Structural and Optical Characterization of g-C3N4 Nanosheet Integrated PVC/PVP Polymer Nanocomposites

The present work considers the integration of g-C3N4 nanosheets into PVC/PVP polymer nanocomposites at ratios of 0.0, 0.3, 0.6, and 1.0 wt%. The XRD data scans showed semicrystalline structures for all PVC/PVP/g-C3N4 polymer blend films. The FTIR and Raman measurements revealed intermolecular hydrogen bonding between the g-C3N4 surface and the OH− groups of the PVC/PVP network. ESEM morphology analysis for PVC/PVP/g-C3N4 nanocomposite films displayed homogeneous surface textures. The data of TGA showed improved thermal stability as the decomposition temperature increased from 262 to 276 °C with the content of g-C3N4 (0.0–1.0 wt%). The optical absorbance data for PVC/PVP films improved after the addition of g-C3N4. The optical energy gaps showed compositional dependence on the g-C3N4 content, which changed from 5.23 to 5.34 eV at indirect allowed transitions. The refractive index for these blend films enhanced (1.83–3.96) with the inclusion of g-C3N4. Moreover, the optical susceptibility for these nanocomposite films increased as the content of g-C3N4 changed from 0.0 to 1.0 wt%. Finally, the values of the nonlinear refractive index showed improvement with the increased percentage of g-C3N4. When g-C3N4 was added up to 1.0 wt%, the DC conductivity improved from 4.21 × 10−8 to 1.78 × 10−6 S/cm. The outcomes of this study prove the suitable application of PVC/PVP/g-C3N4 in optoelectronic fiber sensors.


Introduction
Polymers have been widely used in various applications due to outstanding properties such as their low cost, stability, easy fabrication, etc. The advantages of polymer matrix composites include their low cost and straightforward fabrication processes. Furthermore, polymer composites can be used as the primary material to create lightweight, flexible electronics, which is advantageous considering consumer demand. There are different types of polymers, for example, polyvinyl chloride (PVC) and polyvinylpyrrolidone (PVP). Moreover, polymers have different optical properties which are an essential factor to be investigated since these polymers have wide applications, i.e., energy, photonic, and optoelectronics [1][2][3]. In comparison to polymer composites using traditional micron-scale fillers such as carbon fibers or glass, polymer nanocomposites display significant property improvements at considerably lower filler loadings, which can lead to a significantly reduced component weight and simplify manufacturing. Individual nanoparticles homogeneously dispersed in a matrix polymer help compensate the ideal nanocomposite design. The dispersion state of nanoparticles determines the enhancement of properties to their greatest potential. A significant interfacial area between the components of the nanocomposites may result from the homogeneous dispersion of the nanofillers. Several parameters, including polymer matrix properties, nature and type of nanofiller, polymer and filler concentration, particle size, and particle distribution, are believed to contribute to the enhanced action of the filler [4].
Herein, PVC/PVP polymer blends doped with various g-N 3 C 4 percentages (0.0-1.0 wt%) were prepared via solution casting. The polymer blends' nanocomposites were characterized by advanced techniques, i.e., XRD, Raman, FTIR, SEM, TGA, and optical absorption as well as dielectric measurements. We determined the linear and nonlinear optical parameters of this polymer blend's nanocomposites when increasing the g-N 3 C 4 proportions.

Experimental Section
The g-C 3 N 4 nanosheets were prepared from high-purity urea (MERK, Darmstadt, Germany) by the polycondensation method at 500 • C at a heating rate of 3.0 • C per minute, and the process took 2.0 h [24]. The product was collected and ground well inside an agate mortar. The PVC/PVP polymer blend was developed using analar-grade PVC (MERK, Darmstadt, Germany) and PVP (LOBACEMIE, Mumbai, India) polymer powders. Moreover, the solvent tetrahydrofuran (THF) was supplied from CARLO ERBA (Cornaredo, Italy). For the preparation of PVC/PVP/g-C 3 N 4 nanocomosite films, 0.9 g of PVC powder was dissolved in 30 mL of THF for 60 min at 300 K. In addition, 0.1 g of PVP powder was dissolved in 5.0 mL of THF and added to the PVC clear solution. The PVC/PVP mixture was stirred for another 60 min with the addition of 0.0, 0.1, 0.3, 0.6, and 1.0 wt% of g-C 3 N 4 nanosheets. The solution mixture was subjected to ultrasonic waves for 30 min. Finally, the PVC/PVP/g-C 3 N 4 nanocomposite solution was poured inside a polypropylene dish. The nanocomposite films were collected after drying inside an electric oven at 50 • C for 48 h.
