Novel tri-phase heterostructured ZnO–Yb2O3–Pr2O3 nanocomposite; structural, optical, photocatalytic and antibacterial studies

Journal Pre-proof Novel tri-phase heterostructured ZnO–Yb2O3–Pr2O3 nanocomposite; structural, optical, photocatalytic and antibacterial studies Tauseef Munawar, Sadaf Yasmeen, Murtaza Hasan, Khalid Mahmood, Altaf Hussain, Adnan Ali, M.I. Arshad, Faisal Iqbal PII:

S0272-8842(20)30134-6

DOI:

https://doi.org/10.1016/j.ceramint.2020.01.130

Reference:

CERI 24062

To appear in:

Ceramics International

Received Date: 26 November 2019 Revised Date:

9 January 2020

Accepted Date: 14 January 2020

Please cite this article as: T. Munawar, S. Yasmeen, M. Hasan, K. Mahmood, A. Hussain, A. Ali, M.I. Arshad, F. Iqbal, Novel tri-phase heterostructured ZnO–Yb2O3–Pr2O3 nanocomposite; structural, optical, photocatalytic and antibacterial studies, Ceramics International (2020), doi: https:// doi.org/10.1016/j.ceramint.2020.01.130. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier Ltd.

Novel tri-phase heterostructured ZnO-Yb2O3-Pr2O3 nanocomposite; structural, optical, photocatalytic and antibacterial studies Tauseef Munawara, Sadaf Yasmeena, Khalid Mahmoodc, Altaf Hussaina, Adnan Alic, M. I. Arshadc, and Faisal Iqbala,* a

Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100,

Pakistan. b

Department of biochemistry & biotechnology, The Islamia University of Bahawalpur,

Bahawalpur 63100, Pakistan. c

Department of Physics, Government College University Faisalabad, Faisalabad 3800,

Pakistan. Corresponding authors: E-mail address: [email protected] (F. Iqbal*) Abstract Novel tri-phase ZnO-Yb2O3-Pr2O3 heterostructured nanocomposite was synthesized by the co-precipitation technique, and its application as an efficient antibacterial agent and photocatalyst were studied. The grown sample was characterized by XRD, FTIR, Raman, UV-vis, IV, and SEM to explore the structural, optical, electrical, and morphological properties. The XRD pattern revealed the presence of diffraction peaks related to ZnO (hexagonal), Yb2O3 (cubic) and Pr2O3 (hexagonal) in the nanocomposite. The microstructural parameters were calculated using Scherrer plot, W-H and SSP methods. The optical energy bandgap was 2.8 eV determined from UV-vis spectroscopy, specified that it could be used as a proficient photocatalyst under sunlight illumination. The FTIR spectrum confirmed the presence of characteristics vibrational bands associated with the Zn–O, Pr–O, and Yb–O bond vibrations at 463, 535 and 562 cm-1, respectively. The Raman spectrum exhibits the fundamental optical phonon modes related to ZnO, Yb2O3 and Pr2O3 in the nanocomposite, confirmed the successful formation of the nanocomposite. IV measurement showed the high electrical conductivity of grown nanocomposite. SEM images revealed that nanocomposite has a porous type morphology with high agglomeration. The antibacterial activity was performed against S. aureus (G-positive) and E. coli (G-negative) bacteria. The zone of inhibition (ZOI) shown that the nanocomposite has the highest activity against S. aureus with a ZOI 31 mm. The photocatalytic activity of the ZnO-Yb2O3-Pr2O3 nanocomposite was carried out for the degradation of MB dye under sunlight irradiation, revealed 99.8% degradation in 60 min. The effect of several operational parameters such as catalyst dose, dye

concentrations, pH of reaction along with reusability and radical trapping experiments were performed and discussed in detail. A possible schematic model was proposed to elaborate the photocatalytic mechanism. Furthermore, this work introduces a novel material to enhance the photocatalytic and antibacterial activity for environmental and biomedical application. Keywords:

Rare

earth

oxides;

Antibacterial

activity;

Photocatalytic

activity;

Microstructural parameters; spectroscopy; heterostructured. 1.

Introduction Nowadays, cumulative pollution in the environment or aquatic ecosystems due to

organic pigments and dyes is a frontline concern that provides impetus to continue research for water disinfection, air purification, and hazardous waste remediation [1,2]. Considerable amounts (~5–15%) of synthetic dyes are used in medical laboratories and industrial applications like textile, coloring, staining jute, paint, etc. have a diverse impact on the environment and public health due to their high toxicity [3]. The excess release of these toxic dyes in the wastewater is increasing carcinogenic effects on human life and the biosphere [4,5]. The industrial waste is exonerating causes the contamination of water due to heavy metals-ions released. Different researchers have been working to overcome the negative effect of these heavy-metals to clean the water [6–10]. Different techniques have been employed to eradicate and decompose these organic contaminants such as photocatalytic activity, biological treatment, chemical oxidation routs, advanced oxidation procedures, and adsorption, etc. [11]. In this regard, the solar photocatalytic technology [12] is considered to be an efficient approach for relieving the negative environmental influence of organic pollutants and hazardous water wastes in aquatic ecologies by the reduction of CO2 gas, and production of H2 and O2 gases by water splitting. This technique is more effective due to its eco-friendly characteristics and green processability [13]. Developing the nanomaterials by using metal oxides based materials to eliminate organic pollutants from toxin water and controlling infectious diseases are the most popular fields for the research community [3,14,15]. Among different metal oxides (NiO, CdO, SnO2, and TiO2), ZnO is a prominent material for photocatalytic and antibacterial applications because of its low-cost, high biocompatibility, low toxicity, and eco-friendly characteristics. Zinc oxide (ZnO) is a technologically resourceful material due to its distinct electronic, chemical, electrical and optical properties. Zinc oxide (ZnO) is an n-type semiconductor with

wide direct bandgap 3.37 eV, elevated 60 meV exciton binding energy, high piezoelectric constant, and high chemical stability [16,17]. These fascinating properties are made it a promising material for extensive applications such as chemical sensors, pollution treatment, ultraviolet light-emitting diodes, photodetectors, short-wavelength (UV, blue, green) optoelectronic devices, and biological medicine [18]. The main hindrances of ZnO are the wide direct bandgap and fast recombination rate of photoinduced charge carriers, which hampers their pervasive practical applications and limits its response only to UV light (4% in solar energy as compared to visible light 43% in the solar spectrum) [19]. This may also reduce the reactive oxygen species (ROS) generation efficiency and limits its antibacterial application. To subsist with these constraints, influential methods have been adopted such as tuning the energy bandgap, coupling two or more semiconductors, mono-doping, co-doping, and dual-doping to enhance photo-response of ZnO for better use of full solar spectrum and ROS generation [20,21]. Among these strategies, the coupling of ZnO with other functional materials (having a different energy bandgap) into one system to form a heterojunction has gained much attention for enhancing its absorption in visible-light spectral region and improve quantum efficiency to achieve stable structural, optical, photocatalytic, and antibacterial properties [15,22–24]. The existence of a double heterojunction interface in the mixed metal oxides influences strongly the overall properties of the material by increasing carrier lifetime, charge separation efficiency and charge transferability due to suitable bandgap positions [25,26]. Currently, rare earth oxides (REOs) have attracted remarkable attention to new research community due to their potential applications such as heterogeneous catalysis, biosensors, antibacterial agent, rechargeable batteries, fuel cells, and computer devices [27– 32]. The REOs are the most thermally stable compounds and their different oxidation states lead to high catalytic properties [32]. Among various REOs, the Yb2O3 and Pr2O3 have widely attracted for their unique photocatalytic, chemical, antibacterial, electrical, optical and electronics properties which made them suitable for the fabrication of photocatalysts, dyesensitized solar cell, antibacterial agent, gas sensor, supercapacitors, optoelectronic devices, non-volatile memory and other several applications [33–37]. Nanocomposites of ZnO with rare earth oxides (REOs) have recently been fabricated to enhance the photocatalytic and antibacterial activity, also to obtain new properties that do not exist in pure oxides nanostructure. M.M.Rahman et al. [38] fabricated ZnO/Yb2O3 sensor

