Effect of ZnO on Photocatalytic Degradation of Rh B and Its Inhibition Activity for C. coli Bacteria

Article abstract of DOI:10.1134/S1070427218010226

Zinc oxide (ZnO) nanoparticles have been synthesized by co-precipitation method. The structural properties like average crystallite size, lattice parameters, volume of unit cell, and X-ray density were studied by XRD. The crystallite size was measured by using Scherrer formula. It was observed that the average crystallite size increased with the increase of annealing temperature. Morphology of the synthesized oxides was investigated by SEM. The harmful constituents like organic compounds have been removed from waste water that is toxicant. Metal oxide semiconductors had shown good photocatalytic activity to degrade harmful organics into less harmful molecules under light-illumination. In this regard the dye (Rhodamine B) was degraded with increasing exposure time of UV radiations. Almost 60% dye degradation was observed in 150 min. The ZnO was also employed as an active anti-microbial nanomaterial on the growth of C. coli. A 15 μg of ZnO nanoparticles liquefied in 1 mL of dimethyl sulfoxide revealed outstanding 95.04 ± 1.37 % inhibition activities against growth of C. coli.

Full text of DOI:10.1134/S1070427218010226

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2018, Vol. 91, No. 1, pp. 143−149. © Pleiades Publishing, Ltd., 2018.
VARIOUS TECHNOLOGICAL
PROCESSES
Effect of ZnO on Photocatalytic Degradation
of Rh B and Its Inhibition Activity for C. coli Bacteria1
H. Anwara,*, B. C. Ranaa, Y. Javeda, G. Mustafab, M. Raza Ahmadc,
Y. Jamila, and Hassan Akhtara
a Department of Physics, University of Agriculture, Faisalabad-38040, Pakistan
b Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan
c Centre for Advanced Studies in Physics (CASP) G. C. University, Lahore, Pakistan
*e-mail: hafeez.anwar@gmail.com
Received December 27, 2017
Abstract—Zinc oxide (ZnO) nanoparticles have been synthesized by co-precipitation method. The structural
properties like average crystallite size, lattice parameters, volume of unit cell, and X-ray density were studied by
XRD. The crystallite size was measured by using Scherrer formula. It was observed that the average crystallite
size increased with the increase of annealing temperature. Morphology of the synthesized oxides was investigated
by SEM. The harmful constituents like organic compounds have been removed from waste water that is toxicant.
Metal oxide semiconductors had shown good photocatalytic activity to degrade harmful organics into less harmful
molecules under light-illumination. In this regard the dye (Rhodamine B) was degraded with increasing exposure
time of UV radiations. Almost 60% dye degradation was observed in 150 min. The ZnO was also employed as an
active anti-microbial nanomaterial on the growth of C. coli. A 15 μg of ZnO nanoparticles liquefied in 1 mL of
dimethyl sulfoxide revealed outstanding 95.04 ± 1.37 % inhibition activities against growth of C. coli.
DOI: 10.1134/S1070427218010226
INTRODUCTION
chemical properties. Zinc oxide has a wide band gap (Eg =
3.37eV), high binding energy (60 meV), high thermal
and mechanical energy and shows good piezoelectric
effect [4]. Due to its ferromagnetic properties zinc oxide
is known as a well-known material for spintronics. Zinc
oxide is widely used for the fabrication of dye sensitized
photovoltaic devices, optoelectronic devices and storage
batteries [5]. Some studies reported that zinc oxide has
better efficiency as compared to TiO2 in photo degrada-
tion of some dyes in aqueous solution [6]. It is expected
that zinc oxide will become the most promising photo
catalyst for the degradation of dyes in future. Under UV
illumination through photocatalytic reaction zinc oxide
has been used to decompose harmful dyes into less harm-
ful chemicals [7]. The rhodamine B (Rh B) dye is most
commonly used for industrial purpose such as printing
and dyeing in textile, paints, leather and create many
biological and environmental issues. The present study
focused on the synthesis of zinc oxide nanoparticles by
co-precipitation method and applied as a photo catalyst
Nowadays, metal oxide semiconductors as photo cata-
lysts have much potential for the removal of toxins from
water. The wastes from dye and textile industries are highly
dangerous for human and aquatic life because these efflu-
ents create eutrophication in the aquatic environment [1].
In current situation water pollution has become a serious
issue for the life of creatures due to severe contamination
of the environment. The photo catalysis process is being
used to remove harmful materials from water because
this process effectively eradicates the stable structure of
refractory pollutants. This process is effective due to its low
running cost, high efficiency, and no secondary pollution
[2]. The most important feature of photo catalysis is the
selection of semiconductor material. The ZnO and TiO2 are
considered as ideal photo catalyst due to their wide energy
band gap [3]. Zinc oxide as photo catalyst has gained much
attention due to its unique electrical, optical and photo-
1 The text was submitted by the authors in English.
143

