Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity

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Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity A. Balamurugan a, M. Sudha b, S. Surendhiran c, R. Anandarasu d, S. Ravikumar e, Y.A. Syed Khadar f,⇑ a

Department of Physics, Government Arts and Science College, Avinashi 641654, Tamilnadu, India Department of Physics, Government Arts College, Udhagamandalam 643002, Tamilnadu, India c Centre for Nanoscience and Technology, K S Rangasamy College of Technology, Tiruchengode 637215, Tamilnadu, India d Department of Chemistry, K.S.R College of Arts and Science for Women, Tiruchengode 637215, Tamilnadu, India e Department of Electronics and Communication, Sengunthar Arts and Science College, Tiruchengode 637205, Tamilnadu, India f Department of Physics, K.S.R College of Arts and Science for Women, Tiruchengode 637215, Tamilnadu, India b

a r t i c l e

i n f o

Article history: Received 20 April 2019 Received in revised form 29 June 2019 Accepted 27 August 2019 Available online xxxx Keywords: CeO2 nanoparticles Samarium doped CeO2 Hydrothermal method Morphology Antibacterial activity

a b s t r a c t This work describes the synthesis, characterization and antibacterial activity of samarium (Sm) doped cerium oxide nanoparticles. The Sm doped CeO2 nanoparticles were prepared by hydrothermal method with various concentrations ranges from 2 mol % to 8 mol %. The XRD pattern revealed crystalline nature with size of 58.3 nm–43.47 nm. The Ce–O chemical bonding nature was confirmed using FTIR. FESEM exhibited fascinating shapes like agglomerated octahedral and grow rod arm on octahedral phases of nanoparticles. UV–Vis was used to measure the optical behaviors of CeO2 nanoparticles. The samarium doped CeO2 nanoparticles showed better antibacterial activity against the pathogenic bacteria. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.

1. Introduction Rare earth metal oxides play a vital role in diverse areas such as chemistry, physics, material science and biology. Among the rare earth metals ceria (CeO2) nanoparticles has received enormous interest in the present frontier research, because of their wide application such as UV absorber and blocker, solid oxide fuel cell, optics, antibacterial agents, gas sensor and three way catalyst for automotive emission control [1–5]. There are several methods such as co-precipitation, sol-gel, micelle, chemical vapour deposition, sonochemical micro wave and hydrothermal method for the synthesis of CeO2 nanoparticles [6–10]. Among them hydrothermal methods are finding increasing application in material science and solid state chemistry. Hydrothermal method is technologically important for crystal growth and synthesis of new material with useful properties. In this method the use of high pressure provides an addition parameter for obtaining fundamental information on the structures, behavior and properties of solid [11]. Ceria nanoparticles show tremendous potential in antibacterial activity against the bacteria such as E. coli, B. cereus, S. aureus and S. ⇑ Corresponding author. E-mail address: [email protected] (Y.A. Syed Khadar).

typhi. Fluorite lattice of CeO2 NP’s antibacterial capability is of great influenced by morphology (Cube, octahedral and rod structure etc) with exposed crystal planes of 111, 110 and 100 [12]. In addition, an oxygen vacancy in crystal lattice enhances the CeO2 NPs antibacterial potential. The metal/metal oxides nanoparticles antibacterial activity interacts with microbial cells through different mechanism. The nanoparticles can either directly interact with the microorganism cells (interrupting trans-membrane electron transfer, disrupting or penetrating the cell envelope) or oxidizing cell compound or producing reactive oxygen species (ROS) to damage the microorganism cells. The mechanism of antibacterial activity of CeO2 NPs could be oxidative stress associated with the bacteria. The CeO2 NPs interacts with bacteria membrane, which disturbs the mesosomal process of cellular respiration, DNA replication and cell division [13,14]. In antibacterial activity, intracellular functional damages are due to ROS generation of excess oxygen radical and hydroxyl radicals in CeO2NPs. The oxygen vacancies have great contribution to ROS generation in CeO2 NPs for antibacterial activity [15]. To improve the antibacterial efficiency of CeO2 NPs, oxygen vacancies are better through doping certain amount of trivalent rare earth metals on CeO2 NPs, which decreases the lattice parameter compared with pure CeO2 NPs and results from Ce4+ ions to

https://doi.org/10.1016/j.matpr.2019.08.217 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