The Shimadzu XRD 7000 (Kyoto, Japan) diffractometer produced the crystal structure data for the PVC/PVP/g-C 3 N 4 nanocomposite films. The Shimadzu FTIR-Tracer 100 spectrometer (Kyoto, Japan) recorded the transmittance vs. wavenumber for the PVC/PVP/g-C 3 N 4 blend films. Quattro environmental scanning electron microscope (ESEM) produced surface morphology scans of the PVC/PVP/g-C 3 N 4 nanocomposite films. A Shimadzu TGA-51 thermogravimetric (Kyoto, Japan) analyzer was used for TGA measurements at temperatures 30-600 • C, and the heating rate was 10 • C/min. The Cary 60 UV-Vis spectrophotometer recorded the optical absorption data for the PVC/PVP/g-C 3 N 4 films. The DC conductivity data for the polymer films were completed on two-probe setup at 300 K on an MTZ-35 impedance analyzer.

Results and Discussion
One of the most effective non-destructive methods for determining the crystallographic structure of polymer nanocomposites is X-ray diffraction. X-ray diffraction (XRD) was used to characterize the polymer PVC/PVP doped with nanosheet g-C 3 N 4 , as shown in Figure 1. The highest diffraction peak of g-C 3 N 4 (002) is located at around 27.4 • (Figure 1a), which is consistent with the stacking peak of interplanar aromatic systems [25,26], while the reflection peak (100) located at 13.2 • is consistent with the inter-layer structure packing of the lattice planes [27]. The XRD data reveal the successful synthesis of the g-C 3 N 4 nanosheet. Due to the small amount of g-C 3 N 4 in the polymer composites, the diffraction peaks of g-C 3 N 4 were not observed in the XRD spectra. Two diffuse peaks at 18.0 • and 24.0 • in the spectra of PVC/PVP (Figure 1b) reflect the semicrystalline nature. Additionally, there is a slight shift toward a higher angle in the peak position, which is assigned to the strong interaction between the PVC/PVP polymer blend and the g-C 3 N 4 nanosheet.
The Segal equation was used to calculate the crystallinity index (CI) for PVC/PVP/g-C 3 N 4 nanocomposites, as described below [28]: where I 24 represents the intensity of the peak at 2θ = 24 • , and I 18 at 2θ = 18 • . Accordingly, the crystallinity index data for PVC/PVP films are 1.01, 1.20, 3.0, and 4.26 at 0.0, 0.3, 0.6, and 1.0 wt% of g-C 3 N 4 , respectively. From these data, a slight increase in CI was due to the small content of g-C 3 N 4 . The full width at half maximum (β) of a diffraction peak is inversely proportional to the crystallite size (D), as explained by the Scherer equation [29]: where the X-ray wavelength (λ = 1.54056 Å). As seen in Figure 1b, the peak broadening of PVC/PVP increased with the gradual increase in g-C 3 N 4 content. This, in accordance, led to a decrease in crystallite size. The Segal equation was used to calculate the crystallinity index (CI) for PVC/PVP/g-C3N4 nanocomposites, as described below [28]:

100
(1) where I24 represents the intensity of the peak at 2θ = 24°, and I18 at 2θ = 18°. Accordingly, the crystallinity index data for PVC/PVP films are 1.01, 1.20, 3.0, and 4.26 at 0.0, 0.3, 0.6, and 1.0 wt% of g-C3N4, respectively. From these data, a slight increase in CI was due to the small content of g-C3N4. The full width at half maximum (β) of a diffraction peak is inversely proportional to the crystallite size (D), as explained by the Scherer equation [29]: where the X-ray wavelength (λ = 1.54056 Å). As seen in Figure 1b, the peak broadening of PVC/PVP increased with the gradual increase in g-C3N4 content. This, in accordance, led to a decrease in crystallite size. An efficient method for characterizing polymeric materials is Fourier transform infrared spectroscopy (FTIR). A unique fingerprint is recognized for a sample concerning the measured spectrum. The FTIR spectra of PVC/PVP/g-C 3 N 4 nanocomposites at different concentrations of nanosheet g-C 3 N 4 are shown in Figure 2. The presence of the vibrational frequencies of pure PVC/PVP polymers in the spectrum of the produced blend indicates the formation of hydrogen bonds. PVP and other polymers with electronegative oxygen and ternary amide groups have the potential to be effective proton acceptors due to the nature of the basic functional