144
H. ANWAR et al.
Starch
Zn(NO3)2·6H2O
Dissolve in Dl water
Stir constantly
NaOH
White precipitate settles down
Filter, wash, dry
Annealed at 300°C, 500°C,
700°C,
XRD, SEM, UV-Vis
Fig. 1. Preparation procedure of ZnO nanoparticles.
for the degradation of (Rh B) dye and has employed as
an active antibacterial material.
Characterization
The powder X-ray diffraction was performed through
(XRD) system Model (PANalytical) with Nickel filtered
CuKα (λ = 1.50405) radiation. The particle size was
calculated from broadening of line using Scherer’s
formula. The scanning electron microscope (SEM) studies
were performed using SEM Model (JEOL- JSM 5910)
to study the morphology of the prepared nanoparticles.
EXPERIMENTAL
Chemicals and Synthesis
All chemicals used throughout the research were of
analytical grade and of sigma-Aldrich. The schematic
diagram of preparation of zinc oxide nanoparticles
has been given in Fig 1. The ZnO nanoparticles were
synthesized by co-precipitation method using zinc
nitrate Zn(NO3)2.6H2O and sodium hydroxide (NaOH)
as precursors and soluble starch as a stabilizing agent.
Starch (1.2 g) was dissolved in 40 mL of distilled water
at room temperature. Zinc nitrate (0.8 g) was dissolved
in 40 mL distilled water and it was added to the starch
solution. The obtained solution was stirred continuously
using the magnetic stirrer for 8 h. Then, 40 mLof sodium
hydroxide solution (1.6 M) was added dropwise in the
solution. The reaction was proceeded for 2 h after the
complete addition of sodium hydroxide solution and it
was kept overnight. After this solution was filtered and
washed three times with ethanol to remove the byproducts
and excessive starch from the nanoparticles. The moisture
free content was obtained after drying at 60°C for 2 h in
an oven Model (Shel-Lab). Then the grinded samples
were annealed at 300, 500, and 700°C in furnace Model
(SNOL-LHM01).
Photocatalytic activity. The completely characterized
sample of ZnO nanomaterial was used as an adsorbent
material for the removal of dye, waste water effluents
of the dye industry. Before and after the removal
of dye the waste water was examined using UV-
Vis spectrophotometer of Model (PG- T80). The
photocatalytic activity of ZnO nanoparticles was tested
by the degradation of Rhodamine B (Rh B) in water at
room temperature. Sample annealed at 500°C was taken
as a model sample for the photocatalytic activity. ZnO
nanoparticles (0.01 g) were added to the 10 ppm of (Rh B)
under constant stirring for the effective degradation of
(Rh B). The solution was continuously stirred for 1 h
under dark conditions to reach the equilibrium conditions
between photo catalyst and (Rh B). Under constant stirring
this solution was exposed to the UV illumination. Then
samples were taken from the solution after every 30 min
and centrifuged at 12 000 rpm to separate ZnO powder.
The absorption spectrum of resulting decomposed dye
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EFFECT OF ZnO ON PHOTOCATALYTIC DEGRADATION OF Rh B
Vcell = a2с sin 60°,
145
(3)
(101)
(100)
ZM
D = ‒‒‒‒‒‒‒,
NA Vcell
(4)
(5)
(002)
(110)
(102)
(103)
(112)
(201)
C0 ‒ C
Photo degradation rate = ‒‒‒‒‒‒‒ × 100,
700°C
C
where D is the crystal size, β is the line width (FWHM),
θ is the diffraction angle and the λ is the wavelength
of X-ray radiation. Z is the number of molecules per
unit cell, M is the molar mass of the Zinc Oxide, NA is
Avogadro number, Vcell is the volume of the unit cell, C0
is concentration of (Rh B) when time is zero and C is the
concentration when time is equal to t.
500°C
300°C
70
20
30
40
50
2θ, deg
60
C-Coli biofilm inbition activity. Agar is used to grow
bacteria in petri-dishes. Its quantity for best culture of
bacteria agar cannot be less than 1.2 g in every 4 inch dish
in 60 mLof deionized water. C-coli bacteria was cultured
at 37°C for over night in laboratory and were observed
with the help of microscope in controlled region in the
petri-dish. ZnO nanoparticles were added in 1 mLsolvent
of dimethyl sulfoxide and put in petridish. No bacteria
was ground this region was known as the kill zone, the
amount of colonies in the petri-plates was calculated by
hamocytometer. The colony forming units (CFUs) were
calculted and survial percentage was obtained defined
by formula:
Fig. 2. XRD Pattern of ZnO prepared at different temperature.
was recorded with UV-Vis spectrophotometer . The
spectra were recorded in the range of (450–650 nm).
The average crystallite size (Scherrer’s equation), lattice
parameter, volume of unit cell, X-ray density and photo
degradation rate were measured by using the following
relations [8‒10]:
0.9λ
D = ‒‒‒‒‒‒‒,
β cos θ
(1)
(2)
1
4 (h2 + hk + k2) l2
‒‒ = ‒‒ ‒‒‒‒‒‒‒‒‒‒‒ + ‒‒ ,
Colony number of treated bacteria
d2
3
a2
c2
Survival, % = ––––––––––––––––––––––––––––––,
Colony number of controlled bacteria
(6)
(b)
(a)
1 μm
1 μm
Fig. 3. SEM images of ZnO nanoparticles (a) untreated and (b) annealed at 500°C.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 1 2018

