Enhancement of carbon quantum dot luminescence efficiency through N, S co-doping for rapid ion Fe3+ detection

Abstract

Nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) with enhanced photoluminescence were synthesized via a hydrothermal method using citric acid and thiourea as the precursors. The optimized synthesis yielded a high quantum yield (50.14%), surpassing many previously reported N, S-CQDs, with excellent fluorescence stability and a low detection limit (LOD = 0.184 µM) for Fe³⁺ sensing. Spectroscopic analysis confirmed successful heteroatom incorporation, where C=S and C–N functional groups introduced new defect states, enhancing fluorescence efficiency. Fe³⁺-induced fluorescence quenching followed a dynamic quenching mechanism, as confirmed by Stern–Volmer analysis, fluorescence lifetime measurements, and FTIR spectral shifts. The N, S-CQDs exhibited high selectivity for Fe³⁺ over competing metal ions and demonstrated practical applications in real water sample analysis, with stable recovery rates (96.83–104.19%) in both clean and industrially polluted water. This study provides a high-QY, low-LOD Fe³⁺ fluorescence sensor that offers a balance between sensitivity, selectivity, and environmental applicability, reinforcing the potential of N, S-CQDs for real-world metal ion detection and environmental monitoring.