## 3 Results and Discussion
### Particle Characterization after Reaction  
The XRD patterns of the ZnO after reacting with either As(III) or As(V) are presented in Figure 5A,B, respectively. The patterns of the reacted ZnO show the same diffraction peaks the 100, 002, 101, 102 and 110 at the same position as the unreacted ZnO, indicating that the As does not influence the crystalline structure after reaction. Furthermore, using [PERSON]'s analysis of the diffraction peaks, the average grain size of the ZnO after reaction with As(III) was 61.96 nm \(\pm\) 0.97 and with As(V) was 71.56 nm \(\pm\) 1.58, whereas the unreacted ZnO nanoparticles had an average size of 62.03 \(\pm\) 4.06 nm. The data indicate no significant change in the ZnO nanoparticle size before and after reaction with As, which indicates the ZnO nanoparticles are stable. Furthermore, the Le Bail fitting of the ZnO after reaction with either As(III) or As(V), which is presented in Table 3, shows no change in the lattice parameters of the ZnO after reaction. The \(X^{2}\) values for the fittings indicate a great agreement between the current experimental data and those reported in the literature on the same material. Also, there were no new phases observed in the diffraction patterns.  
Figure 5: Powder X-ray diffraction patterns of ZnO after reaction with As(III) (**A**) and As(V) (**B**).  
Figure 6 shows the Raman spectra collected for the ZnO nanoparticles before and after reaction with As(III) and As(V). The ZnO stretches are identified in red in Figure 6 and the Identified As-O stretches are shown in black. ZnO vibrations were located at 382 cm\({}^{-1}\) (A\({}_{\text{1(LO)}}\)), 333 cm\({}^{-1}\) (E\({}_{\text{1 high}}\)-E\({}_{\text{1 Low}}\)), 438 cm\({}^{-1}\) (E\({}_{\text{2 high}}\)), 546 cm\({}^{-1}\) (2B\({}_{\text{low}}\)), 576 cm\({}^{-1}\) (A\({}_{\text{1 LO}}\)) and 662 cm\({}^{-1}\) (TA + LO); these are consistent with the peaks identified in the literature. The Raman results are consistent with the ZnO spectra in the literature [60; 61; 62].  
In the As-O region, two broad weak vibrations were observed centered at 770 cm\({}^{-1}\) and 856 cm\({}^{-1}\). In several minerals containing As(V), the As-O interaction is observed in the range 767-778 cm\({}^{-1}\)[63; 64; 65; 66]; the authors assigned these stretches asymmetric stretching of the As-O interaction. The As(V) (As-O symmetric stretch) bound to schwertmannite, an Fe-O-based mineral, which has been observed at 854 cm\({}^{-1}\)[67; 68]. In the present study, the stretches at 770 cm\({}^{-1}\) and 856 cm\({}^{-1}\) are consistent with the literature and were assigned to the asymmetric As-O stretching and the symmetric As-O stretch, respectively. The spectra do not show As(III) stretches after binding, signifying that As(III) was oxidized to As(V). The oxidation of the As(III) to As(V) was not completely unexpected as the reactions were  
Figure 6: RAMAN spectra of ZnO reacted with As(III), ZnO reacted with As(V), and pure ZnO nanoparticles.  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Sample** & **a** (\({}^{\circ}\)**A) & **b** (\({}^{\circ}\)**A) & **c** (\({}^{\circ}\)**A) & **a\({}^{\circ}\)** & **\(\beta^{\circ}\)** & **\(\gamma^{\circ}\)** & **\(\chi^{2}\)** \\ \hline As(III)ZnO & 3.245(8) & 3.245(8) & 5.214(8) & 90.0 & 90.0 & 120.0 & 3.08 \\ As(V)ZnO & 3.261(1) & 3.261(1) & 5.220(9) & 90.0 & 90.0 & 120.0 & 3.35 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Le Bail fitting results of ZnO nanoparticles after reaction with As(III) and As(V).  
performed in air; the As(III) may have oxidized after binding to the ZnO surface. However, the data confirm that the arsenic was surface-bound to the ZnO.