Structural, photoluminescence, electrical, anti cancer and visible light driven photocatalytic characteristics of Co doped WO3 nanoplates

Accepted Manuscript Title: Structural, photoluminescence, electrical, anti cancer and visible light driven photocatalytic characteristics of Co doped WO3 nanoplates Authors: Faisal Mehmood, Javed Iqbal, Tariq Jan, Qaisar Mansoor PII: DOI: Reference:

S0924-2031(17)30182-0 https://doi.org/10.1016/j.vibspec.2017.09.005 VIBSPE 2745

To appear in:

VIBSPE

Received date: Revised date: Accepted date:

15-6-2017 30-8-2017 26-9-2017

Please cite this article as: Faisal Mehmood, Javed Iqbal, Tariq Jan, Qaisar Mansoor, Structural, photoluminescence, electrical, anti cancer and visible light driven photocatalytic characteristics of Co doped WO3 nanoplates, Vibrational Spectroscopy https://doi.org/10.1016/j.vibspec.2017.09.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Structural, photoluminescence, electrical, anti cancer and visible light driven photocatalytic characteristics of Co doped WO3 nanoplates Faisal Mehmood1, 2*, Javed Iqbal 2*, Tariq Jan3, Qaisar Mansoor4 1Department

of Physics, International Islamic University, Islamabad, Pakistan

2Department

of Physics, Quaid-i-Azam University, Islamabad, Pakistan

3Department

of Applied Sciences, National Textile University, Faisalabad, Pakistan

4Institute

of Biomedical and Genetic Engineering (IBGE), Islamabad, Pakistan

*Corresponding Author: [email protected] , [email protected]

Abstract In this study, soft chemical route has been adopted for the synthesis of Co doped WO3 nanoplates. The prepared samples crystallized into monoclinic phase of WO 3 and composed of two dimensional (2-D) nanoplates. The substitution of Co 2+ ions on the sites of W6+ ions has been confirmed through X-ray photoelectron spectroscopy (XPS) analysis. The presence of functional groups and chemical bonding has been verified through FTIR and Raman spectra. Narrowing of the optical gap with Co doping has been observed which is linked with formation defects levels in the band of WO3. The Co doping has been found to be very effective in enhancing the visible light driven photodegradation activity of WO3 nanoplates up to 90 % which is attributed to trapping photo-generated electrons by defects. Furthermore, Co doped WO3 nanoplates have also shown good anticancer activities against human breast (MSF-7) and lever (Hep-2) cancer cells. Keywords: WO3 ; Doping; 2-D nanomaterials; Raman Spectroscopy; Photocatalysis.

1. Introduction Water contamination due to the non-biodegradable organic dyes from industrial waste is a very serious environmental hazard [1]. Therefore removal of these dyes from industrial wastewater is highly desirable. For this purpose wide range of techniques has been explored so far, for instant

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chemical oxidation, catalytic and bio degradation, adsorption and solvent extraction [1-3]. Among these, photocatalytic degradation of organic dyes on the surface of photocatalytic semiconductors has been extensively studied [4-6]. Semiconducting metal oxide nanostructures play an important role in developing smart materials that are well efficient for destroying harmful chemical contaminants from the environment. Metal oxide nanomaterials have been widely used to degrade water pollutants using photocatalysis protocol [7]. Among them, Titanium dioxide (TiO2) is the most studied photocatalyst but TiO2 has a drawback that it can operate only under ultraviolet light [8]. In comparison, tungsten oxide (WO3) is a promising photocatalyst because of its photochemical efficiency, stability, non toxic nature and its narrow energy band gap in the range of 2.6 to 3.25 eV depending on particle size which absorb part of blue spectrum [9, 10]. However in photocatalysis, the photo-induced charge carrier undergoes rapid recombination which may lower the photo-catalytic efficiency of WO3 material [11]. Another favorable feature of WO3 nanomaterial is its incredible stability under acidic environments and possible treatment of water contaminated by organic acids. The nanostructures of WO3 have enhanced photodegradation ability as compared to their bulk counterparts, due to their large surface to volume ratio that increases the surface area of the particles and provides enough sites for photochemical reactions [12]. Cancer is another serious problem which affects the human’s life on large scale around the world. Cancer is known as a heterogeneous and complex disease that happens when the normal cell proliferation controls are lost. Among various cancer types, breast cancer and liver cancer are the most prevailing types [13]. The surface defects and optical properties of metal oxide nanostructures have been believed to play very important role for generation of reactive oxygen species which is important for both visible light driven photodegradation and anticancer