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Ce3+ ions [9,16]. The doped ceria nanoparticles restrain high level oxygen vacancies compared with pure CeO2 NPs due to mismatch size, which possess novel properties through the addition of trivalent element entering in the boundary of CeO2 NPs. Several metals doped ceria nanoparticles were studied for antibacterial activity, Syed Khadar et al. demonstrated that various mole of Gd doped ceria nanoparticles were effective against different bacterial cells [17]. Fazal Abbas et al. investigated that Sn doped Ceria nanoparticles were cytotoxic against Neuroblastoma cell and shows great bio-compatibility healthy cells [18]. Paravathi et al. analyzed that different metal ions doped CeO2 NPs performed antibacterial activity against gram positive and gram negative bacteria. They reported that Cu doped CeO2 NPs are good in antibacterial agent than other metal doped [19]. Ciobanu et al. studied that Sm doped hydroxyapatite ceramics were successfully tested against Grampositive and Gram-negative bacteria [20]. In Lanthanide series one of the most privileged for increasing active oxygen vacancies in the CeO2 NPs are samarium ion (Sm3+) [12,16]. Sm3+ ion also have interesting properties of high intensity optical, electrical and antimicrobial activity [21]. In this research article, we have synthesized different mole percentage of samarium (Sm3+) doped cerium oxide nanoparticles by hydrothermal method. The prepared Sm3+ doped CeO2 NPs were characterized using UV–Vis, FT-IR, SEM, XRD and PL studies. Antibacterial properties of these samples were determined against four pathogenic bacteria to know its bacterial killing efficiencies. 2. Experimental 2.1. Synthesis of samarium (Sm3+) doped CeO2 nanoparticles Trisodium phosphate solution (0.02 M), 20 ml was slowly added drop wise to 60 ml of 0.1 M solution of cerium nitrate under magnetic stirring. The reaction mixture under constant stirring was resulted as white colloid. Then, the colloids were transferred to the Teflon coated autoclave vessel (100 ml capacity) for hydrothermal treatment maintained at 180 °C for 15 h. The autoclave vessel was cooled to room temperature. The impurities were removed thoroughly washed with double distilled water followed by ethanol and dried at 60 °C for 5 h. A blank sample (CeO2) synthesized without samarium using the same procedure at same experimental conditions for the purpose of comparison. 2.2. Characterization techniques The crystal structure of CeO2 and Sm doped CeO2 nanoparticles were determined by powder X-ray diffraction. XRD patterns were recorded using X-ray diffractometer (XRD, Shimadzu-6000) using Cu Ka radiation (k = 1.5408 Å). The surface morphology of CeO2 and Sm doped CeO2 nanoparticles were studied using a scanning electron microscope (SEM, JOEL JSM-6390). The presence of functional groups was confirmed using Fourier transform infrared spectrometer (FTIR, Brucker-Tensor 27). UV-absorption spectra of synthesized nanoparticles were carried using spectrophotometer UV–Vis (UV–Vis, Jasco V530). The photoluminescence (PL) emission spectra were measured at an excitation wavelength of 340 nm using Photoluminescence spectroscopy (Horiba Jobin, Flouromax-4) at room temperature. 2.3. Antibacterial activity of samarium doped CeO2 nanoparticles The antibacterial activity of CeO2 and Sm3+ doped CeO2 nanoparticles were studied against pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, Bacillus cereus and Salmonella typhi using agar disc diffusion method. For this study,

CeO2 and Sm/CeO2 nanoparticles were prepared at the concentration of 1 mg/ml using dimethylsulfoxide (DMSO) as solvent [22]. Then, the dispersed nanoparticles were impregnated into each sterile disc using micropipette under aseptic condition. The overnight bacterial culture was prepared using sterile nutrient broth. Then, all the grown bacterial culture was aseptically transferred to the sterile Mueller-Hinton agar medium using sterile cotton swab. Finally, all the inoculated plates were allowed to incubate for 24 h using bacteriological incubator. After incubation, the zone of inhibition was measured against the bacterial strains.

