AgVO3 nanorods: Synthesis, characterization and visible light photocatalytic activity

Accepted Manuscript AgVO3 nanorods: Synthesis, characterization and visible light photocatalytic activity V. Sivakumar, R. Suresh, K. Giribabu, V. Narayanan PII:

S1293-2558(14)00257-X

DOI:

10.1016/j.solidstatesciences.2014.10.016

Reference:

SSSCIE 5036

To appear in:

Solid State Sciences

Received Date: 21 April 2014 Revised Date:

27 October 2014

Accepted Date: 31 October 2014

Please cite this article as: V. Sivakumar, R. Suresh, K. Giribabu, V. Narayanan, AgVO3 nanorods: Synthesis, characterization and visible light photocatalytic activity, Solid State Sciences (2014), doi: 10.1016/j.solidstatesciences.2014.10.016. 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.

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Research highlights


AgVO3 nanorods are synthesized by thermal decomposition method.

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AgVO3 nanorods show enhanced photodegradation towards methylene blue.
AgVO3 also exhibits photocatalytic activity towards industrial effluents.

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Possible photodegradation mechanism has also been proposed.

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ACCEPTED MANUSCRIPT AgVO3 nanorods: Synthesis, Characterization and Visible Light Photocatalytic activity V. Sivakumar1, 2, R. Suresh1, K. Giribabu1, and V. Narayanan1* 1

Department of Inorganic Chemistry, University of Madras, GuindyMaraimalai Campus, Chennai 600 025, India. Orchid Chemicals and Pharmaceuticals Limited, Research and Development Centre, Chennai 600119, India.

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Address for Correspondence*

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Dr. V. Narayanan,

Department of Inorganic Chemistry, School of Chemical Sciences,

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Assistant Professor,

University of Madras, GuindyMaraimalai Campus, Chennai – 25, Tamil Nadu, India.

Phone: 91 44 22202793; Fax: 91 44 22300488.

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*Corresponding author E-mail: [email protected] (V. Narayanan),

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ACCEPTED MANUSCRIPT Abstract: Large scale and high purity silver vanadate (AgVO3) nanorods were synthesized by thermal decomposition method. X-ray diffraction(XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, Ultraviolet-Visible (DRS-UV-Visible) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were

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employed to characterize the structure, light absorption capacity and morphology of the assynthesized sample.The photocatalytic activity of AgVO3 nanorods was examined by degradation of methylene blue (MB) as a model organic pollutant. The degradation efficiency

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is 85.02% in the 120 min visible light illumination. Further, the AgVO3 nanorods were used as a photocatalyst for industrial effluent. 95.4% degradation efficiency was obtained within

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the visible light irradiation of 120 min. The possible photocatalytic mechanism has also been proposed.

Keywords: Silver vanadate, nanorods, photocatalyst, methylene blue, industrial effluent. 1.Introduction

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Photocatalysts based on semiconductor nanoparticles have considerable attention for degradation of environmental pollutant. Over the past decade, many semiconductor nanoparticles such as TiO2[1],ZnO [2], and CuO [3], have been extensively utilized as

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effective photocatalysts for the degradation of many organic dye effluents. However, most of

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them are not active under visible light irradiation, which limits their practical applications. Hence, the development of visible light-driven photocatalystsis necessary for an effective utilization of solar light. There are usually three ways to obtain photocatalysts under the visible light irradiation. 1.Doping of elements such as Fe, Co etc., into UV active photocatalysts [4]. 2. Compositing of UV active photocatalysts with conducting polymers [5]. 3. Development of new materials with visible light driven photocatalytic activity [6]. Among these new photocatalysts, silver vanadates are important materials due to their narrow band gap. The most common phases are AgVO3, AgxV2O5, and Ag2V4O11. Among them, AgVO3

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ACCEPTED MANUSCRIPT has been demonstrated to be efficient photocatalysts under visible light irradiation, due to its visible light absorption capacity, favorable morphology and nanocrystalline nature [7]. Apart from photocatalysis, silvervanadate nanoparticles also finds better use in different applications such as cathode material in lithium ion batteries [8], in electrochemical cells [9],

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and as antibacterial agents [10]. Recently, β-AgVO3 nanowires have been used as a photocatalyst for the degradation of rhodamine B under visible light irradiation [11]. Several methods have been used for the preparation of AgVO3 nanostructures. For instance, Song et

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al. reported β-AgVO3 nanoribbons with length upto 200-300 µm by a hydrothermal method [12]. Singh et al. obtained AgVO3 nanorods by sonochemical synthesis [13]. However,

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thermal decomposition method has advantages than the other methods such as less time consumption, well crystallized products, no need of solvents, and low cost. Therefore we adapted the thermal decomposition method for the synthesis of AgVO3 nanorods. In this work, we report a facile approach to synthesize the AgVO3 nanorods using a

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thermal decomposition method.XRD, FT-IR, UV-Visible, SEM and TEM have been used to characterize the as synthesized sample. These nanorods show considerable photocatalytic activity, which has been studied through the photodegradation of MB in an aqueous solution

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and industrial effluent.

