Hexagonal ZnO nanorods assembled flowers for
photocatalytic dye degradation: Growth,
structural and optical properties
Qazi Inamur Rahman
a,
⇑
, Musheer Ahmad
b
, Sunil Kumar Misra
c
,
Minaxi B. Lohani
a,
⇑
a
Department of Chemistry, Integral University, Lucknow 226026, India
b
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
c
Department of Chemistry, D.A.V College, Kanpur 208001, India
article info
Article history:
Received 4 July 2013
Received in revised form 21 September
2013
Accepted 7 October 2013
Available online 14 October 2013
Key words:
Nanostructures
Chemical synthesis
Catalytic properties

Surfaces
abstract
A facile hydrothermal method was used to synthesize highly crys-
talline hexagonal ZnO nanorods assembled flowers by the reaction
of zinc acetate and hexamethylenetetraamine (HMTA) at 105 °C.
The morphological characterizations revealed that well defined
ZnO nanorods were assembled into flowers morphology. X-rays
diffraction patterns showed the highly crystalline nature of ZnO
with hexagonal wurtzite structure. The structural and optical prop-
erties of hexagonal ZnO nanorods assembled flowers were mea-
sured by Fourier transform infra-red (FT-IR) and ultraviolet–
visible (UV–Vis) measurements. The as-synthesized hexagonal
ZnO nanorods assembled flowers were applied as an efficient pho-
tocatalyst for the photodegradation of organic dyes under UV-light
irradiation. The methylene blue (MB) and rhodamine B (RhB) over
the surface of hexagonal ZnO nanorods assembled flowers consid-
erably degraded by 91% and 80% within 140 min respectively.
The degradation rate constants were found to be k
app
(0.01313 mint
1
) and k
app
(0.0104 mint
1
) for MB and RhB dye
respectively. The enhanced dye degradation might be attributed
to the efficient charge separation and the large number of oxyrad-
icals generation on the surface of the hexagonal ZnO nanorods
assembled flowers.

Ó 2013 Elsevier Ltd. All rights reserved.
0749-6036/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
/>⇑
Corresponding author. Tel.: +91 9889307703.
E-mail addresses: (Q.I. Rahman), (M.B. Lohani).
Superlattices and Microstructures 64 (2013) 495–506
Contents lists available at ScienceDirect
Superlattices and Microstructures
journal homepage: www.elsevier.com/locate/superlattices
1. Introduction
Recently, the effluents of textile and dye industries are the main pollutants in water which cause
serious damage to both flora and fauna life [1,2]. The colored organic dyes are heavily polluted the
water system and imbalanced the eutrophication in the aquatic life [3,4]. The complete remediation
of these dyes into less harmful chemicals is required to overcome these problems [5–7]. Among
various dye remediation process, the heterogeneous photocatalytic process is well known method
for the decomposition of hazardous waste materials especially organic compounds into less harmful
chemicals [8]. In general, the semiconducting materials are required to facilitate the heterogeneous
photocatalytic reaction. So far, many semiconductor materials such as TiO
2
, ZnO, Fe
2
O
3
, CdS, and ZnS
are effectively used as photocatalysts because of their electronic structure of the metal atoms in
chemical combination such as a filled valence band and an empty conduction band at ground
state. Recently, the metal oxide semiconductors (TiO
2
, ZnO, Fe
2

