Synthesis, structural, optical, and dielectric properties of CuWO4/PVP/Cs bio-nanocomposites for some industrial applications

The nanocomposites of biopolymers and bimetallic oxides are exciting classes of materials. Besides the economic and environmental considerations, these materials became the best candidates for various applications in industry and medicine. In this study, CuWO4 nanoparticles (NP) with high purity were prepared by co-precipitation and loaded into poly(vinyl pyrrolidone)/chitosan (PVP/Cs) films. XRD results showed that CuWO4 has a triclinic phase with an average crystallite size of 43 nm. PVP/Cs is semi-crystalline blend and its crystallinity degraded by CuWO4 incorporation. EDX analysis was used to study the chemical composition of all samples. FE-SEM showed that CuWO4 has particle sizes of 50–150 nm and that the crack-free surface of PVP/Cs became rougher and more porous after loading of CuWO4 NP. FTIR confirmed the presence of the reactive functional group of CuWO4, PVP, and Cs and that the low doping ratio of CuWO4 NP restricted the functional group’s vibrations. The UV–vis–NIR investigation showed that the films have a small absorption index and high transmittance in the range of 68–90%. The direct and indirect band gaps (Egdir\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${E}_{g}^{dir}$$\end{document} and Egind\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${E}_{g}^{ind}$$\end{document}) of the blend were found equal to 5.0 and 4.2 eV and can be tuned by CuWO4 content. Similarly, the index of refraction and carrier concentration/electron effective mass ratio (N/m*), the dielectric constant (ε′ = 8.3–24.5), and the dielectric loss depend on the applied frequency, temperature, and CuWO4 filler content. The conductivity (σac) ranges from 1.2 × 10–6 to 9.16 × 10–4 S/m and exhibits the Arrhenius behavior. The optical and dielectric results show that the prepared PNC may suit some energy storage device,s such as supercapacitors, and organic optoelectronic devices, such as light emitting diodes and/or photovoltaic solar cells.