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activities [14, 15]. The described properties of WO3 nanomaterial strongly relies on their size, morphology and presence of dopant concentrations [15-17]. To achieve the nanoparticles of desired size and shape, the chemical co-precipitation method is considered to be the most suitable due to its facile, cost effective and easily reproducible nature [18]. Doping is an effective approach to modify physiochemical properties competently. The optical and catalytic activity of WO3 nanomaterials can be efficiently improved via transition metal ions doping [19]. The generation of charge carriers is one of the key factors for the degradation of organic pollutants. However, the fast recombination rate of photoinduced electron hole pairs becomes detrimental factor to achieve high photocatalytic efficiency. Selective metal ions doping into WO3 nanomaterial is the best choice to lower the recombination rate of the photoinduced charge carriers. The cationic doping into WO3 host matrix has different ionic states which can increase optical and photocatalytic activities because the dopant can generate lot of oxygen vacancies, which can act as a charge trappers, in order to obtain charge neutrality [20-23]. Cobalt (Co) being one of the most common transition metal is considered to be the best dopant for WO 3 because of its comparable ionic radii to W ions. Previous reports suggest that the photodegradation activity of methyl orange could be further enhanced with Co doping intoWO3 nanostructure by tuning its optical band gap energy [24]. Arul et al. reported that the size and morphology also plays important role in the enhancement of catalytic activity of Co doped metal oxide nanomaterial [25]. Fazal et al. reported that the Co doping into metal oxide nanoparticles improves the anti cancer activity against cancer cells due to structural defects like oxygen vacancies [26]. Hasan et al. reported that the biosafe anticancer activities of WO3 nanoparticles against the rat liver cells [27]. Yassin et al. also reported the biocompatible nature of WO 3 nanomaterials with anti cancer activities against both cervix and colon cancer cells [28].

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Till date, to the best of our knowledge, no article has been published on the anti cancerous activities of MCF-7 and Hep2 cells and visible light driven photodegradation of methyl red with Co doped WO3 nanoplates. In the current study, we have examined the effects of Co doping on the structural, optical and photodegradation as well as anti cancerous properties of WO 3 nanoplates.

2 Experimental processes 2.1.

Synthesis of undoped and Co doped tungsten oxide nanoplates

The chemical co-precipitation method was applied for the synthesis of WO 3 nanoplates with Co doping of 0, 1, 3, 5 and 8 mol. %. For the synthesis, sodium tungstate dihydrate (Na 2WO4.2H2O) was used as a precursor, NaCl as a capping agent, and HCl was used to control the pH of the solution. A 0.1M solution of Na2WO4.2H2O was prepared with suitable amount of NaCl in distilled water. The pH value of this solution was maintained at 1 by adding 3M HCl solution drop-wise. The solution was vigorously stirred via magnetic stirrer for one hour. Afterwards, the solution was centrifuged to acquire precipitates. The precipitates were washed several times with distilled water and then dried in an electric oven at 80℃ overnight. Same procedure was also repeated for the synthesis of Co doped WO3 nanoplates with the addition of cobalt chloride hexahydrate (CoCl2.6H2O) of various molarities to obtain a final Co doping concentration of 1, 3, 5 and 8 mol.%. Finally, the prepared samples were annealed at 300℃ for 2 hours in an electric oven and then characterized for various properties [29].

2.2.

