at high
concentration is not as harder as low concentration of pollutants.
Therefore, decreasing the existed BTEX pollutants at ppm level
is more applicable in comparison with pollutant concentration at
ppb level. This can be explained by the difficulty of pollutant
molecule trapping and removing at the ppbv level. Recovering
or degrading the toluene molecule at the ppbv level is among the
concerns of many industries. Photocatalytic method is a
promising method to degrade the BTEX pollutant such as toluene
at the ppbv level. Fig. 9 shows degradation efficiency of toluene
molecules by various ZnO nanorods at the inlet concentration of
100-400 ppbv in the constant flow rate and relative humidity of
200 mL min-1and 10%, respectively. As shown in Fig. 9, at low
inlet concentration of toluene, ZnO nanorods indicate strong
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
degradation ability. However, increasing the toluene relative humidity from 5% up to 20%, degradation efficiency
View Article Online
concentration up to 200 ppbv, the degradation efficiency slightly increases, but after a peak at highest efficDieOnI:c1y0.o10f3290/C%6RrAe0l7a8ti0v1eJ
drops and again by increasing the toluene concentration up to humidity, increasing the relative humidity leads to lower
400 ppbv, the degradation efficiency gradually rises. As efficiency. Some studies examine the effects of relative humidity
previously discussed, the majority of toluene molecule in conversion and mineralization of BTEX pollutant 37. Through
decomposes on the surface of the ZnO nanorods instead of gas these researches, TiO2 was chosen as a photo catalyst for
environment. Thus, the activated sites and generated free radicals photoreactors 35-37. The existence of optimum relative humidity
produced by existing humidity and oxygen molecules play the is different for various photoreactor conditions37, 38. Obee
main role in toluene molecules decomposition. In this state, two showed that there is an optimum level of 5% for relative
mechanisms can describe the behavior of photocatalytic humidity to reach the maximum efficiency of toluene
reactions: a) oxidation of toluene molecules by electron–hole degradation 38. However, in another study, Sleiman et al.
pairs directly on the ZnO nanorods solid-gas interface and; b) reported no optimum for relative humidity. They believe that, the
oxidation of toluene molecules by free radical and super oxides absorption competition between water and toluene molecules on
in the solvent humidity shell on the ZnO nanorods surface. At the photocatalyst surface is the most important mechanism to
the low toluene concentration of 100 ppbv, the free radicals show study the relative humidity effects. They observed a slight
sufficient potential to degrade the absorbed toluene molecules in decrease in conversion and mineralization efficiency by
the water-gas interface. Nevertheless, by increasing the toluene increasing the relative humidity. It must be noted that they used
37
concentration, degradation efficiency drops due to low access of different photoreactor conditions in their study; 120 ppbv
toluene molecules on the wet surface of ZnO nanorods. As versus 290 ppbv 38. Thus, other test condition such as
shown in Fig. 9, by increasing the toluene concentration up to concentration and gas flow rate can obviously affect the results.
400 ppbv, the degradation efficiency slightly increases; which In the present study, there is a rise in the degradation efficiency
can be attributed to the increased toluene molecule absorption on of toluene molecules by increasing the relative humidity up to
the ZnO nanorods. In other words, by increasing the toluene 20% (Fig. 10). Improving the degradation efficiency by
concentration, as well as the free radicals oxidation mechanism, increasing the relative humidity up to 5% was discussed by Obee
direct oxidation mechanism of toluene molecules governs the et al. They reported that this increase can be explained by
oxidation process.
generating the free ·
OH radicals 38. Therefore, the increase of
photodegradation efficiency can be attributed to the generation
of new free radicals and superoxide species of water molecules
existing on the ZnO nanorods surface. Decreasing the
degradation efficiency up to 60% can be because of overloading
of water molecules on the surface and competitive absorption
mechanism which was confirmed by previous works 37, 38. The
interconnected parameter with relative humidity is the reaction
temperature which can directly affect the results of relative
humidity effects. So, the effects of reaction temperature were
also investigated in this study.