for 4-aminophenol having superior sensitivity 5.063 µAµM-1cm-2. N. Baranov et al. [39] prepared ZnO/Yb2O3 nanocomposite for energy transfer luminescence and have reported excellent results for solar cells. Arunachalam et al. [40] have synthesized Nd2O3/ZnO-GO nanocomposite and reported 98.7% and 99.2% degradation of CIP and MB dye in 60 and 35 min, respectively under UV- light irradiation. M.A. Subhan et al. [41] have prepared La2O3.Fe3O4.ZnO and La2O3.AgO.ZnO nanocomposites and gained maximum degradation efficiency for methyl violet (MV) dye under visible light. K. Byrappa et al. [12] have reported photocatalytic performance of Bi2O3–CeO2–ZnO photocatalyst for photodegradation of RhB dye under sunlight irradiations and achieved 97% degradation efficiency. M.A. Subhan et al. [42,43] have synthesized NiO-CeO2-ZnO and CeO2-CuO-ZnO nanocomposites and studied their antibacterial and photocatalytic activities. Some other reports regarding application of nanocomposite as a sensor fabricated by different methods such as ZnO/Ag2O/Co3O4 [44], ZnO/CuO/Co3O4 [45], Ag2O@La2O3 [46], Co3O4@Er2O3 [47], (E)N′-(2-Nitrobenzylidene)-benzenesulfonohydrazide [48] for detection of uric acid, selective melamine, 3-methoxyanaline, 4-Hexylresorcinol, and arsenic sensor, respectively for environmental safety are also attracted much attention. These studies have revealed that nanocomposites have enhanced sensing ability towards organic pollutants compared to single-phase materials [49–52]. To the best of author knowledge, there is no report available on rare earth metal oxides based tri-phase ZnO-Yb2O3-Pr2O3 nanocomposite for photocatalytic and antibacterial application. In this context, we have fabricated a novel ZnO-Yb2O3-Pr2O3 heterojunction photocatalyst for the first time to explore the photocatalytic and antibacterial application along with structural and optical properties. The different techniques are used to fabricate the multi-metal oxides based nanocomposites such as co-precipitation, sol-gel, solid-state reaction, hydrothermal, solvothermal, wet chemical, micro-emulsion, and microwave-assisted technique, etc. Among the above mention techniques, the co-precipitation method is used in the synthesis of nanocomposite because it is simple, efficient, required low growth temperature, eco-friendly, and economical method. In this study, synthesis, photocatalytic and antibacterial activity of a novel ZnOYb2O3-Pr2O3 nanocomposite was carried out. The structural, optical, electrical and morphological properties were studied using XRD, FTIR, Raman, UV–vis, I-V and SEM. The X-ray peak profile analysis was carried out to calculate the average crystallite size (D)

more accurately by considering the contributions of lattice strain effects on the peak broadening using Scherrer, W–H and SSP methods. The photocatalytic activity of the grown sample was evaluated for methylene blue (MB) dye under sunlight irradiation and the antibacterial activity was carried out against S. aureus (G-positive) and E. coli (G-negative) bacteria at different concentrations of the grown nanocomposite. The effect of several operational factors such as catalyst dose, dye concentrations, and pH of reaction along with reusability and radical trapping experiments (EDTA-2Na, AgNO3, DMSO, and ASC) were also performed and discussed in detail. A possible schematic model was also proposed to elaborate on the photocatalytic mechanism of the ZnO-Yb2O3-Pr2O3 heterojunction photocatalyst based on energy band alignment and optical characterization. Furthermore, this work introduces a novel material to enhance the photocatalytic performance and antibacterial activity for the degradation of organic pollutants from industrial/domestic wastewater and treatment against pathogenic bacteria. 2.

Experimental procedure

2.1

Materials In

this

experiment,

nitrates

salts

of

zinc

(Zn(NO3)2.6H2O),

ytterbium

(Yb(NO3)3.6H2O), and praseodymium (Pr(NO3)3.6H2O) were used as a starting material. The sodium hydroxide (NaOH) was used as a precipitating agent, ethanol (C2H5OH) for washing and methylene blue (MB) dye as an organic pollutant. The ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), silver nitrate (AgNO3), dimethyl sulfoxide (DMSO), and ascorbic acid (ASC) were used as scavengers. All reagents from commercial source Sigma Aldrich (99.0% purity) and used without further treatments. 2.2

Synthesis of ZnO-Pr2O2-Yb2O3 nanocomposite photocatalyst In a typical synthesis of the ZnO-Pr2O2-Yb2O3 nanocomposite, an appropriate amount

of Zn salt together with Yb and Pr having equal mole ratio were dissolved in distilled water (100 ml). The precursor’s solution was stirred for 30 min at ambient temperature to form a homogenous solution. Afterward, aqueous NaOH solution of 0.1 M was dropwise added into the former solution to achieve pH 9. The mixed solution was kept stirred for 3 h at room temperature until precipitates were formed. The resulting precipitates were repeatedly washed with water and ethanol to remove the unwanted ions and filtered. The obtained precipitates were dried in an oven at 100oC for 2h. Finally, the dried precipitates were collected, grinded

and annealed at 750oC in an air atmosphere for 2 h in a Muffle furnace. The synthesis procedure is schematically summarized in the scheme. 1. 2.3

Photocatalytic degradation experiment The photocatalytic performance of as-synthesized nanocomposite was evaluated by

monitoring the photodegradation of methylene blue (MB) dye under sunlight irradiation. In a typical experiment, an initial dose of as-prepared catalyst powder 25 mg (conc. 0.5 g/L) was dispersed in 50 ml aqueous solution of MB at initial pH = 5 and concentration 6 mg L-1. Before the light irradiation, the catalyst with dye solution was strongly magnetically stirred (600 rotation/min) in complete darkness for an hour under ambient condition to accomplish an adsorption/desorption equilibrium of dye on the catalyst’s surface; then 5 ml solution was withdrawn as an initial concentration (Co) and exposed to sunlight illumination. After exposure to sunlight, the reaction mixture was stirred and 5 ml suspension was collected after every 15 min (consecutive intervals) to evaluate the photodegradation percentage of MB dye. All the extracted suspensions were centrifuged (6000 rpm for 15 min) to remove suspended catalyst particles. Temporal concentration variations of MB was examined by the change in the maximal absorption peaks of dye in the UV-vis spectra. For comparison, photodegradation experiment was carried out for different dosage of catalyst (0.5 g/L, 1 g/L, and 1.5 g/L), different concentrations of dye (6, 8 and 10 mg/L) and at different solution pH (5, 7, and 9). The controlled scavenger’s experiments were also carried out using reactive species (scavengers) such as EDTA-2Na (h+ scavenger), DMSO (hydroxyl radicals HO*), AgNO3 (e− scavenger), and ASC (superoxide radicals O2*-) to study the mechanistic pathway of photodegradation of MB by ZnO-Yb2O3-Pr2O3 photocatalyst. The degradation efficiency (η) is calculated by using the equation [26]: Degradation efficiency ( ) = [(

˗

)/

] × 100%

(1)

Where Co = initial concentration of dyes when adsorption-desorption equilibrium is achieved and Ct = final concentration of dyes in the presence of photocatalyst under sunlight. 2.4

Antibacterial test The antimicrobial activity of the grown ZnO-Yb2O3-Pr2O3 nanocomposite was

evaluated for both gram-positive and gram-negative bacteria namely Staphylococcus aureus and Escherichia coli using disc diffusion method. The bacterial cultures were swabbed in

nutrient agar (5.6g/200ml) amended plates. The grown nanocomposite was dissolved separately in sterile distilled water (1mg/mL) and Whatmann filter paper discs (5 mm diameter), impregnated with a solution at different concentrations (10, 20 and 40 µg/mL). The discs were smeared on bacterial plates and incubated overnight at 37oC. After incubation, the zones of inhibition (ZOI) were measured. 2.5

Characterization The structural, optical, electrical and morphological analysis was carried out by XRD

(Bruker D8 Advance laboratory diffractometer, CuKα radiation (λ = 1.5406 Å), operated at 40 kV/35 mA), FTIR (Bruker Tensor 27 Fourier Transform Infrared Spectrometer), Raman (Confocal micro-Raman), UV-vis (Cary 60 Agilent Technologies), IV (Keithley picometer 6487) and SEM (Emcrafts cube 2020) [26]. 3.

Results and discussion

3.1

X-ray analysis Fig. 1(a) shows the XRD diffraction pattern of as-prepared ZnO˗Yb2O3-Pr2O3

nanocomposite annealed at 750°C. All observed diffraction peaks are well indexed to ZnO hexagonal wurtzite structure (space group: P63mc), Yb2O3 cubic structure (space group: la-3) and Pr2O3 hexagonal structure (space group: P-3m1), confirmed the formation of the nanocomposite. The characteristic diffraction peaks of ZnO, Yb2O3 and Pr2O3 are well resolved and no peak relating to impurity/secondary phases or hydroxide could be identified which indicates that grown nanocomposite has high purity and crystallinity. The XRD results confirmed the successful synthesis of heterostructured material (ZnO-Yb2O3-Pr2O3) by the facile co-precipitation method at room temperature. The diffraction peaks of ZnO, Yb2O3 and Pr2O3 along with reflection planes are illustrated in Fig. 1 (a), well consistent with JCPDS card No. 01-079-2205, 00-043-1037, and 00-047-1111, respectively. Lattice constants (a, c), unit cell volume (v), and d-spacing for ZnO hexagonal, Yb2O3 cubic and Pr2O3 hexagonal structure [26] for grown nanocomposite were calculated and listed in Table 1. The quantitative data related to the orientation of the crystallites of ZnO, Yb2O3, and Pr2O3 in grown nanocomposite and the prevalence of (hkl) planes can be attained from the texture coefficient (TC(hkl)) values of the prominent diffraction peaks. The texture coefficient (TC(hkl)) values were calculated using the following relation [53]:

(

)

)⁄

(

=

(

(

)

) (

)

(2)

Where, I(hkl) = peak intensity from XRD, Io (hkl) = standard intensity and N = number of measured diffraction peaks. The variation in TC(hkl) values for different planes of ZnO, Yb2O3, and Pr2O3 are presented in Fig. 1 (b). It is known TC(hkl) >1 implies that the growth of the crystallites occurs in a definite preferred orientation. TC(hkl) for ZnO, Yb2O3 and Pr2O3 is high (>1) for (002), (622) and (200) planes respectively as compared to other planes indicate that preferred growth orientation, also suggesting an increased number of grains along that plane. The change in crystallite size, as well as strain, can affect the orientation of the crystallites. The peak broadening arises from crystallite size (D) and lattice strain (ε) in X-ray diffraction. The crystallite size contribution calculated from Scherrer’s formula [54]: =#

!"

