Synthesis and Characterisation of Lanthanum added ZnO ...joics.org/gallery/ics-1925.pdf · ZnO...

Synthesis and Characterisation of Lanthanum added

ZnO Nanostructures

M. Sudha1, A. Balamurugan2*, S. Surendhiran3, P. Manoj Kumar3,

Y.A. Syed Khadar4

1 Department of Physics, Government Arts College

Udhagamandalam – 643002, Tamilnadu, India

2 Department of Physics, Government Arts and Science College

Avinashi – 641654, Tamilnadu, India

3 Centre for Nano Science and Technology, K.S. Rangasamy College of Technology

Tiruchengode -637215,Tamilnadu, India

4Department of Physics, K.S.R College of Arts and Science for Women

Tiruchengode -637215, Tamilnadu, India

Abstract

The pure ZnO and La doped ZnO nanorods were prepared by sonochemical routeand

followed by calcination at 500℃. The prepared nanorods were comprehensively investigated

through X-ray diffraction (XRD), Ultra-violet spectroscopy (UV-Vis), Fourier transform

infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM),

Particle size analysis (PSA) to get a broader understanding about the influence of processing

parameter over the ZnO and La doped ZnO nanorods, structural, optical physico-chemical,

and photo catalytic property, a comparative evaluation was performed. The Degradation

performance on methylene blue (MB) under UV light irradiation was done to explore the

photo catalytic activity.

Keywords: La doped ZnO nanorods; Sonochemical method; Photo catalytic activity

1. Introduction

Nanomaterials deal with promising opportunities for improved and tailored properties

for application in environmental catalysis due to their unique size and dimensional properties

[1-4]. Past few decades, several natural and engineered nano metal oxides have been studied

about their strong dye degradation performances, antimicrobial properties and so on. Among

them, ZnO is increasingly recognized as a proper alternative due to its easily controllable

properties with the wide band gap semiconductors (3.37 eV). Already ZnO was also reported

to exhibit higher quantum efficiency and photocatalytic activity than nano TiO2. It is one of

the widely used photocatalysts due to its high catalytic efficiency, quick response, low cost,

and environmental sustainability [5-8]. However, ZnO still exhibits low photoenergy

conversion efficiency because of their low charge separation efficiency and fast

recombination of charge carriers, and more modification is indeed needed. In order to

increase the physical and chemical properties of ZnO to better photocatalyst, one possible

approach is to dope ZnO with different metal oxides. Recently, a large number of studies

have been focused on improving the ZnO properties by doping with other metal oxides [8-

Journal of Information and Computational Science

Volume 9 Issue 12 - 2019

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11]. A large of synthesis methods have been used to prepare ZnO, such as sol gel, co

precipitation, spray pyrolysis, pulsed laser deposition, chemical vapour deposition, electro-

deposition, the sonication technique. Among these methods, the sonication method is an

attractive process due to the easiness, reproducibility and controllability of physical and

chemical properties [12].

In this present study, pure and lanthanum doped ZnO prepared by sonochemical

method. The influence of La doping, structural and morphology on photocatalytic activity of

ZnO was elaborately investigated.

2. Experimental details

2.1 Materials and Methods

ZnO and Lanthanum doped ZnO nanorods were prepared by sonication method. AR

grade zinc acetate (ZnC4H6O4 - 99.99%), Lanthanum nitrate (H12LaN3O15 - 99.99%), sodium

hydroxide, double distilled water (DD) were used as precursor. The stoichiometry ratio of

zinc acetate and Lanthanum nitrate were dissolved separately in double distilled water. The

Lanthanum nitrate solution in required stoichiometry was slowly added into vigorously

stirred zinc acetate solution. After 15 mins, sodium hydroxide solution was added drop wise

into the above solution. Then this solution was transferred to sonication chamber and

sonicated for 30 mins with 40Hz power. The resultant solid product was dried at 100°C for 6

h and calcined at 500°C for 2 h. The pure ZnO particles were also prepared by the same

procedure without the adding lanthanum nitrate to zinc solution. The lanthanum doping

concentrations (0.1, 0.3, 0.5%) are expressed in wt. %. The synthesis procedure was

schematically shown in figure 1.

2.2. Characterization techniques

Crystalline nature of samples were detected through XRD measurements (X’Pert PRO;

PANalytical, the Netherlands) with CuKα as a radiation source (λ = 1.54060 Å). The

functional groups were traced through Fourier transform infrared spectrometer (FTIR)

(Spectrum 100; Perkin Elmer, USA) in the frequency range between 4000 to 400 cm−1.

Particle size and morphologies was exploited to field emission scanning electron microscopy

(Quanta FEG 250, Germany) and Particle size analyser (Nanophox; Sympatec, Zellerfeld,

Germany) respectively. Optical absorptions and photo degradation studies were absorbed

using UV-Vis spectrometer (UV - Vis; UV-2450, Shimadzu, USA).

