E. tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structure, photoluminescence and photo-catalytic activities

Accepted Manuscript E. Tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structural, photoluminescence and photo-catalytic activities K.H. Sudheer Kumar, N. Dhananjaya, L.S. Reddy Yadav PII:

S2468-2179(18)30027-3

DOI:

10.1016/j.jsamd.2018.07.005

Reference:

JSAMD 174

To appear in:

Journal of Science: Advanced Materials and Devices

Received Date: 16 February 2018 Revised Date:

20 June 2018

Accepted Date: 13 July 2018

Please cite this article as: K.H.S. Kumar, N. Dhananjaya, L.S.R. Yadav, E. Tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structural, photoluminescence and photo-catalytic activities, Journal of Science: Advanced Materials and Devices (2018), doi: 10.1016/ j.jsamd.2018.07.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

E. Tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structural, photoluminescence and photo-catalytic activities K.H. Sudheer Kumar1, N. Dhananjaya2,*, L.S. Reddy Yadav1 Department of Chemistry, BMS Institute of Technology and Management, Bengaluru560064, India

Departmentof Physics, BMS Institute of Technology and Management, Bengaluru -560064,

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E. Tirucalli plant latex mediated green combustion synthesis of ZnO nanoparticles: Structural, photoluminescence and photo-catalytic activities

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Abstract In this present work, ZnO nanoparticles were synthesized using esterases contained E. Tirucalli plant latex as a fuel. The structural, morphological and spectroscopic studies of the synthesized as formed ZnO nanoparticles were analysed using powder X-ray Diffraction (PXRD), Fourier

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infrared spectroscopy (FTIR), UV-Visible absorption and photoluminescence (PL) spectroscopy.

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The structural parameters are refined by the Rietveld refinement method using PXRD data and confirm that the prepared compound is pure hexagonal wurtzite structure with space group P63mc (No. 186). The average crystallite size was estimated by Scherrer’s and W-H plots and found to be in the range 17-23 and 20-26 nm respectively. The band gap of ZnO nanoparticles was estimated using Wood -Tauc relation and found to be in the range of 3.10 - 3.25 eV.

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Photoluminescence (PL) studies revealed that a broad yellow emission peak appeared at 570 nm upon 380 nm excitation peaks. Photocatalytic degradation of Methylene blue (MB) dye was studied under UV irradiations. 5.5 ml of 5% esterases contained E. Tirucalli plant latex used for

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the synthesis of ZnO shows 96 % of degradation (5x10-5 molar MB at PH12). Prepared ZnO

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nanoparticles find the application in optical and photo-catalytic degradations. Keywords: E. Tirucalli, Green synthesis, ZnO nanoparticles, FTIR, SEM, Photocatalytic degradation.

* Corresponding author: [email protected] (N. Dhananjaya), [email protected] (K.H. Sudheer Kumar)

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ACCEPTED MANUSCRIPT 1. Introduction In recent years, synthesis of oxide nanoparticles using green products such as leaves, roots, latex, stem and bark are received much attention by the researchers [1-2]. It was clean, non-toxic, eco-friendly, free from unwanted by-products, non-hazardous [3]. Recently, great

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efforts have been made to the synthesis of size and shape controlled phosphor by different techniques [4, 5]. Among them aqueous combustion synthesis have been used to prepare costeffective and cheap phosphors [6,7]. On the other hand, the production of eco-friendly, low cost

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ZnO nanoparticles in large scale by the existing routes remain difficult [8]. Therefore, it was expected to be an important host material for several applications such as light emitting diodes

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(LED’s), X-ray imaging, scintillations, sensors, optical communication, fluorescence imaging [8-10]. Further, ZnO was non-toxic, compatible with skin and was highly useful as UV-blocker in sun-screen and biomedical applications [11]. Various techniques have been employed to prepare ZnO nanoparticles such as solvothermal, hydrothermal, sol-gel, microwave-assisted

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hydrothermal, co-precipitation, Metal-Organic Chemical Vapour Deposition [12-17]. Most of these techniques need sophisticated equipment’s, time consuming experimental procedure, special precautions of experimental conditions [18]. Green combustion synthesis (GCS) is an

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alternative of a simple, versatile and informal synthesis technique presented with time and energy saving prospect is favoured. Green combustion methodology extended to other oxides

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such as LnCaAlO4, Sm2O3, ZnO, CuO, PdO, Co3O4, NiO with natural plant extract [19 – 24]. In this present study, ZnO nanoparticles were prepared by green combustion technique

with esterases contained E. Tirucalli plant latex as a fuel. The structural, spectroscopic and photo-catalytic studies were discussed in detail for environmental applications.