groups. It is assumed that the interaction will consist of hydrogen bonds between the C-H of CH 2 in PVC and the C-O in PVP. A broad absorptions peak at 3370-3420 cm −1 is ascribed to hydroxyl group O-H stretch vibrations, while a sharp absorptions peak at around 1655 cm −1 is assigned to O-H stretch bending vibrations, respectively [30]. The observed peaks at 1324 and 1425 cm −1 are attributed to C-O and C=C vibrations, respectively [31]. The bands at around 692, 833, and 957 cm −1 correspond to C-H bending vibration out-of-plane [31,32]. The bending and stretching vibrations of C-N correspond to the formation of the absorption bands at 1425 and 1290 cm −1 , while the C-Cl bonds are ascribed to the bands at 611 and 636 cm −1 [33]. As the concentration of g-C 3 N 4 wt% increases, the position of the broad peak in the pure PVA/PVP spectrum shifts from 3370 to 3420 cm −1 . Additionally, the characteristic peak at 1254 cm −1 related to C-N bending vibrations of the pure PVA/PVP shifts to 1290 cm −1 . These variations in peak positions are attributed to the intermolecular hydrogen bonding between the g-C 3 N 4 surface and the -OH groups of PVC/PVP, which indicates the success of the interaction between g-C 3 N 4 nanosheets and PVC/PVP polymers. The distribution of potential energy throughout the host polymeric blend's chains is significantly impacted by this interaction, which also modifies the backbone structure of the blend [34]. This g-C 3 N 4 filling-induced structural modification of the polymeric blend's chains significantly affects the physical properties of the g-C 3 N 4 -filled polymeric nanocomposites [35]. The vibrational, rotational, and other low-frequency modes recorded by Raman spectroscopy allow us to assess the structural properties of materials. Thus, Raman scattering is used in Raman spectroscopy to identify molecular vibrations. The Raman spectra for polymer PVC/PVP doped with different concentrations of g-C3N4 are shown in Figure 3. The stretching vibration of C-Cl bonds causes the high-intensity peaks at 637 and 693 cm −1 . Additionally, the intensity peak at 2915 cm −1 is the result of the stretching vibration of the C-H and C-H2 bonds [36]. The stretching vibrations of C=C bonds in conjugated aromatic composites are ascribed to the bands at around 1428 cm −1 , while the defect structure of carbon material is related to the bands around 1330 cm −1 [37].
Due to the asymmetric stretching vibration, this intensity of quenching validates the interaction between polymer PVC/PVP and nanosheet g-C3N4 in the C-Cl region [11]. The vibrational, rotational, and other low-frequency modes recorded by Raman spectroscopy allow us to assess the structural properties of materials. Thus, Raman scattering is used in Raman spectroscopy to identify molecular vibrations. The Raman spectra for polymer PVC/PVP doped with different concentrations of g-C 3 N 4 are shown in Figure 3. The stretching vibration of C-Cl bonds causes the high-intensity peaks at 637 and 693 cm −1 . Additionally, the intensity peak at 2915 cm −1 is the result of the stretching vibration of the C-H and C-H 2 bonds [36]. The stretching vibrations of C=C bonds in conjugated aromatic composites are ascribed to the bands at around 1428 cm −1 , while the defect structure of carbon material is related to the bands around 1330 cm −1 [37]. Polymers 2023, 15, x FOR PEER REVIEW 3 of 8 In comparison to an optical microscope, scanning electron microscopy is frequently employed to analyze the sample surface morphology. ESEM images were used to examine the morphology and structure of the synthesized g-C3N4 nanosheets. The 2D sheet structure shown in Figure 4 is consistent with reports for g-C3N4 materials. Moreover, the image shows that g-C3N4 is stacked flakes. The ESEM surface morphology analyses for the PVC/PVP/g-C3N4 nanocomposite films are displayed in Figure 4. All the polymer films showed homogeneous surface morphology and interconnection between g-C3N4 and the PVC/PVP blend network. Due to the asymmetric stretching vibration, this intensity of quenching validates the interaction between polymer PVC/PVP and nanosheet g-C 3 N 4 in the C-Cl region [11].
