Accepted Manuscript

Elucidation of photocatalysis, photoluminescence andantibacterial studies of ZnO thin films by spin coating method

K. Kaviyarasu, C. Maria Magdalane, K. Kanimozhi, J. Kennedy,B. Siddhardha, E. Subba Reddy, Naresh Kumar Rotte, ChandraShekhar Sharma, F.T. Thema, Douglas Letsholathebe, GeneneTessema Mola, M. Maaza

PII: S1011-1344(17)30762-5DOI: doi: 10.1016/j.jphotobiol.2017.06.026Reference: JPB 10887

To appear in: Journal of Photochemistry & Photobiology, B: Biology

Received date: 2 June 2017Revised date: 17 June 2017Accepted date: 21 June 2017

Please cite this article as: K. Kaviyarasu, C. Maria Magdalane, K. Kanimozhi, J. Kennedy,B. Siddhardha, E. Subba Reddy, Naresh Kumar Rotte, Chandra Shekhar Sharma, F.T.Thema, Douglas Letsholathebe, Genene Tessema Mola, M. Maaza , Elucidation ofphotocatalysis, photoluminescence and antibacterial studies of ZnO thin films by spincoating method, Journal of Photochemistry & Photobiology, B: Biology (2017), doi:10.1016/j.jphotobiol.2017.06.026

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Elucidation of Photocatalysis, Photoluminescence and Antibacterial studies of ZnO thin

films by spin coating method

K. Kaviyarasu1,2

, C. Maria Magdalane3,4

, K. Kanimozhi5, J. Kennedy

1,6, B. Siddhardha

7, E.

Subba Reddy8, Naresh Kumar Rotte

9, Chandra Shekhar Sharma

9, F.T. Thema

1,2, Douglas

Letsholathebe10

, Genene Tessema Mola11

, M. Maaza1,2

1UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology Laboratories, College of

Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392,

Pretoria, South Africa.

2Nanosciences African network (NANOAFNET), Materials Research Group (MRG),

iThemba LABS-National Research Foundation (NRF), 1 Old Faure Road, 7129, P O Box

722, Somerset West, Western Cape Province, South Africa.

3Department of Chemistry, St. Xavier’s College (Autonomous), Tirunelveli 627002 India.

4LIFE, Department of Chemistry, Loyola College (Autonomous), Chennai 600034 India.

5PG Research & Department of Chemistry, Auxilium College (Autonomous), Vellore, India.

6National Isotope Centre, GNS Science, Lower Hutt, New Zealand.

7Department of Microbiology School of Life Sciences, Pondicherry University, Puducherry

605014, India.

8Department of Chemistry, Andhra Loyola College (Autonomous), Vijayawada, Andhra

Pradesh, 520008 India.

9Department of Chemical Engineering, Indian Institute of Technology, Hyderabad, Kandi,

Telangana, 502285, India.

10Department of Physics, University of Botswana, Private Bag 0022, Gaborone, Botswana.

11

School of Chemistry and Physics, University of Kwazulu-Natal, Private Bag X01,

Scottsville, 3209, Pietermaritzburg, South Africa.

*Corresponding authors: kavi@tlabs.ac.za; kaviyarasuloyolacollege@gmail.com

(K. Kaviyarasu)

Tel. No. +91 – 8056029860

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Abstract

The ZnO thin films have been prepared by spin coating followed by annealing at different

temperatures like 300 ºC, 350 ºC, 400 ºC, 450 ºC, 500 ºC & 550 ºC and ZnO nanoparticles

have been used for photocatalytic and antibacterial applications. The morphological

investigation and phase analysis of synthesized thin films well characterized by X-ray

diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM),

Photoluminescence (PL), Transmission Electron Microscopy (TEM) and Raman studies. The

luminescence peaks detected in the noticeable region between 350 nm to 550 nm for all

synthesized nanosamples are associated to the existence of defects of oxygen sites. The

luminescence emission bands are observed at 487 nm (blue emission), and 530 nm (green

emission) at the RT. It is observed that there are no modification positions of PL peaks in all

ZnO nanoparticles. In the current attempt, the synthesized ZnO particles have been used

photocatalytic and antibacterial applications. The antibacterial activity of characterized

samples was regulated using different concentrations of synthesized ZnO particles

(100µg/ml, 200µg/ml, 300µg/ml, 400µg/ml, 500µg/ml and 600µg/ml) against gram positive

and gram negative bacteria (S. pnemoniae, S. aureus, E. coli and E. hermannii) using agar

well diffusion assay. The increase in concentration, decrease in zone of inhibition. The

prepared ZnO morphologies showed photocatalytic activity under the sunlight enhancing the

degradation rate of Rhodamine-B (RhB), which is one of the common water pollutant

released by textile and paper industries.

Keywords: Zinc Oxide, Thin films, Photoluminescence, Antibacterial studies, Photocatalytic.

1. Introduction

Nanostructure transition metal oxide have drawn a much more deal of consideration due to

their outstanding physical and chemical properties arising out of large surface area, quantum

confinement effect, which are depend on the shape and size of the material. Among the

various transition metal oxide (TMO), Zinc oxide (ZnO) is an encouraging semiconductor

material with wurtzite crystal structure occurs naturally but mostly produced by chemical

routes [1, 2]. Owing to its unique properties, ZnO has been considering a potential material

for wide range of applications exclusively in filed effect transistors [3], dye sensitized solar

cells [4, 5], gas sensors [6], UV detectors [7, 32], photocatalysis [8, 9, 33], biomedical

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applications [10, 34] and thin film transistors due to its wide direct band gap (Eg ~ 3.37 eV)

and higher exciton binding energy (60 meV) at normal room temperature [11]. Besides, the

technological significance of ZnO nanostructures, their quasi-one-dimensional structure with

diameters in the range 10-100 nm, attracted significant interest in scientific point of view.

