Highly stable and selective measurement of Fe3+ ions under environmentally relevant conditions via an excitation-based multiwavelength method using N, S-doped carbon dots.

Fast and accurate detection of Fe3+ under relevant natural conditions is important in environmental monitoring. In this study, an improved and simplified fluorescence method based on the multiwavelength luminescence in the visible region and the avoidance of the self-quenching property of N, S-doped carbon dots (NSC-Dots) was developed for the first time to determine Fe3+ concentration under varied environmental conditions. This method can simultaneously save time and provide accurate information. The as-prepared NSC-Dots exhibit two stable excitation peaks from 200 nm to 450 nm at a fixed emission wavelength (λem = 450 nm). A standard equation (R2 = 0.995) can be derived by measuring the quenching degree of the two peaks and referring to Stern-Volmer theory. Thus, Fe3+ concentration was accurately determined. The interference of the environmentally relevant concentrations of other metal ions, humic acid, and pH on Fe3+ measurement was tested. Results showed that the standard equation can be used to accurately determine Fe3+ concentration within the range of the 95% prediction band. The fast and facile multiwavelength method may facilitate the real-time monitoring of Fe3+ concentration in complex water environments.