3. Results and discussion 3.1. FTIR study The FT-IR spectra of different molar Sm3+ doped CeO2 NPs shown in Fig. 1. A broad peak observed at 3372 cm
1 is attributed to the OH stretching vibrations of moisture content present in atmosphere [23]. The band obtained at 2424 and 1042 cm
1 are due to the presence of organic impurities in the sample. The peak at 2424 cm
1 was due to the presence of dissolved or atmospheric CO2 in the samples. A sharp peak obtained at 1625 cm
1 corresponds to the bending vibrations of H–O–H which is partly overlapping the O–C–O bond [24]. A band at 1382 cm
1 is due to the N–O stretching vibrations of oxygen atom present in the ceria nanoparticles. Peak at 952 cm
1 arise due to Ce–O vibration. A peak noticed at 812 cm
1 is attributed to the O–Ce–O bonding nature of ceria nanoparticles. The small bands obtained at 700, 642 and 543 cm
1 is corresponding to Ce–O stretching mode [25]. When the concentration of samarium increases in the sample, the hydroxyl vibaration band reduced in this region around at 3372 cm
1. The hydroxyl band indicates, increase in crystalline size [20]. The broad band disappeared in 8 mol % Sm3+, due to Sm3+ cation replaced hydroxyl ion in CeO2 NPs. The Sm3+ doped CeO2 FT-IR spectra moves towards higher wave number and confirms the formation of Sm-CeO2 nanoparticles. 3.2. XRD structural studies Fig. 2 show XRD analysis of pure CeO2 NPs and different molar Sm3+ doped CeO2 nanoparticles. The XRD pattern of the Sm3+ doped CeO2 NPs with X-ray diffraction peaks, indexed to 111, 200, 220, 311, 222, 400 and 331 planes are in tremendous concurrence with standard values [JCPDS card no. 75-0162] of a cubic fluorite structure of CeO2 [26,27]. Fig. 2b reveals that the peaks are shifted towards lower Braggs angle for the Sm3+ doped CeO2 NPs, due to difference in the ionic radii of Sm3+ dopant (1.21 A) ion related to Ce4 + ion (0.97 A). With an increase of molar dopant in the CeO2 samples from 2 mol % to 8 mol % at 180 °C, the peaks broadening of the reflection decreases and peaks become sharper due to increase in crystallinity of the sample [28]. The average crystallite size was calculated by using Debye-Scherer’s formula and found that they are in the range from 43.47 to 58.3 nm for pure and doped ceria samples respectively [29]. The d-spacing value attributed that doped ceria inter plane were higher than pure CeO2 nanoparticle due to surface energetic factor change in ceria which attain the microstrain effect stimulated by contraction of the lattice caused by Sm3+ ion doped on the CeO2 NPs structure [27,30]. The d-spacing of 2 mol % Sm3+ doped CeO2 nanoparticles were higher when compared with pure and other mole percentages, with small crystalline size due to the lattice contract. The d-space value decreases for higher molar percent doping due to lattice expansion. The lattice parameter of Sm doped CeO2 NP of plane (1 1 1) calculated by following relation,

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

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Fig. 1. FTIR spectra of a) pure CeO2NPs, b) 2 mol %, c) 4 mol %, d) 6 mol % and e) 8 mol % Sm3+ doped CeO2 NPs.

Fig 2. XRD pattern of (a) undoped CeO2, (b) 2 mol %, (c) 4 mol %, (d) 6 mol % and (e) 8 mol % Sm3+ doped CeO2 NPs.

d¼

k ;a ¼ 2 sin h

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d 2 2 2 h þk þl

where, D is the planar spacing, kis the wavelength of the radiation (k = 0.15418 nm), h is the diffraction angle, and a is the lattice parameter.

The lattice parameter (a) values of Sm3+ doped CeO2 NPs is higher than pure CeO2 NP due to the effect from ionic radii in according to the Vegard’s rules [30]. Doping 2 mol % of Sm3+ has smaller crystalline size, increased lattice parameter and dspacing, shifts towards lower angle position compared with 4, 6, 8 mol % doped and pure CeO2 NPs. This interesting observation