ZnO belongs to a period of inorganic nanostructured phases are available with a wide range

of texture morphologies [12]. Especially this cluster of metal oxides nanoparticles is

appropriate to photocatalysts and photo oxidizing ability against the biochemical and organic

species [13]. The benefits of ZnO nanoparticles overcome to other metal nanoparticles due to

their high efficiency of UV-blocking, catalytic properties of large surface area and the

outstanding applications in the field of agriculture and bio-medical industries [14-16]. ZnO

nanoparticle displays the antibacterial activity against the microbial cells, because of the

formation of hydrogen peroxide or electrostatic binding of the particles on bacterial surface

[17]. There are different strategies has been reported for obtaining ZnO morphologies based

chemical and physical routes. Among them few are very popular methodologies for preparing

ZnO particles such as sol-gel [18-20], solvothermal [21], hydrothermal [22, 23], solution

based routes [24, 25] etc. Now-a-days green synthesis of ZnO nanoparticles is acquiring

importance and has been proposed as possible mechanism of physical and chemical methods

[26]. To modify the structural, optical and magnetic properties of ZnO nanoparticles, it is

significant changes to decorate the ZnO thin films with suitable method. However, in the

present work, we have synthesized the ZnO nanoparticles were investigated the effect of

temperature on structural, optical and antibacterial performance [27]. Dyes are roughly

utilized in many industries like for dyeing nylon, polyacrylonitrile-modified nylon, wool,

silk, and cotton. They are also used by other dyestuff manufacturing industries as a biological

stain and in printing media [28, 29]. Most of these dyes are stable against light, temperature,

and biodegradation and therefore accumulates in the environment as recalcitrant compounds.

In the urban waste water treatment removal of synthetic toxic organic dye is very important,

due to its non-biodegradable nature of the pollutants. Especially, in the transition metal oxide

nanostructured materials are exploited for the decomposition of toxic dye degradation and

become more non-toxic in the presence of UV/vis light [30-31].

According to the usage of pesticides, herbicides are destroying our green environment to the

greater extent [35-38]. Specially Rhodamine-B (RhB) dyes have been used in trade industries

and in our daily life as colorants, the RhB classes of dyes reaction might be produce of

various N-dealkylated primary and secondary aminobenzene structures are like

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aminobenzene carcinogens [39-41]. These organic impurities are highly polluted the

environment and human health, due to their toxicity, carcinogenicity and various hazardous

effects. However, in these carcinogenic organic composites and its detoxification are vital

role to save the environment and this process become current development of research to

preserve human health and safety [42-45]. Hence the prepared of ZnO nanoparticles are

tested for decomposition of synthetic dyes which exhibited the better photocatalytic

properties against Rhodamine-B under Sunlight irradiation.

2. Experimental Procedure

2.1 Materials & Method

ZnO thin films were deposited on the silicon substrate by the sol-gel technique. Zinc acetate

dehydrate [Zn(CH3COO)2.2H2O], which is a precursor, was first dissolved in a 2-

methoxyethanol solution along with monoethanolamide (MEA) as the sol stabilizers. After

stirring for 3 hrs at 90 oC, a homogeneous transparent solution with a concentration of 0.5 M

zinc acetate and a 1:1 molar ratio of MEA/zinc acetate dehydrate has been formed. This

solution was kept for hydrolysis for 45 hrs at room temperature before coating. Then spin-

coated on the above stated on silicon substrates at 3000 rpm for 30 s at room temperature

(RT). To evaporate the solvent, the coatings were then dried in a furnace at 200 oC for 15 min

in air. By repeating the coating 8 periods, ZnO thin film with the thickness of ~180 nm was

obtained.

2.2 Characterization techniques

In ZnO nanoparticles phase and structural information measured by XRD (Rich Seifer) the

optimized parameters were used CuKα radiation (λ= 1.54056 Å), scan rate, operating at 2º/s.

The diffraction patterns were recorded within the 2θ angle range between 20º to 60º. The

surface morphology of the thin films was understood by scanning electron microscopy (JEOL

JEM). SEM images of the sample with different magnification were taken with a 5.5 mm

working distance by applying an accelerating voltage of 15 kV and current of 10 µA. The

microstructures and size of ZnO nanoparticles were observed by transmission electron

microscopy (TEM) it was operating at 200 kV. The chemical state of the films was analyzed

directly using X-ray photoelectron spectroscopy (Thermo-VG Scientific, USA). The Raman

spectra were recorded by using (Renishaw micro-Raman spectrometer RM 2000), the bands

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were observed in the spectral range 200-1200 cm-1

. The optical properties of the products

were measured with UV-Vis spectrometer (VARIAN CARRY 5E) model UV-Vis-NIR

spectrometer.

2.3 Photocatalytic performance test

Degradation of Rhodamine-B (RhB) was carried out by using ZnO in aqueous solution under

sun light (λ ≥ 400 nm). The catalyst loaded in the experiment was 60 mg dispersed in 100 ml

of 10 ppm RhB solution and irradiated with sunlight. The catalyst/RhB solution was kept in

the dark for 6 hrs to achieve adsorption-desorption equilibrium. Decomposition of dye was

carried out with H2O2, which was added to enhance the generation of more OH• radicals

during photodegradation, resulting in rapid degradation of dye. The experiments were carried

out by simultaneous exposure of sunlight through the 60 mg of catalysts 5 ml of H2O2 loaded

100 ml of RhB aqueous solution under stirred conditions. The catalyst loaded RhB solution

was illuminated under visible light was done at different time intervals. At given time

intervals, the photo-reacted solution of the centrifuged sample from visible light illuminated

solution, 2 ml were with-drawn at different time intervals which was analyzed by recording

the changes in the absorption band maximum, using a UV-visible spectrophotometer.

