all of which exhibit different absorbance peaks. In the UV–Vis spectra of the Orange II evaluated in this study, characteristic bands of azo-bonds, naphthalene rings, and benzene rings were observed at 484, 310, and 230 nm, respectively. During the decolorization of Orange II by nZVI reaction, the visible absorbance band became lower and the characteristic band shifted to a different wavelength position. More detailed UV–Vis spectra of Orange II decomposition by zero valent iron are available elsewhere [11]. The efficiency of decolorization was measured at 484 nm. The absorbance band at 484 nm decreased promptly in the first 5 min, after which it continued to decrease gradually over the next 10 min. The color changed from orange to dark red to brown, and then dark green. The solution became clear after the nZVI particles were centrifuged.