Determination of photocatalytic degradation activity of methyl red

The photocatalytic degradation activities of the undoped and Co doped WO 3 nanoplates were tested for the degradation of methyl red dye under visible light irradiation. The

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photodecomposition of methyl red determines the photocatalytic degradation efficiency. 2.0 mg of the photocatalyst (undoped and Co doped WO3 nanoplates) was suspended in 20 mL of an aqueous methyl red solution with concentration of 10 mgL -1 followed by sonication for 10 min in the dark. Then the solutions were stirred at room temperature for 30 min in the dark to obtain the adsorption and desorption equilibrium. The visible light illumination was achieved with 500 W (λ > 400 nm) lamp. Methyl red degradation experiments were performed for 2 h. The degraded sample of about 1.7 mL for each set was taken after 0.5 hour intervals using a micropipette, centrifuging it to remove the catalyst and then finally recording the UV-vis spectrum. The degradation of the dye was monitored as a function of the irradiation time using a UV-visspectrophotometer. Methyl red photodegradation was calculated from the decrease in absorbance of the respective degraded solutions. The photodegradation percentages were calculated using the expression given below: Photodegradation (%) =

Co−C Co

× 100

Where Co is the concentration of MR before irradiation and C is the concentration of MR after a certain irradiation of time. Each experiment was performed in triplicate to make sure the reliability of the photocatalytic degradation activities.

2.3.

Determination of anti cancerous activity

The cancerous and healthy cells were cultured and maintained in RPMI 1640 with addition of 10% fetal bovine serum (FBS) and 5% antibiotics-antimycotic solution (GPPS) at 37oC in CO2 incubator. The fetal bovine serum, GPPS and RPMI 1640 culture media were obtained from Invitrogen (USA). The percent cell viability of cancer and healthy cells, when exposed to 20µg/µL concentration of Co doped WO3 nanoplates, were determined using the MTT assay

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with standardized protocol. The details of protocol were already described in our previous report [29].

3. Results and discussions 3.1. Structural and morphological studies The structural characteristics of undoped and Co doped WO 3 samples have been studied through X-ray diffraction (XRD). Figure 1 depicts the XRD patterns of undoped and Co doped WO 3 samples. All the diffraction peaks match well to the monoclinic crystal structure of crystalline WO3 (JCPDS card No.043-1035) with lattice constants a = 7.297 Å, b = 7.539 Å and c = 7.688Å. The absence of Co related peaks in WO3 samples doped up to 5 mol.% pattern provides the evidence of successful Co doping into the WO3 crystal structure. Only a small variation in the peaks intensity with Co doping suggests good crystallinity for doped samples. The slight change in lattice constant with Co doping is probably linked with the difference in respective ionic radii of W6+ (0.062 nm) and Co2+ (0.072 nm) ions [24]. At higher concentrations of Co doping, a new peak appears at 16.2 theta degree (encircled peak in figure 1) suggests that the thermodynamic solubility limit of Co ions in WO3 matrix is less than 8%. The surface morphology and chemical composition of the undoped and Co doped WO3 samples have been examined by SEM and EDX. SEM images of the prepared samples are shown in figure 2 (a-e). As evident from the SEM images, two dimensional (2-D) square plate-like morphologies are observed in undoped and Co doped samples. The undoped WO3 is composed of nanoplates having average thickness of about 48 nm. However, there is a slight decrease in the thickness of nanoplates with Co doping [29]. The mechanism of nanoplates formation could be explained as hydrated tungsten oxide as growth units are formed with addition of HCl into

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Na2WO4.2H2O solution. At super-saturation of growth units and temperature greater than the decomposition temperature of hydrated tungsten oxide, WO 3 crystal nucleates are obtained. The reduction of more WO3 nuclei on these nucleates lead to crystal growth along lateral axis and results in the formation of nanoplates. Figure 3 depicts the energy-dispersive X-ray spectroscopy (EDX) spectra of undoped and Co doped WO3 nanoplates. The EDX spectra reveals the presence of Co ions in doped nanoplates by displaying Co peaks while this peak is absent in undoped samples which confirm the successful doping of Co ions into WO3 matrix.