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

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indicates the low molar doping increases the micro strain in ceria lattice structure [1]. When increasing the mole % of Sm3+ doping, lattice parameter decreases than 2 mol %. This may be due to extension of Sm3+ ion in mixed valence state and change Ce3+ ion concentration [16,31]. The XRD patterns value confirmed the Sm3+ ion substituted in CeO2 lattice. 3.3. Optical studies Fig. 3 shows UV–Vis spectrum for pure CeO2 NPs and different molar Sm3+ doped CeO2 NPs. A strong absorption peak is observed at 332 nm, 341 nm and 345 nm for pure, 2, 4, 6, and 8 mol % Sm3+ doped CeO2 NPs respectively. A strong peak observed at 332 nm for pure CeO2 NPs, when doped with Sm3+ ions shifts towards the higher wavelength. This shift towards higher wavelength shows the incorporation of Sm3+ ion, changes the electronic band structure [32]. The band gaps of pure and doped ceria were determinate by Tauc’s relation [33,34]. Where, l is the path length and A is the absorbance. The index n = 1/2 represents the direct allowed transition energy gap. To determine the direct transition energy gaps, plot of (ahm) 2 versus hm is the linear function existence of direct allowed band transition in ceria nanoparticle samples. From the plot direct allowed band gap was calculate to 2.85, 2.81, 2.76, 2.72, and 2.68 eV for pure CeO2, 2%, 4%, 6% and 8% doped CeO2 NPs. It is observed that the band gap of doped ceria is smaller than pure CeO2 NPs. It is observed that the presence of higher amount of Ce3+ state when doped with Sm3+ than pure CeO2 NPs. The direct allowed band gaps decreases when increasing the doping (2–8%) concentration. Shehata et al. [16] has reported that CeO2 NPs doped with positive vacancy Sm3+ ions associated with trivalent energy, increases the Ce3+ state and it lead to create higher amount of oxygen vacancies. The increased Ce3+ state leads to the formation of localized energy state closer to the conduction band [35,36]. Shehata et al. has also reported that Sm3+ act as oxygen vacancy generator. 3.4. Photoluminescence studies PL emission spectra of Sm3+ doped CeO2 NPs revealed in Fig. 4. The Sm3+ doped CeO2 NPs showed excitation at 340 nm [37]. Assynthesized sample showed strong emission peak at 397 nm and it resembles to the transition of electron from localized Ce 4f state

Fig. 3. UV absorption spectra of a) undoped CeO2, b) 2 mol % c) 4 mol % d) 6 mol % and e) 8 mol % Sm3+ doped CeO2 NPs. b) Band gap of pure CeO2 and Sm3+ doped CeO2 NPs.

Fig 4. PL emission spectra of (a) pure CeO2, (b) 2 mol % (c) 4 mol % (d) 6 mol % and (e) 8 mol % Sm3+ doped CeO2NPs.

to valence band of O2p. The emission peak at 434 nm and 466 nm was originated from defect states existing between Ce4f states to O2p of valence band. Moreover, an emission nature was gradually decreased beyond the range of 497 nm and also it was extended up to 550 nm. Similarly, from the Sm3+ doped CeO2nanoparticles, the localized Ce4f state to O2p of valence band transition emission takes place due to doping of Sm ions in the CeO2 crystal lattice. The Sm-CeO2 shows broad emission range from 350 nm to 550 nm for the entire sample, due to the oxygen vacancies in the crystal lattice [37]. The excited intense emission indicates that new ions has presented in cubic symmetry environment. This result confirmed that Sm ions present in the CeO2 sites [38]. In steps of increased doping concentration from 2 to 8 mol %, the intensity emission peak of 8 mol % are higher than other doping due to close band gap. The emission from 4f transition is an isolation of Ce3+ and Sm3+ ions.

3.5. SEM & EDAX analysis The images of pure CeO2 exhibit well defined agglomerate of cube and octahedral shape particles. However, some distortion was found in the Sm3+ doped CeO2 nanoparticles. Four samples (CeO2) were synthesized using 2, 4, 6 and 8 mol % of Sm. Among the four doped samples, morphology characterization was taken for two samples of 2 and 8 mol % of Sm3+ doped CeO2 NPs. As shown in Fig. 5A(a) pure CeO2 show cubic and most of them has growing stage of octahedral structure. Morphology of pure CeO2 NP displays clear edges of octahedral shapes [39,40]. The asobtained CeO2 agglomerate as octahedral edges due to insufficient or over time for self assembled to give defined octahedron. The SEM image shows that our hydrothermal system at low temperature achieved growth stage of octahedral edges. The octahedron crystalline structure of 8 mol % Sm3+doped CeO2 shows nanosticks as adhered on surface of octahedral and slight distortion in its structure. Fig. 5A(b) shows some regular octahedron shaped Sm3+ doped CeO2 NPs due to growing nature when introduction of Sm3+ dopant, it may control the structure formations. Similarly, the morphology of CeO2 nanocrystals is evenly distributed during the doping of 8 mol % Sm3+ with slight distortion in Fig. 5A(c). It is clearly revealed that the addition of Sm3+ to CeO2 slightly changes the morphology of CeO2. 8 mol % Sm3+ doped CeO2 NPs

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

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Fig 5A. SEM images of a) pure CeO2NPs, b) 2 mol % Sm3+, c) 8 mol % Sm3+ doped CeO2 NPs.

Fig 5B. EDAX images of a) pure CeO2NPs, b) 2 mol % Sm3+, c) 8 mol % Sm3+ doped CeO2 NPs.

appears stick like arms perpendicular protrude from surface of octahedron CeO2 nanocrystals due to even terminate octahedral morphology and allow the second nucleation site of onedimension orientation of the precursor [40]. Fig. 5A(b&c) nanoparticles possess brightness compared to pure CeO2 and it is attributed that it increase the crystallinity due to increasing the Sm3+ molar on the CeO2 NPs.