2.4 Antibacterial assay

The effect of prepared ZnO materials on Gram-positive and Gram-negative bacteria; (S.

pnemoniae, S. aureus, E. coli and E. hermannii) was examined by the evolution curves of

bacterial cells in liquid medium amended with synthesized ZnO morphologies. Concisely,

100 ml of Luria Bertani (LB) broth was inoculated with fresh gatherings of bacteria mounting

on agar plates. Each culture broth was incubated in a shaking incubator 37 ºC for 24 hrs.

Subsequently, an aliquot from above was added to 100 ml LB broth amended with 100, 200,

300, 400, 500 and 600 µg/mL of ZnO nanomaterials. LB broth without ZnO was used as a

regulator. Growing was firm by computing the optical density at 60 nm after fixed time

interval of 24 hrs.

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3. Results and Discussions

3.1 Structural features

Fig. 1 shows the XRD pattern of as deposited and 300 ºC, 350 ºC, 400 ºC, 450 ºC, 500 ºC &

550 ºC annealed ZnO thin films. The X-ray reflections at 2θ angle of 31.74°, 34.32°, 36.98°,

47.51° and 56.40° are from (100), (002), (101), (102), (110) planes of ZnO [ICDD 36-1451].

The average crystallite size of as-deposited film was calculated by Debye Scherrer’s formula

0.9λ/βcos(θ). It was in the range of 10 to 30 nm. As seen in XRD pattern, the sharpness of the

peaks signifying the sophisticated order crystalline nature with a higher temperature [35].

Crystallinity of ZnO nanoparticles augmented on calcination may be due to the subtraction of

chemical residues and impurities. The presence of pure single phase zinc oxide is confirmed

by the absence of secondary peaks. The peak intensities and the FWHM are found to change

in all the ZnO thin films as deposited at 300 ºC, 350 ºC, 400 ºC, 450 ºC respectively. In our

case the sample deposited at high temperature has maximum intensity and less in FWHM,

which is improved, as result diffraction peaks become sharper and stronger, thus

demonstrating that the crystal quality has been improved and the size of nanoparticles

become higher with increase in the active surface area. Thus, to get smaller nanoparticles

lower temperature is favorable. And comparing the XRD report of all the samples it has been

concluded that the nanosamples calcined at 500 oC and 550

oC gives high intensity and fine

peaks, which can be used for further applications of ZnO nanoparticles. In the diffraction

lines of ZnO NPs were differ from it broadens and intensity, which was dependent on Miller

indices of the respective standards of crystal axis. For the samples calcined at 500 oC & 550

oC gives high intensity fine diffraction line (002) which is sharp than the line (101), were as

(101) is narrower than the line (100) which is less intense peak this proves an asymmetry in

the crystallite structure.

3.2 FESEM Studies

To identify the morphology and particle size distribution of synthesized ZnO nanoparticles

annealed at 300 ºC ,350 ºC ,400 ºC ,450 ºC ,500 ºC & 550 ºC prepared by spin coating

method were initially examined by FESEM. In Fig. 2(a-f). shows the various morphologies of

ZnO nanoparticles. Fig. 2(a-b), shows the presence of uniform circular aggregate loosely and

leaving a disordered arrangement with plenty of interspaces between them and in the inner

blocks of ZnO annealed at 300 ºC and 350 ºC. Also, the image proves that the sample were

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highly porous in nature. Fig. 2(c-d) shows the very small fine particles of the nanosamples

annealed at 400 ºC & 450 ºC. Fig. 2(e-f) shows the rod-shaped ZnO nanosamples annealed at

500 ºC & 550 ºC. The highly porous samples with uniform spherical shape of cluster form in

the sample prepared at low temperature which are highly agglomerated. In all the samples the

meso-porosity is observed may be due to partial formation of the intra particle porosity and

the inter-particle porosity. The particle size increases at high temperature at higher annealing

temperature proposed that the entire particles join to form heavier particles and the upper

level particles fused together due to its synergistic effect, and this leads formation of nanorod

which has bigger particle size with the higher surface to volume ratio. Therefore, HRTEM

images show that the ZnO thin films surface morphology depends upon the annealing

temperature.

3.3 HRTEM Analysis

In the HRTEM images indicate the various morphologies of ZnO nanosamples annealed at

350 ºC, 400 ºC, 450 ºC, 500 ºC & 550 ºC as shown in Fig. 3(a-e) which reveals that the ZnO

nanoparticles of different sizes with an average particle size of 8-10 nm. In Fig. 3(a-e) that

the average size of the nanograins is about 5-20 nm. The HRTEM images of Fig. 3(c-e) show

that the spherical aggregates with good crystallinity which are composed of nanoparticles

with a diameter below 30 nm consistent with XRD data discussed above and the semi

crystalline nature confirmed by SAED pattern as shown in Fig. 3(f). In the FESEM and

HRTEM analysis confirms the different morphologies with highly crystalline nature of ZnO.

The selected area electron diffraction (SAED) illustrations the crystalline network density for

adjustable intention which leads that the synthesized ZnO nanoparticles are not only single

crystals, rather then, aggregates the several single nanocrystals.