146
H. ANWAR et al.
Table 1. Lattice Parameter, volume of unit cell and X-ray density of ZnO nanoparticle samples
Annealing
temperature, °C
Particle size, Lattice parameter Lattice parameter Volume of unit cell,
X-ray density,
g cm–3
nm
24
27
a, Å
3.23
3.23
c, Å
5.20
5.18
Å3
Untreated
300
44.49
44.50
5.018
4.985
500
700
32
34
3.22
3.22
5.19
5.18
44.45
44.52
4.999
4.998
Table 2. Time interval, absorbance, photo degradation rate, cell count before and after treated, survival, and inhibition of ZnO
catalyst
Cell count, CFU, mL–1
Survival, %
Inhibition, %
Time
interval,
min
Photo
degradation
rate, %
Absorbance,
arb. units
before treated n1
after treated n2
S = (n1/ n2) × 100
In = 100 – S
30
1.434
7.3
150000
4150
2.77
97.23
60
90
1.423
1.232
1.023
8
20
34
150000
150000
150000
24500
23500
11500
16.33
15.67
7.67
83.67
84.33
92.33
120
150
0.637
59
150000
8150
5.43
94.57
Inhibtion zone was measured and expermential
results were found using the following relation defined
by formula:
annealing temperatures. The untreated sample has
crystallite size 24 nm. The growth of ZnO gradually
increased with the increase in the heat treatment and
maximizes the crystallite size 34 nm at the temperatures
700°C.
Inhibtion (%) = 100 – S,
RESULTS AND DISCUSSION
Structural Analysis
(7)
SEM Analysis
The scanning electron microscope (SEM) images of
untreated sample of nanoparticles are shown in Fig. 3a.
The morphology of SEM image shows that uniform
distribution of the grains and shape of the synthesized
oxide.
The XRD patterns of prepared ZnO nanoparticles
at different temperatures of 300, 500, and 700°C are
shown in Fig 2. X-ray diffraction patterns confirm the
crystalline structure of zinc oxide nanoparticles. The
observed diffraction peaks at 2θ of 31.92°, 34.62°,
36.44°, 47.79°, 56.69°, 62.93°, 66.47°, 67.87°, 69.17°
referred to XRD planes (100), (002), (101), (102), (110),
(103), (200), (112), (201), respectively. The JCPDS file
no. 36-1451 revealed that the synthesized zinc oxide
has the hexagonal wurtzite type structure. The lattice
parameters, volume of unit cell and X-ray density were
measured from X-ray diffraction data and obtained
results are listed in Table 1.
Photocatalytic Activity
The photocatalytic activity demonstrates the photo-
degradation of (Rh B) under UV illumination over the
surface of zinc oxide nanoparticles. It shows maximum
absorbance at 554 nm. In the presence of zinc oxide
nanoparticles the absorbance intensities of (Rh B)
decrease as exposure time increase. Figure 4 shows the
degradation of (Rh B) in the presence of ZnO (annealed
at 500°C) catalyst as a function of time. The concentration
of dye decreases as the exposure time increase. The
The crystallite size is calculated by Scherrer’s formula
and increased from 24 to 34 nm with the increase in
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 91 No. 1 2018