(3)

$ %&'(

And the contribution of microstrain is given by: )' = 4+ ,-.

(4)

Where, D = the size of crystalline domains, λ = X-ray wavelength, k = 0.94 (shape factor), βD = full width of the angular peak at half maximum associated with instrument broadening, βs = full width of the angular peak at half maximum connected to line broadening and θ = measured Bragg’s angle. Rearrange equation (3) =#

!"

$ %&'(

=> 0 1. =

!" 2

3

#$

(5)

In the Scherrer plot method, the graphs were drawn between 1/βD and cosθ. The crystallite size D was calculated using the slope of the fitted line (see Fig. 2(a)). The contributions of strain and crystallite size can provide total peak broadening given as: )

= )2 + )'

(6)

For Williamson-Hall analysis, the observed peak broadening is the sum of the equation (3) and (4) given as: ) By rearranging equation (7)

"

= 2 567 ( + 4+ ,-.

(7)

)

cos . =

"

2

+ 4+1;-.

(8)

Equation (8) represents the uniform deformation model (UDM), considering the strain to be uniform in all crystallographic directions. By plotting βhklcosθ and 4sinθ (see Fig. 2(b)), the crystallite size and strain were extracted from the y-intercept and slope of linearly fitted data, respectively. The size–strain plot gives a good approximation of size–strain parameters by supposing that crystallite size and strain profile are followed the Lorentzian function and Gaussian function, respectively given as: (<

)

cos .)= =

2

<= )

cos . +

>



=

=

(9) Where K = constant having value 3/4 for spherical particles. By plotting d2hklβhkl cosθ on the x-axis and (dhklβhklcosθ)2 on the y-axis (Fig. 2(c)), the particle size was extracted from slope and strain from the intercept of linearly fitted data [26]. The results obtained from W–H, Scherrer and Size-Strain Plot methods are listed in Table 2. The measured values of D for Pr2O3 were higher as compared to Yb2O3 and ZnO, exhibits better crystalline growth in the nanocomposite. The dislocation density ‘δ’ is measured using relation δ = 1/D2 and calculated values are summarized in Table 2. It gives information about the number of vacancies and defects in the crystal and has a higher value for ZnO in the nanocomposite. The positive values of lattice strain obtained from W–H and SSP methods are implied that ZnO, Yb2O3 and Pr2O3 lattice may have tensile strain. The variation in micro-strain is due to the change in crystallite size, morphology, and shape of grown nanoparticles. The small difference in the values calculated from all the methods could be due to variance in averaging the particle size distribution. By examining all the above methods, the results of SSP were more precise (see Fig. 2(c)). 3.2

FTIR analysis FTIR spectroscopy was used to investigate the chemical composition and functional

groups of grown nanocomposites. FTIR spectrum of ZnO˗Yb2O3-Pr2O3 nanocomposite (4004000 cm-1) is presented in Fig. 3(a). From the spectra, the characteristics vibrational bands positioned at 463, 535 and 562 cm-1 are associated with the Zn–O and Pr–O, and Yb–O bond vibrations (Fig. 3(a), insert) [53,55,56]. The vibrational band observed at 627 cm-1 was due to M–O–M (M = Zn, Yb or Pr) lattice vibrations. The additional band observed at 2350 cm-1 was due to the existence of CO2 from the air [57]. The presence of characteristic peaks

related to the Zn–O, Yb–O and Pr–O bonds vibrations are further confirmed the formation of ZnO˗Yb2O3-Pr2O3 nanocomposite. 3.3

Raman analysis Raman spectroscopy is a useful technique to examine the microstructural properties of

the materials. The Raman spectra of ZnO˗Yb2O3-Pr2O3 nanocomposite in the range of 501000 cm-1 is depicted in Fig. 3(b). The observed peaks at 430.19, 533.98. 588.94, 643.45, 710.07, 786.66, and 972.29 cm-1 are due to the ZnO phase [58] while peaks at 294.39, 370.17, and 610.79 cm-1 related to the Yb2O3 phase [59] and 116.99, 321.01, and 385.22 cm-1 attributed to the Pr2O3 phase [59] in the nanocomposite. The existence of fundamental optical phonon modes of ZnO, Yb2O3 and Pr2O3 in nanocomposite have further confirmed the successful formation of ZnO˗Yb2O3-Pr2O3 nanocomposite, consistent with FTIR results. The change in intensity of observed bands is due to local lattice distortions and structural defects induced due to the interaction of three kinds of oxides that can help the confinement of photoinduced electrons and hinder the electron/hole recombination, aids the photocatalytic process. 3.4

Current-voltage (I-V) measurements Fig. 3(c) shows the room temperature I-V characteristic curve of grown ZnO˗Yb2O3-

Pr2O3 nanocomposite. It can be seen that nanocomposite has ohmic nature. The electrical conductivity (σ) was calculated by equation [26]: ? = @ × A⁄B × C

(10)

Where I = current, V = applied voltage, L = the thickness of the pellet and A = the cross-sectional area of the pellet. The electrical resistivity (ρ) was calculated by using the relation: ρ = 1/σ. The result showed that ZnO˗Yb2O3-Pr2O3 nanocomposite has higher electrical conductivity (1.94 mho-cm-1) and lower resistivity (5.16×10-1Ω cm). The higher value of electrical conductivity is suggesting that it can be used as a high-performance material for photocatalytic as well as gas sensing applications. 3.5

Optical analysis The optical properties of grown nanocomposite were determined by using UV-vis

spectroscopy. Fig. 3(d) illustrates the absorption spectrum of ZnO˗Yb2O3-Pr2O3 nanocomposite in the wavelength range of 200-700 nm. The ZnO˗Yb2O3-Pr2O3 nanocomposite has broad absorption onsets at 370 nm (3.35 eV) and 570 nm (2.18 eV). The

absorption peaks in UV- visible region were due to scattering from ZnO or Yb2O3 or Pr2O3 phase, suggested that grown nanocomposite is sensitive for both UV and visible light. The optical bandgap (Eg) was estimated using Tauc’s relation [54] given as DℎF = D& (ℎF − HI )J , where, hν, α, αo and n are photon energy, absorption coefficient, the band tailing parameter and power factor respectively. The value of n is 1/2 for direct bandgap materials corresponding to the nature of the electronic transition. The absorption coefficient (α) was determined using Beer-Lambert relation, α = 2.303A/d, where A = absorbance and d = the thickness of cuvette. By plotting (αhν)2 on the y-axis and hν on the x-axis and extrapolating linear portion on the energy axis (Fig. 3(d) insert) the value of Eg was obtained. The ZnO˗Yb2O3-Pr2O3 nanocomposite has a direct bandgap of 2.8 eV. The energy bandgap in the visible-region suggested that ZnO˗Yb2O3-Pr2O3 nanocomposite can response to UV-visible light of the solar spectrum which indicates that the grown nanocomposite has potential application in the fields of optoelectronics, photovoltaics, and photocatalysis. 3.6

SEM analysis The surface morphology of ZnO-Yb2O3-Pr2O3 nanocomposite annealed at 750°C is

presented in Fig. 4. The SEM micrographs showed the loosely packed large aggregate of nanoparticles with network type porous morphologies. The high surface area and porous like superstructure with a high rate of agglomeration has a great impact on the photocatalytic and antibacterial properties. 3.7.

Photocatalytic activity The model reaction for MB photodegradation was carried out to assess the

photocatalytic performance of ZnO-Yb2O3-Pr2O3 .nanocomposite under sunlight irradiation. The absorption spectra of the MB solution with photocatalyst at different time intervals are shown in Fig. 5(a). From the photodegradation curves of Fig. 5(b) it can be observed that the degradation efficiency of catalysts toward methylene blue after 60 min sunlight irradiation is 90.0%. Besides this, in order to understand the kinetics of photodegradation reactions of dye quantitatively, a kinetic study was carried out by employing the pseudo-first-order kinetic model [26]: K

=

=> N-(

&L

M K

&⁄ K)

=O

(11) (12)

Here, k is the first-order rate constant. The plot of ln(Co/Ct) versus irradiation time (t) gives the straight line and the linear relationship is shown in Fig. 5(c), the slope of the straight-line gives the value of k. This specifies that photocatalytic degradation of MB dye follows pseudo-first-order kinetics model. The calculated value of the rate constant is 0.03736 min-1. The rate constant of the catalyst increases with the increase in irradiation time, indicating that ZnO-Yb2O3-Pr2O3 nanocomposite is an excellent photocatalyst under sunlight. The feasible aspects accountable for considerable enhancement in sunlight driven photocatalytic activity of synthesized ZnO-Yb2O3-Pr2O3 catalyst includes: (i) The higher absorbance in the visible region and lower energy bandgap as evidenced from UV-visible absorption spectra (Fig. 3(d)) may facilitate excitation of the electron from VB to CB, result in enhance photo-degradation; (ii) The existence of heterojunction in ZnO-Yb2O3-Pr2O3 catalyst may cause interface charge transmission easier, quick and effective separation of electron-hole (e-/h+) pairs (as suggested in Fig. 9) leads to higher degradation efficiency; (iii) The enhanced electrical conductivity of grown nanocomposite can stimulate the separation of the photo-excited electron−hole pairs to act as the donor like center and retard their recombination, thus more holes are permitted to contribute in the catalytic reaction and thereby have improved photocatalytic activity. 3.7.1.

