Microwave-assisted biosynthesis of ZnO-GO particles using orange peel extract for photocatalytic degradation of methylene blue

In this study, ZnO-GO particles for the photocatalytic degradation of methylene blue (MB) dye were successfully biosynthesized. Microwave-assisted biosynthesis was carried out using the extract of orange peel powder, ethylene glycol, and water as solvents. In addition to the formation of spherical ZnO particles, the phytochemicals present in the extract promoted the impregnation of organic compounds that were transformed into graphene oxide due to the annealing process. The effect of the amount of zinc source and the annealing temperature on the variation of the obtained powder structural, optical, morphological, superficial, and photocatalytic properties was studied by XRD, FE-SEM, TEM, XPS, BET, Raman, and UV-vis spectroscopy. Reducing the amount of zinc source and increasing the annealing temperature promoted the reduction of deformation and structural defects (measured as Urbach energy) and increased the superficial area available which improved the photocatalytic performance. On the other hand, it was observed that graphene oxide increased the adsorption of the dye thus improving its removal efficiency. The effect of the catalyst dosage and the pH of the dye solution were also tested, finding the best performance with 75 mg and a pH of 12, with an efficiency of 100% during 90 min of illumination under UV light (55 W). The kinetic study showed to follow a pseudo-first-order for all cases. Also, the stability of the catalyst was tested for 8 cycles, achieving at least 80% removal. Trapping experiments showed that hydroxyl radicals and holes are the more important chemical reactive species in the degradation mechanism of MB. Finally, our synthesized catalyst showed similar photocatalytic performance compared to high-purity commercial TiO2 and ZnO.

Automated summary

ZnO-GO particles were successfully biosynthesized for photocatalytic degradation of dye. Phytochemicals in orange peel extract promoted impregnation of organic compounds, forming graphene oxide during annealing. Reducing zinc source and increasing annealing temperature improved structural and photocatalytic properties.