EFFECT OF ZnO ON PHOTOCATALYTIC DEGRADATION OF Rh B
1.2
147
1.0
0.8
‒1
0

CB
O2
0.6
0.4
O O
H2С
H2С
H2С
CO2
H2O
Mineral salts
1
hv
СOO
0.2
0.0
2
3
OH
VB
0
30
60
90 120 150
Fig. 4. Extent of degradation of Rh B at different time intervals.
Rhodamine B
hv
H+
Green
554
CH3
crystalline
powder
H3C
Cl‒
O2
N
N
O
H3C
CH3
COO

O2
Solubility
in water
mg mL
(20°C)
CB
HOO
–1
hv = Eg
Ethanol
mg mL
C28H31ClNO
g mol
–1
–1
VB
OH
OH
Degradation of Rh B over the surface
of ZnO catalyst
Fig. 5. The schematic diagram of degradation of (Rh B) over the surface of ZnO catalyst.
photodegradation rate was calculated using Eq. 5 and
obtained results has enlisted in the Table 2. The data
shows that most of the dye degrades after 2 h.
This process leads to the effective separation of electron-
hole pair which plays an important role in the degradation
of (Rh–B). The possible equations in the degradation of
(Rh–B) are given below:
Figure 5 is a schematic diagram when UV light
falls, electrons and holes are produced between valence
band and the conduction band on the surface of ZnO
nanoparticles that is responsible for the degradation of
(Rh B). When the UV light falls, in conduction band of
ZnO the electron moves towards the surface and remove
the frequent O2 to produce super oxide anion O–2 and
simultaneously produces HOO• radicals, to produce
an active species as OH•, hole in valence band moves
towards the back side of ZnO surface and react with OH–.
ZnO + hv → e– + h+,
O2 + e– → O–2 + H+ + HOO,
e– + HOO + H+ → H2O2,
H2O2 + e– → OH° + –OH,
(8)
(9)
(10)
(11)
The above reaction shows that due to active oxygen
species (Rh B) decomposes into less harmful organic.
However, the excellent optical and good crystallinity of
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148
H. ANWAR et al.
Disruption of cell
membrane
Protein
damage
Cell membrane
Nucleus
Damages
mitochondria
Damages DNA
structure
Fig. 6. Schematic diagram of inhibition of C. coli by ZnO nanoparticles.
zinc oxide nanoparticles increase the reactive species over
the surface of catalyst which results rapid degradation of
(Rh B) under UV irradiation.
and cause disruption of membrane [11] due to which
photolysis and degradation of the cytoplasm occurs which
cause the cell death. The C. coli cell membrane contains
H2O or hydroxide (OH) ions. When hole reacts with
hydroxide (OH) ions, produce hydroxyl radicals (OH•)
and at the same time, the electron generates superoxide
ions (O2−) by reducing O2. Both holes and hydroxyl
radicals (OH•) are tremendously reactive with contacting
organic compounds, particularly for cell membrane [12]
and the accumulative damage is initiated by these reactive
oxygen species oxidative degradation of lipids and result
in cell death as represent in schematic diagram Fig. 6.
C. Coli Biofilm Inhibition Activity
The amount of 15 μg of ZnO powder was dissolved
in 1 mL solvent of dimethyl sulfoxide which exhibited
exceptional biofilm inhibitory activity 95.04 ± 1.37%
against C. coli (Table 2) as shown in Fig. 6. Additional
sharp edges and site due to larger surface area of ZnO
nanoparticles can penetrate into the bacterial membrane
450 μm
450 μm
450 μm
(c)
(a)
(b)
450 μm
450 μm
450 μm
(d)
(f)
(e)
Fig. 7. Microscopic view of inhibition of C. coli biofilm by ZnO nanoparticles (a) controlled group C. coli biofilm (b) Rifampin treated
(c) biofilm by 3 μg of ZnO nanoparticles (d) biofilm treated by 5 μg of ZnO nanoparticles,(e) biofilm with 10 μg ZnO nanoparticles,
(f) biofilm with 15 μg of ZnO nanoparticles.
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EFFECT OF ZnO ON PHOTOCATALYTIC DEGRADATION OF Rh B
149
Zinc oxide nanoparticles showed high photocatalytic
activity in photo degradation of Rh B. The anti-bacterial
activity of ZnO nanoparticles have also tested on C. coli.
The synthesized ZnO has found to be an effective anti-
microbial nanomaterial and prevented the growth of
C. coli.
ACKNOWLEDGMENTS
The author is thankful to Higher Education Commission
(HEC) of Pakistan for providing financial support to carry out
this work under IRSIP scholarship.
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