O
3
) have shown good photocatalytic
activity toward the decomposition of harmful organic dyes into less harmful molecules under light
illumination [9].
Zinc oxide (ZnO) semiconducting materials with the wurtzite hexagonal phase are recently gained
the special attention among the various metal oxides due to presence of some exotic and fascinating
properties. ZnO is well known n-type semiconductor and showing unique properties such as a wide
band gap of 3.37 eV, high-excitation binding energy (60 meV), high thermo-mechanical stability,
piezoelectric and optoelectric properties [10]. These fascinating properties of ZnO semiconductor
make one of most important multifunctional materials which are used in various applications like
fabrication of light emitting diodes (LEDs), laser diodes, surface acoustic wave filter, photonic crystal,
photodetector, optical modular solar cells and chemical sensor [11]. The ZnO materials in nanoscale
have shown a variety of nanostructures such as nanorods [12], nanobelts [13], nanotubes [14], nano-
springs and nanospirals [15], polyhedral cages [16], porous webby [17], sea urchin and comb like
[18] and other complicated morphologies [19,20]. However, it was reported that ZnO nanomaterials
could absorb more fraction of solar spectrum as compared to other metal oxide nanomaterials [21].
ZnO nanomaterials have presented the impressive catalytic activity and quantum efficiency [22,23].
Usui reported the surfactant assisted chemical synthesis of ZnO nanorods and used as photocatalyst
for efficient degradation of methylene blue (MB) dye with 90% degradation rate in 7 h [24]. While,
Sun et al. demonstrated the photocatalytic degradation of MB dye over the surface of ZnO nanobelts
with 94% degradation rate in 5 h under UV light illumination [25]. Recently, Zhang and Oh reported
a comparative study of degradation of MB, Rhodamine-B and Methylene Orange dye by the activated
carbon composite of TiO
2
[26]. Among various ZnO nanostructures, the nanorods morphology exhibit
the high volume to surface ratio which might helpful for the generation of active sites during
the photocatalytic degradation. In this work, we report on the synthesis of hexagonal shaped ZnO
nanorods through the cationic surfactant cetyltrimethylammonium bromide (CTAB) assisted
hydrothermal method. The possible growth mechanism has illustrated to explain the growth of

hexagonal ZnO nanorods assembled flowers morphology. The synthesized hexagonal ZnO nanorods
assembled flowers have been applied as photocatalysts for the degradation of MB and RhB dyes
under UV light illumination. The kinetics of decoloration of organic dyes such as MB and RhB dyes
are discussed.
2. Experimental details
For the synthesis of hexagonal ZnO nanorods assembled flower morphology, 0.05 M zinc acetate
(Zn(CH
3
COO)
2
2H
2
O, 99.8%), 0.05 M hexamethylenetetramine (HMTA; C
6
H
12
N
4
, 99.8%) and 1 M so-
dium hydroxide (NaOH, Pellets, Sigma–Aldrich) solutions were prepared separately in deionized
(DI) water under continuous stirring at ambient temperature. Firstly, HMTA solution was gradually
added into Zn(CH
3
COO)
2
solution with constant stirring followed by drop wise addition of NaOH solu-
tion to maintain the pH 11–12. The above solution was further stirred for 30 min and then gradually
added into the cetyltrimethylammonium bromide (CTAB, 0.75 mM) solution. Afterward, the whole
reaction mixture was transferred into a 250 ml Teflon-lined stainless steel autoclave and heated up
496 Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506

to 105 ± 5 °C for 10 h. After completion of period, the autoclave was allowed to cool at the room tem-
perature and white precipitate was washed repeatedly with DI water followed by ethanol and acetone
and dried in oven at 50 °C for 30 min.
The morphological properties of as-synthesized hexagonal ZnO nanorods assembled flowers were
examined by field emission scanning electron microscopy (FESEM), transmission electron microscopy
(TEM), and high resolution TEM (HRTEM). For TEM analysis, the synthesized ZnO nanorods dispersed
into acetone and a few drops of acetone containing ZnO nanorods poured on the TEM grid and exam-
ined. The crystal phase and crystallinity were analyzed by powder X-ray diffraction (PXRD) with Cu K
a
radiations k = 1.54178 Å with 4°/min scanning rate in the range of 20–80°. The chemical composition
was analyzed by using energy dispersive spectroscopy (EDX) coupled with FESEM. The quality and
composition were examined by Fourier transform infrared (FTIR) spectroscopy in the range of 400–
4000 cm
1
. The optical property as-prepared ZnO nanorods were analyzed by UV–Vis absorption spec-
troscopy at ambient temperature.
The photocatalytic experiments of synthesized hexagonal ZnO nanorods assembled flower were
measured by monitoring the decomposition of organic dyes (MB and RhB). The photocatalytic reaction
was performed in Pyrex flask reactor under the light illumination with xenon arc lamp (Thoshiba,
SHLS-1002) at ambient temperature. For the photodegradation of organic dyes such as MB and RhB
dye, 0.15 g of synthesized ZnO photocatalyst was added in 10 ppm aqueous dye solution (100 mL) un-
der constant stirring. Prior to illumination, dye suspension was continuously stirred for about 1 h to
develop adsorption–desorption equilibrium between dye and photocatalyst under the dark. After-
ward, the suspension was purged by oxygen to provide the stability of aqueous suspension in order
to scavenge electron from the catalyst surface. Then, the stable aqueous dye suspension was exposed
to UV light illumination under constant stirring. The sample was successively taken out from Pyrex
reactor after every 10 min of time interval and subjected to centrifuge at 10,000 rpm to filter out
ZnO powder, and then measured absorption spectroscopy of degrade dye solution using UV–Vis spec-
trophotometer. Generally, the photo-catalytic degradation of dye followed the pseudo-first order
kinetics and rate constant was determined by following relation;