Introduction
In recent years, the development of nanocomposites based on biopolymers mixed with bimetallic oxides has attracted increasing attention. The predominant reason evoked for this trend is the lower cost and ease of polymer nanocomposites (PNC) preparation with properties that make them suitable candidates for potential applications in various fields of industry, such as environment-friendly electronics, food packaging, and medical and pharmaceutical applications [1][2][3][4][5][6].
Among the bimetallic oxides, the copper tungstates (CuWO 4 ) have attracted considerable attention as photoelectrode owing to its high redox, excellent chemical stability of the crystalline CuWO 4 in aqueous solutions, excellent catalytic performance, and the moderate band gap (E g = 2.2-2.4 eV) which permits a theoretical photocurrent density up to 10.7 mA/cm 2 [7]. It exhibits a photoresponse with a cut-off wavelength of ~ 540 nm. Besides, the metal-to-metal (Cu 2+ → W 6+ ) charge transfer in CuWO 4 results in an absorption band at 850 nm. According to Chen et al. [8], the E g value can be tuned by adjusting the elemental chemical composition CuWO 4 , where an increase in Cu/W ratio from 0.33 to 2.5 decreases the E g to 1.88 eV. Moreover, CuWO 4 is an n-type semiconductor, and the valence band (VB) and conduction band (CB) positions are positive (+ 2.6-2.7 V RHE and + 0.4 V RHE , respectively) on the normal hydrogen electrode scale, leading to the generation of photo-excited holes with strong oxidation ability [9]. The VB consists of strongly hybridized states of O 2p and Cu 3d, while the CB minimum comprises unoccupied Cu 3d states [7]. These properties make the material a candidate for novel functions in the fields of optics, fluorescence detection [10], photodegradation and water decomposition reactions, and fuel cell reactions. Currently, CuWO 4 has gained extensive interest in electrochemical sensors and supercapacitor applications [5,11]. CuWO 4 in the form of nanopowder and films was prepared by several routes; Nong et al. [5] designed an electrochemical Chit-Au/CuWO 4 @MoS 2 immunosensor that showed reproducibility, stability, and good repeatability for detecting cortisol. Lee et al. [7] fabricated CuWO 4 films on FTO substrates by the sol-gel method and spin-coating followed by thermal annealing for PEC water splitting. Serwar et al. [9] prepared CuWO 4 NP and CuWO 4 /graphene QDs photocatalysts by co-precipitation and hydrothermal methods, respectively. Sun et al. [10] prepared CuWO 4 via the polyacrylamide gel method and obtained the pure triclinic phase after calcination of the xerogel at 900 °C. Du et al. [12] prepared MWO 4 (M = Co, Ni, Zn, and Cu) nanosheets on Ni foam by a hydrothermal method for efficient urea oxidation. Jatav et al. [13] fabricated AgI/CuWO 4 by a precipitation method for efficient visible-light photocatalysts for ciprofloxacin and RhB degradation.
One of the naturally occurring and abundant cationic polysaccharides is the chitosan (Cs) biopolymer. Cs obtained from chitin by alkaline N-acetylation via a thermochemical reaction. The low cost, high nitrogen content, biodegradability, hydrophilic properties, nontoxicity, reproducibility, good molecular biocompatibility, and antioxidant, antibacterial, and immunomodulatory properties make Cs a promising polymer for various biomedical, biotechnological, and green packaging applications, as well as for artificial skin, bone substitutes, agriculture, and cosmetics. Because of OH and NH 2 groups, Cs can exhibit interesting chelating and film-forming properties. The NH 2 serves as an electron donor, containing a lone pair electron. It serves the process of complexing and coordinating between the cations of loaded filler into the electrolyte membrane of batteries and acting as a sensor to detect glucose, catechol, and hazardous mercury [4,[14][15][16][17][18]. Moreover, Cs have a semi-crystalline nature and mixing them with another polymer may improve and widen the blend's multi-functionality. In this context, poly(vinyl pyrrolidone) (PVP) is an amorphous polymer and could improve the film-forming ability. In addition, PVP has a higher resistivity than Cs to ultraviolet rays. Therefore, adding PVP into Cs will maintain or improve the physicochemical properties and expand the Cs utilization to include the electrochemical applications, such as batteries and displays [19,20].
Few reports on PNC based on CuWO 4 filler are found. Thiruppathi et al. [6] prepared CuWO 4 /PMMA nanocomposite as a photocatalyst for some dyes and antibiotics. To the best of the authors' knowledge, this is the first attempt to explore the effect of CuWO 4 on the physicochemical properties of the PVP/Cs biopolymer blend. This report focuses on preparing CuWO 4 by the co-precipitation route and CuWO 4 /PVP/Cs nanocomposites by solution casting. The morphological, structural, chemical composition, optical, and dielectric properties of the PVP/Cs biopolymer loaded with different filler ratios were investigated.
As mentioned above, we aim to enhance and expand the technological and medical applications of PVP/Cs bio-blend.

Preparationof CuWO 4 NPs
Sigma-Aldrich provided copper (II) chloride (CuCl 2 ) and sodium tungstate dihydrate (Na 2 WO 4 .2H 2 O) as Cu and W sources. The co-precipitation method generated pure CuWO 4 NPs; the Cu and W salts were first dissolved in different beakers containing 400 mL of deionized water. Both of these solutions were mixed and magnetized strongly for 30 min. The CuWO 4 precipitate was centrifuged and washed three times with deionized water. Finally, a dark green precipitate of pure CuWO 4 NPs was produced by drying the washed CuWO 4 sample at 200 °C for two h before grinding it into powder.

PreparationofPVP/Cs/ CuWO 4 nanocomposite
Cs powder (˃ 70% deacetylated) of molecular weight (M W ) ~ 1.1 × 10 5 g/mol., PVP of k = 30, and M W = 4 × 10 4 g/mol., were used to prepare the PVP/Cs blend. 1.0 g of Cs was dissolved in 75 ml of 2 wt% acetic acid (CH 3 COOH) using magnetic stirring for 2 h. 0.25 g of PVP in 20 ml distilled water solution was added to this solution, and the stirring continued for one hour at RT. The obtained homogeneous solution was cast into Petri dishes of diameters of ~ 10 cm. For CuWO 4 / PVP/Cs PNC, the desired mass x (1.0, 3.0, and 5.0%) of CuWO 4 was calculated according to the following equation: where W filler is the mass of CuWO 4 and "1.25" in the denominator is the total mass of the polymers (PVP + Cs). The calculated W filler was dissolved in distilled water using an ultrasonic bath and magnetic stirring and then added to the PVP solution. The films' composition is summarized in