Photocatalytic degradation of methylene blue dye (MB) in prepared nanorods solution

under UV light was used to evaluate the photocatalytic activity of the prepared pure and La

doped ZnO nanorods. In an aqueous methylene blue solution, prepared ZnO nanorods were

dispersed and kept under constant agitation using a magnetic stirrer connected to the reactor.

For the photocatalytic assessment, 10 ml sample was taken out from the reaction solution at

30 min interval. Before the assessment, to remove any suspended particles the aqueous

samples were centrifuged at 4000 rpm. Following which, the residual solution of methylene

blue was measured at 665 nm against UV–Vis spectrophotometer (Cary 8454; Agilent,

Singapore). The rate of degradation (D%) of methylene blue dye by prepared pure and La

doped ZnO nanorods under UV irradiation was calculated with in virtue of initial absorbance

A0, absorbance At with respect to (t) minutes and is given by [13]



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𝐃 % = 𝐀𝟎 − 𝐀𝐭

𝐀𝟎 %

3. Result and discussion

The powder X-ray diffraction patterns of ZnO and La-doped ZnO with different

lanthanum concentrations (0.1, 0.3, 0.5 % of La) are shown in Fig. 2. The diffraction peaks

and their relative intensities of both pure and La doped ZnO nanorods were in good

agreement with the standard JCPDS card no. 36-1451. The XRD patterns of all the La-doped

ZnO nanorods are almost similar to that of ZnO, suggesting that there is no major change in

the crystal structure upon La doping. However, it should be noted that the La-doped nanorods

have a wider and lower intense diffraction peaks than pure ZnO and also small variation in

peak positions. Moreover, the XRD peaks of La-doped ZnO continuously get broader and

shifts with increasing the La doping. Hence, it was clear that the dopant could not alter the

crystal structure of ZnO, whereas it dispersed uniformly in the ZnO. It is fascinating to note

that the crystal size of La doped ZnO calculated using Debye - Scherrer equation is much

smaller as compared with that of the pure ZnO, which decreases with increasing the La

doping concentration in ZnO [14]. This decrease in the crystal size is due to distortion in the

ZnO by La dopant ions, which control the rate of growth of ZnO [15-16].

The FT-IR spectra of pure and La doped ZnO nanorods were shown in Figure 3. The

absorption band at 1400 - 1500 cm-1 can be interpreted as C=O bonding vibrations arisen

from very small unavoidable traces of carbonate absorbed from environment. The broader

band peaks at 3400 – 3500 cm-1 indicates the presence of O-H molecules in prepared

samples it may be KBr which was used as medium for FTIR analysis. The strong intensity

band at around 505 cm-1 clearly indicates the Zn-O stretching vibration and the band at 607

cm-1 endorses the presence of ZnO and La [17-19]. The 880 cm-1 corresponds to N-O

deformation vibration.It was noted from the FT-IR spectra that the Zn-O vibrational mode

was more obviously observed and this clearly concludes a strong doping exist in La doped

ZnO nanorods.

The surface morphology of prepared nanorodswas scanned and showed in Fig 4, b, c,

d respectively for pure ZnO and different level of La content in ZnO. FESEM image of pure

and La doped ZnO nanorods illustrates that the morphology is well ordered and clearly

indicated the rod-like morphology. The size of the nanoparticle particles are in the range 50 -

100 nm, suggesting a wide range of band gap value in the ZnO nanorods. Furthermore, from

the fig. 3a-d it was noted that as La concentration increases, particle size of the samples

reduced, which was reliable with the XRD results.

The average particle size distributions of prepared samples are shown in Fig. 5.

Average particle size was distributed in the range of 85 - 60 nm size, respectively, for pure

and La doped ZnO samples. Moreover, the mean size distribution (d50) of particles is 83.2±3,

72.9±3, 67.2±3 and 64.1±3 nm, respectively, for Pure ZnO and La doped ZnO (0.1, 0.3, 0.5

%). The size of nanorods decreases from 83.2 to 64.1 nm as the dopant (La ions)

concentration increases in ZnO nanorods. The above results indicate that the doping La ions

can be reason for size effects in ZnO nanorods and plays a dominant role in reducing size of

the prepared nanorods [20-24].



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The optical absorption properties of pure and La doped ZnO nanorods with different

doping concentrations of La were investigated by UV–Vis absorption spectra and shown in

Figure 6. From Figure 5, it was noted that the band-edge absorption of the prepared pure and

La doped ZnO nanorods traced at around 399-369 nm. The optical band gap of Eg is

calculated using the following equation [25]

Band gap energy (Eg) = 𝒉 𝒄

𝝀

The wavelength to the absorbance edge for Pure and La doped ZnO nanorods are 399,

380, 375 and 369 nm, respectively. The band gap which corresponds to the absorption edge

found in UV – Vis spectra of the prepared nanorods are 3.11, 3.26, 3.32, 3.40 eV for pure and

La doped ZnO nanorods, respectively. The energy band gap for the prepared samples was

calculated by using Tauc plot equation. The transition plot of direct band gap [( Ephot) n vs.