Fig. 9. Degradation of toluene molecules by ZnO nanorods at
various gas concentration of 100, 200, 300, and 400 ppbv.
3.2.4. Effect of Relative Humidity
Relative humidity is among the most important factors of the
photocatalytic reactions. To investigate the water molecules
interfering in the photocatalytic reactions, a gas stream with
various relative humidity ranging from 5 to 60% and the constant
gas flow rate and concentration of 200 mL min-1 and 200 ppbv is
chosen, respectively. Fig. 10 shows effects of various relative
humidity on the photo-degradation of toluene molecules in the
by-product species. As depicted in Fig. 10, by increasing the
Fig. 10. Degradation of toluene molecules by ZnO nanorods at
various relative humidity of 5 to 60%.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 10 of 13
ARTICLE
Journal Name
blue or toluene molecules while leaving holes in the valence
3.2.5. Effect of Reaction Temperature
View Article Online
A large number of researchers, who investigated the photo- band which may contribute in photocorroDsiOoIn: 10o.f10Z3n9/OC6sRtAru07c8tu0r1eJ
degradation of VOCs, tried to keep the temperature as a constant (Fig. 12a). In the carbon or nitrogen loaded ZnO nanorods, the
36, 37, 39
parameter, especially in the room temperature
.
lower energy photoexcitation occurs by irradiation of visible
Nevertheless, in some works conducted on temperature effects, light wavelengths with enough energy which could oxidize the
the gas temperature was mentioned as a reaction temperature 40
MB or toluene at higher wavelengths and generating hole at
,
while we believe that the surface temperature of photocatalyst is valence state which could play the same role in photocorrosion
the real reaction temperature since the majority of reactions of ZnO nanorods. Hence, regardless of band gap tuning of ZnO
occur on the surface of the photocatalysts instead of gas nanorods by carbon and nitrogen loading, in case of no electron
environments. This suggestion can be strengthen by increasing or hole scavenger, ZnO nanorods would corrode gradually.
the surface temperature of photocatalyst by UV irradiation Accordingly, the charge scavengers like metals, semiconductors,
during the photoreaction. Therefore, to investigate the reaction and carbon base materials could extract the carriers to make ZnO
temperature of photodegradation process in this study, the K- nanostructures more stable in the photocatalyzing processes.
type thermocouple in contact with ZnO nanorods surface was As discussed, ZnO could face a photocorrosion problem in the
used to adjust the reaction temperature. The ZnO nanorods photocatalyzing processes. The photocorrosion is one of the
surface temperature was controlled by inlet gas temperature important problems in photocatalyst technique.
prepared by thermoelectric heater/cooler system prior to
photoreactor inlet. To investigate the temperature effects on
toluene photodegradation, the surface temperature was adjusted
a
-2.0
between ranging temperature of 10 to 60
℃ with constant gas
flow rate, concentration, and relative humidity of 200 mL min-1,
200 ppbv, and 10%, respectively. As shown in Fig. 11, an
CO2
e-
increase in surface temperature of ZnO nanorods up to 30
to the rise of photodegradation efficiency of toluene molecules.
Besides, by rising the surface temperature up to 60 , the
photodegradation of toluene decreases. Improving the
photodegradation efficiency up to 30 can be described by two
℃ leads
-4.2
-4.4
C7H8
℃
℃
approaches: i) increasing the adsorption ratio of toluene
molecules on the surface of ZnO nanorods; and ii) hydroxide and
superoxide species mobility which in turn can increase the
probability of collision with toluene molecules. Moreover, at the
ZnO
Zn+2
h+
ZnO +2h+→ Zn+2 +1/2O2
-7.4
-8.0
temperatures above 30℃, desorption of toluene and water
ZnO &
C/N loaded ZnO
Al2O3
molecules from the surface is dominant. Also, recombination of
generated electron-hole pairs at high temperature is intensively
accelerated.
Fig. 11. Degradation of toluene molecules by ZnO nanorods at
various reaction temperatures of 10 to 60
℃.