Effect of photocatalyst concentration The effect of the photocatalyst dose on the photodegradation rate of MB dye was

examined by taking a different amount of ZnO-Yb2O3-Pr2O3 nanocomposite (0.5–1.5 g/L) under similar reaction condition (MB dye conc. 6 mg/L). The degradation efficiency with ZnO-Yb2O3-Pr2O3 catalyst concentration of 0.5, 1 and 1.5 g/L are 90%, 95% and 87%, respectively (Fig. 5(b)). The rate constants (k) for degradation of MB dye obeys the pseudofirst-order kinetic model and are 0.03736, 0.04971 and 0.03303 min-1 (Fig. 5(d)) at a catalyst concentration of 0.5, 1 and 1.5 g/L, respectively. The results specify that the degradation efficiency increase with the increase in catalyst amount up to 1 g/L and thereafter decreased. The increment in degradation efficiency is due to the more accessibility of active sites or surface area of the photocatalyst. Contrary, at a higher dosage, the solution becomes opaque and hazy which may decrease the light penetration and increases scattering from the photocatalyst surface, causing a reduction in degradation efficiency. The above results suggested that optimum value for maximum loading of the photocatalyst is 1 g/L and was used in subsequent experiments.

3.7.2.

Effect of initial dye concentration The effect of MB dye concentration on the photocatalytic performance of ZnO-

Yb2O3-Pr2O3 nanocomposite was examined by varying concentrations of dye solution from 6 mg/L to 10 mg/L using 1 g/L of photocatalyst under the sunlight irradiation. Fig. 6(a) shows the photodegradation efficiency of grown photocatalyst against different concentrations of MB dye solution at similar reaction conditions. After 60 min of irradiation, 95%, 91%, and 86% for 6, 8, and 10 mg/L of the MB solution were degraded, respectively. The decolorization of MB obeys the pseudo-first-order kinetics model with rate constants (k) 0.04971, 0.04031, and 0.03532 min-1 (Fig. 6(b)) for dye concentrations of 6, 8, and 10 mg/ L, respectively. The decrement in photodegradation efficiency or rate constant may be due to fact that more dye molecules adsorb on photocatalyst’s surface that caused the reduction of path-length or light intensity entering the solution, resulted in lower no. of photons adsorbed on photocatalyst and alternatively decreased photocatalytic activity. 3.7.3. Effect of pH The solution basicity or acidity is an essential factor for the adsorption process and related to the variation of the photocatalyst surface charge [60–62]. The influence of pH on photodegradation efficiency was investigated by changing the pH of the solution from 5-9 using aqueous NaOH solution with experimental conditions (catalyst = 1 g/L, Dye = 6 m/L). Fig. 6(c) shows the photodegradation of MB at different pH (5, 7 and 9) under sunlight irradiation. After 60 min of irradiation, 95%, 97%, and 99.8% of MB dye were degraded at pH 5, 7 and 9, respectively. The decolorization of MB obeys the pseudo-first-order kinetics model with rate constants (k) 0.004971, 0.06192, and 0.07368 min_1 (Fig. 6(d)) at pH 5, 7 and 9, respectively. It is observed that the degradation of MB increased with the increase of pH. Above pH 7 or in the basic medium the adsorption of a dye molecule was less due to the deprotonation of catalyst surface and alternatively increase negatively charged sites [63]. The higher degradation efficiency in the basic medium is due to higher electrostatic attraction among the +ive charged MB and -ive charged photocatalyst. 3.7.4. Active species responsible for MB degradation The controlled scavenger’s experiments were performed to examine the mechanistic pathway of photodegradation of MB in the presence of ZnO-Yb2O3-Pr2O3 catalyst. The different reactive species (scavengers) such as EDTA-2Na (h+ scavenger), DMSO (hydroxyl radicals HO*), AgNO3 (e− scavenger), ASC (superoxide radicals O2*-) were added (1mM) in

reaction system under the condition (catalyst = 1 g/L, Dye = 6 m/L and pH = 9) and obtained results are presented in Fig. 7(a). The photodegradation of MB was affectedly suppressed by the addition of EDTA-2Na, DMSO, AgNO3, ASC with degradation efficiencies 79%, 40%, 85%, and 44% respectively. It can be seen that photodegradation is quenched by the addition of DMSO and ASC as compared to EDTA-2Na and AgNO3, suggesting that both HO* and O2*- radicals are the main reactive species in the photodegradation process of ZnO-Yb2O3Pr2O3 photocatalyst. 3.7.5. Reusability of the catalyst The reusability of the ZnO-Yb2O3-Pr2O3 catalyst was tested by repeating the photodegradation process for MB dye under the same reaction conditions (catalyst = 1 g/L, Dye = 6 m/L and pH = 9). After completing each cycle, the photocatalyst was washed with distilled water, separated by centrifugation, dried at 100oC for 60 min in an oven and reused for a next cycle. Fig. 8(a) displays the photodegradation efficiencies of the grown photocatalyst in six test runs are 99.8%, 98%, 98%, 97%, 97%, and 96%, respectively, after 60 min of sunlight exposure. In order to investigate the structural variation in the photocatalyst after six cycles of reuse, XRD was carried out. The XRD spectra of ZnOYb2O3-Pr2O3 photocatalyst after six cycles used along with fresh are shown in Fig. 8(b). From XRD analysis of the catalyst it was observed that after six cycles, the basic crystal structure of the nanocomposite is remained unchanged which suggests that the grown photocatalyst has excellent reusability, stability, oxidative resistance and can effectively use for the degradation of synthetic/organic dyes. 3.7.6

Photodegradation mechanism In order to understand the mechanism of photocatalytic degradation, a model

suggested by Lei et al. [23] and A. Hezam et al. [64] was used, also discussed in the previous report [26]. Based on this model, it is assumed that ZnO, Yb2O3 and Pr2O3 are adjacent to each other and built double heterojunction. The band edge potentials (EVB and ECB) of ZnO, Yb2O3 and Pr2O3 at the zero point charge were calculated using equations: HPQ = R − HS − 0.5HI

(13)

HVQ = HPQ + HI

(14)

Where, X refers to electronegativity of semiconductor (X = 5.79 eV for ZnO, 5.47 eV for Yb2O3 and 5.19 eV for Pr2O3 [65]), Ee is the free electron energy on the hydrogen scale (about 4.5 eV) and Eg is the optical bandgap of ZnO, Yb2O3 and Pr2O3 3.37 eV, 4.9 eV and 3.9 eV respectively, as reported in literature [65]. Based on the above data, a schematic model is proposed for heterostructured photocatalyst as shown in Fig. 9. The EVB and ECB values calculated from the equation (13, 14) were 2.975 eV and -0.395 eV for ZnO, 3.42 eV and -1.48 eV for Yb2O3 and 2.64 eV and -1.26 eV for Pr2O3, respectively. Under sunlight irradiation, ZnO, Yb2O3 and Pr2O3 were excited and simultaneously create photo-generated e−/h+ pairs (Eq. 15-17). The electron-hole pairs can move to the surface of photocatalyst and involved in redox reactions. Generally, these photo-generated e−/h+ pairs rapidly recombine and only a segment of charges could contribute to the photocatalytic process. However, when ZnO, Yb2O3, and Pr2O3 are in contact with each other in nanocomposite double heterojunctions built up and photo-generated electrons (e−) from CB of Yb2O3 can easily transfer to the CB of ZnO via an interface of Pr2O3. This is due to the reason that the CB position of Yb2O3 is more negative than Pr2O3 while the CB of Pr2O3 is more negative than ZnO. The electrons (e-) react with molecular oxygen (O2) and produce less toxic superoxide anion radicals (O2*-) through the reductive process (Eq. 18). Simultaneously, holes (h+) tend to shift from VB of ZnO to VB of Pr2O3, as the VB of ZnO is more positive than Pr2O3, also the holes in the VB of Pr2O3 cannot move to VB of Yb2O3 because the VB of Pr2O3 is less positive than Yb2O3. Finally, the reactive holes (h+) at the valence band (VB) of Yb2O3 directly react with dye molecules (Eq. 19) while the holes (h+) at the valence band (VB) of ZnO react with hydroxide ions or water to produce hydroxyl radicals (OH*) through the oxidative process (Eq. 20-21). During the photocatalytic process, the hydroxyl radicals (OH*) and superoxide anion radicals (O2*-) are known to be the strong oxidizing agents, react with organic pollutants (Eq. 22-23) and break their chemical bond structure resulting in intermediate compounds that transform and eventually decompose to green compounds such as mineral acids, CO2 and H2O. The more OH* and O2*- radicals are formed, the more dye will be degraded as consistent with species trapping experiments. The presence of double heterojunction in ZnO-Yb2O3-Pr2O3 photocatalyst has resulted in efficient e−/h+ pairs separation, effects the charge transfer kinetics among ZnO, Yb2O3 and Pr2O3, and inhibited the recombination by prolonging the lifetime of charge carriers, thus lead to enhance photocatalytic activity. The comparison of ZnO-Yb2O3-Pr2O3 photocatalyst for degradation of MB dye with some other metal oxide nanocomposite is presented in Table 3

