Study of the optical properties of ZnO semiconductor nanoparticles using Origanum vulgare and its effect in Rhodamine B degradation

In this work, the effects of different Oregano (Origanum vulgare) extract concentrations on the green synthesis of zinc oxide nanoparticles (ZnO NPs) were studied and their effects on the Band gap values and photocatalytic application in Rhodamine B (RhB) degradation. During the green synthesis of ZnO NPs, a zinc ion source is used as the metal precursor and another of natural extracts as stabilizing agents; with this regard, here in Origanum vulgare extracts were used at 0.1%, 0.5% and 4% (% weight-volume). In order to define the ZnO NPs properties, they were characterized by FTIR, XRD, UV-Vis, HR-TEM, XPS and photoluminescence. In the FTIR analysis, the Zn-O bond can be seen at 384 cm−1; by means of XRD, the hexagonal crystalline phase of ZnO is distinguished (Wurtzite). The extract concentration used influences the ZnO NPs crystallite size and Band gap values as well as the degradation percentage of RhB. The ZnO NPs hold irregular shapes, the majority of which are oval with certain spherical tendencies and they vary in size distribution, which ranges from 37 to 8 nm, the smallest sizes resulting from the highest extract concentrations. The Band gap values are 2.94, 2.77, and 2.29 eV for ZnO-OV-0.1%, ZnO-OV-0.5% and ZnO-OV-4%, respectively, rising as the extract concentrations increase. These materials present good photocatalytic activity, nonetheless, the ZnO NPs synthesized using 4% extract showed the best results, degrading 94.24% of RhB in 100 min in UV light and 93% in 180 min in solar light.