Fig. 12. The photogeneration and photocorrosion mechanism of
ZnO nanorods under UV and visible light irradiation in presence
of toluene or MB molecules (a) and photocorrosion of ZnO
3.3. ZnO nanorods photocorrosion study
Under UV irradiation, the strong photogenerated electron could
reach higher states of conduction band to oxidize the methylene
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
nanorods in UV and visible light irradiation for 36 hours in DI to investigate in degradation ability of toluene molecules. The
View Article Online
water, MB in DI water and gaseous toluene in toluene removal results showed that growth of ZnO nanoDroOdI:s10a.t1033090/C6RA07801J
reactor (b). better photocatalytic activity because of the small grain and
crystal sizes and probably carbon or nitrogen loaded structure of
As previously studied in some works, ZnO could decompose due wurtzite. The grown ZnO nanorods indicate hexagonal wurtzite
to generated species in the aqueous solution 41 42, 43. The possible structure. The ZnO nanorods prepared at 300
display desirable
mechanism was proposed by the strong reaction between band gap for rapid degradation of MB in approximately 20
generated
OH radicals (in presence of H2O) and MV+2 or MB minutes. To study the most important parameters on degradation
℃ shows
℃

(in the polluted environment) with the oxygen of ZnO which ability of toluene molecules by ZnO nanorods, gas concentration,
causes dissolution of ZnO in the solution 44. So many attempts gas flow rate, relative humidity, reaction temperature, and
conducted to prevent the photocorrosion effect such as coupling various light sources were investigated. The results showed that
the ZnO nanostructures by metals (such as Ag and stainless steel) alteration in gas concentration and flow rate affects the toluene
41, semiconductors (such as TiO2 and CdS) 45, 46 and carbon based degradation ability by direct and indirect oxidation and reduction
nanostructures (such as C60, CNT, and graphen)42, 43, 47, 48. In mechanisms and absorption capability of ZnO nanorods surface
this work, we studied the photocorrosion study of grown ZnO in the various flow rates. In this system, 20% relative humidity
nanorods on the Al2O3 microfilter. To investigate the different and 30
℃ reaction temperature were found as the optimum
photocorrosion effect we designed some experiments. 1) parameters in maximum toluene conversion.
Irradiation of ZnO nanorods by UV and visible light in pure
water. 2) Irradiation of ZnO nanorods by UV and visible light in
Acknowledgements
MB polluted aqueous solution. 3) Irradiation of ZnO nanorods
by UV or visible light in toluene removal reactor with 200 ppbv
of toluene gas stream, 200 mL min-1 flow rate and 10% relative
The authors acknowledge financial support from ACECR at
Tarbiat Modares University. The authors also acknowledge the
Iran nanotechnology initiative council (INIC) for the partial
support of this project.
humidity at 25
℃
. The concentration of Zn+2 was measured to
compare the photocorrosion effect. In the toluene removal
reactor, after the appointed time, the grown ZnO on Al2O3
microfilter was washed by same quantity of DI water used in
study of ZnO photocorrosion by pure and MB polluted solution.
According to the fact that alumina has a wide band gap with no
electron or hole affinity in contacting with ZnO nanorods (Fig.
12.b), the generated electrons and holes in the grown ZnO
nanorods on the Al2O3 substrate act like the single ZnO
nanorods. As shown in Fig. 12.b, ZnO nanorods show
photocorrosion in the UV and visible light irradiation
simultaneous with degrading the MB in the aqueous solution.
This means, concurrent with decomposition of methylene blue
Notes and references
1. J. Zhao and X. Yang, Build. Environ., 2003, 38, 645-654.
2. S. Wang, H. M. Ang and M. O. Tade, Environ. Int., 2007, 33, 694-
705.
3. D. W. VanOsdell, M. K. Owen, L. B. Jaffe and L. E. Sparks, J. Air
Waste Manag. Assoc., 1996, 46, 883-890.
4. J. Peral, X. Domènech and D. F. Ollis, J. Chem. Technol.
Biotechnol., 1997, 70, 117-140.