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ACCEPTED MANUSCRIPT 2. Experimental 2.1. Synthesis of ZnO nanoparticles In a typical synthesis of ZnO nanoparticles, 3 ml of 5 % esterases contained E.Tirucalli plant latex was added in borosil glass dish containing 2 g of Zn (NO3)3. 6H2O already dissolved

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in 10 ml of double distilled water. This reaction mixture were mixed well using magnetic stirrer for ~ 5-10 min. and then placed in a preheated muffle furnace maintained at 350 ± 10 oC. The liquids of E.Tirucalli plant latex containing fats, unsaturated oils containing double bonds,

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flavonoids and tannins are inclined to spontaneous ignition of the mixture. The reaction mixture boils froths and thermally dehydrates forming a foam. The entire process was completed in a few

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minutes. A similar procedure was repeated by taking the different volume of 5 % esterases contained E. Tirucalli plant latex (4-8 ml) [4, 25]. 2.2. Characterization

The crystal structure of ZnO nanoparticles was determined using Shimadzu powder X-

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ray diffractometer using Cu Kα radiation. The Fourier transform infrared (FTIR) spectra of the sample were recorded using Perkin Elmer Spectrometer (Spectrum 1000) with KBr pellets. The UV-Visible absorption spectra of the samples were measured with SL 159 ELICO UV–VIS

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Spectrophotometer. Photoluminescence (PL) spectra were measured using Horiba Delta Flex

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TCSPC system. Photocatalytic studies under UV light are carried out in-house fabricated photochemical reactor.

2.3 Photocatalytic degradation of dye Photocatalytic experiments were carried out using 250 W high-pressure mercury lamps

as the UV radiation source. An aqueous suspension was prepared by dispersing known quantity (20 mg) of ZnO nanoparticles in 30 ml of known concentration (5 x 10-5 molar) methylene blue dye solution. During the photocatalytic experiments, the slurry composed of dye solution and catalyst was placed in the reactor and stirred magnetically for agitation with simultaneous 3

ACCEPTED MANUSCRIPT exposure to UV light. A known volume (5 ml) of the exposed solution was withdrawn at a specific interval of time (initially 20 min. and then 30 min.). ZnO nanoparticles were removed from the solution by centrifugation to assess the extent of degradation. The rate of degradation of

determined using the following formula. % degradation =

Ci - Cf Ci

X 100

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dye was measured using spectrophotometer at 664 nm. The % degradation of dye can be

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where Ci and Cf are the initial and final dye concentrations respectively.

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3. Results and discussions

3.1. Structural characterization (PXRD and Rietveld refinement) Figure 1(a) shows the PXRD patterns of ZnO nanoparticles prepared by different volume of esterases contained E.Tirucalli plant latex (3-8 ml; 5% latex). It was evident from the Figure

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1, for all the plant latex content, a broadening was observed, which indicates that the particle sizes were in the nanoscale range. All the diffraction peaks were well indexed to pure hexagonal wurtzite ZnO (JCPDS card no. 36-1451) having the lattice parameters a = 3.2537 (Å), c =

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5.2063 (Å). No other impurity peaks are detected.

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The average crystallite size for hexagonal ZnO nanoparticles for a different volume of esterases contained E.Tirucalli plant latex were estimated by Scherer’s (d) and Williamson and Hall (W-H) plots (d′) using following relations [26,27]:

d=

kλ β cosθ

(1)

kλ (2) d′ where λ; the wavelength of the X-ray radiation (1.5418 Å), k; the shape factor (0.9), θ; scattering

β cosθ = ε (4 sin θ ) +

angle, β; (full width at half maximum, FWHM in radian) measured for different XRD lines 4

ACCEPTED MANUSCRIPT corresponding to different planes, ε; strain. The equation represents a straight line βcosθ (Yaxis) verses 4 sinθ (X-axis), the slope of line gives the strain (ε) and intercept (kλ/d′) of this line on the Y-axis gives average crystallite size (d′) (Figure 1(b)). It was observed that slightly d′> d (Table 1), because the strain component is assumed to be zero for calculating d and observed

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broadening of the diffraction peak, in this case, is considered as a result of reducing crystallite size.

The structural parameters were refined by the Rietveld method using powder PXRD data.