3.4 μ-Raman & XPS Analysis

Raman spectra of ZnO nanoparticles as shown in Fig. 4, were the significant bands of ZnO

could be identified in all deposited thin films. The acoustic phonon overtone and optical

overtone with A1 symmetry located at 203 cm-1

and 332 cm-1

respectively. The E2 (high)

mode at 439 cm-1

which indicating the crystal quality of ZnO. The bands at 537 cm-1

, 588 cm-

1 are the contributions of the E1 (LO) mode of ZnO associated with oxygen atoms. The

additional peaks at 698.5 cm-1

and 718.9 cm-1

contributes the 2E1 (LO) mode. The bands

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appeared in the range 1050 cm-1

- 1200 cm-1

are overtones and/or combination bands in ZnO.

To further ascertain the bonding characteristics of the obtained ZnO powder, XPS has been

carried out the XPS spectra as shown in Fig. 5. XPS spectra of ZnO thin film, to further

study the composition of ZnO, X-ray photoelectron spectroscopy (XPS) was also conducted.

In Fig. 5, display the XPS spectra of ZnO films only C, Zn and O signals are observed, C

representation derives from the substrate, which reveals the great purity of the nanosamples.

In the Zn2p core level spectrum contains Zn2p3/2 and Zn2p1/2 are located at binding energies

of 1022.1 eV & 1044.2 eV, which are reliable with the standards reports in available

literature [3, 9].

3.5 Photoluminescence studies

The optical properties of ZnO shaped nanorod morphological structures were examined by

PL spectrum at room temperature (RT). In Fig. 6(a-e) shows a typical room temperature PL

spectrum of ZnO morphologies with the excitation wavelength of 325 nm, which can give

more information about the sub-bandgap defect states, emission and excitation spectra of the

pure nanoparticles. The surface states and density of defects can change with the formation

settings, morphology size and shape of the nanocrystallites, which could be exciting by

studying the various defect levels. The luminescence peaks detected in the noticeable region

between 350 nm to 550 nm for all synthesized nanosamples are associated to the existence of

defects of oxygen sites. The luminescence emission bands are observed at 487 nm (blue

emission), and 530 nm (green emission) at the RT. It is observed that there are no

modification positions of PL peaks in all ZnO nanoparticles. A strong peak at 487 nm

corresponds to the blue emission and it could signify a deep level visible emission that is

related to the localized levels in the bandgap energy. A weak emission band observed at 530

nm may be qualified to the oxygen positions, which bounce advance to green emissions. This

peak is usually stated to as profound-level or trap-course emission are individually ionized

oxygen site. This green emission is emitted, due to the recombination course of photo-

generated hole with the ionized charge of the specific defect.

3.6 Diffuse reflectance spectroscopy (DRS) studies

The optical properties of ZnO nanoparticles annealed at different temperatures like 300 ºC,

350 ºC, 400 ºC, 450 ºC & 500 ºC nanoparticles were recorded in UV-visible DRS

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measurements. The bandgap principles of pure ZnO nanoparticles were intended using the

Tauc-plot relation. In general, the Kubelka-Munk function model is used to adapt the diffused

reflectance into equivalent absorption coefficient as given in Eq.

F(R) = α-(1-R2)/2R …………… (1)

Where R, the reflectance; F(R) is Kubelka-Munk function and α is the absorption coefficient

therefore, the Tauc relation is given by Eq.

[F(R)hν] = A (hν - Eg)n

…………… (2)

Where n=1/2 & 2 which represents the direct and indirect energy transitions, thereby giving

the direct and indirect bandgap correspondingly. A graph is plotted between [F(R)hυ]2 and

wavelength (nm), and the intercept rate is the bandgap energy and it is represented in Fig.

7(a-e). The extrapolation of linear range of these plots to [F(R)hυ]2 = 0 gives the direct

bandgap principles. The predicted bandgap values of ZnO nanoparticles are initiate to be 3.4

eV, 3.43 eV, 3.48 eV, 3.52 eV & 3.56 eV respectively as shown in Fig. 7. These results

evidently indicate that there is a growth in the bandgap values with increase with the

annealed temperature and decrease in the crystallite size for the ZnO nanoparticles. The

increase in the energy gap (Eg) values is linked to the quantum confinement effects (QCE).

3.7 Photocatalytic degradation of RhB dye

The ultra-violet visible absorption spectrum of Rhodamine-B (RhB) in the presence of

catalysts shows at 554 nm. Once ZnO nanoparticles were used as photocatalyst under

sunlight/visible light, the wavelength of maximum absorption was observed at 554 nm and

gradually decrease. To demonstrate the photocatalytic effect ZnO nanoparticles for RhB dye

solution, experiments were carried out by using catalyst in the sun light irradiation shown in

Fig. 8(a). The aqueous medium of Rhodamine-B (RhB) solution of (100 ml) containing 60

mg catalyst/5ml of 10% H2O2, placed in the sunlight and the absorbance of dye solution was

exact at different time intervals using UV-vis spectrophotometer. The pH of the mixture

solution was maintained as neutral and the competent decrease in the absorption rate of RhB

at 554 nm equivalent to the RhB fragments. The scheme of Ct/Co versus irradiation time for

the photocatalytic degradation of RhB dye solution as shown in Fig. 8(b), the dye degradation

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efficiency was 93% of RhB dye matrix, which were degraded subsequently at 240 min of

irradiation time, thus suggesting that the latent use of these resources as catalyst. The

catalytic action depends on the aptitude of the catalyst to distinct the electron-hole pairs. The

rate of electron-hole pair split and recombination is the greatest important aspect in the

photocatalytic performance. The decrease in the absorption maximum exposes leaks that the

degradation of aqueous medium of RhB solution was firmly due to the catalytic activity

under visible light irradiation. A photon from the sunlight occurrences the catalyst surface,

excited electrons from valence band (VB) jumps to conduction band (CB) by leaving holes.