The stoichiometry ratio of the elements existing in the prepared Sm doped CeO2 nanoparticles was traced by EDAX analysis was shown in Fig. 5B. The EDAX analysis confirmed that the prepared Sm doped CeO2 nanoparticles were the composition of Sm, Ce and O. Therefore, the obtained values of the atomic percentage of the present elements from EDAX are close to the starting composition of the prepared Sm doped CeO2 nanoparticles. The variation in

Table 1 EDAX Analysis of Sm doped CeO2 nanoparticles. Elements

Ce Sm O

Atomic % 0%

2%

4%

6%

8%

28.44 0 71.56

28.08 0.82 71.10

27.79 1.49 70.72

26.29 3.04 70.67

25.79 3.6 70.61

Fig 6. Anti-bacterial activity of different mole % Sm3+ doped CeO2 NPs with bacterial strains a) E. coli, b) B. cereus, c) S. aureus and d) S. typhi.

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

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Table 2 Comparative assessment on antibacterial activity of pure CeO2, 2%, 4% and 8% Sm doped CeO2nanoparticles with earlier reports. S. No.

Np’s

CeO2

CeO2

CeO2

CeO2

CeO2

CeO2

Antibacterial activity Type of Bacteria

Zone of Inhibitions (mm)

E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa B. cereus E. coli B. cereus S. aureus S. typhi

8 8 7 8 8 8 7 8 8 8 7 8 8 8 7 8 – – – – – – – –

Dopant

Antibacterial activity Type of Bacteria

Zone of Inhibitions (mm)

Zn

E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa S. dysenteriae E. coli S. aureus P. aeruginosa B. cereus E. coli B. cereus S. aureus S. typhi

09 09 08 08 10 08 08 09 11 12 10 08 08 09 10 08 09 11 08 15 22 20 25 24

Ni

Cu

Co

Mg

Sm

distribution of Sm and Ce elements in the prepared sample depends on the ratio taken were clearly shown in Table 1. 3.6. Evaluation of antibacterial activity Antibacterial activity of pure and Sm-CeO2 nanoparticles were evaluated against pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, Bacillus cereus and Salmonella typhi. The antibacterial results of nanoparticles are shown in Fig. 6. The pure CeO2 did not show any activity against four bacteria under this condition. Whereas, the Sm3+ doped CeO2 nanoparticles showed good antibacterial activity. The result obtained from the antibacterial study reveals that the killing efficiency of Sm-CeO2 increased with increasing the concentration of Sm3+ [41]. The zone of inhibition clearly showed that the killing potential of CeO2 significantly increased by increasing the concentration of Sm3+ dopant. The 2 mol % Sm doped CeO2 showed 13, 13, 13 and 12 mm zone of inhibition against E. coli, B. cereus, S. aureus and S. typhi, respectively. After increasing the concentration of Sm to 4 mol %, the antibacterial activity against the same bacteria increased to 15, 18, 15 and 15 mm. In 6 mol %, the measured zone of inhibition was 18, 21, 18 and 19 mm to 4 mol % Sm doped CeO2. As shown in Fig. 5, 8 mol % Sm doped CeO2 showed maximum zone of inhibition against all those bacteria as 22, 25, 20 and 24 mm. Among the four tested samples, 8 mol % Sm doped CeO2 nanoparticles exhibit maximum bacterial activity against B. cereus. Finding new biomaterials to kill such bacteria is a needy one. The nanoparticles interact with microbial cells through a variety of mechanism. The nanoparticles can either directly interact with the microorganism cells, e.g. interrupting trans-membrane electron transfer, disrupting or penetrating the cell envelope, or oxidizing cell compound or producing reactive oxygen species (ROS) that cause damage to microorganism cells (19,14). The metal oxide nanoparticles have maximum antibacterial due to presence of tendency of oxygen vacancies. The oxygen vacancy increases the generation of ROS. Generally, ROS generation depends on the prevention of the recombination of the photo generated electronhole pairs. The oxygen vacancies capture the generated electron and reduce the recombine with hole [18,19,41,42,17,43,44]. This

Enhancement

References

13

[43]

15

[43]

43

[43]

28

[43]

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[42]

