Facile synthesis of a ZnO/Fe2O3 heterostructure and its graphene-reinforced composite for boosting the photo-mineralization of crystal violet and phenol

Abstract

Abstract Herein, a nanostructured ZnO/Fe2O3 heterostructure and its graphene (Gr)-reinforced composite (ZnO/Fe2O3@Gr) have been synthesized via co-precipitation and post-ultrasonication approaches. The formation of heterojunction at the ZnO–Fe2O3 interface reduces the bandgap and keeps the electron-hole pairs apart. The graphene plays multiple roles to boost the dye removal effectively of the ZnO/Fe2O3@Gr composite. The charge transfer aptitude, isolation of charge carriers, and resistance at the ZnO/Fe2O3-Graphene interface were also examined by Mott–Schottky, chronoamperometric, and impedance experiments. The performance of an as-synthesized ZnO/Fe2O3@Gr catalyst was explored for the mineralization of a cationic dye (crystal violet, CV) and phenol in visible-light (λ above 400 nm) for 2 h. The ZnO/Fe2O3@Gr catalyst has mineralized 92.8 % CV dye and 50.86 % phenol after 2 h of visible-light irradiation. Moreover, the mineralization constant (k) comes to be 0.019 min−1, which is 4.2, 2.3, and 1.7 times higher than ZnO, Fe2O3, and ZnO/Fe2O3 catalysts, respectively. Increasing the dosage of the ZnO/Fe2O3@Gr catalyst from 10 mg to 30 mg increased the rate constant from 0.006 min−1 to 0.019 min−1, thereby increasing the efficiency of CV dye mineralization from 58.5 % to 92.8 %. The tuned photocatalytic activity of the ZnO/Fe2O3@Gr is due to the formation of the ZnO–Fe2O3 heterostructure and, preferentially, its conductive graphene. In fact, graphene serves the roles of an efficient electron collector, a transporter, and an effective UV/Vis light absorber, enabling the creation of active species that further boost the photocatalytic performance. According to the results of this study, the easiest and cheapest way to deal with toxic dyes in industrial waste is to make photocatalysts from semiconductive and carbonaceous materials that have integrated properties.