The electrons drift to the catalyst outward, where it responds with free radicals to ensure the

secondary responses prime to degradation of the dye.

3.8 Mechanism of Photocatalysis

When the surface of ZnO NPs was illuminated by sun light/visible light, the electrons in the

lowest energy valance bond gets excited by absorption of photon from the solar light. The

excited electron from the valence band of NPs migrated to conduction band of ZnO and

results in the separation of electron-hole pairs on the surface of the ZnO nanoparticles. The

holes are generated in the valence band of NPs which are captured by the water molecules

thereby forming an active hydroxyl radicals (˙OH). It is a second strongest oxidant agent

involves in the decomposition process of RhB dye. The excited electron in the conduction

band forms superoxides (O2˙, HO2˙). The photo excitation state of semiconductor generates

electrons in the conduction band which reacts with oxygen molecule to form superoxide

radical anions (O2-). Usually the various organic dyes undergo the photocatalytic degradation

under visible light irradiation is attributed to their oxidation by the reactive oxygen species

(ROS) has an ability to oxidize the organic pollutant and yielding H2O, CO2 molecules. The

reaction steps are shown below; based on these results, it can be concluded that the ZnO

sample acts as a good photocatalyst towards the degradation of RhB and RhB have a greater

affinity towards the catalyst. The RhB photodegradation mechanism could be explained by

the electron-hole (e- - h

+) separation between conduction and the valance band of ZnO shown

in the Fig. 9.

ZnO+hν→ZnO(e–+h

+) ……………… (3)

e–(CB,ZnO)+O2→O2

•– ….…………… (4)

O2-+H2O→OH

. ….…………… (5)

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h+(VB ZnO)+H2O → ZnO +H

+ + HO

•– …….…………… (6)

RhB + (O2•–

+ h+ + HO

•–) (ROS) → mineralized products→CO2+H2O …………..… (7)

3.9 Antibacterial studies

The effect of similar concentrations of synthesized ZnO morphologies against S. pnemoniae,

S. aureus, E. coli and E. hermannii were studied using well diffusion technique as a purpose

of ZnO absorption as shown in Table 1&2 summarizes the antibacterial activity of ZnO

morphologies. The antibacterial inhibition progress of gram positive bacteria and gram

negative bacteria was deliberate by using ZnO nanoparticles and nitrofurantoin was used as

the standard. The inhibitory result of ZnO nanoparticles and the standard Nitrofurantoin are

plotted in Fig. 10. ZnO nanoparticles exhibits the better inhibition in the growth against a

panel of bacteria. Among these S. aurei was found to be sensitive to the ZnO nanoparticles at

a concentration of 200 μg/ml of sample with a zone of inhibition of 15 mm. The ZnO

nanoparticles exhibited potent activity against E. hermannii with a zone of inhibition

diameter of 16 mm at 400 μg/ml. whereas nanoparticles show less activity in the growth

inhibition and antibacterial activity towards the E. coli and S. pnemoniae bacteria at all the

concentration of nanoparticles. The probable maneuver for the development of inhibition

outcome of bacteria by the nanoparticles can be deliberated in two dissimilar ways as labelled

in Fig. 11. Here, in the first case Zn2+

from the nanoparticles will pass in the bacterial cell and

relates with the negative portion of the bacteria and principals to the advance inhibition and

conclusively bacterial cell dies. In the second case light energy was illuminated on the

nanoparticles in which the photon energy is greater than the bandgap, the higher energy

electrons (e−) from the valence band are excited to conduction band, leaves the positive hole

(h+) in valence band and results in the production of reactive oxygen species (ROS) like

superoxide anion (O2−•

) via reductive process and highly reactive hydroxyl radicals (OH.−

)

through oxidative process. The superoxide anion reacts with H2O molecules to produce

hydrogen peroxide created on the superficial of the nanoparticles, and has aptitude to abolish

the bacterial cell membrane. Hence, these results are confirmed that the concentration of

nanoparticles in nano-level has better antibacterial activity and can be used in the destruction

of microbes.

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4. Conclusion

The most potent solar light /visible-light driven photocatalyst of ZnO nanoparticles were

prepared by spin coating chemical route method for the photodecomposition of RhB dye. The

crystalline studies reveal the formation of well-crystalline NPs. Also, shows the enhanced

optical properties with significant red shift. The photoluminescence measurements prove the

visible light emission in the thin films samples, arising from the zinc metal ion and oxygen

vacancies, and zinc interstitial defects in the samples. The ZnO nanoparticles 10% H2O2 is an

effective photocatalyst presents enormously decompose the RhB dye nearly 93% 240 min

under the solar light/visible-light irradiation. Because of the higher adsorption capacity and

the better e− - h

+ pair separation under light illumination leads to generation of less harmful

chemical. Our results also proved that the ROS like hydroxyl radicals and superoxide anion

do not can penetrate inside the cell membrane and therefore remain in direct contact with the

outer surface of bacteria which leads to destruction of microbes.

Acknowledgement

The authors gratefully acknowledge research funding from UNESCO-UNISA Africa Chair in

Nanosciences/Nanotechnology Laboratories, College of Graduate Studies, University of

South Africa (UNISA), Muckleneuk Ridge, Pretoria, South Africa, (Research Grant

Fellowship of framework Post-Doctoral Fellowship program under contract number Research

Fund: 139000). One of the authors (Dr. K. Kaviyarasu) is grateful to Prof. M. Maaza,

Nanosciences African network (NANOAFNET), Materials Research Department (MSD),

iThemba LABS-National Research Foundation (NRF), Somerset West, South Africa for his

constant support, help and encouragement.