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Present work

free hole interacts with water by generating ROS and kills the bacteria. Sm3+ doping CeO2 NPs has higher bacterial inhibition compared with pure, due to increase in oxygen vacancies. The obtained antibacterial activity results were compared with previous reports which are tabulated in Table 2. Among the tested samples, 8 mol % Sm3+ doped CeO2 NPs has maximum antibacterial potential associated with higher amount of oxygen vacancies. Increasing oxygen vacancy is confirmed by UV–Vis studies. There is 8% doped sample peak towards red shifted and that sample has lower band gap. 4. Conclusions The undoped and samarium doped CeO2 nanoparticles were successfully synthesized by using hydrothermal method. Main conclusion of this research articles to analysis the induced oxygen vacancies related to Sm3+ doped CeO2 NPs and it’s the antimicrobial activity. A simple cubic crystal structure was confirmed from XRD patterns and their calculated crystalline sizes were 58– 43 nm. A red-shifted absorption was observed from UV optical spectrum and their calculated bandgap energy values were 2.68– 2.85 eV. The Ce–O chemical bonding nature and the presence of functional groups were confirmed from FTIR spectrum. A changeable cubic shaped surface morphology was observed from SEM images. Further, the anti-bacterial activity of nanoparticles were studied against different types of bacteria and observed enhanced killing effects. Our research articles reported that active oxygen vacancies of Sm3+ doped CeO2 NPs could be ROS (reactive oxygen Species) generation and gives rise to oxygen stress for the bacteria to death at visible light. References [1] F. Yen Pei, W. Shaw Bing, L. Chi Hua, Preparation and characterization of samaria-doped ceria electrolyte materials for solid oxide fuel cells, J. Am. Ceram. Soc. 91 (1) (2008) 127–131. [2] Benjaram M. Reddy, Ataullah Khan, Yusuke Yamada, Tetsuhiko Kobayashi, Stéphane Loridant, Jean Claude Volta, Structural Characterization of CeO2
TiO2 and V2O5/CeO2
TiO2 catalysts by Raman and XPS Techniques, J. Phys. Chem. B 107 (2003) 5162–5167.