lnðC

=CÞ¼kt
The k was calculated from graph between ln(C°/C) vs. time interval, where C° and C denote the dye
concentration at time, t = 0 and t = t respectively.
3. Results and discussion
3.1. Structural and optical properties of synthesized hexagonal ZnO nanorods assembled flowers
Fig. 1 shows the FESEM images of synthesized hexagonal ZnO Nanorods assembled flowers. The
low magnification FESEM image (Fig. 1(a)) depicts the uniform and dense growth of hexagonal ZnO
nanorods wherein these hexagonal ZnO nanorods are assembled into flower morphology. From
Fig. 1(b), well defined hexagonal ZnO nanorods make an assembly of flower shape. Each ZnO nanorods
possess the average diameter in the range of 250 ± 20 nm. Moreover, the hexagonal ZnO nanorods are
tapering at their end and exhibit clean and smooth surface throughout their lengths.
The crystallinity and crystal phase of as-synthesized hexagonal ZnO nanorods assembled flowers
are analyzed by XRD, as shown in Fig. 1(c). The major reflections are appeared at 32.41°, 35.19°,
36.96°, 48.25°, 57.28°, and 63.41° corresponding to lattice planes of (1010), (0002), (1011),
(1012), (1120), and (1 013) respectively. All the diffraction peaks in XRD are fully matched with pure
wurtzite phase of ZnO crystals (JCPDS: 36-1451). No other peaks have been detected in XRD patterns,
confirming that the synthesized nanorods exhibit pure ZnO crystal with hexagonal wurtzite phase.
Furthermore, the energy dispersive X-ray (EDX) spectroscopy has been executed to investigate the
chemical composition of synthesized hexagonal ZnO nanorods assembled flowers, as shown in
Fig. 1(d). Only Zn and O peaks are observed in EDX spectrum, indicating the full agreement of stoichi-
ometric value of zinc and oxygen in ZnO nanorods. It is noticed that any stray peaks in EDX spectrum
are not detected; confirming the high purity of the synthesized hexagonal ZnO nanorods assembled
Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506
497
flowers. Thus, XRD pattern and EDX spectrum clearly deduce that the synthesized hexagonal ZnO
nanorods assembled flowers are constituted of Zn and O atoms only.
The detailed morphological characterizations of synthesized hexagonal ZnO nanorods assembled
flowers have further analyzed by TEM, as shown in Fig. 2. The low magnification TEM image

(Fig. 2(a)) depicts the hexagonal ZnO nanorods which assembled in flowers manner which is consis-
tent with FESEM results in terms of their morphology and dimensions. Fig. 2(b) shows the HR-TEM
Fig. 1. FE-SEM (a) low magnification image, (b) high magnification image, (c) X-ray diffraction pattern of ZnO, and (d) EDX
spectrum of synthesized hexagonal ZnO nanorods assembled flowers via hydrothermal method.
Fig. 2. Distinctive (a) low magnification TEM image, (b) HR-TEM images of hexagonal ZnO nanorods assembled flowers.
498 Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506
image of ZnO nanorods which exhibits very clear lattice fringes with the distance between two par-
allel lattice fringes of 0.52 nm. This value belongs to [0001] crystal plane of wurtzite phase of
ZnO [27], indicating the defect free and good crystallinity of hexagonal ZnO nanorods. Hence, these
observations affirm that synthesized hexagonal ZnO nanorods exhibit typical wurtzite single crystal-
line structure with the preferential growth oriented along c axis [0001].
The quality and structure of as-synthesized hexagonal ZnO nanorods assembled flowers are char-
acterized by Fourier transform infrared (FTIR) spectroscopy in the range of 400–4000 cm
1
as shown
in Fig. 3(a). The appearance of strong IR band at 561 cm
1
represents the Zn–O stretching, indicating
the formation of wurtzite phase ZnO [28]. The weak IR band at 862 cm
1
is attributed to presence of
carbonate ion CO
2
3