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H.J. Sung, Nanoforest of hydrothermally grown hierarchical ZnO nanowires for a high

efficiency dye-sensitized solar cell. Nano letters. 11 (2011) 666-671.

[5] V. Kumar, N. Singh, V. Kumar, L.P. Purohit, A. Kapoor, O.M. Ntwaeaborwa, H.C.

Swart, Doped zinc oxide window layers for dye sensitized solar cells. J. Appl. Phy. 114

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[6] H. Xu, X. Liu, D. Cui, M. Li, M. Jiang, A novel method for improving the performance of

ZnO gas sensors, Sensors and Actuators B: Chemical, 114 (2006) 301-307.

[7] Y. Shimura, S. Ashwyn Srinivasan, R. Loo, Microwave assisted synthesis of ZnO nano-

sheets and their application in UV-detector. ECS J. Sol. St. Sci. & Tech. 1 (2012) Q140-

Q143.

[8] J.B. Shim, H. Chang, S. Kim, Rapid Hydrothermal Synthesis of Zinc Oxide Nanowires by

Annealing Methods on Seed Layers, Journal of Nanomaterials, 6 (2011) 582764.

[9] Z.R. Tian, J.A. Voigt, J. Liu, B. McKenzie, M.J. McDermott, M.A. Rodriguez, H.

Konishi, H. Xu, Complex and oriented ZnO nanostructures, Nature Materials. 2 (2003) 821-

826.

[10] D. Chu, Y. Masuda, T. Ohji, K. Kato, Formation and photocatalytic application of ZnO

nanotubes using aqueous solution, Langmuir, 26 (2009) 2811-2815.

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[11] S.A. Ansari, Q. Husain, S. Qayyum, A. Azam, Designing and surface modification of

zinc oxide nanoparticles for biomedical applications, Food and Chemical Toxicology, 49

(2011) 2107-2115.

[12] Y. Zhang, Tapas R. Nayak, H. Hong, C. Weibo, Biomedical applications of zinc oxide

nanomaterials, Cur. Mol. Med. 13 (2013) 1633-1645.

[13] Z. Jun, N. Sheng Xu, Zhong L. Wang, Dissolving behavior and stability of ZnO wires in

biofluids: a study on biodegradability and biocompatibility of ZnO nanostructures, Adv.

Mater. 18 (2006) 2432-2435.

[14] C.M. Magdalane, K. Kaviyarasu, J. Judith Vijaya, B. Siddhardha, B. Jeyaraj,

Photocatalytic activity of binary metal oxide nanocomposites of CeO2/CdO nanospheres:

investigation of optical and antimicrobial activity, J. Photochem. Photobiol. B Biol. 163

(2016) 77-86.

[15] K. Kaviyarasu, P.P. Murmu, J. Kennedy, F.T. Thema, Douglas Letsholathebe, L.

Kotsedi, M. Maaza, Structural, optical and magnetic investigation of Gd implanted CeO2

nanocrystals, Nucl. Instr. Meth. B (2017), http://dx.doi.org/10.1016/j.nimb.2017.02.055.

[16] K. Kasinathan, J. Kennedy, E. Manikandan, M. Henini, M. Maaza, Photodegradation of

organic pollutants RhB dye using UV simulated sunlight on ceria based TiO2 nanomaterials

for antibacterial applications, Sci. Rep., 6 (2016) 38064.

[17] C.M. Magdalane, K. Kaviyarasu, J. Judith Vijaya, C. Jayakumar, M. Maaza, B. Jeyaraj,

Photocatalytic degradation effect of malachite green and catalytic hydrogenation by UV–

illuminated CeO2/CdO multilayered nanoplatelet arrays: Investigation of antifungal and

antimicrobial activities, J. Photochem. Photobiol. B: Bio., 169 (2017) 110-123.

[18] K. Kaviyarasu, A. Mariappan, K. Neyvasagam, A. Ayeshamariam, P. Pandi, R.

Rajeshwara Palanichamy, C. Gopinathan, Genene T. Mola, M. Maaza, Photocatalytic

performance and antimicrobial activities of HAp-TiO2 nanocomposite thin films by sol-gel

method, Surfaces and Interfaces, 6 (2017) 247-255.

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[19] S.K. Jesudoss, J. Judith Vijaya, L. John Kennedy, P. Iyyappa Rajan, Hamad. A. Al-

Lohedan, R. Jothi Ramalingam, K. Kaviyarasu, M. Bououdina, Studies on the efficient dual

performance of Mn1–xNixFe2O4 spinel nanoparticles in photodegradation and antibacterial

activity, J. Photochem. & Photobio. B: Bio. 165 (2016) 121-132.

[20] K. Kaviyarasu, A. Raja, P.A. Devarajan, Structural elucidation and spectral

characterizations of Co3O4 nanoflakes, Spectrochimica Acta Part A: Molecular and

Biomolecular Spectroscopy 114 (2013) 586-591.

[21] K. Kaviyarasu, D. Sajan, P.A. Devarajan, A rapid and versatile method for solvothermal

synthesis of Sb2O3 nanocrystals under mild conditions, Applied Nanoscience, 3(6) (2013)

529-533.

[22] J. Kennedy, F. Fang, J. Futter, J. Leveneur, P.P. Murmu, G.N. Panin, T.W. Kang, E.