In comparison to an optical microscope, scanning electron microscopy is frequently employed to analyze the sample surface morphology. ESEM images were used to examine the morphology and structure of the synthesized g-C 3 N 4 nanosheets. The 2D sheet structure shown in Figure 4 is consistent with reports for g-C 3 N 4 materials. Moreover, the image shows that g-C 3 N 4 is stacked flakes. The ESEM surface morphology analyses for the PVC/PVP/g-C 3 N 4 nanocomposite films are displayed in Figure 4. All the polymer films showed homogeneous surface morphology and interconnection between g-C 3 N 4 and the PVC/PVP blend network.
Thermogravimetric analysis (TGA) was used to characterize the thermophysical properties and examine the thermal stability of polymer films. Moreover, TGA is used to measure thermal stability of a sample, the amount of solvent still present, and the amount of water absorbed. This technique measures the mass changes in a sample as a function of time and/or temperature. The thermal stability of a copolymer is typically between that of two homopolymers and varies depending on the copolymer composition. Moreover, TGA analysis has also been used to investigate the effect of filler on a polymeric sample's thermal stability. The TGA and DTG graphs for PVC/PVP/g-C 3 N 4 nanocomposites are displayed in Figure 5a,b. The data describing the mass loss vs. temperature shown in Figure 5a revealed a main degradation stage between 180 and 316 • C, which corresponds to the dehydrochlorination of the PVC/PVP polymer blend [38]. The maximum decomposition temperature correlated with this stage was determined from Figure 5b, which shifted from 262 to 276 • C as the content of g-C 3 N 4 changed from 0.0 to 1.0 wt%. Therefore, the increase in g content resists the dehydrochlorination of the PVC/PVP polymer blend and improves the thermal stability.     A second degradative stage observed at temperatures higher than 400 • C belongs to the scission of covalent bonds in PVC/PVP chains [39]. The decomposition temperature at this stage increased from 509 to 520 • C when the content of g-C 3 N 4 increased from 0.0 to 1.0 wt%. Moreover, the residual mass % at 600 • C were 13.14, 17.50, 18.12, and 19.71% for the content of g-C 3 N 4 (0.0, 0.3, 0.6 and 1.0 wt%). All these outcomes prove the enhanced thermal stability of PVC/PVP/g-C 3 N 4 nanocomposites.
The absorption spectrum of a material is determined using ultraviolet-visible (UV-Vis) spectroscopy in the specified spectral band. This method is especially beneficial for polymers, because both the π-electrons and non-bonding electrons (n-electrons) enclosed in the molecules can absorb from the ultraviolet to visible ranges at the spectrum energy. In this section, we have studied the optical properties of the PVC/PVP polymer blend matrix doped with g-C 3 N 4 concentrations of 0.0, 0.3, 0.6, and 1.0 wt%. The absorbance and optical transmittance curves of PVC/PVP/g-C 3 N 4 nanocomposites have been investigated. Figure 6a represents the absorbance band of PVC/PVP polymer that appears at 280 nm; this could be from the transitions of two unsaturated bonds, C=O and C=C [40,41]. It is notable that a small shift appeared at the absorption band, which is regarded as a redshift. This redshift of absorption bands increases with increasing g-C 3 N 4 concentrations. Figure 6b shows that the optical transmissions gradually reduce with increasing g-C 3 N 4 concentrations. The decrease in optical transmissions may be explained by an increase in the photon scattering due to the dense nanoparticles of the polymer blend [14].
Polymers 2023, 15, x FOR PEER REVIEW 5 of 8 Figure 6. Graphs of (a) absorbance against wavelength and (b) transmittance against wavelength for the PVC/PVP/g-C3N4 nanocomposite films.