Characterization
The surface morphology and elemental composition of CuWO 4 and CuWO 4 /PVP/Cs PNC films, the crosssection, and film thickness were studied using field emission-scanning electron microscopy (FE-SEM; Carl ZEISS Sigma 500 VP, coupled with EDS). The X-ray diffraction patterns of CuWO 4 and CuWO 4 /PVP/Cs were recorded using XRD Shimadzu 6000 diffractometer, in the 2θ range of 4°-90°, with a Cu K α source of wavelength λ = 1.5406 Å. The vibrational modes of the samples were studied using Fourier transform infrared (FTIR) spectroscopy (JASCO, FT/IR-6200) in the wavenumber range 4000-400 cm −1 .
Optical measurements (absorbance, transmittance, and reflectance) were evaluated using a Shimadzu UV-3600 UV-VIS-NIR spectrophotometer at room temperature (RT) and in the wavelength range 200-1600 nm, with an accuracy of ± 0.2 nm. The dielectric constant ( ′ ), loss tangent (tan ) , and ac conductivity ( ac ) were measured in the frequency range 200 Hz-8 MHz and temperature range 293-393 K, using a Hioki model 3532 High Tester LCR (Ueda, Nagano, Japan), with a highly accurate and stable capacitance measurement of the order of 1.0 × 10 −4 pF. The following equations were used: where d denotes the thickness of CuWO 4 /PVP/Cs film, r represents the radius of CuWO 4 /PVP/Cs film contact area, ε o = 8.854 × 10 −12 F/m is the dielectric permittivity of the air, C p is the capacitance, and ε′′ is the dielectric loss.

Structuralandmorphologicalproperties
The XRD pattern of the co-precipitated CuWO 4 is shown in Fig. 1a. In this pattern, the peaks at  Fig. 1a. This pattern corresponds to the triclinic (an orthic) phase of CuWO 4 (SG: P1) and is consistent with the data of JCPDS file 88-0269 [9,13]. The high intensity and narrow width of the XRD peaks indicate the crystallization quality of the CuWO 4 [27]. Considering the three major peaks at 29.32° (111), 28.58° Thiruppathi et al. [6] prepared CuWO 4 with D av = 44 nm, using 0.1-M CuCl 2 and Na 2 WO 4 .2H 2 O via a hydrothermal process.
The inset of Fig. 1a shows the FE-SEM image of CuWO 4 that seems as particles of various sizes in the range of 50-150 nm. This value is bigger than D av given by XRD. This difference is because SEM gives the particle or grain size, while each grain may contain several crystallites. For the sol-gel prepared Y 2 O 3 NPs the grain size was slightly smaller than 100 nm and D av was in the range of 18.4-19.5 nm [28].   Figure 2 shows the X-ray diffraction patterns of PVP/Cs and CuWO 4 /PVP/Cs PNC. The pure blend exhibits characteristic peaks at 2θ ≈ 8.5°, 11.2°, 18.1°, and 22.85°. The first three peaks indicate the existence of crystalline or arranged regions in the blend, which could arise due to the intramolecular interaction between the OH and NH 2 ‫‬ groups in the blend [29]. However, the wide peak at 2θ = 22.85° belongs to the amorphous phase [30,31]. Three main notes here: (i) the blend has a semi-crystalline nature. (ii) CuWO 4 has been distributed effectively in the amorphous regions of the blend and the XRD instrument is not able to detect this nanofiller. (iii) The intensity of the crystalline peaks decreased, and the wide of the amorphous peak increased with increasing CuWO 4 loading. The crystallinity degree , where A c and A a are the areas under the crystalline and amorphous peaks, respectively. X c of the pure blend is 18.5% decreased to 12.6% at 1.0-wt% CuWO 4 loading and marginally decreased till 10.4% with the further increase in CuWO 4 ratio 5.0 wt%. This decrease in X C indicates increasing the biodegradability of the blend loaded with CuWO 4 [32], and the blend flexibility and chain motion which in turn will improve the conductivity of the material. Figure 3 shows the EDS spectra, chemical (elemental) composition, and the inset tables of PVP/Cs loaded with 1.0-and 3.0-wt% CuWO 4 . In the two samples, the main components are C (55.64-56.49 at%), O (33.42-33.60 at%), and N (7.87-8.57%). These ratios are consistent with the chemical structure of both Cs (C 56 H 103 N 9 O 39 ) n and PVP (C 6 H 10 NO) n . Although XRD did not detect any peaks for CuWO 4    porosity from 105.86, for the pure blend, to 129.71% for the blend loaded with 5.0-wt% CuWO 4 [23]. This is consistent with the observation of FE-SEM, Fig. 4. Additionally, incorporation of this dense metal oxide (ρ CuWO4 = 7.48 g/cm 3 ) result in increasing the ρ of CuWO 4 /PVP/Cs PNC from 0.507 to 1.633 g/cm 3 . Similar results were reported in [24][25][26]. In addition, the bands at 472 and 903 cm -1 are assigned to the stretching vibration of WO 4 tetrahedra [6,10,33]. This result indicates the high purity of our co-precipitated CuWO 4 .

