Green, facial zinc doped hydrothermal synthesis of cinnamon derived fluorescent carbon dots (Zn-Cn-CDs) for highly selective and sensitive Cr6+ and Mn7+ metal ion sensing application.

Carbon dots have demonstrated a great potential as luminescent nanoparticles in energy, drug delivery, sensors, and various biomedical applications as well as environmental pollutants and water analysis. Although, such nanoparticles appear to exhibit low toxicity compared to other semiconductor and metal based luminescent nanomaterials. Today, we know that toxicity of carbon dots (CDs) strongly depends on the protocol of fabrication. The various dopants or heteroatoms have been used to enhance the optical and physicochemical properties. In this work, zinc doped aqueous fluorescent Zn-Cn-CDs have been synthesized from cinnamon by hydrothermal synthesis method. The synthesized Zn-Cn-CDs were confirmed for their physicochemical properties by using various characterization techniques viz. UV-Vis. and spectrofluorometer for optical properties, Fourier transform infrared spectroscopy (FTIR) and XRD, as well as TEM and XPS, was done for morphological and chemical analysis. The successfully synthesized Zn-Cn-CDs showed outstanding optical performance for metal ion sensing applications. The developed heteroatom doped Zn-Cn-CDs as a fluorescent probe exhibited higher selectivity and sensitivity for Cr⁶⁺ and Mn⁷⁺ metal ions. The obtained results showed a better linear range with excellent limit of detection (LOD) 3.97 µg/mL and 2.05 µg/mL for Cr⁶⁺ and Mn⁷⁺ metal ions respectively. The low cost, simple and highly fluorescent probe can be effectively applicable for development of environmental pollutants sensing purposes.