3.2. FTIR spectroscopic studies The FTIR analysis was carried out in order to gain information about the surface chemistry of nanomaterial and the modes of vibrations of chemical bond present in the samples. The room temperature FTIR spectra of undoped and Co doped WO3 nanoplates are shown in figure 4. The broad band located at 550 to 1050 cm-1 is linked with the O-W-O stretching mode and the bands found at 1415cm-1 and 1628 cm-1 belongs to the bending modes of O–H groups [30]. The broad band obtained at 3300-3600 cm-1 may be associated with the stretching modes of O−H groups. The presence of WO3 stretching mode and absence of any impurity (Co) related modes further validate the successful doping of Co ions into the WO3 monoclinic crystalline structure.

3.3. Raman spectroscopic analysis Raman spectroscopy has been employed to further confirm the phase purity of the prepared samples. Raman spectroscopy is a vital technique for investigating the secondary phases in doped nanoplates that may easily escape from the detection limit of conventional techniques. Raman spectra of undoped and Co doped WO3 nanoplates were recorded at room temperature 7

and shown in figure 5. Well defined Raman bands are observed at 690 and 803 cm-1 which corresponds to the υ (O–W–O) stretching vibrational modes and the bands found at 250 cm-1 is attributed to the δ(O–W–O) bending vibrational modes of monoclinic WO3 [31]. These observed Raman bands confirm the monoclinic crystal structure of undoped and Co doped WO 3 nanoplates. The observation of slight shift in Raman peak position upon Co doping may be linked to the formation of structural defects in the crystal structure of WO 3 which are an inevitable consequence of the different valance states of Co 2+ and W6+ ions [32, 33]. In doped samples, no Raman band is found related to Co related vibrations that validate successful substitution of Co ions on the sites of host cations. These results are consistent with the XRD and FTIR findings.

3.4. X-ray photoelectron spectroscopy (XPS) study XPS technique was employed in order to examine the surface elements and valance states of W and Co ions in undoped and Co doped WO3 nanoplates. The XPS survey scan spectra of undoped WO3 nanoplates depict that all the main peaks could be attributed to O and W elements as shown in figure 6 (a). There is also presence of some minute impurities related peaks which could be assigned to C1s and N1s elements. Figure 6 (b) depicts the core level XPS W4f spectrum demonstrating the presence of two peaks linked to 4f7/2 and 4f5/2 which hints that W elements in the sample exist in the form of W6+ [34]. Figure 6 (c) and (d) show the XPS spectra of 3 and 5 mol. % Co doped WO3 nanoplates respectively, which indicates the presence of same peaks as for undoped sample except one peak which is related to Co2p. The core level XPS spectrum of Co2p for 5 mol. % Co doped WO3 nanoplates is the inset of figure 6 (d) depicting two peaks related to Co2p3/2 and Co2p1/2. This demonstrates that Co ions with valance state of +2 are successfully doped into WO3 nanoplates. 8

3.5.

Diffusion reflectance spectroscopy

The precise information about optical absorption characteristics of nanostructure has utmost significance regarding photocatalytic degradation applications. Diffused reflectance spectroscopy (DRS) was applied to inspect the optical characteristics of prepared nanoplates. Figure 7 depicts the DRS spectra of the undoped and Co doped WO3 nanoplates in the wavelength range of 200900 nm. Sharp absorption edge can be seen below 450 nm in undoped WO 3nanoplates which undergoes a red shift with Co doping .The optical band gap energies of the prepared nanoplates have been calculated by Kubelka-Munk relation given by the following equation [35]. 𝐹 (𝑅 ) =

(1−𝑅)2 2𝑅

……………..…… (1)

Where F(R) is Kubelka-Munk function and R represents the diffuse reflectance. The indirect bang gap energies can be obtained by extrapolating linear part (both along x-axis and y-axis) in plot of (F(R)hʋ)1/2 vs photon energy (hʋ) as shown in the inset of figure 7. The undoped WO3 sample has shown energy band gap of about 2.55 eV which is observed to decrease down to 2.49 eV with 8 % Co doping. This decrease in the band gap energies with Co ions doping may be due to the creation of localized states in the band gap which are caused by the creation of crystal defects like dislocations, stacking faults and more oxygen vacancies [36]. The reduction in the band gap energy with Co doping may facilitate absorption of more light in the visible region and can help to improve the photocatalytic activities.