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2 Experimental sections

2.1 Synthesis of AgVO3 nanorods Ammonium metavanadate (NH4VO3, 99%), silver nitrate (AgNO3, 99%), and 1-

dodecanol (99%) used in the experimental work were of analytical grade, supplied by SigmaAldrich and used as received. The typical synthesis procedure is as follow: ammonium metavanadate (0.1 mmol), silver nitrate (0.1 mmol) and 1.0 mL of 1-dodecanol were mixed, ground for 1 h in a mortar with and then calcined at 450 °C for 5 h in a muffle furnace. The resulting AgVO3nanoparticles were collected and subjected to further analysis.

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ACCEPTED MANUSCRIPT 2.2 Characterization XRD pattern was obtained on Rich Siefert 3000 diffractometer,operating with Cu-Kα1 radiation (λ = 1.5406 Å). Silicon was used as an external standard for correction due to instrumental broadening. FT-IR analysis was carried out by a Schimadzu FT-IR 8300 series

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instrument. Raman spectrum was recorded using laser Raman microscope, Raman-11 Nanophoton Corporation, Japan. DRS UV-Vis absorption spectrum was obtained on a Perkin-Elmer lambda650 spectrophotometer. SEM and TEM analysis were carried out by

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using a HITACHI SU6600 field emission-scanning electron microscopy and FEI TECNAI G2 model T-30 at accelerating voltage of 250 kV respectively.

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2.3 Photocatalytic experiment

The visible light photocatalytic activity of AgVO3 nanorods were performed by using MB and industrial effluent (IE) at ambient condition. The experiment was conducted as follows: 0.05 g of AgVO3 nanorods was dispersed into aqueous MB/IE solution (10-5 M, 100

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mL) in a beaker. Prior to visible light irradiation, the suspension was stirred magnetically in dark for 20 min to reach adsorption–desorption equilibrium between AgVO3 and MB/IE. The mixture was then exposed to visible light irradiation under constant magnetic stirring. At

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regular intervals of 15 min, samples were collected and analyzed by a UV-Vis absorption

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spectrophotometer. The characteristic absorption peak of MB and IE at about 663 nm and 670 nm respectively was chosen for the photocatalytic degradation analysis. The photodegradation efficiency was calculated using the following formula: photodegradation efficiency

E =

A0 − Α

X 100%

(Eq-1)

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Where A0 is the absorbance at t = 0 min and A is the absorbance after complete degradation, at t =∞ min.

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ACCEPTED MANUSCRIPT 3. Results and Discussion 3.1 Characterization of AgVO3 nanorods The XRD pattern of the as-prepared AgVO3 nanorods is shown in Fig. 1. The observed diffraction peaks can be easily indexed to monoclinic AgVO3(JCPDS No. 29-

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1154).The observed diffraction peaks, 20.3°, 20.5°, 22.6°, 22.8°, 25.7°, 26.6°, 27.3°, 28.4°, 29.9°, 32.9°, 33.5°, 34.4°, 34.9°, 39.2°, 39.7°, 40.3°, 43.0°, 44.2°, 46.7°, 49.4°, 50.5°, 51.0°, 52.2°, 53.5°, 54.7°, 56.6°, 57.6°, 61.8°, 62.0°, 63.1°, and 64.6° corresponding to (400), (301),

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(002), (2ത02), (5ത01), (202), (011), (2ത11), (501), (4ത11), (1ത12), (6ത02), (112), (312), (701), (303), തതതത03), (1ത23), (8ത02), (710), (4ത04), (204), (6ത04), (020), (220), (910), (404), (2ത22), (1ത05), (11

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(7ത05), and (015) planes respectively. AgVO3 has the lattice parameter value a = 7.685 Å, b = 8.007 Å, c = 10.090 Å. No diffraction peaks from other impurity phases have been observed, indicating that the product is highly pure. Further, the diffraction peaks are narrow which indicated that the synthesized product is highly crystalline nature. The average crystallite size

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of the AgVO3 nanorods was calculated by from full width of half maximum of the diffraction peak at 29.9° (501) by using Scherrer formula,

D = 0.9λ /(β cos θ)Eq-2

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Where, 0.9 is a shape factor, λ is the wavelength, β is the full width at the half-