The vertical excitation energy from the ground state to the first dipole-allowed excited state corresponds to the optical energy gap, which is the lowest energy transition identified in the experimental absorption spectra [42]. We have estimated the optical band gap (Eopt) from the variation in ( ℎ ) vs. photon energy (h ) via the Tauc formula [43,44];  The vertical excitation energy from the ground state to the first dipole-allowed excited state corresponds to the optical energy gap, which is the lowest energy transition identified in the experimental absorption spectra [42]. We have estimated the optical band gap (E opt ) from the variation in (αhυ) vs. photon energy (hυ) via the Tauc formula [43,44]; where k is a constant. The direct E dir and indirect E ind band gap for allowed transitions are represented by two values: x = 2 and x = 0.5, respectively. To estimate the optical band gap energy E opt , we have extrapolated the linear part at zero photon absorption, as represented in Figure 7a identified in the experimental absorption spectra [42]. We have estimated the optical band gap (Eopt) from the variation in ( ℎ ) vs. photon energy (h ) via the Tauc formula [43,44]; where k is a constant. The direct Edir and indirect Eind band gap for allowed transitions are represented by two values: x = 2 and x = 0.5, respectively. To estimate the optical band gap energy Eopt, we have extrapolated the linear part at zero photon absorption, as represented in Figure 7a,b. The values of the Edir and Eind are reduced for 0.3 and 0.6 wt%, while they are improved for 1 wt%. The decrease in band gap corresponds to the formation of new energy levels between the valence and conduction band. Figure 7. Graphs of (a) (αhυ) 0.5 against hυ and (b) (αhυ) 2 against hυ for the PVC/PVP/g-C 3 N 4 nanocomposite films. Figure 8a shows the variation in optical reflectance (R) vs. wavelength for the PVC/PVP/g-C 3 N 4 blend matrix at different g-C 3 N 4 concentrations. The values of R enhanced when we added 1.0 wt% of g-C 3 N 4 , while they reduced for 0.3 and 0.6 wt% of g-C 3 N 4 , respectively. We also estimated the refractive index (n) from the optical reflectance shown in Figure 8a. To calculate the n, we use the following Equation [45]: where k represents the extinction coefficient, and it is determined from k= αλ/4π. Figure 8b shows that the estimated values of n increased when we doped different g-C 3 N 4 concentrations (0.3, 0.6, and 1.0 wt%) to the PVC/PVP polymer. The integration of g-C 3 N 4 nanosheets enhanced the refractive index (n), as shown in Figure 8b. This increase resulted from the higher absorption of g-C 3 N 4 in the visible light range [14]. Many applications, such as optical sensors, solar cells [46,47], emissive displays, and light emitting diodes (LEDs) [48] require materials with a refractive index ≥ 1.65 [49]. As the present PVC/PVP/g-C 3 N 4 films have a refractive index 1.83-3.96, they are therefore suitable for optical sensors, LEDs, and cladding in optical frequency modulators.
Equation (3) represents the refractive index dispersion as a function of photon energy [50]: where n, E 0 , E d , and hυ are the refractive index, the single-oscillator energy, dispersion energy, and the energy of the incident photons, respectively [51]. Table 1 represents the values of E 0 and E d which are calculated from the slope and the intercept of the plots in Figure 9. The E 0 values decrease from 4.21 to 3.14 eV with an increase in the g-C 3 N 4 concentrations (0.0-1.0 wt%), while the E d values enhance (9.88-46.08 eV) with the increase in g-C 3 N 4 .
centrations (0.3, 0.6, and 1.0 wt%) to the PVC/PVP polymer. The integration of g-C3N4 nanosheets enhanced the refractive index (n), as shown in Figure 8b. This increase resulted from the higher absorption of g-C3N4 in the visible light range [14]. Many applications, such as optical sensors, solar cells [46,47], emissive displays, and light emitting diodes (LEDs) [48] require materials with a refractive index ≥ 1.65 [49]. As the present PVC/PVP/g-C3N4 films have a refractive index 1.83-3.96, they are therefore suitable for optical sensors, LEDs, and cladding in optical frequency modulators. Equation (3) represents the refractive index dispersion as a function of photon energy [50]: where n, E0, Ed, and h are the refractive index, the single-oscillator energy, dispersion energy, and the energy of the incident photons, respectively [51]. Table 1 represents the values of E0 and Ed which are calculated from the slope and the intercept of the plots in Figure 9. The E0 values decrease from 4.21 to 3.14 eV with an increase in the g-C3N4 concentrations (0.0-1.0 wt%), while the Ed values enhance (9.88-46.08 eV) with the increase in g-C3N4.   From Equation (4), the static refractive index (n0) is evaluated at ℎ → 0 as follows [47]: The refractive index values are enhanced when we add different ratios of g-C3N4, as listed in Table 1  The oscillator strength (f) is presented as follows [52]: where Ed is the dispersion energy, and E0 is the single oscillator energy. Table 1 shows the f values improved when different g-C3N4 concentrations increased. From Equation (4), the static refractive index (n 0 ) is evaluated at hv → 0 as follows [47]: The refractive index values are enhanced when we add different ratios of g-C 3 N 4 , as listed in Table 1. The estimated values of n 0 are 1.83, 2.90, 3.67, and 3.96 for 0.0, 0.3, 0.6, and 1.0 wt%, respectively.