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The optimized parameters were scale factor, background, global thermal factor, asymmetric

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factor, profile half-width parameters (u, v, w), lattice parameters (a, c) and site occupancy factors (Wyckoff) were used to obtain a structural refinement with better quality and reliability. Figure 2(a) shows the Rietveld refinement performed on the green combustion synthesized ZnO nanoparticles. The refined parameters are displayed in Table 2. The crystal structure of ZnO was modelled using Rietveld refined structural parameters by Diamond program (Figure 2(b)). In this

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structure, Zn is connected to 4 oxygen atoms in a tetrahedral configuration. 3.2. Spectroscopic studies (FTIR, UV-Visible and PL)

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Figure 3 (a-c) shows the FTIR spectra of 5 % esterases contained E.Tirucalli plant latex and ZnO nanoparticles prepared with 3 and 5.5 ml, 5 % esterases contained E.Tirucalli plant

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latexrespectively. The absorption band near 3398 cm-1 was due to O-H mode and 1400-1649 cmwere attributed to C=O stretching mode. As the volume of 5 % latex increases the band at

1400-1649 cm-1 peak decreases. The peak at ~2340 cm-1 arises due to absorption of atmospheric CO2 on the metallic cations. The bands at 431 cm-1 correspond to the bonding between Zn-O [28]. The UV-Visible absorption spectra of ZnO nanoparticles (3, 5.5 and 8 ml 5 % esterases contained E.Tirucalli plant latex) were shown in Figure 4 (a-c) respectively. The abrupt change

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ACCEPTED MANUSCRIPT at ~380 nm is due to lamp change over from UV to visible region in UV Visible spectrophotometer. The direct energy band gap for the ZnO nanoparticles was estimated by Wood and Tauc relation [29].

(αhυ ) 2 = A(hν − E g )

(3)

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where, ‘α’; optical absorption coefficient, hν; photon energy, Eg; the direct bandgap and ‘A’; a constant. The plots of (αhν)1/2 vs photon energy of ZnO nanoparticles were shown in Figure 5. It was found to be in the range 3.10-3.25eV. These Eg values were smaller than that of bulk ZnO

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(3.37 eV) [30].

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The excitation spectrum of ZnO nanoparticles (5.5 ml; 5 % latex) recorded at room temperature (RT) and was shown in Figure 6. The near-band-edge (NBE) excitation peak at 380 nm was recorded at an emission wavelength of 270 nm (inset of Figure 6). The defect emission in the visible region is attributed to ZnO surface detects, in which oxygen deficiencies are the most suggested defects. Further, the emission spectrum of pure ZnO showed a broad yellow

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emission at 570 nm along with sharp peaks at ~430 and ~460 nm, which indicates the existence of a large number of surface defects. The broad ~570 nm peak may be due to the transition

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between single charged oxygen vacancy and the photoexcited holes in the valence band of the ZnO nanoparticles [31].

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Figure 7 shows the SEM image of ZnO nanoparticles (5.5 ml; 5 % latex). The image clearly shows the presence of almost spherically shaped particles with agglomeration. The porous nature was observed in SEM images, this is due the liberation of a large amount of gases during green combustion process. 3.3. Photo-catalytic activity The photocatalytic activities of ZnO nanoparticles (5.5 ml; 5 % latex) were estimated by monitoring the degradation of Methylene Blue (MB) as a model pollutant in a self-assembled apparatus with a 250 W high-pressure mercury lamps as the UV radiation source. Typically, for 6

ACCEPTED MANUSCRIPT the photocatalytic experiment, 20 mg photocatalysts (ZnO nanoparticles) were suspended in 30 mL MB aqueous solution with a concentration of 5 x 10-5 molar in a beaker. The suspension was magnetically stirred for 30 min. to reach the adsorption/desorption equilibration without light exposure. Following this, the photocatalytic reaction was started by exposure to UV light (20-

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120 min). After 3 ml sample was centrifuged and collected for UV-Visible absorption measurement. The intensity of the main absorption peak (664 nm) of the MB dye was referred to as a measure of the residual dye concentration [31].

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Figure 8 (A) shows the degradation of MB in the presence of 20 mg of ZnO (5.5 ml; 5 % plant latex) nanoparticles with 20-120 min. UV irradiation. It was found that 120 min. irradiation

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degrade 40 % of 5 x 10-5 molar MB. Photocatalytic activity of ZnO was attributed both to the donor states caused by a large number of defect sites such as oxygen vacancies and interstitial zinc atom and to the acceptor states which arise from zinc vacancies and interstitial oxygen atoms. Oxygen vacancies located at energy positions 2.35–2.50 eV was responsible for green

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luminescence upon illumination with UV light. Here we assume that interfacial electron transfer takes place predominantly between these donor states (oxygen vacancies and interstitial Zn atom). Being a cationic dye MB acquires electron from excited donor states and decomposes.