which clearly demonstrated that the degradation efficiency of grown material is greater for the same period of time. The reactions mechanism in the heterostructured ZnO-CeO2-Yb2O3 photocatalyst for the degradation of MB dye is given below. WX= YZ + ℎF → L M (WX= YZ ) + ℎ\ (WX= YZ )

(15)

]^= YZ + ℎF → L M ( LY= ) + ℎ\ ( LY= )

(16)

_-Y + ℎF → L M (_-Y) + ℎ\ (_-Y)

(17)

L M (_-Y) + Y= → Y=∗M

(18)

ℎ\ (WX= YZ ) + aL → Lb^,<, ; - c^
(20)

ℎ\ (_-Y) + OH M → ZnO + OH ∗

(21)

Y=∗M + aL → Lb^,<, ; - c^
(19)

(22) (23)

Antibacterial activities

The antibacterial activity of as-synthesized ZnO-Yb2O3-Pr2O3 nanocomposite was carried out against the human pathogenic bacteria like Staphylococcus aureus and Escherichia coli. The zone of inhibition (ZOI) is shown in Fig. 10 and the values of the antibacterial activity are summarized in Table 4. It is well-recognized that if ZOI diameter is higher than 6 mm, the materials have good antibacterial activity and if ≤ 6 mm then have poor antibacterial activity. It is noteworthy to mention that grown nanocomposite exhibited superior activity against S. aureus and E.coli bacterial strain (Fig. 10(a, b)) but has the highest antibacterial activity against S. aureus with a zone of inhibition 31 mm. The comparison of the antibacterial activity of ZnO-Yb2O3-Pr2O3 nanocomposite with some other metal oxide nanocomposite is presented in Table 5, revealed that the grown nanocomposite has superior antibacterial activity. As the S. aureus bacteria mainly causes skin diseases such as pimples, impetigo, boils, cellulitis, folliculitis, and carbuncles, etc., hence the synthesized nanocomposite can be used in the treatment of these diseases. The small crystallite size (XRD analysis) and larger surface area (SEM images) may generally cause the higher production rate of ROS species also facilitate the mass transportation and diffusion of reactant molecules. The high ability to produce ROS species such as hydroxyl radical, superoxide radical and hydrogen peroxide

that can cause destruction of cellular proteins and DNA or may cause the death of the cell. The generated hydrogen peroxide can interact with cell walls cause to rupture or deformation of the cell membrane by penetrating and kills the bacteria may also inhibit cell growth. The above results suggested that in the near future fabrication of ZnO and REOs based nanocomposite for biomedical applications are conceivable.

4. Conclusion In summary, the ZnO-Yb2O3-Pr2O3 photocatalyst was successfully prepared via the coprecipitation method followed by annealing at 750oC. Peak broadening analysis was used to calculate crystallite size and micro-strain. The FTIR confirmed the existence of Zn-O, Pr-O and Yb-O vibrational modes at 463, 535 and 562 cm-1, respectively. Raman spectra demonstrate the presence of optical phonon modes of ZnO, Yb2O3 and Pr2O3 in photocatalyst. The optical energy bandgap value determined from UV-vis spectra by Tauc’s plot was 2.8 eV which indicates the grown nanocomposite is an efficient photocatalyst for sunlight. The IV measurements revealed higher electrical conductivity. SEM images show the porous type morphology of nanocomposite with high agglomeration. The grown nanocomposite acted as a good antibacterial agent towards S. aureus (G-positive) and E. coli (G-negative) bacteria. Moreover, the highest antibacterial activity against S. aureus with a zone of inhibition 31 mm suggested that the grown nanocomposite is an excellent antibacterial agent. The photodegradation of MB solution under the sunlight illumination by ZnO-Yb2O3-Pr2O3 photocatalyst at different catalyst loading, dye concentrations, and pH of solution ascribed that 1 g/L catalyst, 6 mg/L dye and pH 9 exhibits the highest photocatalytic activity for the same duration of time. The reactive species trapping experiments (EDTA2Na, AgNO3, DMSO, and ASC) revealed that the OH* and O2*- radicals are the major active species for the photodegradation of MB. The recyclability test has shown that the grown nanocomposite has excellent stability and reusability up to the 6th cycles. Thus, this work introduces an innovative route of potential applications of tri-phase heterostructured ZnOYb2O3-Pr2O3 nanocomposite for optical, environmental, and biomedical fields.

References: [1]

C. Santhosh, V. Velmurugan, G. Jacob, S.K. Jeong, A.N. Grace, A. Bhatnagar, Role of nanomaterials in water treatment applications: A review, Chem. Eng. J. 306 (2016) 1116–1137. doi:10.1016/j.cej.2016.08.053.

[2]

M. Elimelech, W.A. Phillip, The future of seawater desalination: Energy, technology, and the environment, Science (80). 333 (2011) 712–717. doi:10.1126/science.1200488.

[3]

S. Steplin Paul Selvin, A. Ganesh Kumar, L. Sarala, R. Rajaram, A. Sathiyan, J. Princy Merlin, I. Sharmila Lydia, Photocatalytic Degradation of Rhodamine B Using Zinc Oxide Activated Charcoal Polyaniline Nanocomposite and Its Survival Assessment Using Aquatic Animal Model, ACS Sustain. Chem. Eng. 6 (2018) 258–267. doi:10.1021/acssuschemeng.7b02335.

[4]

M.R. Awual, M.M. Hasan, A. Islam, M.M. Rahman, A.M. Asiri, M.A. Khaleque, M.C. Sheikh, Offering an innovative composited material for effective lead(II) monitoring and removal from polluted water, J. Clean. Prod. 231 (2019) 214–223. doi:10.1016/j.jclepro.2019.05.125.

[5]

M.R. Awual, M.M. Hasan, A. Islam, M.M. Rahman, A.M. Asiri, M.A. Khaleque, M.C. Sheikh, Introducing an amine functionalized novel conjugate material for toxic nitrite detection and adsorption from wastewater, J. Clean. Prod. 228 (2019) 778–785. doi:10.1016/j.jclepro.2019.04.280.

[6]

M.R. Awual, M.M. Hasan, M.M. Rahman, A.M. Asiri, Novel composite material for selective copper(II) detection and removal from aqueous media, J. Mol. Liq. 283 (2019) 772–780. doi:10.1016/j.molliq.2019.03.141.

[7]

M.R. Awual, A.M. Asiri, M.M. Rahman, N.H. Alharthi, Assessment of enhanced nitrite removal and monitoring using ligand modified stable conjugate materials, Chem. Eng. J. 363 (2019) 64–72. doi:10.1016/j.cej.2019.01.125.

[8]

M.R. Awual, M.M. Hasan, A.M. Asiri, M.M. Rahman, Novel optical composite material for efficient vanadium(III) capturing from wastewater, J. Mol. Liq. 283 (2019) 704–712. doi:10.1016/j.molliq.2019.03.119.

[9]

M.R. Awual, N.H. Alharthi, M.M. Hasan, M.R. Karim, A. Islam, H. Znad, M.A. Hossain, M.E. Halim, M.M. Rahman, M.A. Khaleque, Inorganic-organic based novel nano-conjugate material for effective cobalt(II) ions capturing from wastewater, Chem. Eng. J. 324 (2017) 130–139. doi:10.1016/j.cej.2017.05.026.

[10] M.R. Awual, M.M. Hasan, G.E. Eldesoky, M.A. Khaleque, M.M. Rahman, M. Naushad, Facile mercury detection and removal from aqueous media involving ligand

impregnated conjugate nanomaterials, Chem. Eng. J. 290 (2016) 243–251. doi:10.1016/j.cej.2016.01.038. [11] K. Yao, J. Li, S. Shan, Q. Jia, One-step synthesis of urchinlike SnS/SnS2 heterostructures with superior visible-light photocatalytic performance, Catal. Commun. 101 (2017) 51–56. doi:10.1016/j.catcom.2017.07.019. [12] A. Hezam, K. Namratha, Q.A. Drmosh, Z.H. Yamani, K. Byrappa, Synthesis of heterostructured

Bi2O3–CeO2–ZnO

photocatalytic

activity,

photocatalyst

Ceram.