Ephot, Ephot is the photon energy] is tabulated in table 1. Here n is a constant, equal to 1/2

for the direct and 2 for indirect band gap semiconductors. The energy band gap values (Eg)

obtained from direct plot of transitions are 2.97, 3.04, 3.10 and 3.27 eV and from indirect

transitions are 2.81, 2.90, 2.99 and 3.18 eV for respectively pure and La doped ZnO. From

the above results, the Eg values increases while La doping concentrations increase in pure

ZnO [26-30]. It clearly shows that the prepared ZnO and La doped ZnO samples revelation

the semiconducting behaviour due to its band gap values.

The photocatalytic behaviour of the as prepared pure and La doped ZnO nanorods

with different La doping concentrations are explored by analysis the photocatalytic

degradation of methylene blue dye. In order to conclude the best dopant and doping

concentration to synthesise the most effective ZnO as photocatalyst to demonstrate its

potential environmental application for the removal of contaminants in waste water is tested,

where in methylene blue is used as a typical contaminant [31].

It confirms that the degradation decolourisation of methylene blue is due to the

photocatalytic reaction of ZnO nanorods under UV illumination. The photocatalytic

degradation process is confirmed out by noticing the absorption peak of methylene blue at λ=

665 nm [32-35]. It is noted that the photo degradation decolourisation of methylene blue dye

with the pure and La doped ZnO nanorods are very steep for the first 30 min. and then it

slows down with time.

The 0.5 % La doped ZnO nanorods shows higher degree of dye degradation (91%)

than that of lower La concentration doped and pure ZnO nanorods during the assessed time

(210 min.). This adverse photocatalytic behaviour of high concentration La doped ZnO

nanorods can be coined to the fact that the 0.5 % La doped ZnO nanorods shows lower

crystal size and lower average particle size distribution and also shows distinct rod like

structure [36-41]. It is observed from the results that the prepared ZnO nanorods samples

show higher effectiveness with respect to photocatalytic degradation of MB dye, a

comparative assessment with earlier reports on ZnO as well as doped ZnO nanorods was

done and tabulated in table 2.

4. Conclusion

In summary, pure and La-doped ZnO with different concentrations of La were

successfully prepared by sonication method and characterized elaborately. The crystalline



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size of the prepared pure and La doped ZnO nanorods are ranged from nm. The average

crystal size and particle sizes were decreased while La doping concentration increases. From

the FESEM results, the nanorods are in rod like morphology. The calculated band gap

energies of pure and La doped ZnO nanorods were increased from 3.11 eV to 3.40 eV with

increasing the lanthanum doping concentration. Hence, these results indicated that the

lanthanum doping concentration plays an important role in tuning the size, band gap and

photoluminescence property of the ZnO nanorods. In addition the prepared La doped ZnO

nanorods possess the significant degradation property against methylene blue dye.The 0.5%

La doped ZnO nanorods possess the outstanding degradation property against methylene blue

dye has been concluded.

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Table 1. The crystal size, particle size and band gap values of pure ZnO and La doped

ZnO nanorods

Sample code

Crystal

size

(nm)

Particle

size

(nm)

λmax

(nm)

Energy band

gap (eV)

by absorption

peak

Energy band gap (eV)

by Tauc plot

Direct Indirect

Pure ZnO 33 83.2 399 3.11 2.97 2.81

ZnO: 0.1 % La 29 72.9 380 3.26 3.04 2.90

ZnO: 0.3 % La 27 67.2 375 3.32 3.10 2.99

ZnO: 0.5 % La 24 64.1 369 3.40 3.27 3.18

Table. 2. Comparative assessment with earlier reports on photocatalytic performance of pure

ZnO and Doped ZnO nanorods

S. No Photocatalyst – Method Degradation

efficiency (%) Dopant

Improvement

in degradation

efficiency (%)

Reference

1. ZnO – Sol Gel 75 Ni 88 15

2. ZnO – Precipitation 72 Ag 81 29

3. ZnO – Sol Gel 73 Sr 86 30

4. ZnO – Hydrothermal 70 Co 78 39

5. ZnO – Sonication

(proposed work) 76 La 94 -



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Fig. 1. Schematic representation of La doped ZnO synthesis procedure

Fig. 2. XRD pattern of pure and La doped ZnO nanorods calcined at 300° C



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Fig. 3. FTIR spectra of pure and La doped ZnO nanorods

Fig. 4. FESEM images of pure and La doped ZnO nanorods



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Fig. 5 Particle size distribution of pure and La doped ZnO nanorods

Fig. 6. UV-Vis absorption spectra of pure and La doped ZnO nanorods



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Fig. 7. Photocatalytic activity of pure and La doped ZnO nanorods



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