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maximum of the line and θ is the diffraction angle. The calculated average crystallite size of the AgVO3 nanorods was 73 nm. Fig. 2 shows the FTIR spectrum ofAgVO3 nanorods acquired in the range of 400–

4000 cm-1 which is very similar to that reported for AgVO3 [14]. Fig. 2 shows bands at 3432, 1639, 1394, 1116, 919, 846, 710 and 511 cm-1. The band observed at 3432 and 1639 cm-1 correspond to O-H stretching vibration and bending vibration of physisorbed water molecules and surface hydroxyl groups [15]. Band at 919 cm-1 is due to the VO3 symmetric stretching vibrations and bands at 846, and 710 cm-1 are associated to the VO3antisymmetric stretching

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ACCEPTED MANUSCRIPT vibrations. A band at 511 cm-1 is corresponding to the symmetric stretching mode of V–O–V units. Furthermore, the band observed at 1394cm-1 is caused by overtone band [16]. The Raman spectrum of AgVO3 nanorods is shown in Fig. 3. It shows the Raman band at 912, 882, 811, 624, 489, 350 and 215 cm-1. All the Raman bands are well matched

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with that reported for AgVO3preparedby the hydrothermal method [17].Raman band at 912 and 882 cm-1 correspond to stretching vibration of V=O. The bands at 624 and 489 cm-1 are attributed to the stretching vibration of oxygen shared by two vanadium atoms (V-O-V). A

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band present at 811 cm-1 is due to the stretching vibration of V-O-Ag bond [18]. A bending vibration of VO43- was observed by the presence of Raman band at 350 cm-1.

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The morphology of the as prepared AgVO3 was examined by SEM and TEM. The SEM image of AgVO3, prepared by calcination of the mixture of NH3VO4 and AgNO3 at 450 °

C for 5 h is shown in Fig. 4A. It shows that the synthesized sample is mostly rod-like

particles. The length and breadth of the rods are several µm and 270 nm respectively.

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Moreover, some irregular shaped particles are also deposited on the surface of the rod-like particles.These particles are the broken pieces of AgVO3 rods which can infer from the SEM image. The formation of nanorods was further confirmed by TEM images (Fig. 4A, image c

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and d). From the TEM image (inset in Fig. 4A, image d), it can be seen that the surface of the

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particles are quite rough which may be the release of gaseous product from the interior of the precursor particles. The energy dispersive spectroscopy (EDS) shows that they consist of Ag, V and O only (Fig. 4B). Further quantitative analysis of EDS finds that the atomic ratio of Ag:V:O is about 1:1:3, indicating that a stoichiometric sample (Ag/V/O = 1 : 1: 3) is obtained and is consistent with stoichiometric AgVO3, in agreement with XRD results. 3.2 Optical property The DRS UV-Visible absorption spectrum of AgVO3 nanorods is shown in Fig. 5A.Absorption band at319 nm and 440 nm are due to the electronic excitation form O 2p/Ag

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ACCEPTED MANUSCRIPT 4d to empty V-3d orbital [19]. Generally, the optical property of the nanoparticles is determined by their energy band. The optical bandgap (Eg) can be obtained by Tauc’s equation as given below (αhν)n= B(hν− Eg) ----------------(3)

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Where, hνis the photon energy, α is the absorption coefficient, B is a constant relative to the material and n is equal to 2 and 1/2 for a direct transition and indirect transition respectively. The estimated band gap of the synthesized AgVO3 nanoparticles is about 1.9eV

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which agrees with Konta et al.[20] 3.3Photocatalytic property

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To determine photocatalytic activity of AgVO3 nanorods, we performed the photodegradation experiment of MB under visible light irradiation. The absorption characteristic of MB centered at 663 nm was monitored to reveal the photodegradation efficiency of the AgVO3 nanorods. Fig. 6A shows the UV-visible absorption spectrum of the

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1×10-5 M MB solution with 0.05 g of AgVO3 nanorods for photocatalytic degradation at different equal time intervals. It can be seen that the concentration of MB decreases with the visible light irradiation time. To clearly illustrate the photocatalytic activity of AgVO3

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nanorods, a plot of C/C0 versus visible light irradiation time is shown in Fig. 6B. It shows the

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gradual decrease of C/C0 with increase in visible light irradiation time. The photodegradation efficiency is 85.02% in the120 min illumination. The photodegradation efficiency becomes almost constant after 30 min. The photocatalytic performance of the AgVO3 nanorods is better or comparable with other typical photocatalysts for the degradation of MB (Table 1)[21-24]. The photocatalytic mechanism of AgVO3nanorods can be explained as follows: photoelectron (e¯ ) and hole (h+) pairs in theAgVO3nanorods are created under visible light irradiation. Then, these photoelectrons and holes react with the adsorbed O2, OH¯ and H2O,