Int.

with 43

enhanced (2017)

sunlight

5292–5301.

doi:10.1016/j.ceramint.2017.01.059. [13] X. Li, J. Zhu, H. Li, Comparative study on the mechanism in photocatalytic degradation of different-type organic dyes on SnS2 and CdS, Appl. Catal. B Environ. 123–124 (2012) 174–181. doi:10.1016/j.apcatb.2012.04.009. [14] J.M. Herrmann, Heterogeneous photocatalysis: Fundamentals and applications to the removal of various types of aqueous pollutants, Catal. Today. 53 (1999) 115–129. doi:10.1016/S0920-5861(99)00107-8. [15] S. Xia, L. Zhang, G. Pan, P. Qian, Z. Ni, Photocatalytic degradation of methylene blue with a nanocomposite system: synthesis, photocatalysis and degradation pathways, Phys. Chem. Chem. Phys. 17 (2015) 5345–5351. doi:10.1039/c4cp03877k. [16] M.S.S. Padmanaban Sivakumar, Minjong Lee, Yoon-Seok Kim, Photo-triggered antibacterial and anticancer activities of zinc oxide nanoparticles Padmanaban, 2018. doi:10.1039/C8TB00948A. [17] K.M. Lee, C.W. Lai, K.S. Ngai, J.C. Juan, Recent developments of zinc oxide based photocatalyst in water treatment technology: A review, Water Res. 88 (2016) 428–448. doi:10.1016/j.watres.2015.09.045. [18] Y. Zhang, M.K. Ram, E.K. Stefanakos, D.Y. Goswami, Synthesis, Characterization, and Applications of ZnO Nanowires, J. Nanomater. 2012 (2012) 1–22. doi:10.1155/2012/624520. [19] H. Huang, S. Wang, Y. Zhang, P.K. Chu, Band gap engineering design for construction of energy-levels well-matched semiconductor heterojunction with enhanced visible-light-driven photocatalytic activity, RSC Adv. 40 (2014) 41219– 41227. doi:10.1039/c4ra05708b. [20] M. Samadi, M. Zirak, A. Naseri, E. Khorashadizade, A.Z. Moshfegh, Recent progress on doped ZnO nanostructures for visible-light photocatalysis, Thin Solid Films. 605 (2016) 2–19. doi:10.1016/j.tsf.2015.12.064.

[21] J. Liu, Y. Wang, J. Ma, Y. Peng, A. Wang, A review on bidirectional analogies between the photocatalysis and antibacterial properties of ZnO, J. Alloys Compd. 783 (2019) 898–918. doi:10.1016/j.jallcom.2018.12.330. [22] S.K. Mandal, K. Dutta, S. Pal, S. Mandal, A. Naskar, P.K. Pal, T.S. Bhattacharya, A. Singha, R. Saikh, S. De, D. Jana, Engineering of ZnO/rGO nanocomposite photocatalyst towards rapid degradation of toxic dyes, Mater. Chem. Phys. 223 (2019) 456–465. doi:10.1016/j.matchemphys.2018.11.002. [23] Y. Lei, J. Huo, H. Liao, Microstructure and photocatalytic properties of polyimide/heterostructured NiO-Fe2O3-ZnO nanocomposite films via an ion-exchange technique, RSC Adv. 7 (2017) 40621–40631. doi:10.1039/c7ra07611h. [24] S. Harish, J. Archana, M. Sabarinathan, M. Navaneethan, K.D. Nisha, S. Ponnusamy, C. Muthamizhchelvan, H. Ikeda, D.K. Aswal, Y. Hayakawa, Controlled structural and compositional characteristic of visible light active ZnO/CuO photocatalyst for the degradation of organic pollutant, Appl. Surf. Sci. 418 (2017) 103–112. doi:10.1016/j.apsusc.2016.12.082. [25] F.T. Johra, W.G. Jung, RGO-TiO2-ZnO composites: Synthesis, characterization, and application

to

photocatalysis,

Appl.

Catal.

A

Gen.

491

(2015)

52–57.

doi:10.1016/j.apcata.2014.11.036. [26] T. Munawar, F. Iqbal, S. Yasmeen, K. Mahmood, A. Hussain, Multi metal oxide NiOCdO-ZnO nanocomposite – synthesis , structural , optical , electrical properties and enhanced sunlight driven photocatalytic activity, Ceram. Int. (2019) 0–1. doi:10.1016/j.ceramint.2019.09.236. [27] D. Joung, V. Singh, S. Park, A. Schulte, S. Seal, S.I. Khondaker, Anchoring ceria nanoparticles on reduced graphene oxide and their electronic transport properties, J. Phys. Chem. C. 115 (2011) 24494–24500. doi:10.1021/jp206485v. [28] C. Maria Magdalane, K. Kaviyarasu, J. Judith Vijaya, B. Siddhardha, B. Jeyaraj, Facile synthesis of heterostructured cerium oxide/yttrium oxide nanocomposite in UV light induced photocatalytic degradation and catalytic reduction: Synergistic effect of antimicrobial studies, J. Photochem. Photobiol. B Biol. 173 (2017) 23–34. doi:10.1016/j.jphotobiol.2017.05.024. [29] C. Maria Magdalane, K. Kaviyarasu, A. Raja, M. V. Arularasu, G.T. Mola, A.B. Isaev, N.A. Al-Dhabi, M.V. Arasu, B. Jeyaraj, J. Kennedy, M. Maaza, Photocatalytic decomposition effect of erbium doped cerium oxide nanostructures driven by visible light irradiation: Investigation of cytotoxicity, antibacterial growth inhibition using

catalyst,

J.

Photochem.

Photobiol.

B

Biol.

185

(2018)

275–282.

doi:10.1016/j.jphotobiol.2018.06.011. [30] C.M. Magdalane, K. Kaviyarasu, J.J. Vijaya, B. Siddhardha, B. Jeyaraj, J. Kennedy, M. Maaza, Evaluation on the heterostructured CeO2/Y2O3 binary metal oxide nanocomposites for UV/Vis light induced photocatalytic degradation of Rhodamine B dye for textile engineering application, J. Alloys Compd. 727 (2017) 1324–1337. doi:10.1016/j.jallcom.2017.08.209. [31] S. Prabhu, S. Megala, S. Harish, M. Navaneethan, P. Maadeswaran, S. Sohila, R. Ramesh, Enhanced photocatalytic activities of ZnO dumbbell/reduced graphene oxide nanocomposites for degradation of organic pollutants via efficient charge separation pathway, Appl. Surf. Sci. 487 (2019) 1279–1288. doi:10.1016/j.apsusc.2019.05.086. [32] G.Y. Adachi, N. Imanaka, The binary rare earth oxides, Chem. Rev. 98 (1998) 1479– 1514. doi:10.1021/cr940055h. [33] H.C. Tseng, T.C. Chang, J.J. Huang, Y.T. Chen, P.C. Yang, H.C. Huang, D.S. Gan, N.J. Ho, S.M. Sze, M.J. Tsai, Resistive switching characteristics of ytterbium oxide thin film for nonvolatile memory application, Thin Solid Films. 520 (2011) 1656– 1659. doi:10.1016/j.tsf.2011.07.026. [34] Z. Guo, A. Liu, Y. Meng, C. Fan, B. Shin, G. Liu, F. Shan, Solution-processed ytterbium oxide dielectrics for low-voltage thin-film transistors and inverters, Ceram. Int. 43 (2017) 15194–15200. doi:10.1016/j.ceramint.2017.08.052. [35] K.W. Park, S. Ahn, S.H. Lim, M.H. Jin, J. Song, S.Y. Yun, H.M. Kim, G.J. Kim, K.M. Ok, J. Hong, Ytterbium oxide nanodots via block copolymer self-assembly and their efficacy to dye-sensitized solar cells, Appl. Surf. Sci. 364 (2016) 573–578. doi:10.1016/j.apsusc.2015.12.077. [36] N. Chen, A. Younis, D. Chu, S. Li, Controlled fabrication of Pr(OH) 3 nanowires for enhanced

photocatalytic

activities,

J.

Rare

Earths.