[29]. Additionally, the IR band at 1424 cm
1
is due to the C–O bond in stretching
mode which is usually come from the atmosphere. The synthesized hexagonal ZnO nanorods assem-
bled flowers is further characterized by UV–Vis absorption spectrum to explain the structural and

optical properties which is shown in Fig. 3(b). A strong absorption band at 372 nm is obtained by syn-
thesized ZnO, which is matched up with the characteristic UV absorption band for bulk ZnO [30].No
other absorption peak is detected in the spectrum, confirming the high purity of synthesized hexag-
onal ZnO nanorods assembled flowers.
3.2. Plausible growth mechanism of hexagonal ZnO nanorods assembled flowers
To investigate the growth of synthesized hexagonal ZnO nanorods assembled flower morphology, a
possible mechanism is illustrated as Fig. 4. The mechanism can be explored by considering the in-
volved reactions in the synthesis process. In this hydrothermal process, the hexamethylenetetramine
(HMTA) solution gradually pours into zinc acetate solution, and subsequently release of hydroxyl ions
by the thermal degradation of HMTA which further react with Zn
2+
ions to form zinc hydroxide
(Zn(OH)
2
) [31]. The sequential reactions are as follows;
ZnðCH
3
COOÞ
2
 2H
2
O þ H
2
O ! Zn
2þ
þ 2CH
3
COO

ðCH

2
Þ
6
N
4
þ 6H
2
O $ 6HCHO þ 4NH
3
NH
3
þ H
2
O $ NH
þ
4
þ OH

Zn
2þ
þ 2OH

$ ZnðOHÞ
2
Later, Zn(OH)
2
again reacts with hydroxyl ions to form ZnðOHÞ
2
4
,

Fig. 3. (a) FTIR spectrum and (b) UV–Vis spectrum of synthesized hexagonal ZnO nanorods assembled flowers via hydrothermal
method.
Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506
499
ZnðOHÞ
2
þ 2OH

ðfrom NaOHÞ!ZnðOHÞ
2
4
The addition of cetyltrimethylammonium bromide (CTAB) solution as a surfactant in reaction mixture
reduces the surface tension and inhibits the formation of new phase due to its cationic behavior. Usu-
ally, CTAB surfactant plays two pivotal roles in the synthesis, (i) CTAB can effectively control the mor-
phology of building blocks for synthesis of hexagonal ZnO nanorods by selective adsorption of
surfactants [32] and (ii) CTAB can facilitate the molecular aggregation above Critical Micelle Concen-
tration (CMC) producing spherical micelles at relatively low concentration. The CTAB also facilitates to
transport of ZnðOHÞ
2
4
growth units which come together to form individual hexagonal rod-like struc-
tures which are further self-assembled into flower morphology. As the reaction aged at 105 °C for 10 h,
ZnðOHÞ
2
4
ions dissociate to form ZnO nuclei as follow;
ZnðOHÞ
2
4
! ZnO þ H

2
O þ 2OH

The formation of ZnO nanorods assembled flower is usually preceded by two steps mechanism in
aqueous solution. First nucleation involves the formation of aggregated ZnðOHÞ
2
4
nanoparticles and
then covered by CTAB micelles which might take part of forming the hexagonal rod morphology.
The second nucleation involves the formation of ZnO nanorods from the aggregated nanoparticle fol-
lowed by thermal dissociation of ZnðOHÞ
2
4
to ZnO nuclei. In general, ZnO is polar crystal in which
O
2
ions are in hexagonal close packing and Zn
2+
ions lie in the tetrahedral hole of four O
2
ions.
The growth velocities of ZnO crystal in the different planes are as follows; [0001] >
[00