Manikandan, Synthesis and enhanced field emission of zinc oxide incorporated carbon

nanotubes, Diamond & Related Mater. 71 (2017) 79-84.

[23] K. Kaviyarasu, N. Geetha, K. Kanimozhi, C. Maria Magdalane, S. Sivaranjani, A.

Ayeshamariam, J. Kennedy, M. Maaza, In vitro cytotoxicity effect and antibacterial

performance of human lung epithelial cells A549 activity of zinc oxide doped TiO2

nanocrystals: investigation of bio-medical application by chemical method, Mater. Sci. &

Eng. C, 74 (2017) 325-333.

[24] A. Angel Ezhilarasi, J. Judith Vijaya, K. Kaviyarasu, M. Maaza, A. Ayeshamariam, L.

John Kennedy, Green synthesis of NiO nanoparticles using Moringa oleifera extract and their

biomedical applications: Cytotoxicity effect of nanoparticles against HT-29 cancer cells, J.

Photochem. & Photobio. B: Bio. 164 (2016) 352-360.

[25] R. Zamiri, A. Zakaria, H.A. Ahangar, M. Darroudi, A.K. Zak, G.P.C. Drummen,

Aqueous starch as a stabilizer in zinc oxide nanoparticle synthesis via laser ablation, J. Alloy.

Compd. 516 (2012) 41-48.

[26] R. Razali, A.K. Zak, W.H.A. Majid, M. Darroudi, Solvothermal synthesis of

microsphere ZnO nanostructures in DEA media, Ceram. Int. 37 (2011) 3657-3663.

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[27] D. Ramimoghadam, M. Bin Hussein, Y. Taufiq Yap, Hydrothermal synthesis of zinc

oxide nanoparticles using rice as soft biotemplate, Chem. Cent. J. 7 (2013) 136.

[28] B. Baruwati, D.K. Kumar, S.V. Manorama, Hydrothermal synthesis of highly

Crystalline ZnO nanoparticles: a competitive sensor for LPG and EtOH, Sens. Actuators B:

Chem. 119 (2006) 676-682.

[29] R.K. Sharma, R. Ghose, Synthesis of zinc oxide nanoparticles by homogeneous

Precipitation method and its application in antifungal activity against Candida albicans,

Ceram. Int. 41 (2015) 967-975.

[30] R.P. Singh, V.K. Shukla, R.S. Yadav, P.K. Sharma, P.K. Singh, A.C. Pandey, Adv.

Mater. Lett. 2 (2011) 313-317.

[31] T. Bhuyan, K. Mishra, M. Khanuja, R. Prasad, A. Varma, Biosynthesis of zinc oxide

nanoparticles from Azadirachta indica for antibacterial and photocatalytic applications,

Mater. Sci. Semi. Proc. 32 (2015) 55-61.

[32] P.P. Murmu, J. Kennedy, G.V.M. Williams, B.J. Ruck, S. Granville, S.V. Chong,

Observation of magnetism, low resistivity, and magnetoresistance in the near-surface region

of Gd implanted ZnO, Appl. Phy. Lett. 101(8) (2012) 082408.

[33] J. Kennedy, G.V.M. Williams, P.P. Murmu, B.J. Ruck, Intrinsic magnetic order and

inhomogeneous transport in Gd-implanted zinc oxide, Phy. Rev. B. 88(21) (2013) 214423.

[34] P.P. Murmu, J. Kennedy, B.J. Ruck, S. Rubanov, Microstructural, electrical and

magnetic properties of erbium doped zinc oxide single crystals, Elec. Mater. Lett. 11(6)

(2015) 998-1002.

[35] J. Kennedy, P.P. Murmu, J. Leveneur, A. Markwitz, J. Futter, Controlling preferred

orientation and electrical conductivity of zinc oxide thin films by post growth annealing

treatment, Appl. Sur. Sci. 367 (2016) 52-58.

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[36] K. Kaviyarasu, C.M. Magdalane, K. Anand, E. Manikandan, M. Maaza, Synthesis and

characterization studies of MgO:CuO nanocrystals by wet-chemical method, Spectrochimica

Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 405-409.

[37] K. Kaviyarasu, P.A. Devarajan, A convenient route to synthesize hexagonal pillar

shaped ZnO nanoneedles via CTAB surfactant, Adv. Mater. Lett 4 (2013) 582-585.

[38] C.M. Magdalane, K. Kaviyarasu, J.J. Vijaya, C. Jayakumar, M. Maaza, B Jeyaraj,

Photocatalytic degradation effect of malachite green and catalytic hydrogenation by UV–

illuminated CeO2/CdO multilayered nanoplatelet arrays: Investigation of antifungal and

antimicrobial activities, Journal of Photochemistry and Photobiology B: Biology 169 (2017)

110-123.

[39] K. Kaviyarasu, L. Kotsedi, Aline Simo, Xolile Fuku, Genene. T. Mola, J. Kennedy, M.

Maaza, Photocatalytic activity of ZrO2 doped lead dioxide nanocomposites: Investigation of

structural and optical microscopy of RhB organic dye, Applied Surface Science, Available

online 21 November 2016 - https://doi.org/10.1016/j.apsusc.2016.11.149,

[40] K. Kaviyarasu, K. Kanimozhi, N. Matinise, C.M. Magdalane, Genene. T. Mola, J.

Kennedy, M. Maaza, Antiproliferative effects on human lung cell lines A549 activity of

cadmium selenide nanoparticles extracted from cytotoxic effects: Investigation of bio-

electronic application, Materials Science and Engineering: C 76 (2017) 1012-1025.

