Green Synthesis of Carbon Quantum Dots with Good Photoluminescence Properties from Prosopis farcta and Their Applications as Fe3+ Ion Detectors and Optical Nanothermometers

Abstract

Carbon quantum dots (CQDs) derived from biological sources have gained a great attention in healthcare and environmental applications, including biosensing bioimaging, electrocatalytic oxidation, and metal ion detection. In this study, for the first-time, the fabrication of water-soluble CQDs is reported using Prosopis farcta as a natural precursor via a one-pot hydrothermal synthesis. The green-synthesized CQDs were characterized in terms of their functional groups and morphology. Transmission electron microscopy (TEM) revealed an average particle size of 1.95 nm, while spectroscopic analysis confirmed a strong fluorescence emission with a quantum yield (QY) of 27.6%. The CQDs possess carbonaceous cores with surface functional groups and show a maximum green emission wavelength at 495 nm. Particularly, the characterized CQDs show excellent sensitivity toward Fe³⁺ ions, leading to fluorescence quenching, enabling the development of a facile and efficient fluorescent sensing method for Fe³⁺ detection. This sensor demonstrated a linear response in the range of 0.1–0.5 µM with a detection limit as low as 15 nM. Furthermore, the method was successfully adapted for the analysis of environmental water samples, achieving satisfactory recovery rates. This work introduces a novel, eco-friendly approach to CQD synthesis from Prosopis farcta and presents a promising strategy for highly sensitive and selective Fe³⁺ detection, with potential applications in optical nano-thermometry and environmental monitoring.