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217

A. Balamurugan et al. / Materials Today: Proceedings xxx (xxxx) xxx [3] D. Tian, Z. Chongrong, X. Yuyuan, X. Anran, P. Yue, Y. Zhao, One-step synthesis of samarium-doped ceria and its CO catalysis, Bull. Mater. Sci. 38 (5) (2015) 1149–1154. [4] X. Yueping, Y. Katsuhiko, H. Teruhisa, S. Natsuko, Y. Harumi, Hole and electron conductivities of 20 mol % REO1.5 doped CeO2 (RE=Yb, Y, Gd, Sm, Nd, La), J. Electrochem. Soc. 151 (3) (2004) A407–A412. [5] M. Qaisar, N. Mudassar, N. Sania, H. Talib, J. Nyla, K. Rizwan, A. Sadaf, A. Fazal, J. Tariq, Antimicrobial potential of green synthesized CeO2 nanoparticles from Olea europaea leaf extract, Int. J. Nanomed. 11 (2016) 5015–5025. [6] X. Haiyan, A. Zhihui, Z. Lizhi, Nonaqueous sol
gel synthesized hierarchical CeO2 nanocrystal microspheres as novel adsorbents for wastewater treatment, J. Phys. Chem. C 113 (2009) 16625–16630. [7] C. Rongrong, L. Wencong, Z. Liangmiao, Y. Baohua, S. Shanshan, Template-free synthesis and self-assembly of CeO2 nanospheres fabricated with foursquare nanoflakes, J. Phys. Chem. C 113 (2009) 21520–21525. [8] E. Kumar, P. Selvarajan, D. Muthuraj, Synthesis and characterization of CeO2 nanocrystals by solvothermal route, Mat. Res. 16 (2) (2013) 269–276. [9] A. Cristina, P. Marcella, C. Maria Maddalena, B. Maria Teresa, P. Jasper Rikkert, C. Giorgio Andrea, Structural features of Sm and Gd doped ceria studied by synchrotron X-ray diffraction and l-Raman spectroscopy, Inorg. Chem. 548 (2015) 4126–4137. [10] W. Xun, Z. Jing, P. Qing, L. Yadong, Hydrothermal synthesis of rare-earth fluoride nanocrystals, Inorg. Chem. 4517 (2006) 6661–6665. [11] R.W. Anthony, Solid State Chemistry and its Applications, second ed., John Wiley, 2003. [12] W. Zhen, W. Qi, L. Yuchao, S. Genli, G. Xuzhong, H. Ning, L. Haidi, C. Yunfa, Comparative study of CeO2 and doped CeO2 with tailored oxygen vacancies for CO oxidation, Chem. Phys. Chem. 12 (2011) 2763. [13] K. Gopinath, V. Karthika, C. Sundaravadivelan, S. Gowri, A. Arumugam, Mycogenesis of cerium oxide nanoparticles using Aspergillus niger culture filtrate and their applications for antibacterial and larvicidal activities, J. Nanostruct. Chem. 5 (2015) 295. [14] P. Humberto, Antimicrobial Polymers with Metal Nanoparticles, Int. J. Mol. Sci. 16 (1) (2015) 2099–2116. [15] M. Tiziano, M. Michele, M. Matteo, F. Paolo, Fundamentals and catalytic applications of CeO2-based materials, Chem. Rev. 116 (10) (2016) 5987–6041. [16] N. Shehata, K. Meehan, M. Hudait, N.J. Hudait, Control of oxygen vacancies and Ce+3 concentrations in doped ceria nanoparticles via the selection of lanthanide element, J. Nanopart. Res. 14 (2012) 1173. [17] Y.A. Syed Khadar, A. Balamurugan, V.P. Devarajan, R. Subramanian, Hydrothermal synthesis of gadolinium (Gd) doped cerium oxide (CeO2) nanoparticles: characterization and antibacterial activity, Ori. J. Chem. 33 (2017) 2405. [18] A. Fazal, J. Tariq, I. Javed, M. Sajjad Haider, A. Naqvi Ishaq, Inhibition of Neuroblastoma cancer cells viability by ferromagnetic Mn doped CeO2 monodisperse nanoparticles mediated through reactive oxygen species, Mater. Chem. Phys. 173 (2016) 146. [19] D.S. Parvathya, B.R. Venkatramanb, In vitro antibacterial and anticancer potential of CeO2 nanoparticles prepared by co-precipitation and green synthesis method, J. Nanosci. Curr. Res. 2 (2017) 111. [20] C.S. Ciobanu, S.L. Iconaru, P. Le Coustumer, Antibacterial activity of silverdoped hydroxyapatite nanoparticles against gram-positive and gram-negative bacteria, Nanoscale Res. Lett. 7 (2012) 324. [21] V. Venkatramua, P. Babu, C.K. Jayasankar, Th Tröster, W. Sievers, G. Wortmann, Optical spectroscopy of Sm3+ ions in phosphate and fluorophosphate glasses, Opt. Mater. 29 (2007) 1429. [22] R.V. Geetha, A. Roy, T. Lakshmi, Evaluation of anti-bacterial activity of fruit rind extract of Garcinia mangostana Linn on enteric pathogens-an in vitro study, Asian J. Pharm. Clin. Res. 4 (2011) 115–118. [23] C. Qizheng, D. Xiangting, J. Wang, L. Mei, Direct fabrication of cerium oxide hollow nanofibers by electrospinning, J. Rare Earth 26 (5) (2008) 664–669. [24] L. Dan, X. Younan, Direct fabrication of composite and ceramic hollow nano fibers by electrospinning, Nano Lett. 4 (5) (2004) 933–938. [25] W. Tao, S. Du-Cheng, Preparation and characterization of nanometer-scale powders ceria by electrochemical deposition method, Mater. Res. Bull. 43 (2008) 1754.

