Innovative Sol-Gel Green Synthesis and Physical Properties of Cobalt and Zinc Oxide Nanoparticles for the Development as Photocatalysts

Abstract

This work outlines some interesting results regarding physical properties and the photoactivity of Co₃O₄ and ZnO nanoparticles synthesized by the sol-gel method. The chemical sol-gel method yields (Co₃O₄)_c and (ZnO)_c samples, whereas the green synthesis method using eggplant as extract produces (Co₃O₄)_gs and (ZnO)_gs samples. Structural studies using the XRD technique reveal the formation of the cubic and the hexagonal phases for Co₃O₄ and ZnO samples, respectively. No valuable changes occur in lattice parameters upon green synthesis. The FT-IR studies confirm the formation of oxide networks for both. It also reveals the creation of −OH groups that enhance the photodegradation efficiency. Optical data demonstrate the shift of the absorption edge to higher energy for (Co₃O₄)_gs. On the contrary, (ZnO)_c shows a decrease in the E_g value upon green synthesis. Regarding the detected photoluminescence peaks, (Co₃O₄)_c and (Co₃O₄)_gs show respectively blue and green emission colors, whereas both (ZnO)_c and (ZnO)_gs produce green emissions. Photoactivity of both (Co₃O₄)_c and (Co₃O₄)_gs catalysts towards the degradation of indigo carmine (IC) dye under UV irradiation was examined. The photodegradation reaches 70% and 54% after 180 min for (Co₃O₄)_gs and (Co₃O₄)_c, respectively. The photodegradation of congo red (CR) dye under UV irradiation was also examined. The photodegradation reaches 93% and 63% for (ZnO)_c and (ZnO)_gs catalysts after 180 min under UV irradiation. The photodegradation of IC dye and CR dye using (Co₃O₄)_gs and (ZnO)_c, respectively in the presence of scavengers was also measured. Recycling of the prepared photocatalysts for four successive runs has indicated the feasibility of reusing them for several times. The results are discussed regarding the photocatalytic reaction mechanism expected.