The oscillator strength (f ) is presented as follows [52]: where E d is the dispersion energy, and E 0 is the single oscillator energy. Table 1 shows the f values improved when different g-C 3 N 4 concentrations increased. Nonlinear effects result from high-intensity light propagating across a material. The most basic of these is the Kerr effect, which is defined as a change in the refractive index in proportion to the optical intensity. Moreover, the nonlinear optical parameters such as linear optical susceptibility (χ (1) ) and the third-order nonlinear optical susceptibility (x (3) ) were analyzed for the PVC/PVP/g-C 3 N 4 nanocomposite films. The estimations of χ (1) and x (3) were completed via the following relations [53]: The data calculations are listed in Table 2 and showed higher values of χ (1) and x (3) for the PVC/PVP/g-C 3 N 4 films concerning the pure PVC/PVP. The enhanced optical susceptibility performance of these nanocomposite films after the addition of g-C 3 N 4 nanosheet increase the applicability in optoelectronic devices. The data of the nonlinear refractive index (n 2 ) are estimated depending on the thirdorder nonlinear optical susceptibility (x (3) ) as follows [14,49]: The values of n 2 recorded in Table 2 show a large increase with an increase in the content of the g-C 3 N 4 nanosheet. These data of n 2 for the present PVC/PVP/g-C 3 N 4 are higher than those listed in the literature [54][55][56].
Many factors influence the electrical conductivity of materials. The nature of the materials, their dimensions, the temperature, and frequency of electrical fields are the main factors affecting electrical conductivity. Moreover, the polymer-nanofiller interface contributes to the variation in electrical conductivity. The DC conductivity (σ DC ) of the PVC/PVP/g-C 3 N 4 films was measured at 300 K and is plotted in Figure 10. When g-C 3 N 4 was added up to 1.0 wt%, the DC conductivity improved from 4.21 × 10 −8 to 1.78 × 10 −6 S/cm. These findings indicate that the g-C 3 N 4 nanosheet contributes more free ions and ion pairs to the PVC/PVP polymer blend. Higher charge carriers are observed in the polymer film containing 1.0 wt% of g-C 3 N 4 due to the presence of more π-π * bonds. The reduced band gap in the g-C 3 N 4 nanosheet accounts for the increased conductivity [57]. The data of the nonlinear refractive index (n2) are estimated depending on the thirdorder nonlinear optical susceptibility ( ) as follows [14,49]: 12 (9) Figure 10. Variation in DC conductivity against g-C3N4 content for the PVC/PVP nanocomposite films. Figure 10. Variation in DC conductivity against g-C 3 N 4 content for the PVC/PVP nanocomposite films.

Conclusions
The current work investigated the preparation, structural, and optical properties of g-C 3 N 4 integrated PVC/PVP blend nanocomposites. The data of XRD showed two diffuse peaks at 18.0 • and 24.0 • in the spectra of blend films which correspond to a semicrystalline structure. FTIR and Raman spectra showed that the g-C 3 N 4 filling-induced structural modification of the polymeric blend chains significantly affects the physical properties of the g-C 3 N 4 -filled polymeric nanocomposites. From ESEM micrographs, all the polymer films showed homogeneous surface morphologies and strong interconnections between g-C 3 N 4 and the PVC/PVP blend network. The thermal stability of the PVC/PVP blend nanocomposites improved with the inclusion of g-C 3 N 4 nanosheets. The refractive index showed higher values (1.83-3.96) after the addition of g-C 3 N 4 . Moreover, the optical band gaps for the PVC/PVP/g-C 3 N 4 blend films changed with the integration of g-C 3 N 4 nanosheets. Finally, the data of the nonlinear refractive index (n 2 ) and the third-order nonlinear optical susceptibility (x (3) ) for these nanocomposite films showed higher performance and thus are suitable for optoelectronic frequency modulators.