Porphyrin-based carbon dots as fluorescence probe for sensing of Fe 3+ ion and S 2- anion in aqueous solution

In this work, a facile bottom-up approach was employed to synthesize the porphyrin-citric acid-derived fluorescent carbon dots (Por-CA-CDs) using a single-step hydrothermal method. As-prepared Por-CA-CDs were well characterized using spectroscopic techniques such as FT-IR, high-resolution transmission electron microscopy, P-XRD, UV-Vis absorption, and photoluminescence spectroscopy. The synthesized Por-CA-CDs exhibited blue fluorescence with excellent photostability and diameter ranging from 2.4 to 6.4 nm. Por-CA-CDs show excitation-dependent emission behavior, with a quantum yield of 26% and were used for sensing of Fe3+ and S2− ions in an aqueous solution. Por-CA-CDs demonstrated a robust and selective reaction to Fe3+ compared to the other cations utilized in this investigation. The sensing capability of Por-CA-CDs with Fe3+ ions was evaluated with fluorescence spectroscopy, and results show a "Turn-Off" emission mode upon binding of Fe3+ with Por-CA-CDs. In metal ion sensing studies, the fluorescence intensity of Por-CA-CDs exhibited significant quenching upon the addition of Fe3+ at concentrations ranging from 0 to 230 μM, with a detection limit (LOD) of 3.2 × 10−8 M. The quenching efficiency and Stern-Volmer quenching constant were computed as 99.45% and 4.4 × 106 M−1, respectively. Interestingly, fluorescence of Por-CA-CDs can be regained with the addition of S2− (0-160 µM) with LOD of 4.3 × 10−6 M and Stern-Volmer quenching constant of 6 × 105 M−1. Most importantly, the toxicity assay revealed good reliability for samples in deionized, tap, and river water, suggesting applications for Fe3+ monitoring in complex environments.