Insights into the complementary behaviour of Gd doping in GO/Gd/ZnO composites as an efficient candidate towards photocatalytic degradation of indigo carmine dye

Water pollution caused by the discharge of hazardous organic pollutants from the food, textile, leather and paper industries is becoming a task for sustainable development. Photocatalysis is considered to be an effective method for removing organic contaminants from dye wastewater. The photocatalytic activity of ZnO-based catalyst based on its ability to generate electron–hole pairs upon photoillumination is limited due to its wide bandgap. In this study, novel GO/Gd/ZnO composites with varying percentages (0.3–1%) of Gd were fabricated via a hydrothermal approach and their photocatalytic degradation processes and performance of indigo carmine (IC) dye were investigated under light irradiation. The chemical composition and morphological features of the prepared GO/Gd/ZnO composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, energy-dispersive spectroscopy, Brunauer–Emmett–Teller, Raman and Fourier–transform infrared spectroscopy. GO/Gd/ZnO composites show much higher photocatalytic performance with complete IC dye degradation within 30 min of irradiation than bulk ZnO and GO/ZnO composite. Moreover, the optimal performance was revealed by the GO/Gd/ZnO (0.6% Gd) composite (nearly 96% degradation of IC dye). Using density functional theory, we explore the potential drop across the interface, electronic and structural properties of GO/ZnO and GO/Gd/ZnO composites. The photodegradation rate of IC dye by GO/Gd/ZnO (0.6% Gd) composite was 7.65 and 2.94-fold higher than those of bulk ZnO and GO/ZnO composite. The capture experiments revealed ˙O₂⁻ and ˙OH as the main active radicals during the photodegradation process. The theoretical and experimental findings obtained in this study indicate that GO/Gd/ZnO photocatalyst has great potential application for eliminating environmental pollutants.