[41] X. Fuku, K. Kaviyarasu, N. Matinise, M. Maaza, Punicalagin Green Functionalized

Cu/Cu2O/ZnO/CuO Nanocomposite for Potential Electrochemical Transducer and Catalyst,

Nanoscale Research Letters 11 (1) (2016) 386.

[42] C Maria Magdalane, K Kaviyarasu, J Judith Vijaya, B Siddhardha, B Jeyaraj, Facile

synthesis of heterostructured cerium oxide/yttrium oxide nanocomposite in UV light induced

photocatalytic degradation and catalytic reduction: Synergistic effect of antimicrobial studies,

Journal of Photochemistry and Photobiology B: Biology, Available online 20 May 2017, In

Press, Accepted Manuscript - https://doi.org/10.1016/j.jphotobiol.2017.05.024.

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[43] N. Matinise, X.G. Fuku, K. Kaviyarasu, N. Mayedwa, M. Maaza, ZnO nanoparticles via

Moringa oleifera green synthesis: Physical properties & mechanism of formation, Applied

Surface Science 406 (2017) 339-347.

[44] K. Kaviyarasu, C. Maria Magdalane, E. Manikandan, M. Jayachandran, R.

Ladchumananandasivam, S. Neelamani, M. Maaza, Well-aligned graphene oxide nanosheets

decorated with zinc oxide nanocrystals for high performance photocatalytic application,

International Journal of Nanoscience 14 (03) (2015) 1550007.

[45] K. Kaviyarasu, E. Manikandan, Z.Y. Nuru, M. Maaza, Investigation on the structural

properties of CeO2 nanofibers via CTAB surfactant, Materials Letters 160 (2015) 61-63.

List of Figure Captions

Fig. 1. X-ray diffraction patterns of ZnO thin films annealed at (a) 300 ºC (b) 350 ºC (c) 400

ºC (d) 450 ºC (e) 500 ºC (f) 550 ºC.

Fig. 2(a-f). FESEM images of ZnO nanoparticles at different morphologies.

Fig. 3(a-f). HRTEM micrographs of various morphologies structure of ZnO nanoparticles.

Fig. 4(a-e). μ-Raman spectrum of ZnO nanoparticles at different temperature.

Fig. 5. XPS spectrum of ZnO nanoparticles at different temperature.

Fig. 6(a-e). PL spectra of ZnO nanoparticles at different temperature.

Fig. 7(a-e). [F(R)hυ]2 vs hv plot for the ZnO nanoparticles at different temperature.

Fig. 8(a-b). Effect of Photocatalytic degradation plot for RhB dye solution in the dark and

under UV light irradiation at different time intervals.

Fig. 9. Schematic energy-band diagram of ZnO nanocomposite showing the charge

transportation processes leading to visible light-driven photocatalytic degradation dye.

Fig. 10(a-d). Inhibitory effect of ZnO thin film on bacteria’s in composite structure.

Fig. 11. Bar diagram effect of ZnO nanoparticles at different morphologies.

Fig. 12. Possible mechanism of photoexcitation in composite structure.

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List of Table

Table. 1. The wavenumbers (in cm−1

) of the first and second order Raman spectra observed in

ZnO films heated at different temperatures.

Table 2: Antimicrobial activity of ZnO films nanocomposites determined by agar well

diffusion assay

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Fig. 1

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Fig. 2

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Fig. 3

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Fig. 4

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Fig. 5

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Fig. 6

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Fig. 7

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Fig. 8a

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Fig. 8b

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Fig. 9

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Fig. 10

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Fig. 11

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Fig. 12

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Table. 1. The wavenumbers (in cm−1

) of the first and second order Raman spectra observed

in ZnO films heated at different temperatures

Sl.

No

Process

Observed Ref.

Wavenumber (cm-1

)

250 oC 300

oC 350

oC 400

oC 450

oC

1 2TA; 2E2 low

203.0 203.0 203.2 204.4 205.1 203.2

2 E2high

– E2low

333.0 332.4 332.4 330.9 330.8 331.9

3 E1(TO) 410.0 --- --- --- --- 408.1

4 E2high

438.0 438.6 438.9 438.9 438.9 438.9

5 2B1low

; 2LA 536.0 537.7 537.3 --- --- 541.0

6 A1(LO) 574.0 --- 584.7 583.3 --- 579.0

7 E1(LO) 590.0 588.4 --- --- 583.7 590.1

8 LA+TO 700.0 --- --- --- 695.1 698.5

9 LA+TO 723.0 --- --- --- --- 718.9

10 TO+LO 1072.0 1051.3 1054.4 --- 1051.4 1062.1

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Table 2: Antimicrobial activity of ZnO films nanocomposites determined by agar well

diffusion assay

Types of bacteria

Antibacterial zone of inhibition (mm)

(100

µg/ml)

(200

µg/ml)

(300

µg/ml)

(400

µg/ml)

(500

µg/ml)

(600

µg/ml)

E. coli

S. pnemoniae

S. aureus

E. hermannii

2.5 mm

2.2 mm

6 mm

6 mm

4.5 mm

5 mm

15 mm

9 mm

2 mm

1mm

2 mm

10 mm

3.5 mm

3 mm

9 mm

16 mm

4.1 mm

1 mm

10 mm

9 mm

3.2 mm

5 mm

6 mm

11 mm

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Graphical abstract

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Highlights

The effect of RhB dye particle on the photocatalytic performance

(h+) & (

•OH) played a major role than the superoxide radical (O

2•−)

Photocatalytic activity under the sunlight enhancing the degradation rate

Antibacterial activity of characterized was regulated using different concentrations

ZnO thin films were deposited on the silicon substrate by the sol-gel technique

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