5. P. Pichat, J. Disdier, C. Hoang-Van, D. Mas, G. Goutailler and C.
Gaysse, Catal. Today, 2000, 63, 363-369.
molecules into smaller groups, the photogenerated MB and
OH
could react with the oxygen of ZnO nanorods corroding the ZnO
nanostructure into Zn+2 ions in the solution. To study the ZnO
nanorods in degradation of Toluene molecules, we conducted the
same analysis using irradiation of UV and visible light in
presence of toluene molecules. The photocorrosion of ZnO
nanorods in presence of toluene molecules was almost same as
pure water molecules showing low potential of toluene species
radicals in corrosion of ZnO nanorods. It is worthy to mention
that the present contents of moisture in the toluene removal
reactor could play a main role in dissolving the toluene
6. H. Huang, Y. He, Z. Lin, L. Kang and Y. Zhang, J. Phys. Chem. C,
2013, 117, 22986-22994.
7. H. Huang, K. Xiao, K. Liu, S. Yu and Y. Zhang, Crystal Growth &
Design, 2016, 16, 221-228.
8. C.-H. Xue, R.-L. Wang, J. Zhang, S.-T. Jia and L.-Q. Tian, Mater.
Lett., 2010, 64, 327-330.
9. Y. Sun, G. M. Fuge, N. A. Fox, D. J. Riley and M. N. R. Ashfold,
Adv. Mater., 2005, 17, 2477-2481.
10. P. X. Gao and Z. L. Wang, JACS, 2003, 125, 11299-11305.
11. L. Vayssieres, K. Keis, A. Hagfeldt and S.-E. Lindquist, Chem.
Mater., 2001, 13, 4395-4398.
12. B. Liu, C. Feng, X. Zhang, L. Zhu, X. Wang, G. Zhang and D. Xu,
CrystEngComm, 2016, 18, 1215-1222.
13. D. Fu, G. Han and C. Meng, Mater. Lett., 2012, 72, 53-56.
14. G. Du, L. Zhang, Y. Feng, Y. Xu, Y. Sun, B. Ding and Q. Wang,
Mater. Lett., 2012, 73, 86-88.
15. L. Wang, Y. Kang, X. Liu, S. Zhang, W. Huang and S. Wang, Sens.
Actuators, B, 2012, 162, 237-243.
molecules and providing the OH radicals which could capture
the oxygen from ZnO nanorods. Hence, to protect the
photocorrosion of ZnO nanorods, coupling the ZnO nanorods by
proposed metals, semiconductors, or carbon base materials in the
previous reports would enhance the performance of reactor
including the photocatalyst activity and photocorrosion stability.
16. L. F. Da Silva, O. F. Lopes, A. C. Catto, W. Avansi, M. I. B.
Bernardi, M. S. Li, C. Ribeiro and E. Longo, RSC Advances, 2016,
6, 2112-2118.
Conclusions
Vertical and uniform ZnO nanorods are grown by ESAP
technique at various growth temperature of 300, 400, and 500
℃
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 12 of 13
ARTICLE
Journal Name
17. N. Han, P. Hu, A. Zuo, D. Zhang, Y. Tian and Y. Chen, Sens. 46. X. Wang, G. Liu, G. Q. Lu and H.-M. Cheng, Int. J. Hydrogen
View Article Online
Actuators, B, 2010, 145, 114-119.
18. C. Thiandoume, J. Barjon, O. Ka, A. Lusson, P. Galtier and V. 47. H. Fu, T. Xu, S. Zhu and Y. Zhu, Environ. Sci. Technol., 2008, 42,
Sallet, J. Cryst. Growth, 2009, 311, 4311-4316. 8064-8069.
19. Y. W. Heo, K. Ip, S. J. Pearton, D. P. Norton and J. D. Budai, Appl. 48. L. Zhang, H. Cheng, R. Zong and Y. Zhu, J. Phys. Chem. C, 2009,
Energy, 2010, 35, 8199-8205.
DOI: 10.1039/C6RA07801J
Surf. Sci., 2006, 252, 7442-7448.
20. B. A. Nejand, S. Sanjabi and V. Ahmadi, Vacuum, 2010, 85, 400-
405.
113, 2368-2374.