FTIR spectra of CuWO 4 and PVP/Cs PNC
The spectra of CuWO4/PVP/Cs PNC contain a wide and broadband in the range of 3000-3600 cm -1 , which can be divided into two bands, as shown in Fig. 6; the first centered at 3360 cm -1 can be assigned to the asymmetrical stretching of N-H group in the PVP/Cs blend [34], and the second is centered at 3265 cm -1 arising from the OH stretching vibration overlapping with the symmetric stretching o N-H through the carbohydrate ring in the C S [1,4]. Similarly, the two bands at 2935 and 2875 cm -1 arise from the C-H symmetric and asymmetric stretching vibrations in the CH 2 groups [35]. The absorption band at 1650 cm -1 is attributed to the -C=O stretching of amide I in Cs. The relatively broad and strong band at 1547 cm −1 can be assigned to the symmetric deformation of −NH + 3 (resulting from the ionization of NH 2 groups by adding acetic acid during the dissolving Cs) [36]. In addition, the stretching vibration of -C=N of amide-III in Cs appears at 1397 cm -1 [35]. The small absorption band at 1290 cm -1 is owing to the frequencies of (CH + OH) combination [37]. The three absorption bands at 1150 cm -1 , 1068 cm -1 , and 1025 cm -1 can be ascribed to the asymmetric stretching vibration of C-O-C and the stretching of C-O in the C-OH groups [18]. The small band at 647 cm −1 may be owing to twisting vibrations in the blend [38]. All films have similar spectra and no obvious shift in the peak position due to CuWO 4 incorporation. However, it is seen that the width and intensity of the peaks decreased after loading 1.0-wt% CuWO 4 but increased with increasing the ratio of the filler to 3.0 and 5.0 wt%. This result indicates

UV-visstudyandopticalconstants
Investigating the optical properties of semi-crystalline materials and determining their optical constants are important for elucidating the electronic and band structures for optical communication and device fabrications. Figure 7a and b shows the absorption index ( k = 4 ) and transmittance spectra (T%) of the CuWO 4 / PVP/Cs PNT, where = 2.303Abs. d and d is the film thickness. The films show low k values (k ≤ 2.0 × 10 −3 ), Fig. 7a. The PVP/Cs show two weak absorption peaks at 278 and 310 nm, assigned to π→π* and n→π* transitions, respectively, that are arising due to the existence of unsaturated bonds [39]. The intensity of these two peaks is significantly improved after doping with 1.0-wt% CuWO 4 and then decreased and left-shifted with increasing loading ratio of CuWO 4 to 3.0 and 5.0 wt%. This results from the induced changes in X C % of the PVP/Cs after mixing with CuWO 4 [40], as shown in XRD results. For comparison purposes, the value of T% at 600 nm of all samples is listed in Table 2. At λ ≥ 600 nm, the PVP/Cs show a motivating T% in the range of 85-90%, Fig. 7b. The PNC films have T = 57% at λ = 600 nm. In the studied λ range, 1.0-wt% CuWO 4 / PVP/Cs film exhibits a maximum T of 78% decreases to 68% with increasing the ratio of the filler to 5.0 wt%. With decreasing the λ toward the UV region, the T% of the films decreases sharply, and the absorption edge shifts to higher λ especially at 1.0-wt% doping, indicating a narrowing of the optical band gap of the blend. The T% values of the films emphasize the homogeneity and CuWO 4 /PVP/Cs composites and their convenience for optical devices.
Using Tauc's relations: where h is the incident photon energy ( ∼ 1242(eV) (nm) ) , C is a constant, m = 1 2 or 2 for allowed direct and indirect transitions, respectively, and the direct ( E dir g ) and indirect ( E ind g ) optical band gap can be determined. Figure 8a and b shows the ( h ) 2 vs. h and ( h ) 1∕2 vs. hυ. Extrapolating the linear parts of these plots to α = 0, gives the E dir g and E ind g values which are listed in Table 2. PVP/Cs blend has E dir g and E ind g of 5.0 and 4.2 eV, respectively, significantly reduced to 4.4 and 3.1 eV after loading 1.0-wt% CuWO 4 . However, increasing the content of the filler to 5.0 wt% widens the E dir g and E ind g of PNC films to 4.8 and 3.8 eV, respectively, but still lower than the values of the pure blend. In the previous work, the incorporation of 2.0-wt% hematite nanorods narrowed the E dir g of PVP/Cs from   to the effective mass of the electron, respectively. The  Table 2. The value of N m * e 2 c 2 increased from 1.96 × 10 -7 to 1.37 × 10 -6 nm −2 after loading 1.0-wt% CuWO 4 into the blend but slightly reduced to 1.06 × 10 -6 and 6.52 × 10 -7 nm −2 with increasing the content of the filler to 3.0 and 5.0 wt%, respectively. The observed change in N m * e 2 c 2 is consistent with the variation in E dir g and E ind g of PNC films, where increasing/decreasing carrier concentration results in decreasing/increasing the E g values. Moreover, these results indicate that the optical properties of the PVP/Cs blend can be tuned by the ratio of CuWO 4 nanofiller. These enhancements in the optical properties make these compositions suitable for optoelectronic devices, such as organic lightemitting diodes and photovoltaic cells [42].