3.6.

Photoluminescence spectra investigations

The photoluminescence (PL) spectra of undoped and Co doped WO 3 nanoplates are shown in figure 8. In PL spectra, the peak located at 417 nm belongs to the recombination of free excitons

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and is designated as near band edge emission (NBE). The other wider and high intensity peak observed at 536 nm is usually assigned to the deep level (DL) emissions caused by crystal defects such as oxygen vacancies and anionic or cationic interstitial defects. Similar results have also been reported for undoped and metal ions doped WO3 nanoparticles [22]. The particle morphology and size play vital role in the variation of PL intensities of prepared samples [3739]. The NBE and defects peaks intensities significantly decrease with Co doping as a consequence of large number of defect densities. The lower PL intensity for Co doped WO 3 nanoplates may imply the lower recombination rate of photo generated electrons and holes due to defects under visible light irradiation. Similar results were also reported for monoclinic WO3 nanoplates [11]. These defects can play a crucial role to increase the photodegradation activity of the prepared samples.

3.7.

Dielectric and Electrical Analysis

The frequency dependent dielectric characteristics of undoped and Co doped WO3 nanoplates were examined at room temperature. Dielectric constant (ε ʹ), dielectric loss (𝜀 ̋) and alternating current (AC) conductivity of prepared nanoplates were measured in the range of 1 KHz to 1MHz as a function of AC frequency using circular shape compressed pellets. Following relation was utilized to determine dielectric constant (εʹ) [40]. εʹ = (t × Cp) / (A× εo)………………………. (2) Where t is the thickness of the pellets, Cp is the equivalent parallel capacitance attained experimentally, A is the area of the pellets and εo is the vacuum permittivity. Figure 9 shows the behavior of the dielectric constant of undoped and Co doped WO 3 nanoplates as a function of frequency. In all cases, initially a high value of dielectric constant (ε ʹ) is seen. It then decreases 10

and stabilize with the increase in frequency. This dielectric constant behavior is well matched with Maxwell–Wagner dielectric model [41]. The space charge polarization and interfacial polarization phenomenon are responsible for the high value of ε ʹ at lower frequencies [42]. In Co doped samples, the initial value of εʹ at lower frequency range decreases with Co doping. This variable nature of εʹ is directly linked with the polarization which varies due to electronegativity difference between dopant Co (1.88) and host matrix W (2.36 ) [40]. Figure 10 depicts the dielectric loss (εʹʹ) of prepared samples. Dielectric loss (εʹʹ) was measured from experimental data using following relation [40]. εʹʹ = εʹ tanδ ………………… (3) Where tanδ = εʹʹ/ εʹ Dielectric loss (εʹʹ) has similar trend as the dielectric constant as a function of frequency. This dielectric loss (εʹʹ) behavior is in well accordance with Koop's model. Accordance to this model, higher value of resistivity in the lower frequency range is happened due to the grain boundaries [43]. Therefore, extra energy is required for the exchange of electrons between W6+ and Co2+ ions. The εʹʹsignificantly decreases with Co doping due to less electrical polarization and it can be useful for high frequency based bio-sensing applications [44]. The AC conductivity (σac) of the as synthesized nanoplates was measured by the following relation [40]; σac = 2πfεoεʹtanδ……………… (4) Figure 11 shows the σac of undoped and Co doped WO3 nanoplates. The constant response of conductivity is found in the low frequency range due to the grain boundaries conduction effects.