37

(2019)

60–67.

doi:10.1016/j.jre.2018.03.035. [37] H.J. Osten, E. Bugiel, J. Dabrowski, A. Fissel, T. Guminskaya, J.P. Liu, H.J. Müssig, P. Zaumseil, Epitaxial praseodymium oxide: A new high-k dielectric, Ext. Abstr. Int. Work. Gate Insul. IWGI 2001. 47 (2001) 100–106. doi:10.1109/IWGI.2001.967555. [38] M.M. Rahman, M.M. Alam, A.M. Asiri, M.R. Awual, Fabrication of 4-aminophenol sensor based on hydrothermally prepared ZnO/Yb2O3 nanosheets, New J. Chem. 41 (2017) 9159–9169. doi:10.1039/c7nj01623a. [39] M. V. Shestakov, A.N. Baranov, V.K. Tikhomirov, Y. V. Zubavichus, A.S. Kuznetsov,

A.A. Veligzhanin, A.Y. Kharin, R. Rösslhuber, V.Y. Timoshenko, V. V. Moshchalkov, Energy-transfer luminescence of a zinc oxide/ytterbium oxide nanocomposite, RSC Adv. 2 (2012) 8783–8788. doi:10.1039/c2ra20755a. [40] M. Arunpandian, K. Selvakumar, A. Raja, P. Rajasekaran, M. Thiruppathi, E.R. Nagarajan, S. Arunachalam, Fabrication of novel Nd2O3/ZnO-GO nanocomposite: An efficient photocatalyst for the degradation of organic pollutants, Colloids Surfaces A Physicochem. Eng. Asp. 567 (2019) 213–227. doi:10.1016/j.colsurfa.2019.01.058. [41] Md Abdus Subhan, Abul Monsur M. Fahim, Pallab Chandra Saha, Mohammed M. Rahman, Kulsuma Begum, Structural study, photoluminescence and photocatalytic properties

of

nanocomposites,

La2O3·Fe3O4·ZnO, Nano-Structures

AgO·NiO·ZnO &

Nano-Objects.

and 10

La2O3·AgO·ZnO (2017)

30–41.

doi:10.1016/j.nanoso.2017.03.001. [42] A. Subhan, T. Ahmed, N. Uddin, A. Kalam, K. Begum, Spectrochimica Acta Part A : Molecular and Biomolecular Spectroscopy Synthesis , characterization , PL properties , photocatalytic and antibacterial activities of nano multi-metal oxide NiO.CeO2.ZnO, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 136 (2015) 824–831. doi:10.1016/j.saa.2014.09.100. [43] M.A. Subhan, N. Uddin, P. Sarker, A.K. Azad, K. Begum, Photoluminescence, photocatalytic and antibacterial activities of CeO2·CuO·ZnO nanocomposite fabricated by co-precipitation method, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 149 (2015) 839–850. doi:10.1016/j.saa.2015.05.024. [44] M.M. Alam, A.M. Asiri, M.T. Uddin, M.A. Islam, M.R. Awual, M.M. Rahman, Detection of uric acid based on doped ZnO/Ag2O/Co3O4 nanoparticle loaded glassy carbon electrode, New J. Chem. 43 (2019) 8651–8659. doi:10.1039/c9nj01287g. [45] M.M. Alam, A.M. Asiri, M.T. Uddin, Inamuddin, M.A. Islam, M.R. Awual, M.M. Rahman, One-step wet-chemical synthesis of ternary ZnO/CuO/Co3O4 nanoparticles for sensitive and selective melamine sensor development, New J. Chem. 43 (2019) 4849–4858. doi:10.1039/c8nj06361c. [46] M.M. Rahman, T.A. Sheikh, A.M. Asiri, M.R. Awual, Development of 3methoxyaniline sensor probe based on thin Ag2O@La2O3 nanosheets for environmental safety, New J. Chem. 43 (2019) 4620–4632. doi:10.1039/c9nj00415g. [47] T.A. Sheikh, M.M. Rahman, A.M. Asiri, H.M. Marwani, M.R. Awual, 4Hexylresorcinol sensor development based on wet-chemically prepared Co3O4@Er2O3 nanorods: A practical approach, J. Ind. Eng. Chem. 66 (2018) 446–455.

doi:10.1016/j.jiec.2018.06.012. [48] M.M. Rahman, M.M. Hussain, M.N. Arshad, M.R. Awual, A.M. Asiri, Arsenic sensor development

based

on

modification

with

(E)-N′-(2-nitrobenzylidine)-

benzenesulfonohydrazide: A real sample analysis, New J. Chem. 43 (2019) 9066– 9075. doi:10.1039/c9nj01567a. [49] M.M. Rahman, K.A. Alamry, M.R. Awual, A.E.M. Mekky, Efficient Hg(II) ionic probe development based on one-step synthesized diethyl thieno[2,3-b]thiophene-2,5dicarboxylate (DETTDC2) onto glassy carbon electrode, Microchem. J. 152 (2020) 104291. doi:10.1016/j.microc.2019.104291. [50] T.A. Sheikh, M.N. Arshad, M.M. Rahman, A.M. Asiri, H.M. Marwani, M.R. Awual, W.A. Bawazir, Trace electrochemical detection of Ni2+ ions with bidentate N,N′(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide) [EDBDMBS] as a chelating agent, Inorganica Chim. Acta. 464 (2017) 157–166. doi:10.1016/j.ica.2017.05.024. [51] M.N. Arshad, T.A. Sheikh, M.M. Rahman, A.M. Asiri, H.M. Marwani, M.R. Awual, Fabrication of cadmium ionic sensor based on (E)-4-Methyl-N′-(1-(pyridin-2yl)ethylidene)benzenesulfonohydrazide (MPEBSH) by electrochemical approach, J. Organomet. Chem. 827 (2017) 49–55. doi:10.1016/j.jorganchem.2016.11.009. [52] M.M. Hussain, M.M. Rahman, A.M. Asiri, M.R. Awual, Non-enzymatic simultaneous detection of l-glutamic acid and uric acid using mesoporous Co3O4 nanosheets, RSC Adv. 6 (2016) 80511–80521. doi:10.1039/c6ra12256f. [53] C. Belkhaoui, N. Mzabi, H. Smaoui, P. Daniel, Enhancing the structural, optical and electrical properties of ZnO nanopowders through (Al + Mn) doping, Results Phys. 12 (2019) 1686–1696. doi:10.1016/j.rinp.2019.01.085. [54] S. Yasmeen, F. Iqbal, T. Munawar, M.A. Nawaz, M. Asghar, A. Hussain, Synthesis, structural and optical analysis of surfactant assisted ZnO–NiO nanocomposites prepared by homogeneous precipitation method, Ceram. Int. (2019) 1–15. doi:10.1016/j.ceramint.2019.06.001. [55] M. Piz, P. Dulian, E. Filipek, K. Wieczorek-Ciurowa, P. Kochmanski, Characterization of phases in the V2O5–Yb2O3 system obtained by high-energy ball milling and hightemperature treatment, J. Mater. Sci. 53 (2018) 13491–13500. doi:10.1007/s10853018-2449-3. [56] B.M. Abu-Zied, Controlled synthesis of praseodymium oxide nanoparticles obtained by combustion route: Effect of calcination temperature and fuel to oxidizer ratio, Appl. Surf. Sci. 471 (2019) 246–255. doi:10.1016/j.apsusc.2018.12.007.

[57] M. Sathya, K. Pushpanathan, Synthesis and Optical Properties of Pb Doped ZnO Nanoparticles,

Appl.

Surf.

Sci.

449

(2018)

346–357.

doi:10.1016/j.apsusc.2017.11.127. [58] R. Cuscó, E. Alarcón-Lladó, J. Ibáñez, L. Artús, J. Jiménez, B. Wang, M.J. Callahan, Temperature dependence of Raman scattering in ZnO, Phys. Rev. B - Condens. Matter Mater. Phys. 75 (2007) 1–11. doi:10.1103/PhysRevB.75.165202. [59] S.D. Pandey, K. Samanta, J. Singh, N.D. Sharma, A.K. Bandyopadhyay, Anharmonic behavior and structural phase transition in Yb2O3, AIP Adv. 3 (2013). doi:10.1063/1.4858421. [60] M.R. Awual, N.H. Alharthi, Y. Okamoto, M.R. Karim, M.E. Halim, M.M. Hasan, M.M. Rahman, M.M. Islam, M.A. Khaleque, M.C. Sheikh, Ligand field effect for Dysprosium(III) and Lutetium(III) adsorption and EXAFS coordination with novel composite

nanomaterials,

Chem.

Eng.

J.

320

(2017)

427–435.

doi:10.1016/j.cej.2017.03.075. [61] M.R. Awual, A. Islam, M.M. Hasan, M.M. Rahman, A.M. Asiri, M.A. Khaleque, M. Chanmiya Sheikh, Introducing an alternate conjugated material for enhanced lead(II) capturing

from

wastewater,

J.

Clean.

Prod.

224

(2019)

920–929.

doi:10.1016/j.jclepro.2019.03.241. [62] M.R. Awual, M. Khraisheh, N.H. Alharthi, M. Luqman, A. Islam, M. Rezaul Karim, M.M. Rahman, M.A. Khaleque, Efficient detection and adsorption of cadmium(II) ions using innovative nano-composite materials, Chem. Eng. J. 343 (2018) 118–127. doi:10.1016/j.cej.2018.02.116. [63] M.R.

Awual,

M.M.

Hasan,

A.M.

Asiri,

M.M.

Rahman,

Cleaning

the

arsenic(V)contaminated water for safe-guarding the public health using novel composite

material,

Compos.

Part

B

Eng.