7

[26] L.D. Jadhav, M.G. Chourashiya, A.P. Jamale, A.U. Chavan, Synthesis and characterization of nano-crystalline Ce(1-x)Gd(x)O(2-x/2)(x=0-0.30) solid solutions, J. Alloys Comp. 506 (2010) 739–744. [27] S. Narottam, S. Apurba, P. Sandip, J. Muthirulandi, S. Balasubramanian, C.B. Hari, P. Asit Baran, Facile low-temperature synthesis of ceria and samariumdoped ceria nanoparticles and catalytic allylic oxidation of cyclohexene, J. Phys. Chem. C 11 (2011) 515. [28] J. Deshetti, M.T. Katie, J.I. Samuel, M.S. Ylias, T. James, K.B. Suresh, M.R. Benjaram, Structural characterization and catalytic evaluation of transition and rare earth metal doped ceria-based solid solutions for elemental mercury oxidation, RSC Adv. 3 (2013) 12963–12974. [29] C.B. Joseph, D.M. Paul, S. Paul, B. Paul, W.D. Charles, Nickel-doped ceria nanoparticles: the effect of annealing on room temperature ferromagnetism, Crystals 5 (3) (2015) 312–326. [30] D. Hari Prasad, S.Y. Park, H.I. Ji, H.R. Kim, J.W. Son, B.K. Kim, H.W. Lee, J.H. Lee, Structural characterization and catalytic activity of Ce0.65Zr0.25RE0.1O2
d nanocrystalline powders synthesized by the glycine-nitrate process, J. Phys. Chem. C 116 (2012) 3467–3476. [31] M.R. Benjaram, S. Pranjal, B. Pankaj, Y. Yusuke, K. Tetsuhiko, M. Martin, G. Wolfgang, Structural characterization and catalytic activity of nanosized Ceria–Terbia solid solutions, J. Phys. Chem. C 11 (2008) 242. [32] M. Bappaditya, M. Aparna, S. Sirsendu, K. Amar, Sm doped mesoporous CeO2 nanocrystals: aqueous solution-based surfactant assisted low temperature synthesis, characterization and their improved autocatalytic activity, Dalton Trans. 45 (2016) 1679–1692. [33] K. Gopalakrishnan, M. Elango, M. Thamilselvan, Optical studies on nanostructured conducting polyaniline prepared by chemical oxidation method, Arch. Phys. Res. 3 (4) (2012) 315–319. [34] A.A. Anees, M.A.M. Khan, M. Naziruddin Khan, A.A. Salman, M. Alhoshan, M.S. Alsalhi, Optical and electrical properties of electrochemically deposited polyaniline/CeO2 hybrid nanocomposite film, J. Semicond. 32 (2011) 043001. [35] B. Tatar, E.D. Sam, K. Kutlu, Synthesis and optical properties of CeO2 nanocrystalline films grown by pulsed electron beam deposition, J. Mater. Sci. 43 (2008) 5102. [36] P. Patsalas, S. Logothetidis, L. Sygellou, S. Kennou, Structure-dependent electronic properties of nanocrystalline cerium oxide films, Phys. Rev. B 68 (2003) 035104. [37] K.K. Babitha, A. Sreedevi, K.P. Priyanka, B. Sabu, T. Varghese, Structural characterization and optical studies of CeO2 nanoparticles synthesized by chemical precipitation, IJPAP 53 (9) (2015) 596–603. [38] B. Matteo, C. Silviu, G. Mathieu, S. Guy, Z. Marc, G. Pierre, D. Aziz, Photoluminescence properties of rare earth (Nd, Yb, Sm, Pr)-doped CeO2 pellets prepared by solid-state reaction, J. Mater. Chem. C 3 (2015) 7014–7021. [39] L. Bo, Y. Mingguang, L. Bingbing, L. Zepeng, L. Ran, L. Quanjun, L. Dongmei, Z. Bo, C. Tian, Z. Guangtian, L. Jing, C. Zhiqiang, High-pressure studies on CeO2 nano-octahedrons with a (111)-terminated surface, J. Phys. Chem. C 1 (2011) 15–111. [40] Y. Lai, Y. Ranbo, C. Jun, X. Xianran, Template-free hydrothermal synthesis of CeO2 nano-octahedrons and nanorods: investigation of the morphology evolution, Cryst. Growth Des. 8 (2008) 5. [41] A. Fazal, I. Javed, M. Qaisar, J. Tariq, O.U. Muhammad, N. Bushra, N. Mudassar, N. Haider, A. Ishaq, ROS. mediated malignancy cure performance of morphological, optical, and electrically tuned Sn doped CeO2 nanostructures, AIP Adv. 7 (2017) 095205. [42] A. Fazal, I. Javed, J. Tariq, B. Noor, M. Qaisar, I. Muhammad, Structural, morphological, Raman, optical, magnetic, and antibacterial characteristics of CeO2 nanostructures, Int. J. Miner. Metall. Mater. 23 (2016) 02. [43] S. Parvathy, B.R. Venkatraman, Synthesis and characterization of various metal ions doped CeO2 nanoparticles derived from the Azadirachta indica leaf extracts, Chem. Sci. Trans. 6 (4) (2017) 513–522. [44] Y.A. Syed Khadar, A. Balamurugan, V.P. Devarajan, R. Subramanian, S.D. Kumar, Synthesis, characterization and antibacterial activity of cobalt doped cerium oxide (CeO2: Co) nanoparticles by using hydrothermal method, J. Mater. Res. Technol 8 (2019) 267.

Please cite this article as: A. Balamurugan, M. Sudha, S. Surendhiran et al., Hydrothermal synthesis of samarium (Sm) doped cerium oxide (CeO2) nanoparticles: Characterization and antibacterial activity, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.217