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The kinetic behaviour of ZnO nanoparticles is shown in Figure 8 (B). It is observed that the

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nanoparticles exhibit first-order kinetics in agreement with a general Langmuir–Hinshelwood mechanism [32].

R = -dC/dt = kKC/1 + KC

(4)

where r is the degradation rate of reactant (mg/l min), C is the concentration of reactant (mg/l), t the illumination time, K is the adsorption coefficient of reactant (l/mg) and k is the reaction rate constant (mg/l min). If C is very small then the above equation could be simplified to ln(C0/C) = kKt = kappt

(5)

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ACCEPTED MANUSCRIPT where C0 is the initial concentration (0 min) of the MB aqueous solution and C is the concentration of the MB aqueous solution for different times of UV illuminations. From the plot of ln(C0/C) vs. the irradiation time (t) (Figure 10), the reaction rate constant (k) value are

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calculated and found to be 0.0038 min-1. UV irradiation for different pH was recorded and shown in Figure 9. The 96% degradation of 5 x 10-5 molar MB (20 mg ZnO) was observed for pH 12. This compound may be useful for catalytic applications.

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Figure 10 shows mechanism of photo catalysis in ZnO nanoparticles under UV light.

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When a photon incident on ZnO nanoparticles, it will generate photoelectron (e-cb) and photoinduced holes (h+vb). The photoelectrons are trapped by adsorbed O2 as electron accepters and the photo-induced holes are accepted by the negative species like OH- or organic pollutants, to oxidize organic dyes such as MB. The oxygen vacancies are beneficial to the degradation of the MB. It will restrain the combination of e-cb and h+vb. The corresponding photocatalytic

e-cb+ O2
.O-2 h+vb + OH-
.OH

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ZnO + hυ
e-cb+ h+vb

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reaction process is as follows.

O-2 + C16H18N3SCl
Oxidation products

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OH + C16H18N3SCl
Oxidation products

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4. Conclusions

We have successfully synthesized ZnO nanoparticles via the green synthesis technique using E. tirucalli plant latex as a fuel. Pure hexagonal wurtzite structure was observed from PXRD studies. The particle size was estimated from Scherer’s and W–H plots and found to be in the range 17–26 nm. The emission peaks at 570 nm were observed under the excitations of 380 nm. 8

ACCEPTED MANUSCRIPT The synthesized nanoparticles are employed to study the catalytic activity of Methylene blue dye degradation. UV-Visible spectra of Methylene blue (5x10-5 molar) dye degradation as a function of different UV irradiation time and pH were performed. ZnO nanoparticles prepared with 5.5 ml of 5% esterases contained E.Tirucalli plant latex show 96 % dye degradation at pH 12.

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Further, the green combustion synthesised ZnO nanoparticles compounds may be useful in display and catalytic applications.

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Acknowledgement

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One of the authors N Dhananjaya greatly acknowledge the Department of Science and Technology (DST), Government of India, Science and Engineering Research Board (SERB) for their financial support under Seed Money to Young Scientist for Research (Ref:

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SERB/F/6219/2014-15, Grant: DST/SERB No: SR/FTP/PS-188/2013)).

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Lists of Figures Fig.1 (a) PXRD patterns and (b) W-H plots of ZnO nanoparticles for different volume of esterases contained E.Tirucalli plant latex (3-8 ml; 5 % latex).

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Fig.2 (a) Rietveld refinement and (b) wurtzite hexagonal crystal structure of ZnO nanoparticles prepared using 5.5 ml of 5 % esterases contained E. Tirucalli plant latex.

Fig. 3 FTIR spectra of (a) 5 % esterases contained E.Tirucalli plant latex and ZnO nanoparticles

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prepared by (a) 3 ml and (c) 5.5 ml of 5 % esterases contained E.Tirucalli plant latex.

Fig. 4 UV-Visible spectra of ZnO nanoparticles prepared by (a) 3 ml (b) 5.5 ml and (c) 8 ml of 5

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% esterases contained E.Tirucalli plant latex.

Fig. 5 Bandgap of ZnO nanoparticles prepared by (a) 3 ml (b) 5.5 ml and (c) 8 ml of 5 % esterases contained E.Tirucalli plant latex.