Dielectricconstantandlossof CuWO 4 / PVP/Cs
Improving the dielectric property of a material by increasing the number of charges it can store is essential for device applications, such as supercapacitors and batteries.  Fig. S2. At low f, the accumulated charge carriers yield a high ɛ′ and tend to build up a space-charge layer at the interface between the PVP/Cs film and the electrode, and any charge has the time required to change the direction according to the change in f-direction. However, increasing f is combined with a short periodic time in which the dipoles fail to reorient fast enough. Therefore, the dipolar polarization diminishes and may disappear and hence ɛ′ values decrease [43,44]. The temperature dependence is somewhat different. The curves (ɛ′ vs. T) can be divided into two regions, in the first one, the ε′ increases with increasing the temperature that supplies thermal energy enough to free localized dipoles which in turn align themselves in the f-direction. In the second region, the high temperatures increase the specific volume of the blend, hence the dipole concentration (dipole number/unit volume) decreases resulting in the observed decrease in ε′.
The separation between the two regions is called the relaxation peak or the α-process, which shifts to the right with increasing the applied f. This α-process is assigned to the micro-Brownian motion along the PVP/Cs main chains found in its amorphous regions. Two additional notes on the behavior of ε′: (i) the dispersion of the curves at a lower temperature is higher than that at higher temperatures. This means f has the decisive effect at low temperatures, and this effect reduces at a higher temperature, after the α-process. (ii) At low temperatures, the PVP/Cs blend has ε′ in the range of 8.3-17.8 that significantly increased to 9.8-24.5 after loading 1.0-wt% CuWO 4 , where the heterogeneity created inside the blend and the contribution of the interfacial polarization increase ε′. However, a further increase in the added CuWO 4 ratio decreases the ε′ range to 9.0-19, but still higher than that of the pure blend. The higher filler content may not be distributed uniformly and induce structural changes that act as trapping centers for the charges.
The dependence of the dielectric loss (ε″) with f at different temperatures is given in Fig. 11a-d and Fig. S3. At the low f (≤ 40 kHz), the ε″ is small and decreases with increasing temperatures up to a certain limit (the gained thermal energy is small and cannot affect the motion of the PVP/Cs chains) then increases with temperature (the temperature above a certain limit improves the motion of the chains and rise ɛ″).
At higher f (≥ 0.2 MHz), ɛ″ increases with increasing temperature till a certain limit then decreases with further increase in the temperature, where the free charge carriers, the polar groups in the blend, and the motion of the chain become fail to in phase with the oscillating f. Moreover, the observed relaxation peaks in the PVP/Cs and CuWO 4 /PVP/Cs spectra shifted to higher f with increasing temperature, Fig. 11, or shifted to higher temperatures with increasing f,  [46]. Incorporation of CuWO 4 into PVP/Cs blend improved ε′ significantly maintaining similar ε″ values. These composites, therefore, can be further improved to be suitable for batteries and supercapacitors (energy storage devices), and the electrostriction systems utilized in the artificial muscles [47]. Moreover, 1.0-wt% CuWO 4 /PVP/Cs has the higher ε′ and therefore the higher dielectric displacement ( D = o � E) and high energy density ( U e = ∫ EdD) , in the presence of the applied electric field E [48].
The conductivity (σ ac ) of the dielectric materials (, ω = 2πf is the angular frequency) is related to the temperature by the Arrhenius equation: , where k B is the Boltzmann constant, σ o is a pre-exponential factor, E a is the activation energy, and T is the temperature (K). The conductivity of pure and 1.0-wt% CuWO 4 -doped PVP/ Cs and the log (σ ac ) vs. 1000/T are shown in Fig. 12. The σ ac of PVP/Cs is in the order of 1.2 × 10 -6 -7.3 × 10 -4 S/m and this high σ ac may be due to the polycationic characteristic of the blend. The NPs of CuWO 4 semiconductor may form 3D connected networks inside the blend where the σ ac range of 1.0-wt% CuWO 4 /PVP/ Cs increased to 4.95 × 10 -6 -9.16 × 10 -4 S/m. The σ ac curves could be divided into two regions showing an Arrhenius behavior; in the region I, the conductivity improvement is due to the available thermal activation