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ACCEPTED MANUSCRIPT to form highly oxidizing species like O2• ─, •OH, etc., These reactive species degrade [25] the MB into the small molecules like CO2, H2O etc., The schematic diagram for photocatalytic degradation mechanism of MB at the surface of AgVO3 nanorods under visible light irradiation is illustrated in Fig. 7. The photocatalytic activity is also dependent on the

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morphology and structure of AgVO3. According to the XRD analysis, the as-prepared AgVO3nanorods are well-crystallized, with less grain boundaries. It is well known that the grain boundaries serve as recombination centers of photogenerated electrons-holes. Since the

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as prepared AgVO3 nanorods having less grain boundaries, the rate of recombination of e¯ h+ reduces and hence higher the photocatalytic efficiency.

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3.4 Practical application

In order to determine the practical utility of AgVO3 nanorods as photocatalyst, we performed the photocatalytic degradation of industrial effluent which is obtained from local dye industry. Fig. 8 shows the UV-visible spectrum of IE solution with 0.05 g of AgVO3

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nanorods at different equal time intervals. It can be seen that the concentration of IE decreases with the visible light irradiation time. The photodegradation efficiency is 95.4% in the 120 min illumination. The photodegradation efficiency becomes almost constant after 30

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min. These results suggest that the prepared AgVO3 nanorods can be used as a photocatalyst

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for the degradation of industrial effluents. 4.Conclusions

In summary, we demonstrated the facile synthesis and photocatalytic activity of

AgVO3 nanorods. The XRD, FTIR and Raman spectroscopy confirm the formation of AgVO3. The optical absorption property was studied by UV-visible spectroscopy. The photocatalytic activity of AgVO3 nanoparticles was examined by using MB as a model organic pollutant and IE. The results suggest that the AgVO3 nanorods have higher

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ACCEPTED MANUSCRIPT photocatalytic activity for the degradation of MB and IE. Hence, we hope that the AgVO3 nanoparticles will have a great potential for photodegradation of other organic pollutants. Acknowledgments V. Sivakumar wishes to thank Orchid chemicals and pharmaceuticals limited,

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Chennai for providing the XRD, FTIR and UV-Visible spectroscopy Support. The authors acknowledge the SEM and TEM facility provided by the National Centre for Nanoscience

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and Nanotechnology, University of Madras, Tamil Nadu, India.

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ACCEPTED MANUSCRIPT Figure caption Fig. 1: XRD pattern of AgVO3 nanorods. Fig. 2:FT-IR spectrum of AgVO3nanorods. Fig. 3: Raman spectrum of AgVO3 nanorods.

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Fig. 4: DRS UV-Visible absorption spectrum of AgVO3 nanorods.

Fig.5: (A) SEM images (a and b, → indicated the broken rods), TEM images (c and d), (B) EDS spectrum of AgVO3 nanorods.

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Fig.6:(A) UV-Vis spectra of aqueous MB solution taken (1×10-5 M, 100 mL) at (a) 0 min, (b) 15 min, (c) 30 min, (d) 45 min, (e) 60 min (f) 75, (g) 90 min, (h) 105 min and (i) 120 min

Plot of C/C0 versus irradiation time.

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during photodegradation experiment by using 0.05 g ofAgVO3 nanorods as photocatalyst. (B)

Fig. 7: Possible photocatalytic degradation mechanism of MB at the surface of AgVO3 nanorods.

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Fig.8: UV-Vis spectra of aqueous IE solution taken at (a) 0 min, (b) 15 min, (c) 30 min, (d) 45 min, (e) 60 min (f) 75, (g) 90 min, (h) 105 min and (i) 120 min during

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photodegradation of IE by using 0.05 g of AgVO3nanorods as photocatalyst.

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Table 1: Comparison of photocatalytic activity of some photocatalysts with the present photocatalyst for the degradation of methylene blue.

Light source

92.0

8h

Visible light

-

[21]

92.5

25 min

Visible light

-

[22]

97.8

6h

Visible light

-

[23]

85.0

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95.3

Practical References utilization

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Degradation time

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Bi2S3-TiO2/polymer fiber composites (NA) AgVO3 Nanorod (270 nm) NA-not available

Degradation efficiency (%)

180 min

Solar irradiation

-

[24]

120 min

Visible light

95% degradation of IE

Present work

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Photocatalysts (particle size) Ag/ZnO Nanoparticles (10 nm) CdS nanorod (150 nm) ZnO/CdO Nanorod (33 nm)

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