Fig. 6 Excitation and emission spectra of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained E.Tirucalli plant latex.

E.Tirucalli plant latex.

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Fig. 7 (a) SEM Image of ZnO nanoparticles prepared using 5.5 ml of 5% esterases contained

Fig. 8 (a) Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared

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using 5.5 ml of 5 % esterases contained E.Tirucalli plant latex) with different UV irradiation time and (b) First order kinetic reactions for ZnO nanoparticles.

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Fig. 9 Degradation of MB in the presence of photocatalysts (ZnO nanoparticles prepared using 5.5 ml of 5 % esterases contained E.Tirucalli plant latex) with different pH (5-12 pH). Fig. 10 Mechanism of photo catalysis in ZnO nanoparticles under UV light.

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(g) 8 ml (g) 8 ml

(f) 7 ml

(e) 6 ml

(e) 6 ml

50

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Figure 1

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(b) 4 ml

(103) (200) (112) (201) 60

2θ (degrees)

(a)

(c) 5 ml

(a) 3 ml

(110)

(102)

40

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(101)

(100) (002)

(b) 4 ml

(d) 5.5 ml

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β cosθ

(d) 5.5 ml

(c) 5 ml

20

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Intensity (a.u.)

(f) 7 ml

1.2

(a) 3 ml

1.4

1.6

4sinθ

(b)

1.8

2.0

2.2

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(b)

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Figure 2

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(a)

(b)

(a)

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4000 3500 3000 2500 2000 1500 1000 -1

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Wavenumber (cm )

Figure 3

431

1400

2340

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3398 (c)

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Transmittance (a.u.)

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500

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Absorbance (a.u.)

(c)

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Lamp change over

(b)

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Wavelength (nm)

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Figure 4

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Eg=3.28

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E=hυ (eV)

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460

PL Intensity (a.u.)

570

250

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Wavelength (nm)

450

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400

575

Wavelength (nm)

EP

TE D

Figure 6

AC C

600

M AN U

425

SC

200

RI PT

380

430

450

625

650

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Figure 7

ACCEPTED MANUSCRIPT

(b)

0.7 k = 0.0038 min Linear fit

0.5 0.4 0.3

0.1

550

600

650

700

Wavelength (nm)

750

800

0.0

TE D EP

40

60

80

Time (min)

Figure 8

AC C

20

M AN U

500

SC

0.2

450

-1

RI PT

0.6

ln (C o/C )

Absorbance (a.u.)

0.8

-5 Stock (dark 2h strring) 5 x10 molar MB (a) 0 min UV (a) (b) 20 min UV (c) 40 min UV (d) 60 min UV (e) 90 min UV (f) 120 min UV (g)

(a) (b) (c) (d) (e) (f) (g)

100

120

-5

(a)

Stock pH 5 pH 6 pH 9 pH 10 pH 11 pH 12

(b) (c) (d)

SC

(a) (b) (c) (d) (e) (f) (g)

(e)

(f)

M AN U

Absorbance (a.u.)

5 X 10 molar MB

RI PT

ACCEPTED MANUSCRIPT

(g)

500

550

600

650

TE D

Wavelength (nm)

AC C

EP

Figure 9

700

750

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 10

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List of Tables Table 1 Various parameters of ZnO nanoparticles prepared with different volume of esterases contained E.Tirucalli plant latex.

Table 1 Average crystallite size (nm)

3 4 5 5.5 6 7 8

17 18 19 20 21 22 23

W-H plots (d′′)

EP AC C

Strain, ε (10-3)

Band gap (eV)

0.74 0.84 1.08 1.10 1.15 1.19 1.21

3.28 3.26 3.10

M AN U

Scherrer’s equation (d)

TE D

Plant latex (ml)

SC

RI PT

Table 2 Rietveld refined structural parameters for ZnO nanoparticles prepared with 5.5 ml of 5% plant latex.

20 21 22 23 24 25 26

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Table 2

EP AC C

M AN U

SC

3.2537(1) 5.2063(2) 47.73(4) (2b) 0.3330 0.6667 0.0000 (2b) 0.3330 0.6667 0.3828(2)

RI PT

ZnO Hexagonal P63-mc (186)

TE D

Compound Crystal system Space group Lattice parameter a (Å) b (Å) Cell volume (Å)3 Zn1 (2) x y z O1 (-2) x y z R-factors RP RWP Rexp χ2 RBragg RF

8.08 8.85 8.14 1.18 4.17 3.85