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The conductivity enhances rapidly at high frequency range because of dominant grain conduction effects. These σac responses are in well accordance with power law [40]. Moreover, conductivity also decreases markedly with the Co doping. This may be due to segregation of the grain boundaries, oxygen vacancies and tungsten interstitials in the WO3 host matrix with metal ions doping [45].

3.8.

Visible light driven degradation of methyl red using undoped and Co doped WO3 nanoplates

Photocatalytic advanced oxidation process is an environmentally friendly technology for water pollutant degradation [46]. In this regard, 2-D metal oxide materials have attracted enormous interest due to their high surface area, increased number of reaction sites and minimal difference in the catalytic activity at different sites [47]. Figure 12 (a-d) depicts the photocatalytic degradation of methyl red under the visible light illumination using undoped and Co doped WO 3 nanoplates. Photodegradation activities have been found to enhance up to 90% in 2 hours with 5% Co doped WO3 nanoplates. The mechanism involved in photocatalytic dye degradation is shown in figure 13 and can be explained as fallows. When the undoped and Co doped WO 3 nanoplates as photocatalyst are allowed to be exposed under visible light radiations, the promotion of electrons from valence band to the conduction band take place and as result electron-hole pairs are generated. These pairs react with oxygen and water molecules or hydroxyl groups adsorbed on the surface of the photocatalyst and form highly reactive dye scavengers, such as (•OH), superoxide ions ( •O2-) or hydroperoxyl radicals ( •OOH) [48]. The hydroxyl radicals (•OH) attack methyl red, which results in various reaction intermediates. Furthermore, the (•OH) radical reacts with the intermediates resulting into CO 2 and H2O as final products [4851]. It is also shown in figure 12 (c) that methyl red does not undergo any significant degradation 12

under visible light illumination in the lack of photocatalyst. There is one major drawback related to photocatalysis technique and that is its photoinduced electrons and holes recombination that reduces the efficiency of dye degradation. However, the oxygen vacancies play a vital role to enhance the photocatalytic activity and act as the active centers to capture photoinduced electrons and reduce the electron hole pairs recombination rate in oxide based semiconductors like WO3, ZnO and TiO2 [52]. The PL spectra confirm the existence of large number of oxygen vacancies. As already described that the numbers of oxygen vacancies have been increased due energy band gap reduction with Co doping into WO3 nanoplates and as a consequence the photo generated electron hole pairs recombination rate has been decreased. Therefore, photocatalytic dye degradation efficiency is remarkably increased with Co doping. The small space-charge regions and least band bending are produced in nano scaled WO 3 which allows the photogenerated charge carriers to migrate easily to surface and react with dye molecules. Apart from defects, the doping of metal ions lead the optimum band structure of WO 3 at nano scale due to effective intercalation of dopants which results in higher photocatalytic performance of doped WO3 nanoplates [9]. Furthermore, the dopants may likely support the more adsorption of dye molecules on the surface of WO3 nanoplates which may also cause enhancement in photocatalytic activity of Co doped WO3 nanoplates [53]. It is also vital to observe the stability and durability of the photocatalysts. The recyclability performance of 5% Co doped WO3 nanoplates have been studied under similar conditions. Figure 12 (d) revealed that there is no significant loss of photocatalytic activity during three successive visible light driven degradation experiments. These results signify that Co doped WO3 nanoplates can becomes an excellent photocatalyst under the visible light irradiation for water treatment purposes.

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3.9.