1

1] > [01

10] > [01


11] > [000

1] in the aqueous phase condition [33]. The [000 1] faces are the
most rapid-growth-rate planes of hexagonal ZnO crystals as compared to other growth facets [34].
However, the morphology of ZnO nanostructures is greatly affected by the growth velocity into the
different directions. It is reported that Zn and O atoms are arranged alternatively along the c-axis
Fig. 4. Plausible growth mechanism of hexagonal ZnO nanorods assembled flowers.
500 Q.I. Rahman et al. / Superlattices and Microstructures 64 (2013) 495–506
and top surface-plane where Zn is terminated to [0001] and is catalytically active along with chem-
ically inert terminated O at the bottom surface [35]. At high pH and temperature, ZnO nuclei grow
very rapid and form hexagonal rods like morphology. At prolonged heating, the hexagonal ZnO nano-
rods might be assembled into flower shape due to electrostatic interaction between ions and polar
surface. Importantly, the synthesized ZnO nanorods follow the same growth pattern as reported in
the literature for ideal growth of hexagonal wurtzite ZnO crystals [36].
3.3. Photocatalytic decomposition of organic dyes (methylene blue and rhodamine-B) using hexagonal ZnO
nanorods assembled flowers
The synthesized hexagonal ZnO nanorods assembled flowers are used as catalyst to study photo-
catalytic activity towards the efficient degradation of organic dyes (MB and RhB). Fig. 5 shows the
UV–Vis absorption spectra of degraded MB and RhB dye over the surface of synthesized ZnO under
UV light illumination. In case of MB dye (Fig. 5(a)), the maximum absorption at k
max
= 661 nm of
MB dye is continuously decreased with the increase of expose time from 0 to 140 min. Similarly,
the maximum absorption at k
max
= 554 nm of RhB dye decrease as increasing the expose time from
0 to 140 min, as depicted in Fig. 5(b). The decreased in the relative intensities of absorption indicates
the degradation of MB and RhB dye by synthesized hexagonal ZnO nanorods assembled flower as pho-
tocatalyst under UV light illumination.
Figs. 6 and 7 exhibit the typical time dependent photodegradation reaction efficiency plots with

and without ZnO photocatalysts for MB and RhB dye. In general, the extent of dye degradation reaction
mediated over the surface of ZnO nanorods is calculated by the following relation:
Extent of degradation ð%Þ¼ðC
o
 C=C
o
Þ100 ¼ðA
o
 A=A
o
Þ100
where C
o
represents the initial concentration at time t = 0, while denotes C is the concentration at
time = t, and A
o
shows initial absorbance and A corresponds to absorbance at time = t respectively.
In both cases, no appreciable degradation occurs under UV light illumination in the absence of ZnO
photocatalyst, suggesting the degradation facilitates by the ZnO nanomaterials. The degradation rates
of MB and RhB dye are gradually increased with the increase of exposed time. The synthesized hex-
agonal ZnO nanorods assembled flowers show the high degradation rate of 91% for MB dye as com-
pared to RhB dye degradation (80%) within 140 min of expose time under UV-light illumination. The
pie charts of MB and RhB dye degradation are shown in Figs. 6(b) and 7(b). The pie charts reveal that
most of MB dye is degraded within 70 min (Fig. 6(b)) and then slower down, whereas most of RhB dye
Fig. 5. (a) UV–Vis absorbance spectra of methylene blue, and (b) rhodamine B dye solution as function of time under UV-light
illumination over hexagonal ZnO nanorods assembled flowers. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article.)
Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506
501
degrades within 100 min (Fig. 7(b)). This suggests that the synthesized hexagonal ZnO nanorods

assembled flowers presents highly active catalyst for MB dye as compared to RhB dye.
Furthermore, the kinetics of organic dyes (MB and RhB) degradation reactions are presented in
Fig. 8. Usually, the organic dyes follow apparent first order kinetics which is in good agreement with
a general Langmuir–Hinshelwood mechanism;
r ¼dC=dt ¼ kKC=1 þ KC
where, r is the degradation rate of reactant (mg/1 min), C concentration of reactant (mg/l), t illumina-
tion time, K adsorption coefficient of reactant (l/mg) and k reaction rate constant (mg/l min). If C is
very small then the above equation could be simplified into;
lnðC
o
=CÞ¼kKt  k
app
t
In general, the plots between ln(C
o
/C) vs. time represents a straight line and the slope is equal to the
apparent first order rate constant. The rate constants for MB and RhB dye are estimated to k
app
Fig. 6. (a) Extent of degradation rate of methylene blue dye in every successive time interval, and (b) pie chart of methylene
blue dye degradation as function of time. (For interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
Fig. 7. (a) Extent of degradation rate of rhodamine B dye in every successive time interval, (b) pie chart of rhodamine B dye
degradation as function of time.
502 Q.I. Rahman et al. / Superlattices and Microstructures 64 (2013) 495–506
(0.01313 mint
1
) and k
app
(0.0104 mint
1

