Si,N co-doped carbon quantum dots in mesoporous molecular sieves: A fluorescence sensing platform for Cr(VI) detection

Carbon quantum dots (CQDs) are highly efficient fluorescent probes for metal ion detection; however, they are limited by non -uniform particle size, aggregation, and the inability to facilitate quantitative analysis. Herein, a smart host-guest strategy is utilized, wherein CQDs are immobilized in mesoporous molecular sieves, proving to be an effective method to minimize these drawbacks. Si,N-CQDs@SBA-15 is successfully synthesized by the onestep hydrothermal route using Si,N-CQDs precursor materials as guests and the mesoporous molecular sieve SBA15 as the host. A good linear relationship between the concentration of Cr(VI) ions and fluorescent intensity is observed from 0 mu M to 100 mu M ( R 2 = 0.9986). The limit of detection (LOD) is 0.213 mu M, approximately three times lower than that of pristine Si,N-CQDs (0.677 mu M). Additionally, Si,N-CQDs@SBA-15 exhibit good detection selectivity for Cr(VI) detection over other metal ions. Moreover, a smartphone-based laboratory device and RGB analysis app are employed to capture and analyze fluorescence images, revealing a LOD for Cr(VI) of 0.201 mu M. Fo <spacing diaeresis>rster Resonance Energy Transfer (FRET) is identified as the possible mechanism for the fluorescence quenching of Si,N-CQDs@SBA-15 by Cr(VI) through UV-vis and fluorescence experiments. The practicability of the synthesized fluorescent probes is further validated in river water, yielding satisfactory spiked recoveries ranging from 99.24 % to 106.21 %.