Modified ZnO mediated dye detoxification by a heterogeneous Fenton process

The continuous and unchecked discharge of effluents by the dyeing industry in water bodies, have lead to the rising importance of water treatment. This study focusses on the successful abatement of Auramine O (AM) dye in the aqueous system by a heterogeneous Fenton process using ultrasonication. Zinc oxide (ZnO) nanoparticles (NPs) were obtained by a straightforward precipitation method and then modified by glycine (M-ZnO). The NPs size sharply decreased upon modification with glycine. Light absorbing capacity and band gap were determined by Ultra Violet (UV) visible spectrophotometry. X-ray diffraction (XRD) was used to determine the basic crystal properties, such as crystallinity. Changes in crystal size and morphology were determined by scanning electron microscopy (SEM), while high-resolution transmission electron microscopy (HRTEM) provide more information on the shape and size of NPs. It was observed that the size of NPs sharply decreased from 24.6 nm (pure ZnO) to 17.3 nm upon modification of ZnO with glycine. A bandgap of 3.4 eV was determined for M-ZnO using UV-visible spectrophotometer. Fourier transform infrared (FTIR) spectroscopy was used to find different functional groups along with the presence of ZnO, which further confirmed the modification of ZnO with glycine. Thermal gravimetric analysis revealed the excellent thermal stability of M-ZnO compared with ZnO. The catalytic activity for AM abatement was determined using a Fenton process at pH 6. Detoxification assays showed pure H2O2 or pure ZnO exhibited 38% and 37% AM dye degradation respectively. However, M-ZnO showed 97% of AM dye degradation in 240 min. A plausible mechanism has been proposed for AM abatement using ZnO.