Biosynthesis of zinc aluminate nanoparticles for effective photocatalytic degradation of direct blue 129 dye

ZnAl2O4 spinel belongs to Fd3̅m space group and has a close-packed face-centered cubic structure. In ZnAl2O4, the valence band is formed by the hybridization of 2p orbitals of O2− and 3d orbitals of Zn2+ while the conduction band is made up of 2p and s orbitals of Al3+ atom [1]. It is transparent for light of the wavelengths 320 nm, thus, it finds applications in ultraviolet (UV) photoelectronic devices. If the surface area of ZnAl2O4 spinel is high, it is a useful catalyst and catalyst support as well as photocatalyst for the degradation of dyes. The surface charge of the photocatalyst also plays important role in dye adsorption and degradation process, anionic dyes adsorb well on the surface of a material with the positive value of zeta potential or vice versa, due to the attraction of opposite charge particles [2]. The photocatalytic degradation of organic pollutants in the water and air, such as dyes [1], phenols, pesticides, and acetone, using different semiconductor materials has attracted much attention recently [3,4]. In this work, ZnAl2O4 nanocrystals were successfully synthesized by using sol-gel method. The structural properties of the photo-catalyst were investigated by energy dispersive X-ray analysis (EDX), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR), and percent of DB129 degradation which was followed by UV–Visible spectroscopy. The photocatalytic activity of ZnAl2O4 nanoparticles was evaluated in the degradation of direct blue 129 dye at room temperature in aqueous solution so that 90% of direct blue 129 dye was degraded in 60 min. Therefore, the ZnAl2O4 nanocrystals were able to be employed for the removal of dyes from wastewater under visible light irradiation.