21. B. A. Nejand, S. Sanjabi and V. Ahmadi, Appl. Surf. Sci., 2011,
257, 10434-10442.
22. C. Zhang, J. Phys. Chem. Solids, 2010, 71, 364-369.
23. M. Eskandari, V. Ahmadi and S. Ahmadi, Physica E: Low-
dimensional Systems and Nanostructures, 2010, 42, 1683-1686.
24. M. Guo, C. Yang, M. Zhang, Y. Zhang, T. Ma, X. Wang and X.
Wang, Electrochimica Acta, 2008, 53, 4633-4641.
25. D. Mishra, J. Mohapatra, M. Sharma, R. Chattarjee, S. Singh, S.
Varma, S. Behera, S. K. Nayak and P. Entel, J. Magn. Magn.
Mater., 2013, 329, 146-152.
26. M. Khatamian, A. Khandar, B. Divband, M. Haghighi and S.
Ebrahimiasl, J. Mol. Catal. A: Chem., 2012, 365, 120-127.
27. U. Seetawan, S. Jugsujinda, T. Seetawan, C. Euvananont, C.
Junin, C. Thanachayanont, P. Chainaronk and V.
Amornkitbamrung, Solid State Sciences, 2011, 13, 1599-1603.
28. X. Li, Y. Wang, W. Liu, G. Jiang and C. Zhu, Mater. Lett., 2012,
85, 25-28.
29. M. Ghosh, S. Ghosh, M. Seibt, K. Y. Rao, P. Peretzki and G.
Mohan Rao, CrystEngComm, 2016, 18, 622-630.
30. N. S. Han, H. S. Shim, J. H. Seo, S. Y. Kim, S. M. Park and J. K.
Song, J. Appl. Phys., 2010, 107, 084306.
31. D. F. Wang and T. J. Zhang, Solid State Commun., 2009, 149,
1947-1949.
32. L. Vlasenko and G. Watkins, Physical Review B, 2005, 71,
125210.
33. Z. Li and S. Miyake, Appl. Surf. Sci., 2009, 255, 9149-9153.
34. J. M. Chappé, F. Vaz, L. Cunha, C. Moura, M. C. Marco de Lucas,
L. Imhoff, S. Bourgeois and J. F. Pierson, Surf. Coat. Technol.,
2008, 203, 804-807.
35. H. P. Kuo, C. T. Wu and R. C. Hsu, Powder Technol., 2011, 210,
225-229.
36. L. Zou, Y. Luo, M. Hooper and E. Hu, Chemical Engineering and
Processing: Process Intensification, 2006, 45, 959-964.
37. M. Sleiman, P. Conchon, C. Ferronato and J.-M. Chovelon,
Applied Catalysis B: Environmental, 2009, 86, 159-165.
38. T. N. Obee and R. T. Brown, Environ. Sci. Technol., 1995, 29,
1223-1231.
39. J. Mo, Y. Zhang and Q. Xu, Applied Catalysis B: Environmental,
2013, 132, 212-218.
40. W. Liang, H. He and J. Li, Photo-catalytic degradation of volatile
organic compounds (VOCs) over titanium dioxide thin film,
INTECH Open Access Publisher, 2012.
41. C. Jiang, S. J. Moniz, M. Khraisheh and J. Tang, Chemistry–A
European Journal, 2014, 20, 12954-12961.
42. C. Han, M.-Q. Yang, B. Weng and Y.-J. Xu, PCCP, 2014, 16,
16891-16903.
43. H. Zhang, R. Zong and Y. Zhu, J. Phys. Chem. C, 2009, 113, 4605-
4611.
44. Y.-Q. Cao, J. Chen, H. Zhou, L. Zhu, X. Li, Z.-Y. Cao, D. Wu and A.-
D. Li, Nanotechnology, 2014, 26, 024002.
45. R. Sapkal, S. Shinde, T. Waghmode, S. Govindwar, K. Rajpure
and C. Bhosale, Journal of Photochemistry and Photobiology B:
Biology, 2012, 110, 15-21.
12 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 13 of 13
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C6RA07801J
TOC
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 13
Please do not adjust margins