171

(2019)

294–301.

doi:10.1016/j.compositesb.2019.05.078. [64] A. Hezam, K. Namratha, Q.A. Drmosh, D. Ponnamma, A.M. Nagi Saeed, V. Ganesh, B. Neppolian, K. Byrappa, Direct Z-scheme Cs2O-Bi2O3-ZnO heterostructures for photocatalytic overall water splitting, J. Mater. Chem. A. 6 (2018) 21379–21388. doi:10.1039/c8ta08033j. [65] K. Dagenais, M. Chamberlin, C. Constantin, Modeling Energy Band Gap as a Function of Optical Electronegativity for Binary Oxides, J. Young Investig. 25 (2013) 1–6. [66] D.R. Kumar, K.S. Ranjith, R.T.R. Kumar, Optik Structural , optical , photocurrent and solar driven photocatalytic properties of vertically aligned samarium doped ZnO

nanorod

arrays,

Opt.-Int.

J.

Light

Electron

Opt.

154

(2018)

115–125.

doi:10.1016/j.ijleo.2017.10.004. [67] U. Alam, Comparative photocatalytic activity of sol–gel derived rare earth metal (La, Nd, Sm and Dy)-doped ZnO photocatalysts for degradation of dyes, RSC Adv. 8 (2018) 17582–17594. doi:10.1039/C8RA01638K. [68] Q. Wang, X. Lei, F. Pan, D. Xia, Y. Shang, W. Sun, A new type of activated carbon fi bre supported titanate nanotubes for high- capacity adsorption and degradation of methylene

blue,

Colloids

Surfaces

A.

555

(2018)

605–614.

doi:10.1016/j.colsurfa.2018.07.016. [69] M. Rani, U. Shanker, Sun-light driven rapid photocatalytic degradation of methylene blue by poly ( methyl methacrylate )/ metal oxide nanocomposites, Colloids Surfaces A. 559 (2018) 136–147. doi:10.1016/j.colsurfa.2018.09.040. [70] K. Karthik, S. Dhanuskodi, C. Gobinath, S. Prabukumar, S. Sivaramakrishnan, Multifunctional properties of microwave assisted CdO–NiO–ZnO mixed metal oxide nanocomposite: enhanced photocatalytic and antibacterial activities, J. Mater. Sci. Mater. Electron. 29 (2018) 5459–5471. doi:10.1007/s10854-017-8513-y. [71] V. Revathi, K. Karthik, Microwave assisted CdO–ZnO–MgO nanocomposite and its photocatalytic and antibacterial studies, J. Mater. Sci. Mater. Electron. 29 (2018) 18519–18530. doi:10.1007/s10854-018-9968-1. [72] M.A. Subhan, N. Uddin, P. Sarker, H. Nakata, R. Makioka, Synthesis, characterization, low temperature solid state PL and photocatalytic activities of Ag2O·CeO2·ZnO nanocomposite, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 151 (2015) 56–63. doi:10.1016/j.saa.2015.06.094. [73] T.K. Jana, S.K. Maji, A. Pal, R.P. Maiti, T.K. Dolai, K. Chatterjee, Photocatalytic and Antibacterial Activity of Cadmium Sulphide / Zinc Oxide Nanocomposite with Varied Morphology, J. Colloid Interface Sci. (2016). doi:10.1016/j.jcis.2016.06.073. [74] K. Ravichandran, N. Chidhambaram, S. Gobalakrishnan, Copper and graphene activated ZnO nanopowders for enhanced photocatalytic and antibacterial activities, J. Phys. Chem. Solids. (2016). doi:10.1016/j.jpcs.2016.02.013.

Table 1 Geometric parameters of ZnO, Yb2O3 and Pr2O3 in the grown ZnO-Yb2O3-Pr2O3 nanocomposite determined from XRD analysis. Oxides ZnO Yb2O3 Pr2O3

a(Å) 3.2478 10.4389 3.8361

c(Å) 5.2073 6.1919

c/a 1.603 1 1.614

Volume (Å3) 47.5689 1137.5231 164.0388

d-spacing 1.961 1.964 1.842

Table 2 Average crystallite size and lattice strain calculated from Debye Scherrer,

Samples

ZnO Yb2O3 Pr2O3

Scherrer Scherrer Williamson-Hall method plot method method D (nm) D (nm) D (nm) ε (×10-4) 57 68 66 2.17 59 76 67 2.09 65 72 69 1.14 Williamson Hall, and Size-Strain method.

Size-Strain Plot method D (nm) ε (×10-3) 58 0.76 54 2.43 64 1.88

Dislocation Density δ (nm)-2×10-4 2.996 2.991 2.377

Photocatalysts Degradation efficiency (%) References Bare ZnO 83.02 [66] Commercial ZnO 38.0 [67] [40] ZnO 75.0 Nd2O3/ZnO 96.0 [40] 96.2 [68] TNTs@ACF ZnO-PMMA, Ni2O3-PMMA 99, 98 [69] CuO-PMMA, Fe3O4-PMMA 93, 90 [69] CdO–NiO–ZnO 86.0 [70] CdO–ZnO–MgO 91.0 [71] 99.8 Present ZnO-Yb2O3-Pr2O3 Table 3 Comparison of MB dye degradation with some other metal oxide nanocomposite.

Table 4 Antimicrobial activity of grown nanocomposite at concentrations (10, 20, and 40 µg/mL).

Sample ZnO-Yb2O3-Pr2O3

Zone of inhibition (mm) Gram +iv (S. aureus) 10 20 40 26 29 31

Zone of inhibition (mm) Gram –iv ( E.coli) 10 20 40 29 29 30

Table 5 The comparison of antibacterial activity of ZnO-Yb2O3-Pr2O3 nanocomposite with some other metal oxide nanocomposite

Bacteria

Materials

Zone

of

inhibition References

(mm) S. aureus

E.coli

NiO.CeO2.ZnO

14

[42]

Ag2O.CeO2.ZnO

11

[72]

CdS–ZnO

22

[73]

ZnO:Cu/graphene

16

[74]

CeO2-CuO-ZnO

14

[43]

ZnO-Yb2O3-Pr2O3

31

Present

NiO.CeO2.ZnO

11

[42]

Ag2O.CeO2.ZnO

12

[72]

CdS-ZnO

14

[73]

ZnO:Cu/graphene

16

[74]

CdO–NiO–ZnO

16

[70]

CdO–ZnO–MgO

[71]

CeO2-CuO-ZnO

10

[43]

ZnO-Yb2O3-Pr2O3

30

Present

Scheme. 1. Scheme representing the synthesis procedure of nanocomposite.

Fig. 1. (a) XRD patterns of ZnO-Yb2O3-Pr2O3 nanocomposite and (b) Texture coefficient (TC(hkl)) for prominent peaks of ZnO, Yb2O3, and Pr2O3 in the nanocomposite.

Fig. 2. (a) Scherrer plots, (b) W-H plots and (c) Size-strain plots to estimate crystallite size and micro-strain.

Fig. 3. FTIR spectra in the wavenumber range from 400-4000 cm-1 and insert shows enlarge view in the wavenumber range from 400-750 cm-1, (b) Raman spectra, (c) I–V characteristics curve, and (d) Variation of absorbance as a function of incident photon wavelength, the insert shows Tauc’s plot for energy bandgap (Eg), of grown ZnO-Yb2O3-Pr2O3 nanocomposite.

(a)

(b)

(c)

Fig. 4. SEM images of ZnO-Yb2O3-Pr2O3 nanocomposite at (a) 5 µm, (b) 3µm and (b) 1µm.

Fig. 5. (a) Absorption spectra of methylene blue (MB) degradation at different time interval for grown ZnO-Yb2O3-Pr2O3 nanocomposite at conditions, catalyst = 0.5 g/L, Dye = 6 m/L and pH = 5, (b) Degradation efficiency (%) of grown catalyst against MB at different catalyst dosage, (c) The plot of ln (Co/Ct) versus irradiation time (t) at different catalyst dosage, and (d) Variation of the kinetic constant (k) for MB degradation during the photocatalytic reaction at different catalyst dosage.

Fig. 6. (a) Degradation efficiency (%) of grown catalyst at different concentrations of dye, (b) Variation of the kinetic constant (k) at different concentrations of dye, (c) Degradation efficiency (%) of grown catalyst at different pH of solution and (d) Variation of the kinetic constant (k) at different pH of solution, for MB degradation.

Fig. 7. (a) Effect of different scavengers on the degradation of MB in the presence of the ZnO-Yb2O3-Pr2O3 nanocomposite and (b) Variation of the kinetic constant (k) for MB degradation for different scavengers.

Fig. 8. (a) Photocatalytic activity of the grown ZnO-Yb2O3-Pr2O3 nanocomposite for the MB degradation with six cycles, and (b) XRD pattern of ZnO-Yb2O3-Pr2O3 nanocomposite before the degradation and after being reused for six cycles.

Fig. 9. The scheme represents the photocatalytic mechanism of grown ZnO-Yb2O3-Pr2O3 nanocomposite for the degradation of MB dye.

Staphylococcus aureus

Escherichia coli

Fig. 10. Antibacterial activity of ZnO-Yb2O3-Pr2O3 nanocomposite against (a) gram-positive Staphylococcus aureus bacteria and (b) gram-negative Escherichia coli bacteria at different concentrations 10, 20 and 40 µg/mL.

Conflict of interest The author’s declare no conflict of interest.

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