) respectively, showing the first order kinetics. These results
are consistent with previously reported works for MB and RhB dye degradation [37,4].
The mechanism of dye degradation over ZnO under UV light illumination is explained on the basis
of reported literatures [4]. Upon illumination, an electron is excited and moves to conduction band
(CB) and leaves hole in valence band (VB). This phenomenon creates the electron–hole pairs which
might help in the degradation of dye. It is known that the adsorbed oxygen on the surface of ZnO play
a pivotal role in the dye degradation reaction by combining with electron (

e) in conduction band and
generate superoxide radical anion O
Å
2
, instantaneously superoxide radical anion O
Å
2
ÀÁ
get protonated
to yield HOO
Å
radicals [37]. On the other hand, the photo generated h
+
in VB reacts with H
2
O/OH

and
dye molecules to generate an active species such as OH
Å
and dye
+

. The following steps are possible in
the dye degradation over ZnO semiconductor under light illumination;
ZnO þ hv !

eðconduction bandÞþh
þ
ðvalence bandÞ
O
2
þ

e ! O

2
þ H
þ
! HOO

h
þ
þ H
2
O !

OH þ H
þ
e

þ HOO


þ H
þ
! H
2
O
2
ðFormation of H
2
O
2
Þ
H
2
O
2
þ

e !

OH þ OH

ðFormation of

OH radicalsÞ
Dye
þ
þfO
2
; O


2
; HOO

; or

OHg!peroxy or hydroxylated Intermediate !
! Mineralized product
Therefore, the formation of active oxygen species fO
2
; O

2
; HOO

; or

OHg over the surface of ZnO pho-
tocatalyst significantly leads to the degradation of organic dye into less harmful material. Inclusively,
the good optical and structural properties of synthesized hexagonal ZnO nanorods assembled flowers
greatly affects their photocatalytic activity towards the degradation of MB and RhB dye under UV-light
illumination. Additionally, the enhanced photocatalytic degradation might result from the high con-
centration of defects over the surface of synthesized hexagonal ZnO nanorods assembled flowers
[38]. Herein, as compared to degradation rate of RhB dye, the high degradation rate towards MB
dye might be associated to its simple chemical structure. Moreover, the degradation rate with synthe-
sized hexagonal ZnO nanorods assembled flowers is better than of those literatures on dye degrada-
tion with ZnO flowers [39–41]. In order to check the stability and reproducibility of synthesized ZnO
Fig. 8. Kinetics study of dye degradation of (a) methylene blue and (b) rhodamine B dye, exhibiting typical first order liner plot
ln C
o
/C = f(t). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this

article.)
Q.I. Rahman et al. /Superlattices and Microstructures 64 (2013) 495–506
503
photocatalysts, the used photocatalysts are further characterized by XRD patterns (as presented in
Fig. 9) which present the almost similar patterns of as-synthesized ZnO photocatalysts. No other dif-
fraction peak is detected, confirming the stability of ZnO nanorods assembled flowers and reproduc-
ibility of photocatalysts. Thus, the synthesized hexagonal ZnO nanorods assembled nanorods could be
a suitable and excellent photocatalyst for dye remediation due to its good crystal quality, optical and
structural properties.
4. Conclusion
Highly crystalline hexagonal ZnO nanorods assembled flowers were synthesized by a facile hydro-
thermal method using zinc acetate and hexamethylenetetraamine (HMTA) at 105 °C. Well defined
ZnO nanorods were self-assembled into flowers morphology during the synthetic process. FT-IR and
UV–Vis studies revealed good structural and optical properties of hexagonal ZnO nanorods assembled
flowers. The photocatalytic activities of synthesized hexagonal ZnO nanorods assembled flowers car-
ried out for the photodegradation of organic dyes (MB and RhB dye) under UV-light irradiation. The
MB and RhB dye over the surface of hexagonal ZnO nanorods assembled flowers exhibited the degra-
dation rates of 91% and 80% within 140 min respectively. The degradation rate constants were
found to be k
app
(0.01313 mint
1
) and k
app
(0.0104 mint
1
) for MB and RhB dye respectively. The en-
hanced dye degradation might be attributed to the efficient charge separation, generation of the large
number of oxyradicals on the surface of the hexagonal ZnO nanorods assembled flowers and the
chemical structure of dye molecule.

Acknowledgement
We are expressing our sincere thanks for Dr. A.R. Khan chairman of department of chemistry Inte-
gral University Lucknow India, for his kind support and encouragement for our research work.
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