Anti cancerous characteristics

The anticancer activities of the synthesized WO3 nanoplates doped with different molar percentages of Co were carried out via MTT assay against breast (MCF-7) and lever (Hep-2) cancer cells. The viability of these cancer cells in the presence of Co doped WO3 nanoplates are shown in figure 14. It can be seen from this figure that undoped WO 3 nanoplates have reduced percent cell viability of both type of cancer cells down to 70%. The Co doping resulted in systematic reduction in cell viability of these tested cancer cells down to 60%. There are number of mechanisms proposed for the anticancer characteristics of metal oxide nanomaterials such as accumulation of nanoparticles inside the cells, electrostatic rupturing of cell wall and excessive oxidative stress due to production of reactive oxygen species [52, 54-56]. The nanoparticles may attack the redox active mitochondria, which are considered to be the major site for ROS production in cells exposed to nanomaterials [57, 58]. Therefore, it may change the production of ROS and influence the antioxidant defenses leading to oxidative stress. This oxidative stress may result in DNA damage and apoptosis leading to cell death [58, 59]. Hence, Co doping may result in the higher uptake of WO3 nanoplates in the cells and higher ROS production which causes higher anticancer activity of doped WO3 nanoplates.

Conclusion In summary, the chemical co-precipitation method has been successfully applied to achieve desired Co doped WO3 nanoplates. The stable monoclinic phase has been verified for all samples through structural investigations with successful Co doping. The nanoplate like morphology has been observed for all samples. The optical bandgap experienced a red shift due to the Co doping into WO3 nanoplates owing to the presence of large number of impurity defects. Furthermore, the 14

recombination rate of photo induced electron hole pair has been decreased with Co doping. Dielectric properties have been significantly altered with Co doping. Photodegradation activities of methyl red have been found to increase up to 90% in 2 hours with 5% Co doped WO 3 nanoplates under visible light irradiations which is attributed to band gap narrowing and defects. Moreover, the percent cell viability of MCF-7 and Hep-2 cancers cells, when treated with 8% Co doped WO3 nanoplates, have been decreased up to 40 %. This shows that Co doped WO3 nanoplates can be considered as a promising visible light driven photocatalyst for rapid dye degradation as well as a promising anticancer agent for MCF-7 and Hep-2 cancers cells.

Acknowledgment The corresponding author would like to acknowledge the support by Higher Education Commission (HEC) through NRPU grant (Grant No. 20-4861/R & D/ HEC/14).

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Figure 1

Figure 1: XRD patterns of undoped and Co doped WO3nanoplates.

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Figure 2

Figure 2: SEM images of (a) undoped (b) 1% (c) 3% (d) 5% and (e) 8% Co doped WO 3 nanoplates. 24

Figure 3

Figure 3: EDX spectra of (a) undoped (b) 1% (c) 3%, (d) 5% and (e) 8% Co doped WO 3 nanoplates.

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Figure 4

Figure 4: FTIR spectra of the undoped and Co doped WO3 nanoplates.

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Figure 5

Figure 5: Raman spectra of undoped and Co doped WO3 nanoplates.

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Figure 6

Figure 6: XPS spectra of (a) undoped WO3 nanoplates (b) core level spectra of undoped WO3 nanoplates (c) 3 % Co doped and (d) 5% Co doped WO3 nanoplates (Inset of the figure depicts the plot Co2p)

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Figure 7

Figure 7: DRS spectra of undoped and Co doped WO3 nanoplates (Inset of the figure shows band gap energies calculation).

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Figure 8

Figure 8: PL spectra of undoped and Co doped WO3 nanoplates.

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Figure 9

Figure 9: Variation of real dielectric constant ( ε )́ as a function of AC frequency.

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Figure 10

Figure 10: Variation of dielectric loss (ε̋ ) as a function of AC frequency

.

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Figure 11

Figure 11: Variation of AC conductivity (σac ) as a function of frequency

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Figure 12

Figure 12 (a): Photodegradation of methyl red under visible light illumination by undoped WO3 nanoplates. (b): Photodegradation of methyl red under visible light irradiation using Co doped WO3 nanoplates. (c): C/Co versus time plot for the visible light driven photodegradation of methyl red (MR) using undoped and Co doped WO3 nanoplates. (d): The recyclability performance of 5% Co doped WO3 nanoplates.

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Figure 13

Figure 13: Schematic mechanism of photodegradation using WO3 nanomaterial.

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Figure 14

Figure 14: Effect of undoped and Co doped WO3 nanoplates on MCF-7 and Hep-2 cells viability.

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