Conclusion
CuWO 4 NP and CuWO 4 /PVP/Cs PNC were successfully prepared with co-precipitation and solution casting techniques. XRD and EDX showed the formation of CuWO 4 in the triclinic crystal structure with D av = 43.1 nm, where the sample was found to composed of 87.48 at.% O, 6.83 at.% W, and 5.96 at.% Cu with a uniform distribution. PVP/Cs is a semi-crystalline blend and X C of the blend decreased from 18.5 to 10.4% after doping, where the EDX analysis confirmed the presence of both Cu and W in the blend. FE-SEM showed that the grain size of CuWO 4 is in the range of 50-150 nm. PVP/Cs has a crack-free surface and the incorporation of CuWO 4 NP induced some heterogeneity, roughness, and pores formation and increased both the density and porosity of the PVP/Cs. FTIR confirmed the high purity of CuWO 4 and the existence of all the reactive functional groups of the polymers, which were more restricted at 1.0-wt% CuWO 4 loading. The films exhibited small k values (≤ 2.0 × 10 −3 ) and the transmittance of the blend, which decreased from 85-90-68% at 5.0-wt% CuWO 4 doping ratio. Direct and indirect band gaps were decreased from E dir g and E ind g from 5.0 and 4.2 eV to 4.4 and 3.1 eV at 1.0 wt%, but then increased to 4.8 and 3.8 eV, respectively. Both the index of refraction and N m * increased from 1.79 and 1.96 × 10 -7 nm -2 to 2.29 and 1.37 × 10 -6 nm -2 after doping with 1.0-wt% CuWO 4 and then decreased with increasing filler content. The ε′ of PVP/Cs is in the range of 8.3-17.8, increased to 9.8-24.5 at 1.0-wt% filler content. The maximum values of ɛ″ for PVP/Cs and CuWO 4 / PVP/Cs is small (2.75-4.0). The σ ac increased from 1.2 × 10 -6 -7.3 × 10 -4 S/m to 4.95 × 10 -6 -9.16 × 10 -4 S/m at 1.0-wt% filler content. In summary, the structural, optical, and dielectric properties can be controlled by CuWO 4 NP content. Therefore, these composites can be improved to be suitable for some energy storage devices such as supercapacitors as well as some optoelectronic applications, such as light-emitting diodes and photovoltaic solar cells.

Authorcontributions
AMElS contributed to conceptualization; methodology; data curation; writing of the original draft; and editing of the manuscript. MIAAM contributed to conceptualization; methodology; data curation; investigation; writing of the original draft; and writing, reviewing, & editing of the manuscript. SMK contributed to data curation and writing of the original draft. ASA contributed to data curation; writing of the original draft; and writing, reviewing, & editing of the manuscript.

Funding
Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB). None.

Dataavailability
Data will be made available on reasonable request.

Declarations
Conflict of interest The authors declare that they have no conflicts of interest.

Consent to publish Not applicable.
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