# One-Step Synthesis of Bunsenite Cadmium Oxide Nanoparticles
## 3 Results
### UV-Visible Analysis  
The diffuse reflectance spectra of bunsenite cadmium oxide nanoparticles were measured using a UV-visible spectrophotometer. Figure 7 shows the reflectance spectra of the produced samples that were calcined at various temperatures in a wavelength range of 220-800 nm. Regarding the two reflection peaks at around 357 nm and 625 nm, Figure 7 illustrates the Ni\({}^{2+}\) and Cd\({}^{2+}\) species identified in the prepared samples. These (357 nm and 625 nm) were assumed to be the origins of the reflection peaks at 340-400 and 625 nm. All of the samples also showed an absorption band at around 340-400 and 625 nm, which were assumed to be caused by a charge transfer transition from oxygen to metal. The presence of both Ni\({}^{2+}\) and Cd\({}^{2+}\) ions in all samples confirms the production of bunsenite cadmium oxide nanoparticles [21; 33]. The relatively high intensity of the aforementioned peaks, as  
Figure 5: The EDX spectrum of the prepared sample was calcined at 700 \({}^{\circ}\)C.  
well as the blue shift in their wavelengths, attested to this. The band at 589 nm indicated that Cd\({}^{2+}\) was present in the samples and was caused by Cd\({}^{2+}\) ions. This band was found in all of the prepared samples, regardless of the temperature they were calcined at [30]. An absorption broadband of between 340 and 625 nm was exhibited by every sample as well. This band was considered to originate from an O2-Ni\({}^{2+}\) charge transfer transition. The confirmation that all samples contained both Ni\({}^{2+}\) and Cd\({}^{2+}\) ions validated the synthesis of bunsenite cadmium oxide. The results from Figure 7 were employed to determine the absorption coefficient from the Kubelka-Munk (KM) function based on Formula (2):  
\[\mathrm{F}\left(\mathrm{R}\infty\right)=\left(\alpha/\mathrm{S}\right)=\left(1 \,-\,\mathrm{R}\infty\right)/2\mathrm{R} \tag{2}\]  
In Formula (2), the absorption coefficient, scattering coefficient, and KM function are respectively signified by \(\alpha\), S, and F(R\(\infty\)). The KM function could be used instead of \(\alpha\) for the diffused reflectance spectra to measure the optical absorption edge energy. It was observed that a plot of F(R\(\infty\)) E with E was linear near the edge for the direct allowed transition (\(\eta=1/2\)). The value of that energy for the sample is indicated by the intercept of the line on the abscissa (F(R\(\infty\)) E = 0) [9; 33; 47]. Figure 6: FTIR spectra of (**a**) PVP and bunsenite cadmium oxide at different temperatures: (**a**) room temperature, (**b**) 500, (**c**) 600, (**d**) 700, and (**e**) 800 \({}^{\circ}\)C.  
The Kubelka-Munk equation and reflectance spectra data were employed to determine the optical band gap for every sample subjected to calcination [48]:  
\[(\mathrm{F}\,(\mathrm{R}\mathrm{o}\mathrm{o})\cdot\mathrm{h}\mathrm{v})^{2}=( \mathrm{A}\,(\mathrm{h}\mathrm{v}-\mathrm{E}\mathrm{g})) \tag{3}\]  
In Formula (3), the apparent remission parameter or Kubelka-Munk function is denoted by \(\mathrm{F}(\mathrm{R}\mathrm{o})\), the incident photon energy is denoted by \(\mathrm{h}\mathrm{v}\), the constant given by the transition probability is denoted by \(\mathrm{A}\), and the diffuse reflectance derived from the \(\mathrm{R}\mathrm{o}\) that obtained from \(\mathrm{R}\mathrm{o}\) = \(\mathrm{R}\mathrm{sample}\)/\(\mathrm{R}\mathrm{standard}\)[49]. The mapped values of \((\mathrm{F}(\mathrm{R}\mathrm{o}\mathrm{h}\mathrm{v}))^{2}\) against \(\mathrm{h}\mathrm{v}\) are presented in Figure 6. The linear plot ranges with extrapolation to the (h\(\mathrm{v}\)) axis were employed to determine the values of the optical bandgap of the prepared samples at various temperatures of calcination. Every sample subjected to calcination exhibited the two optical band gaps presented in Figure 8 and Table 2. The initial band gaps at 3.94, 3.83, 3.67, and 3.53 eV, respectively corresponding to the calcination temperatures of 500, 600, 700, and 800 \({}^{\circ}\)C, were explained by the presence of NiO nanoparticles in the samples.