Green synthesis capacitor of carbon quantum dots from Stachys euadenia

Carbon quantum dots (CQDs) are a new type of carbon nanomaterial that has recently attracted great attention as a potential competitor to standard semiconductor quantum dots. There are various ways to synthesis CQDs, and one of harmless way is undoubtedly green synthesis. In this study, hydrothermal synthesis based on the green way was employed to synthesize CQDs. The CQDs were obtained using the green leaves of the Stachys euadenia plant extract, an endemic species located in Turkey. The CQDs were characterized by fluorescent and UV-Visible spectroscopy, and results confirmed blue emission (430-480 nm) and absorption around 280 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed C=C, C-N and C-O interactions. X-ray diffractometer (XRD) patterns confirmed structure of carbon with a broad peak of (002) plane. High resolution tunneling electron microscopy (HRTEM) and dynamic light scattering (DLS) analysis was used to determine the shape and size of CQDs. The CQDs obtained from Stachys euadenia were employed as electrode materials for capacitor application, and they were tested in Swagelok-type cell by cyclic voltammetry (CV) measurements. CQD capacitors exhibited 2.12 F/g charge and 1.24 F/g discharge capacitances were obtained with similar to 58% coulombic efficiency rate for the first cycle. Results highlights that CQDs are synthesized successfully by green synthesis method and can be used for capacitor applications.